Influence of caffeine and caffeine withdrawal on headache and cerebral blood flow velocities

NARCIS (Netherlands)

Couturier, EGM; Laman, DM; vanDuijn, MAJ; vanDuijn, H

Caffeine consumption may cause headache, particularly migraine. Its withdrawal also produces headaches and may be related to weekend migraine attacks. Transcranial Doppler sonography (TCD) has shown changes in cerebral blood flow velocities (BFV) during and between attacks of migraine. In order to

Accelerated time-resolved three-dimensional MR velocity mapping of blood flow patterns in the aorta using SENSE and k-t BLAST

International Nuclear Information System (INIS)

Stadlbauer, Andreas; Riet, Wilma van der; Crelier, Gerard; Salomonowitz, Erich

2010-01-01

Purpose: To assess the feasibility and potential limitations of the acceleration techniques SENSE and k-t BLAST for time-resolved three-dimensional (3D) velocity mapping of aortic blood flow. Furthermore, to quantify differences in peak velocity versus heart phase curves. Materials and methods: Time-resolved 3D blood flow patterns were investigated in eleven volunteers and two patients suffering from aortic diseases with accelerated PC-MR sequences either in combination with SENSE (R = 2) or k-t BLAST (6-fold). Both sequences showed similar data acquisition times and hence acceleration efficiency. Flow-field streamlines were calculated and visualized using the GTFlow software tool in order to reconstruct 3D aortic blood flow patterns. Differences between the peak velocities from single-slice PC-MRI experiments using SENSE 2 and k-t BLAST 6 were calculated for the whole cardiac cycle and averaged for all volunteers. Results: Reconstruction of 3D flow patterns in volunteers revealed attenuations in blood flow dynamics for k-t BLAST 6 compared to SENSE 2 in terms of 3D streamlines showing fewer and less distinct vortices and reduction in peak velocity, which is caused by temporal blurring. Solely by time-resolved 3D MR velocity mapping in combination with SENSE detected pathologic blood flow patterns in patients with aortic diseases. For volunteers, we found a broadening and flattering of the peak velocity versus heart phase diagram between the two acceleration techniques, which is an evidence for the temporal blurring of the k-t BLAST approach. Conclusion: We demonstrated the feasibility of SENSE and detected potential limitations of k-t BLAST when used for time-resolved 3D velocity mapping. The effects of higher k-t BLAST acceleration factors have to be considered for application in 3D velocity mapping.

Vessel Sampling and Blood Flow Velocity Distribution With Vessel Diameter for Characterizing the Human Bulbar Conjunctival Microvasculature.

Science.gov (United States)

Wang, Liang; Yuan, Jin; Jiang, Hong; Yan, Wentao; Cintrón-Colón, Hector R; Perez, Victor L; DeBuc, Delia C; Feuer, William J; Wang, Jianhua

2016-03-01

This study determined (1) how many vessels (i.e., the vessel sampling) are needed to reliably characterize the bulbar conjunctival microvasculature and (2) if characteristic information can be obtained from the distribution histogram of the blood flow velocity and vessel diameter. Functional slitlamp biomicroscope was used to image hundreds of venules per subject. The bulbar conjunctiva in five healthy human subjects was imaged on six different locations in the temporal bulbar conjunctiva. The histograms of the diameter and velocity were plotted to examine whether the distribution was normal. Standard errors were calculated from the standard deviation and vessel sample size. The ratio of the standard error of the mean over the population mean was used to determine the sample size cutoff. The velocity was plotted as a function of the vessel diameter to display the distribution of the diameter and velocity. The results showed that the sampling size was approximately 15 vessels, which generated a standard error equivalent to 15% of the population mean from the total vessel population. The distributions of the diameter and velocity were not only unimodal, but also somewhat positively skewed and not normal. The blood flow velocity was related to the vessel diameter (r=0.23, Psampling size of the vessels and the distribution histogram of the blood flow velocity and vessel diameter, which may lead to a better understanding of the human microvascular system of the bulbar conjunctiva.

Automated measurement and classification of pulmonary blood-flow velocity patterns using phase-contrast MRI and correlation analysis.

Science.gov (United States)

van Amerom, Joshua F P; Kellenberger, Christian J; Yoo, Shi-Joon; Macgowan, Christopher K

2009-01-01

An automated method was evaluated to detect blood flow in small pulmonary arteries and classify each as artery or vein, based on a temporal correlation analysis of their blood-flow velocity patterns. The method was evaluated using velocity-sensitive phase-contrast magnetic resonance data collected in vitro with a pulsatile flow phantom and in vivo in 11 human volunteers. The accuracy of the method was validated in vitro, which showed relative velocity errors of 12% at low spatial resolution (four voxels per diameter), but was reduced to 5% at increased spatial resolution (16 voxels per diameter). The performance of the method was evaluated in vivo according to its reproducibility and agreement with manual velocity measurements by an experienced radiologist. In all volunteers, the correlation analysis was able to detect and segment peripheral pulmonary vessels and distinguish arterial from venous velocity patterns. The intrasubject variability of repeated measurements was approximately 10% of peak velocity, or 2.8 cm/s root-mean-variance, demonstrating the high reproducibility of the method. Excellent agreement was obtained between the correlation analysis and radiologist measurements of pulmonary velocities, with a correlation of R2=0.98 (P<.001) and a slope of 0.99+/-0.01.

The effect of lipid emulsion of different concentration on blood flow velocity: an experimental study

International Nuclear Information System (INIS)

Li Qiang; Wang Maoqiang; Duan Liuxin; Song Peng; Ao Guokun

2009-01-01

Objective: To investigate the function mechanism of lipid emulsion (LE), used as a carrier, by observing the effect of intra-arterial infusion of LE in different concentration and dosage on blood flow velocity. Methods: According to the concentration and dosage used in arterial infusion, the experiments were divided into four groups:group A (20% LE, 2 ml), group B (20% LE, 20 ml), group C (30% LE, 2 ml) and group D (30% LE, 20 ml). Two healthy hybrid dogs were used for the study. Under DSA guidance, the 4 F catheter was placed in the splenic artery and in the hepatic artery respectively. DSA frames were counted in order to calculate the time that the contrast took from the catheter tip to the selected tertiary branches of the splenic or hepatic artery. Results LE infusion, regardless of its concentration level or its dosage, could reduce the blood velocity. The lasting time and the maximal peak value of the blood velocity reduction were significantly different among groups (P < 0.05). The lasting time was 5 minutes, 5-10 minutes, 20 minutes and 20-30 minutes among group A, B, C and D, respectively. The peak value of the reduction appeared at the 18th frames (1.44 s), 30th frames (2.4 s), 9th frames (0.9 s) and 14th frames (1.12 s) in group A, B, C and D, respectively. Conclusion Intra-arterial infusion of LE can reduce the blood flow velocity. The lasting time of the reduction in 30% LE groups is longer than that in 20% LE groups, while the blood velocity reduction in 30% LE groups is less than that in 20% LE groups. (authors)

Preliminary evaluation of vector flow and spectral velocity estimation

DEFF Research Database (Denmark)

Pedersen, Mads Møller; Pihl, Michael Johannes; Haugaard, Per

Spectral estimation is considered as the golden standard in ultrasound velocity estimation. For spectral velocity estimation the blood flow angle is set by the ultrasound operator. Vector flow provides temporal and spatial estimates of the blood flow angle and velocity. A comparison of vector flow...... line covering the vessel diameter. A commercial ultrasound scanner (ProFocus 2202, BK Medical, Denmark) and a 7.6 MHz linear transducer was used (8670, BK Medical). The mean vector blood flow angle estimations were calculated {52(18);55(23);60(16)}°. For comparison the fixed angles for spectral...... estimation were obtained {52;56;52}°. The mean vector velocity estimates at PS {76(15);95(17);77(16)}cm/s and at end diastole (ED) {17(6);18(6);24(6)}cm/s were calculated. For comparison spectral velocity estimates at PS {77;110;76}cm/s and ED {18;18;20}cm/s were obtained. The mean vector angle estimates...

Cerebral blood flow velocity changes during upright positioning in bed after acute stroke : An observational study

NARCIS (Netherlands)

Aries, Marcel J; Elting, Jan Willem; Stewart, Roy; De Keyser, Jacques; Kremer, Berry; Vroomen, Patrick

2013-01-01

Objectives: National guidelines recommend mobilisation in bed as early as possible after acute stroke. Little is known about the influence of upright positioning on real-time cerebral flow variables in patients with stroke. We aimed to assess whether cerebral blood flow velocity (CBFV) changes

MR velocity mapping measurement of renal artery blood flow in patients with impaired kidney function

DEFF Research Database (Denmark)

Cortsen, M; Petersen, L.J.; Stahlberg, F

1996-01-01

Renal blood flow (RBF) was measured in 9 patients with chronic impaired kidney function using MR velocity mapping and compared to PAH clearance and 99mTc-DTPA scintigraphy. An image plane suitable for flow measurement perpendicular to the renal arteries was chosen from 2-dimensional MR angiography....... MR velocity mapping was performed in both renal arteries using an ECG-triggered gradient echo pulse sequence previously validated in normal volunteers. Effective renal plasma flow was calculated from the clearance rate of PAH during constant infusion and the split of renal function was evaluated...... by 99mTc-DTPA scintigraphy. A reduction of RBF was found, and there was a significant correlation between PAH clearance multiplied by 1/(1-hematocrit) and RBF determined by MR velocity mapping. Furthermore, a significant correlation between the distribution of renal function and the percent distribution...

Variation of velocity profile according to blood viscosity in a microfluidic channel

Science.gov (United States)

Yeom, Eunseop; Kang, Yang Jun; Lee, Sang-Joon

2014-11-01

The shear-thinning effect of blood flows is known to change blood viscosity. Since blood viscosity and motion of red blood cells (RBCs) are closely related, hemorheological variations have a strong influence on hemodynamic characteristics. Therefore, understanding on the relationship between the hemorheological and hemodynamic properties is importance for getting more detailed information on blood circulation in microvessels. In this study, the blood viscosity and velocity profiles in a microfluidic channel were systematically investigated. Rat blood was delivered in the microfluidic device which can measure blood viscosity by monitoring the flow-switching phenomenon. Velocity profiles of blood flows in the microchannel were measured by using a micro-particle image velocimetry (PIV) technique. Shape of velocity profiles measured at different flow rates was quantified by using a curve-fitting equation. It was observed that the shape of velocity profiles is highly correlated with blood viscosity. The study on the relation between blood viscosity and velocity profile would be helpful to understand the roles of hemorheological and hemodynamic properties in cardiovascular diseases. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea Government (MSIP) (No. 2008-0061991).

Middle cerebral artery blood velocity during running

DEFF Research Database (Denmark)

Lyngeraa, Tobias; Pedersen, Lars Møller; Mantoni, T

2013-01-01

for eight subjects, respectively, were excluded from analysis because of insufficient signal quality. Running increased mean arterial pressure and mean MCA velocity and induced rhythmic oscillations in BP and in MCA velocity corresponding to the difference between step rate and heart rate (HR) frequencies....... During running, rhythmic oscillations in arterial BP induced by interference between HR and step frequency impact on cerebral blood velocity. For the exercise as a whole, average MCA velocity becomes elevated. These results suggest that running not only induces an increase in regional cerebral blood flow...

Differential increases in blood flow velocity in the middle cerebral artery after tourniquet deflation during sevoflurane, isoflurane or propofol anaesthesia.

Science.gov (United States)

Kadoi, Y; Kawauchi, C H; Ide, M; Saito, S; Mizutani, A

2009-07-01

The purpose of this study was to examine the comparative effects of sevoflurane, isoflurane or propofol on cerebral blood flow velocity after tourniquet deflation during orthopaedic surgery. Thirty patients undergoing elective orthopaedic surgery were randomly divided into sevoflurane, isoflurane and propofol groups. Anaesthesia was maintained with sevoflurane, isoflurane or propofol infusion in 33% oxygen and 67% nitrous oxide, in whatever concentrations were necessary to keep bispectral index values between 45 and 50. Ventilatory rate or tidal volume was adjusted to target PaCO2 of 35 mmHg. A 2.0 MHz transcranial Doppler probe was attached to the patient's head at the temporal window and mean blood flow velocity in the middle cerebral artery was continuously measured. The extremity was exsanguinated with an Esmarch bandage and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, velocity in the middle cerebral artery and arterial blood gas analysis were measured every minute for 10 minutes after release of the tourniquet in all three groups. Velocity in the middle cerebral artery in the three groups increased for five minutes after tourniquet deflation. Because of the different cerebrovascular effects of the three agents, the degree of increase in flow velocity in the isoflurane group was greater than in the other two groups, the change in flow velocity in the propofol group being the lowest (at three minutes after deflation 40 +/- 7%, 32 +/- 6% and 28 +/- 10% in the isoflurane, sevoflurane and propofol groups respectively, P < 0.05).

Non-invasive pulmonary blood flow analysis and blood pressure mapping derived from 4D flow MRI

Science.gov (United States)

Delles, Michael; Rengier, Fabian; Azad, Yoo-Jin; Bodenstedt, Sebastian; von Tengg-Kobligk, Hendrik; Ley, Sebastian; Unterhinninghofen, Roland; Kauczor, Hans-Ulrich; Dillmann, Rüdiger

2015-03-01

In diagnostics and therapy control of cardiovascular diseases, detailed knowledge about the patient-specific behavior of blood flow and pressure can be essential. The only method capable of measuring complete time-resolved three-dimensional vector fields of the blood flow velocities is velocity-encoded magnetic resonance imaging (MRI), often denoted as 4D flow MRI. Furthermore, relative pressure maps can be computed from this data source, as presented by different groups in recent years. Hence, analysis of blood flow and pressure using 4D flow MRI can be a valuable technique in management of cardiovascular diseases. In order to perform these tasks, all necessary steps in the corresponding process chain can be carried out in our in-house developed software framework MEDIFRAME. In this article, we apply MEDIFRAME for a study of hemodynamics in the pulmonary arteries of five healthy volunteers. The study included measuring vector fields of blood flow velocities by phase-contrast MRI and subsequently computing relative blood pressure maps. We visualized blood flow by streamline depictions and computed characteristic values for the left and the right pulmonary artery (LPA and RPA). In all volunteers, we observed a lower amount of blood flow in the LPA compared to the RPA. Furthermore, we visualized blood pressure maps using volume rendering and generated graphs of pressure differences between the LPA, the RPA and the main pulmonary artery. In most volunteers, blood pressure was increased near to the bifurcation and in the proximal LPA, leading to higher average pressure values in the LPA compared to the RPA.

Collision Based Blood Cell Distribution of the Blood Flow

Science.gov (United States)

Cinar, Yildirim

2003-11-01

Introduction: The goal of the study is the determination of the energy transferring process between colliding masses and the application of the results to the distribution of the cell, velocity and kinetic energy in arterial blood flow. Methods: Mathematical methods and models were used to explain the collision between two moving systems, and the distribution of linear momentum, rectilinear velocity, and kinetic energy in a collision. Results: According to decrease of mass of the second system, the velocity and momentum of constant mass of the first system are decreased, and linearly decreasing mass of the second system captures a larger amount of the kinetic energy and the rectilinear velocity of the collision system on a logarithmic scale. Discussion: The cause of concentration of blood cells at the center of blood flow an artery is not explained by Bernoulli principle alone but the kinetic energy and velocity distribution due to collision between the big mass of the arterial wall and the small mass of blood cells must be considered as well.

Mean blood velocities and flow impedance in the fetal descending thoracic aortic and common carotid artery in normal pregnancy.

Science.gov (United States)

Bilardo, C M; Campbell, S; Nicolaides, K H

1988-12-01

A linear array pulsed Doppler duplex scanner was used to establish reference ranges for mean blood velocities and flow impedance (Pulsatility Index = PI) in the descending thoracic aorta and in the common carotid artery from 70 fetuses in normal pregnancies at 17-42 weeks' gestation. The aortic velocity increased with gestation up to 32 weeks, then remained constant until term, when it decreased. In contrast, the velocity in the common carotid artery increased throughout pregnancy. The PI in the aorta remained constant throughout pregnancy, while in the common carotid artery it fell steeply after 32 weeks. These results suggest that with advancing gestation there is a redistribution of the fetal circulation with decreased impedance to flow to the fetal brain, presumably to compensate for the progressive decrease in fetal blood PO2.

Transcranial Doppler ultrasonography in children with sickle cell anemia: Clinical and laboratory correlates for elevated blood flow velocities.

Science.gov (United States)

Lagunju, IkeOluwa; Sodeinde, Olugbemiro; Brown, Biobele; Akinbami, Felix; Adedokun, Babatunde

2014-02-01

Transcranial Doppler (TCD) sonography of major cerebral arteries is now recommended for routine screening for stroke risk in children with sickle cell disease (SCD). We performed TCD studies on children with sickle cell anemia (SCA) seen at the pediatric hematology clinic over a period of 2 years. TCD scans were repeated yearly in children with normal flow velocities and every 3 months in children with elevated velocities. Findings were correlated with clinical variables, hematologic indices, and arterial oxygen saturation. Predictors of elevated velocities were identified by multiple linear regressions. We enrolled 237 children and performed a total of 526 TCD examinations. Highest time-averaged maximum flow velocities were ≥170 cm/s in 72 (30.3%) cases and ≥200 cm/s in 20 (8.4%). Young age, low hematocrit, low hemoglobin, and arterial oxygen desaturation <95% showed significant correlations with presence of increased cerebral flow velocities. Low hematocrit, low hemoglobin concentration, young age, and low arterial oxygen desaturation predicted elevated cerebral blood flow velocities and, invariably, increased stroke risk, in children with SCA. Children who exhibit these features should be given high priority for TCD examination in the setting of limited resources. Copyright © 2013 Wiley Periodicals, Inc.

No relationship between cerebral blood flow velocity and cerebrovascular reserve capacity and contemporaneously measured glucose and insulin concentrations in diabetes mellitus

NARCIS (Netherlands)

Fülesdi, B.; Limburg, M.; Bereczki, D.; Molnár, C.; Michels, R. P.; Leányvári, Z.; Csiba, L.

1999-01-01

Blood glucose and insulin concentrations have been reported to influence cerebral hemodynamics. We studied the relationship between actual blood glucose and insulin concentrations and resting cerebral blood flow velocity in the middle cerebral artery and cerebrovascular reserve capacity after

X-ray PIV measurements of blood flows without tracer particles

International Nuclear Information System (INIS)

Kim, Guk Bae; Lee, Sang Joon

2006-01-01

We analyzed the non-Newtonian flow characteristics of blood moving in a circular tube flow using an X-ray PIV method and compared the experimental results with hemodynamic models. The X-ray PIV method was improved for measuring quantitative velocity fields of blood flows using a coherent synchrotron X-ray. Without using any contrast media, this method can visualize flow pattern of blood by enhancing the phase-contrast and interference characteristics of blood cells. The enhanced X-ray images were achieved by optimizing the sample-to-scintillator distance, the sample thickness, and hematocrit in detail. The quantitative velocity fields of blood flows inside opaque conduits were obtained by applying a two-frame PIV algorithm to the X-ray images of the blood flows. The measured velocity data show typical features of blood flow such as the yield stress and shear-thinning effects. (orig.)

Carotid Velocities Determine Cerebral Blood Flow Deficits in Elderly Men with Carotid Stenosis <50%

Directory of Open Access Journals (Sweden)

Arkadiusz Siennicki-Lantz

2012-01-01

Full Text Available To examine if mild carotid stenosis correlates with silent vascular brain changes, we studied a prospective population-based cohort “Men born in 1914.” Data from followups at ages 68 and 81, have been used. Carotid ultrasound was performed at age 81, and cerebral blood flow (CBF was measured with SPECT at age 82. Out of 123 stroke-free patients, carotid stenosis <50% was observed in 94% in the right and 89% in the left internal carotid arteries (ICAs. In these subjects, Peak Systolic Velocities in ICA correlated negatively with CBF in a majority of several brain areas, especially in mesial temporal area. Results were limited to normotensive until their seventies, who developed late-onset hypertension with a subsequent blood pressure, pulse pressure, and ankle-brachial index growth. Elderly with asymptomatic carotid stenosis <50% and peak systolic velocities in ICA 0.7–1.3 m/s, should be offered an intensified pharmacotherapy to prevent stroke or silent cerebrovascular events.

Daily rhythm of cerebral blood flow velocity

Directory of Open Access Journals (Sweden)

Spielman Arthur J

2005-03-01

Full Text Available Abstract Background CBFV (cerebral blood flow velocity is lower in the morning than in the afternoon and evening. Two hypotheses have been proposed to explain the time of day changes in CBFV: 1 CBFV changes are due to sleep-associated processes or 2 time of day changes in CBFV are due to an endogenous circadian rhythm independent of sleep. The aim of this study was to examine CBFV over 30 hours of sustained wakefulness to determine whether CBFV exhibits fluctuations associated with time of day. Methods Eleven subjects underwent a modified constant routine protocol. CBFV from the middle cerebral artery was monitored by chronic recording of Transcranial Doppler (TCD ultrasonography. Other variables included core body temperature (CBT, end-tidal carbon dioxide (EtCO2, blood pressure, and heart rate. Salivary dim light melatonin onset (DLMO served as a measure of endogenous circadian phase position. Results A non-linear multiple regression, cosine fit analysis revealed that both the CBT and CBFV rhythm fit a 24 hour rhythm (R2 = 0.62 and R2 = 0.68, respectively. Circadian phase position of CBT occurred at 6:05 am while CBFV occurred at 12:02 pm, revealing a six hour, or 90 degree difference between these two rhythms (t = 4.9, df = 10, p Conclusion In conclusion, time of day variations in CBFV have an approximately 24 hour rhythm under constant conditions, suggesting regulation by a circadian oscillator. The 90 degree-phase angle difference between the CBT and CBFV rhythms may help explain previous findings of lower CBFV values in the morning. The phase difference occurs at a time period during which cognitive performance decrements have been observed and when both cardiovascular and cerebrovascular events occur more frequently. The mechanisms underlying this phase angle difference require further exploration.

The Effects of Taekwondo Training on Peripheral Neuroplasticity-Related Growth Factors, Cerebral Blood Flow Velocity, and Cognitive Functions in Healthy Children: A Randomized Controlled Trial

Directory of Open Access Journals (Sweden)

Su-Youn Cho

2017-04-01

Full Text Available Although regular Taekwondo (TKD training has been reported to be effective for improving cognitive function in children, the mechanism underlying this improvement remains unclear. The purpose of the present study was to observe changes in neuroplasticity-related growth factors in the blood, assess cerebral blood flow velocity, and verify the resulting changes in children’s cognitive function after TKD training. Thirty healthy elementary school students were randomly assigned to control (n = 15 and TKD (n = 15 groups. The TKD training was conducted for 60 min at a rating of perceived exertion (RPE of 11–15, 5 times per week, for 16 weeks. Brain-derived neurotrophic factor (BDNF, vascular endothelial growth factor (VEGF, and insulin-like growth factor-1 (IGF-1 levels were measured by blood sampling before and after the training, and the cerebral blood flow velocities (peak systolic [MCAs], end diastolic [MCAd], mean cerebral blood flow velocities [MCAm], and pulsatility index [PI] of the middle cerebral artery (MCA were measured using Doppler ultrasonography. For cognitive function assessment, Stroop Color and Word Tests (Word, Color, and Color-Word were administered along with other measurements. The serum BDNF, VEGF, and IGF-1 levels and the Color-Word test scores among the sub-factors of the Stroop Color and Word Test scores were significantly higher in the TKD group after the intervention (p < 0.05. On the other hand, no statistically significant differences were found in any factors related to cerebral blood flow velocities, or in the Word test and Color test scores (p > 0.05. Thus, 16-week TKD training did not significantly affect cerebral blood flow velocities, but the training may have been effective in increasing children’s cognitive function by inducing an increase in the levels of neuroplasticity-related growth factors.

Reduced Arteriovenous Shunting Capacity After Local Heating and Redistribution of Baseline Skin Blood Flow in Type 2 Diabetes Assessed With Velocity-Resolved Quantitative Laser Doppler Flowmetry

Science.gov (United States)

Fredriksson, Ingemar; Larsson, Marcus; Nyström, Fredrik H.; Länne, Toste; Östgren, Carl J.; Strömberg, Tomas

2010-01-01

OBJECTIVE To compare the microcirculatory velocity distribution in type 2 diabetic patients and nondiabetic control subjects at baseline and after local heating. RESEARCH DESIGN AND METHODS The skin blood flow response to local heating (44°C for 20 min) was assessed in 28 diabetic patients and 29 control subjects using a new velocity-resolved quantitative laser Doppler flowmetry technique (qLDF). The qLDF estimates erythrocyte (RBC) perfusion (velocity × concentration), in a physiologically relevant unit (grams RBC per 100 g tissue × millimeters per second) in a fixed output volume, separated into three velocity regions: v 10 mm/s. RESULTS The increased blood flow occurs in vessels with a velocity >1 mm/s. A significantly lower response in qLDF total perfusion was found in diabetic patients than in control subjects after heat provocation because of less high-velocity blood flow (v >10 mm/s). The RBC concentration in diabetic patients increased sevenfold for v between 1 and 10 mm/s, and 15-fold for v >10 mm/s, whereas no significant increase was found for v <1 mm/s. The mean velocity increased from 0.94 to 7.3 mm/s in diabetic patients and from 0.83 to 9.7 mm/s in control subjects. CONCLUSIONS The perfusion increase occurs in larger shunting vessels and not as an increase in capillary flow. Baseline diabetic patient data indicated a redistribution of flow to higher velocity regions, associated with longer duration of diabetes. A lower perfusion was associated with a higher BMI and a lower toe-to-brachial systolic blood pressure ratio. PMID:20393143

Is the measurement of inferior thyroid artery blood flow velocity by color-flow Doppler ultrasonography useful for differential diagnosis between gestational transient thyrotoxicosis and Graves' disease? A prospective study.

Science.gov (United States)

Zuhur, Sayid Shafi; Ozel, Alper; Velet, Selvinaz; Buğdacı, Mehmet Sait; Cil, Esra; Altuntas, Yüksel

2012-01-01

To determine the role of peak systolic velocity, end-diastolic velocity and resistance indices of both the right and left inferior thyroid arteries measured by color-flow Doppler ultrasonography for a differential diagnosis between gestational transient thyrotoxicosis and Graves' disease during pregnancy. The right and left inferior thyroid artery-peak systolic velocity, end-diastolic velocity and resistance indices of 96 patients with thyrotoxicosis (41 with gestational transient thyrotoxicosis, 31 age-matched pregnant patients with Graves' disease and 24 age- and sex-matched non-pregnant patients with Graves' disease) and 25 age and sex-matched healthy euthyroid subjects were assessed with color-flow Doppler ultrasonography. The right and left inferior thyroid artery-peak systolic and end-diastolic velocities in patients with gestational transient thyrotoxicosis were found to be significantly lower than those of pregnant patients with Graves' disease and higher than those of healthy euthyroid subjects. However, the right and left inferior thyroid artery peak systolic and end-diastolic velocities in pregnant patients with Graves' disease were significantly lower than those of non-pregnant patients with Graves' disease. The right and left inferior thyroid artery peak systolic and end-diastolic velocities were positively correlated with TSH-receptor antibody levels. We found an overlap between the inferior thyroid artery-blood flow velocities in a considerable number of patients with gestational transient thyrotoxicosis and pregnant patients with Graves' disease. This study suggests that the measurement of inferior thyroid artery-blood flow velocities with color-flow Doppler ultrasonography does not have sufficient sensitivity and specificity to be recommended as an initial diagnostic test for a differential diagnosis between gestational transient thyrotoxicosis and Graves' disease during pregnancy.

In vivo visualization method by absolute blood flow velocity based on speckle and fringe pattern using two-beam multipoint laser Doppler velocimetry

Energy Technology Data Exchange (ETDEWEB)

Kyoden, Tomoaki, E-mail: kyouden@nc-toyama.ac.jp; Naruki, Shoji; Akiguchi, Shunsuke; Momose, Noboru; Homae, Tomotaka; Hachiga, Tadashi [National Institute of Technology, Toyama College, 1-2 Ebie-Neriya, Imizu, Toyama 933-0293 (Japan); Ishida, Hiroki [Department of Applied Physics, Faculty of Science, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005 (Japan); Andoh, Tsugunobu [Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194 (Japan); Takada, Yogo [Graduate School of Engineering, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi, Osaka 558-8585 (Japan)

2016-08-28

Two-beam multipoint laser Doppler velocimetry (two-beam MLDV) is a non-invasive imaging technique able to provide an image of two-dimensional blood flow and has potential for observing cancer as previously demonstrated in a mouse model. In two-beam MLDV, the blood flow velocity can be estimated from red blood cells passing through a fringe pattern generated in the skin. The fringe pattern is created at the intersection of two beams in conventional LDV and two-beam MLDV. Being able to choose the depth position is an advantage of two-beam MLDV, and the position of a blood vessel can be identified in a three-dimensional space using this technique. Initially, we observed the fringe pattern in the skin, and the undeveloped or developed speckle pattern generated in a deeper position of the skin. The validity of the absolute velocity value detected by two-beam MLDV was verified while changing the number of layers of skin around a transparent flow channel. The absolute velocity value independent of direction was detected using the developed speckle pattern, which is created by the skin construct and two beams in the flow channel. Finally, we showed the relationship between the signal intensity and the fringe pattern, undeveloped speckle, or developed speckle pattern based on the skin depth. The Doppler signals were not detected at deeper positions in the skin, which qualitatively indicates the depth limit for two-beam MLDV.

Middle cerebral artery blood velocity and cerebral blood flow and O2 uptake during dynamic exercise

DEFF Research Database (Denmark)

Madsen, P L; Sperling, B K; Warming, T

1993-01-01

Results obtained by the 133Xe clearance method with external detectors and by transcranial Doppler sonography (TCD) suggest that dynamic exercise causes an increase of global average cerebral blood flow (CBF). These data are contradicted by earlier data obtained during less-well-defined conditions....... To investigate this controversy, we applied the Kety-Schmidt technique to measure the global average levels of CBF and cerebral metabolic rate of oxygen (CMRO2) during rest and dynamic exercise. Simultaneously with the determination of CBF and CMRO2, we used TCD to determine mean maximal flow velocity...... in the middle cerebral artery (MCA Vmean). For values of CBF and MCA Vmean a correction for an observed small drop in arterial PCO2 was carried out. Baseline values for global CBF and CMRO2 were 50.7 and 3.63 ml.100 g-1.min-1, respectively. The same values were found during dynamic exercise, whereas a 22% (P

Recent advances in blood flow vector velocity imaging

DEFF Research Database (Denmark)

Jensen, Jørgen Arendt; Nikolov, Svetoslav; Udesen, Jesper

2011-01-01

tracking. The key advantages of these techniques are very fast imaging that can attain an order of magnitude higher precision than conventional methods. SA flow imaging was implemented on the experimental scanner RASMUS using an 8-emission spherical emission sequence and reception of 64 channels on a BK...... investigated using both simulations, flow rig measurements, and in-vivo validation against MR scans. The TO method obtains a relative accuracy of 10% for a fully transverse flow in both simulations and flow rig experiments. In-vivo studies performed on 11 healthy volunteers comparing the TO method...... been acquired using a commercial implementation of the method (BK Medical ProFocus Ultraview scanner). A range of other methods are also presented. This includes synthetic aperture imaging using either spherical or plane waves with velocity estimation performed with directional beamforming or speckle...

Modeling cerebral blood flow during posture change from sitting to standing

DEFF Research Database (Denmark)

Ottesen, Johnny T.; Olufsen, M.; Tran, H.T.

2004-01-01

extremities, the brain, and the heart. We use physiologically based control mechanisms to describe the regulation of cerebral blood flow velocity and arterial pressure in response to orthostatic hypotension resulting from postural change. To justify the fidelity of our mathematical model and control......Abstract Hypertension, decreased cerebral blood flow, and diminished cerebral blood flow velocity regulation, are among the first signs indicating the presence of cerebral vascular disease. In this paper, we will present a mathematical model that can predict blood flow and pressure during posture...

Brain blood flow and blood pressure during hypoxia in the epaulette shark Hemiscyllium ocellatum, a hypoxia-tolerant elasmobranch.

Science.gov (United States)

Söderström, V; Renshaw, G M; Nilsson, G E

1999-04-01

The key to surviving hypoxia is to protect the brain from energy depletion. The epaulette shark (Hemiscyllium ocellatum) is an elasmobranch able to resist energy depletion and to survive hypoxia. Using epi-illumination microscopy in vivo to observe cerebral blood flow velocity on the brain surface, we show that cerebral blood flow in the epaulette shark is unaffected by 2 h of severe hypoxia (0.35 mg O2 l-1 in the respiratory water, 24 C). Thus, the epaulette shark differs from other hypoxia- and anoxia-tolerant species studied: there is no adenosine-mediated increase in cerebral blood flow such as that occurring in freshwater turtles and cyprinid fish. However, blood pressure showed a 50 % decrease in the epaulette shark during hypoxia, indicating that a compensatory cerebral vasodilatation occurs to maintain cerebral blood flow. We observed an increase in cerebral blood flow velocity when superfusing the normoxic brain with adenosine (making sharks the oldest vertebrate group in which this mechanism has been found). The adenosine-induced increase in cerebral blood flow velocity was reduced by the adenosine receptor antagonist aminophylline. Aminophylline had no effect upon the maintenance of cerebral blood flow during hypoxia, however, indicating that adenosine is not involved in maintaining cerebral blood flow in the epaulette shark during hypoxic hypotension.

Maximum Likelihood Blood Velocity Estimator Incorporating Properties of Flow Physics

DEFF Research Database (Denmark)

Schlaikjer, Malene; Jensen, Jørgen Arendt

2004-01-01

)-data under investigation. The flow physic properties are exploited in the second term, as the range of velocity values investigated in the cross-correlation analysis are compared to the velocity estimates in the temporal and spatial neighborhood of the signal segment under investigation. The new estimator...... has been compared to the cross-correlation (CC) estimator and the previously developed maximum likelihood estimator (MLE). The results show that the CMLE can handle a larger velocity search range and is capable of estimating even low velocity levels from tissue motion. The CC and the MLE produce...... for the CC and the MLE. When the velocity search range is set to twice the limit of the CC and the MLE, the number of incorrect velocity estimates are 0, 19.1, and 7.2% for the CMLE, CC, and MLE, respectively. The ability to handle a larger search range and estimating low velocity levels was confirmed...

Algorithms for estimating blood velocities using ultrasound

DEFF Research Database (Denmark)

Jensen, Jørgen Arendt

2000-01-01

Ultrasound has been used intensively for the last 15 years for studying the hemodynamics of the human body. Systems for determining both the velocity distribution at one point of interest (spectral systems) and for displaying a map of velocity in real time have been constructed. A number of schemes...... have been developed for performing the estimation, and the various approaches are described. The current systems only display the velocity along the ultrasound beam direction and a velocity transverse to the beam is not detected. This is a major problem in these systems, since most blood vessels...... are parallel to the skin surface. Angling the transducer will often disturb the flow, and new techniques for finding transverse velocities are needed. The various approaches for determining transverse velocities will be explained. This includes techniques using two-dimensional correlation (speckle tracking...

Hybrid PIV-PTV technique for measuring blood flow in rat mesenteric vessels.

Science.gov (United States)

Ha, Hojin; Nam, Kweon-Ho; Lee, Sang Joon

2012-11-01

The micro-particle tracking velocimetry (μ-PTV) technique is used to obtain the velocity fields of blood flow in the microvasculature under in vivo conditions because it can provide the blood velocity distribution in microvessels with high spatial resolution. The in vivo μ-PTV technique usually requires a few to tens of seconds to obtain a whole velocity profile across the vessel diameter because of the limited number density of tracer particles under in vivo conditions. Thus, the μ-PTV technique alone is limited in measuring unsteady blood flows that fluctuate irregularly due to the heart beating and muscle movement in surrounding tissues. In this study, a new hybrid PIV-PTV technique was established by combining PTV and particle image velocimetry (PIV) techniques to resolve the drawbacks of the μ-PTV method in measuring blood flow in microvessels under in vivo conditions. Images of red blood cells (RBCs) and fluorescent particles in rat mesenteric vessels were obtained simultaneously. Temporal variations of the centerline blood velocity were monitored using a fast Fourier transform-based cross-correlation PIV method. The fluorescence particle images were analyzed using the μ-PTV technique to extract the spatial distribution of the velocity vectors. Data from the μ-PTV and PIV methods were combined to obtain a better estimate of the velocity profile in actual blood flow. This technique will be useful in investigating hemodynamics in microcirculation by measuring unsteady irregular blood flows more accurately. Copyright © 2012 Elsevier Inc. All rights reserved.

Effect of head rotation on cerebral blood velocity in the prone position

DEFF Research Database (Denmark)

Højlund, Jakob; Sandmand, Marie; Sonne, Morten

2012-01-01

for cerebral blood flow. We tested in healthy subjects the hypothesis that rotating the head in the prone position reduces cerebral blood flow. Methods. Mean arterial blood pressure (MAP), stroke volume (SV), and CO were determined, together with the middle cerebral artery mean blood velocity (MCA V...... V(mean) ~10% in spite of an elevated MAP. Prone positioning with rotated head affects both CBF and cerebrovenous drainage indicating that optimal brain perfusion requires head centering....

Inner ocular blood flow responses to an acute decrease in blood pressure in resting humans

International Nuclear Information System (INIS)

Ikemura, Tsukasa; Kashima, Hideaki; Yamaguchi, Yuji; Miyaji, Akane; Hayashi, Naoyuki

2015-01-01

Whether inner ocular vessels have an autoregulatory response to acute fluctuations in blood pressure is unclear. We tried to examine the validity of acute hypotension elicited by thigh-cuff release as to assess the dynamic autoregulation in the ocular circulation. Blood flow velocity in the superior nasal and inferior temporal retinal arterioles, and in the retinal and choroidal vasculature were measured with the aid of laser speckle flowgraphy before and immediately after an acute decrease in blood pressure in 20 healthy subjects. Acute hypotension was induced by a rapid release of bilateral thigh occlusion cuffs that had been inflated to 220 mmHg for 2 min. The ratio of the relative change in retinal and choroidal blood flow velocity to the relative change in mean arterial blood pressure (MAP) was calculated. Immediately after cuff release, the MAP and blood flows in the all ocular target vessels decreased significantly from the baseline values obtained before thigh-cuff release. The ratio of the relative change in inner ocular blood flow velocity to that in the MAP exceeded 1% / %mmHg. An explicit dynamic autoregulation in inner ocular vessels cannot be demonstrated in response to an acute hypotension induced by the thigh-cuff release technique. (paper)

Ocular blood flow decreases during passive heat stress in resting humans.

Science.gov (United States)

Ikemura, Tsukasa; Miyaji, Akane; Kashima, Hideaki; Yamaguchi, Yuji; Hayashi, Naoyuki

2013-12-06

Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow. Ocular blood flow, end-tidal carbon dioxide (P(ET)CO2) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35 °C (normothermia) for 30 min and (2) at 50 °C for 90 min (passive heat stress). The blood-flow velocities in the superior temporal retinal arteriole (STRA), superior nasal retinal arteriole (SNRA), and the retinal and choroidal vessels (RCV) were measured using laser-speckle flowgraphy. Blood flow in the STRA and SNRA was calculated from the integral of a cross-sectional map of blood velocity. PETCO2 was clamped at the normothermia level by adding 5% CO2 to the inspired gas. Passive heat stress had no effect on the subjects' blood pressures. The blood-flow velocity in the RCV was significantly lower after 30, 60 and 90 min of passive heat stress than the normothermic level, with a peak decrease of 18 ± 3% (mean ± SE) at 90 min. Blood flow in the STRA and SNRA decreased significantly after 90 min of passive heat stress conditions, with peak decreases of 14 ± 3% and 14 ± 4%, respectively. The findings of this study suggest that passive heat stress decreases ocular blood flow irrespective of the blood pressure or arterial partial pressure of CO2.

Thermographic venous blood flow characterization with external cooling stimulation

Science.gov (United States)

Saxena, Ashish; Ng, E. Y. K.; Raman, Vignesh

2018-05-01

Experimental characterization of blood flow in a human forearm is done with the application of continuous external cooling based active thermography method. Qualitative and quantitative detection of the blood vessel in a thermal image is done, along with the evaluation of blood vessel diameter, blood flow direction, and velocity in the target blood vessel. Subtraction based image manipulation is performed to enhance the feature contrast of the thermal image acquired after the removal of external cooling. To demonstrate the effect of occlusion diseases (obstruction), an external cuff based occlusion is applied after the removal of cooling and its effect on the skin rewarming is studied. Using external cooling, a transit time method based blood flow velocity estimation is done. From the results obtained, it is evident that an external cooling based active thermography method can be used to develop a diagnosis tool for superficial blood vessel diseases.

Influence of hemodialysis on the mean blood flow velocity in the middle cerebral artery.

Science.gov (United States)

Stefanidis, I; Bach, R; Mertens, P R; Liakopoulos, V; Liapi, G; Mann, H; Heintz, B

2005-08-01

Several effects of hemodialysis, including hemoconcentration, alterations of hemostasis or hemorheology and endothelial activation, could potentially interfere with cerebral blood flow (CBF) regulation. These treatment-specific changes may also be crucial for the enhanced incidence of stroke in uremic patients. Nevertheless, the influence of hemodialysis on CBF has not been yet adequately studied. We registered mean blood flow velocity (MFV) in the middle cerebral artery (MCA) during hemodialysis treatment in order to evaluate its contribution on CBF changes. Transcranial Doppler ultrasonography (TCD) of the MCA was performed continuously during hemodialysis treatment in 18 stable patients (10 males and 8 females, mean age 62 +/- 11 years) with end-stage renal disease of various origin. Blood pressure (mmHg), heart rate (/min), ultrafiltration volume (ml), BV changes (deltaBV by hemoglobinometry, %), arterial blood gases (pO2, blood oxygen content, pCO2), hemostasis activation (thrombin-antithrombin III complex, ELISA) and fibrinogen (Clauss) were measured simultaneously at the beginning of treatment and every hour thereafter. Before the hemodialysis session the MFV in the MCA was within normal range (57.5 +/- 13.0 cm/s, ref. 60 +/- 12) and was mainly dependent on the patients' age (r = -0.697, p delta%MFV) were interrelated to the ultrafiltration volume (r = -0.486, p delta%acO2, r = -0.420, p delta%fibrinogen, r = 0.244, p < 0.05). A significant continuous decrease of the MFV in the MCA was observed during hemodialysis treatment, which inversely correlated both with ultrafiltration volume, BV changes and changes of plasma fibrinogen. The ultrafiltration-induced hemoconcentration with concomitant rise of hematocrit and oxygen transport capacity, may partly explain the alterations in the cerebral MFV observed during hemodialysis.

Velocity estimation using synthetic aperture imaging [blood flow

DEFF Research Database (Denmark)

Nikolov, Svetoslav; Jensen, Jørgen Arendt

2001-01-01

Presented an approach for synthetic aperture blood flow ultrasound imaging. Estimates with a low bias and standard deviation can be obtained with as few as eight emissions. The performance of the new estimator is verified using both simulations and measurements. The results demonstrate that a fully...

Simulation of blood flow in a small-diameter vascular graft model with a swirl (spiral) flow guider.

Science.gov (United States)

Zhang, ZhiGuo; Fan, YuBo; Deng, XiaoYan; Wang, GuiXue; Zhang, He; Guidoin, Robert

2008-10-01

Small-diameter vascular grafts are in large demand for coronary and peripheral bypass procedures, but present products still fail in long-term clinical application. In the present communication, a new type of small-diameter graft with a swirl flow guider was proposed to improve graft patency rate. Flow pattern in the graft was simulated numerically and compared with that in a conventional graft. The numerical results revealed that the swirl flow guider could indeed make the blood flow rotate in the new graft. The swirling flow distal to the flow guider significantly altered the flow pattern in the new graft and the velocity profiles were re-distributed. Due to the swirling flow, the blood velocity near the vessel wall and wall shear rate were greatly enhanced. We believe that the increased blood velocity near the wall and the wall shear rate can impede the occurrence of acute thrombus formation and intimal hyperplasia, hence can improve the graft patency rate for long-term clinical use.

Evaluation of arterial digital blood flow using Doppler ultrasonography in healthy dairy cows.

Science.gov (United States)

Müller, H; Heinrich, M; Mielenz, N; Reese, S; Steiner, A; Starke, A

2017-06-06

Local circulatory disturbances have been implicated in the development of foot disorders in cattle. The goals of this study were to evaluate the suitability of the interdigital artery in the pastern region in both hind limbs using pulsed-wave (PW) Doppler ultrasonography and to investigate quantitative arterial blood flow variables at that site in dairy cows. An Esaote MyLabOne ultrasound machine with a 10-MHz linear transducer was used to assess blood flow in the interdigital artery in the pastern region in both hind limbs of 22 healthy German Holstein cows. The cows originated from three commercial farms and were restrained in a standing hoof trimming chute without sedation. A PW Doppler signal suitable for analysis was obtained in 17 of 22 cows. The blood flow profiles were categorised into four curve types, and the following quantitative variables were measured in three uniform cardiac cycles: vessel diameter, pulse rate, maximum systolic velocity, maximum diastolic velocity, end-diastolic velocity, reverse velocity, maximum time-averaged mean velocity, blood flow rate, resistance index and persistence index. The measurements did not differ among cows from the three farms. Maximum systolic velocity, vessel diameter and pulse rate did not differ but other variables differed significantly among blood flow profiles. Differences in weight-bearing are thought to be responsible for the normal variability of blood flow profiles in healthy cows. The scanning technique used in this report for evaluation of blood flow in the interdigital artery appears suitable for further investigations in healthy and in lame cows.

Transesophageal Doppler measurement of renal arterial blood flow velocities and indices in children.

Science.gov (United States)

Zabala, Luis; Ullah, Sana; Pierce, Carol D'Ann; Gautam, Nischal K; Schmitz, Michael L; Sachdeva, Ritu; Craychee, Judith A; Harrison, Dale; Killebrew, Pamela; Bornemeier, Renee A; Prodhan, Parthak

2012-06-01

Doppler-derived renal blood flow indices have been used to assess renal pathologies. However, transesophageal ultrasonography (TEE) has not been previously used to assess these renal variables in pediatric patients. In this study, we (a) assessed whether TEE allows adequate visualization of the renal parenchyma and renal artery, and (b) evaluated the concordance of TEE Doppler-derived renal blood flow measurements/indices compared with a standard transabdominal renal ultrasound (TAU) in children. This prospective cohort study enrolled 28 healthy children between the ages of 1 and 17 years without known renal dysfunction who were undergoing atrial septal defect device closure in the cardiac catheterization laboratory. TEE was used to obtain Doppler renal artery blood velocities (peak systolic velocity, end-diastolic velocity, mean diastolic velocity, resistive index, and pulsatility index), and these values were compared with measurements obtained by TAU. Concordance correlation coefficient (CCC) was used to determine clinically significant agreement between the 2 methods. The Bland-Altman plots were used to determine whether these 2 methods agree sufficiently to be used interchangeably. Statistical significance was accepted at P ≤ 0.05. Obtaining 2-dimensional images of kidney parenchyma and Doppler-derived measurements using TEE in children is feasible. There was statistically significant agreement between the 2 methods for all measurements. The CCC between the 2 imaging techniques was 0.91 for the pulsatility index and 0.66 for the resistive index. These coefficients were sensitive to outliers. When the highest and lowest data points were removed from the analysis, the CCC between the 2 imaging techniques was 0.62 for the pulsatility index and 0.50 for the resistive index. The 95% confidence interval (CI) for pulsatility index was 0.35 to 0.98 and for resistive index was 0.21 to 0.89. The Bland-Altman plots indicate good agreement between the 2 methods; for the

Tissue motion in blood velocity estimation and its simulation

DEFF Research Database (Denmark)

Schlaikjer, Malene; Torp-Pedersen, Søren; Jensen, Jørgen Arendt

1998-01-01

to the improvement of color flow imaging. Optimization based on in-vivo data is difficult since the blood and tissue signals cannot be accurately distinguished and the correct extend of the vessel under investigation is often unknown. This study introduces a model for the simulation of blood velocity data in which...... tissue motion is included. Tissue motion from breathing, heart beat, and vessel pulsation were determined based on in-vivo RF-data obtained from 10 healthy volunteers. The measurements were taken at the carotid artery at one condition and in the liver at three conditions. Each measurement was repeated 10....... The motion due to the heart, when the volunteer was asked to hold his breath, gave a peak velocity of 4.2±1.7 mm/s. The movement of the carotid artery wall due to changing blood pressure had a peak velocity of 8.9±3.7 mm/s over the cardiac cycle. The variations are due to differences in heart rhythm...

In vivo analysis of physiological 3D blood flow of cerebral veins

Energy Technology Data Exchange (ETDEWEB)

Schuchardt, Florian; Schroeder, Laure; Baeuerle, Jochen; Harloff, Andreas [University Medical Centre, Department of Neurology, Freiburg (Germany); Anastasopoulos, Constantin [University Medical Center, Department of Neuropaediatrics and Muscle Disorders, Freiburg (Germany); University Medical Centre, Department of Neuroradiology, Freiburg (Germany); Markl, Michael [Northwestern University, Department of Radiology, Feinberg School of Medicine and McCormick School of Engineering, Chicago, IL (United States); Hennemuth, Anja; Drexl, Johann [Fraunhofer MEVIS, Bremen (Germany); Valdueza, Jose M. [Neurological Center, Segeberger Kliniken, Bad Segeberg (Germany); Mader, Irina [University Medical Centre, Department of Neuroradiology, Freiburg (Germany)

2015-08-15

To visualize and quantify physiological blood flow of intracranial veins in vivo using time-resolved, 3D phase-contrast MRI (4D flow MRI), and to test measurement accuracy. Fifteen healthy volunteers underwent repeated ECG-triggered 4D flow MRI (3 Tesla, 32-channel head coil). Intracranial venous blood flow was analysed using dedicated software allowing for blood flow visualization and quantification in analysis planes at the superior sagittal, straight, and transverse sinuses. MRI was evaluated for intra- and inter-observer agreement and scan-rescan reproducibility. Measurements of the transverse sinuses were compared with transcranial two-dimensional duplex ultrasound. Visualization of 3D blood flow within cerebral sinuses was feasible in 100 % and within at least one deep cerebral vein in 87 % of the volunteers. Blood flow velocity/volume increased along the superior sagittal sinus and was lower in the left compared to the right transverse sinus. Intra- and inter-observer reliability and reproducibility of blood flow velocity (mean difference 0.01/0.02/0.02 m/s) and volume (mean difference 0.0002/-0.0003/0.00003 l/s) were good to excellent. High/low velocities were more pronounced (8 % overestimation/9 % underestimation) in MRI compared to ultrasound. Four-dimensional flow MRI reliably visualizes and quantifies three-dimensional cerebral venous blood flow in vivo and is promising for studies in patients with sinus thrombosis and related diseases. (orig.)

Computational Analysis of Human Blood Flow

Science.gov (United States)

Panta, Yogendra; Marie, Hazel; Harvey, Mark

2009-11-01

Fluid flow modeling with commercially available computational fluid dynamics (CFD) software is widely used to visualize and predict physical phenomena related to various biological systems. In this presentation, a typical human aorta model was analyzed assuming the blood flow as laminar with complaint cardiac muscle wall boundaries. FLUENT, a commercially available finite volume software, coupled with Solidworks, a modeling software, was employed for the preprocessing, simulation and postprocessing of all the models.The analysis mainly consists of a fluid-dynamics analysis including a calculation of the velocity field and pressure distribution in the blood and a mechanical analysis of the deformation of the tissue and artery in terms of wall shear stress. A number of other models e.g. T branches, angle shaped were previously analyzed and compared their results for consistency for similar boundary conditions. The velocities, pressures and wall shear stress distributions achieved in all models were as expected given the similar boundary conditions. The three dimensional time dependent analysis of blood flow accounting the effect of body forces with a complaint boundary was also performed.

Blood flow patterns during incremental and steady-state aerobic exercise.

Science.gov (United States)

Coovert, Daniel; Evans, LeVisa D; Jarrett, Steven; Lima, Carla; Lima, Natalia; Gurovich, Alvaro N

2017-05-30

Endothelial shear stress (ESS) is a physiological stimulus for vascular homeostasis, highly dependent on blood flow patterns. Exercise-induced ESS might be beneficial on vascular health. However, it is unclear what type of ESS aerobic exercise (AX) produces. The aims of this study are to characterize exercise-induced blood flow patterns during incremental and steady-state AX. We expect blood flow pattern during exercise will be intensity-dependent and bidirectional. Six college-aged students (2 males and 4 females) were recruited to perform 2 exercise tests on cycleergometer. First, an 8-12-min incremental test (Test 1) where oxygen uptake (VO2), heart rate (HR), blood pressure (BP), and blood lactate (La) were measured at rest and after each 2-min step. Then, at least 48-hr. after the first test, a 3-step steady state exercise test (Test 2) was performed measuring VO2, HR, BP, and La. The three steps were performed at the following exercise intensities according to La: 0-2 mmol/L, 2-4 mmol/L, and 4-6 mmol/L. During both tests, blood flow patterns were determined by high-definition ultrasound and Doppler on the brachial artery. These measurements allowed to determine blood flow velocities and directions during exercise. On Test 1 VO2, HR, BP, La, and antegrade blood flow velocity significantly increased in an intensity-dependent manner (repeated measures ANOVA, pflow velocity did not significantly change during Test 1. On Test 2 all the previous variables significantly increased in an intensity-dependent manner (repeated measures ANOVA, pflow patterns during incremental and steady-state exercises include both antegrade and retrograde blood flows.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

Science.gov (United States)

Lee, Sang Joon; Park, Han Wook; Jung, Sung Yong

2014-09-01

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Study of microvascular non-Newtonian blood flow modulated by electroosmosis.

Science.gov (United States)

Tripathi, Dharmendra; Yadav, Ashu; Anwar Bég, O; Kumar, Rakesh

2018-05-01

An analytical study of microvascular non-Newtonian blood flow is conducted incorporating the electro-osmosis phenomenon. Blood is considered as a Bingham rheological aqueous ionic solution. An externally applied static axial electrical field is imposed on the system. The Poisson-Boltzmann equation for electrical potential distribution is implemented to accommodate the electrical double layer in the microvascular regime. With long wavelength, lubrication and Debye-Hückel approximations, the boundary value problem is rendered non-dimensional. Analytical solutions are derived for the axial velocity, volumetric flow rate, pressure gradient, volumetric flow rate, averaged volumetric flow rate along one time period, pressure rise along one wavelength and stream function. A plug swidth is featured in the solutions. Via symbolic software (Mathematica), graphical plots are generated for the influence of Bingham plug flow width parameter, electrical Debye length and Helmholtz-Smoluchowski velocity (maximum electro-osmotic velocity) on the key hydrodynamic variables. This study reveals that blood flow rate accelerates with decreasing the plug width (i.e. viscoplastic nature of fluids) and also with increasing the Debye length parameter. Copyright © 2018 Elsevier Inc. All rights reserved.

MR flow velocity measurement using 2D phase contrast, assessment of imaging parameters

International Nuclear Information System (INIS)

Akata, Soichi; Fukushima, Akihiro; Abe, Kimihiko; Darkanzanli, A.; Gmitro, A.F.; Unger, E.C.; Capp, M.P.

1999-01-01

The two-dimensional (2D) phase contrast technique using balanced gradient pulses is utilized to measure flow velocities of cerebrospinal fluid and blood. Various imaging parameters affect the accuracy of flow velocity measurements to varying degrees. Assessment of the errors introduced by changing the imaging parameters are presented and discussed in this paper. A constant flow phantom consisting of a pump, a polyethylene tube and a flow meter was assembled. A clinical 1.5 Tesla MR imager was used to perform flow velocity measurements. The phase contrast technique was used to estimate the flow velocity of saline through the phantom. The effects of changes in matrix size, flip angle, flow compensation, and velocity encoding (VENC) value were tested in the pulse sequence. Gd-DTPA doped saline was used to study the effect of changing T1 on the accuracy of flow velocity measurement. Matrix size (within practical values), flip angle, and flow compensation had minimum impact on flow velocity measurements. T1 of the solution also had no effect on the accuracy of measuring the flow velocity. On the other hand, it was concluded that errors as high as 20% can be expected in the flow velocity measurements if the VENC value is not properly chosen. (author)

MR flow velocity measurement using 2D phase contrast, assessment of imaging parameters

Energy Technology Data Exchange (ETDEWEB)

Akata, Soichi; Fukushima, Akihiro; Abe, Kimihiko [Tokyo Medical Coll. (Japan); Darkanzanli, A.; Gmitro, A.F.; Unger, E.C.; Capp, M.P.

1999-11-01

The two-dimensional (2D) phase contrast technique using balanced gradient pulses is utilized to measure flow velocities of cerebrospinal fluid and blood. Various imaging parameters affect the accuracy of flow velocity measurements to varying degrees. Assessment of the errors introduced by changing the imaging parameters are presented and discussed in this paper. A constant flow phantom consisting of a pump, a polyethylene tube and a flow meter was assembled. A clinical 1.5 Tesla MR imager was used to perform flow velocity measurements. The phase contrast technique was used to estimate the flow velocity of saline through the phantom. The effects of changes in matrix size, flip angle, flow compensation, and velocity encoding (VENC) value were tested in the pulse sequence. Gd-DTPA doped saline was used to study the effect of changing T1 on the accuracy of flow velocity measurement. Matrix size (within practical values), flip angle, and flow compensation had minimum impact on flow velocity measurements. T1 of the solution also had no effect on the accuracy of measuring the flow velocity. On the other hand, it was concluded that errors as high as 20% can be expected in the flow velocity measurements if the VENC value is not properly chosen. (author)

Dogs with hearth diseases causing turbulent high-velocity blood flow have changes in patelet function and von Willebrand factor multimer distribution

DEFF Research Database (Denmark)

Tarnow, Inge; Kristensen, Annemarie Thuri; Olsen, Lisbeth Høier

2005-01-01

The purpose of this prospective study was to investigate platelet function using in vitro tests based on both high and low shear rates and von Willebrand factor (vWf) multimeric composition in dogs with cardiac disease and turbulent high-velocity blood flow. Client-owned asymptomatic, untreated d...

The effect of ventricular assist devices on cerebral blood flow and blood pressure fractality

International Nuclear Information System (INIS)

Bellapart, Judith; Fraser, John F; Chan, Gregory S H; Tzeng, Yu-Chieh; Ainslie, Philip N; Dunster, Kimble R; Barnett, Adrian G; Boots, Rob

2011-01-01

Biological signals often exhibit self-similar or fractal scaling characteristics which may reflect intrinsic adaptability to their underlying physiological system. This study analysed fractal dynamics of cerebral blood flow in patients supported with ventricular assist devices (VAD) to ascertain if sustained modifications of blood pressure waveform affect cerebral blood flow fractality. Simultaneous recordings of arterial blood pressure and cerebral blood flow velocity using transcranial Doppler were obtained from five cardiogenic shock patients supported by VAD, five matched control patients and five healthy subjects. Computation of a fractal scaling exponent (α) at the low-frequency time scale by detrended fluctuation analysis showed that cerebral blood flow velocity exhibited 1/f fractal scaling in both patient groups (α = 0.95 ± 0.09 and 0.97 ± 0.12, respectively) as well as in the healthy subjects (α = 0.86 ± 0.07). In contrast, fluctuation in blood pressure was similar to non-fractal white noise in both patient groups (α = 0.53 ± 0.11 and 0.52 ± 0.09, respectively) but exhibited 1/f scaling in the healthy subjects (α = 0.87 ± 0.04, P < 0.05 compared with the patient groups). The preservation of fractality in cerebral blood flow of VAD patients suggests that normal cardiac pulsation and central perfusion pressure changes are not the integral sources of cerebral blood flow fractality and that intrinsic vascular properties such as cerebral autoregulation may be involved. However, there is a clear difference in the fractal scaling properties of arterial blood pressure between the cardiogenic shock patients and the healthy subjects

Pulmonary branch arterial flow can be measured with cine MR velocity mapping

International Nuclear Information System (INIS)

Caputo, G.R.; Kondo, C.; Masui, T.; Foster, E.; Geraci, S.J.; O'Sullivan, M.; Higgins, C.B.

1990-01-01

This paper assesses the capability of cine MR phase velocity mapping (CVM) to measure main, right-sided, and left-sided pulmonary arterial (PA) blood flow. The authors examined a constant-flow phantom and nine healthy volunteers with use of 1.5-T MR imaging system (GE Signa) with phase velocity cine sequences. CVM correctly measured constant-flow phantom velocities (range, 20-190 cm/sec; r = .998, SEE = 4.2 cm/sec), and velocity with use of angulated planes to section the phantom tube perpendicularly. CVM peak systolic main PA velocity (79 cm/sec ± 10) correlated well with Doppler US measurements (80 cm/sec ± 7). CVM main PA flow correlated well with conventional cine MR LV stroke volume measurements (r = .98, SEE = 4.8 mL). Left and right PA flow on the angulated planes were 29 mL ± 7 and 34 mL ± 10, respectively

In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles.

Science.gov (United States)

Lima, Rui; Wada, Shigeo; Takeda, Motohiro; Tsubota, Ken-ichi; Yamaguchi, Takami

2007-01-01

A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-microm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements.

Blood transfusion in preterm infants improves intestinal tissue oxygenation without alteration in blood flow.

Science.gov (United States)

Banerjee, J; Leung, T S; Aladangady, N

2016-11-01

The objective of the study was to investigate the splanchnic blood flow velocity and oximetry response to blood transfusion in preterm infants according to postnatal age. Preterm infants receiving blood transfusion were recruited to three groups: 1-7 (group 1; n = 20), 8-28 (group 2; n = 21) and ≥29 days of life (group 3; n = 18). Superior mesenteric artery (SMA) peak systolic (PSV) and diastolic velocities were measured 30-60 min pre- and post-transfusion using Doppler ultrasound scan. Splanchnic tissue haemoglobin index (sTHI), tissue oxygenation index (sTOI) and fractional tissue oxygen extraction (sFTOE) were measured from 15-20 min before to post-transfusion using near-infrared spectroscopy. The mean pretransfusion Hb in group 1, 2 and 3 was 11, 10 and 9 g/dl, respectively. The mean (SD) pretransfusion SMA PSV in group 1, 2 and 3 was 0·63 (0·32), 0·81 (0·33) and 0·97 (0·40) m/s, respectively, and this did not change significantly following transfusion. The mean (SD) pretransfusion sTOI in group 1, 2 and 3 was 36·7 (19·3), 44·6 (10·4) and 41·3 (10·4)%, respectively. The sTHI and sTOI increased (P transfusion in all groups. On multivariate analysis, changes in SMA PSV and sTOI following blood transfusion were not associated with PDA, feeding, pretransfusion Hb and mean blood pressure. Pretransfusion baseline splanchnic tissue oximetry and blood flow velocity varied with postnatal age. Blood transfusion improved intestinal tissue oxygenation without altering mesenteric blood flow velocity irrespective of postnatal ages. © 2016 International Society of Blood Transfusion.

Differential effects of hyperventilation on cerebral blood flow velocity after tourniquet deflation during sevoflurane, isoflurane, or propofol anesthesia.

Science.gov (United States)

Hinohara, Hiroshi; Kadoi, Yuji; Ide, Masanobu; Kuroda, Masataka; Saito, Shigeru; Mizutani, Akio

2010-08-01

The purpose of this study was to compare the degree of increase in middle cerebral artery (MCA) blood flow velocity after tourniquet deflation when modulating hyperventilation during orthopedic surgery under sevoflurane, isoflurane, or propofol anesthesia. Twenty-four patients undergoing elective orthopedic surgery were randomly divided into sevoflurane, isoflurane, and propofol groups. Anesthesia was maintained with sevoflurane, isoflurane, or propofol administration with 33% oxygen and 67% nitrous oxide at anesthetic drug concentrations adequate to maintain bispectral values between 45 and 50. A 2.0-MHz transcranial Doppler probe was attached to the patient's head at the temporal window, and mean blood flow velocity in the MCA (V (mca)) was continuously measured. The extremity was exsanguinated with an Esmarch bandage, and the pneumatic tourniquet was inflated to a pressure of 450 mmHg. Arterial blood pressure, heart rate, V (mca) and arterial blood gases were measured every minute for 10 min after release of the tourniquet in all three groups. Immediately after tourniquet release, the patients' respiratory rates were increased to tightly maintain end-tidal carbon dioxide (PetCO(2)) at 35 mmHg. No change in partial pressure of carbon dioxide in arterial blood (PaCO(2)) was observed pre- and posttourniquet deflation in any of the three groups. Increase in V (mca) in the isoflurane group was greater than that in the other two groups after tourniquet deflation. In addition, during the study period, no difference in V (mca) after tourniquet deflation was observed between the propofol and sevoflurane groups. Hyperventilation could prevent an increase in V (mca) in the propofol and sevoflurane groups after tourniquet deflation. However, hyperventilation could not prevent an increase in V (mca) in the isoflurane group.

Animal models of surgically manipulated flow velocities to study shear stress-induced atherosclerosis.

Science.gov (United States)

Winkel, Leah C; Hoogendoorn, Ayla; Xing, Ruoyu; Wentzel, Jolanda J; Van der Heiden, Kim

2015-07-01

Atherosclerosis is a chronic inflammatory disease of the arterial tree that develops at predisposed sites, coinciding with locations that are exposed to low or oscillating shear stress. Manipulating flow velocity, and concomitantly shear stress, has proven adequate to promote endothelial activation and subsequent plaque formation in animals. In this article, we will give an overview of the animal models that have been designed to study the causal relationship between shear stress and atherosclerosis by surgically manipulating blood flow velocity profiles. These surgically manipulated models include arteriovenous fistulas, vascular grafts, arterial ligation, and perivascular devices. We review these models of manipulated blood flow velocity from an engineering and biological perspective, focusing on the shear stress profiles they induce and the vascular pathology that is observed. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Examples of Vector Velocity Imaging

DEFF Research Database (Denmark)

Hansen, Peter M.; Pedersen, Mads M.; Hansen, Kristoffer L.

2011-01-01

To measure blood flow velocity in vessels with conventional ultrasound, the velocity is estimated along the direction of the emitted ultrasound wave. It is therefore impossible to obtain accurate information on blood flow velocity and direction, when the angle between blood flow and ultrasound wa...

EFFICACY OF LASER PULSE FREQUENCIES ON BLOOD FLOW IN TYPE 2 DIABETIC PATIENTS

Directory of Open Access Journals (Sweden)

Amir Nazih Wadee

2017-04-01

Full Text Available Background: Research reports had noted an apparent increase in cutaneous and deep blood flow as a result of low-intensity laser therapy (LLLT in normal subjects. The purpose of te study was to investigate the effective laser pulse frequency either (200 or 2000 Hz on improving blood flow in type 2 diabetic patients. Forty-five diabetic patients selected from out clinic of Kasr El-Aini Hospital, Cairo University assigned randomly into three groups. The blood flow volume, blood flow velocity and caliper of the blood vessel were evaluated before laser application and after twelve sessions using duplex Doppler ultrasound. Methods: Combined He-Ne and infrared LILT was administered three times a week for twelve sessions at intensity of 3 J, power 500 mW, 808 nm duration 15 min and pulse frequency 200 Hz for group I, 2000 Hz for group II, and sham LILT for group III on the sural artery at posterior aspect of dominant leg. Result: Paired t-test revealed that low pulse frequency (200 Hz LILT produced significant improvement in blood flow volume and blood flow velocity (t= 1.76, p= 0.001 and t= 2.8, p= 0.01 respectively (P<0.05. While there was no significant changes in caliper of the blood vessel of group I, blood flow volume, blood flow velocity or caliper of the blood vessel of group II and group III (t= 2.15, p= 1, t= 2.15, p= 1, t= 1.11 p= 0.31, t= 1.54, p= 0.15, t= 2.51, p= 1, t= 1.21 p= 0.33, t= 1.45, p= 0.15 respectively (P<0.05. ANOVA test in between groups revealed insignificant changes in all pre and post- measures except significant results in blood flow volume and velocity which indicating the superiority of group I on both group II and III by post hoc test. Conclusion: low pulse frequency of LILT (200 Hz could improve blood flow than high pulse frequency (2000 Hz.

Unsteady Blood Flow with Nanoparticles Through Stenosed Arteries in the Presence of Periodic Body Acceleration

Science.gov (United States)

Fatin Jamil, Dzuliana; Roslan, Rozaini; Abdulhameed, Mohammed; Che-Him, Norziha; Sufahani, Suliadi; Mohamad, Mahathir; Ghazali Kamardan, Muhamad

2018-04-01

The effects of nanoparticles such as Fe 3O4,TiO2, and Cu on blood flow inside a stenosed artery are studied. In this study, blood was modelled as non-Newtonian Bingham plastic fluid subjected to periodic body acceleration and slip velocity. The flow governing equations were solved analytically by using the perturbation method. By using the numerical approaches, the physiological parameters were analyzed, and the blood flow velocity distributions were generated graphically and discussed. From the flow results, the flow speed increases as slip velocity increases and decreases as the values of yield stress increases.

Alterations of Blood Flow Through Arteries Following Atherectomy and the Impact on Pressure Variation and Velocity.

Science.gov (United States)

Plourde, Brian D; Vallez, Lauren J; Sun, Biyuan; Nelson-Cheeseman, Brittany B; Abraham, John P; Staniloae, Cezar S

2016-09-01

Simulations were made of the pressure and velocity fields throughout an artery before and after removal of plaque using orbital atherectomy plus adjunctive balloon angioplasty or stenting. The calculations were carried out with an unsteady computational fluid dynamic solver that allows the fluid to naturally transition to turbulence. The results of the atherectomy procedure leads to an increased flow through the stenotic zone with a coincident decrease in pressure drop across the stenosis. The measured effect of atherectomy and adjunctive treatment showed decrease the systolic pressure drop by a factor of 2.3. Waveforms obtained from a measurements were input into a numerical simulation of blood flow through geometry obtained from medical imaging. From the numerical simulations, a detailed investigation of the sources of pressure loss was obtained. It is found that the major sources of pressure drop are related to the acceleration of blood through heavily occluded cross sections and the imperfect flow recovery downstream. This finding suggests that targeting only the most occluded parts of a stenosis would benefit the hemodynamics. The calculated change in systolic pressure drop through the lesion was a factor of 2.4, in excellent agreement with the measured improvement. The systolic and cardiac-cycle-average pressure results were compared with measurements made in a multi-patient study treated with orbital atherectomy and adjunctive treatment. The agreements between the measured and calculated systolic pressure drop before and after the treatment were within 3%. This excellent agreement adds further confidence to the results. This research demonstrates the use of orbital atherectomy to facilitate balloon expansion to restore blood flow and how pressure measurements can be utilized to optimize revascularization of occluded peripheral vessels.

Relationship of antral follicular blood flow velocity to superovulatory responses in ewes.

Science.gov (United States)

Oliveira, M E F; Bartlewski, P M; Jankowski, N; Padilha-Nakaghi, L C; Oliveira, L G; Bicudo, S D; Fonseca, J F; Vicente, W R R

2017-07-01

The aim of this study was to examine the association between antral follicular blood flow velocity and the response of ewes to hormonal ovarian superstimulation. Ten Santa Inês ewes were subjected to a short- (7days; Group 1) or long-term (13days; Group 2) progesterone (CIDR ® ; InterAg, Hamilton, New Zealand) priming, and a superovulatory treatment with porcine follicle-stimulating hormone (pFSH; Folltropin ® -V; Bioniche Animal Health, Belleville, ON, Canada), given twice daily for four consecutive days in decreasing doses and initiated four or ten days after CIDR insertion, respectively. Embryos were recovered surgically seven days after the last pFSH dose. From one day prior to until the end of the pFSH regimen (Days -1 to 3), all ewes underwent daily transrectal ultrasonography of ovaries. The number of high-velocity pixels (HVPs; 0.055-0.11m/s or upper 50% of recordable velocities) on Day 1 correlated directly with the number of corpora lutea (CL; r=0.92, P=0.0002) and of viable embryos (r=0.77, P=0.01). Correlations were also recorded between the number of HVPs on Day 3 and the recovery rate (r=-0.69, P=0.03), viability rate (r=-0.64, P=0.05), and percentage of degenerated embryos (r=0.65, P=0.04). The percentage of HVPs relative to the total area of ovarian cross section on Day 1 was correlated with the number of CL (r=0.95, Pflow has the makings of a useful non-invasive method to predict the outcome of the superovulatory treatment in ewes. Copyright © 2017 Elsevier B.V. All rights reserved.

Investigation of spiral blood flow in a model of arterial stenosis.

Science.gov (United States)

Paul, Manosh C; Larman, Arkaitz

2009-11-01

The spiral component of blood flow has both beneficial and detrimental effects in human circulatory system [Stonebridge PA, Brophy CM. Spiral laminar flow in arteries? Lancet 1991; 338: 1360-1]. We investigate the effects of the spiral blood flow in a model of three-dimensional arterial stenosis with a 75% cross-sectional area reduction at the centre by means of computational fluid dynamics (CFD) techniques. The standard k-omega model is employed for simulation of the blood flow for the Reynolds number of 500 and 1000. We find that for Re=500 the spiral component of the blood flow increases both the total pressure and velocity of the blood, and some significant differences are found between the wall shear stresses of the spiral and non-spiral induced flow downstream of the stenosis. The turbulent kinetic energy is reduced by the spiral flow as it induces the rotational stabilities in the forward flow. For Re=1000 the tangential component of the blood velocity is most influenced by the spiral speed, but the effect of the spiral flow on the centreline turbulent kinetic energy and shear stress is mild. The results of the effects of the spiral flow are discussed in the paper along with the relevant pathological issues.

[Assessment of maternal cerebral blood flow in patients with preeclampsia].

Science.gov (United States)

Mandić, Vesna; Miković, Zeljko; Dukić, Milan; Vasiljević, Mladenko; Filimonović, Dejan; Bogavac, Mirjana

2005-01-01

Systemic vasoconstriction in preeclamptic patients increases vascular resistance, and is manifested by increased arterial blood flow velocity. The aim of the study is to evaluate if there is a change of Doppler indices in maternal medial cerbral artery (MCA) in severe preeclampsia due to: 1) severity of clinical symptoms, 2) the begining of eclamptic attack and 3) the application of anticonvulsive therapy. A prospective clinical study included 92 pregnant women, gestational age 28-36 weeks. They were divided into three groups: normotensive (n=30), mild preeclampsia (n=33), and severe preeclampsia (n=29). We investigated maternal cerebral circulation by assessing the MCA. We registrated: pulsatility index (Pi), resistance index (Ri), systolic/diastolic ratio (S/D), and the maximum systolic, end diastolic and medium velocity. Patients with severe preeclampsia were divided into two subgroups. subgroup 1 included patients without symptoms of threatening eclampsia (n=18; 62.06%); while subgroup 2 included those with symptoms of preeclampsia (n=11; 37.94%). All patients with severe preeclampsia were treated with magnesium sulfate (MgSO4), and cerebral blood flow was measured before and after the treatment. Statistical analysis was done by oneway ANOVA, Student t-test and t-paired sample test. The difference was considered to be significant if ppreclampsia we found increased velocity values, Pi and Ri, especially in patients with signs of threatened eclampsia, suggesting that blood vessels changes are most prominent in severe preeclampsia. Cerebral blood flow meassurements can be used as a clinical test for the prediction of eclampsia. Magnesium-sulfate (MgSO4) has a signifficant role in prophylaxis and treatment of eclampsia, and, therefore, positive influence on reduction of cerebral ishemic lesions can be expected. We can conclude that changes of the cerebral blood flow can be evaluated by evaluating blood flow velocities in the medial cerebral artery. Velocities tend

Estimation of vessel diameter and blood flow dynamics from laser speckle images

DEFF Research Database (Denmark)

Postnov, Dmitry D.; Tuchin, Valery V.; Sosnovtseva, Olga

2016-01-01

Laser speckle imaging is a rapidly developing method to study changes of blood velocity in the vascular networks. However, to assess blood flow and vascular responses it is crucial to measure vessel diameter in addition to blood velocity dynamics. We suggest an algorithm that allows for dynamical...

Diastolic coronary artery pressure-flow velocity relationships in conscious man.

Science.gov (United States)

Dole, W P; Richards, K L; Hartley, C J; Alexander, G M; Campbell, A B; Bishop, V S

1984-09-01

We characterised the diastolic pressure-flow velocity relationship in the normal left coronary artery of conscious man before and after vasodilatation with angiographic contrast medium. Phasic coronary artery pressure and flow velocity were measured in ten patients during individual diastoles (0.5 to 1.0 s) using a 20 MHz catheter-tipped, pulsed Doppler transducer. All pressure-flow velocity curves were linear over the diastolic pressure range of 110 +/- 15 (SD) mmHg to 71 +/- 7 mmHg (r = 0.97 +/- 0.01). In the basal state, values for slope and extrapolated zero flow pressure intercept averaged 0.35 +/- 0.12 cm X s-1 X mmHg-1 and 51.7 +/- 8.6 mmHg, respectively. Vasodilatation resulted in a 2.5 +/- 0.5 fold increase in mean flow velocity. The diastolic pressure-flow velocity relationship obtained during peak vasodilatation compared to that during basal conditions was characterised by a steeper slope (0.80 +/- 0.48 cm X s-1 X mmHg-1, p less than 0.001) and lower extrapolated zero flow pressure intercept (37.9 +/- 9.8 mmHg, p less than 0.05). Mean right atrial pressure for the group averaged 4.4 +/- 1.7 mmHg, while left ventricular end-diastolic pressure averaged 8.7 +/- 2.8 mmHg. These observations in man are similar to data reported in the canine coronary circulation which are consistent with a vascular waterfall model of diastolic flow regulation. In this model, coronary blood flow may be regulated by changes in diastolic zero flow pressure as well as in coronary resistance.

Real-Time GPU Implementation of Transverse Oscillation Vector Velocity Flow Imaging

DEFF Research Database (Denmark)

Bradway, David; Pihl, Michael Johannes; Krebs, Andreas

2014-01-01

Rapid estimation of blood velocity and visualization of complex flow patterns are important for clinical use of diagnostic ultrasound. This paper presents real-time processing for two-dimensional (2-D) vector flow imaging which utilizes an off-the-shelf graphics processing unit (GPU). In this work...... vector flow acquisition takes 2.3 milliseconds seconds on an Advanced Micro Devices Radeon HD 7850 GPU card. The detected velocities are accurate to within the precision limit of the output format of the display routine. Because this tool was developed as a module external to the scanner’s built...

Acoustic radiation force impulse elastography of the kidneys: is shear wave velocity affected by tissue fibrosis or renal blood flow?

Science.gov (United States)

Asano, Kenichiro; Ogata, Ai; Tanaka, Keiko; Ide, Yoko; Sankoda, Akiko; Kawakita, Chieko; Nishikawa, Mana; Ohmori, Kazuyoshi; Kinomura, Masaru; Shimada, Noriaki; Fukushima, Masaki

2014-05-01

The aim of this study was to identify the main influencing factor of the shear wave velocity (SWV) of the kidneys measured by acoustic radiation force impulse elastography. The SWV was measured in the kidneys of 14 healthy volunteers and 319 patients with chronic kidney disease. The estimated glomerular filtration rate was calculated by the serum creatinine concentration and age. As an indicator of arteriosclerosis of large vessels, the brachial-ankle pulse wave velocity was measured in 183 patients. Compared to the degree of interobserver and intraobserver deviation, a large variance of SWV values was observed in the kidneys of the patients with chronic kidney disease. Shear wave velocity values in the right and left kidneys of each patient correlated well, with high correlation coefficients (r = 0.580-0.732). The SWV decreased concurrently with a decline in the estimated glomerular filtration rate. A low SWV was obtained in patients with a high brachial-ankle pulse wave velocity. Despite progression of renal fibrosis in the advanced stages of chronic kidney disease, these results were in contrast to findings for chronic liver disease, in which progression of hepatic fibrosis results in an increase in the SWV. Considering that a high brachial-ankle pulse wave velocity represents the progression of arteriosclerosis in the large vessels, the reduction of elasticity succeeding diminution of blood flow was suspected to be the main influencing factor of the SWV in the kidneys. This study indicates that diminution of blood flow may affect SWV values in the kidneys more than the progression of tissue fibrosis. Future studies for reducing data variance are needed for effective use of acoustic radiation force impulse elastography in patients with chronic kidney disease.

THE ALGORITHM OF DETERMINATION OF EYE FUNDUS VESSELS BLOOD FLOW CHARACTERISTICS ON VIDEOSEQUENCE

Directory of Open Access Journals (Sweden)

O. V. Nedzvedz

2018-01-01

Full Text Available The method of determination of the dynamic characteristics like the vessel diameter change, the linear and volume blood velocities in the vessels of the eye fundus is considered. Such characteristics allow to determine blood flow changes in the microvasculature affecting the blood flow in the brain, kidneys and coronary vessels. Developed algorithm includes four stages: the video sequence stabilization, the vessels segmentation with the help of a neural network, the determination of the instantaneous velocity in the vessels based on the optical flow and the analysis of the results.

High Frame-Rate Blood Vector Velocity Imaging Using Plane Waves: Simulations and Preliminary Experiments

DEFF Research Database (Denmark)

Udesen, Jesper; Gran, Fredrik; Hansen, Kristoffer Lindskov

2008-01-01

) The ultrasound is not focused during the transmissions of the ultrasound signals; 2) A 13-bit Barker code is transmitted simultaneously from each transducer element; and 3) The 2-D vector velocity of the blood is estimated using 2-D cross-correlation. A parameter study was performed using the Field II program......, and performance of the method was investigated when a virtual blood vessel was scanned by a linear array transducer. An improved parameter set for the method was identified from the parameter study, and a flow rig measurement was performed using the same improved setup as in the simulations. Finally, the common...... carotid artery of a healthy male was scanned with a scan sequence that satisfies the limits set by the Food and Drug Administration. Vector velocity images were obtained with a frame-rate of 100 Hz where 40 speckle images are used for each vector velocity image. It was found that the blood flow...

Retinal hemodynamic oxygen reactivity assessed by perfusion velocity, blood oximetry and vessel diameter measurements

DEFF Research Database (Denmark)

Klefter, Oliver Niels; Lauritsen, Anne Øberg; Larsen, Michael

2015-01-01

PURPOSE: To test the oxygen reactivity of a fundus photographic method of measuring macular perfusion velocity and to integrate macular perfusion velocities with measurements of retinal vessel diameters and blood oxygen saturation. METHODS: Sixteen eyes in 16 healthy volunteers were studied at two...... is a valid method for assessing macular perfusion. Results were consistent with previous observations of hyperoxic blood flow reduction using blue field entoptic and laser Doppler velocimetry. Retinal perfusion seemed to be regulated around individual set points according to blood glucose levels. Multimodal...

Prediction of blood pressure and blood flow in stenosed renal arteries using CFD

Science.gov (United States)

Jhunjhunwala, Pooja; Padole, P. M.; Thombre, S. B.; Sane, Atul

2018-04-01

In the present work an attempt is made to develop a diagnostive tool for renal artery stenosis (RAS) which is inexpensive and in-vitro. To analyse the effects of increase in the degree of severity of stenosis on hypertension and blood flow, haemodynamic parameters are studied by performing numerical simulations. A total of 16 stenosed models with varying degree of stenosis severity from 0-97.11% are assessed numerically. Blood is modelled as a shear-thinning, non-Newtonian fluid using the Carreau model. Computational Fluid Dynamics (CFD) analysis is carried out to compute the values of flow parameters like maximum velocity and maximum pressure attained by blood due to stenosis under pulsatile flow. These values are further used to compute the increase in blood pressure and decrease in available blood flow to kidney. The computed available blood flow and secondary hypertension for varying extent of stenosis are mapped by curve fitting technique using MATLAB and a mathematical model is developed. Based on these mathematical models, a quantification tool is developed for tentative prediction of probable availability of blood flow to the kidney and severity of stenosis if secondary hypertension is known.

Measurement of blood flow in the carotid arteries using color doppler in healthy Korean adults

International Nuclear Information System (INIS)

Moon, Ki Ho; Jeon, Do Ig; Choi, Chang Ho; Ro, Young Jin; Kim, Hak Jin; Lee, Suck Hong; Kim, Byung Soo

1994-01-01

To evaluate the blood flow patterns and velocities of the carotid arteries in healthy Korean adults. We evaluated the blood flow patterns and measured the peak systolic and end-diastolic velocities of the common, internal and external carotid arteries in 48 healthy adults who did not have cardiovascular disorders and neck lesions. The velocity difference was analyzed according to different age groups. In addition, peak systolic and end-diastolic velocity ratio of the internal to common carotid artery was estimated, and our data were compared with values reported by other authors. Generally, the velocity in the younger age group tends be to higher than in older group. The peak systolic and end diastolic velocities of the internal carotid artery were 84.5 cm/sec and 30.5 cm/sec. The peak systolic and end diastolic velocity ratio of the internal to common carotid artery were 0.715 and 0.966. The internal carotid artery was less resistant in blood flow than the external carotid artery. Our data were lower than the values which were reported by Bluth et al. The blood flow velocities of the internal carotid artery in healthy adults were lower than those of previous reported foreign values, but the patterns were similar

Regulation of pulpal blood flow

International Nuclear Information System (INIS)

Kim, S.

1985-01-01

The regulation of blood flow of the dental pulp was investigated in dogs and rats anesthetized with sodium pentobarbital. Pulpal blood flow was altered by variations of local and systemic hemodynamics. Macrocirculatory blood flow (ml/min/100 g) in the dental pulp was measured with both the 133 Xe washout and the 15-microns radioisotope-labeled microsphere injection methods on the canine teeth of dogs, to provide a comparison of the two methods in the same tooth. Microcirculatory studies were conducted in the rat incisor tooth with microscopic determination of the vascular pattern, RBC velocity, and intravascular volumetric flow distribution. Pulpal resistance vessels have alpha- and beta-adrenergic receptors. Activation of alpha-receptors by intra-arterial injection of norepinephrine (NE) caused both a reduction in macrocirculatory Qp in dogs and decreases in arteriolar and venular diameters and intravascular volumetric flow (Qi) in rats. These responses were blocked by the alpha-antagonist PBZ. Activation of beta-receptors by intra-arterial injection of isoproterenal (ISO) caused a paradoxical reduction of Qp in dogs. In rats, ISO caused a transient increase in arteriolar Qi followed by a flow reduction; arteriolar dilation was accompanied by venular constriction. These macrocirculatory and microcirculatory responses to ISO were blocked by the alpha-antagonist propranolol

Quantitative measurement of portal blood flow by magnetic resonance phase contrast. Comparative study of flow phantom and Doppler ultrasound in vivo

International Nuclear Information System (INIS)

Tsunoda, Masatoshi; Kimoto, Shin; Hamazaki, Keisuke; Takeda, Yoshihiro; Hiraki, Yoshio.

1994-01-01

A non-invasive method for measuring portal blood flow by magnetic resonance (MR) phase contrast was evaluated in a flow phantom and 20 healthy volunteers. In a flow phantom study, the flow volumes and mean flow velocities measured by MR phase contrast showed close correlations with those measured by electromagnetic flow-metry. In 20 healthy volunteers, the cross-sectional areas, flow volumes and mean flow velocities measured by MR phase contrast correlated well with those measured by the Doppler ultrasound method. Portal blood flow averaged during the imaging time could be measured under natural breathing conditions by using a large number of acquisitions without the limitations imposed on the Doppler ultrasound method. MR phase contrast is considered to be useful for the non-invasive measurement of portal blood flow. (author)

Effect of blood transfusion on intestinal blood flow and oxygenation in extremely preterm infants during first week of life.

Science.gov (United States)

Banerjee, Jayanta; Leung, Terence S; Aladangady, Narendra

2016-04-01

Extremely preterm infants receive frequent blood transfusions in the first week of life. The aim of this study was to measure the effect of blood transfusion on intestinal blood flow and oxygenation during the first week of life in extremely preterm infants. Superior mesenteric artery (SMA) peak systolic velocity (PSV) and diastolic velocities were measured 30 to 60 minutes before and after transfusion. Splanchnic tissue hemoglobin index (sTHI), splanchnic tissue oxygenation index (sTOI), and splanchnic fractional tissue oxygen extraction (sFTOE) were measured continuously from 15 to 20 minutes before to after transfusion along with vital variables. Twenty infants were studied (median gestational age, 26 weeks). Ten infants were partially fed (15-68 mL/kg/day). Heart rate and SaO2 remained unaltered; blood pressure increased significantly (p transfusion. Mean SMA PSV (p = 0.63) and diastolic velocity (p = 0.65) remained unaltered. Mean pretransfusion SMA PSV was similar in partially fed (0.78 m/sec) compared to unfed infants (0.52 m/sec; p = 0.06) and the response to transfusion was not dissimilar. There was a significant increase in sTHI (mean difference, 32.3%; p transfusion. There was no significant difference in sTHI or sTOI between fed and unfed infants and their response to transfusion. Blood transfusion increased blood pressure and intestinal tissue oxygenation but did not alter blood flow velocities. Partial feeding had no impact on intestinal blood flow and tissue oxygenation changes. © 2015 AABB.

2-D blood vector velocity estimation using a phase shift estimator

DEFF Research Database (Denmark)

Udesen, Jesper

are presented. Here the TO method is tested both in simulations using the Field II program and in flow phantom experiments using the RASMUS scanner. Both simulations and flow phantom experiments indicate that the TO method can estimate the 2-D vector velocity with an acceptable low bias and standard deviation...... velocity estimation is discussed. The TO method is introduced, and the basic theory behind the method is explained. This includes the creation of the acoustic fields, beamforming, echo-canceling and the velocity estimator. In the second part of the thesis the eight papers produced during this PhD project...... when the angle between the blood and the ultrasound beam is above $50^\\circ$. Furthermore, the TO method is tested in-vivo where the scannings are performed by skilled sonographers. The in-vivo scannings resulted in a sequence of 2-D vector CFM images which showed 2-D flow patterns in the bifurcation...

Self-separation of blood plasma from whole blood during the capillary flow in microchannel

Science.gov (United States)

Nunna, Bharath Babu; Zhuang, Shiqiang; Lee, Eon Soo

2017-11-01

Self-separation of blood plasma from whole blood in microchannels is of great importance due to the enormous range of applications in healthcare and diagnostics. Blood is a multiphase complex fluid, composed of cells suspended in blood plasma. RBCs are the suspended particles whose shape changes during the flow of blood. The primary constituents of blood are erythrocytes or red blood cells (RBCs), leukocytes or white blood cells (WBCs), thrombocytes or platelets and blood plasma. The existence of RBCs in blood makes the blood a non-Newtonian fluid. The current study of separation of blood plasma from whole blood during self-driven flows in a single microchannel without bifurcation, by enhancing the capillary effects. The change in the capillary effect results in a change in contact angle which directly influences the capillary flow. The flow velocity directly influences the net force acting on the RBCs and influence the separation process. The experiments are performed on the PDMS microchannels with different contact angles by altering the surface characteristics using plasma treatment. The change in the separation length is studied during the capillary flow of blood in microchannel. Bharath Babu Nunna is a researcher in mechanical engineering and implementing the novel and innovative technologies in the biomedical devices to enhance the sensitivity of the disease diagnosis.

Simple Radiowave-Based Method For Measuring Peripheral Blood Flow Project

Science.gov (United States)

Oliva-Buisson, Yvette J.

2014-01-01

Project objective is to design small radio frequency based flow probes for the measurement of blood flow velocity in peripheral arteries such as the femoral artery and middle cerebral artery. The result will be the technological capability to measure peripheral blood flow rates and flow changes during various environmental stressors such as microgravity without contact to the individual being monitored. This technology may also lead to an easier method of detecting venous gas emboli during extravehicular activities.

Comparative study of methods for blood flow measurement within transverse sinuses by using MR

International Nuclear Information System (INIS)

Gao Gejun; Feng Xiaoyuan; Yang Bojie; Geng Daoying

2003-01-01

Objective: To assess the accuracy of two-dimensional phase contrast (2D-PC) MR method for blood flow measurement within transverse sinuses by comparing this method with cine phase contrast (cine-PC) MR and Doppler in volunteers and patients. Methods: (1) A total of 12 transverse sinuses were examined in 8 healthy volunteers. 2D-PC MR and cine-PC MR were used respectively to measure the transverse area of flow, the flow velocities, and the volumetric flow rates in the same position in every transverse sinus. Paired t-test was used for comparison between the results determined by 2D-PC MR and that determined by cine-PC MR. (2) A total of 6 transverse sinuses were examined in 5 patients who needed operation. 2D-PC MR was used to determine the blood flow velocity of transverse sinus before operation, and Doppler was used to determine the blood flow velocity of the same transverse sinus during operation. The linear regression analysis was used for statistical analysis. Results: (1) Statistical analysis indicated that there were no significant difference among the transverse area of flow (t = -1.106, P = 0.293), the flow velocities (t = 0.262, P = 0.798), and the volumetric flow rates (t = 0.439, P = 0.669) measured by using 2D-PC MR and cine PC MR, respectively. (2) The correlation between flow velocities determined by 2D-PC MR imaging before operation and that determined by Doppler during operation was in excellent agreement (Y-circumflex = 1.303 x + 0.62, r 2 = 0.88). Conclusion: 2D-PC MR may be a practical convenient method for blood flow measurement within transverse sinuses system

Skin cooling maintains cerebral blood flow velocity and orthostatic tolerance during tilting in heated humans

Science.gov (United States)

Wilson, Thad E.; Cui, Jian; Zhang, Rong; Witkowski, Sarah; Crandall, Craig G.

2002-01-01

Orthostatic tolerance is reduced in the heat-stressed human. The purpose of this project was to identify whether skin-surface cooling improves orthostatic tolerance. Nine subjects were exposed to 10 min of 60 degrees head-up tilting in each of four conditions: normothermia (NT-tilt), heat stress (HT-tilt), normothermia plus skin-surface cooling 1 min before and throughout tilting (NT-tilt(cool)), and heat stress plus skin-surface cooling 1 min before and throughout tilting (HT-tilt(cool)). Heating and cooling were accomplished by perfusing 46 and 15 degrees C water, respectively, though a tube-lined suit worn by each subject. During HT-tilt, four of nine subjects developed presyncopal symptoms resulting in the termination of the tilt test. In contrast, no subject experienced presyncopal symptoms during NT-tilt, NT-tilt(cool), or HT-tilt(cool). During the HT-tilt procedure, mean arterial blood pressure (MAP) and cerebral blood flow velocity (CBFV) decreased. However, during HT-tilt(cool), MAP, total peripheral resistance, and CBFV were significantly greater relative to HT-tilt (all P heat-stressed humans.

Ocular blood flow decreases during passive heat stress in resting humans

OpenAIRE

Ikemura, Tsukasa; Miyaji, Akane; Kashima, Hideaki; Yamaguchi, Yuji; Hayashi, Naoyuki

2013-01-01

Background Heat stress induces various physiological changes and so could influence ocular circulation. This study examined the effect of heat stress on ocular blood flow. Findings Ocular blood flow, end-tidal carbon dioxide (P ETCO2) and blood pressure were measured for 12 healthy subjects wearing water-perfused tube-lined suits under two conditions of water circulation: (1) at 35°C (normothermia) for 30 min and (2) at 50°C for 90 min (passive heat stress). The blood-flow velocities in the s...

Particle size, magnetic field, and blood velocity effects on particle retention in magnetic drug targeting.

Science.gov (United States)

Cherry, Erica M; Maxim, Peter G; Eaton, John K

2010-01-01

A physics-based model of a general magnetic drug targeting (MDT) system was developed with the goal of realizing the practical limitations of MDT when electromagnets are the source of the magnetic field. The simulation tracks magnetic particles subject to gravity, drag force, magnetic force, and hydrodynamic lift in specified flow fields and external magnetic field distributions. A model problem was analyzed to determine the effect of drug particle size, blood flow velocity, and magnetic field gradient strength on efficiency in holding particles stationary in a laminar Poiseuille flow modeling blood flow in a medium-sized artery. It was found that particle retention rate increased with increasing particle diameter and magnetic field gradient strength and decreased with increasing bulk flow velocity. The results suggest that MDT systems with electromagnets are unsuitable for use in small arteries because it is difficult to control particles smaller than about 20 microm in diameter.

Altered phase interactions between spontaneous blood pressure and flow fluctuations in type 2 diabetes mellitus: Nonlinear assessment of cerebral autoregulation

Science.gov (United States)

Hu, Kun; Peng, C. K.; Huang, Norden E.; Wu, Zhaohua; Lipsitz, Lewis A.; Cavallerano, Jerry; Novak, Vera

2008-04-01

Cerebral autoregulation is an important mechanism that involves dilatation and constriction in arterioles to maintain relatively stable cerebral blood flow in response to changes of systemic blood pressure. Traditional assessments of autoregulation focus on the changes of cerebral blood flow velocity in response to large blood pressure fluctuations induced by interventions. This approach is not feasible for patients with impaired autoregulation or cardiovascular regulation. Here we propose a newly developed technique-the multimodal pressure-flow (MMPF) analysis, which assesses autoregulation by quantifying nonlinear phase interactions between spontaneous oscillations in blood pressure and flow velocity during resting conditions. We show that cerebral autoregulation in healthy subjects can be characterized by specific phase shifts between spontaneous blood pressure and flow velocity oscillations, and the phase shifts are significantly reduced in diabetic subjects. Smaller phase shifts between oscillations in the two variables indicate more passive dependence of blood flow velocity on blood pressure, thus suggesting impaired cerebral autoregulation. Moreover, the reduction of the phase shifts in diabetes is observed not only in previously-recognized effective region of cerebral autoregulation (type 2 diabetes mellitus alters cerebral blood flow regulation over a wide frequency range and that this alteration can be reliably assessed from spontaneous oscillations in blood pressure and blood flow velocity during resting conditions. We also show that the MMPF method has better performance than traditional approaches based on Fourier transform, and is more suitable for the quantification of nonlinear phase interactions between nonstationary biological signals such as blood pressure and blood flow.

Electromagnetohydrodynamic flow of blood and heat transfer in a capillary with thermal radiation

International Nuclear Information System (INIS)

Sinha, A.; Shit, G.C.

2015-01-01

This paper presents a comprehensive theoretical study on heat transfer characteristics together with fully developed electromagnetohydrodynamic flow of blood through a capillary, having electrokinetic effects by considering the constant heat flux at the wall. The effect of thermal radiation and velocity slip condition have been taken into account. A rigorous mathematical model for describing Joule heating in electro-osmotic flow of blood including the Poisson–Boltzmann equation, the momentum equation and the energy equation is developed. The alterations in the thermal transport phenomenon, induced by the variation of imposed electromagnetic effects, are thoroughly explained through an elegant mathematical formalism. Results presented here pertain to the case where the height of the capillary is much greater than the thickness of electrical double layer comprising the stern and diffuse layers. The essential features of the electromagnetohydrodynamic flow of blood and associated heat transfer characteristics through capillary are clearly highlighted by the variations in the non-dimensional parameters for velocity profile, temperature profile and the Nusselt number. The study reveals that the temperature of blood can be controlled by regulating Joule heating parameter. - Highlights: • Electromagnetohydrodynamic flow of blood in capillary is studied. • Potential electric field is applied for driving elecroosmotic flow of blood. • Effect of thermal radiation, Joule heating and velocity slip is investigated. • Thermal radiation bears the significant change in the temperature field

Electromagnetohydrodynamic flow of blood and heat transfer in a capillary with thermal radiation

Energy Technology Data Exchange (ETDEWEB)

Sinha, A. [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Shit, G.C., E-mail: gopal_iitkgp@yahoo.co.in [Department of Mathematics, Jadavpur University, Kolkata 700032 (India); Institute of Mathematical Sciences, Chennai 600113 (India)

2015-03-15

This paper presents a comprehensive theoretical study on heat transfer characteristics together with fully developed electromagnetohydrodynamic flow of blood through a capillary, having electrokinetic effects by considering the constant heat flux at the wall. The effect of thermal radiation and velocity slip condition have been taken into account. A rigorous mathematical model for describing Joule heating in electro-osmotic flow of blood including the Poisson–Boltzmann equation, the momentum equation and the energy equation is developed. The alterations in the thermal transport phenomenon, induced by the variation of imposed electromagnetic effects, are thoroughly explained through an elegant mathematical formalism. Results presented here pertain to the case where the height of the capillary is much greater than the thickness of electrical double layer comprising the stern and diffuse layers. The essential features of the electromagnetohydrodynamic flow of blood and associated heat transfer characteristics through capillary are clearly highlighted by the variations in the non-dimensional parameters for velocity profile, temperature profile and the Nusselt number. The study reveals that the temperature of blood can be controlled by regulating Joule heating parameter. - Highlights: • Electromagnetohydrodynamic flow of blood in capillary is studied. • Potential electric field is applied for driving elecroosmotic flow of blood. • Effect of thermal radiation, Joule heating and velocity slip is investigated. • Thermal radiation bears the significant change in the temperature field.

On the flow dependency of the electrical conductivity of blood

NARCIS (Netherlands)

Hoetink, AE; Faes, TJC; Visser, KR; Heethaar, RM

Experiments presented in the literature show that the electrical conductivity of flowing blood depends on flow velocity. The aim of this study is to extend the Maxwell-Fricke theory, developed for a dilute suspension of ellipsoidal particles in an electrolyte, to explain this flow dependency of the

Spiral blood flow in aorta-renal bifurcation models.

Science.gov (United States)

Javadzadegan, Ashkan; Simmons, Anne; Barber, Tracie

2016-01-01

The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta-renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta-renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta-renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries.

Relationship of neonatal cerebral blood flow velocity asymmetry with early motor, cognitive and language development in term infants.

Science.gov (United States)

Wu, Ying-Chin; Hsieh, Wu-Shiun; Hsu, Chyong-Hsin; Chiu, Nan-Chang; Chou, Hung-Chieh; Chen, Chien-Yi; Peng, Shinn-Forng; Hung, Han-Yang; Chang, Jui-Hsing; Chen, Wei J; Jeng, Suh-Fang

2013-05-01

The objective of this study was to examine the relationships of Doppler cerebral blood flow velocity (CBFV) asymmetry measures with developmental outcomes in term infants. Doppler CBFV parameters (peak systolic velocity [PSV] and mean velocity [MV]) of the bilateral middle cerebral arteries of 52 healthy term infants were prospectively examined on postnatal days 1-5, and then their motor, cognitive and language development was evaluated with the Bayley Scales of Infant and Toddler Development, Third Edition, at 6, 12, 18 and 24 months of age. The left CBFV asymmetry measure (PSV or MV) was calculated by subtracting the right-side value from the left-side value. Left CBFV asymmetry measures were significantly positively related to motor scores at 6 (r = 0.3-0.32, p cognitive or language outcome. Thus, the leftward hemodynamic status of the middle cerebral arteries, as measured by cranial Doppler ultrasound in the neonatal period, predicts early motor outcome in term infants. Copyright © 2013 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Comparative study of Newtonian physiological blood flow through normal and stenosed carotid artery

Science.gov (United States)

Rahman, Mohammad Matiur; Hossain, Md. Anwar; Mamun, Khairuzzaman; Akhter, Most. Nasrin

2017-06-01

A numerical simulation is performed to investigate Newtonian physiological flows behavior on three dimensional idealized carotid artery (CA) and single stenosed (75% by area) carotid artery(SCA). The wall vessel is set as rigid during simulation. Bifurcated blood vessel are simulated by using three-dimensional flow analysis. Physiological and parabolic velocity profiles are set out to fix the conditions of inlet boundaries of artery. In other hand, physiological waveform is an important part of compilation and it is successfully done by utilization of Fourier series having sixteen harmonics. The investigation has a Reynolds number range of 94 to 1120. Low Reynolds number k — ω model has been used as governing equation. The investigation has been carried out to characterize the flow behavior of blood in two geometry, namely, (i) Normal carotid artery (CA) and (ii) Stenosed carotid artery (SCA). The Newtonian model has been used to study the physics of fluid. The findings of the two models are thoroughly compared in order to observe there behavioral sequence of flows. The numerical results were presented in terms of velocity, pressure, wall shear stress distributions and cross sectional velocities as well as the streamlines contour. Stenosis disturbs the normal pattern of blood flow through the artery as reduced area. At stenosis region velocity and peak Reynolds number rapidly increase and Reynolds number reach transitional and turbulent region. These flow fluctuation and turbulence have bad effect to the blood vessel which makes to accelerate the progress of stenosis.

Multimodal quantitation of the effects of endovascular therapy for vasospasm on cerebral blood flow, transcranial doppler ultrasonographic velocities, and cerebral artery diameters.

Science.gov (United States)

Oskouian, Rod J; Martin, Neil A; Lee, Jae Hong; Glenn, Thomas C; Guthrie, Donald; Gonzalez, Nestor R; Afari, Arash; Viñuela, Fernando

2002-07-01

The goal of this study was to quantify the effects of endovascular therapy on vasospastic cerebral vessels. We reviewed the medical records for 387 patients with ruptured intracranial aneurysms who were treated at a single institution (University of California, Los Angeles) between May 1, 1993, and March 31, 2001. Patients who developed cerebral vasospasm and underwent cerebral arteriographic, transcranial Doppler ultrasonographic, and cerebral blood flow (CBF) studies before and after endovascular therapy for cerebral arterial spasm (vasospasm) were included in this study. Forty-five patients fulfilled the aforementioned criteria and were treated with either papaverine infusion, papaverine infusion with angioplasty, or angioplasty alone. After balloon angioplasty (12 patients), CBF increased from 27.8 +/- 2.8 ml/100 g/min to 28.4 +/- 3.0 ml/100 g/min (P = 0.87); the middle cerebral artery blood flow velocity was 1 57.6 +/- 9.4 cm/s and decreased to 76.3 +/- 9.3 cm/s (P < 0.05), with a mean increase in cerebral artery diameters of 24.4%. Papaverine infusion (20 patients) transiently increased the CBF from 27.5 +/- 2.1 ml/100 g/min to 38.7 +/- 2.8 ml/100 g/min (P < 0.05) and decreased the middle cerebral artery blood flow velocity from 109.9 +/- 9.1 cm/s to 82.8 +/- 8.6 cm/s (P < 0.05). There was a mean increase in vessel diameters of 30.1% after papaverine infusion. Combined treatment (13 patients) significantly increased the CBF from 33.3 +/- 3.2 ml/100 g/min to 41.7 +/- 2.8 ml/100 g/min (P< 0.05) and decreased the transcranial Doppler velocities from 148.9 +/- 12.7 cm/s to 111.4 +/- 10.6 cm/s (P < 0.05), with a mean increase in vessel diameters of 42.2%. Balloon angioplasty increased proximal vessel diameters, whereas papaverine treatment effectively dilated distal cerebral vessels. In our small series, we observed no correlation between early clinical improvement or clinical outcomes and any of our quantitative or physiological data (CBF, transcranial Doppler

X-ray PIV measurement of blood flow in deep vessels of a rat: An in vivo feasibility study.

Science.gov (United States)

Park, Hanwook; Yeom, Eunseop; Lee, Sang Joon

2016-01-18

X-ray PIV measurement is a noninvasive approach to measure opaque blood flows. However, it is not easy to measure real pulsatile blood flows in the blood vessels located at deep position of the body, because the surrounding tissues significantly attenuate the contrast of X-ray images. This study investigated the effect of surrounding tissues on X-ray beam attenuation by measuring the velocity fields of blood flows in deep vessels of a live rat. The decrease in image contrast was minimized by employing biocompatible CO2 microbubbles as tracer particles. The maximum measurable velocity of blood flows in the abdominal aorta of a rat model was found through comparative examination between the PIV measurement accuracy and the level of image contrast according to the input flow rate. Furthermore, the feasibility of using X-ray PIV to accurately measure in vivo blood flows was demonstrated by determining the velocity field of blood flows in the inferior vena cava of a rat. This study may serve as a reference in conducting in vivo X-ray PIV measurements of pulsatile blood flows in animal disease models and investigating hemodynamic characteristics and circulatory vascular diseases.

In-vitro study on haemodiluted blood flow in a sinusoidal microstenosis.

Science.gov (United States)

Kang, M J; Ji, H-S; Lee, S J

2010-01-01

In-vitro experiments were carried out to investigate the haemodynamic and haemorheological behaviours of haemodiluted blood flow through a microstenosis using a micro-particle image velocimetry (PIV) technique. The micro-PIV system employed in this study consisted of a two-head neodymium:yttrium-aluminium-garnet (Nd:YAG) laser, a cooled charge-coupled device camera, and a delay generator. To simulate blood flow in a stenosed vascular vessel, a polydimethylsiloxane (PDMS) microchannel with a sinusoidal throat of 80 per cent severity was employed. The width and depth of the microchannel were 100 microm and 50 microm, respectively. To compare the flow characteristics in the microstenosis, the same experiments were repeated in a straight microchannel under the same flow conditions. Using a syringe pump, human blood with 5 per cent haematocrit was supplied into the microstenosis channel. The flow characteristics and transport of blood cells through the microstenosis were investigated with various flowrates. The mean velocity fields were nearly symmetric with respect to the channel centreline. In the contraction section, the oncoming blood flow was accelerated rapidly, and the maximum velocity at the throat was almost 4.99 times faster than that of the straight microchannel without stenosis. In the diffusion section, the blood cells show rolling, deformation, twisting, and tumbling motion due to the flow-choking characteristics at the stenotic region. The results from this study will provide useful basic data for comparison with those obtained by clinical researchers.

Vector blood velocity estimation in medical ultrasound

DEFF Research Database (Denmark)

Jensen, Jørgen Arendt; Gran, Fredrik; Udesen, Jesper

2006-01-01

Two methods for making vector velocity estimation in medical ultrasound are presented. All of the techniques can find both the axial and transverse velocity in the image and can be used for displaying both the correct velocity magnitude and direction. The first method uses a transverse oscillation...... in the ultrasound field to find the transverse velocity. In-vivo examples from the carotid artery are shown, where complex turbulent flow is found in certain parts of the cardiac cycle. The second approach uses directional beam forming along the flow direction to estimate the velocity magnitude. Using a correlation...... search can also yield the direction, and the full velocity vector is thereby found. An examples from a flow rig is shown....

Spatial Temporal Image Correlation Spectroscopy (STICS) for Flow Analysis with Application for Blood Flow Mapping

International Nuclear Information System (INIS)

Rossow, Molly; Gratton, Enrico; Mantulin, William M.

2009-01-01

It is important for surgeons to be able to measure blood flow in exposed arterioles during surgery. We report our progress in the development of an optical technique that will measure blood flow in surgically exposed blood vessels and enable previously difficult measurements. By monitoring optical fluctuations, the optical technique, based on Spatial Temporal Image Correlation (STICS), will directly measure the velocity of micron-scale particles--such as red blood cells. It will complement existing technology and provide qualitative measurements that were not previously possible. It relies on the concept that blood, when viewed on a small enough scale, is an inhomogeneous substance. Individual blood cells passing between a near-infrared light source and a detector will cause fluctuations in the transmitted optical signal. The speed, direction, and flow pattern of blood cells can be determined from these optical fluctuations. We present a series of computer simulations and experiments on phantom and animal systems to test this technique's ability to map complex flow patterns.

Altered cerebral blood flow velocity features in fibromyalgia patients in resting-state conditions.

Science.gov (United States)

Rodríguez, Alejandro; Tembl, José; Mesa-Gresa, Patricia; Muñoz, Miguel Ángel; Montoya, Pedro; Rey, Beatriz

2017-01-01

The aim of this study is to characterize in resting-state conditions the cerebral blood flow velocity (CBFV) signals of fibromyalgia patients. The anterior and middle cerebral arteries of both hemispheres from 15 women with fibromyalgia and 15 healthy women were monitored using Transcranial Doppler (TCD) during a 5-minute eyes-closed resting period. Several signal processing methods based on time, information theory, frequency and time-frequency analyses were used in order to extract different features to characterize the CBFV signals in the different vessels. Main results indicated that, in comparison with control subjects, fibromyalgia patients showed a higher complexity of the envelope CBFV and a different distribution of the power spectral density. In addition, it has been observed that complexity and spectral features show correlations with clinical pain parameters and emotional factors. The characterization features were used in a lineal model to discriminate between fibromyalgia patients and healthy controls, providing a high accuracy. These findings indicate that CBFV signals, specifically their complexity and spectral characteristics, contain information that may be relevant for the assessment of fibromyalgia patients in resting-state conditions.

Blood pressure and blood flow variation during postural change from sitting to standing: model development and validation

DEFF Research Database (Denmark)

Olufsen, M.S.; Ottesen, Johnny T.; Tran, H.T.

2005-01-01

Short-term cardiovascular responses to postural change from sitting to standing involve complex interactions between the autonomic nervous system, which regulates blood pressure, and cerebral autoregulation, which maintains cerebral perfusion. We present a mathematical model that can predict...... dynamic changes in beat-to-beat arterial blood pressure and middle cerebral artery blood flow velocity during postural change from sitting to standing. Our cardiovascular model utilizes 11 compartments to describe blood pressure, blood flow, compliance, and resistance in the heart and systemic circulation....... To include dynamics due to the pulsatile nature of blood pressure and blood flow, resistances in the large systemic arteries are modeled using nonlinear functions of pressure. A physiologically based submodel is used to describe effects of gravity on venous blood pooling during postural change. Two types...

Trial on MR portal blood flow measurement with phase contrast technique

International Nuclear Information System (INIS)

Tsunoda, Masatoshi; Kimoto, Shin; Togami, Izumi

1991-01-01

Portal blood flow measurement is considered to be important for the analysis of hemodynamics in various liver diseases. The Doppler ultrasound method has been used extensively during the past several years for measuring portal blood flow, as a non-invasive method. However, the Doppler ultrasound technique do not allow the portal blood flow to be measured in cases of obesity, with much intestinal gas, and so on. In this study, we attempted to measure the blood flow in the main trunk of portal vein as an application of MR phase contrast technique to the abdominal region. In the flow phantom study, the flow volumes and the velocities measured by phase contrast technique showed a close correlation with those measured by electromagnetic flowmeter. In the clinical study with 10 healthy volunteers, various values of portal blood flow were obtained. Mean portal blood flow could be measured within the measuring time (about 8 minutes) under natural breathing conditions. Phase contrast technique is considered to be useful for the non-invasive measurement of portal blood flow. (author)

Ultrasonic 3-D Vector Flow Method for Quantitative In Vivo Peak Velocity and Flow Rate Estimation

DEFF Research Database (Denmark)

Holbek, Simon; Ewertsen, Caroline; Bouzari, Hamed

2017-01-01

Current clinical ultrasound (US) systems are limited to show blood flow movement in either 1-D or 2-D. In this paper, a method for estimating 3-D vector velocities in a plane using the transverse oscillation method, a 32×32 element matrix array, and the experimental US scanner SARUS is presented...... is validated in two phantom studies, where flow rates are measured in a flow-rig, providing a constant parabolic flow, and in a straight-vessel phantom ( ∅=8 mm) connected to a flow pump capable of generating time varying waveforms. Flow rates are estimated to be 82.1 ± 2.8 L/min in the flow-rig compared...

Blood flow velocity in the Popliteal Vein using Transverse Oscillation Ultrasound

DEFF Research Database (Denmark)

Bechsgaard, Thor; Lindskov Hansen, Kristoffer; Brandt, Andreas Hjelm

2016-01-01

. Transverse Oscillation US (TOUS), a non-invasive angle independent method, has been implemented on a commercial scanner. TOUS’s advantage compared to SDUS is a more elaborate visualization of complex flow. The aim of this study was to evaluate, whether TOUS perform equal to SDUS for recording velocities...

Examples of in-vivo blood vector velocity estimation

DEFF Research Database (Denmark)

Udesen, Jesper; Nielsen, Michael Bachmann; Nielsen, Kristian R.

2007-01-01

In this paper examples of in-vivo blood vector velocity images of the carotid artery are presented. The transverse oscillation (TO) method for blood vector velocity estimation has been used to estimate the vector velocities and the method is first evaluated in a circulating flowrig where...

Magnetic field effect on flow parameters of blood along with magnetic particles in a cylindrical tube

Energy Technology Data Exchange (ETDEWEB)

Sharma, Shashi, E-mail: shashisharma1984@gmail.com; Singh, Uaday; Katiyar, V.K.

2015-03-01

In this paper, the effect of external uniform magnetic field on flow parameters of both blood and magnetic particles is reported through a mathematical model using magnetohydrodynamics (MHD) approach. The fluid is acted upon by a varying pressure gradient and an external uniform magnetic field is applied perpendicular to the cylindrical tube. The governing nonlinear partial differential equations were solved numerically and found that flow parameters are affected by the influence of magnetic field. Further, artificial blood (75% water+25% Glycerol) along with iron oxide magnetic particles were prepared and transported into a glass tube with help of a peristaltic pump. The velocity of artificial blood along with magnetic particles was experimentally measured at different magnetic fields ranging from 100 to 600 mT. The model results show that the velocity of blood and magnetic particles is appreciably reduced under the influence of magnetic field, which is supported by our experimental results. - Highlights: • Effect of magnetic field on flow parameters of blood and magnetic particles is studied. • The velocity of blood and magnetic particles is appreciably reduced under a magnetic field. • Experimental results of the velocity of magnetic particles within blood support the mathematical model results.

A segmented K-space velocity mapping protocol for quantification of renal artery blood flow during breath-holding

DEFF Research Database (Denmark)

Thomsen, C; Cortsen, M; Söndergaard, L

1995-01-01

for renal artery flow determination. The protocol uses 16 phase-encoding lines per heart beat during 16 heart cycles and gives a temporal velocity resolution of 160 msec. Comparison with a conventional ECG-triggered velocity mapping protocol was made in phantoms as well as in volunteers. In our study, both...... methods showed sufficient robustness toward complex flow in a phantom model. In comparison with the ECG technique, the segmentation technique reduced vessel blurring and pulsatility artifacts caused by respiratory motion, and average flow values obtained in vivo in the left renal artery agreed between......Two important prerequisites for MR velocity mapping of pulsatile motion are synchronization of the sequence execution to the time course of the flow pattern and robustness toward loss of signal in complex flow fields. Synchronization is normally accomplished by using either prospective ECG...

Middle cerebral artery flow velocity waveforms in fetal hypoxaemia.

Science.gov (United States)

Vyas, S; Nicolaides, K H; Bower, S; Campbell, S

1990-09-01

In 81 small-for-gestational age fetuses (SGA) colour flow imaging was used to identify the fetal middle cerebral artery for subsequent pulsed Doppler studies. Impedence to flow (pulsatility index; PI) was significantly lower, and mean blood velocity was significantly higher, than the respective reference ranges with gestation. Fetal blood sampling by cordocentesis was performed in all SGA fetuses and a significant quadratic relation was found between fetal hypoxaemia and the degree of reduction in the PI of FVWs from the fetal middle cerebral artery. Thus, maximum reduction in PI is reached when the fetal PO2 is 2-4 SD below the normal mean for gestation. When the oxygen deficit is greater there is a tendency for the PI to rise, and this presumably reflects the development of brain oedema.

Influence of Gravity on Blood Volume and Flow Distribution

Science.gov (United States)

Pendergast, D.; Olszowka, A.; Bednarczyk, E.; Shykoff, B.; Farhi, L.

1999-01-01

increased and if there is edema in space. Anecdotal evidence suggests there may be cerebral edema early in flight. Cerebral artery velocity has been shown to be elevated in simulated microgravity. The elevated cerebral artery velocity during simulated microgravity may reflect vasoconstriction of the arteries and not increased cerebral blood flow. The purpose of our investigations was to evaluate the effects of alterations in simulated gravity (+/-), resulting in changes in cardiac output (+/-), and on the blood flow and volume distribution in the lung and brain of human subjects. The first hypothesis of these studies was that blood flow and volume would be affected by gravity, but their distribution in the lung would be independent of gravity and due to vasoactivity changing vascular resistance in lung vessels. The vasodilitation of the lung vasculature (lower resistance) along with increased "compliance" of the heart could account for the absence of increased central venous pressure in microgravity. Secondly, we postulate that cerebral blood velocity is increased in microgravity due to large artery vasoconstriction, but that cerebral blood flow would be reduced due to autoregulation.

Glaucoma patients demonstrate faulty autoregulation of ocular blood flow during posture change

Science.gov (United States)

Evans, D.; Harris, A.; Garrett, M.; Chung, H. S.; Kagemann, L.

1999-01-01

BACKGROUND/AIMS—Autoregulation of blood flow during posture change is important to ensure consistent organ circulation. The purpose of this study was to compare the change in retrobulbar ocular blood flow in glaucoma patients with normal subjects during supine and upright posture.
METHODS—20 open angle glaucoma patients and 20 normal subjects, similar in age and sex distribution, were evaluated. Blood pressure, intraocular pressure, and retrobulbar blood velocity were tested after 30 minutes of sitting and again after 30 minutes of lying. Retrobulbar haemodynamic measures of peak systolic velocity (PSV), end diastolic velocity (EDV), and resistance index (RI) were obtained in the ophthalmic and central retinal arteries using colour Doppler imaging (CDI).
RESULTS—When changing from the upright to supine posture, normal subjects demonstrated a significant increase in OA EDV (p = 0.016) and significant decrease in OA RI (p = 0.0006) and CRA RI (p = 0.016). Glaucoma patients demonstrated similar changes in OA measures of EDV (p = 0.02) and RI (p = 0.04), but no change in CRA measures.
CONCLUSION—Glaucoma patients exhibit faulty autoregulation of central retinal artery blood flow during posture change.

 PMID:10381668

Effect of fluid friction on interstitial fluid flow coupled with blood flow through solid tumor microvascular network.

Science.gov (United States)

Sefidgar, Mostafa; Soltani, M; Raahemifar, Kaamran; Bazmara, Hossein

2015-01-01

A solid tumor is investigated as porous media for fluid flow simulation. Most of the studies use Darcy model for porous media. In Darcy model, the fluid friction is neglected and a few simplified assumptions are implemented. In this study, the effect of these assumptions is studied by considering Brinkman model. A multiscale mathematical method which calculates fluid flow to a solid tumor is used in this study to investigate how neglecting fluid friction affects the solid tumor simulation. The mathematical method involves processes such as blood flow through vessels and solute and fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. The sprouting angiogenesis model is used for generating capillary network and then fluid flow governing equations are implemented to calculate blood flow through the tumor-induced capillary network. Finally, the two models of porous media are used for modeling fluid flow in normal and tumor tissues in three different shapes of tumors. Simulations of interstitial fluid transport in a solid tumor demonstrate that the simplifications used in Darcy model affect the interstitial velocity and Brinkman model predicts a lower value for interstitial velocity than the values that Darcy model predicts.

Spatial Temporal Image Correlation Spectroscopy (STICS) for Flow Analysis with Application for Blood Flow Mapping (abstract)

Science.gov (United States)

Rossow, Molly; Mantulin, William M.; Gratton, Enrico

2009-04-01

It is important for surgeons to be able to measure blood flow in exposed arterioles during surgery. We report our progress in the development of an optical technique that will measure blood flow in surgically exposed blood vessels and enable previously difficult measurements. By monitoring optical fluctuations, the optical technique, based on Spatial Temporal Image Correlation (STICS), will directly measure the velocity of micron-scale particles-such as red blood cells. It will complement existing technology and provide qualitative measurements that were not previously possible. It relies on the concept that blood, when viewed on a small enough scale, is an inhomogeneous substance. Individual blood cells passing between a near-infrared light source and a detector will cause fluctuations in the transmitted optical signal. The speed, direction, and flow pattern of blood cells can be determined from these optical fluctuations. We present a series of computer simulations and experiments on phantom and animal systems to test this technique's ability to map complex flow patterns.

Cluster headache: transcranial Doppler ultrasound and regional cerebral blood flow studies

International Nuclear Information System (INIS)

Dahl, A.; Russell, D.; Nyberg-Hansen, R.; Rootwelt, K.

1990-01-01

Transcranial Doppler and rCBF examinations were carried out in 25 cluster headache patients. Spontaneous glyceryl trinitrate (nitroglycerin) provoked attacks were accompanied by a bilateral decrease in middle cerebral artery blood flow velocities. This decrease was more pronounced on the symptomatic side, but the difference did not reach statistical significance. Mean hemispheric blood flow and rCBF were within normal limits during provoked attacks and similar to those found when patients were attack-free. During cluster periods middle cerebral artery velocities were significantly higher on the symptomatic side. Glyceryl trinitrate caused a bilateral middle cerebral artery velocity decrease which was significantly greater on the symptomatic side. Attacks provoked by glyceryl trinitrate appeared to begin when the vasodilatory effect of this substance was received. 17 refs., 2 figs., 5 tabs

Effects of intermittent theta burst stimulation on cerebral blood flow and cerebral vasomotor reactivity.

Science.gov (United States)

Pichiorri, Floriana; Vicenzini, Edoardo; Gilio, Francesca; Giacomelli, Elena; Frasca, Vittorio; Cambieri, Chiara; Ceccanti, Marco; Di Piero, Vittorio; Inghilleri, Maurizio

2012-08-01

To determine whether intermittent theta burst stimulation influences cerebral hemodynamics, we investigated changes induced by intermittent theta burst stimulation on the middle cerebral artery cerebral blood flow velocity and vasomotor reactivity to carbon dioxide (CO(2)) in healthy participants. The middle cerebral artery flow velocity and vasomotor reactivity were monitored by continuous transcranial Doppler sonography. Changes in cortical excitability were tested by transcranial magnetic stimulation. In 11 healthy participants, before and immediately after delivering intermittent theta burst stimulation, we tested cortical excitability measured by the resting motor threshold and motor evoked potential amplitude over the stimulated hemisphere and vasomotor reactivity to CO(2) bilaterally. The blood flow velocity was monitored in both middle cerebral arteries throughout the experimental session. In a separate session, we tested the effects of sham stimulation under the same experimental conditions. Whereas the resting motor threshold remained unchanged before and after stimulation, motor evoked potential amplitudes increased significantly (P = .04). During and after stimulation, middle cerebral artery blood flow velocities also remained bilaterally unchanged, whereas vasomotor reactivity to CO(2) increased bilaterally (P = .04). The sham stimulation left all variables unchanged. The expected intermittent theta burst stimulation-induced changes in cortical excitability were not accompanied by changes in cerebral blood flow velocities; however, the bilateral increased vasomotor reactivity suggests that intermittent theta burst stimulation influences the cerebral microcirculation, possibly involving subcortical structures. These findings provide useful information on hemodynamic phenomena accompanying intermittent theta burst stimulation, which should be considered in research aimed at developing this noninvasive, low-intensity stimulation technique for safe

4-D flow magnetic resonance imaging: blood flow quantification compared to 2-D phase-contrast magnetic resonance imaging and Doppler echocardiography

Energy Technology Data Exchange (ETDEWEB)

Gabbour, Maya [Ann and Robert H. Lurie Children' s Hospital of Chicago, Department of Medical Imaging 9, Chicago, IL (United States); Schnell, Susanne [Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States); Jarvis, Kelly [Northwestern University, Department of Biomedical Engineering, McCormick School of Engineering, Evanston, IL (United States); Robinson, Joshua D. [Ann and Robert H. Lurie Children' s Hospital of Chicago, Department of Pediatrics, Division of Pediatric Cardiology, Chicago, IL (United States); Northwestern University Feinberg School of Medicine, Department of Pediatrics, Chicago, IL (United States); Markl, Michael [Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States); Northwestern University, Department of Biomedical Engineering, McCormick School of Engineering, Evanston, IL (United States); Rigsby, Cynthia K. [Ann and Robert H. Lurie Children' s Hospital of Chicago, Department of Medical Imaging 9, Chicago, IL (United States); Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States)

2015-06-15

Doppler echocardiography (echo) is the reference standard for blood flow velocity analysis, and two-dimensional (2-D) phase-contrast magnetic resonance imaging (MRI) is considered the reference standard for quantitative blood flow assessment. However, both clinical standard-of-care techniques are limited by 2-D acquisitions and single-direction velocity encoding and may make them inadequate to assess the complex three-dimensional hemodynamics seen in congenital heart disease. Four-dimensional flow MRI (4-D flow) enables qualitative and quantitative analysis of complex blood flow in the heart and great arteries. The objectives of this study are to compare 4-D flow with 2-D phase-contrast MRI for quantification of aortic and pulmonary flow and to evaluate the advantage of 4-D flow-based volumetric flow analysis compared to 2-D phase-contrast MRI and echo for peak velocity assessment in children and young adults. Two-dimensional phase-contrast MRI of the aortic root, main pulmonary artery (MPA), and right and left pulmonary arteries (RPA, LPA) and 4-D flow with volumetric coverage of the aorta and pulmonary arteries were performed in 50 patients (mean age: 13.1 ± 6.4 years). Four-dimensional flow analyses included calculation of net flow and regurgitant fraction with 4-D flow analysis planes similarly positioned to 2-D planes. In addition, 4-D flow volumetric assessment of aortic root/ascending aorta and MPA peak velocities was performed and compared to 2-D phase-contrast MRI and echo. Excellent correlation and agreement were found between 2-D phase-contrast MRI and 4-D flow for net flow (r = 0.97, P < 0.001) and excellent correlation with good agreement was found for regurgitant fraction (r = 0.88, P < 0.001) in all vessels. Two-dimensional phase-contrast MRI significantly underestimated aortic (P = 0.032) and MPA (P < 0.001) peak velocities compared to echo, while volumetric 4-D flow analysis resulted in higher (aortic: P = 0.001) or similar (MPA: P = 0.98) peak

High-resolution measurement of the unsteady velocity field to evaluate blood damage induced by a mechanical heart valve.

Science.gov (United States)

Bellofiore, Alessandro; Quinlan, Nathan J

2011-09-01

We investigate the potential of prosthetic heart valves to generate abnormal flow and stress patterns, which can contribute to platelet activation and lysis according to blood damage accumulation mechanisms. High-resolution velocity measurements of the unsteady flow field, obtained with a standard particle image velocimetry system and a scaled-up model valve, are used to estimate the shear stresses arising downstream of the valve, accounting for flow features at scales less than one order of magnitude larger than blood cells. Velocity data at effective spatial and temporal resolution of 60 μm and 1.75 kHz, respectively, enabled accurate extraction of Lagrangian trajectories and loading histories experienced by blood cells. Non-physiological stresses up to 10 Pa were detected, while the development of vortex flow in the wake of the valve was observed to significantly increase the exposure time, favouring platelet activation. The loading histories, combined with empirical models for blood damage, reveal that platelet activation and lysis are promoted at different stages of the heart cycle. Shear stress and blood damage estimates are shown to be sensitive to measurement resolution.

Evaluation of MR angiography and blood flow measurement in abdominal and peripheral arterial occlusive disease

Energy Technology Data Exchange (ETDEWEB)

Tabuchi, Kenji [Dokkyo Univ. School of Medicine, Mibu, Tochigi (Japan)

2000-03-01

To assess the characteristics of blood flow measurement with MR Angiography (MRA) to evaluate the status of vascular stenoses, two or three dimensional time-of-flight MRA and velocity-encoded cine MR were performed in the 230 segments of 35 patients, with abdominal and peripheral arterial occlusive diseases. In 11 of these 35 patients digital subtraction angiography was additionally underwent, and the stenotic findings was compared with MRA. There were 17 segments in which the velocity could not be measured, because the blood flow exceeded the upper limit of peak-encoded velocity (VENC) which was set at 120 cm/sec. Therefore, it is necessary to set the upper limit of VENC at higher than 120 cm/sec. There were 11 stenotic findings in DSA and 20 stenotic findings in MRA. Pulsatility Index (PI=(max velocity-min. velocity)/average velocity) were used for evaluating the blood flow waveform, and there were significant difference between the 11 stenotic findings of DSA and the others'. In summery, MRA was considered as useful examination to assess the degree of the vascular stenoses in abdominal and peripheral arterial occlusive disease. (author)

Reproduction of pressure field in ultrasonic-measurement-integrated simulation of blood flow.

Science.gov (United States)

Funamoto, Kenichi; Hayase, Toshiyuki

2013-07-01

Ultrasonic-measurement-integrated (UMI) simulation of blood flow is used to analyze the velocity and pressure fields by applying feedback signals of artificial body forces based on differences of Doppler velocities between ultrasonic measurement and numerical simulation. Previous studies have revealed that UMI simulation accurately reproduces the velocity field of a target blood flow, but that the reproducibility of the pressure field is not necessarily satisfactory. In the present study, the reproduction of the pressure field by UMI simulation was investigated. The effect of feedback on the pressure field was first examined by theoretical analysis, and a pressure compensation method was devised. When the divergence of the feedback force vector was not zero, it influenced the pressure field in the UMI simulation while improving the computational accuracy of the velocity field. Hence, the correct pressure was estimated by adding pressure compensation to remove the deteriorating effect of the feedback. A numerical experiment was conducted dealing with the reproduction of a synthetic three-dimensional steady flow in a thoracic aneurysm to validate results of the theoretical analysis and the proposed pressure compensation method. The ability of the UMI simulation to reproduce the pressure field deteriorated with a large feedback gain. However, by properly compensating the effects of the feedback signals on the pressure, the error in the pressure field was reduced, exhibiting improvement of the computational accuracy. It is thus concluded that the UMI simulation with pressure compensation allows for the reproduction of both velocity and pressure fields of blood flow. Copyright © 2012 John Wiley & Sons, Ltd.

Coded Ultrasound for Blood Flow Estimation Using Subband Processing

DEFF Research Database (Denmark)

Gran, Fredrik; Udesen, Jesper; Nielsen, Michael Bachamnn

2008-01-01

the excitation signal is broadband and has good spatial resolution after pulse compression. This means that time can be saved by using the same data for B-mode imaging and blood flow estimation. Two different coding schemes are used in this paper, Barker codes and Golay codes. The performance of the codes......This paper investigates the use of coded excitation for blood flow estimation in medical ultrasound. Traditional autocorrelation estimators use narrow-band excitation signals to provide sufficient signal-to-noise-ratio (SNR) and velocity estimation performance. In this paper, broadband coded...... signals are used to increase SNR, followed by subband processing. The received broadband signal is filtered using a set of narrow-band filters. Estimating the velocity in each of the bands and averaging the results yields better performance compared with what would be possible when transmitting a narrow...

Effects of bee venom acupuncture on heart rate variability, pulse wave, and cerebral blood flow for types of Sasang Constitution

Directory of Open Access Journals (Sweden)

Lee Sang-min

2009-03-01

Full Text Available 1. Objectives: To evaluate effects of bee venom acupuncture on cardiovascular system and differences according to each constitution. 2. Methods: Heart rate variability, pulse wave and the velocity of cerebral blood flow were measured before bee venom acupuncture(BVA, right after and after 30 minuets, had been applied to 20 subjects. 3. Results: 1. BVA did not have effects on measurement variables of heart rate variability. 2. BVA had effects on pulse wave, showing total time, radial augmentation index up and height of percussion wave, time to percussion wave, sum of pulse pressure down. 3. BVA did not have effects on the cerebral blood flow velocity when considering not Sasang Constitution 4. Considering Sasang Constitution, BVA demonstrates different responses in time to preincisura wave, mean blood flow velocity, peak systolic velocity and end diastolic velocity. 4.Conclusion: From those results, the following conclusions are obtained. Cause BVA alters pulse wave and makes differences in the cerebral blood flow velocity according to Sasang Constitution. Various methods of BVA treatment are needed considering Sasang Constitution.

A randomized, controlled, double-blind crossover study on the effects of 2-L infusions of 0.9% saline and plasma-lyte® 148 on renal blood flow velocity and renal cortical tissue perfusion in healthy volunteers.

Science.gov (United States)

Chowdhury, Abeed H; Cox, Eleanor F; Francis, Susan T; Lobo, Dileep N

2012-07-01

We compared the effects of intravenous infusions of 0.9% saline ([Cl] 154 mmol/L) and Plasma-Lyte 148 ([Cl] 98 mmol/L, Baxter Healthcare) on renal blood flow velocity and perfusion in humans using magnetic resonance imaging (MRI). Animal experiments suggest that hyperchloremia resulting from 0.9% saline infusion may affect renal hemodynamics adversely, a phenomenon not studied in humans. Twelve healthy adult male subjects received 2-L intravenous infusions over 1 hour of 0.9% saline or Plasma-Lyte 148 in a randomized, double-blind manner. Crossover studies were performed 7 to 10 days apart. MRI scanning proceeded for 90 minutes after commencement of infusion to measure renal artery blood flow velocity and renal cortical perfusion. Blood was sampled and weight recorded hourly for 4 hours. Sustained hyperchloremia was seen with saline but not with Plasma-Lyte 148 (P Blood volume changes were identical (P = 0.867), but there was greater expansion of the extravascular fluid volume after saline (P = 0.029). There was a significant reduction in mean renal artery flow velocity (P = 0.045) and renal cortical tissue perfusion (P = 0.008) from baseline after saline, but not after Plasma-Lyte 148. There was no difference in concentrations of urinary neutrophil gelatinase-associated lipocalin after the 2 infusions (P = 0.917). This is the first human study to demonstrate that intravenous infusion of 0.9% saline results in reductions in renal blood flow velocity and renal cortical tissue perfusion. This has implications for intravenous fluid therapy in perioperative and critically ill patients. NCT01087853.

Numerical analysis of the internal flow field in screw centrifugal blood pump based on CFD

Science.gov (United States)

Han, W.; Han, B. X.; Y Wang, H.; Shen, Z. J.

2013-12-01

As to the impeller blood pump, the high speed of the impeller, the local high shear force of the flow field and the flow dead region are the main reasons for blood damage. The screw centrifugal pump can effectively alleviate the problems of the high speed and the high shear stress for the impeller. The softness and non-destructiveness during the transfer process can effectively reduce the extent of the damage. By using CFD software, the characteristics of internal flow are analyzed in the screw centrifugal pump by exploring the distribution rules of the velocity, pressure and shear deformation rate of the blood when it flows through the impeller and the destructive effects of spiral blades on blood. The results show that: the design of magnetic levitation solves the sealing problems; the design of regurgitation holes solves the problem of the flow dead zone; the magnetic levitated microcirculation screw centrifugal pump can effectively avoid the vortex, turbulence and high shear forces generated while the blood is flowing through the pump. Since the distribution rules in the velocity field, pressure field and shear deformation rate of the blood in the blood pump are comparatively uniform and the gradient change is comparatively small, the blood damage is effectively reduced.

Flow velocity change in the cortical vein during motor activation and its effect on functional brain MRI

Energy Technology Data Exchange (ETDEWEB)

Nakajima, Kazuhiro [Kyoto Prefectural Univ. of Medicine (Japan)

1998-06-01

On the brain functional magnetic resonance imaging (fMRI) using the gradient-recalled echo technique with clinical MR scanner, the activated areas nearly correspond with the cortical veins. This suggests that the fMRI signal mainly originates from the cortical veins. In this study, we analyzed the flow velocity in the cortical vein quantitatively during brain activation and resting status using 2 dimensional time-of-flight cine MR venography (2D-TOF-cine-MRV) and 2 dimensional phase contrast MRV (2D-PC-MRV) techniques, and demonstrated that the flow velocity increased in the cortical vein corresponding to the activated area during activation status. The increase of flow velocity was calculated to be about 20%. The reason for the increased flow velocity is probably due to the increased regional cerebral blood flow and volume in the activated area. We should be careful to analyze the data of the fMRI because the flow velocity affects the fMRI signal such as the inflow effect and the oblique flow effect. When using the gradient echo method, the effect of the flow velocity is one of the important factors of the fMRI signal. (author)

A dual-phantom system for validation of velocity measurements in stenosis models under steady flow.

Science.gov (United States)

Blake, James R; Easson, William J; Hoskins, Peter R

2009-09-01

A dual-phantom system is developed for validation of velocity measurements in stenosis models. Pairs of phantoms with identical geometry and flow conditions are manufactured, one for ultrasound and one for particle image velocimetry (PIV). The PIV model is made from silicone rubber, and a new PIV fluid is made that matches the refractive index of 1.41 of silicone. Dynamic scaling was performed to correct for the increased viscosity of the PIV fluid compared with that of the ultrasound blood mimic. The degree of stenosis in the models pairs agreed to less than 1%. The velocities in the laminar flow region up to the peak velocity location agreed to within 15%, and the difference could be explained by errors in ultrasound velocity estimation. At low flow rates and in mild stenoses, good agreement was observed in the distal flow fields, excepting the maximum velocities. At high flow rates, there was considerable difference in velocities in the poststenosis flow field (maximum centreline differences of 30%), which would seem to represent real differences in hydrodynamic behavior between the two models. Sources of error included: variation of viscosity because of temperature (random error, which could account for differences of up to 7%); ultrasound velocity estimation errors (systematic errors); and geometry effects in each model, particularly because of imperfect connectors and corners (systematic errors, potentially affecting the inlet length and flow stability). The current system is best placed to investigate measurement errors in the laminar flow region rather than the poststenosis turbulent flow region.

Bulk velocity extraction for nano-scale Newtonian flows

Energy Technology Data Exchange (ETDEWEB)

Zhang, Wenfei, E-mail: zwenfei@gmail.com [Key Laboratory of Mechanical Reliability for Heavy Equipments and Large Structures of Hebei Province, Yanshan University, Qinhuangdao 066004 (China); Sun, Hongyu [Key Laboratory of Mechanical Reliability for Heavy Equipments and Large Structures of Hebei Province, Yanshan University, Qinhuangdao 066004 (China)

2012-04-16

The conventional velocity extraction algorithm in MDS method has difficulty to determine the small flow velocity. This study proposes a new method to calculate the bulk velocity in nano-flows. Based on the Newton's law of viscosity, according to the calculated viscosities and shear stresses, the flow velocity can be obtained by numerical integration. This new method can overcome the difficulty existed in the conventional MDS method and improve the stability of the computational process. Numerical results show that this method is effective for the extraction of bulk velocity, no matter the bulk velocity is large or small. -- Highlights: ► Proposed a new method to calculate the bulk velocity in nano-flows. ► It is effective for the extraction of small bulk velocity. ► The accuracy, convergence and stability of the new method is good.

Bulk velocity extraction for nano-scale Newtonian flows

International Nuclear Information System (INIS)

Zhang, Wenfei; Sun, Hongyu

2012-01-01

The conventional velocity extraction algorithm in MDS method has difficulty to determine the small flow velocity. This study proposes a new method to calculate the bulk velocity in nano-flows. Based on the Newton's law of viscosity, according to the calculated viscosities and shear stresses, the flow velocity can be obtained by numerical integration. This new method can overcome the difficulty existed in the conventional MDS method and improve the stability of the computational process. Numerical results show that this method is effective for the extraction of bulk velocity, no matter the bulk velocity is large or small. -- Highlights: ► Proposed a new method to calculate the bulk velocity in nano-flows. ► It is effective for the extraction of small bulk velocity. ► The accuracy, convergence and stability of the new method is good.

Validation of Patient-Specific Cerebral Blood Flow Simulation Using Transcranial Doppler Measurements

Directory of Open Access Journals (Sweden)

Derek Groen

2018-06-01

Full Text Available We present a validation study comparing results from a patient-specific lattice-Boltzmann simulation to transcranial Doppler (TCD velocity measurements in four different planes of the middle cerebral artery (MCA. As part of the study, we compared simulations using a Newtonian and a Carreau-Yasuda rheology model. We also investigated the viability of using downscaled velocities to reduce the required resolution. Simulations with unscaled velocities predict the maximum flow velocity with an error of less than 9%, independent of the rheology model chosen. The accuracy of the simulation predictions worsens considerably when simulations are run at reduced velocity, as is for example the case when inflow velocities from healthy individuals are used on a vascular model of a stroke patient. Our results demonstrate the importance of using directly measured and patient-specific inflow velocities when simulating blood flow in MCAs. We conclude that localized TCD measurements together with predictive simulations can be used to obtain flow estimates with high fidelity over a larger region, and reduce the need for more invasive flow measurement procedures.

Pressure-driven occlusive flow of a confined red blood cell.

Science.gov (United States)

Savin, Thierry; Bandi, M M; Mahadevan, L

2016-01-14

When red blood cells (RBCs) move through narrow capillaries in the microcirculation, they deform as they flow. In pathophysiological processes such as sickle cell disease and malaria, RBC motion and flow are severely restricted. To understand this threshold of occlusion, we use a combination of experiment and theory to study the motion of a single swollen RBC through a narrow glass capillary of varying inner diameter. By tracking the movement of the squeezed cell as it is driven by a controlled pressure drop, we measure the RBC velocity as a function of the pressure gradient as well as the local capillary diameter, and find that the effective blood viscosity in this regime increases with both decreasing RBC velocity and tube radius by following a power-law that depends upon the length of the confined cell. Our observations are consistent with a simple elasto-hydrodynamic model and highlight the role of lateral confinement in the occluded pressure-driven slow flow of soft confined objects.

Multimodal in vivo blood flow sensing combining particle image velocimetry and optical tweezers-based blood steering

Science.gov (United States)

Meissner, Robert; Sugden, Wade W.; Siekmann, Arndt F.; Denz, Cornelia

2018-02-01

All higher developed organisms contain complex hierarchical networks of arteries, veins and capillaries. These constitute the cardiovascular system responsible for supplying nutrients, gas and waste exchange. Diseases related to the cardiovascular system are among the main causes for death worldwide. In order to understand the processes leading to arteriovenous malformation, we studied hereditary hemorrhagic telangiectasia (HHT), which has a prevalence of 1:5000 worldwide and causes internal bleeding. In zebrafish, HHT is induced by mutation of the endoglin gene involved in HHT and observed to reduce red blood cell (RBC) flow to intersegmental vessels (ISVs) in the tail due to malformations of the dorsal aorta (DA) and posterior cardinal vein (PCV). However, these capillaries are still functional. Changes in the blood flow pattern are observed from in vivo data from zebrafish embryos through particle image velocimetry (PIV). Wall shear rates (WSRs) and blood flow velocities are obtained non-invasively with millisecond resolution. We observe significant increases of blood flow velocity in the DA for endoglin-deficient zebrafish embryos (mutants) at 3 days post fertilization. In the PCV, this increase is even more pronounced. We identified an increased similarity between the DA and the PCV of mutant fish compared to siblings, i.e., unaffected fish. To counteract the reduced RBC flow to ISVs we implement optical tweezers (OT). RBCs are steered into previously unperfused ISVs showing a significant increase of RBC count per minute. We discuss limitations with respect to biocompatibility of optical tweezers in vivo and determination of in vivo wall shear stress (WSS) connected to normal and endoglin-deficicent zebrafish embryos.

Local viscosity distribution in bifurcating microfluidic blood flows

Science.gov (United States)

Kaliviotis, E.; Sherwood, J. M.; Balabani, S.

2018-03-01

The red blood cell (RBC) aggregation phenomenon is majorly responsible for the non-Newtonian nature of blood, influencing the blood flow characteristics in the microvasculature. Of considerable interest is the behaviour of the fluid at the bifurcating regions. In vitro experiments, using microchannels, have shown that RBC aggregation, at certain flow conditions, affects the bluntness and skewness of the velocity profile, the local RBC concentration, and the cell-depleted layer at the channel walls. In addition, the developed RBC aggregates appear unevenly distributed in the outlets of these channels depending on their spatial distribution in the feeding branch, and on the flow conditions in the outlet branches. In the present work, constitutive equations of blood viscosity, from earlier work of the authors, are applied to flows in a T-type bifurcating microchannel to examine the local viscosity characteristics. Viscosity maps are derived for various flow distributions in the outlet branches of the channel, and the location of maximum viscosity magnitude is obtained. The viscosity does not appear significantly elevated in the branches of lower flow rate as would be expected on the basis of the low shear therein, and the maximum magnitude appears in the vicinity of the junction, and towards the side of the outlet branch with the higher flow rate. The study demonstrates that in the branches of lower flow rate, the local viscosity is also low, helping us to explain why the effects of physiological red blood cell aggregation have no adverse effects in terms of in vivo vascular resistance.

FDM Analysis for Blood Flow through Stenosed Tapered Arteries

Directory of Open Access Journals (Sweden)

Sankar DS

2010-01-01

Full Text Available Abstract A computational model is developed to analyze the unsteady flow of blood through stenosed tapered narrow arteries, treating blood as a two-fluid model with the suspension of all the erythrocytes in the core region as Herschel-Bulkley fluid and the plasma in the peripheral layer as Newtonian fluid. The finite difference method is employed to solve the resulting system of nonlinear partial differential equations. The effects of stenosis height, peripheral layer thickness, yield stress, viscosity ratio, angle of tapering and power law index on the velocity, wall shear stress, flow rate and the longitudinal impedance are analyzed. It is found that the velocity and flow rate increase with the increase of the peripheral layer thickness and decrease with the increase of the angle of tapering and depth of the stenosis. It is observed that the flow rate decreases nonlinearly with the increase of the viscosity ratio and yield stress. The estimates of the increase in the longitudinal impedance to flow are considerably lower for the two-fluid Herschel-Bulkley model compared with those of the single-fluid Herschel-Bulkley model. Hence, it is concluded that the presence of the peripheral layer helps in the functioning of the diseased arterial system.

The relationship of flow velocities to vessel diameters differs between extracranial carotid and vertebral arteries of stroke patients.

Science.gov (United States)

Owolabi, Mayowa O; Agunloye, Atinuke M; Ogunniyi, Adesola

2014-01-01

Chronic changes in flow rate through arteries produce adjustment of arterial diameters. We compared the relationship between flow velocity and diameter in the carotid and in the vertebral arteries of stroke patients. Using triplex ultrasonography, the internal diameter and flow velocities of the common carotid, internal carotid, and vertebral arteries of 176 consecutive stroke patients were measured. Correlations were examined with Pearson's statistics at an alpha level of 0.05. Mean age of the patients was 59.3 ± 12 years, and 66% had cerebral infarcts. Diameter and blood flow velocities showed significant negative correlations (-0.115 ≥ r ≥ -0.382) in the carotid arteries on both sides, but positive correlations (0.211 ≤ r ≤ 0.320) in the vertebral arteries, even after controlling for age, gender, and blood pressure. Our study demonstrated different diameter/flow relationships in the carotid and the vertebral arteries of stroke patients, which may suggest pathologic changes in the adaptive processes governing vessel diameter and growth, especially in the carotid arteries. Copyright © 2013 Wiley Periodicals, Inc.

The measurement of low air flow velocities

NARCIS (Netherlands)

Aghaei, A.; Mao, X.G.; Zanden, van der A.J.J.; Schaik, W.H.J.; Hendriks, N.A.

2005-01-01

Air flow velocity is measured with an acoustic sensor, which can be used especially for measuring low air flow velocities as well as the temperature of the air simultaneously. Two opposite transducers send a sound pulse towards each other. From the difference of the transit times, the air flow

Blood flow in curved pipe with radiative heat transfer

International Nuclear Information System (INIS)

Ogulu, A.; Bestman, A.R.

1992-03-01

Blood flow in a curved pipe such as the aorta is modelled in this study. The aorta is modelled as a curved pipe of slowly varying cross-section. Asymptotic series expansions about a small parameter δ, which is a measure of the curvature ratio is employed to obtain the velocity and temperature distributions. The study simulates the effect of radio-frequency heating, for instance during physiotherapy, on the flow of blood in the cardiovascular system assuming an external constant pressure gradient; and our results agree very well with results obtained by Pedley. (author). 9 refs, 2 figs

Establishing the diffuse correlation spectroscopy signal relationship with blood flow.

Science.gov (United States)

Boas, David A; Sakadžić, Sava; Selb, Juliette; Farzam, Parisa; Franceschini, Maria Angela; Carp, Stefan A

2016-07-01

Diffuse correlation spectroscopy (DCS) measurements of blood flow rely on the sensitivity of the temporal autocorrelation function of diffusively scattered light to red blood cell (RBC) mean square displacement (MSD). For RBCs flowing with convective velocity [Formula: see text], the autocorrelation is expected to decay exponentially with [Formula: see text], where [Formula: see text] is the delay time. RBCs also experience shear-induced diffusion with a diffusion coefficient [Formula: see text] and an MSD of [Formula: see text]. Surprisingly, experimental data primarily reflect diffusive behavior. To provide quantitative estimates of the relative contributions of convective and diffusive movements, we performed Monte Carlo simulations of light scattering through tissue of varying vessel densities. We assumed laminar vessel flow profiles and accounted for shear-induced diffusion effects. In agreement with experimental data, we found that diffusive motion dominates the correlation decay for typical DCS measurement parameters. Furthermore, our model offers a quantitative relationship between the RBC diffusion coefficient and absolute tissue blood flow. We thus offer, for the first time, theoretical support for the empirically accepted ability of the DCS blood flow index ([Formula: see text]) to quantify tissue perfusion. We find [Formula: see text] to be linearly proportional to blood flow, but with a proportionality modulated by the hemoglobin concentration and the average blood vessel diameter.

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length

International Nuclear Information System (INIS)

Liu, Wenzhong; Yi, Ji; Chen, Siyu; Jiao, Shuliang; Zhang, Hao F.

2015-01-01

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as −0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31μl/min among four wild-type rats. The authors’ measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length.

Science.gov (United States)

Liu, Wenzhong; Yi, Ji; Chen, Siyu; Jiao, Shuliang; Zhang, Hao F

2015-09-01

Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as -0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31 μl/min among four wild-type rats. The authors' measured flow rates were consistent with results in the literature. By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.

Measuring retinal blood flow in rats using Doppler optical coherence tomography without knowing eyeball axial length

Energy Technology Data Exchange (ETDEWEB)

Liu, Wenzhong; Yi, Ji; Chen, Siyu [Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208 (United States); Jiao, Shuliang [Department of Biomedical Engineering, Florida International University, Miami, Florida 33174 (United States); Zhang, Hao F., E-mail: hfzhang@northwestern.edu [Department of Biomedical Engineering, Northwestern University, Evanston, Illinois 60208 and Department of Ophthalmology, Northwestern University, Chicago, Illinois 60611 (United States)

2015-09-15

Purpose: Doppler optical coherence tomography (OCT) is widely used for measuring retinal blood flow. Existing Doppler OCT methods require the eyeball axial length, in which empirical values are usually used. However, variations in the axial length can create a bias unaccounted for in the retinal blood flow measurement. The authors plan to develop a Doppler OCT method that can measure the total retinal blood flow rate without requiring the eyeball axial length. Methods: The authors measured the retinal blood flow rate using a dual-ring scanning protocol. The small and large scanning rings entered the eye at different incident angles (small ring: 4°; large ring: 6°), focused on different locations on the retina, and detected the projected velocities/phase shifts along the probing beams. The authors calculated the ratio of the projected velocities between the two rings, and then used this ratio to estimate absolute flow velocity. The authors tested this method in both Intralipid phantoms and in vivo rats. Results: In the Intralipid flow phantom experiments, the preset and measured flow rates were consistent with the coefficient of determination as 0.97. Linear fitting between preset and measured flow rates determined the fitting slope as 1.07 and the intercept as −0.28. In in vivo rat experiments, the measured average total retinal blood flow was 7.02 ± 0.31μl/min among four wild-type rats. The authors’ measured flow rates were consistent with results in the literature. Conclusions: By using a dual-ring scanning protocol with carefully controlled incident angle difference between the two scanning rings in Doppler OCT, the authors demonstrated that it is feasible to measure the absolute retinal blood flow without knowing the eyeball axial length.

Evolution of velocity dispersion along cold collisionless flows

International Nuclear Information System (INIS)

Banik, Nilanjan; Sikivie, Pierre

2016-01-01

We found that the infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We also discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components

Blood velocity estimation using spatio-temporal encoding based on frequency division approach

DEFF Research Database (Denmark)

Gran, Fredrik; Nikolov, Svetoslav; Jensen, Jørgen Arendt

2005-01-01

In this paper a feasibility study of using a spatial encoding technique based on frequency division for blood flow estimation is presented. The spatial encoding is carried out by dividing the available bandwidth of the transducer into a number of narrow frequency bands with approximately disjoint...... spectral support. By assigning one band to one virtual source, all virtual sources can be excited simultaneously. The received echoes are beamformed using Synthetic Transmit Aperture beamforming. The velocity of the moving blood is estimated using a cross- correlation estimator. The simulation tool Field...

Muscle blood flow at onset of dynamic exercise in humans.

Science.gov (United States)

Rådegran, G; Saltin, B

1998-01-01

To evaluate the temporal relationship between blood flow, blood pressure, and muscle contractions, we continuously measured femoral arterial inflow with ultrasound Doppler at onset of passive exercise and voluntary, one-legged, dynamic knee-extensor exercise in humans. Blood velocity and inflow increased (P dicrotic and diastolic blood pressure notches, respectively. Mechanical hindrance occurred (P dicrotic notch. The increase in blood flow (Q) was characterized by a one-component (approximately 15% of peak power output), two-component (approximately 40-70% of peak power output), or three-component exponential model (> or = 75% of peak power output), where Q(t) = Qpassive + delta Q1.[1 - e-(t - TD1/tau 1)]+ delta Q2.[1 - e-(t - TD2/tau 2)]+ delta Q3.[1 - e-(t - TD3/tau 3)]; Qpassive, the blood flow during passive leg movement, equals 1.17 +/- 0.11 l/min; TD is the onset latency; tau is the time constant; delta Q is the magnitude of blood flow rise; and subscripts 1-3 refer to the first, second, and third components of the exponential model, respectively. The time to reach 50% of the difference between passive and voluntary asymptotic blood flow was approximately 2.2-8.9 s. The blood flow leveled off after approximately 10-150 s, related to the power outputs. It is concluded that the elevation in blood flow with the first duty cycle(s) is due to muscle mechanical factors, but vasodilators initiate a more potent amplification within the second to fourth contraction.

Intraoperative changes of transcranial Doppler velocity: relation to arterial oxygen content and whole-blood viscosity

NARCIS (Netherlands)

Schuurman, P. R.; Albrecht, K. W.

1999-01-01

The association of arterial oxygen content (CaO2) and viscosity with transcranial Doppler (TCD) blood flow velocity in the middle cerebral artery was studied in 20 adults without cerebrovascular disease undergoing abdominal surgery associated with significant fluctuations in hematology. TCD

Non-gated fetal MRI of umbilical blood flow in an acardiac twin

Energy Technology Data Exchange (ETDEWEB)

Hata, Nobuhiko [University of Tokyo, Graduate School of Information Science and Technology, Tokyo (Japan); Brigham and Women' s Hospital, Department of Radiology, Boston, MA (United States); Wada, Toru [University of Tokyo, Graduate School of Information Science and Technology, Tokyo (Japan); Kashima, Kyoko; Okada, Yoshiyuki [National Center for Child Health and Development, Department of Radiology, Tokyo (Japan); Unno, Nobuya [Nagano Children' s Hospital, Center for Perinatal Medicine, Nagano (Japan); Kitagawa, Michihiro [National Center for Child Health and Development, Department of Prenatal Medicine and Maternal Care, Tokyo (Japan); Chiba, Toshio [National Center for Child Health and Development, Department of Strategic Medicine, Tokyo (Japan)

2005-08-01

Currently, the standard method of diagnosis of twin reversed arterial perfusion (TRAP) sequence is ultrasound imaging. The use of MRI for flow visualization may be a useful adjunct to US imaging for assessing the presence of retrograde blood flow in the acardiac fetus and/or umbilical artery. The technical challenge in fetal MRI flow imaging, however, is that fetal electrocardiogram (ECG) monitoring required for flow imaging is currently unavailable in the MRI scanner. A non-gated MRI flow imaging technique that requires no ECG monitoring was developed using the t-test to detect blood flow in 20 slices of phase-contrast MRI images randomly scanned at the same location over multiple cardiac cycles. A feasibility study was performed in a 24-week acardiac twin that showed no umbilical flow sonographically. Non-gated MRI flow images clearly indicated the presence of blood flow in the umbilical artery to the acardiac twin; however, there was no blood flow beyond the abdomen. This study leads us to conjecture that non-gated MRI flow imaging is sensitive in detecting low-range blood flow velocity and can be an adjunct to Doppler US imaging. (orig.)

Non-gated fetal MRI of umbilical blood flow in an acardiac twin

International Nuclear Information System (INIS)

Hata, Nobuhiko; Wada, Toru; Kashima, Kyoko; Okada, Yoshiyuki; Unno, Nobuya; Kitagawa, Michihiro; Chiba, Toshio

2005-01-01

Currently, the standard method of diagnosis of twin reversed arterial perfusion (TRAP) sequence is ultrasound imaging. The use of MRI for flow visualization may be a useful adjunct to US imaging for assessing the presence of retrograde blood flow in the acardiac fetus and/or umbilical artery. The technical challenge in fetal MRI flow imaging, however, is that fetal electrocardiogram (ECG) monitoring required for flow imaging is currently unavailable in the MRI scanner. A non-gated MRI flow imaging technique that requires no ECG monitoring was developed using the t-test to detect blood flow in 20 slices of phase-contrast MRI images randomly scanned at the same location over multiple cardiac cycles. A feasibility study was performed in a 24-week acardiac twin that showed no umbilical flow sonographically. Non-gated MRI flow images clearly indicated the presence of blood flow in the umbilical artery to the acardiac twin; however, there was no blood flow beyond the abdomen. This study leads us to conjecture that non-gated MRI flow imaging is sensitive in detecting low-range blood flow velocity and can be an adjunct to Doppler US imaging. (orig.)

Heat stress exacerbates the reduction in middle cerebral artery blood velocity during prolonged self-paced exercise.

Science.gov (United States)

Périard, J D; Racinais, S

2015-06-01

This study examined the influence of hyperthermia on middle cerebral artery mean blood velocity (MCA Vmean). Eleven cyclists undertook a 750 kJ self-paced time trial in HOT (35 °C) and COOL (20 °C) conditions. Exercise time was longer in HOT (56 min) compared with COOL (49 min; P blood flow, and heart rate were higher throughout HOT compared with COOL (P blood pressure and oxygen uptake were lower from 50% of work completed onward in HOT compared with COOL (P heat appears to have exacerbated the reduction in MCA Vmean, in part via increases in peripheral blood flow and a decrease in arterial blood pressure. © 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Time-resolved blood flow measurement in the in vivo mouse model by optical frequency domain imaging

Science.gov (United States)

Walther, Julia; Mueller, Gregor; Meissner, Sven; Cimalla, Peter; Homann, Hanno; Morawietz, Henning; Koch, Edmund

2009-07-01

In this study, we demonstrate that phase-resolved Doppler optical frequency domain imaging (OFDI) is very suitable to quantify the pulsatile blood flow within a vasodynamic measurement in the in vivo mouse model. For this, an OFDI-system with a read-out rate of 20 kHz and a center wavelength of 1320 nm has been used to image the time-resolved murine blood flow in 300 μμm vessels. Because OFDI is less sensitive to fringe washout due to axial sample motion, it is applied to analyze the blood flow velocities and the vascular dynamics in six-week-old C57BL/6 mice compared to one of the LDLR knockout strain kept under sedentary conditions or with access to voluntary wheel running. We have shown that the systolic as well as the diastolic phase of the pulsatile arterial blood flow can be well identified at each vasodynamic state. Furthermore, the changes of the flow velocities after vasoconstriction and -dilation were presented and interpreted in the entire physiological context. With this, the combined measurement of time-resolved blood flow and vessel diameter provides the basis to analyze the vascular function and its influence on the blood flow of small arteries of different mouse strains in response to different life styles.

Sickle cell disease: reference values and interhemispheric differences of nonimaging transcranial Doppler blood flow parameters.

Science.gov (United States)

Arkuszewski, M; Krejza, J; Chen, R; Kwiatkowski, J L; Ichord, R; Zimmerman, R; Ohene-Frempong, K; Desiderio, L; Melhem, E R

2011-09-01

TCD screening is widely used to identify children with SCD at high risk of stroke. Those with high mean flow velocities in major brain arteries have increased risk of stroke. Thus, our aim was to establish reference values of interhemispheric differences and ratios of blood flow Doppler parameters in the tICA, MCA, and ACA as determined by conventional TCD in children with sickle cell anemia. Reference limits of blood flow parameters were established on the basis of a consecutive cohort of 56 children (mean age, 100 ± 40 months; range, 29-180 months; 30 females) free of neurologic deficits and intracranial stenosis detectable by MRA, with blood flow velocities <170 cm/s by conventional TCD. Reference limits were estimated by using tolerance intervals, within which are included with a probability of .90 of all possible data values from 95% of a population. Average peak systolic velocities were significantly higher in the right hemisphere in the MCA and ACA (185 ± 28 cm/s versus 179 ± 27 and 152 ± 30 cm/s versus 143 ± 34 cm/s respectively). Reference limits for left-to-right differences in the mean flow velocities were the following: -43 to 33 cm/s for the MCA; -49 to 38 cm/s for the ACA, and -38 to 34 cm/s for the tICA, respectively. Respective reference limits for left-to-right velocity ratios were the following: 0.72 to 1.25 cm/s for the MCA; 0.62 to 1.39 cm/s for the ACA, and 0.69 to 1.27 cm/s for the tICA. Flow velocities in major arteries were inversely related to age and Hct or Hgb. The study provides reference intervals of TCD flow velocities and their interhemispheric differences and ratios that may be helpful in identification of intracranial arterial stenosis in children with SCD undergoing sonographic screening for stroke prevention.

Influence of immune-mediated hemolytic anemia on flow velocities in the portal vein and caudal vena cava measured by use of pulsed-wave Doppler ultrasonography in dogs.

Science.gov (United States)

Smith, Rachel Policelli; Koenigshof, Amy M; Smith, Daniel J; Strom, Phillip R; Nelson, Nathan C

2018-05-01

OBJECTIVE To compare blood flow velocities of the portal vein (PV) and caudal vena cava (CVC) measured by use of pulsed-wave Doppler ultrasonography in clinically normal dogs and dogs with primary immune-mediated hemolytic anemia (IMHA). ANIMALS 11 client-owned dogs admitted to a veterinary teaching hospital for management of primary IMHA and 21 staff- or student-owned clinically normal dogs. PROCEDURES Flow velocities in the PV and CVC at the porta hepatis were evaluated in conscious unsedated dogs with concurrent ECG monitoring; evaluations were performed before dogs with IMHA received heparin or blood transfusions. Three measurements of peak velocity at end expiration were obtained for each vessel, and the mean was calculated. Results were compared between IMHA and control groups. RESULTS Mean ± SD blood flow velocity in the CVC differed between control (63.0 ± 18.6 cm/s) and IMHA (104 ± 36.9 cm/s) groups. Variance in dogs with IMHA was significantly greater than that for the clinically normal dogs. No significant difference in blood flow velocity in the PV was detected between IMHA and control dogs. CONCLUSIONS AND CLINICAL RELEVANCE Higher blood flow velocities were detected by use of pulsed-wave Doppler ultrasonography in the CVC of dogs with naturally occurring IMHA and may be used to predict anemia in patients suspected of having IMHA.

Blood flow in cerebral aneurysms: comparison of phase contrast magnetic resonance and computational fluid dynamics - preliminary experience

Energy Technology Data Exchange (ETDEWEB)

Karmonik, C.; Benndorf, G. [The Methodist Hospital Research Inst., Houston (United States). Radiology; Klucznik, R. [The Methodist Hospital, Houston (United States). Radiology

2008-03-15

Purpose: computational fluid dynamics (CFD) simulations are increasingly used to model cerebral aneurysm hemodynamics. We investigated the capability of phase contrast magnetic resonance imaging (pcMRI), guided by specialized software for optimal slice definition (NOVA, Vassol Inc.) as a non-invasive method to measure intra-aneurysmal blood flow patterns in-vivo. In a novel approach, these blood flow patterns measured with pcMRI were qualitatively compared to the ones calculated with CFD. Materials end methods: the volumetric inflow rates into three unruptured cerebral aneurysms and the temporal variations of the intra-aneurysmal blood flow patterns were recorded with pcMRI. Transient CFD simulations were performed on geometric models of these aneurysms derived from 3D digital subtraction angiograms. Calculated intra-aneurysmal blood flow patterns were compared at the times of maximum and minimum arterial inflow to the ones measured with pcMRI and the temporal variations of these patterns during the cardiac cycle were investigated. Results: in all three aneurysms, the main features of intra-aneurysmal flow patterns obtained with pcMRI consisted of areas with positive velocities components and areas with negative velocities components. The measured velocities ranged from approx. {+-}60 to {+-}100 cm/sec. Comparison with calculated CFD simulations showed good correlation with regard to the spatial distribution of these areas, while differences in calculated magnitudes of velocities were found. (orig.)

Blood flow in cerebral aneurysms: comparison of phase contrast magnetic resonance and computational fluid dynamics - preliminary experience

International Nuclear Information System (INIS)

Karmonik, C.; Benndorf, G.; Klucznik, R.

2008-01-01

Purpose: computational fluid dynamics (CFD) simulations are increasingly used to model cerebral aneurysm hemodynamics. We investigated the capability of phase contrast magnetic resonance imaging (pcMRI), guided by specialized software for optimal slice definition (NOVA, Vassol Inc.) as a non-invasive method to measure intra-aneurysmal blood flow patterns in-vivo. In a novel approach, these blood flow patterns measured with pcMRI were qualitatively compared to the ones calculated with CFD. Materials end methods: the volumetric inflow rates into three unruptured cerebral aneurysms and the temporal variations of the intra-aneurysmal blood flow patterns were recorded with pcMRI. Transient CFD simulations were performed on geometric models of these aneurysms derived from 3D digital subtraction angiograms. Calculated intra-aneurysmal blood flow patterns were compared at the times of maximum and minimum arterial inflow to the ones measured with pcMRI and the temporal variations of these patterns during the cardiac cycle were investigated. Results: in all three aneurysms, the main features of intra-aneurysmal flow patterns obtained with pcMRI consisted of areas with positive velocities components and areas with negative velocities components. The measured velocities ranged from approx. ±60 to ±100 cm/sec. Comparison with calculated CFD simulations showed good correlation with regard to the spatial distribution of these areas, while differences in calculated magnitudes of velocities were found. (orig.)

Measurement of LBE flow velocity profile by UDVP

International Nuclear Information System (INIS)

Kikuchi, Kenji; Takeda, Yasushi; Obayashi, Hiroo; Tezuka, Masao; Sato, Hiroshi

2006-01-01

Measurements of liquid metal lead-bismuth eutectic (LBE), flow velocity profile were realized in the spallation neutron source target model by the ultrasonic Doppler velocity profiler (UVDP) technique. So far, it has not been done well, because both of poor wetting property of LBE with stainless steels and poor performance of supersonic probes at high temperatures. The measurement was made for a return flow in the target model, which has coaxially arranged annular and tube channels, in the JAEA Lead Bismuth Loop-2 (JLBL-2). The surface treatment of LBE container was examined. It was found that the solder coating was effective to enhance an intensity of reflected ultrasonic wave. This treatment has been applied to the LBE loop, which was operated up to 150 deg. C. The electro magnetic pump generates LBE flow and the flow rate was measured by the electro magnetic flow meter. By changing the flow rate of LBE, velocity profiles in the target were measured. It was confirmed that the maximum velocity in the time-averaged velocity distribution on the target axis was proportional to the flow rate measured by the electro magnetic flow meter

Three-dimensional power Doppler sonography: imaging and quantifying blood flow and vascularization.

Science.gov (United States)

Pairleitner, H; Steiner, H; Hasenoehrl, G; Staudach, A

1999-08-01

To assess the feasibility of imaging low-velocity blood flow in adnexal masses by transvaginal three-dimensional power Doppler sonography, to analyze three-dimensional power Doppler sonography data sets with a new computer-assisted method and to test the reproducibility of the technique. A commercially available 5-MHz Combison 530 ultrasound system was used to perform three-dimensional power Doppler sonography transvaginally. A cube (= volume of interest) was defined enclosing the vessels of the cyst and the Cartesian characteristics were stored on a hard disk. This cube was analyzed using specially designed software. Five indices representing vascularization (the vascularization index (VI) or blood flow (the flow index (FI)) or both (the vascularization-flow index (VFI)) were calculated. The intraobserver repeatability of cube definition and scan repetition was assessed using Hartley's test for homogeneous variances. Interobserver agreement was assessed by the Pearson correlation coefficient. Imaging of vessels with low-velocity blood flow by three-dimensional power Doppler sonography and cube definition was possible in all adnexal massed studied. In some cases even induced non-vascular flow related to endometriosis was detected. The calculated F value with intraobserver repeated Cartesian file-saving ranged from 0 to 18.8, with intraobserver scan repetition from 4.74 to 24.8 for VI, FI 1, FI 2 and VFI 1; for VFI 2 the calculated F value was 64. The interobserver correlation coefficient ranged between 0.83 and 0.92 for VI, FI 1, FI 2 and VFI 1; for VFI 2 the correlation coefficient was less than 0.75. Vessels with low-velocity blood flow can be imaged using three-dimensional power Doppler sonography. Induced non-vascular flow was detected in endometriotic cyst fluid. Three-dimensional power Doppler sonography combined with the cube method gave reproducible information for all indices except VFI 2. These indices might prove to be a new predictor in all fields of

In vitro blood flow in a rectangular PDMS microchannel: experimental observations using a confocal micro-PIV system.

Science.gov (United States)

Lima, Rui; Wada, Shigeo; Tanaka, Shuji; Takeda, Motohiro; Ishikawa, Takuji; Tsubota, Ken-ichi; Imai, Yohsuke; Yamaguchi, Takami

2008-04-01

Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 microm wide, 45 microm deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability

Liquid velocity in upward and downward air-water flows

International Nuclear Information System (INIS)

Sun Xiaodong; Paranjape, Sidharth; Kim, Seungjin; Ozar, Basar; Ishii, Mamoru

2004-01-01

Local characteristics of the liquid phase in upward and downward air-water two-phase flows were experimentally investigated in a 50.8-mm inner-diameter round pipe. An integral laser Doppler anemometry (LDA) system was used to measure the axial liquid velocity and its fluctuations. No effect of the flow direction on the liquid velocity radial profile was observed in single-phase liquid benchmark experiments. Local multi-sensor conductivity probes were used to measure the radial profiles of the bubble velocity and the void fraction. The measurement results in the upward and downward two-phase flows are compared and discussed. The results in the downward flow demonstrated that the presence of the bubbles tended to flatten the liquid velocity radial profile, and the maximum liquid velocity could occur off the pipe centerline, in particular at relatively low flow rates. However, the maximum liquid velocity always occurred at the pipe center in the upward flow. Also, noticeable turbulence enhancement due to the bubbles in the two-phase flows was observed in the current experimental flow conditions. Furthermore, the distribution parameter and the void-weighted area-averaged drift velocity were obtained based on the definitions

Effect of Metoclopramide on Portal Blood Flow in Patients with Liver Cirrhosis: Evaluation by the Pulsed Doppler System

International Nuclear Information System (INIS)

Baik, Soon Koo; Lee, Yong Gyu; Hong, Sa Joon; Lee, Seong Wu; Lee, Dong Ki; Kwong, Sang Ok

1994-01-01

Metoclopramide is known to lower the intravariceal flow by raising the lower esophageal sphincter pressure and consequently decreases the portal blood flow. So we designed this study to assess the effect of metoclopramide on portal blood flow in cirrhotic patients using pulsed Doppler system. By using pulsed Doppler ultrasound, portal blood velocity, diameter of the portal vein, portal blood flow, blood pressure and pulse rate were measured at 15, 30 and 60 minutes after administration of 20mg metoclopramide in 16cirrhotic patients and compared with the basal values. In order 10 cirrhotic patients, normal saline was administrated, and the above mentioned parameters were measured. Wothin 15 minutes after intravenous administration of 20mg metoclopramide, portal blood velocity and portal blood flow decreased significantly, from 12.45+2.64 to 11.80+2.55cm/sec and from 1006.3+407.1 to 974.4+414.7ml/min, respectively(P<0.05). In placebo group,there was no significant change in measured parameters after administration of normal saline. These results support the hypothesis that metoclopramide significantly decreases the portal blood flow transiently in cirrhotic patients with portal hypertension

Modeling Cerebral Blood Flow Control During Posture Change from Sitting to Standing

DEFF Research Database (Denmark)

Olufsen, Mette; Tran, Hien; Ottesen, Johnny T.

2004-01-01

, the heart, and venous valves. We use physiologically based control mechanisms to describe the regulation of cerebral blood velocity and arterial pressure in response to orthostatic hypotension resulting from postural change. Beyond active control mechanisms we also have to include certain passive non......Hypertension, decreased cerebral blood flow, and diminished cerebral blood flow regulation, are among the first signs indicating the presence of cerebral vascular disease. In this paper, we will present a mathematical model that can predict blood flow and pressure during posture change from sitting......-linearities in some of the compliance-pressure and resistance-pressure relationships. Futhermore, an acurate and physiologically based submodel, describing the dynamics of how gravity effects the blood distribution during suspine changes, is included. To justify the fidelity of our mathematical model and control...

Doppler Flow Wire Evaluation of Renal Blood Flow Reserve in Hypertensive Patients with Normal Renal Arteries

International Nuclear Information System (INIS)

Beregi, Jean-Paul; Mounier-Vehier, Claire; Devos, Patrick; Gautier, Corinne; Libersa, Christian; McFadden, Eugene P.; Carre, Alain

2000-01-01

Purpose: To study the vasomotor responses of the renal microcirculation in patients with essential hypertension.Methods: We studied the reactivity of the renal microcirculation to papaverine, with intraarterial Doppler and quantitative arteriography, in 34 renal arteries of 19 hypertensive patients without significant renal artery stenosis. Isosorbide dinitrate was given to maximally dilate proximal renal arteries. APV (average peak blood flow velocity) was used as an index of renal blood flow.Results: Kidneys could be divided into two distinct subgroups based on their response to papaverine. An increase in APV of up to 55% occurred in 21 kidneys, an increase > 55% in 13 kidneys. Within each group the values were normally distributed. Both baseline APV and the effect of papaverine on mean velocity differed significantly between groups.Conclusion: There seems to be a subgroup of patients with essential hypertension that has an impaired reactivity to papaverine, consistent with a functional impairment of the renal microcirculation. Further studies are required to determine whether this abnormality contributes to or results from elevated blood pressure

Demonstration of a Vector Velocity Technique

DEFF Research Database (Denmark)

Hansen, Peter Møller; Pedersen, Mads M.; Hansen, Kristoffer L.

2011-01-01

With conventional Doppler ultrasound it is not possible to estimate direction and velocity of blood flow, when the angle of insonation exceeds 60–70°. Transverse oscillation is an angle independent vector velocity technique which is now implemented on a conventional ultrasound scanner. In this pa......With conventional Doppler ultrasound it is not possible to estimate direction and velocity of blood flow, when the angle of insonation exceeds 60–70°. Transverse oscillation is an angle independent vector velocity technique which is now implemented on a conventional ultrasound scanner...

Transition of unsteady velocity profiles with reverse flow

Science.gov (United States)

Das, Debopam; Arakeri, Jaywant H.

1998-11-01

This paper deals with the stability and transition to turbulence of wall-bounded unsteady velocity profiles with reverse flow. Such flows occur, for example, during unsteady boundary layer separation and in oscillating pipe flow. The main focus is on results from experiments in time-developing flow in a long pipe, which is decelerated rapidly. The flow is generated by the controlled motion of a piston. We obtain analytical solutions for laminar flow in the pipe and in a two-dimensional channel for arbitrary piston motions. By changing the piston speed and the length of piston travel we cover a range of values of Reynolds number and boundary layer thickness. The velocity profiles during the decay of the flow are unsteady with reverse flow near the wall, and are highly unstable due to their inflectional nature. In the pipe, we observe from flow visualization that the flow becomes unstable with the formation of what appears to be a helical vortex. The wavelength of the instability [simeq R: similar, equals]3[delta] where [delta] is the average boundary layer thickness, the average being taken over the time the flow is unstable. The time of formation of the vortices scales with the average convective time scale and is [simeq R: similar, equals]39/([Delta]u/[delta]), where [Delta]u=(umax[minus sign]umin) and umax, umin and [delta] are the maximum velocity, minimum velocity and boundary layer thickness respectively at each instant of time. The time to transition to turbulence is [simeq R: similar, equals]33/([Delta]u/[delta]). Quasi-steady linear stability analysis of the velocity profiles brings out two important results. First that the stability characteristics of velocity profiles with reverse flow near the wall collapse when scaled with the above variables. Second that the wavenumber corresponding to maximum growth does not change much during the instability even though the velocity profile does change substantially. Using the results from the experiments and the

Numerical investigations of the unsteady blood flow in the end-to-side arteriovenous fistula for hemodialysis.

Science.gov (United States)

Jodko, Daniel; Obidowski, Damian; Reorowicz, Piotr; Jóźwik, Krzysztof

2016-01-01

The aim of this study was to investigate the blood flow in the end-to-side arteriovenous (a-v) fistula, taking into account its pulsating nature and the patient-specific geometry of blood vessels. Computational Fluid Dynamics (CFD) methods were used for this analysis. DICOM images of the fistula, obtained from the angio-computed tomography, were a source of the data applied to develop a 3D geometrical model of the fistula. The model was meshed, then the ANSYS CFX v. 15.0 code was used to perform simulations of the flow in the vessels under analysis. Mesh independence tests were conducted. The non-Newtonian rheological model of blood and the Shear Stress Transport model of turbulence were employed. Blood vessel walls were assumed to be rigid. Flow patterns, velocity fields, the volume flow rate, the wall shear stress (WSS) propagation on particular blood vessel walls were shown versus time. The maximal value of the blood velocity was identified in the anastomosis - the place where the artery is connected to the vein. The flow rate was calculated for all veins receiving blood. The blood flow in the geometrically complicated a-v fistula was simulated. The values and oscillations of the WSS are the largest in the anastomosis, much lower in the artery and the lowest in the cephalic vein. A strong influence of the mesh on the results concerning the maximal and area-averaged WSS was shown. The relation between simulations of the pulsating and stationary flow under time-averaged flow conditions was presented.

Transient electro-magneto-hydrodynamic two-phase blood flow and thermal transport through a capillary vessel.

Science.gov (United States)

Mirza, I A; Abdulhameed, M; Vieru, D; Shafie, S

2016-12-01

Therapies with magnetic/electromagnetic field are employed to relieve pains or, to accelerate flow of blood-particles, particularly during the surgery. In this paper, a theoretical study of the blood flow along with particles suspension through capillary was made by the electro-magneto-hydrodynamic approach. Analytical solutions to the non-dimensional blood velocity and non-dimensional particles velocity are obtained by means of the Laplace transform with respect to the time variable and the finite Hankel transform with respect to the radial coordinate. The study of thermally transfer characteristics is based on the energy equation for two-phase thermal transport of blood and particles suspension with viscous dissipation, the volumetric heat generation due to Joule heating effect and electromagnetic couple effect. The solution of the nonlinear heat transfer problem is derived by using the velocity field and the integral transform method. The influence of dimensionless system parameters like the electrokinetic width, the Hartman number, Prandtl number, the coefficient of heat generation due to Joule heating and Eckert number on the velocity and temperature fields was studied using the Mathcad software. Results are presented by graphical illustrations. Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.

Influence of cerebrovascular resistance on the dynamic relationship between blood pressure and cerebral blood flow in humans.

Science.gov (United States)

Smirl, J D; Tzeng, Y C; Monteleone, B J; Ainslie, P N

2014-06-15

We examined the hypothesis that changes in the cerebrovascular resistance index (CVRi), independent of blood pressure (BP), will influence the dynamic relationship between BP and cerebral blood flow in humans. We altered CVRi with (via controlled hyperventilation) and without [via indomethacin (INDO, 1.2 mg/kg)] changes in PaCO2. Sixteen subjects (12 men, 27 ± 7 yr) were tested on two occasions (INDO and hypocapnia) separated by >48 h. Each test incorporated seated rest (5 min), followed by squat-stand maneuvers to increase BP variability and improve assessment of the pressure-flow dynamics using linear transfer function analysis (TFA). Beat-to-beat BP, middle cerebral artery velocity (MCAv), posterior cerebral artery velocity (PCAv), and end-tidal Pco2 were monitored. Dynamic pressure-flow relations were quantified using TFA between BP and MCAv/PCAv in the very low and low frequencies through the driven squat-stand maneuvers at 0.05 and 0.10 Hz. MCAv and PCAv reductions by INDO and hypocapnia were well matched, and CVRi was comparably elevated (P flow dynamics. These findings are consistent with the concept of CVRi being a key factor that should be considered in the correct interpretation of cerebral pressure-flow dynamics as indexed using TFA metrics. Copyright © 2014 the American Physiological Society.

Magnetization Transfer Effects on the Efficiency of Flow-driven Adiabatic Fast Passage Inversion of Arterial Blood

OpenAIRE

Hernandez-Garcia, Luis; Lewis, David P.; Moffat, Bradford; Branch, Craig A.

2007-01-01

Continuous arterial spin labeling experiments typically use flow-driven adiabatic fast passage (AFP) inversion of the arterial blood water protons. In this article, we measure the effect of magnetization transfer in blood and how it affects the inversion label. We use modified Bloch equations to model flow-driven adiabatic inversion in the presence of magnetization transfer in blood flowing at velocities from 1 to 30 cm/s in order to explain our findings. Magnetization transfer results in a r...

3-D MDT with spherical targets by bilinear interpolation for determining blood velocity profiles including the vessel wall effect

Science.gov (United States)

Choomphon-anomakhun, Natthaphon; Natenapit, Mayuree

2018-02-01

A numerical simulation of three-dimensional (3-D) implant assisted-magnetic drug targeting (IA-MDT) using ferromagnetic spherical targets, including the effect from the vessel wall on the blood flow, is presented. The targets were implanted within arterioles and subjected to an externally uniform applied magnetic field in order to increase the effectiveness of targeting magnetic drug carrier particles (MDCPs). The capture area (As) of the MDCPs was determined by inspection of the particle trajectories simulated from the particle equations of motion. The blood flow velocities at any particle position around the target were obtained by applying bilinear interpolation to the numerical blood velocity data. The effects on As of the type of ferromagnetic materials in the targets and MDCPs, average blood flow rates, mass fraction of the ferromagnetic material in the MDCPs, average radii of MDCPs (Rp) and the externally applied magnetic field strength (μ0H0) were evaluated. Furthermore, the appropriate μ0H0 and Rp for the IA-MDT design is suggested. In the case of the SS409 target and magnetite MDCPs, dimensionless capture areas ranging from 4.1- to 12.4 and corresponding to particle capture efficiencies of 31-94% were obtained with Rp ranging from 100- to 500 nm, weight fraction of 80%, μ0H0 of 0.6 T and an average blood flow rate of 0.01 ms-1. In addition, the more general 3-D modelling of IA-MDT in this work is applicable to IA-MDT using spherical targets implanted within blood vessels for both laminar and potential blood flows including the wall effect.

In Vivo Validation of a Blood Vector Velocity Estimator with MR Angiography

DEFF Research Database (Denmark)

Hansen, Kristoffer Lindskov; Udesen, Jesper; Thomsen, Carsten

2009-01-01

Conventional Doppler methods for blood velocity estimation only estimate the velocity component along the ultrasound beam direction. This implies that a Doppler angle under examination close to 90° results in unreliable information about the true blood direction and blood velocity. The novel method...... indicate that reliable vector velocity estimates can be obtained in vivo using the presented angle-independent 2-D vector velocity method. The TO method can be a useful alternative to conventional Doppler systems by avoiding the angle artifact, thus giving quantitative velocity information....

Automated segmentation of blood-flow regions in large thoracic arteries using 3D-cine PC-MRI measurements.

Science.gov (United States)

van Pelt, Roy; Nguyen, Huy; ter Haar Romeny, Bart; Vilanova, Anna

2012-03-01

Quantitative analysis of vascular blood flow, acquired by phase-contrast MRI, requires accurate segmentation of the vessel lumen. In clinical practice, 2D-cine velocity-encoded slices are inspected, and the lumen is segmented manually. However, segmentation of time-resolved volumetric blood-flow measurements is a tedious and time-consuming task requiring automation. Automated segmentation of large thoracic arteries, based solely on the 3D-cine phase-contrast MRI (PC-MRI) blood-flow data, was done. An active surface model, which is fast and topologically stable, was used. The active surface model requires an initial surface, approximating the desired segmentation. A method to generate this surface was developed based on a voxel-wise temporal maximum of blood-flow velocities. The active surface model balances forces, based on the surface structure and image features derived from the blood-flow data. The segmentation results were validated using volunteer studies, including time-resolved 3D and 2D blood-flow data. The segmented surface was intersected with a velocity-encoded PC-MRI slice, resulting in a cross-sectional contour of the lumen. These cross-sections were compared to reference contours that were manually delineated on high-resolution 2D-cine slices. The automated approach closely approximates the manual blood-flow segmentations, with error distances on the order of the voxel size. The initial surface provides a close approximation of the desired luminal geometry. This improves the convergence time of the active surface and facilitates parametrization. An active surface approach for vessel lumen segmentation was developed, suitable for quantitative analysis of 3D-cine PC-MRI blood-flow data. As opposed to prior thresholding and level-set approaches, the active surface model is topologically stable. A method to generate an initial approximate surface was developed, and various features that influence the segmentation model were evaluated. The active surface

An Approach to Predict Debris Flow Average Velocity

Directory of Open Access Journals (Sweden)

Chen Cao

2017-03-01

Full Text Available Debris flow is one of the major threats for the sustainability of environmental and social development. The velocity directly determines the impact on the vulnerability. This study focuses on an approach using radial basis function (RBF neural network and gravitational search algorithm (GSA for predicting debris flow velocity. A total of 50 debris flow events were investigated in the Jiangjia gully. These data were used for building the GSA-based RBF approach (GSA-RBF. Eighty percent (40 groups of the measured data were selected randomly as the training database. The other 20% (10 groups of data were used as testing data. Finally, the approach was applied to predict six debris flow gullies velocities in the Wudongde Dam site area, where environmental conditions were similar to the Jiangjia gully. The modified Dongchuan empirical equation and the pulled particle analysis of debris flow (PPA approach were used for comparison and validation. The results showed that: (i the GSA-RBF predicted debris flow velocity values are very close to the measured values, which performs better than those using RBF neural network alone; (ii the GSA-RBF results and the MDEE results are similar in the Jiangjia gully debris flow velocities prediction, and GSA-RBF performs better; (iii in the study area, the GSA-RBF results are validated reliable; and (iv we could consider more variables in predicting the debris flow velocity by using GSA-RBF on the basis of measured data in other areas, which is more applicable. Because the GSA-RBF approach was more accurate, both the numerical simulation and the empirical equation can be taken into consideration for constructing debris flow mitigation works. They could be complementary and verified for each other.

Ultrasound systems for blood velocity estimation

DEFF Research Database (Denmark)

Jensen, Jørgen Arendt

1998-01-01

Medical ultrasound scanners can be used both for displayinggray-scale images of the anatomy and for visualizing theblood flow dynamically in the body.The systems can interrogate the flow at a single position in the bodyand there find the velocity distribution over time. They can also show adynamic...

Blood flow analysis with considering nanofluid effects in vertical channel

Science.gov (United States)

Noreen, S.; Rashidi, M. M.; Qasim, M.

2017-06-01

Manipulation of heat convection of copper particles in blood has been considered peristaltically. Two-phase flow model is used in a channel with insulating walls. Flow analysis has been approved by assuming small Reynold number and infinite length of wave. Coupled equations are solved. Numerical solution are computed for the pressure gradient, axial velocity function and temperature. Influence of attention-grabbing parameters on flow entities has been analyzed. This study can be considered as mathematical representation to the vibrance of physiological systems/tissues/organs provided with medicine.

Energy Demodulation Algorithm for Flow Velocity Measurement of Oil-Gas-Water Three-Phase Flow

Directory of Open Access Journals (Sweden)

Yingwei Li

2014-01-01

Full Text Available Flow velocity measurement was an important research of oil-gas-water three-phase flow parameter measurements. In order to satisfy the increasing demands for flow detection technology, the paper presented a gas-liquid phase flow velocity measurement method which was based on energy demodulation algorithm combing with time delay estimation technology. First, a gas-liquid phase separation method of oil-gas-water three-phase flow based on energy demodulation algorithm and blind signal separation technology was proposed. The separation of oil-gas-water three-phase signals which were sampled by conductance sensor performed well, so the gas-phase signal and the liquid-phase signal were obtained. Second, we used the time delay estimation technology to get the delay time of gas-phase signals and liquid-phase signals, respectively, and the gas-phase velocity and the liquid-phase velocity were derived. At last, the experiment was performed at oil-gas-water three-phase flow loop, and the results indicated that the measurement errors met the need of velocity measurement. So it provided a feasible method for gas-liquid phase velocity measurement of the oil-gas-water three-phase flow.

Voluntary suppression of hyperthermia-induced hyperventilation mitigates the reduction in cerebral blood flow velocity during exercise in the heat.

Science.gov (United States)

Tsuji, Bun; Honda, Yasushi; Ikebe, Yusuke; Fujii, Naoto; Kondo, Narihiko; Nishiyasu, Takeshi

2015-04-15

Hyperthermia during prolonged exercise leads to hyperventilation, which can reduce arterial CO2 pressure (PaCO2 ) and, in turn, cerebral blood flow (CBF) and thermoregulatory response. We investigated 1) whether humans can voluntarily suppress hyperthermic hyperventilation during prolonged exercise and 2) the effects of voluntary breathing control on PaCO2 , CBF, sweating, and skin blood flow. Twelve male subjects performed two exercise trials at 50% of peak oxygen uptake in the heat (37°C, 50% relative humidity) for up to 60 min. Throughout the exercise, subjects breathed normally (normal-breathing trial) or they tried to control their minute ventilation (respiratory frequency was timed with a metronome, and target tidal volumes were displayed on a monitor) to the level reached after 5 min of exercise (controlled-breathing trial). Plotting ventilatory and cerebrovascular responses against esophageal temperature (Tes) showed that minute ventilation increased linearly with rising Tes during normal breathing, whereas controlled breathing attenuated the increased ventilation (increase in minute ventilation from the onset of controlled breathing: 7.4 vs. 1.6 l/min at +1.1°C Tes; P flow velocity (MCAV) with rising Tes, but controlled breathing attenuated those reductions (estimated PaCO2 -3.4 vs. -0.8 mmHg; MCAV -10.4 vs. -3.9 cm/s at +1.1°C Tes; P = 0.002 and 0.011, respectively). Controlled breathing had no significant effect on chest sweating or forearm vascular conductance (P = 0.67 and 0.91, respectively). Our results indicate that humans can voluntarily suppress hyperthermic hyperventilation during prolonged exercise, and this suppression mitigates changes in PaCO2 and CBF. Copyright © 2015 the American Physiological Society.

Investigation of blood flow rheology using second-grade viscoelastic model (Phan-Thien-Tanner) within carotid artery.

Science.gov (United States)

Ramiar, Abas; Larimi, Morsal Momenti; Ranjbar, Ali Akbar

2017-01-01

Hemodynamic factors, such as Wall Shear Stress (WSS), play a substantial role in arterial diseases. In the larger arteries, such as the carotid artery, interaction between the vessel wall and blood flow affects the distribution of hemodynamic factors. The fluid is considered to be non-Newtonian, whose flow is governed by the equation of a second-grade viscoelastic fluid and the effects of viscoelastic on blood flow in carotid artery is investigated. Pulsatile flow studies were carried out in a 3D model of carotid artery. The governing equations were solved using finite volume C++ based on open source code, OpenFOAM. To describe blood flow, conservation of mass and momentum, a constitutive relation of simplified Phan-Thien-Tanner (sPTT), and appropriate relations were used to explain shear thinning behavior. The first recirculation was observed at t = 0.2 s, in deceleration phase. In the acceleration phase from t = 0.3 s to t = 0.5 s, vortex and recirculation sizes in bulb regions in both ECA and ICA gradually increased. As is observed in the line graphs based on extracted data from ICA, at t = 0.2 s, τyy is the maximum amount of wall shear stress and τxy the minimum one. The maximum shear stress occurred in the inner side of the main branch (inner side of ICA and ECA) because the velocity of blood flow in the inner side of the bulb region was maximum due to the created recirculation zone in the opposite side in this area. The rheology of blood flow and shear stress in various important parts (the area that are in higher rates of WSS such as bifurcation region and the regions after bulb areas in both branches, Line1-4 in Fig. 7) were also analyzed. The investigation of velocity stream line, velocity profile and shear stress in various sections of carotid artery showed that the maximum shear stress occurred in acceleration phase and in the bifurcation region between ECA and ICA which is due to velocity gradients and changes in thinning behavior of blood and

Effects of coil closure of patent ductus arteriosus on left anterior descending coronary artery blood flow using transthoracic Doppler echocardiography.

Science.gov (United States)

Harada, Kenji; Toyono, Manotomo; Tamura, Masamichi

2004-06-01

Transthoracic Doppler echocardiography provides noninvasive measurements of coronary blood flow in the left anterior descending coronary artery (LAD). This method has the potential to show the effects of acute changes in loading conditions on blood flow. Coil closure of patent ductus arteriosus (PDA) is a model of acute changes in blood pressure and left ventricular (LV) preload that influences coronary blood flow. We applied this technique to assess the coronary blood flow changes for patients with PDA before and immediately after PDA coil closure. We examined 9 patients (1.8 +/- 1.1 years) with simple PDA and 8 age-matched healthy children. LV dimensions and LV mass were measured. Maximum peak flow velocity and flow volume in the LAD were measured. Pulmonary to systemic flow ratios (Qp/Qs) were obtained by cardiac catheterization. After PDA coil closure, LV end-diastolic dimension decreased, and systolic and diastolic blood pressures increased significantly. The maximum peak flow velocity, LAD flow volume, and the ratio of LAD flow volume to LV mass increased significantly. The changes in maximum peak flow velocity and the ratio of LAD flow volume to LV mass (F/M) correlated positively with the changes in diastolic pressure and Qp/Qs. In 5 patients who had Qp/Qs > 1.5, the mean F/M was significantly lower compared with control subjects, but they increased to normal values after coil closure of PDA. PDA coil closure increases diastolic pressure and decreases Qp/Qs, resulting in improvement of myocardial perfusion. These findings provide new insights into the relationship between cardiac function and coronary circulation in pediatric patients with heart diseases associated with PDA.

Two-Fluid Mathematical Models for Blood Flow in Stenosed Arteries: A Comparative Study

Directory of Open Access Journals (Sweden)

Sankar DS

2009-01-01

Full Text Available The pulsatile flow of blood through stenosed arteries is analyzed by assuming the blood as a two-fluid model with the suspension of all the erythrocytes in the core region as a non-Newtonian fluid and the plasma in the peripheral layer as a Newtonian fluid. The non-Newtonian fluid in the core region of the artery is assumed as a (i Herschel-Bulkley fluid and (ii Casson fluid. Perturbation method is used to solve the resulting system of non-linear partial differential equations. Expressions for various flow quantities are obtained for the two-fluid Casson model. Expressions of the flow quantities obtained by Sankar and Lee (2006 for the two-fluid Herschel-Bulkley model are used to get the data for comparison. It is found that the plug flow velocity and velocity distribution of the two-fluid Casson model are considerably higher than those of the two-fluid Herschel-Bulkley model. It is also observed that the pressure drop, plug core radius, wall shear stress and the resistance to flow are significantly very low for the two-fluid Casson model than those of the two-fluid Herschel-Bulkley model. Hence, the two-fluid Casson model would be more useful than the two-fluid Herschel-Bulkley model to analyze the blood flow through stenosed arteries.

In-vivo imaging of blood flow in human retinal vessels using color Doppler optical coherence tomography

Science.gov (United States)

Yazdanfar, Siavash; Rollins, Andrew M.; Izatt, Joseph A.

1999-04-01

Quantification of retinal blood flow may lead to a better understanding of the progression and treatment of several ocular disorders, including diabetic retinopathy, age- related macular degeneration, and glaucoma. Current techniques, such as fluorescein angiography and laser Doppler velocimetry are limited, failing to provide sufficient information to the clinician. Color Doppler optical coherence tomography (CDOCT) is a novel technique using coherent heterodyne detection for simultaneous cross- sectional imaging of tissue microstructure and blood flow. This technique is capable of high spatial and velocity resolution imaging in highly scattering media. We implemented CDOCT for retinal blood flow mapping in human subjects. No dilation of the pupil was necessary. CDOCT is demonstrated for determining bidirectional flow in sub- 100micrometers diameter vessels in the retina. Additionally, we calculated Doppler broadening using the variance of depth- resolved spectra to identify regions with large velocity gradients within the Xenopus heart. This technique may be useful in quantifying local tissue perfusion in highly vascular retinal tissue.

Cerebral blood flow and oximetry response to blood transfusion in relation to chronological age in preterm infants.

Science.gov (United States)

Banerjee, J; Leung, T S; Aladangady, N

2016-06-01

Preterm infants frequently receive blood transfusion (BT) and the aim of this study was to measure the effect of BT on cerebral blood flow and oxygenation in preterm infants in relation to chronological age. Preterm infants undergoing intensive care recruited to three chronological age groups: 1 to 7 (Group 1; n=20), 8 to 28 (Group 2; n=21) & ≥29days of life (Group 3; n=18). Pre and post-BT anterior cerebral artery (ACA) time averaged mean velocity (TAMV) and superior vena cava (SVC) flow were measured. Cerebral Tissue Haemoglobin Index (cTHI) and Oxygenation Index (cTOI) were measured from 15-20min before to 15-20min post-BT using NIRS. Vital parameters and blood pressure were measured continuously. Mean BP increased significantly, and there was no significant change in vital parameters following BT. Pre-BT ACA TAMV was higher in Group 2 and 3 compared to Group 1 (pBlood transfusion increased cTOI and cTHI and decreased ACA TAMV in all groups. PDA had no impact on the baseline cerebral oximetry and blood flow as well as changes following blood transfusion. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Exploiting LSPIV to assess debris-flow velocities in the field

Science.gov (United States)

Theule, Joshua I.; Crema, Stefano; Marchi, Lorenzo; Cavalli, Marco; Comiti, Francesco

2018-01-01

The assessment of flow velocity has a central role in quantitative analysis of debris flows, both for the characterization of the phenomenology of these processes and for the assessment of related hazards. Large-scale particle image velocimetry (LSPIV) can contribute to the assessment of surface velocity of debris flows, provided that the specific features of these processes (e.g. fast stage variations and particles up to boulder size on the flow surface) are taken into account. Three debris-flow events, each of them consisting of several surges featuring different sediment concentrations, flow stages, and velocities, have been analysed at the inlet of a sediment trap in a stream in the eastern Italian Alps (Gadria Creek). Free software has been employed for preliminary treatment (orthorectification and format conversion) of video-recorded images as well as for LSPIV application. Results show that LSPIV velocities are consistent with manual measurements of the orthorectified imagery and with front velocity measured from the hydrographs in a channel recorded approximately 70 m upstream of the sediment trap. Horizontal turbulence, computed as the standard deviation of the flow directions at a given cross section for a given surge, proved to be correlated with surface velocity and with visually estimated sediment concentration. The study demonstrates the effectiveness of LSPIV in the assessment of surface velocity of debris flows and permit the most crucial aspects to be identified in order to improve the accuracy of debris-flow velocity measurements.

Quantification of blood flow in the middle cerebral artery with phase-contrast MR imaging

Energy Technology Data Exchange (ETDEWEB)

Stock, K.W.; Wetzel, S.G.; Radue, E.W. [Dept. of Radiology, Division of Neuroradiology, University Hospital of Basel (Switzerland); Lyrer, P.A. [Dept. of Neurology, University Hospital of Basel (Switzerland)

2000-11-01

The aim of this study was to assess blood flow in the middle cerebral artery (MCA) according to age, gender, and side. Eighty-eight subjects without carotid obstruction were measured for mean velocity, vessel area, and volume flow rates of both MCA with phase-contrast MR. A high-resolution sequence with a matrix of 300 x 512 and a double oblique localizing strategy was used for measurement. A mean velocity of 33 {+-} 6.8 cm/s, a mean vessel area of 6.2 {+-} 1.2 mm{sup 2} and a mean flow rate of 121 {+-} 28 ml/min were measured in the MCA. Lower volume flow rates were seen in subjects aged over 50 years (p < 0.01). When comparing women with men, a lower vessel area (p < 0.05) of the MCA was counterbalanced by a higher velocity, resulting in no significant difference of the volume flow rate. No difference occurred between the right and the left side. Flow reduction occurs in the elderly. A lower vessel area of the MCA in women is compensated by a higher velocity. (orig.)

Quantification of blood flow in the middle cerebral artery with phase-contrast MR imaging

International Nuclear Information System (INIS)

Stock, K.W.; Wetzel, S.G.; Radue, E.W.; Lyrer, P.A.

2000-01-01

The aim of this study was to assess blood flow in the middle cerebral artery (MCA) according to age, gender, and side. Eighty-eight subjects without carotid obstruction were measured for mean velocity, vessel area, and volume flow rates of both MCA with phase-contrast MR. A high-resolution sequence with a matrix of 300 x 512 and a double oblique localizing strategy was used for measurement. A mean velocity of 33 ± 6.8 cm/s, a mean vessel area of 6.2 ± 1.2 mm 2 and a mean flow rate of 121 ± 28 ml/min were measured in the MCA. Lower volume flow rates were seen in subjects aged over 50 years (p < 0.01). When comparing women with men, a lower vessel area (p < 0.05) of the MCA was counterbalanced by a higher velocity, resulting in no significant difference of the volume flow rate. No difference occurred between the right and the left side. Flow reduction occurs in the elderly. A lower vessel area of the MCA in women is compensated by a higher velocity. (orig.)

The in situ permeable flow sensor: A device for measuring groundwater flow velocity

International Nuclear Information System (INIS)

Ballard, S.; Barker, G.T.; Nichols, R.L.

1994-03-01

A new technology called the In Situ Permeable Flow Sensor has been developed at Sandia National Laboratories. These sensors use a thermal perturbation technique to directly measure the direction and magnitude of the full three dimensional groundwater flow velocity vector in unconsolidated, saturated, porous media. The velocity measured is an average value characteristic of an approximately 1 cubic meter volume of the subsurface. During a test at the Savannah River Site in South Carolina, two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer and the well was pumped at four different pumping rates. In this situation horizontal flow which is radially directed toward the pumping well is expected. The flow sensors measured horizontal flow which was directed toward the pumping well, within the uncertainty in the measurements. The observed magnitude of the horizontal component of the flow velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured horizontal component of the flow velocity differed from the predicted flow velocity, which was calculated with the assumptions that the hydraulic properties of the aquifer were radially homogeneous and isotropic, by less than a factor of two. Drawdown data obtained from other wells near the pumping well during the pump test indicate that the hydraulic properties of the aquifer are probably not radially homogeneous but the effect of the inhomogeneity on the flow velocity field around the pumping well was not modeled because the degree and distribution of the inhomogeneity are unknown. Grain size analysis of core samples from wells in the area were used to estimate the vertical distribution of hydraulic conductivity

Normalization of thyroid blood flow in Graves' hyperthyroidism following radioactive iodine therapy

Energy Technology Data Exchange (ETDEWEB)

Chang, D.C.S.; Woodcock, J.P.; Shedden, E.J.; Lazarus, J.H.; Wheeler, M.H.; McGregor, A.M. (University Hospital of Wales, Cardiff (UK). Medical Physics Dept.)

1990-05-01

In a group of 12 patients with Graves' hyperthyroidism, administration of 514 {plus minus} 43 (mean {plus minus} SD) MBq iodine-131 was associated with a fall of superior thyroid artery (STA) blood flow in two at 6 months and in eight at 11 months. The reduction in time-averaged velocity at 11 months correlated with the reduction in FT4 and in FT3 at this time. In four patients who had persistent elevated STA blood flow, two were still hyperthyroid. The diameter of the STA was unchanged at 6 months and only half the patients had reduction of their STA size at 11 months after radioiodine (RAI) therapy. These data indicate that normalization of STA blood flow precedes normalization of STA size in patients treated with RAI. Further work is required to determine whether STA blood flow measurements are of predictive value in treatment outcome. (author).

A randomized, controlled, double-blind crossover study on the effects of 1-L infusions of 6% hydroxyethyl starch suspended in 0.9% saline (voluven) and a balanced solution (Plasma Volume Redibag) on blood volume, renal blood flow velocity, and renal cortical tissue perfusion in healthy volunteers.

Science.gov (United States)

Chowdhury, Abeed H; Cox, Eleanor F; Francis, Susan T; Lobo, Dileep N

2014-05-01

We compared the effects of intravenous administration of 6% hydroxyethyl starch (maize-derived) in 0.9% saline (Voluven; Fresenius Kabi, Runcorn, United Kingdom) and a "balanced" preparation of 6% hydroxyethyl starch (potato-derived) [Plasma Volume Redibag (PVR); Baxter Healthcare, Thetford, United Kingdom] on renal blood flow velocity and renal cortical tissue perfusion in humans using magnetic resonance imaging. Hyperchloremia resulting from 0.9% saline infusion may adversely affect renal hemodynamics when compared with balanced crystalloids. This phenomenon has not been studied with colloids. Twelve healthy adult male subjects received 1-L intravenous infusions of Voluven or PVR over 30 minutes in a randomized, double-blind manner, with crossover studies 7 to 10 days later. Magnetic resonance imaging proceeded for 60 minutes after commencement of infusion to measure renal artery blood flow velocity and renal cortical perfusion. Blood was sampled, and weight was recorded at 0, 30, 60, 120, 180, and 240 minutes. Mean peak serum chloride concentrations were 108 and 106 mmol/L, respectively, after Voluven and PVR infusion (P = 0.032). Changes in blood volume (P = 0.867), strong ion difference (P = 0.219), and mean renal artery flow velocity (P = 0.319) were similar. However, there was a significant increase in mean renal cortical tissue perfusion after PVR when compared with Voluven (P = 0.033). There was no difference in urinary neutrophil gelatinase-associated liopcalin to creatinine ratios after the infusion (P = 0.164). There was no difference in the blood volume-expanding properties of the 2 preparations of 6% hydroxyethyl starch. The balanced starch produced an increase in renal cortical tissue perfusion, a phenomenon not seen with starch in 0.9% saline.

Deterministic nonlinear characteristics of in vivo blood flow velocity and arteriolar diameter fluctuations

International Nuclear Information System (INIS)

Parthimos, D; Osterloh, K; Pries, A R; Griffith, T M

2004-01-01

We have performed a nonlinear analysis of fluctuations in red cell velocity and arteriolar calibre in the mesenteric bed of the anaesthetized rat. Measurements were obtained under control conditions and during local superfusion with N G -nitro-L-arginine (L-NNA, 30 μM) and tetrabutylammonium (TBA, 0.1 mM), which suppress NO synthesis and block Ca 2+ activated K + channels (K Ca ), respectively. Time series were analysed by calculating correlation dimensions and largest Lyapunov exponents. Both statistics were higher for red cell velocity than diameter fluctuations, thereby potentially differentiating between global and local mechanisms that regulate microvascular flow. Evidence for underlying nonlinear structure was provided by analysis of surrogate time series generated from the experimental data following randomization of Fourier phase. Complexity indices characterizing time series under control conditions were in general higher than those derived from data obtained during superfusion with L-NNA and TBA

Pulsatile blood flow, shear force, energy dissipation and Murray's Law

Directory of Open Access Journals (Sweden)

Bengtsson Hans-Uno

2006-08-01

Full Text Available Abstract Background Murray's Law states that, when a parent blood vessel branches into daughter vessels, the cube of the radius of the parent vessel is equal to the sum of the cubes of the radii of daughter blood vessels. Murray derived this law by defining a cost function that is the sum of the energy cost of the blood in a vessel and the energy cost of pumping blood through the vessel. The cost is minimized when vessel radii are consistent with Murray's Law. This law has also been derived from the hypothesis that the shear force of moving blood on the inner walls of vessels is constant throughout the vascular system. However, this derivation, like Murray's earlier derivation, is based on the assumption of constant blood flow. Methods To determine the implications of the constant shear force hypothesis and to extend Murray's energy cost minimization to the pulsatile arterial system, a model of pulsatile flow in an elastic tube is analyzed. A new and exact solution for flow velocity, blood flow rate and shear force is derived. Results For medium and small arteries with pulsatile flow, Murray's energy minimization leads to Murray's Law. Furthermore, the hypothesis that the maximum shear force during the cycle of pulsatile flow is constant throughout the arterial system implies that Murray's Law is approximately true. The approximation is good for all but the largest vessels (aorta and its major branches of the arterial system. Conclusion A cellular mechanism that senses shear force at the inner wall of a blood vessel and triggers remodeling that increases the circumference of the wall when a shear force threshold is exceeded would result in the observed scaling of vessel radii described by Murray's Law.

[Preclinical diagnostics and correction of the disturbed renal blood flow in the children presenting with diabetic nephropathy].

Science.gov (United States)

Aver'ianov, A P; Tkacheva, E N; Bolotova, N V; Filina, N Iu; Ivanova, Iu V; Nikolaeva, N V; Tikhonova, L A

2011-01-01

The present study included 86 children aged between 7 and 17 years with type 1 diabetes mellitus from 1 to 15 years in duration. In all the patients, renal blood flow was investigated with the use of ultrasonic dopplerography. The results of the study suggest disturbances of intrarenal hemodynamics that manifested themselves as enhanced resistance of renal arteries from periphery to the centre in the patients at the hyperfiltration stage of diabetic nephropathy (DN) in conjunction with the reduced velocity of blood flow in inter-lobular and segmental arteries. In contrast, the patients at the microalbuminuric stage of diabetic nephropathy exhibited increased resistance and reduced velocity of blood flow in the main renal veins. In 35 patients presenting with diabetic nephropathy, hemodynamic correction was achieved by the application of the traveling pulsed magnetic field (TP-MF) to the renal region using an AMO-ATOS-E apparatus (Russia). This treatment resulted in normalization of the characteristics of renal blood flow. It is concluded that TPMF has good prospects for the use as a component of the combined treatment of diabetic nephropathy.

Dual-beam optical coherence tomography system for quantification of flow velocity in capillary phantoms

Science.gov (United States)

Daly, S. M.; Silien, C.; Leahy, M. J.

2012-03-01

The quantification of (blood) flow velocity within the vasculature has potent diagnostic and prognostic potential. Assessment of flow irregularities in the form of increased permeability (micro haemorrhaging), the presence of avascular areas, or conversely the presence of vessels with enlarged or increased tortuosity in the acral regions of the body may provide a means of non-invasive in vivo assessment. If assessment of dermal flow dynamics were performed in a routine manner, the existence and prevalence of ailments such as diabetes mellitus, psoriatic arthritis and Raynaud's condition may be confirmed prior to clinical suspicion. This may prove advantageous in cases wherein the efficacy of a prescribed treatment is dictated by a prompt diagnosis and to alleviate patient discomfort through early detection. Optical Coherence Tomography (OCT) is an imaging modality which utilises the principle of optical interferometry to distinguish between spatial changes in refractive index within the vasculature and thus formulate a multi-dimensional representation of the structure of the epi- and dermal skin layers. The use of the Doppler functionality has been the predominant force for the quantification of moving particles within media, elucidated via estimation of the phase shift in OCT A-scans. However, the theoretical formulation for the assessment of these phase shifts dictates that the angle between the incident light source and the vessel under question be known a priori; this may be achieved via excisional biopsy of the tissue segment in question, but is counter to the non-invasive premise of the OCT technique. To address the issue of angular dependence, an alternate means of estimating absolute flow velocity is presented. The design and development of a dual-beam (db) system incorporating an optical switch mechanism for signal discrimination of two spatially disparate points enabling quasi-simultaneous multiple specimen scanning is described. A crosscorrelation (c

A wave propagation model of blood flow in large vessels using an approximate velocity profile function

NARCIS (Netherlands)

Bessems, D.; Rutten, M.C.M.; Vosse, van de F.N.

2007-01-01

Lumped-parameter models (zero-dimensional) and wave-propagation models (one-dimensional) for pressure and flow in large vessels, as well as fully three-dimensional fluid–structure interaction models for pressure and velocity, can contribute valuably to answering physiological and patho-physiological

Noninvasive calculation of the aortic blood pressure waveform from the flow velocity waveform: a proof of concept.

Science.gov (United States)

Vennin, Samuel; Mayer, Alexia; Li, Ye; Fok, Henry; Clapp, Brian; Alastruey, Jordi; Chowienczyk, Phil

2015-09-01

Estimation of aortic and left ventricular (LV) pressure usually requires measurements that are difficult to acquire during the imaging required to obtain concurrent LV dimensions essential for determination of LV mechanical properties. We describe a novel method for deriving aortic pressure from the aortic flow velocity. The target pressure waveform is divided into an early systolic upstroke, determined by the water hammer equation, and a diastolic decay equal to that in the peripheral arterial tree, interposed by a late systolic portion described by a second-order polynomial constrained by conditions of continuity and conservation of mean arterial pressure. Pulse wave velocity (PWV, which can be obtained through imaging), mean arterial pressure, diastolic pressure, and diastolic decay are required inputs for the algorithm. The algorithm was tested using 1) pressure data derived theoretically from prespecified flow waveforms and properties of the arterial tree using a single-tube 1-D model of the arterial tree, and 2) experimental data acquired from a pressure/Doppler flow velocity transducer placed in the ascending aorta in 18 patients (mean ± SD: age 63 ± 11 yr, aortic BP 136 ± 23/73 ± 13 mmHg) at the time of cardiac catheterization. For experimental data, PWV was calculated from measured pressures/flows, and mean and diastolic pressures and diastolic decay were taken from measured pressure (i.e., were assumed to be known). Pressure reconstructed from measured flow agreed well with theoretical pressure: mean ± SD root mean square (RMS) error 0.7 ± 0.1 mmHg. Similarly, for experimental data, pressure reconstructed from measured flow agreed well with measured pressure (mean RMS error 2.4 ± 1.0 mmHg). First systolic shoulder and systolic peak pressures were also accurately rendered (mean ± SD difference 1.4 ± 2.0 mmHg for peak systolic pressure). This is the first noninvasive derivation of aortic pressure based on fluid dynamics (flow and wave speed) in the

The assessment of the breath hold and the free breath methods about the blood flow evaluation by using phase contrast MRI

Energy Technology Data Exchange (ETDEWEB)

Kim, Seong Ho [Dept. of Radiology, Konkuk Medical center, Seoul (Korea, Republic of)

2016-06-15

Measurement of cardiac blood flow using the magnetic resonance imaging has been limited due to breathing and involuntary movements of the heart. The present study attempted to improve the accuracy of cardiac blood flow testing through phase contrast magnetic resonance imaging by presenting the adequate breathing method and imaging variables by comparing the measurement values of cardiac blood flow. Each was evaluated by comparing the breath hold retrospective 1NEX and non breath hold retrospective 1-3NEX in the ascending aorta and descending aorta. As a result, the average blood flow amount/ velocity of the breath hold retrosepctive 1NEX method in the ascending aorta were 96.17±19.12 ml/sec, 17.04±4.12 cm/sec respectively, which demonstrates a statistically significant difference(p<0.05) with the non-breath hold retrospective method 1NEX of 72.31±13.27 ml and 12.32±3.85. On the other hand, the average 2NEX blood flow and mean flow velocity is 101.90±24.09, 16.84±4.32, 3NEX 103.06±25.49, 16.88±4.19 did not show statistically significant differences(p>0.05).The average blood flow amount/ velocity of the breath hold retrospective 1NEX method in the descending aorta were 76.68±19.72 ml/s, and 22.23±4.8, which did not demonstrate a significant difference in comparison to non-breath hold retrospective method 1-3 NEX. Therefore, the non breath hold retrospective method does not significantly differ in terms of cardiac blood flow in comparison with the breath hold retrospective method in accordance with the increase of NEX, so pediatric patients or patients who are not able to breathe well must have the diagnostic value of their cardiac blood flow tests improved.

Predicting bifurcation angle effect on blood flow in the microvasculature.

Science.gov (United States)

Yang, Jiho; Pak, Y Eugene; Lee, Tae-Rin

2016-11-01

Since blood viscosity is a basic parameter for understanding hemodynamics in human physiology, great amount of research has been done in order to accurately predict this highly non-Newtonian flow property. However, previous works lacked in consideration of hemodynamic changes induced by heterogeneous vessel networks. In this paper, the effect of bifurcation on hemodynamics in a microvasculature is quantitatively predicted. The flow resistance in a single bifurcation microvessel was calculated by combining a new simple mathematical model with 3-dimensional flow simulation for varying bifurcation angles under physiological flow conditions. Interestingly, the results indicate that flow resistance induced by vessel bifurcation holds a constant value of approximately 0.44 over the whole single bifurcation model below diameter of 60μm regardless of geometric parameters including bifurcation angle. Flow solutions computed from this new model showed substantial decrement in flow velocity relative to other mathematical models, which do not include vessel bifurcation effects, while pressure remained the same. Furthermore, when applying the bifurcation angle effect to the entire microvascular network, the simulation results gave better agreements with recent in vivo experimental measurements. This finding suggests a new paradigm in microvascular blood flow properties, that vessel bifurcation itself, regardless of its angle, holds considerable influence on blood viscosity, and this phenomenon will help to develop new predictive tools in microvascular research. Copyright © 2016 Elsevier Inc. All rights reserved.

Magnetic field effect on blood flow of Casson fluid in axisymmetric cylindrical tube: A fractional model

Energy Technology Data Exchange (ETDEWEB)

Ali, Farhad, E-mail: farhadaliecomaths@yahoo.com [Department of Mathematics, City University of Science and Information Technology, Peshawar 25000 (Pakistan); Sheikh, Nadeem Ahmad [Department of Mathematics, City University of Science and Information Technology, Peshawar 25000 (Pakistan); Khan, Ilyas [Basic Engineering Sciences Department, College of Engineering Majmaah University, Majmaah 11952 (Saudi Arabia); Saqib, Muhammad [Department of Mathematics, City University of Science and Information Technology, Peshawar 25000 (Pakistan)

2017-02-01

The effects of magnetohydrodynamics on the blood flow when blood is represented as a Casson fluid, along with magnetic particles in a horizontal cylinder is studied. The flow is due to an oscillating pressure gradient. The Laplace and finite Hankel transforms are used to obtain the closed form solutions of the fractional partial differential equations. Effects of various parameters on the flow of both blood and magnetic particles are shown graphically. The analysis shows that, the model with fractional order derivatives bring a remarkable changes as compared to the ordinary model. The study highlights that applied magnetic field reduces the velocities of both the blood and magnetic particles.

Magnetic field effect on blood flow of Casson fluid in axisymmetric cylindrical tube: A fractional model

International Nuclear Information System (INIS)

Ali, Farhad; Sheikh, Nadeem Ahmad; Khan, Ilyas; Saqib, Muhammad

2017-01-01

The effects of magnetohydrodynamics on the blood flow when blood is represented as a Casson fluid, along with magnetic particles in a horizontal cylinder is studied. The flow is due to an oscillating pressure gradient. The Laplace and finite Hankel transforms are used to obtain the closed form solutions of the fractional partial differential equations. Effects of various parameters on the flow of both blood and magnetic particles are shown graphically. The analysis shows that, the model with fractional order derivatives bring a remarkable changes as compared to the ordinary model. The study highlights that applied magnetic field reduces the velocities of both the blood and magnetic particles.

Point-of-care Devices: Non-Newtonian Whole Blood Behavior and Capillary Flow on Reagent-coated Walls

Directory of Open Access Journals (Sweden)

Jean BERTHIER

2016-08-01

Full Text Available Most point-of-care (POC and patient self-testing (PST devices are based on the analysis of whole blood taken from a finger prick. Whole blood contains a bountiful of information about the donor’s health. We analyze here two particularities of microsystems for blood analysis: the blood non-Newtonian behavior, and the capillary flow in reagent-coated channels. Capillarity is the most commonly used method to move fluids in portable systems. It is shown first that the capillary flow of blood does not follow the Lucas-Washburn-Rideal law when the capillary flow velocity is small, due to its non-Newtonian rheology and to the formation of rouleaux of RBCs. In a second step, the capillary flow of blood on reagent-coated surfaces is investigated; first experimentally by observing the spreading of a droplet of blood on different reagent-coated substrates; second theoretically and numerically using the general law for spontaneous capillary flows and the Evolver numerical program.

Quantification of aortic regurgitation by magnetic resonance velocity mapping

DEFF Research Database (Denmark)

Søndergaard, Lise; Lindvig, K; Hildebrandt, P

1993-01-01

The use of magnetic resonance (MR) velocity mapping in the quantification of aortic valvular blood flow was examined in 10 patients with angiographically verified aortic regurgitation. MR velocity mapping succeeded in identifying and quantifying the regurgitation in all patients, and the regurgit......The use of magnetic resonance (MR) velocity mapping in the quantification of aortic valvular blood flow was examined in 10 patients with angiographically verified aortic regurgitation. MR velocity mapping succeeded in identifying and quantifying the regurgitation in all patients...

Variability in lateralised blood flow response to language is associated with language development in children aged 1-5 years.

Science.gov (United States)

Kohler, M; Keage, H A D; Spooner, R; Flitton, A; Hofmann, J; Churches, O F; Elliott, S; Badcock, N A

2015-01-01

The developmental trajectory of language lateralisation over the preschool years is unclear. We explored the relationship between lateralisation of cerebral blood flow velocity response to object naming and cognitive performance in children aged 1-5 years. Functional transcranial Doppler ultrasound was used to record blood flow velocity bilaterally from middle cerebral arteries during a naming task in 58 children (59% male). At group level, the Lateralisation Index (LI) revealed a greater relative increase in cerebral blood flow velocity within the left as compared to right middle cerebral artery. After controlling for maternal IQ, left-lateralised children displayed lower expressive language scores compared to right- and bi-lateralised children, and reduced variability in LI. Supporting this, greater variability in lateralised response, rather than mean response, was indicative of greater expressive language ability. Findings suggest that a delayed establishment of language specialisation is associated with better language ability in the preschool years. Copyright © 2015 Elsevier Inc. All rights reserved.

Unsteady MHD blood flow through porous medium in a parallel plate channel

Science.gov (United States)

Latha, R.; Rushi Kumar, B.

2017-11-01

In this study, we have analyzed heat and mass transfer effects on unsteady blood flow through parallel plate channel in a saturated porous medium in the presence of a transverse magnetic field with thermal radiation. The governing higher order nonlinear PDE’S are converted to dimensionless equations using dimensionless variables. The dimensionless equations are then solved analytically using boundary conditions by choosing the axial flow transport and the fields of concentration and temperature apart from the normal velocity as a function of y and t. The effects of different pertinent parameters appeared in this model viz thermal radiation, Prandtl number, Heat source parameter, Hartmann number, Permeability parameter, Decay parameter on axial flow transport and the normal velocity are analyzed in detail.

Middle cerebral artery flow velocity and blood flow during exercise and muscle ischemia in humans

DEFF Research Database (Denmark)

Jørgensen, L G; Perko, M; Hanel, B

1992-01-01

Changes in middle cerebral artery flow velocity (Vmean), measured by transcranial Doppler ultrasound, were used to determine whether increases in mean arterial pressure (MAP) or brain activation enhance cerebral perfusion during exercise. We also evaluated the role of "central command......, they support the hypothesis that cerebral perfusion during exercise reflects an increase in brain activation that is independent of MAP, central command, and muscle metaboreceptors but is likely to depend on influence of mechanoreceptors.......," mechanoreceptors, and/or muscle "metaboreceptors" on cerebral perfusion. Ten healthy subjects performed two levels of dynamic exercise corresponding to a heart rate of 110 (range 89-134) and 148 (129-170) beats/min, respectively, and exhaustive one-legged static knee extension. Measurements were continued during 2...

[Changes of renal blood flow during organ-associated foot reflexology measured by color Doppler sonography].

Science.gov (United States)

Sudmeier, I; Bodner, G; Egger, I; Mur, E; Ulmer, H; Herold, M

1999-06-01

Using colour Doppler sonography blood flow changes of the right kidney during foot reflexology were determined in a placebo-controlled, double-blind, randomised study. 32 healthy young adults (17 women, 15 men) were randomly assigned to the verum or placebo group. The verum group received foot reflexology at zones corresponding to the right kidney, the placebo group was treated on other foot zones. Before, during and after foot reflexology the blood flow of three vessels of the right kidney was measured using colour Doppler sonography. Systolic peak velocity and end diastolic peak velocity were measured in cm/s, and the resistive index, a parameter of the vascular resistance, was calculated. The resistive index in the verum group showed a highly significant decrease (p foot reflexology. There was no difference between men and women and no difference between smokers and non-smokers. Verum and placebo group significantly differed concerning alterations of the resistive index both between the measuring points before versus during foot reflexology (p = 0.002) and those during versus after foot reflexology (p = 0.031). The significant decrease of the resistive index during foot reflexology in the verum group indicates a decrease of flow resistance in renal vessels and an increase of renal blood flow. These findings support the hypothesis that organ-associated foot reflexology is effective in changing renal blood flow during therapy.

The feasibility of measuring renal blood flow using transesophageal echocardiography in patients undergoing cardiac surgery.

Science.gov (United States)

Yang, Ping-Liang; Wong, David T; Dai, Shuang-Bo; Song, Hai-Bo; Ye, Ling; Liu, Jin; Liu, Bin

2009-05-01

There is no reliable method to monitor renal blood flow intraoperatively. In this study, we evaluated the feasibility and reproducibility of left renal blood flow measurements using transesophageal echocardiography during cardiac surgery. In this prospective noninterventional study, left renal blood flow was measured with transesophageal echocardiography during three time points (pre-, intra-, and postcardiopulmonary bypass) in 60 patients undergoing cardiac surgery. Sonograms from 6 subjects were interpreted by 2 blinded independent assessors at the time of acquisition and 6 mo later. Interobserver and intraobserver reproducibility were quantified by calculating variability and intraclass correlation coefficients. Patients with Doppler angles of >30 degrees (20 of 60 subjects) were eliminated from renal blood flow measurements. Left renal blood flow was successfully measured and analyzed in 36 of 60 (60%) subjects. Both interobserver and intraobserver variability were renal blood flow measurements were good to excellent (intraclass correlation coefficients 0.604-0.999). Left renal arterial luminal diameter for the pre, intra, and postcardiopulmonary bypass phases, ranged from 3.8 to 4.1 mm, renal arterial velocity from 25 to 35 cm/s, and left renal blood flow from 192 to 299 mL/min. In patients undergoing cardiac surgery, it was feasible in 60% of the subjects to measure left renal blood flow using intraoperative transesophageal echocardiography. The interobserver and intraobserver reproducibility of renal blood flow measurements was good to excellent.

Plasma flow velocity measurements using a modulated Michelson interferometer

International Nuclear Information System (INIS)

Howard, J.

1997-01-01

This paper discusses the possibility of flow velocity reconstruction using passive spectroscopic techniques. We report some preliminary measurements of the toroidal flow velocity of hydrogen atoms in the RTP tokamak using a phase modulated Michelson interferometer. (orig.)

PIV Investigations of the Flow Field in the Volute of a Rotary Blood Pump

Science.gov (United States)

Sankovic, John M.; Kadambi, Jaikrishnan R.; Smith, William A.; Wernet, Mark P.

2004-01-01

A full-size acrylic model of a rotary blood pump was developed in order to utilize Particle Image Velocimetry (PIV) to make measurements of the fluid velocities and turbulent stresses throughout the device. The development of an understanding of the hemodynamics within the blood pump is critical to the development and validation of computational models. A blood analog solution, consisting of sodium iodide solution and glycerin, was developed to match physiological kinematic viscosity. The refractive indices of the fluid, the pump casing, and the impeller were matched to facilitate the use of PIV to make velocity measurements. Velocity measurements made in the volute exit/diffuser region are presented for pumps speeds of 3000-3850 rpm. At each speed data were obtained at a physiological pressure of 12 kPa and at a maximum flow condition. Four hundred data pairs were used for each resultant mean velocity vector value, representing greater than an order of magnitude more data pairs than reported previously in the literature on similar devices and resulting in velocity uncertainty levels of approximately 22.9%.

Instrument for measuring flow velocities

International Nuclear Information System (INIS)

Griffo, J.

1977-01-01

The design described here means to produce a 'more satisfying instrument with less cost' than comparable instruments known up to now. Instead of one single turbine rotor, two similar ones but with opposite blade inclination and sense of rotation are to be used. A cylindrical measuring body is carrying in its axis two bearing blocks whose shape is offering little flow resistance. On the shaft, supported by them, the two rotors run in opposite direction a relatively small axial distance apart. The speed of each rotor is picked up as pulse recurrence frequency by a transmitter and fed to an electronic measuring unit. Measuring errors as they are caused for single rotors by turbulent flow, profile distortion of the velocity, or viscous flow are to be eliminated by means of the contrarotating turbines and the subsequently added electronic unit, because in these cases the adulterating increase of the angular velocity of one rotor is compensated by a corresponding deceleration of the other rotor. The mean value then indicated by the electronic unit has high accurancy of measurement. (RW) [de

Altered aortic shape in bicuspid aortic valve relatives influences blood flow patterns.

Science.gov (United States)

Schnell, Susanne; Smith, Danielle A; Barker, Alex J; Entezari, Pegah; Honarmand, Amir R; Carr, Maria L; Malaisrie, S Chris; McCarthy, Patrick M; Collins, Jeremy; Carr, James C; Markl, Michael

2016-11-01

Bicuspid aortic valve (BAV) is known to exhibit familial inheritance and is associated with aortopathy and altered aortic haemodynamics. However, it remains unclear whether BAV-related aortopathy can be inherited independently of valve morphology. Four-dimensional flow magnetic resonance imaging for the in vivo assessment of thoracic aortic 3D blood flow was performed in 24 BAV relatives with trileaflet aortic valves (age = 40 ± 14 years) and 15 healthy controls (age = 37 ± 10 years). Data analysis included aortic dimensions, shape (round/gothic/cubic), and 3D blood flow characteristics (semi-quantitative vortex/helix grading and peak velocities). Cubic and gothic aortic shapes were markedly more prevalent in BAV relatives compared with controls (38 vs. 7%). Ascending aorta (AAo) vortex flow in BAV relatives was significantly increased compared with controls (grading = 1.5 ± 1.0 vs. 0.6 ± 0.9, P = 0.015). Aortic haemodynamics were influenced by aortic shape: peak velocities were reduced for gothic aortas vs. round aortas (P = 0.003); vortex flow was increased for cubic aortas in the AAo (P gothic aortas in the AAo and descending aorta (P = 0.003, P = 0.029). Logistic regression demonstrated significant associations of shape with severity of vortex flow in AAo (P < 0.001) and aortic arch (P = 0.016) in BAV relatives. BAV relatives expressed altered aortic shape and increased vortex flow despite the absence of valvular disease or aortic dilatation. These data suggest a heritable component of BAV-related aortopathy affecting aortic shape and aberrant blood flow, independent of valve morphology. Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2016. For permissions please email: journals.permissions@oup.com.

Time course of changes in cerebral blood flow velocity after tourniquet deflation in patients with diabetes mellitus or previous stroke under sevoflurane anesthesia.

Science.gov (United States)

Hinohara, Hiroshi; Kadoi, Yuji; Takahashi, Kenichiro; Saito, Shigeru; Kawauchi, Chikara; Mizutani, Akio

2011-06-01

We observed an increase in mean middle cerebral artery blood flow velocity (V(mca)) after tourniquet deflation during orthopedic surgery under sevoflurane anesthesia in patients with diabetes mellitus or previous stroke. Eight controls, seven insulin-treated diabetic patients, and eight previous stroke patients were studied. Arterial blood pressure, heart rate, V(mca), arterial blood gases, and plasma lactate levels were measured every minute for 10 min after tourniquet release in all patients. V(mca) was measured using a transcranial Doppler probe. V(mca) in all three groups increased after tourniquet deflation, the increase lasting for 4 or 5 min. However, the degree of increase in V(mca) in the diabetic patients was smaller than that in the other two groups after tourniquet deflation (at 2 min after tourniquet deflation: control 58.5 ± 3.3, previous stroke 58.4 ± 4.6, diabetes 51.7 ± 2.3; P < 0.05 compared with the other two groups). In conclusion, the degree of increase in V (mca) in diabetic patients is smaller than that in controls and patients with previous stroke.

Dynamic exercise enhances regional cerebral artery mean flow velocity

DEFF Research Database (Denmark)

Linkis, P; Jørgensen, L G; Olesen, H L

1995-01-01

Dynamic exercise enhances regional cerebral artery mean flow velocity. J. Appl. Physiol. 78(1): 12-16, 1995.--Anterior (ACA) and middle (MCA) cerebral artery mean flow velocities (Vmean) and pulsatility indexes were determined using transcranial Doppler in 14 subjects during dynamic exercise afte...

Plasma flow velocity measurements using a modulated Michelson interferometer

NARCIS (Netherlands)

Howard, J.; Meijer, F. G.

1997-01-01

This paper discusses the possibility of flow velocity reconstruction using passive spectroscopic techniques. We report some preliminary measurements of the toroidal flow velocity of hydrogen atoms in the RTP tokamak using a phase modulated Michelson interferometer. (C) 1997 Elsevier Science S.A.

Brachial blood flow under relative levels of blood flow restriction is decreased in a nonlinear fashion.

Science.gov (United States)

Mouser, J Grant; Ade, Carl J; Black, Christopher D; Bemben, Debra A; Bemben, Michael G

2018-05-01

Blood flow restriction (BFR), the application of external pressure to occlude venous return and restrict arterial inflow, has been shown to increase muscular size and strength when combined with low-load resistance exercise. BFR in the research setting uses a wide range of pressures, applying a pressure based upon an individual's systolic pressure or a percentage of occlusion pressure; not a directly determined reduction in blood flow. The relationship between relative pressure and blood flow has not been established. To measure blood flow in the arm under relative levels of BFR. Forty-five people (18-40 years old) participated. Arterial occlusion pressure in the right arm was measured using a 5-cm pneumatic cuff. Blood flow in the brachial artery was measured at rest and at pressures between 10% and 90% of occlusion using ultrasound. Blood flow decreased in a nonlinear, stepped fashion. Blood flow decreased at 10% of occlusion and remained constant until decreasing again at 40%, where it remained until 90% of occlusion. The decrease in brachial blood flow is not proportional to the applied relative pressure. The prescription of blood flow restriction should take into account the stimulus provided at each relative level of blood flow. © 2017 Scandinavian Society of Clinical Physiology and Nuclear Medicine. Published by John Wiley & Sons Ltd.

Validation of Transverse Oscillation Vector Velocity Estimation In-Vivo

DEFF Research Database (Denmark)

Hansen, Kristoffer Lindskov; Udesen, Jesper; Thomsen, Carsten

2007-01-01

Conventional Doppler methods for blood velocity estimation only estimate the velocity component along the ultrasound (US) beam direction. This implies that a Doppler angle under examination close to 90deg results in unreliable information about the true blood direction and blood velocity. The novel...... the presented angle independent 2-D vector velocity method. The results give reason to believe that the TO method can be a useful alternative to conventional Doppler systems bringing forth new information to the US examination of blood flow....

Influence of Flow Velocity on Tsunami Loss Estimation

Directory of Open Access Journals (Sweden)

Jie Song

2017-11-01

Full Text Available Inundation depth is commonly used as an intensity measure in tsunami fragility analysis. However, inundation depth cannot be taken as the sole representation of tsunami impact on structures, especially when structural damage is caused by hydrodynamic and debris impact forces that are mainly determined by flow velocity. To reflect the influence of flow velocity in addition to inundation depth in tsunami risk assessment, a tsunami loss estimation method that adopts both inundation depth and flow velocity (i.e., bivariate intensity measures in evaluating tsunami damage is developed. To consider a wide range of possible tsunami inundation scenarios, Monte Carlo-based tsunami simulations are performed using stochastic earthquake slip distributions derived from a spectral synthesis method and probabilistic scaling relationships of earthquake source parameters. By focusing on Sendai (plain coast and Onagawa (ria coast in the Miyagi Prefecture of Japan in a case study, the stochastic tsunami loss is evaluated by total economic loss and its spatial distribution at different scales. The results indicate that tsunami loss prediction is highly sensitive to modelling resolution and inclusion of flow velocity for buildings located less than 1 km from the sea for Sendai and Onagawa of Miyagi Prefecture.

Experimental investigation of the flow of a blood analogue fluid in a replica of a bifurcated small artery.

Science.gov (United States)

Anastasiou, A D; Spyrogianni, A S; Koskinas, K C; Giannoglou, G D; Paras, S V

2012-03-01

The scope of this work is to study the pulsatile flow of a blood mimicking fluid in a micro channel that simulates a bifurcated small artery, in which the Fahraeus-Lindqvist effect is insignificant. An aqueous glycerol solution with small amounts of xanthan gum was used for simulating viscoelastic properties of blood and in vivo flow conditions were reproduced. Local flow velocities were measured using micro Particle Image Velocimetry (μ-PIV). From the measured velocity distributions, the wall shear stress (WSS) and its variation during a pulse were estimated. The Reynolds numbers employed are relatively low, i.e. similar to those prevailing during blood flow in small arteries. Experiments both with a Newtonian and a non-Newtonian fluid (having asymptotic viscosity equal to the viscosity of the Newtonian one) proved that the common assumption that blood behaves as a Newtonian fluid is not valid for blood flow in small arteries. It was also shown that the outer wall of the bifurcation, which is exposed to a lower WSS, is more predisposed to atherosclerotic plaque formation. Moreover, this region in small vessels is shorter than the one in large arteries, as the developed secondary flow decays faster. Finally, the WSS values in small arteries were found to be lower than those in large ones. Copyright © 2011 IPEM. Published by Elsevier Ltd. All rights reserved.

Analysis of blood flow with nanoparticles induced by uniform magnetic field through a circular cylinder with fractional Caputo derivatives

Science.gov (United States)

Abdullah, M.; Butt, Asma Rashid; Raza, Nauman; Alshomrani, Ali Saleh; Alzahrani, A. K.

2018-01-01

The magneto hydrodynamic blood flow in the presence of magnetic particles through a circular cylinder is investigated. To calculate the impact of externally applied uniform magnetic field, the blood is electrically charged. Initially the fluid and circular cylinder is at rest but at time t =0+ , the cylinder starts to oscillate along its axis with velocity fsin (Ωt) . To obtain the mathematical model of blood flow with fractional derivatives Caputo fractional operator is employed. The solutions for the velocities of blood and magnetic particles are procured semi analytically by using Laplace transformation method. The inverse Laplace transform has been calculated numerically by using MATHCAD computer software. The obtained results of velocities are presented in Laplace domain in terms of modified Bessel function I0 (·) . The obtained results satisfied all imposed initial and boundary conditions. The hybrid technique that is employed here less computational effort and time cost as compared to other techniques used in literature. As the limiting cases of our results the solutions of the flow model with ordinary derivatives has been procured. Finally, the impact of Reynolds number Re, fractional parameter α and Hartmann number Ha is analyzed and portrayed through graphs. It is worthy to pointing out that fractional derivatives brings remarkable differences as compared to ordinary derivatives. It also has been observed that velocity of blood and magnetic particles is weaker under the effect of transverse magnetic field.

In-Situ Characterization of Tissue Blood Flow, Blood Content, and Water State Using New Techniques in Magnetic Resonance Imaging.

Science.gov (United States)

Conturo, Thomas Edward

Tissue blood flow, blood content, and water state have been characterized in-situ with new nuclear magnetic resonance imaging techniques. The sensitivities of standard techniques to the physiologic tissue parameters spin density (N_{rm r}) and relaxation times (T_1 and T_2 ) are mathematically defined. A new driven inversion method is developed so that tissue T_1 and T_2 changes produce cooperative intensity changes, yielding high contrast, high signal to noise, and sensitivity to a wider range of tissue parameters. The actual tissue parameters were imaged by automated collection of multiple-echo data having multiple T _1 dependence. Data are simultaneously fit by three-parameters to a closed-form expression, producing lower inter-parameter correlation and parameter noise than in separate T_1 or T_2 methods or pre-averaged methods. Accurate parameters are obtained at different field strengths. Parametric images of pathology demonstrate high sensitivity to tissue heterogeneity, and water content is determined in many tissues. Erythrocytes were paramagnetically labeled to study blood content and relaxation mechanisms. Liver and spleen relaxation were enhanced following 10% exchange of animal blood volumes. Rapid water exchange between intracellular and extracellular compartments was validated. Erythrocytes occupied 12.5% of renal cortex volume, and blood content was uniform in the liver, spleen and kidney. The magnitude and direction of flow velocity was then imaged. To eliminate directional artifacts, a bipolar gradient technique sensitized to flow in different directions was developed. Phase angle was reconstructed instead of intensity since the former has a 2pi -fold higher dynamic range. Images of flow through curves demonstrated secondary flow with a centrifugally-biased laminar profile and stationary velocity peaks along the curvature. Portal vein flow velocities were diminished or reversed in cirrhosis. Image artifacts have been characterized and removed. The

Optical tweezers for measuring the interaction of the two single red blood cells in flow condition

Science.gov (United States)

Lee, Kisung; Muravyov, Alexei; Semenov, Alexei; Wagner, Christian; Priezzhev, Alexander

2017-03-01

Aggregation of red blood cells (RBCs) is an intrinsic property of blood, which has direct effect on the blood viscosity and therefore affects overall the blood circulation throughout the body. It is attracting interest for the research in both fundamental science and clinical application. Despite of the intensive research, the aggregation mechanism is remaining not fully clear. Recent advances in methods allowed measuring the interaction between single RBCs in a well-defined configuration leading the better understanding of the mechanism of the process. However the most of the studies were made on the static cells. Thus, the measurements in flow mimicking conditions are missing. In this work, we aim to study the interaction of two RBCs in the flow conditions. We demonstrate the characterization of the cells interaction strength (or flow tolerance) by measuring the flow velocity to be applied to separate two aggregated cells trapped by double channel optical tweezers in a desired configuration. The age-separated cells were used for this study. The obtained values for the minimum flow velocities needed to separate the two cells were found to be 78.9 +/- 6.1 μm/s and 110 +/- 13 μm/s for old and young cells respectively. The data obtained is in agreement with the observations reported by other authors. The significance of our results is in ability for obtaining a comprehensible and absolute physical value characterizing the cells interaction in flow conditions (not like the Aggregation Index measured in whole blood suspensions by other techniques, which is some abstract parameter)

Effects of anesthesia on the cerebral capillary blood flow in young and old mice

Science.gov (United States)

Moeini, Mohammad; Tabatabaei, Maryam S.; Bélanger, Samuel; Avti, Pramod; Castonguay, Alexandre; Pouliot, Philippe; Lesage, Frédéric

2015-03-01

Despite recent findings on the possible role of age-related cerebral microvasculature changes in cognition decline, previous studies of capillary blood flow in aging (using animal models) are scarce and limited to anesthetized conditions. Since anesthesia can have different effects in young and old animals, it may introduce a confounding effect in aging studies. The present study aimed to eliminate the potential confound introduced by anesthesia by measuring capillary blood flow parameters in both awake conditions and under isoflurane anesthesia. We used 2-photon laser scanning fluorescence microscopy to measure capillary diameter, red blood cell velocity and flux, hematocrit and capillary volumetric flow in individual capillaries in the barrel cortex of 6- and 24-month old C57Bl/6 mice. It was observed that microvascular properties are significantly affected by anesthesia leading to different trends in capillary blood flow parameters with aging when measured under awake or anesthetized conditions. The findings in this study suggest taking extra care in interpreting aging studies from anesthetized animals.

Estimation of the blood velocity spectrum using a recursive lattice filter

DEFF Research Database (Denmark)

Jensen, Jørgen Arendt; Buelund, Claus; Jørgensen, Allan

1996-01-01

acquired for showing the blood velocity distribution are inherently non-stationary, due to the pulsatility of the flow. All current signal processing schemes assume that the signal is stationary within the window of analysis, although this is an approximation. In this paper a recursive least......-stationarity are incorporated through an exponential decay factor, that sets the exponential horizon of the filter. A factor close to 1 gives a long horizon with low variance estimates, but can not track a highly non-stationary flow. Setting the factor is therefore a compromise between estimate variance and the filter...... with the actual distributions that always will be smooth. Setting the exponential decay factor to 0.99 gives satisfactory results for in-vivo data from the carotid artery. The filter can easily be implemented using a standard fixed-point signal processing chip for real-time processing...

Development of an optical fiber flow velocity sensor.

Science.gov (United States)

Harada, Toshio; Kamoto, Kenji; Abe, Kyutaro; Izumo, Masaki

2009-01-01

A new optical fiber flow velocity sensor was developed by using an optical fiber information network system in sewer drainage pipes. The optical fiber flow velocity sensor operates without electric power, and the signals from the sensor can be transmitted over a long distance through the telecommunication system in the optical fiber network. Field tests were conducted to check the performance of the sensor in conduits in the pumping station and sewage pond managed by the Tokyo Metropolitan Government. Test results confirmed that the velocity sensor can be used for more than six months without any trouble even in sewer drainage pipes.

Portal venous blood flow while breath-holding after inspiration or expiration and during normal respiration in controls and cirrhotics

International Nuclear Information System (INIS)

Sugano, Shigeo; Yamamoto, Kunihiro; Sasao, Ken-ichiro; Watanabe, Manabu

1999-01-01

In this study, we used magnetic resonance (MR) imaging to measure portal blood flow in 12 healthy controls and 17 cirrhotics while they were breath-holding after inspiration and after expiration. We then compared the results with measurements made during normal respiration in the healthy controls and cirrhotics. Blood flow in the main portal vein under basal fasting conditions was quantitated using the cine phase-contrast MR velocity mapping method. Three measurements were made on one occasion, as follows: throughout the cardiac cycle during normal respiration, with the subject breath-holding after maximal inspiration, and with the subject breath-holding after maximal expiration. During normal respiration, portal blood flow was 1.3±0.2 l/min in controls vs 1.0±0.1 l/min in cirrhotics (P<0.0001); while subjects were breath-holding after inspiration, portal blood flow was 1.0±0.2 l/min in controls vs 0.9±0.1 l/min in cirrhotics; and while subjects were breath-holding after expiration, portal blood flow was 1.5±0.2 l/min in controls vs 1.1±0.2 l/min in cirrhotics (P<0.0001). The differences were primarily due to changes in flow velocity. When the magnitude of these hemodynamic changes in the three respiratory conditions was compared in controls and cirrhotics, analysis of variance (ANOVA) showed a significant difference (P<0.0001). In controls, portal blood flow decreased during maximal inspiration relative to flow during normal respiration (-24.6±8.3%). Changes in portal blood flow in controls were greater than in cirrhotics (-13.5±4.5%) (P<0.0001); however, the difference in blood flow increase associated with maximal expiration between the two groups (+11.8±9.4% vs +5.9±11.5%) was not significant. We found that the respiration-induced hemodynamic variation in portal blood flow was less in cirrhotics than in the healthy controls. Portal blood flow measurements made during normal respiration using MR imaging closely reflect nearly physiologic conditions

Portal venous blood flow while breath-holding after inspiration or expiration and during normal respiration in controls and cirrhotics

Energy Technology Data Exchange (ETDEWEB)

Sugano, Shigeo; Yamamoto, Kunihiro; Sasao, Ken-ichiro; Watanabe, Manabu [Saiseikai Wakakusa Hospital, Yakohama (Japan)

1999-07-01

In this study, we used magnetic resonance (MR) imaging to measure portal blood flow in 12 healthy controls and 17 cirrhotics while they were breath-holding after inspiration and after expiration. We then compared the results with measurements made during normal respiration in the healthy controls and cirrhotics. Blood flow in the main portal vein under basal fasting conditions was quantitated using the cine phase-contrast MR velocity mapping method. Three measurements were made on one occasion, as follows: throughout the cardiac cycle during normal respiration, with the subject breath-holding after maximal inspiration, and with the subject breath-holding after maximal expiration. During normal respiration, portal blood flow was 1.3{+-}0.2 l/min in controls vs 1.0{+-}0.1 l/min in cirrhotics (P<0.0001); while subjects were breath-holding after inspiration, portal blood flow was 1.0{+-}0.2 l/min in controls vs 0.9{+-}0.1 l/min in cirrhotics; and while subjects were breath-holding after expiration, portal blood flow was 1.5{+-}0.2 l/min in controls vs 1.1{+-}0.2 l/min in cirrhotics (P<0.0001). The differences were primarily due to changes in flow velocity. When the magnitude of these hemodynamic changes in the three respiratory conditions was compared in controls and cirrhotics, analysis of variance (ANOVA) showed a significant difference (P<0.0001). In controls, portal blood flow decreased during maximal inspiration relative to flow during normal respiration (-24.6{+-}8.3%). Changes in portal blood flow in controls were greater than in cirrhotics (-13.5{+-}4.5%) (P<0.0001); however, the difference in blood flow increase associated with maximal expiration between the two groups (+11.8{+-}9.4% vs +5.9{+-}11.5%) was not significant. We found that the respiration-induced hemodynamic variation in portal blood flow was less in cirrhotics than in the healthy controls. Portal blood flow measurements made during normal respiration using MR imaging closely reflect nearly

Computer Simulations of Coronary Blood Flow Through a Constriction

Science.gov (United States)

2014-03-01

for clinical translation. Journal of the American College of Cardiology . 59(15): 1337–1349. Leimgruber, P., Roubin, G., Hollman, J., Cotsonis, G...the artery and increase blood flow. Generally a stent, or a mesh wire tube, is permanently inserted in order to scaffold open the artery wall...central regions of the channel, so the magnitude of the velocity has to be higher in the open area of the channel, overshooting the experimental results

Prognostic value of coronary blood flow velocity and myocardial perfusion in intermediate coronary Narrowings and multivessel disease

NARCIS (Netherlands)

Chamuleau, SAJ; Tio, RA; de Cock, CC; de Muinck, ED; Pijls, NHJ; van Eck-Smit, BLF; Koch, KT; Meuwissen, M; Dijkgraaf, MGW; Verberne, HJ; van Liebergen, RAM; Laarman, GJ; Tijssen, JGP; Piek, JJ; de Jong, A.

2002-01-01

OBJECTIVES This study aimed to investigate the roles of intracoronary derived coronary flow velocity reserve (CFVR) and myocardial perfusion scintigraphy (single photon emission computed tomography, or SPECT) for management of an intermediate lesion in patient, with multivessel coronary artery

Velocity measurement accuracy in optical microhemodynamics: experiment and simulation

International Nuclear Information System (INIS)

Chayer, Boris; Cloutier, Guy; L Pitts, Katie; Fenech, Marianne

2012-01-01

Micro particle image velocimetry (µPIV) is a common method to assess flow behavior in blood microvessels in vitro as well as in vivo. The use of red blood cells (RBCs) as tracer particles, as generally considered in vivo, creates a large depth of correlation (DOC), even as large as the vessel itself, which decreases the accuracy of the method. The limitations of µPIV for blood flow measurements based on RBC tracking still have to be evaluated. In this study, in vitro and in silico models were used to understand the effect of the DOC on blood flow measurements using µPIV RBC tracer particles. We therefore employed a µPIV technique to assess blood flow in a 15 µm radius glass tube with a high-speed CMOS camera. The tube was perfused with a sample of 40% hematocrit blood. The flow measured by a cross-correlating speckle tracking technique was compared to the flow rate of the pump. In addition, a three-dimensional mechanical RBC-flow model was used to simulate optical moving speckle at 20% and 40% hematocrits, in 15 and 20 µm radius circular tubes, at different focus planes, flow rates and for various velocity profile shapes. The velocity profiles extracted from the simulated pictures were compared with good agreement with the corresponding velocity profiles implemented in the mechanical model. The flow rates from both the in vitro flow phantom and the mathematical model were accurately measured with less than 10% errors. Simulation results demonstrated that the hematocrit (paired t tests, p = 0.5) and the tube radius (p = 0.1) do not influence the precision of the measured flow rate, whereas the shape of the velocity profile (p < 0.001) and the location of the focus plane (p < 0.001) do, as indicated by measured errors ranging from 3% to 97%. In conclusion, the use of RBCs as tracer particles makes a large DOC and affects the image processing required to estimate the flow velocities. We found that the current µPIV method is acceptable to estimate the flow rate

Determination of Testicular Blood Flow in Camelids Using Vascular Casting and Color Pulsed-Wave Doppler Ultrasonography

OpenAIRE

Kutzler, Michelle; Tyson, Reid; Grimes, Monica; Timm, Karen

2011-01-01

We describe the vasculature of the camelid testis using plastic casting. We also use color pulsed-wave Doppler ultrasonography to measure testicular blood flow and compare the differences between testicular blood flow in fertile and infertile camelids. The testicular artery originates from the ventral surface of the aorta, gives rise to an epididymal branch, and becomes very tortuous as it approaches the testis. Within the supratesticular arteries, peak systolic velocity (PSV) was higher in f...

Is there any influence of breastfeeding on the cerebral blood flow? A review of 256 healthy newborns

Directory of Open Access Journals (Sweden)

Alexandra Maria Vieira Monteiro

2012-10-01

Full Text Available OBJECTIVE: To investigate whether breastfeeding influence the cerebral blood-flow velocity. MATERIALS AND METHODS: The present study included 256 healthy term neonates, all of them with appropriate weight for gestational age, 50.8% being female. Pulsatility index, resistance index and mean velocity were measured during breastfeeding or resting in the anterior cerebral artery, in the left middle cerebral artery, and in the right middle cerebral artery of the neonates between their first 10 and 48 hours of life. The data were analyzed by means of a paired t-test, Brieger's f-test for analysis of variance and linear regression, with p < 0.01 being accepted as statistically significant. RESULTS: Mean resistance index decreased as the mean velocity increased significantly during breastfeeding. Pulsatility index values decreased as much as the resistance index, but in the right middle cerebral artery it was not statistically significant. CONCLUSION: Breastfeeding influences the cerebral blood flow velocities.

A multichannel bioimpedance monitor for full-body blood flow monitoring

Czech Academy of Sciences Publication Activity Database

Vondra, Vlastimil; Jurák, Pavel; Viščor, Ivo; Halámek, Josef; Leinveber, P.; Matějková, M.; Soukup, L.

2016-01-01

Roč. 61, č. 1 (2016), s. 107-118 ISSN 0013-5585 R&D Projects: GA MŠk(CZ) LO1212; GA MŠk ED0017/01/01; GA ČR GAP102/12/2034 Institutional support: RVO:68081731 Keywords : bioimpedance * blood flow * cardiac output * multichannel measurement * non- invasive measurements * pulse wave velocity Subject RIV: FS - Medical Facilities ; Equipment Impact factor: 0.915, year: 2016

Role of blood flow and blood flow modifiers in clinical hyperthermia therapy

International Nuclear Information System (INIS)

Olch, A.J.

1986-01-01

A quantitative assessment of the effect of localized magnetic-loop hyperthermia on blood flow was performed on 12 patients (19 tumor studies) using the Xenon-133 clearance method. After it was discovered that blood flow in most of the tumors increased in response to needle injection, a physiologically based, one compartment model was developed that included both a hyperemic (transient) and a steady state component. In the tumors of six patients, increases in blood flow induced by heat were also observed. The same model was used to describe the measured clearance data for both types of hyperemic response. The ability of tumor vessels to respond dynamically to stress and the degree of response may be predictive of tumor heating efficiency and subsequent therapeutic response. Many tumors treated by hyperthermia, therefore, do not reach therapeutic temperatures (42 0 C). One explanation for this may be that some tumors react to thermal stress in a manner similar to normal tissues; i.e., they increase blood flow during hyperthermia in order to dissipate heat. Higher temperatures might be achieved in these heat-resistant tumors by administering vasoconstrictive agents in an effort to reduce blood flow. In the second part of this research study, the extent to which pharmacologic inhibition of local blood flow might allow higher temperatures to develop in normal muscles exposed to localized radiofrequency hyperthermia was determined. It was found that the local muscle temperature rise could be increased by at least 90% in dogs and rabbits with the use of a local vasoconstrictive drug

Real-time three-dimensional color Doppler echocardiography for characterizing the spatial velocity distribution and quantifying the peak flow rate in the left ventricular outflow tract

Science.gov (United States)

Tsujino, H.; Jones, M.; Shiota, T.; Qin, J. X.; Greenberg, N. L.; Cardon, L. A.; Morehead, A. J.; Zetts, A. D.; Travaglini, A.; Bauer, F.;

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles.

Science.gov (United States)

Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

2015-03-06

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases.

Measurement of real pulsatile blood flow using X-ray PIV technique with CO2 microbubbles

Science.gov (United States)

Park, Hanwook; Yeom, Eunseop; Seo, Seung-Jun; Lim, Jae-Hong; Lee, Sang-Joon

2015-01-01

Synchrotron X-ray imaging technique has been used to investigate biofluid flows in a non-destructive manner. This study aims to investigate the feasibility of the X-ray PIV technique with CO2 microbubbles as flow tracer for measurement of pulsatile blood flows under in vivo conditions. The traceability of CO2 microbubbles in a pulsatile flow was demonstrated through in vitro experiment. A rat extracorporeal bypass loop was used by connecting a tube between the abdominal aorta and jugular vein of a rat to obtain hemodynamic information of actual pulsatile blood flows without changing the hemorheological properties. The decrease in image contrast of the surrounding tissue was also investigated for in vivo applications of the proposed technique. This technique could be used to accurately measure whole velocity field information of real pulsatile blood flows and has strong potential for hemodynamic diagnosis of cardiovascular diseases. PMID:25744850

Effect of flow velocity on erosion-corrosion behaviour of QSn6 alloy

Science.gov (United States)

Huang, Weijiu; Zhou, Yongtao; Wang, Zhenguo; Li, Zhijun; Zheng, Ziqing

2018-05-01

The erosion-corrosion behaviour of QSn6 alloy used as propellers in marine environment was evaluated by erosion-corrosion experiments with/without cathodic protection, electrochemical tests and scanning electron microscope (SEM) observations. The analysis was focused on the effect of flow velocity. The dynamic polarization curves showed that the corrosion rate of the QSn6 alloy increased as the flow velocity increased, due to the protective surface film removal at higher velocities. The lowest corrosion current densities of 1.26 × 10‑4 A cm‑2 was obtained at the flow velocity of 7 m s‑1. Because of the higher particle kinetic energies at higher flow velocity, the mass loss rate of the QSn6 alloy increased as the flow velocity increased. The mass loss rate with cathodic protection was lower than that without cathodic protection under the same conditions. Also, the lowest mass loss rate of 0.7 g m‑2 · h‑1 was acquired at the flow velocity of 7 m s‑1 with cathodic protection. However, the increase rate of corrosion rate and mass loss were decreased with increasing the flow velocity. Through observation the SEM morphologies of the worn surfaces, the main wear mechanism was ploughing with/without cathodic protection. The removal rates of the QSn6 alloy increased as the flow velocity increased in both pure erosion and erosion-corrosion, whereas the erosion and corrosion intensified each other. At the flow velocity of 7 m s‑1, the synergy rate (ΔW) exceeded by 5 times the erosion rate (Wwear). Through establishment and observation the erosion-corrosion mechanism map, the erosion-corrosion was the dominant regime in the study due to the contribution of erosion on the mass loss rate exceeded the corrosion contribution. The QSn6 alloy with cathodic protection is feasible as propellers, there are higher security at lower flow velocity, such as the flow velocity of 7 m s‑1 in the paper.

Change in coronary blood flow after percutaneous coronary intervention in relation to baseline lesion physiology: results of the JUSTIFY-PCI study.

Science.gov (United States)

Nijjer, Sukhjinder S; Petraco, Ricardo; van de Hoef, Tim P; Sen, Sayan; van Lavieren, Martijn A; Foale, Rodney A; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S; Mikhail, Ghada W; Hughes, Alun D; Mayet, Jamil; Francis, Darrel P; Di Mario, Carlo; Escaned, Javier; Piek, Jan J; Davies, Justin E

2015-06-01

Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (PPCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; PPCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. © 2015 American Heart Association, Inc.

Change in Coronary Blood Flow After Percutaneous Coronary Intervention in Relation to Baseline Lesion Physiology Results of the JUSTIFY-PCI Study

Science.gov (United States)

Nijjer, Sukhjinder S.; Petraco, Ricardo; van de Hoef, Tim P.; Sen, Sayan; van Lavieren, Martijn A.; Foale, Rodney A.; Meuwissen, Martijn; Broyd, Christopher; Echavarria-Pinto, Mauro; Al-Lamee, Rasha; Foin, Nicolas; Sethi, Amarjit; Malik, Iqbal S.; Mikhail, Ghada W.; Hughes, Alun D.; Mayet, Jamil; Francis, Darrel P.; Di Mario, Carlo; Escaned, Javier; Piek, Jan J.; Davies, Justin E.

2016-01-01

Background Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters. Methods and Results Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (PPCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; PPCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI. PMID:26025217

Assessment of cerebral blood flow following administration of surfactant in premature newborns

International Nuclear Information System (INIS)

Calvo, M.J.; Matias, M.; Serrano, I.; Lubian, S.; Vallejos, E.; Canovas, S.

1998-01-01

To assess, by Doppler ultrasound, the possible changes in the patterns of cerebral blood flow after administration of a surfactant. Fifteen newborns with a period of gestation of less than 30 weeks received low-dose surfactant, as prophylaxis in six cases and as treatment in nine, administered slowly via endo tracheal tube with indwelling catheter. The Doppler recordings in anterior cerebral artery (ACA) and descending aorta (DAo) were assessed prior to administration of the surfactant, immediately afterwards and 15 minutes, 30 minutes, one hour and 24 hours later. The findings were correlated with simultaneous oxygen saturation and arterial blood pressure readings. There was little change in the systolic and diastolic velocities, although both tended to rise progressively throughout the 24 hours of the study period. The mean initial resistance index (R I) in ACA was elevated (0.84±0.11), tending in every case to diminish by 24 hours post administration (0.78±0.11) to levels that are considered normal in the newborn. Lower velocities (p<0.001 and higher RI(p<0.001) were recorded when reversed diastolic velocity was observed in the DAo in relation to patent ducts arteriosus. There were no significant changes in the oxygen saturation or mean arterial pressure. One infant presented a grade I germinal matrix hemorrhage. The findings suggest that this treatment does not produce significant changes in the cerebral blood flow under the circumstances described here. (Author) 40 refs

Experimental study on liquid velocity in upward and downward two-phase flows

International Nuclear Information System (INIS)

Sun, X.; Paranjape, S.; Kim, S.; Ozar, B.; Ishii, M.

2003-01-01

Local characteristics of the liquid phase in upward and downward air-water two-phase flows were experimentally investigated in a 50.8-mm inner-diameter round pipe. An integral Laser Doppler Anemometry (LDA) system was used to measure the axial liquid velocity and its fluctuations. No effect of the flow direction on the liquid velocity radial profile was observed in single-phase liquid benchmark experiments. Local multi-sensor conductivity probes were used to measure the radial profiles of the bubble velocity and the void fraction. The measurement results in the upward and downward two-phase flows are compared and discussed. The results in the downward flow demonstrated that the presence of the bubbles tended to flatten the liquid velocity radial profile, and the maximum liquid velocity could occur off the pipe centerline, in particular at relatively low flow rates. However, the maximum liquid velocity always occurred at the pipe center in the upward flow. Also, noticeable turbulence enhancement due to the bubbles in the two-phase flows was observed in the current experimental flow conditions. Furthermore, the distribution parameter and the void weighted area-averaged drift velocity were obtained based on the definitions

Aortic blood flow subtraction: an alternative method for measuring total renal blood flow in conscious dogs

DEFF Research Database (Denmark)

Sandgaard, N C F; Andersen, J L; Holstein-Rathlou, N-H

2002-01-01

We have measured total renal blood flow (TRBF) as the difference between signals from ultrasound flow probes implanted around the aorta above and below the renal arteries. The repeatability of the method was investigated by repeated, continuous infusions of angiotensin II and endothelin-1 seven...... arterial blood pressure by 49% and decreased TRBF by 12%, providing an increase in renal vascular resistance of 69%. Dynamic analysis showed autoregulation of renal blood flow in the frequency range ... of TRBF by aortic blood flow subtraction is a practical and reliable method that allows direct comparison of excretory function and renal blood flow from two kidneys. The method also allows direct comparison between TRBF and flow in the caudal aorta....

The Physics of Coronary Blood Flow

CERN Document Server

Zamir, M

2005-01-01

Coronary blood flow is blood flow to the heart for its own metabolic needs. In the most common form of heart disease there is a disruption in this flow because of obstructive disease in the vessels that carry the flow. The subject of coronary blood flow is therefore associated mostly with the pathophysiology of this disease, rarely with dynamics or physics. Yet, the system responsible for coronary blood flow, namely the "coronary circulation," is a highly sophisticated dynamical system in which the dynamics and physics of the flow are as important as the integrity of the conducting vessels. While an obstruction in the conducting vessels is a fairly obvious and clearly visible cause of disruption in coronary blood flow, any discord in the complex dynamics of the system can cause an equally grave, though less conspicuous, disruption in the flow. This book is devoted specifically to the dynamics and physics of coronary blood flow. While relevance to the clinical and pathophysiological issues is clearly maintaine...

Blood flow measurement of transverse sinuses by using MR: a phantom study of its influence factors

International Nuclear Information System (INIS)

Gao Gejun; Feng Xiaoyuan; Li Yuan; Geng Daoying; Yao Zhengyu

2003-01-01

Objective: (1) To determine the relationship between the MR signal intensity and the actual flow velocity under steady flow condition. (2) to analyze the influence produced by the angle (θ) between the flow direction and the velocity-encoded gradient direction, and flip angle as well as section thickness on the velocity measurement under oblique flow condition. (3) to develop a suitable protocol for using this method to measure volumetric flow rate in the transverse sinus system. Methods: Flow phantom, which simulated blood-flow conditions in the transverse sinus system, consisted of a fluid-filled cylinder and a bent tube with a 3.4 mm internal diameter. A 1.5 T superconductive MR imager and VIGRE sequence were used for these studies. A suitable protocol was based on consideration of the effects of (1) the accuracy of velocity and transverse area measurement of flow, and (2) signal-to-noise ratio (SNR). Results: (1) Signal intensity (y) determined by MR and the actual flow velocity (x) showed straight-line correlation, y=68.914x + 357.206, R 2 =0.998. (2) As the angle (θ) increased, the transverse area of the signal determined by MR also increased, but the value of flow velocity decreased. (3) As the flip angle increased, the SNR varied from 5.7 to 11.2. The maximum SNR was obtained with 30 degree flip angle. (4) As the section thickness increased, the SNR and the transverse area of the signal determined by MR slightly increased. Conclusions: Phase-contrast MR imaging is a practical method for measuring volumetric flow rates. The angle (θ influenced the accuracy of flow velocity and the measurement of transverse area of flow whereas the flip angle and the section thickness substantially influenced the signal-to-noise ratio and the transverse area of flow

Effects of fenoldopam on renal blood flow in hypertensive chronic kidney disease.

Science.gov (United States)

Rovella, Valentina; Ferrannini, Michele; Tesauro, Manfredi; Marrone, Giulia; Busca, Andrea; Sorge, Roberto; Manca di Villahermosa, Simone; Casasco, Maurizio; Di Daniele, Nicola; Noce, Annalisa

2018-05-15

The synthetic drug fenoldopam mesylate (FM) may have a renoprotective role, and a "renal dose" of 0.1 µg/kg/min intravenous (IV) infusion of FM has been reported as able to increase renal blood flow without affecting systemic blood pressure. But conclusive data are still lacking. We aimed to investigate by color-Doppler ultrasonography the effects of IV administration of FM at this dosage in hypertensive chronic kidney disease (CKD) patients, and verify whether it may induce any systemic hemodynamic alteration. In 60 hypertensive CKD patients, we measured by duplex Doppler ultrasonography, at baseline and during infusion of 0.1 µg/kg/min of FM, the systolic and diastolic flow velocity (sampled at the renal hilum, intermediate section and origin of both renal arteries) and the intra-parenchymal renal resistive index (RRI) sampled on interlobular arteries of both kidneys. Patients were divided into four subgroups (I-IV) according to classification of National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF-DOQI). Infusion of 0.1 µg/kg/min FM significantly decreased the RRI (0.73 ± 0.05 vs. 0.65 ± 0.06; p flow velocities in all renal artery tracts examined. No single episode of systemic hypotension was observed. Very low-dose FM may significantly increase renal blood flow and exert a renal protective effect in hypertensive CKD patients. Infusion of FM at such low dosage appears also to be quite safe, even in CKD and hypertensive patients.

A flow meter for ultrasonically measuring the flow velocity of fluids

DEFF Research Database (Denmark)

2015-01-01

The invention regards a flow meter for ultrasonically measuring the flow velocity of fluids comprising a duct having a flow channel with an internal cross section comprising variation configured to generate at least one acoustic resonance within the flow channel for a specific ultrasonic frequency......, and at least two transducers for generating and sensing ultrasonic pulses, configured to transmit ultrasonic pulses at least at said specific ultrasonic frequency into the flow channel such that the ultrasonic pulses propagate through a fluid flowing in the flow channel, wherein the flow meter is configured...

Velocity Profile measurements in two-phase flow using multi-wave sensors

Science.gov (United States)

Biddinika, M. K.; Ito, D.; Takahashi, H.; Kikura, H.; Aritomi, M.

2009-02-01

Two-phase flow has been recognized as one of the most important phenomena in fluid dynamics. In addition, gas-liquid two-phase flow appears in various industrial fields such as chemical industries and power generations. In order to clarify the flow structure, some flow parameters have been measured by using many effective measurement techniques. The velocity profile as one of the important flow parameter, has been measured by using ultrasonic velocity profile (UVP) technique. This technique can measure velocity distributions along a measuring line, which is a beam formed by pulse ultrasounds. Furthermore, a multi-wave sensor can measure the velocity profiles of both gas and liquid phase using UVP method. In this study, two types of multi-wave sensors are used. A sensor has cylindrical shape, and another one has square shape. The piezoelectric elements of each sensor have basic frequencies of 8 MHz for liquid phase and 2 MHz for gas phase, separately. The velocity profiles of air-water bubbly flow in a vertical rectangular channel were measured by using these multi-wave sensors, and the validation of the measuring accuracy was performed by the comparison between the velocity profiles measured by two multi-wave sensors.

Velocity Profile measurements in two-phase flow using multi-wave sensors

International Nuclear Information System (INIS)

Biddinika, M K; Ito, D; Takahashi, H; Kikura, H; Aritomi, M

2009-01-01

Two-phase flow has been recognized as one of the most important phenomena in fluid dynamics. In addition, gas-liquid two-phase flow appears in various industrial fields such as chemical industries and power generations. In order to clarify the flow structure, some flow parameters have been measured by using many effective measurement techniques. The velocity profile as one of the important flow parameter, has been measured by using ultrasonic velocity profile (UVP) technique. This technique can measure velocity distributions along a measuring line, which is a beam formed by pulse ultrasounds. Furthermore, a multi-wave sensor can measure the velocity profiles of both gas and liquid phase using UVP method. In this study, two types of multi-wave sensors are used. A sensor has cylindrical shape, and another one has square shape. The piezoelectric elements of each sensor have basic frequencies of 8 MHz for liquid phase and 2 MHz for gas phase, separately. The velocity profiles of air-water bubbly flow in a vertical rectangular channel were measured by using these multi-wave sensors, and the validation of the measuring accuracy was performed by the comparison between the velocity profiles measured by two multi-wave sensors.

Coded excitation and sub-band processing for blood velocity estmation in medical ultrasound

DEFF Research Database (Denmark)

Gran, Fredrik; Udesen, Jesper; Jensen, Jørgen Arendt

2007-01-01

This paper investigates the use of broadband coded excitation and subband processing for blood velocity estimation in medical ultrasound. In conventional blood velocity estimation a long (narrow-band) pulse is emitted and the blood velocity is estimated using an auto-correlation based approach....... However, the axial resolution of the narrow-band pulse is too poor for brightness-mode (B-mode) imaging. Therefore, a separate transmission sequence is used for updating the B-mode image, which lowers the overall frame-rate of the system. By using broad-band excitation signals, the backscattered received...... signal can be divided into a number of narrow frequency bands. The blood velocity can be estimated in each of the bands and the velocity estimates can be averaged to form an improved estimate. Furthermore, since the excitation signal is broadband, no secondary B-mode sequence is required, and the frame...

Cerebral blood flow response to flavanol-rich cocoa in healthy elderly humans

Directory of Open Access Journals (Sweden)

Farzaneh A Sorond

2008-04-01

Full Text Available Farzaneh A Sorond1,2, Lewis A Lipsitz2,4, Norman K Hollenberg3,5, Naomi DL Fisher31Department of Neurology, Stroke Division; 2Institute for Aging Research, Hebrew SeniorLife, Boston, MA; 3Department of Medicine, Endocrine-Hypertension Division; 4Department of Medicine, Gerontology, Beth Israel Deaconess Medical Center, Boston, MA, USA; 5Department of Radiology, Brigham and Women’s Hospital, Boston, MABackground and Purpose: Cerebral ischemia is a common, morbid condition accompanied by cognitive decline. Recent reports on the vascular health benefits of flavanol-containing foods signify a promising approach to the treatment of cerebral ischemia. Our study was designed to investigate the effects of flavanol-rich cocoa (FRC consumption on cerebral blood flow in older healthy volunteers.Methods: We used transcranial Doppler (TCD ultrasound to measure mean blood flow velocity (MFV in the middle cerebral artery (MCA in thirty-four healthy elderly volunteers (72 ± 6 years in response to the regular intake of FRC or flavanol-poor cocoa (FPC.Results: In response to two weeks of FRC intake, MFV increased by 8% ± 4% at one week (p = 0.01 and 10% ± 4% (p = 0.04 at two weeks. In response to one week of cocoa, significantly more subjects in the FRC as compared with the FPC group had an increase in their MFV (p < 0.05.Conclusions: In summary, we show that dietary intake of FRC is associated with a significant increase in cerebral blood flow velocity in the MCA as measured by TCD. Our data suggest a promising role for regular cocoa flavanol’s consumption in the treatment of cerebrovascular ischemic syndromes, including dementias and stroke.Keywords: cerebral blood flow, flavanol, cocoa, transcranial Doppler ultrasound

Changes in inferior vena cava blood flow velocity and diameter during breathing movements in the human fetus

NARCIS (Netherlands)

T. Huisman (T.); S. van den Eijnde (Stefan); P.A. Stewart (Patricia); J.W. Wladimiroff (Juriy)

1993-01-01

textabstractBreathing movements in the human fetus cause distinct changes in Doppler flow velocity measurements at arterial, venous and cardiac levels. In adults, breathing movements result in a momentary inspiratory collapse of the inferior vena cava vessel wall. The study objective was to quantify

Intermittent Lagrangian velocities and accelerations in three-dimensional porous medium flow.

Science.gov (United States)

Holzner, M; Morales, V L; Willmann, M; Dentz, M

2015-07-01

Intermittency of Lagrangian velocity and acceleration is a key to understanding transport in complex systems ranging from fluid turbulence to flow in porous media. High-resolution optical particle tracking in a three-dimensional (3D) porous medium provides detailed 3D information on Lagrangian velocities and accelerations. We find sharp transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity, superlinear evolution of particle dispersion, and double-peak behavior in the propagators. The velocity distribution is quantified in terms of pore geometry and flow connectivity, which forms the basis for a continuous-time random-walk model that sheds light on the observed Lagrangian flow and transport behaviors.

Influence of model boundary conditions on blood flow patterns in a patient specific stenotic right coronary artery.

Science.gov (United States)

Liu, Biyue; Zheng, Jie; Bach, Richard; Tang, Dalin

2015-01-01

In literature, the effect of the inflow boundary condition was investigated by examining the impact of the waveform and the shape of the spatial profile of the inlet velocity on the cardiac hemodynamics. However, not much work has been reported on comparing the effect of the different combinations of the inlet/outlet boundary conditions on the quantification of the pressure field and flow distribution patterns in stenotic right coronary arteries. Non-Newtonian models were used to simulate blood flow in a patient-specific stenotic right coronary artery and investigate the influence of different boundary conditions on the phasic variation and the spatial distribution patterns of blood flow. The 3D geometry of a diseased artery segment was reconstructed from a series of IVUS slices. Five different combinations of the inlet and the outlet boundary conditions were tested and compared. The temporal distribution patterns and the magnitudes of the velocity, the wall shear stress (WSS), the pressure, the pressure drop (PD), and the spatial gradient of wall pressure (WPG) were different when boundary conditions were imposed using different pressure/velocity combinations at inlet/outlet. The maximum velocity magnitude in a cardiac cycle at the center of the inlet from models with imposed inlet pressure conditions was about 29% lower than that from models using fully developed inlet velocity data. Due to the fact that models with imposed pressure conditions led to blunt velocity profile, the maximum wall shear stress at inlet in a cardiac cycle from models with imposed inlet pressure conditions was about 29% higher than that from models with imposed inlet velocity boundary conditions. When the inlet boundary was imposed by a velocity waveform, the models with different outlet boundary conditions resulted in different temporal distribution patterns and magnitudes of the phasic variation of pressure. On the other hand, the type of different boundary conditions imposed at the

Development of Hydroxyl Tagging Velocimetry for Low Velocity Flows

Science.gov (United States)

Andre, Matthieu A.; Bardet, Philippe M.; Burns, Ross A.; Danehy, Paul M.

2016-01-01

Hydroxyl tagging velocimetry (HTV) is a molecular tagging technique that relies on the photo-dissociation of water vapor into OH radicals and their subsequent tracking using laser induced fluorescence. Velocities are then obtained from time-of-flight calculations. At ambient temperature in air, the OH species lifetime is relatively short (<50 µs), making it suited for high speed flows. Lifetime and radicals formation increases with temperature, which allows HTV to also probe low-velocity, high-temperature flows or reacting flows such as flames. The present work aims at extending the domain of applicability of HTV, particularly towards low-speed (<10 m/s) and moderate (<500 K) temperature flows. Results are compared to particle image velocimetry (PIV) measurements recorded in identical conditions. Single shot and averaged velocity profiles are obtained in an air jet at room temperature. By modestly raising the temperature (100-200 degC) the OH production increases, resulting in an improvement of the signal-to-noise ratio (SNR). Use of nitrogen - a non-reactive gas with minimal collisional quenching - extends the OH species lifetime (to over 500 µs), which allows probing of slower flows or, alternately, increases the measurement precision at the expense of spatial resolution. Instantaneous velocity profiles are resolved in a 100degC nitrogen jet (maximum jet-center velocity of 6.5 m/s) with an uncertainty down to 0.10 m/s (1.5%) at 68% confidence level. MTV measurements are compared with particle image velocimetry and show agreement within 2%.

Intraocular pressure, blood pressure, and retinal blood flow autoregulation: a mathematical model to clarify their relationship and clinical relevance.

Science.gov (United States)

Guidoboni, Giovanna; Harris, Alon; Cassani, Simone; Arciero, Julia; Siesky, Brent; Amireskandari, Annahita; Tobe, Leslie; Egan, Patrick; Januleviciene, Ingrida; Park, Joshua

2014-05-29

This study investigates the relationship between intraocular pressure (IOP) and retinal hemodynamics and predicts how arterial blood pressure (BP) and blood flow autoregulation (AR) influence this relationship. A mathematical model is developed to simulate blood flow in the central retinal vessels and retinal microvasculature as current flowing through a network of resistances and capacitances. Variable resistances describe active and passive diameter changes due to AR and IOP. The model is validated by using clinically measured values of retinal blood flow and velocity. The model simulations for six theoretical patients with high, normal, and low BP (HBP-, NBP-, LBP-) and functional or absent AR (-wAR, -woAR) are compared with clinical data. The model predicts that NBPwAR and HBPwAR patients can regulate retinal blood flow (RBF) as IOP varies between 15 and 23 mm Hg and between 23 and 29 mm Hg, respectively, whereas LBPwAR patients do not adequately regulate blood flow if IOP is 15 mm Hg or higher. Hemodynamic alterations would be noticeable only if IOP changes occur outside of the regulating range, which, most importantly, depend on BP. The model predictions are consistent with clinical data for IOP reduction via surgery and medications and for cases of induced IOP elevation. The theoretical model results suggest that the ability of IOP to induce noticeable changes in retinal hemodynamics depends on the levels of BP and AR of the individual. These predictions might help to explain the inconsistencies found in the clinical literature concerning the relationship between IOP and retinal hemodynamics. Copyright 2014 The Association for Research in Vision and Ophthalmology, Inc.

Measurement of aortic blood flow by magnetic resonance below and above the origin of the coronary arteries in postmenopausal hormone replacement therapy

DEFF Research Database (Denmark)

Sørensen, Morten Beck; Fritz-Hansen, Thomas; Jensen, Henrik Halvor

2004-01-01

PURPOSE: Principal blood flow measures might be assessable by velocity-encoded cine magnetic resonance (VENC MR) of aortic blood flow. The feasibility of using VENC MR for clinical research was tested in a contemporary and controversial human model: the effects of 17beta-estradiol (E) and cyclic...

Measurement of cerebral blood flow in normal subjects by phase contrast MR imaging

International Nuclear Information System (INIS)

Kashimada, Akio; Machida, Kikuo; Honda, Norinari; Mamiya, Toshio; Takahashi, Taku; Kamano, Tsuyoshi; Inoue, Yusuke; Osada, Hisato

1994-01-01

Global cerebral blood flow (CBF) was quantitatively measured with a two-dimensional phase contrast cine magnetic resonance (MR) imaging technique in 24 normal subjects (mean age, 38.6 years; range, 12-70 years). Cine transverse images of the upper cervical region (32 phases/cardiac cycle) were acquired with a 1.5 Tesla MR imaging unit. In five subjects, measurement of CBF was performed before and after intravenous administration of acetazolamide (DIAMOX, 15 mg/kg). Inter- and intra-observer variations in flow volume measurement were small (r=0.970, standard error of the estimate (SEE)=2.9 ml/min, n=8; r=0.963, SEE=4.6 ml/min, n=40, respectively). In measuring flow velocity, they were inferior to those of flow volume measurement. On a visually determined setting of region of interest (ROI), reproducibility of the measurement of flow velocity was not satisfactory in this study. Thus only the results of flow volume measurement are presented. Mean summed vertebral flow volume (171 ml/min, SD=40.6) was significantly less than mean summed internal carotid flow volume (523 ml/min, SD=111). Total blood flow volume showed a significant decline with age (r=-0.45, p<0.05). The mean proportions of carotid and vertebral flow volume to total flow volume were 75.3% and 24.7%, respectively, and showed no significant change with age. The left-to-right ratio of vertebral flow volume (1.39) was significantly higher than that of internal carotid flow volume (0.99, r=0.05). After DIAMOX i.v., the mean rate of increase in total flow volume was 157%. Mean rates of increase in carotid and vertebral flow volume were 154% and 166%, respectively, which were not significantly different. In conclusion, this method is useful for estimating carotid and vertebral flow volume. (author)

Velocity bias induced by flow patterns around ADCPs and associated deployment platforms

Science.gov (United States)

Mueller, David S.

2015-01-01

Velocity measurements near the Acoustic Doppler Current Profiler (ADCP) are important for mapping surface currents, measuring velocity and discharge in shallow streams, and providing accurate estimates of discharge in the top unmeasured portion of the water column. Improvements to ADCP performance permit measurement of velocities much closer (5 cm) to the transducer than has been possible in the past (25 cm). Velocity profiles collected by the U.S. Geological Survey (USGS) with a 1200 kHz Rio Grande Zedhead ADCP in 2002 showed a negative bias in measured velocities near the transducers. On the basis of these results, the USGS initiated a study combining field, laboratory, and numerical modeling data to assess the effect of flow patterns caused by flow around the ADCP and deployment platforms on velocities measured near the transducers. This ongoing study has shown that the negative bias observed in the field is due to the flow pattern around the ADCP. The flow pattern around an ADCP violates the basic assumption of flow homogeneity required for an accurate three-dimensional velocity solution. Results, to date (2014), have indicated velocity biases within the measurable profile, due to flow disturbance, for the TRDI 1200 kHz Rio Grande Zedhead and the SonTek RiverSurveyor M9 ADCPs. The flow speed past the ADCP, the mount and the deployment platform have also been shown to play an important role in the magnitude and extent of the velocity bias.

Measurement system of bubbly flow using ultrasonic velocity profile monitor and video data processing unit. 2. Flow characteristics of bubbly countercurrent flow

International Nuclear Information System (INIS)

Aritomi, Masanori; Zhou, Shirong; Nakajima, Makoto; Takeda, Yasushi; Mori, Michitsugu.

1997-01-01

The authors have developed a measurement system which is composed of an ultrasonic velocity profile monitor and a video data processing unit in order to clarify its multi-dimensional flow characteristics in bubbly flows and to offer a data base to validate numerical codes for multi-dimensional two-phase flow. In this paper, the measurement system was applied for bubbly countercurrent flows in a vertical rectangular channel. At first, both bubble and water velocity profiles and void fraction profiles in the channel were investigated statistically. Next, turbulence intensity in a continuous liquid phase was defined as a standard deviation of velocity fluctuation, and the two-phase multiplier profile of turbulence intensity in the channel was clarified as a ratio of the standard deviation of flow fluctuation in a bubbly countercurrent flow to that in a water single phase flow. Finally, the distribution parameter and drift velocity used in the drift flux model for bubbly countercurrent flows were calculated from the obtained velocity profiles of both phases and void fraction profile, and were compared with the correlation proposed for bubbly countercurrent flows. (author)

Axial and radial velocities in the creeping flow in a pipe

Directory of Open Access Journals (Sweden)

Zuykov Andrey L'vovich

2014-05-01

Full Text Available The article is devoted to analytical study of transformation fields of axial and radial velocities in uneven steady creeping flow of a Newtonian fluid in the initial portion of the cylindrical channel. It is shown that the velocity field of the flow is two-dimensional and determined by the stream function. The article is a continuation of a series of papers, where normalized analytic functions of radial axial distributions in uneven steady creeping flow in a cylindrical tube with azimuthal vorticity and stream function were obtained. There is Poiseuille profile for the axial velocity in the uniform motion of a fluid at an infinite distance from the entrance of the pipe (at x = ∞, here taken equal to zero radial velocity. There is uniform distribution of the axial velocity in the cross section at the tube inlet at x = 0, at which the axial velocity is constant along the current radius. Due to the axial symmetry of the flow on the axis of the pipe (at r = 0, the radial velocities and the partial derivative of the axial velocity along the radius, corresponding to the condition of the soft function extremum, are equal to zero. The authors stated vanishing of the velocity of the fluid on the walls of the pipe (at r = R , where R - radius of the tube due to its viscous sticking and tightness of the walls. The condition of conservation of volume flow along the tube was also accepted. All the solutions are obtained in the form of the Fourier - Bessel. It is shown that the hydraulic losses at uniform creeping flow of a Newtonian fluid correspond to Poiseuille - Hagen formula.

Intensive blood pressure control affects cerebral blood flow in type 2 diabetes mellitus patients

DEFF Research Database (Denmark)

Kim, Yu-Sok; Davis, Shyrin C A T; Truijen, Jasper

2011-01-01

Type 2 diabetes mellitus is associated with microvascular complications, hypertension, and impaired dynamic cerebral autoregulation. Intensive blood pressure (BP) control in hypertensive type 2 diabetic patients reduces their risk of stroke but may affect cerebral perfusion. Systemic hemodynamic...... variables and transcranial Doppler-determined cerebral blood flow velocity (CBFV), cerebral CO2 responsiveness, and cognitive function were determined after 3 and 6 months of intensive BP control in 17 type 2 diabetic patients with microvascular complications (T2DM+), in 18 diabetic patients without (T2DM......-) microvascular complications, and in 16 nondiabetic hypertensive patients. Cerebrovascular reserve capacity was lower in T2DM+ versus T2DM- and nondiabetic hypertensive patients (4.6±1.1 versus 6.0±1.6 [P

Simultaneous effects of slip and MHD on peristaltic blood flow of Jeffrey fluid model through a porous medium

Directory of Open Access Journals (Sweden)

M.M. Bhatti

2016-06-01

Full Text Available In this article, the simultaneous effects of slip and Magnetohydrodynamics (MHD on peristaltic blood flow of Jeffrey fluid model have been investigated in a non-uniform porous channel. The governing equation of blood flow for Jeffrey fluid model is solved with the help of long wavelength and creeping flow regime. The solution of the resulting differential equation is solved analytically and a closed form solution is presented. The impact of all the physical parameters is plotted for velocity profile and pressure rise. Nowadays, Magnetohydrodynamics is applicable in various magnetic drug targeting for cancer diseases and also very helpful to control the flow. The present analysis is also described for Newtonian fluid (λ1→0 as a special case of our study. It is observed that magnitude of the velocity is opposite near the walls due to slip effects whereas similar behavior has been observed for magnetic field.

Pulsatile Flow and Transport of Blood past a Cylinder: Basic Transport for an Artificial Lung.

Science.gov (United States)

Zierenberg, Jennifer R.

2005-11-01

The fluid mechanics and transport for flow of blood past a single cylinder is investigated using CFD. This work refers to an artificial lung in which oxygen travels through fibers oriented perpendicularly to the incoming blood flow. A pulsatile blood flow was considered: Ux=U0[ 1+A( φt ) ], where Ux is the velocity far from the cylinder. The Casson equation was used to describe the shear thinning and yield stress properties of blood. The presence of hemoglobin (i.e. facilitated diffusion) was considered. We examined the effect of A, U0 and φ on the flow and transport by varying the dimensionless parameters: A; Reynolds number, Re; and Womersley parameter, α. Two different feed gases were considered: pure O2 and air. The flow and concentration fields were computed for Re = 5, 10, and 40, 0 transport is found to primarily depend on Re and to increase with increasing Re, α and decreasing A. The presence of hemoglobin increases mass transport. Supported by NIH HL69420, NSF Fellowship

Influence of cold water immersion on limb and cutaneous blood flow at rest.

Science.gov (United States)

Gregson, Warren; Black, Mark A; Jones, Helen; Milson, Jordon; Morton, James; Dawson, Brian; Atkinson, Greg; Green, Daniel J

2011-06-01

Cold water immersion reduces exercise-induced muscle damage. Benefits may partly arise from a decline in limb blood flow; however, no study has comprehensively investigated the influence of different degrees of cooling undertaken via cold water immersion on limb blood flow responses. To determine the influence of cold (8°C) and cool (22°C) water immersion on lower limb and cutaneous blood flow. Controlled laboratory study. Nine men were placed in a semireclined position and lowered into 8°C or 22°C water to the iliac crest for two 5-minute periods interspersed with 2 minutes of nonimmersion. Rectal and thigh skin temperature, deep and superficial muscle temperature, heart rate, mean arterial pressure, thigh cutaneous blood velocity (laser Doppler), and superficial femoral artery blood flow (duplex ultrasound) were measured during immersion and for 30 minutes after immersion. Indices of vascular conductance were calculated (flux and blood flow/mean arterial pressure). Reductions in rectal temperature (8°C, 0.2° ± 0.1°C; 22°C, 0.1° ± 0.1°C) and thigh skin temperature (8°C, 6.2° ± 0.5°C; 22°C, 3.2° ± 0.2°C) were greater in 8°C water than in 22°C (P water compared with 22°C (P = .01). These data suggest that immersion at both temperatures resulted in similar whole limb blood flow but, paradoxically, more blood was distributed to the skin in the colder water. This suggests that colder temperatures may be associated with reduced muscle blood flow, which could provide an explanation for the benefits of cold water immersion in alleviating exercise-induced muscle damage in sports and athletic contexts. Colder water temperatures may be more effective in the treatment of exercise-induced muscle damage and injury rehabilitation because of greater reductions in muscle blood flow.

Light therapy modulates serotonin levels and blood flow in women with headache. A preliminary study.

Science.gov (United States)

Tomaz de Magalhães, Miriam; Núñez, Silvia Cristina; Kato, Ilka Tiemy; Ribeiro, Martha Simões

2016-01-01

In this study, we looked at the possible effects of low-level laser therapy (LLLT) on blood flow velocity, and serotonin (5-HT) and cholinesterase levels in patients with chronic headache associated with temporomandibular disorders (TMD). LLLT has been clinically applied over the past years with positive results in analgesia and without the report of any side effects. The understanding of biological mechanisms of action may improve clinical results and facilitate its indication. Ten patients presenting headache associated with TMD completed the study. An 830-nm infrared diode laser with power of 100 mW, exposure time of 34 s, and energy of 3.4 J was applied on the tender points of masseter and temporal muscle. Blood flow velocity was determined via ultrasound Doppler velocimetry before and after laser irradiation. The whole blood 5-HT and cholinesterase levels were evaluated three days before, immediately, and three days after laser irradiation. Pain score after treatment decreased to a score of 5.8 corresponding to 64% of pain reduction (P  0.05). Our findings indicated that LLLT regulates blood flow in the temporal artery after irradiation and might control 5-HT levels in patients suffering with tension-type headache associated to TMD contributing to pain relief. © 2016 by the Society for Experimental Biology and Medicine.

Middle cerebral artery blood velocity during running

NARCIS (Netherlands)

Lyngeraa, T. S.; Pedersen, L. M.; Mantoni, T.; Belhage, B.; Rasmussen, L. S.; van Lieshout, J. J.; Pott, F. C.

2013-01-01

Running induces characteristic fluctuations in blood pressure (BP) of unknown consequence for organ blood flow. We hypothesized that running-induced BP oscillations are transferred to the cerebral vasculature. In 15 healthy volunteers, transcranial Doppler-determined middle cerebral artery (MCA)

Thermistor based, low velocity isothermal, air flow sensor

International Nuclear Information System (INIS)

Cabrita, Admésio A C M; Mendes, Ricardo; Quintela, Divo A

2016-01-01

The semiconductor thermistor technology is applied as a flow sensor to measure low isothermal air velocities (<2 ms −1 ). The sensor is subjected to heating and cooling cycles controlled by a multifunctional timer. In the heating stage, the alternating current of a main AC power supply source guarantees a uniform thermistor temperature distribution. The conditioning circuit assures an adequate increase of the sensors temperature and avoids the thermal disturbance of the flow. The power supply interruption reduces the consumption from the source and extends the sensors life time. In the cooling stage, the resistance variation of the flow sensor is recorded by the measuring chain. The resistive sensor parameters proposed vary significantly and feature a high sensitivity to the flow velocity. With the aid of a computer, the data transfer, storage and analysis provides a great advantage over the traditional local anemometer readings. The data acquisition chain has a good repeatability and low standard uncertainties. The proposed method measures isothermal air mean velocities from 0.1 ms −1 to 2 ms −1 with a standard uncertainty error less than 4%. (paper)

Tracking flow of leukocytes in blood for drug analysis

Science.gov (United States)

Basharat, Arslan; Turner, Wesley; Stephens, Gillian; Badillo, Benjamin; Lumpkin, Rick; Andre, Patrick; Perera, Amitha

2011-03-01

Modern microscopy techniques allow imaging of circulating blood components under vascular flow conditions. The resulting video sequences provide unique insights into the behavior of blood cells within the vasculature and can be used as a method to monitor and quantitate the recruitment of inflammatory cells at sites of vascular injury/ inflammation and potentially serve as a pharmacodynamic biomarker, helping screen new therapies and individualize dose and combinations of drugs. However, manual analysis of these video sequences is intractable, requiring hours per 400 second video clip. In this paper, we present an automated technique to analyze the behavior and recruitment of human leukocytes in whole blood under physiological conditions of shear through a simple multi-channel fluorescence microscope in real-time. This technique detects and tracks the recruitment of leukocytes to a bioactive surface coated on a flow chamber. Rolling cells (cells which partially bind to the bioactive matrix) are detected counted, and have their velocity measured and graphed. The challenges here include: high cell density, appearance similarity, and low (1Hz) frame rate. Our approach performs frame differencing based motion segmentation, track initialization and online tracking of individual leukocytes.

Ultrasonic velocity profiling rheometry based on a widened circular Couette flow

International Nuclear Information System (INIS)

Shiratori, Takahisa; Tasaka, Yuji; Oishi, Yoshihiko; Murai, Yuichi

2015-01-01

We propose a new rheometry for characterizing the rheological properties of fluids. The technique produces flow curves, which represent the relationship between the fluid shear rate and shear stress. Flow curves are obtained by measuring the circumferential velocity distribution of tested fluids in a circular Couette system, using an ultrasonic velocity profiling technique. By adopting a widened gap of concentric cylinders, a designed range of the shear rate is obtained so that velocity profile measurement along a single line directly acquires flow curves. To reduce the effect of ultrasonic noise on resultant flow curves, several fitting functions and variable transforms are examined to best approximate the velocity profile without introducing a priori rheological models. Silicone oil, polyacrylamide solution, and yogurt were used to evaluate the applicability of this technique. These substances are purposely targeted as examples of Newtonian fluids, shear thinning fluids, and opaque fluids with unknown rheological properties, respectively. We find that fourth-order Chebyshev polynomials provide the most accurate representation of flow curves in the context of model-free rheometry enabled by ultrasonic velocity profiling. (paper)

Flow of magnetic particles in blood with isothermal heating: A fractional model for two-phase flow

Science.gov (United States)

Ali, Farhad; Imtiaz, Anees; Khan, Ilyas; Sheikh, Nadeem Ahmad

2018-06-01

In the sixteenth century, medical specialists were of the conclusion that magnet can be utilized for the treatment or wipe out the illnesses from the body. On this basis, the research on magnet advances day by day for the treatment of different types of diseases in mankind. This study aims to investigate the effect of magnetic field and their applications in human body specifically in blood. Blood is a non-Newtonian fluid because its viscosity depends strongly on the fraction of volume occupied by red cells also called the hematocrit. Therefore, in this paper blood is considered as an example of non-Newtonian Casson fluid. The blood flow is considered in a vertical cylinder together with heat transfer due to mixed conviction caused by buoyancy force and the external pressure gradient. Effect of magnetic field on the velocities of blood and magnetic particles is also considered. The problem is modelled using the Caputo-Fabrizio derivative approach. The governing fractional partial differential equations are solved using Laplace and Hankel transformation techniques and exact solutions are obtained. Effects of different parameters such as Grashof number, Prandtl number, Casson fluid parameter and fractional parameters, and magnetic field are shown graphically. Both velocity profiles increase with the increase of Grashoff number and Casson fluid parameter and reduce with the increase of magnetic field.

Instability of shallow open channel flow with lateral velocity gradients

Energy Technology Data Exchange (ETDEWEB)

Lima, A C; Izumi, N, E-mail: adriano@eng.hokudai.ac.jp, E-mail: nizumi@eng.hokudai.ac.jp [River and Watershed Engineering Laboratory, Hokkaido University, Sapporo, 060-8628 (Japan)

2011-12-22

The turbulent flow in a wide rectangular open channel partially covered with vegetation is studied using linear stability analysis. In the base state normal flow condition, the water depth is constant and the transverse velocity vanishes, while there is a lateral gradient in the streamwise velocity with an inflexion point at the boundary between the vegetated zone and the main channel. The Reynolds stress is expressed by introducing the eddy viscosity, which is obtained from assuming a logarithmic distribution of the velocity near the bed. Perturbation expansions are introduced to the streamwise and transverse velocities, as well as to the water depth. The system of governing equations was solved in order to determine the maximum growth rate of the perturbations as a function of parameters which describe physical characteristics of the channel and the flow.

Pulsatile flow of blood and heat transfer with variable viscosity under magnetic and vibration environment

International Nuclear Information System (INIS)

Shit, G.C.; Majee, Sreeparna

2015-01-01

Unsteady flow of blood and heat transfer characteristics in the neighborhood of an overlapping constricted artery have been investigated in the presence of magnetic field and whole body vibration. The laminar flow of blood is taken to be incompressible and Newtonian fluid with variable viscosity depending upon temperature with an aim to provide resemblance to the real situation in the physiological system. The unsteady flow mechanism in the constricted artery is subjected to a pulsatile pressure gradient arising from systematic functioning of the heart and from the periodic body acceleration. The numerical computation has been performed using finite difference method by developing Crank–Nicolson scheme. The results show that the volumetric flow rate, skin-friction and the rate of heat transfer at the wall are significantly altered in the downstream of the constricted region. The axial velocity profile, temperature and flow rate increases with increase in temperature dependent viscosity, while the opposite trend is observed in the case of skin-friction and flow impedance. - Highlights: • We have investigated the pulsatile MHD flow of blood and heat transfer in arteries. • The influence of periodic body acceleration has been taken into account. • The temperature dependent viscosity of blood is considered. • The variable viscosity has an increasing effect on blood flow and heat transfer. • The overall temperature distribution enhances in the presence of magnetic field

Pulsatile flow of blood and heat transfer with variable viscosity under magnetic and vibration environment

Energy Technology Data Exchange (ETDEWEB)

Shit, G.C., E-mail: gopal_iitkgp@yahoo.co.in; Majee, Sreeparna

2015-08-15

Unsteady flow of blood and heat transfer characteristics in the neighborhood of an overlapping constricted artery have been investigated in the presence of magnetic field and whole body vibration. The laminar flow of blood is taken to be incompressible and Newtonian fluid with variable viscosity depending upon temperature with an aim to provide resemblance to the real situation in the physiological system. The unsteady flow mechanism in the constricted artery is subjected to a pulsatile pressure gradient arising from systematic functioning of the heart and from the periodic body acceleration. The numerical computation has been performed using finite difference method by developing Crank–Nicolson scheme. The results show that the volumetric flow rate, skin-friction and the rate of heat transfer at the wall are significantly altered in the downstream of the constricted region. The axial velocity profile, temperature and flow rate increases with increase in temperature dependent viscosity, while the opposite trend is observed in the case of skin-friction and flow impedance. - Highlights: • We have investigated the pulsatile MHD flow of blood and heat transfer in arteries. • The influence of periodic body acceleration has been taken into account. • The temperature dependent viscosity of blood is considered. • The variable viscosity has an increasing effect on blood flow and heat transfer. • The overall temperature distribution enhances in the presence of magnetic field.

A 2D nonlinear multiring model for blood flow in large elastic arteries

Science.gov (United States)

Ghigo, Arthur R.; Fullana, Jose-Maria; Lagrée, Pierre-Yves

2017-12-01

In this paper, we propose a two-dimensional nonlinear ;multiring; model to compute blood flow in axisymmetric elastic arteries. This model is designed to overcome the numerical difficulties of three-dimensional fluid-structure interaction simulations of blood flow without using the over-simplifications necessary to obtain one-dimensional blood flow models. This multiring model is derived by integrating over concentric rings of fluid the simplified long-wave Navier-Stokes equations coupled to an elastic model of the arterial wall. The resulting system of balance laws provides a unified framework in which both the motion of the fluid and the displacement of the wall are dealt with simultaneously. The mathematical structure of the multiring model allows us to use a finite volume method that guarantees the conservation of mass and the positivity of the numerical solution and can deal with nonlinear flows and large deformations of the arterial wall. We show that the finite volume numerical solution of the multiring model provides at a reasonable computational cost an asymptotically valid description of blood flow velocity profiles and other averaged quantities (wall shear stress, flow rate, ...) in large elastic and quasi-rigid arteries. In particular, we validate the multiring model against well-known solutions such as the Womersley or the Poiseuille solutions as well as against steady boundary layer solutions in quasi-rigid constricted and expanded tubes.

CORRELATION BETWEEN UTERINE ARTERY FLOW VELOCITY ...

African Journals Online (AJOL)

CORRELATION BETWEEN UTERINE ARTERY FLOW VELOCITY WAVEFORMS AND ENDOMETRIAL HISTOPATHOLOGY IN WOMEN WITH PERIMENOPAUSAL AND POSTMENOPAUSAL BLEEDING. Dr. Ebtesam Saied, Dr. Ismail El Garhy(MD), Dr. Farid I. Hassan(MD), Dr. Adel-Gamil Abd-Allah, Abd El Shafy Ibrahim ...

Quantitative imaging of cerebral blood flow velocity and intracellular motility using dynamic light scattering-optical coherence tomography.

Science.gov (United States)

Lee, Jonghwan; Radhakrishnan, Harsha; Wu, Weicheng; Daneshmand, Ali; Climov, Mihail; Ayata, Cenk; Boas, David A

2013-06-01

This paper describes a novel optical method for label-free quantitative imaging of cerebral blood flow (CBF) and intracellular motility (IM) in the rodent cerebral cortex. This method is based on a technique that integrates dynamic light scattering (DLS) and optical coherence tomography (OCT), named DLS-OCT. The technique measures both the axial and transverse velocities of CBF, whereas conventional Doppler OCT measures only the axial one. In addition, the technique produces a three-dimensional map of the diffusion coefficient quantifying nontranslational motions. In the DLS-OCT diffusion map, we observed high-diffusion spots, whose locations highly correspond to neuronal cell bodies and whose diffusion coefficient agreed with that of the motion of intracellular organelles reported in vitro in the literature. Therefore, the present method has enabled, for the first time to our knowledge, label-free imaging of the diffusion-like motion of intracellular organelles in vivo. As an example application, we used the method to monitor CBF and IM during a brief ischemic stroke, where we observed an induced persistent reduction in IM despite the recovery of CBF after stroke. This result supports that the IM measured in this study represent the cellular energy metabolism-related active motion of intracellular organelles rather than free diffusion of intracellular macromolecules.

Dehydration accelerates reductions in cerebral blood flow during prolonged exercise in the heat without compromising brain metabolism

DEFF Research Database (Denmark)

Trangmar, Steven J; Chiesa, Scott T; Llodio, Iñaki

2015-01-01

Dehydration hastens the decline in cerebral blood flow (CBF) during incremental exercise, whereas the cerebral metabolic rate for O2 (CMRO2 ) is preserved. It remains unknown whether CMRO2 is also maintained during prolonged exercise in the heat and whether an eventual decline in CBF is coupled...... to fatigue. Two studies were undertaken. In study 1, 10 male cyclists cycled in the heat for ∼2 h with (control) and without fluid replacement (dehydration) while internal and external carotid artery blood flow and core and blood temperature were obtained. Arterial and internal jugular venous blood samples...... were assessed with dehydration to evaluate CMRO2 . In study 2, in 8 male subjects, middle cerebral artery blood velocity was measured during prolonged exercise to exhaustion in both dehydrated and euhydrated states. After a rise at the onset of exercise, internal carotid artery flow declined...

Channel flow analysis. [velocity distribution throughout blade flow field

Science.gov (United States)

Katsanis, T.

1973-01-01

The design of a proper blade profile requires calculation of the blade row flow field in order to determine the velocities on the blade surfaces. An analysis theory is presented for several methods used for this calculation and associated computer programs that were developed are discussed.

Measurement uncertainty budget of an interferometric flow velocity sensor

Science.gov (United States)

Bermuske, Mike; Büttner, Lars; Czarske, Jürgen

2017-06-01

Flow rate measurements are a common topic for process monitoring in chemical engineering and food industry. To achieve the requested low uncertainties of 0:1% for flow rate measurements, a precise measurement of the shear layers of such flows is necessary. The Laser Doppler Velocimeter (LDV) is an established method for measuring local flow velocities. For exact estimation of the flow rate, the flow profile in the shear layer is of importance. For standard LDV the axial resolution and therefore the number of measurement points in the shear layer is defined by the length of the measurement volume. A decrease of this length is accompanied by a larger fringe distance variation along the measurement axis which results in a rise of the measurement uncertainty for the flow velocity (uncertainty relation between spatial resolution and velocity uncertainty). As a unique advantage, the laser Doppler profile sensor (LDV-PS) overcomes this problem by using two fan-like fringe systems to obtain the position of the measured particles along the measurement axis and therefore achieve a high spatial resolution while it still offers a low velocity uncertainty. With this technique, the flow rate can be estimated with one order of magnitude lower uncertainty, down to 0:05% statistical uncertainty.1 And flow profiles especially in film flows can be measured more accurately. The problem for this technique is, in contrast to laboratory setups where the system is quite stable, that for industrial applications the sensor needs a reliable and robust traceability to the SI units, meter and second. Small deviations in the calibration can, because of the highly position depending calibration function, cause large systematic errors in the measurement result. Therefore, a simple, stable and accurate tool is needed, that can easily be used in industrial surroundings to check or recalibrate the sensor. In this work, different calibration methods are presented and their influences to the

Blood velocity estimation using ultrasound and spectral iterative adaptive approaches

DEFF Research Database (Denmark)

Gudmundson, Erik; Jakobsson, Andreas; Jensen, Jørgen Arendt

2011-01-01

-mode images are interleaved with the Doppler emissions. Furthermore, the techniques are shown, using both simplified and more realistic Field II simulations as well as in vivo data, to outperform current state-of-the-art techniques, allowing for accurate estimation of the blood velocity spectrum using only 30......This paper proposes two novel iterative data-adaptive spectral estimation techniques for blood velocity estimation using medical ultrasound scanners. The techniques make no assumption on the sampling pattern of the emissions or the depth samples, allowing for duplex mode transmissions where B...

Regional cerebral blood flow in schizophrenia

International Nuclear Information System (INIS)

Mathew, R.J.; Duncan, G.C.; Weinman, M.L.; Barr, D.L.

1982-01-01

Regional cerebral blood flow (rCBF) was measured via xenon133 inhalation technique in 23 patients with schizophrenia and 18 age- and sex-matched controls. The mean blood flow to both hemispheres was found to be lower for the patients. The patients and their controls did not differ on interhemispheric differences in blood flow. There were no differences in rCBF between medicated and unmedicated, subchronic and chronic, and paranoid and nonparanoid patients. Hallucinations were associated with reduced blood flow to several postcentral regions

Regional cerebral blood flow in schizophrenia

Energy Technology Data Exchange (ETDEWEB)

Mathew, R.J.; Duncan, G.C.; Weinman, M.L.; Barr, D.L.

1982-10-01

Regional cerebral blood flow (rCBF) was measured via xenon133 inhalation technique in 23 patients with schizophrenia and 18 age- and sex-matched controls. The mean blood flow to both hemispheres was found to be lower for the patients. The patients and their controls did not differ on interhemispheric differences in blood flow. There were no differences in rCBF between medicated and unmedicated, subchronic and chronic, and paranoid and nonparanoid patients. Hallucinations were associated with reduced blood flow to several postcentral regions.

Generation of net sediment transport by velocity skewness in oscillatory sheet flow

Science.gov (United States)

Chen, Xin; Li, Yong; Chen, Genfa; Wang, Fujun; Tang, Xuelin

2018-01-01

This study utilizes a qualitative approach and a two-phase numerical model to investigate net sediment transport caused by velocity skewness beneath oscillatory sheet flow and current. The qualitative approach is derived based on the pseudo-laminar approximation of boundary layer velocity and exponential approximation of concentration. The two-phase model can obtain well the instantaneous erosion depth, sediment flux, boundary layer thickness, and sediment transport rate. It can especially illustrate the difference between positive and negative flow stages caused by velocity skewness, which is considerably important in determining the net boundary layer flow and sediment transport direction. The two-phase model also explains the effect of sediment diameter and phase-lag to sediment transport by comparing the instantaneous-type formulas to better illustrate velocity skewness effect. In previous studies about sheet flow transport in pure velocity-skewed flows, net sediment transport is only attributed to the phase-lag effect. In the present study with the qualitative approach and two-phase model, phase-lag effect is shown important but not sufficient for the net sediment transport beneath pure velocity-skewed flow and current, while the asymmetric wave boundary layer development between positive and negative flow stages also contributes to the sediment transport.

Modelling of two-phase flow based on separation of the flow according to velocity

International Nuclear Information System (INIS)

Narumo, T.

1997-01-01

The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors

Flow velocity calculation to avoid instability in a typical research reactor core

International Nuclear Information System (INIS)

Oliveira, Carlos Alberto de; Mattar Neto, Miguel

2011-01-01

Flow velocity through a research reactor core composed by MTR-type fuel elements is investigated. Core cooling capacity must be available at the same time that fuel-plate collapse must be avoided. Fuel plates do not rupture during plate collapse, but their lateral deflections can close flow channels and lead to plate over-heating. The critical flow velocity is a speed at which the plates collapse by static instability type failure. In this paper, critical velocity and coolant velocity are evaluated for a typical MTR-type flat plate fuel element. Miller's method is used for prediction of critical velocity. The coolant velocity is limited to 2/3 of the critical velocity, that is a currently used criterion. Fuel plate characteristics are based on the open pool Australian light water reactor. (author)

Doppler ultrasonographic measurement of short-term effects of valsalva maneuver on retrobulbar blood flow.

Science.gov (United States)

Kimyon, Sabit; Mete, Ahmet; Mete, Alper; Mete, Duçem

2017-11-12

To investigate the effects of Valsalva maneuver (VM) on retrobulbar blood flow parameters in healthy subjects. Participants without any ophthalmologic or systemic pathology were examined in supine position with color and pulsed Doppler imaging for blood flow measurement, via a paraocular approach, in the ophthalmic artery (OA), central retinal artery (CRA), central retinal vein (CRV), nasal posterior ciliary artery (NPCA), and temporal posterior ciliary artery (TPCA), 10 seconds after a 35- to 40-mm Hg expiratory pressure was reached. Peak systolic velocity (PSV), end-diastolic velocity (EDV), pulsatility index (PI), and resistivity index (RI) values were recorded for each artery. PSV and EDV values were recorded for CRV. There were significant differences between resting and VM values of PSV and EDV of CRA, RI of NPCA, and PI, RI, and EDV of TPCA. Resting CRA-EDV, CRV-PSV, and CRV-EDV were positively correlated whereas resting OA-PSV and CRA-PI, and OA-PSV, CRA-PSV, and CRA-EDV during VM, were negatively correlated with age. VM induces a short-term increase in CRA blood flow and a decrease in NPCA and TPCA RI. Additional studies with a longer Doppler recording during VM, in a larger population sample, are required to allow definitive interpretation. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:551-555, 2017. © 2017 Wiley Periodicals, Inc.

Measurement of organ blood flow using tritiated water. II. Uterine blood flow in conscious pregnant ewes

International Nuclear Information System (INIS)

Brown, B.W.; Oddy, V.H.; Jones, A.W.

1982-01-01

Total uterine blood flow was measured with a tritiated water (TOH) diffusion method and with radioactive microspheres in six, conscious, pregnant ewes. With continuous infusion of TOH, equilibrium between the TOH concentration in utero-ovarian venous blood and arterial blood was attained within 50 min of the start of the infusion. The concentration of TOH in uterine and foetal tissue and in foetal blood water was the same as that in uterine venous water by 40 min; at this time, the concentration of TOH in the water of amniotic and allantoic fluids was 96% of that in uterine venous blood water. Estimates of total uterine blood flow obtained using TOH were highly correlated with those obtained with microspheres and the corresponding mean flow values obtained with the two techniques did not significantly differ. The percentage of the total uterine blood flow passing through arteriovenous anastomoses ranged from 1.4 to 3.3%

Transition of unsteady velocity profiles with reverse flow

OpenAIRE

Das, Debopam; Arakeri, Jaywant H

1998-01-01

This paper deals with the stability and transition to turbulence of wall-bounded unsteady velocity profiles with reverse flow. Such flows occur, for example, during unsteady boundary layer separation and in oscillating pipe flow. The main focus is on results from experiments in time-developing flow in a long pipe, which is decelerated rapidly. The flow is generated by the controlled motion of a piston. We obtain analytical solutions for laminar flow in the pipe and in a two-dimensional channe...

Intraoperative vascular anatomy, arterial blood flow velocity, and microcirculation in unilateral and bilateral cleft lip repair

NARCIS (Netherlands)

Mueller, A.A.; Schumann, D.; Reddy, R.R.; Schwenzer-Zimmerer, K.; Mueller-Gerbl, M.; Zeilhofer, H.F.; Sailer, H.F.; Reddy, S.G.

2012-01-01

BACKGROUND: Cleft lip repair aims to normalize the disturbed anatomy and function. The authors determined whether normalization of blood circulation is achieved. METHODS: The authors measured the microcirculatory flow, oxygen saturation, and hemoglobin level in the lip and nose of controls (n = 22)

Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

International Nuclear Information System (INIS)

Meng, Yiqing; Lucas, Gary P

2017-01-01

This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas–water and oil–gas–water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate. In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the

Imaging water velocity and volume fraction distributions in water continuous multiphase flows using inductive flow tomography and electrical resistance tomography

Science.gov (United States)

Meng, Yiqing; Lucas, Gary P.

2017-05-01

This paper presents the design and implementation of an inductive flow tomography (IFT) system, employing a multi-electrode electromagnetic flow meter (EMFM) and novel reconstruction techniques, for measuring the local water velocity distribution in water continuous single and multiphase flows. A series of experiments were carried out in vertical-upward and upward-inclined single phase water flows and ‘water continuous’ gas-water and oil-gas-water flows in which the velocity profiles ranged from axisymmetric (single phase and vertical-upward multiphase flows) to highly asymmetric (upward-inclined multiphase flows). Using potential difference measurements obtained from the electrode array of the EMFM, local axial velocity distributions of the continuous water phase were reconstructed using two different IFT reconstruction algorithms denoted RT#1, which assumes that the overall water velocity profile comprises the sum of a series of polynomial velocity components, and RT#2, which is similar to RT#1 but which assumes that the zero’th order velocity component may be replaced by an axisymmetric ‘power law’ velocity distribution. During each experiment, measurement of the local water volume fraction distribution was also made using the well-established technique of electrical resistance tomography (ERT). By integrating the product of the local axial water velocity and the local water volume fraction in the cross section an estimate of the water volumetric flow rate was made which was compared with a reference measurement of the water volumetric flow rate. In vertical upward flows RT#2 was found to give rise to water velocity profiles which are consistent with the previous literature although the profiles obtained in the multiphase flows had relatively higher central velocity peaks than was observed for the single phase profiles. This observation was almost certainly a result of the transfer of axial momentum from the less dense dispersed phases to the water

Intravaginal Administration of Sildenafil Citrate Increases Blood Flow in the Bovine Uterus

Directory of Open Access Journals (Sweden)

Dzięcioł Michał

2015-04-01

Full Text Available The aim of the study was to evaluate the influence of sildenafil citrate administrated intravaginaly on the blood flow in the bovine uterus during dioestrus. Uterine blood flow was examined in six healthy adult cows. Sildenafil was administrated intravaginaly to each co w between the 6th and 8th d of the ovarian cycle, in the form of vaginal suppositories containing 100 mg of active substance at a dose of 100, 200, or 300 mg per animal. Uterine perfusion was estimated by the colour Doppler examination, and obtained results were analysed with the Pixel Flux Software (Chameleon, Germany. Moreover, cardiovascular parameters were also evaluated. Animals were examined before and five times after drug application (two times at 15 min intervals, and three times at 2 h intervals. A placebo suppository was also given to the cows. The analysis of the intensity and velocity of blood flow in the uterus proved that sildenafil administrated intravaginaly significantly increased blood flow in the uterus and the effect of increased perfusion was observed for 4 h and 30 min after administration. The effect of increased uterine perfusion was observed after low as well as high doses of sildenafil. Significant changes in the cardio-vascular parameters were not detected. There were no changes in the uterine perfusion as well as in cardiovascular parameters after placebo administration.

Blood flow and blood volume in a transplanted rat fibrosarcoma

International Nuclear Information System (INIS)

Tozer, G.M.; Morris, C.C.

1990-01-01

Blood flow measurements following i.v. infusion of iodi-antipyrine labelled with 14 C ( 14 C-IAP) and blood volume measurements following i.v. injection of 125 I human serum albumin and 51 Cr-labelled red blood cells were made in a transplanted rat fibrosarcoma for comparison with various normal tissues. The tumour-blood partition co-efficient for 14 C-IAP w as found to be 0.79 ± 0.07 which is similar to most of the normal tissues studied. The solubility of 14 C-IAP in plasma was found to be higher than that in whole blood. Blood flow to tumours 3 was found to be 17.9 ± 4.0 ml blood 100 g tissue -1 xmin -1 . These values were considered to be primarily measurements of nutritive flow. Blood in the tumours was found to occupy around 1% of the tissue space which was similar to that found for normal muscle and skin. There was no direct correlation between % blood volume and blood flow for the different tissues studied. Th haematocrit of blood contained in tumour tissue was calculated to be significantly lower than that of blood contained in the normal tissues. It was suspected that permeability of tumour blood vessel walls to 125 I-HSA could have accounted for this difference. (author). 41 refs.; 2 figs.; 3 tabs

Modelling of two-phase flow based on separation of the flow according to velocity

Energy Technology Data Exchange (ETDEWEB)

Narumo, T. [VTT Energy, Espoo (Finland). Nuclear Energy

1997-12-31

The thesis concentrates on the development work of a physical one-dimensional two-fluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model one-dimensional two-phase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. In the SFAV approach, the two-phase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for non-uniform transverse profile of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on two-phase flow wave phenomena Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtual-mass models that are typically optimized for special flow regimes like bubbly flow. The SFAV model has proved to be applicable in describing two-phase flow physically correctly because both the dynamics and steady-state behaviour of the model has been considered and found to agree well with experimental data This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors. 45 refs. The thesis includes also five previous publications by author.

Cerebral blood flow and metabolism during exercise: implications for fatigue

DEFF Research Database (Denmark)

Seifert, T.; Lieshout, J.J. van; Secher, Niels

2008-01-01

During exercise: the Kety-Schmidt-determined cerebral blood flow (CBF) does not change because the jugular vein is collapsed in the upright position. In contrast, when CBF is evaluated by (133)Xe clearance, by flow in the internal carotid artery, or by flow velocity in basal cerebral arteries......, a approximately 25% increase is detected with a parallel increase in metabolism. During activation, an increase in cerebral O(2) supply is required because there is no capillary recruitment within the brain and increased metabolism becomes dependent on an enhanced gradient for oxygen diffusion. During maximal...... whole body exercise, however, cerebral oxygenation decreases because of eventual arterial desaturation and marked hyperventilation-related hypocapnia of consequence for CBF. Reduced cerebral oxygenation affects recruitment of motor units, and supplemental O(2) enhances cerebral oxygenation and work...

Radioisotopic flow scanning for portal blood flow and portal hypertension

International Nuclear Information System (INIS)

Hesdorffer, C.S.; Bezwoda, W.R.; Danilewitz, M.D.; Esser, J.D.; Tobias, M.

1987-01-01

The use of a simple, noninvasive, isotope scanning technique for the determination of relative portal blood flow and detection of portal hypertension is described. Using this technique the presence of portal hypertension was demonstrated in seven of nine patients known to have elevated portal venous pressure. By contrast, esophageal varices were demonstrated in only five of these patients, illustrating the potential value of the method. Furthermore, this technique has been adapted to the study of portal blood flow in patients with myeloproliferative disorders with splenomegaly but without disturbances in hepatic architecture. Results demonstrate that the high relative splenic flow resulting from the presence of splenomegaly may in turn be associated with elevated relative portal blood flow and portal hypertension. The theoretic reasons for the development of flow-related portal hypertension and its relationship to splenic blood flow are discussed

The structure of a jet in cross flow at low velocity ratios

International Nuclear Information System (INIS)

Gopalan, Shridhar; Abraham, Bruce M.; Katz, Joseph

2004-01-01

This paper examines in detail the flow structure and associated wall pressure fluctuations caused by the injection of a round, turbulent jet into a turbulent boundary layer. The velocity ratio, r, ratio of mean jet velocity to the mean cross flow, varies from 0.5 to 2.5 and the Reynolds number based on the cross flow speed and jet diameter is 1.9x10 4 . Particle image velocimetry is used to measure the flow and flush mounted pressure sensors installed at several locations used to determine the wall pressure. The results consist of sample instantaneous flow structures, distributions of mean velocity, vorticity and turbulence intensity, as well as wall pressure spectra. The flow structure depends strongly on the velocity ratio and there are two distinctly different regions. At low velocity ratios, namely r 2, the near-wall flow behind the jet resembles a Karman vortex street and the wall-normal vortical structures contain cross flow boundary layer vorticity. Autospectra of the pressure signals show that the effect of the jet is mainly in the 15-100 Hz range. At r 2, the wall pressure levels reach a plateau demonstrating the diminishing effect of the jet on the near-wall flow. Consistent with the flow structure, the highest wall pressure fluctuations occur off the jet centerline for r 2. Also, the advection speed of near-wall vortical structures increase with r at r 2 it is a constant

Estimation of left ventricular blood flow parameters: clinical application of patient-specific CFD simulations from 4D echocardiography

Science.gov (United States)

Larsson, David; Spühler, Jeannette H.; Günyeli, Elif; Weinkauf, Tino; Hoffman, Johan; Colarieti-Tosti, Massimiliano; Winter, Reidar; Larsson, Matilda

2017-03-01

Echocardiography is the most commonly used image modality in cardiology, assessing several aspects of cardiac viability. The importance of cardiac hemodynamics and 4D blood flow motion has recently been highlighted, however such assessment is still difficult using routine echo-imaging. Instead, combining imaging with computational fluid dynamics (CFD)-simulations has proven valuable, but only a few models have been applied clinically. In the following, patient-specific CFD-simulations from transthoracic dobutamin stress echocardiography have been used to analyze the left ventricular 4D blood flow in three subjects: two with normal and one with reduced left ventricular function. At each stress level, 4D-images were acquired using a GE Vivid E9 (4VD, 1.7MHz/3.3MHz) and velocity fields simulated using a presented pathway involving endocardial segmentation, valve position identification, and solution of the incompressible Navier-Stokes equation. Flow components defined as direct flow, delayed ejection flow, retained inflow, and residual volume were calculated by particle tracing using 4th-order Runge-Kutta integration. Additionally, systolic and diastolic average velocity fields were generated. Results indicated no major changes in average velocity fields for any of the subjects. For the two subjects with normal left ventricular function, increased direct flow, decreased delayed ejection flow, constant retained inflow, and a considerable drop in residual volume was seen at increasing stress. Contrary, for the subject with reduced left ventricular function, the delayed ejection flow increased whilst the retained inflow decreased at increasing stress levels. This feasibility study represents one of the first clinical applications of an echo-based patient-specific CFD-model at elevated stress levels, and highlights the potential of using echo-based models to capture highly transient flow events, as well as the ability of using simulation tools to study clinically complex

New linear theory of hydrodynamic instability of the Hagen-Poiseuille flow and the blood swirling flows formation

Directory of Open Access Journals (Sweden)

Sergey G. Chefranov

2012-11-01

Full Text Available Aims This paper deals with solving of a century-old paradox of linear stability for the Hagen-Poiseuille flow. A new mechanism of dissipative hydrodynamic instability has been established herein, and a basis for the forming of helical structural organization of bloodstream and respective energy effectiveness of the cardiovascular system functioning has been defined by the authors. Materials and methods Theory of hydrodynamic instability, Galerkin’s approximation. Results A new condition Re > Reth-min ≈ 124 of linear (exponential instability of the Hagen-Poisseuille (HP flow with respect to extremely small by magnitude axially-symmetric disturbances of the tangential component of the velocity field is obtained. The disturbances necessarily shall have quasi-periodic longitudinal variability along the pipe axis that corresponds to the observed data. Conclusion We show that the obtained estimate of value of Reth-min corresponds to the condition of independence of the main result (on the linear instability of the HP flow when Re > Reth-min from the procedure of averaging used in the Galerkin approximation. Thus, we obtain the possible natural mechanism for the blood swirling flows formations observed in the aorta and the large blood vessels.

Nutrient and nonnutrient renal blood flow

International Nuclear Information System (INIS)

Young, J.S.; Passmore, J.C.; Hartupee, D.A.; Baker, C.H.

1990-01-01

The role of prostaglandins in the distribution of total renal blood flow (TRBF) between nutrient and nonnutrient compartments was investigated in anesthetized mongrel dogs. Renal blood flow distribution was assessed by the xenon 133 freeze-dissection technique and by rubidium 86 extraction after ibuprofen treatment. Ibuprofen (13 mg/kg) significantly decreased TRBF by 16.3% +/- 1.2% (mean +/- SEM electromagnetic flow probe; p less than 0.005), but did not alter blood flows to the outer cortex (3.7 vs 4.3 ml/min per gram), the inner cortex (2.6 vs 2.7 ml/min per gram), and the other medulla (1.5 vs 1.5 ml/min per gram), which suggests a decrease in nonnutrient flow. In a separate group of animals the effect of reduced blood flow on the nutrient and nonnutrient components was determined by mechanically reducing renal arterial blood flow by 48%. Unlike the ibuprofen group, nutrient blood flows were proportionally reduced with the mechanical decrease in TRBF in the outer cortex (1.9 ml/min per gram, p less than 0.05), the inner cortex (1.4 ml/min per gram, p less than 0.05), and the outer medulla (0.8 ml/min per gram, p less than 0.01). These results indicate no shift between nutrient and nonnutrient compartments. Nutrient and nonnutrient renal blood flows of the left kidney were also determined by 86Rb extraction. After ibuprofen treatment, nonextracted 86Rb decreased to 12.1% from the control value of 15.6% (p less than 0.05). Mechanical reduction of TRBF did not significantly decrease the proportion of unextracted 86Rb (18.7%)

Determination of testicular blood flow in camelids using vascular casting and color pulsed-wave Doppler ultrasonography.

Science.gov (United States)

Kutzler, Michelle; Tyson, Reid; Grimes, Monica; Timm, Karen

2011-01-01

We describe the vasculature of the camelid testis using plastic casting. We also use color pulsed-wave Doppler ultrasonography to measure testicular blood flow and compare the differences between testicular blood flow in fertile and infertile camelids. The testicular artery originates from the ventral surface of the aorta, gives rise to an epididymal branch, and becomes very tortuous as it approaches the testis. Within the supratesticular arteries, peak systolic velocity (PSV) was higher in fertile males compared to infertile males (P = 0.0004). In addition, end diastolic velocity (EDV) within the supratesticular arteries was higher for fertile males when compared to infertile males (P = 0.0325). Within the marginal arteries, PSV was also higher in fertile males compared to infertile males (P = 0.0104). However, EDV within the marginal arteries was not significantly different between fertile and infertile males (P = 0.121). In addition, the resistance index was not significantly different between fertile and infertile males within the supratesticular (P = 0.486) and marginal arteries (P = 0.144). The significance of this research is that in addition to information obtained from a complete reproductive evaluation, a male camelid's fertility can be determined using testicular blood flow measured by Doppler ultrasonography.

Determination of Testicular Blood Flow in Camelids Using Vascular Casting and Color Pulsed-Wave Doppler Ultrasonography

Directory of Open Access Journals (Sweden)

Michelle Kutzler

2011-01-01

Full Text Available We describe the vasculature of the camelid testis using plastic casting. We also use color pulsed-wave Doppler ultrasonography to measure testicular blood flow and compare the differences between testicular blood flow in fertile and infertile camelids. The testicular artery originates from the ventral surface of the aorta, gives rise to an epididymal branch, and becomes very tortuous as it approaches the testis. Within the supratesticular arteries, peak systolic velocity (PSV was higher in fertile males compared to infertile males (P=0.0004. In addition, end diastolic velocity (EDV within the supratesticular arteries was higher for fertile males when compared to infertile males (P=0.0325. Within the marginal arteries, PSV was also higher in fertile males compared to infertile males (P=0.0104. However, EDV within the marginal arteries was not significantly different between fertile and infertile males (P=0.121. In addition, the resistance index was not significantly different between fertile and infertile males within the supratesticular (P=0.486 and marginal arteries (P=0.144. The significance of this research is that in addition to information obtained from a complete reproductive evaluation, a male camelid's fertility can be determined using testicular blood flow measured by Doppler ultrasonography.

Microsphere estimates of blood flow: Methodological considerations

International Nuclear Information System (INIS)

von Ritter, C.; Hinder, R.A.; Womack, W.; Bauerfeind, P.; Fimmel, C.J.; Kvietys, P.R.; Granger, D.N.; Blum, A.L.

1988-01-01

The microsphere technique is a standard method for measuring blood flow in experimental animals. Sporadic reports have appeared outlining the limitations of this method. In this study the authors have systematically assessed the effect of blood withdrawals for reference sampling, microsphere numbers, and anesthesia on blood flow estimates using radioactive microspheres in dogs. Experiments were performed on 18 conscious and 12 anesthetized dogs. Four blood flow estimates were performed over 120 min using 1 x 10 6 microspheres each time. The effects of excessive numbers of microspheres pentobarbital sodium anesthesia, and replacement of volume loss for reference samples with dextran 70 were assessed. In both conscious and anesthetized dogs a progressive decrease in gastric mucosal blood flow and cardiac output was observed over 120 min. This was also observed in the pancreas in conscious dogs. The major factor responsible for these changes was the volume loss due to the reference sample withdrawals. Replacement of the withdrawn blood with dextran 70 led to stable blood flows to all organs. The injection of excessive numbers of microspheres did not modify hemodynamics to a greater extent than did the injection of 4 million microspheres. Anesthesia exerted no influence on blood flow other than raising coronary flow. The authors conclude that although blood flow to the gastric mucosa and the pancreas is sensitive to the minor hemodynamic changes associated with the microsphere technique, replacement of volume loss for reference samples ensures stable blood flow to all organs over a 120-min period

Quantitative blood flow measurements in the small animal cardiopulmonary system using digital subtraction angiography

Energy Technology Data Exchange (ETDEWEB)

Lin Mingde; Marshall, Craig T.; Qi, Yi; Johnston, Samuel M.; Badea, Cristian T.; Piantadosi, Claude A.; Johnson, G. Allan [Department of Radiology, Center for In Vivo Microscopy and Department of Biomedical Engineering, Duke University Medical Center, Box 3302, Durham, North Carolina 27710 (United States); Division of Pulmonary and Critical Care Medicine and Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Box 3823, Durham, North Carolina 27710 (United States); Department of Radiology, Center for In Vivo Microscopy, Duke University Medical Center, Box 3302, Durham, North Carolina 27710 (United States); Department of Radiology, Center for In Vivo Microscopy and Department of Biomedical Engineering, Duke University Medical Center, Box 3302, Durham, North Carolina 27710 (United States); Department of Radiology, Center for In Vivo Microscopy, Duke University Medical Center, Box 3302, Durham, North Carolina 27710 (United States); Division of Pulmonary and Critical Care Medicine and Center for Hyperbaric Medicine and Environmental Physiology, Duke University Medical Center, Box 3823, Durham, North Carolina 27710 (United States); Department of Radiology, Center for In Vivo Microscopy and Department of Biomedical Engineering, Duke University Medical Center, Box 3302, Durham, North Carolina 27710 (United States)

2009-11-15

Purpose: The use of preclinical rodent models of disease continues to grow because these models help elucidate pathogenic mechanisms and provide robust test beds for drug development. Among the major anatomic and physiologic indicators of disease progression and genetic or drug modification of responses are measurements of blood vessel caliber and flow. Moreover, cardiopulmonary blood flow is a critical indicator of gas exchange. Current methods of measuring cardiopulmonary blood flow suffer from some or all of the following limitations--they produce relative values, are limited to global measurements, do not provide vasculature visualization, are not able to measure acute changes, are invasive, or require euthanasia. Methods: In this study, high-spatial and high-temporal resolution x-ray digital subtraction angiography (DSA) was used to obtain vasculature visualization, quantitative blood flow in absolute metrics (ml/min instead of arbitrary units or velocity), and relative blood volume dynamics from discrete regions of interest on a pixel-by-pixel basis (100x100 {mu}m{sup 2}). Results: A series of calibrations linked the DSA flow measurements to standard physiological measurement using thermodilution and Fick's method for cardiac output (CO), which in eight anesthetized Fischer-344 rats was found to be 37.0{+-}5.1 ml/min. Phantom experiments were conducted to calibrate the radiographic density to vessel thickness, allowing a link of DSA cardiac output measurements to cardiopulmonary blood flow measurements in discrete regions of interest. The scaling factor linking relative DSA cardiac output measurements to the Fick's absolute measurements was found to be 18.90xCO{sub DSA}=CO{sub Fick}. Conclusions: This calibrated DSA approach allows repeated simultaneous visualization of vasculature and measurement of blood flow dynamics on a regional level in the living rat.

Quantitative blood flow measurements in the small animal cardiopulmonary system using digital subtraction angiography

International Nuclear Information System (INIS)

Lin Mingde; Marshall, Craig T.; Qi, Yi; Johnston, Samuel M.; Badea, Cristian T.; Piantadosi, Claude A.; Johnson, G. Allan

2009-01-01

Purpose: The use of preclinical rodent models of disease continues to grow because these models help elucidate pathogenic mechanisms and provide robust test beds for drug development. Among the major anatomic and physiologic indicators of disease progression and genetic or drug modification of responses are measurements of blood vessel caliber and flow. Moreover, cardiopulmonary blood flow is a critical indicator of gas exchange. Current methods of measuring cardiopulmonary blood flow suffer from some or all of the following limitations--they produce relative values, are limited to global measurements, do not provide vasculature visualization, are not able to measure acute changes, are invasive, or require euthanasia. Methods: In this study, high-spatial and high-temporal resolution x-ray digital subtraction angiography (DSA) was used to obtain vasculature visualization, quantitative blood flow in absolute metrics (ml/min instead of arbitrary units or velocity), and relative blood volume dynamics from discrete regions of interest on a pixel-by-pixel basis (100x100 μm 2 ). Results: A series of calibrations linked the DSA flow measurements to standard physiological measurement using thermodilution and Fick's method for cardiac output (CO), which in eight anesthetized Fischer-344 rats was found to be 37.0±5.1 ml/min. Phantom experiments were conducted to calibrate the radiographic density to vessel thickness, allowing a link of DSA cardiac output measurements to cardiopulmonary blood flow measurements in discrete regions of interest. The scaling factor linking relative DSA cardiac output measurements to the Fick's absolute measurements was found to be 18.90xCO DSA =CO Fick . Conclusions: This calibrated DSA approach allows repeated simultaneous visualization of vasculature and measurement of blood flow dynamics on a regional level in the living rat.

Viscosity estimation utilizing flow velocity field measurements in a rotating magnetized plasma

International Nuclear Information System (INIS)

Yoshimura, Shinji; Tanaka, Masayoshi Y.

2008-01-01

The importance of viscosity in determining plasma flow structures has been widely recognized. In laboratory plasmas, however, viscosity measurements have been seldom performed so far. In this paper we present and discuss an estimation method of effective plasma kinematic viscosity utilizing flow velocity field measurements. Imposing steady and axisymmetric conditions, we derive the expression for radial flow velocity from the azimuthal component of the ion fluid equation. The expression contains kinematic viscosity, vorticity of azimuthal rotation and its derivative, collision frequency, azimuthal flow velocity and ion cyclotron frequency. Therefore all quantities except the viscosity are given provided that the flow field can be measured. We applied this method to a rotating magnetized argon plasma produced by the Hyper-I device. The flow velocity field measurements were carried out using a directional Langmuir probe installed in a tilting motor drive unit. The inward ion flow in radial direction, which is not driven in collisionless inviscid plasmas, was clearly observed. As a result, we found the anomalous viscosity, the value of which is two orders of magnitude larger than the classical one. (author)

Relation between plasma plume density and gas flow velocity in atmospheric pressure plasma

International Nuclear Information System (INIS)

Yambe, Kiyoyuki; Taka, Shogo; Ogura, Kazuo

2014-01-01

We have studied atmospheric pressure plasma generated using a quartz tube, helium gas, and copper foil electrode by applying RF high voltage. The atmospheric pressure plasma in the form of a bullet is released as a plume into the atmosphere. To study the properties of the plasma plume, the plasma plume current is estimated from the difference in currents on the circuit, and the drift velocity is measured using a photodetector. The relation of the plasma plume density n plu , which is estimated from the current and the drift velocity, and the gas flow velocity v gas is examined. It is found that the dependence of the density on the gas flow velocity has relations of n plu ∝ log(v gas ). However, the plasma plume density in the laminar flow is higher than that in the turbulent flow. Consequently, in the laminar flow, the density increases with increasing the gas flow velocity

Coded ultrasound for blood flow estimation using subband processing

DEFF Research Database (Denmark)

Gran, Fredrik; Udesen, Jesper; Nielsen, Michael bachmann

2007-01-01

This paper further investigates the use of coded excitation for blood flow estimation in medical ultrasound. Traditional autocorrelation estimators use narrow-band excitation signals to provide sufficient signal-to-noise-ratio (SNR) and velocity estimation performance. In this paper, broadband...... coded signals are used to increase SNR, followed by sub-band processing. The received broadband signal, is filtered using a set of narrow-band filters. Estimating the velocity in each of the bands and averaging the results yields better performance compared to what would be possible when transmitting...... a narrow-band pulse directly. Also, the spatial resolution of the narrow-band pulse would be too poor for brightness-mode (B-mode) imaging and additional transmissions would be required to update the B-mode image. In the described approach, there is no need for additional transmissions, because...

Modified Beer-Lambert law for blood flow.

Science.gov (United States)

Baker, Wesley B; Parthasarathy, Ashwin B; Busch, David R; Mesquita, Rickson C; Greenberg, Joel H; Yodh, A G

2014-11-01

We develop and validate a Modified Beer-Lambert law for blood flow based on diffuse correlation spectroscopy (DCS) measurements. The new formulation enables blood flow monitoring from temporal intensity autocorrelation function data taken at single or multiple delay-times. Consequentially, the speed of the optical blood flow measurement can be substantially increased. The scheme facilitates blood flow monitoring of highly scattering tissues in geometries wherein light propagation is diffusive or non-diffusive, and it is particularly well-suited for utilization with pressure measurement paradigms that employ differential flow signals to reduce contributions of superficial tissues.

Proposed method for reconstructing velocity profiles using a multi-electrode electromagnetic flow meter

International Nuclear Information System (INIS)

Kollár, László E; Lucas, Gary P; Zhang, Zhichao

2014-01-01

An analytical method is developed for the reconstruction of velocity profiles using measured potential distributions obtained around the boundary of a multi-electrode electromagnetic flow meter (EMFM). The method is based on the discrete Fourier transform (DFT), and is implemented in Matlab. The method assumes the velocity profile in a section of a pipe as a superposition of polynomials up to sixth order. Each polynomial component is defined along a specific direction in the plane of the pipe section. For a potential distribution obtained in a uniform magnetic field, this direction is not unique for quadratic and higher-order components; thus, multiple possible solutions exist for the reconstructed velocity profile. A procedure for choosing the optimum velocity profile is proposed. It is applicable for single-phase or two-phase flows, and requires measurement of the potential distribution in a non-uniform magnetic field. The potential distribution in this non-uniform magnetic field is also calculated for the possible solutions using weight values. Then, the velocity profile with the calculated potential distribution which is closest to the measured one provides the optimum solution. The reliability of the method is first demonstrated by reconstructing an artificial velocity profile defined by polynomial functions. Next, velocity profiles in different two-phase flows, based on results from the literature, are used to define the input velocity fields. In all cases, COMSOL Multiphysics is used to model the physical specifications of the EMFM and to simulate the measurements; thus, COMSOL simulations produce the potential distributions on the internal circumference of the flow pipe. These potential distributions serve as inputs for the analytical method. The reconstructed velocity profiles show satisfactory agreement with the input velocity profiles. The method described in this paper is most suitable for stratified flows and is not applicable to axisymmetric flows in

Pressure and velocity dependence of flow-type cavitation erosion

CSIR Research Space (South Africa)

Auret, JG

1993-12-01

Full Text Available Previous results on the influence of water pressure and velocity on flow-type cavitations erosion, i.e. an increase in erosion rate with increasing velocity and peaking of erosion rate as a function of pressure, were confirmed by measurements with a...

Assessment of effect of intravitreal ranibizumab injection on the ocular blood flow in patients with neovascular age-related macular degeneration

Directory of Open Access Journals (Sweden)

V. V. Neroev

2014-07-01

Full Text Available Purpose: To evaluate the effect of intravitreal ranibizumab injection on the ocular blood flow in patients with neovascular agerelatedmacular degeneration (AMD.Methods: 35 patients with wet AMD undergone intravitreal 0.5 mg ranibizumab injection. Color Doppler Imaging (CDI and dopplerographywere used to measure hemodynamic parameters including the peak systolic velocity (Vsyst, cm / s, end-diastolic velocity (V diast, cm / s, and resistance index (RI of blood flow in the central retinal artery (CRA, the short posterior ciliary arteries (PCA, and the ophthalmic artery (OA. All patients were examined before and after injection on day 1‑7 and 30 day during the 3‑month follow up period.Results: Before intravitreal injection Vsyst was decreased in short PCA (p<0.05, RI in CRA and in short PCA significantly increased in comparison with normal index in same vessels. The peak systolic velocity in OA, in CRA and in short PCA was not significantly changed. After second injection resistance index in CRA and in short PCA was normalized.Conclusion: There was not impairment of ocular blood flow in retinal and choroidal after monthly intravitreal injection of ranibizumab during the 3‑month follow up period.

Assessment of effect of intravitreal ranibizumab injection on the ocular blood flow in patients with neovascular age-related macular degeneration

Directory of Open Access Journals (Sweden)

V. V. Neroev

2013-01-01

Full Text Available Purpose: To evaluate the effect of intravitreal ranibizumab injection on the ocular blood flow in patients with neovascular agerelatedmacular degeneration (AMD.Methods: 35 patients with wet AMD undergone intravitreal 0.5 mg ranibizumab injection. Color Doppler Imaging (CDI and dopplerographywere used to measure hemodynamic parameters including the peak systolic velocity (Vsyst, cm / s, end-diastolic velocity (V diast, cm / s, and resistance index (RI of blood flow in the central retinal artery (CRA, the short posterior ciliary arteries (PCA, and the ophthalmic artery (OA. All patients were examined before and after injection on day 1‑7 and 30 day during the 3‑month follow up period.Results: Before intravitreal injection Vsyst was decreased in short PCA (p<0.05, RI in CRA and in short PCA significantly increased in comparison with normal index in same vessels. The peak systolic velocity in OA, in CRA and in short PCA was not significantly changed. After second injection resistance index in CRA and in short PCA was normalized.Conclusion: There was not impairment of ocular blood flow in retinal and choroidal after monthly intravitreal injection of ranibizumab during the 3‑month follow up period.

A Comparison Study of Vector Velocity, Spectral Doppler and Magnetic Resonance of Blood Flow in the Common Carotid Artery

DEFF Research Database (Denmark)

Brandt, Andreas Hjelm; Hansen, Kristoffer Lindskov; Ewertsen, Caroline

2018-01-01

Magnetic resonance phase contrast angiography (MRA) is the gold standard for blood flow evaluation. Spectral Doppler ultrasound (SDU) is the first clinical choice, although the method is angle dependent. Vector flow imaging (VFI) is an angle-independent ultrasound method. The aim of the study...

Velocity measurements and identification of the flow pattern of vertical air-water flows with light-beam detectors

International Nuclear Information System (INIS)

Luebbesmeyer, D.; Leoni, B.

1980-07-01

A new detector for measuring fluid velocities in two-phase flows by means of Noise-Analysis (especially Transient-Cross-Correlation-technique) has been developed. The detector utilizes a light-beam which is modulated by changes in the transparency of the two-phase flow. The results of nine measurements for different flow-regimes of vertical air/water-flows are shown. A main topic of these investigations was to answer the question if it is possible to identify the flow-pattern by looking at the shape of different 'Noise-Analytical-functions' (like APSD, CPSD, CCF etc.). The results prove that light-beam sensors are good detectors for fluid-velocity measurements in different flow regimes and in a wide range of fluid velocities starting with values of about 0.08 m/s up to values of 40 m/s. With respect to flow-pattern identification only the time-signals and the shape of the cross-power-density-function (CPSD) seem to be useful. (Auth.)

Modeling and analysis of biomagnetic blood Carreau fluid flow through a stenosis artery with magnetic heat transfer: A transient study.

Science.gov (United States)

Abdollahzadeh Jamalabadi, Mohammad Yaghoub; Daqiqshirazi, Mohammadreza; Nasiri, Hossein; Safaei, Mohammad Reza; Nguyen, Truong Khang

2018-01-01

We present a numerical investigation of tapered arteries that addresses the transient simulation of non-Newtonian bio-magnetic fluid dynamics (BFD) of blood through a stenosis artery in the presence of a transverse magnetic field. The current model is consistent with ferro-hydrodynamic (FHD) and magneto-hydrodynamic (MHD) principles. In the present work, blood in small arteries is analyzed using the Carreau-Yasuda model. The arterial wall is assumed to be fixed with cosine geometry for the stenosis. A parametric study was conducted to reveal the effects of the stenosis intensity and the Hartman number on a wide range of flow parameters, such as the flow velocity, temperature, and wall shear stress. Current findings are in a good agreement with recent findings in previous research studies. The results show that wall temperature control can keep the blood in its ideal blood temperature range (below 40°C) and that a severe pressure drop occurs for blockages of more than 60 percent. Additionally, with an increase in the Ha number, a velocity drop in the blood vessel is experienced.

Phase Resolved Angular Velocity Control of Cross Flow Turbines

Science.gov (United States)

Strom, Benjamin; Brunton, Steven; Polagye, Brian

2015-11-01

Cross flow turbines have a number of operational advantages for the conversion of kinetic energy in marine or fluvial currents, but they are often less efficient than axial flow devices. Here a control scheme is presented in which the angular velocity of a cross flow turbine with two straight blades is prescribed as a function of azimuthal blade position, altering the time-varying effective angle of attack. Flume experiments conducted with a scale model turbine show approximately an 80% increase in turbine efficiency versus optimal constant angular velocity and constant resistive torque control schemes. Torque, drag, and lateral forces on one- and two-bladed turbines are analyzed and interpreted with bubble flow visualization to develop a simple model that describes the hydrodynamics responsible for the observed increase in mean efficiency. Challenges associated with implementing this control scheme on commercial-scale devices are discussed. If solutions are found, the performance increase presented here may impact the future development of cross flow turbines.

Calculation of afterbody flows with a composite velocity formulation

Science.gov (United States)

Swanson, R. C.; Rubin, S. G.; Khosla, P. K.

1983-01-01

A recently developed technique for numerical solution of the Navier-Stokes equations for subsonic, laminar flows is investigated. It is extended here to allow for the computation of transonic and turbulent flows. The basic approach involves a multiplicative composite of the appropriate velocity representations for the inviscid and viscous flow regions. The resulting equations are structured so that far from the surface of the body the momentum equations lead to the Bernoulli equation for the pressure, while the continuity equation reduces to the familiar potential equation. Close to the body surface, the governing equations and solution techniques are characteristic of those describing interacting boundary layers. The velocity components are computed with a coupled strongly implicity procedure. For transonic flows the artificial compressibility method is used to treat supersonic regions. Calculations are made for both laminar and turbulent flows over axisymmetric afterbody configurations. Present results compare favorably with other numerical solutions and/or experimental data.