scholarly journals The Importance of Velocity Acceleration to Flow-Mediated Dilation

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Lee Stoner ◽  
Joanna M. Young ◽  
Simon Fryer ◽  
Manning J. Sabatier
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Vascular Tone ◽  
Cardiac Cycle ◽  
Blood Velocity ◽  
Rate Of Change ◽  
Flow Mediated Dilation ◽  
Flow Pulsatility ◽  
Poiseuille's Law ◽  
Poiseuille’S Law

The validity of the flow-mediated dilation test has been questioned due to the lack of normalization to the primary stimulus, shear stress. Shear stress can be calculated using Poiseuille's law. However, little attention has been given to the most appropriate blood velocity parameter(s) for calculating shear stress. The pulsatile nature of blood flow exposes the endothelial cells to two distinct shear stimuli during the cardiac cycle: a large rate of change in shear at the onset of flow (velocity acceleration), followed by a steady component. The parameter typically entered into the Poiseuille's law equation to determine shear stress is time-averaged blood velocity, with no regard for flow pulsatility. This paper will discuss (1) the limitations of using Posieuille's law to estimate shear stress and (2) the importance of the velocity profile—with emphasis on velocity acceleration—to endothelial function and vascular tone.

Serial assessment of local peripheral vascular function after eccentric exercise

2013 ◽  
Vol 38 (12) ◽  
pp. 1181-1186 ◽  
Author(s):  
Mitchel R. Stacy ◽  
Kallie J. Bladon ◽  
Jennifer L. Lawrence ◽  
Sarah A. McGlinchy ◽  
Barry W. Scheuermann
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Muscle Damage ◽  
Eccentric Exercise ◽  
Vascular Function ◽  
Muscle Blood Flow ◽  
Isometric Strength ◽  
Flow Mediated Dilation ◽  
Vascular Responses ◽  
Study Results

Muscle damage is a common response to unaccustomed eccentric exercise; however, the effects of skeletal muscle damage on local vascular function and blood flow are poorly understood. This study examined serial local vascular responses to flow-mediated (endothelial-dependent) and nitroglycerin-mediated (endothelial-independent) dilation in the brachial artery after strenuous eccentric exercise and serially assessed resting blood flow. Ten healthy males performed 50 maximal eccentric unilateral arm contractions to induce muscle damage to the biceps brachii. Changes in maximal isometric strength and vascular responses were assessed 1, 24, 48, and 96 h after exercise. Mean blood velocities and arterial diameters, measured with Doppler ultrasound, were used to calculate blood flow and shear stress (expressed as area under the curve). Eccentric exercise resulted in impaired maximal isometric strength for up to 96 h (p < 0.001). Reductions in flow-mediated dilation (before exercise, 9.4% ± 2.6%; 1 h after exercise, 5.1% ± 2.2%) and nitroglycerin responses (before exercise, 26.3% ± 6.5%; 1 h after exercise, 20.7% ± 4.7%) were observed in the 1 h after exercise and remained lower for 96 h (p < 0.05). The shear stress response was attenuated immediately after exercise and remained impaired for 48 h (p < 0.05). Resting blood pressure and muscle blood flow remained similar throughout the study. Results suggest that muscle damage from eccentric exercise leads to impaired local endothelial and vascular smooth muscle function. Lower shear stress after exercise might contribute to the observed reduction in flow-mediated dilation responses, but the mechanism responsible for the attenuated endothelial-independent vasodilation remains unclear.

Abstract P152: Low Memory Recall And High Common Carotid Artery Flow Pulsatility In Non-Dialysis Chronic Kidney Disease Patients

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Ninette Shenouda ◽  
Nicholas Chouramanis ◽  
Matthew Cohen ◽  
Raymond R Townsend ◽  
David G Edwards
Keyword(s):  
Chronic Kidney Disease ◽  
Blood Flow ◽  
Executive Function ◽  
Kidney Disease ◽  
Episodic Memory ◽  
Pulsatility Index ◽  
Verbal Learning ◽  
Blood Velocity ◽  
Memory Recall ◽  
Flow Pulsatility

A significant proportion of patients with non-dialysis chronic kidney disease (CKD) present with mild-to-moderate deficits in the cognitive domains of executive function and episodic memory. Excess blood flow pulsatility is damaging to the microvasculature of high-flow, low-resistance organs like the brain and may contribute to the cognitive deficits prevalent among CKD patients. We tested the hypothesis that patients with moderate-to-severe non-dialysis CKD have excess flow pulsatility along their carotid and cerebral vasculature that is associated with deficits in executive function and episodic memory. We recruited 10 non-dialysis CKD patients (age=68±8 yrs; estimated glomerular filtration rate, eGFR=36±18 mL/min/1.73 m 2 ) and 7 healthy age-matched adults (age=65±5 yrs; eGFR=81±17 mL/min/1.73 m 2 ). Global cognitive function was assessed with the Montreal Cognitive Assessment (MoCA). Executive function and episodic memory were assessed using the NIH Toolbox Flanker Inhibitory Control and Attention Test and California Verbal Learning Test III, respectively, and reported as standardized scores (mean=100, SD=15). Pulsatility index [(systolic blood velocity - diastolic blood velocity)/ mean blood velocity] was measured in the common carotid (CCA), internal carotid (ICA), and middle cerebral arteries (MCA) via Doppler and transcranial Doppler ultrasound. Compared to healthy adults, CKD patients did not differ in total brain blood flow (p=0.42) but had lower MoCA (CKD=26±3, Healthy=29±1; p=0.01) and memory recall scores (CKD=92±21, Healthy=110±9; p=0.05). CKD patients did not differ from our healthy control group in executive function (CKD=91±10, Healthy=90±11; p=0.80) but did produce a mean score that was 0.6 SD lower than the NIH Toolbox reference sample. CKD patients had a higher pulsatility index in the CCA (CKD=2.3±0.5, Healthy=1.9±0.3; p=0.05) but not in the ICA (p=0.68) or MCA (p=0.57). CCA pulsatility index was strongly and inversely associated with episodic memory recall scores (r=-0.64, p<0.01, n=17). This data suggests that although the higher CCA flow pulsatility in non-dialysis CKD patients does not appear to be transmitted to the cerebrovasculature, it nevertheless may still be contributing to memory impairments.

scholarly journals Blood flow and coherent vortices in the normal and aneurysmatic aortas: a fluid dynamical approach to intra-luminal thrombus formation

2011 ◽  
Vol 8 (63) ◽  
pp. 1449-1461 ◽  
Author(s):  
Jacopo Biasetti ◽  
Fazle Hussain ◽  
T. Christian Gasser
Keyword(s):  
Fluid Dynamics ◽  
Blood Flow ◽  
Shear Stress ◽  
Cardiac Cycle ◽  
Thrombus Formation ◽  
Aortic Aneurysms ◽  
Patient Specific ◽  
Clear Correlation ◽  
Complex Flow ◽  
Dynamics Simulations

Abdominal aortic aneurysms (AAAs) are frequently characterized by the development of an intra-luminal thrombus (ILT), which is known to have multiple biochemical and biomechanical implications. Development of the ILT is not well understood, and shear–stress-triggered activation of platelets could be the first step in its evolution. Vortical structures (VSs) in the flow affect platelet dynamics, which motivated the present study of a possible correlation between VS and ILT formation in AAAs. VSs educed by the λ 2 -method using computational fluid dynamics simulations of the backward-facing step problem, normal aorta, fusiform AAA and saccular AAA were investigated. Patient-specific luminal geometries were reconstructed from computed tomography scans, and Newtonian and Carreau–Yasuda models were used to capture salient rheological features of blood flow. Particularly in complex flow domains, results depended on the constitutive model. VSs developed all along the normal aorta, showing that a clear correlation between VSs and high wall shear stress (WSS) existed, and that VSs started to break up during late systole. In contrast, in the fusiform AAA, large VSs developed at sites of tortuous geometry and high WSS, occupying the entire lumen, and lasting over the entire cardiac cycle. Downward motion of VSs in the AAA was in the range of a few centimetres per cardiac cycle, and with a VS burst at that location, the release (from VSs) of shear-stress-activated platelets and their deposition to the wall was within the lower part of the diseased artery, i.e. where the thickest ILT layer is typically observed. In the saccular AAA, only one VS was found near the healthy portion of the aorta, while in the aneurysmatic bulge, no VSs occurred. We present a fluid-dynamics-motivated mechanism for platelet activation, convection and deposition in AAAs that has the potential of improving our current understanding of the pathophysiology of fluid-driven ILT growth.

Distinct contributions of skin and core temperatures to flow-mediated dilation of the brachial artery following passive heating

2020 ◽  
Author(s):  
Geoff B. Coombs ◽  
Joshua C. Tremblay ◽  
Daria A. Shkredova ◽  
Jay M.J.R. Carr ◽  
Denis J. Wakeham ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Skin Temperature ◽  
Brachial Artery ◽  
Whole Body ◽  
Flow Mediated Dilation ◽  
Dependent Manner ◽  
Esophageal Temperature ◽  
Passive Heating ◽  
Time Control

We measured acute vascular responses to heat stress to examine the hypothesis that macrovascular endothelial-dependent dilation is improved in a shear-dependent manner, which is further modified by skin temperature. Twelve healthy males performed whole-body heating (+1.5°C esophageal temperature), bilateral forearm heating (~38°C skin temperature), and a time-matched (~60 min) control condition on separate days in counterbalanced order. Bilateral assessments of blood flow and brachial artery flow-mediated dilation (FMD) were performed before and 10 min after each condition protocols with duplex Doppler ultrasound. To isolate the influence of shear stress, a pneumatic cuff was inflated (~90 mmHg) around the right forearm during each condition to attenuate heat-induced rises in blood flow and shear stress. After forearm heating, FMD increased [cuffed: 4.7 (2.9) to 6.8 (1.5)%, non-cuffed: 5.1 (2.8) to 6.4 (2.6)%] in both arms (time P<0.01). Whole-body heating also increased FMD in the non-cuffed arm from 3.6 (2.2) to 9.2 (3.2)% and in the cuffed arm from to 5.6 (3.0)% to 8.6 (4.9)% (time P<0.01). After the time control, FMD decreased [cuffed: 6.3 (2.4) to 4.7 (2.2)%, non-cuffed: 6.1 (3.0) to 4.5 (2.6)%] in both arms (time P=0.03). Multiple linear regression (adjusted r2=0.263, P=0.003) revealed that changes in esophageal temperature, skin temperatures, and heart rate explained the majority of the variance in this model (34%, 31% and 21%, respectively). Our findings indicate that, in addition to shear stress, skin and core temperatures are likely important contributors to passive heating-induced vascular adaptations.

The impact of acute mental stress on brachial artery flow-mediated dilation differs when shear stress is elevated by reactive hyperemia versus handgrip exercise

2013 ◽  
Vol 38 (5) ◽  
pp. 498-506 ◽  
Author(s):  
Ingrid C. Szijgyarto ◽  
Trevor J. King ◽  
Jennifer Ku ◽  
Veronica J. Poitras ◽  
Brendon J. Gurd ◽  
...  
Keyword(s):  
Shear Stress ◽  
Brachial Artery ◽  
Mental Stress ◽  
Stress Reactivity ◽  
Reactive Hyperemia ◽  
Blood Velocity ◽  
Flow Mediated Dilation ◽  
Handgrip Exercise ◽  
Stress Task ◽  
The Impact

Acute mental stress can impair brachial artery (BA) flow-mediated dilation (FMD) in response to reactive hyperemia (RH) induced increases in shear stress. Handgrip exercise (HGEX) is emerging as a useful tool to increase shear stress for FMD assessment; however, the impact of acute mental stress on HGEX-FMD is unknown. The purpose of this study was to determine whether acute mental stress attenuates RH- and HGEX-induced BA-FMD to a similar extent. In 2 counterbalanced visits, 16 healthy males (19–27 years of age) performed RH-FMD or HGEX-FMD tests after a counting control task (prestress FMD) and a speech and arithmetic stress task (poststress FMD). BA diameter and mean blood velocity were assessed with echo and Doppler ultrasound, respectively. Shear stress was estimated using shear rate (SR = BA blood velocity/BA diameter). Mean arterial pressure (MAP), heart rate (HR), and salivary cortisol were used to assess stress reactivity. Results are expressed as mean ± SE. The stress task elevated MAP (Δ24.0 ± 2.6 mm Hg) and HR (Δ15.5 ± 1.9 beats·min–1), but not cortisol (prestress vs. poststress: 4.4 ± 0.7 nmol·L–1 vs. 4.7 ± 0.7 nmol·L–1; p = 0.625). There was no difference between the pre- and poststress SR stimulus for RH (p = 0.115) or HGEX (p = 0.664). RH-FMD decreased from 5.2% ± 0.6% prestress to 4.1% ± 0.5% poststress (p = 0.071); however, stress did not attenuate HGEX-FMD (prestress vs. poststress: 4.1% ± 0.6% vs. 5.3% ± 0.6%; p = 0.154). The pre- to poststress change in FMD was significantly different in the RH-FMD vs. the HGEX-FMD test (–1.1% ± 0.6% vs. +1.1% ± 0.8%; p = 0.015). In conclusion, acute mental stress appears to have a disparate impact on FMD stimulated by RH vs. HGEX induced increases in shear stress.

scholarly journals FloWave.US: validated, open-source, and flexible software for ultrasound blood flow analysis

2016 ◽  
Vol 121 (4) ◽  
pp. 849-857 ◽  
Author(s):  
Crystal L. Coolbaugh ◽  
Emily C. Bush ◽  
Charles F. Caskey ◽  
Bruce M. Damon ◽  
Theodore F. Towse
Keyword(s):  
Blood Flow ◽  
Muscle Contraction ◽  
Open Source ◽  
Cardiac Cycle ◽  
Flow Analysis ◽  
Vessel Diameter ◽  
Blood Velocity ◽  
Lower Extremity Muscle ◽  
Blood Flow Analysis

Automated software improves the accuracy and reliability of blood velocity, vessel diameter, blood flow, and shear rate ultrasound measurements, but existing software offers limited flexibility to customize and validate analyses. We developed FloWave.US —open-source software to automate ultrasound blood flow analysis—and demonstrated the validity of its blood velocity (aggregate relative error, 4.32%) and vessel diameter (0.31%) measures with a skeletal muscle ultrasound flow phantom. Compared with a commercial, manual analysis software program, FloWave.US produced equivalent in vivo cardiac cycle time-averaged mean (TAMean) velocities at rest and following a 10-s muscle contraction (mean bias <1 pixel for both conditions). Automated analysis of ultrasound blood flow data was 9.8 times faster than the manual method. Finally, a case study of a lower extremity muscle contraction experiment highlighted the ability of FloWave.US to measure small fluctuations in TAMean velocity, vessel diameter, and mean blood flow at specific time points in the cardiac cycle. In summary, the collective features of our newly designed software—accuracy, reliability, reduced processing time, cost-effectiveness, and flexibility—offer advantages over existing proprietary options. Further, public distribution of FloWave.US allows researchers to easily access and customize code to adapt ultrasound blood flow analysis to a variety of vascular physiology applications.

scholarly journals Comparison of Exercise-induce Endothelial Shear Stress Between Poiseuille’S Law and Womersley’S Approximation

2018 ◽  
Vol 50 (5S) ◽  
pp. 181
Author(s):  
Francisco J. Morales ◽  
Brycen J. Ratcliffe ◽  
Caleb D. Harrison ◽  
Evan J. Bockover ◽  
Sierra Crowe ◽  
...  
Keyword(s):  
Shear Stress ◽  
Poiseuille's Law ◽  
Endothelial Shear Stress ◽  
Poiseuille’S Law

Characterization of blood flow patterns and endothelial shear stress during flow‐mediated dilation

2019 ◽  
Vol 39 (4) ◽  
pp. 240-245
Author(s):  
Francisco Morales‐Acuna ◽  
Luis Ochoa ◽  
Carolina Valencia ◽  
Alvaro N. Gurovich
Keyword(s):  
Blood Flow ◽  
Shear Stress ◽  
Flow Patterns ◽  
Flow Mediated Dilation ◽  
Endothelial Shear Stress ◽  
Blood Flow Patterns

scholarly journals Computational analysis of aortic haemodynamics in the presence of ascending aortic aneurysm

2021 ◽  
pp. 1-14
Author(s):  
Aleksandra Petuchova ◽  
Algirdas Maknickas
Keyword(s):  
Blood Flow ◽  
Aortic Aneurysm ◽  
Computational Analysis ◽  
Aortic Wall ◽  
Cardiac Cycle ◽  
Vascular Wall ◽  
Blood Velocity ◽  
Oscillatory Shear Index ◽  
Ascending Aortic Aneurysm ◽  
Haemodynamic Parameters

BACKGROUND: The usefulness of numerical modelling of a patient’s cardiovascular system is growing in clinical treatment. Understanding blood flow mechanics can be crucial in identifying connections between haemodynamic factors and aortic wall pathologies. OBJECTIVE: This work investigates the haemodynamic parameters of an ascending aorta and ascending aortic aneurysm in humans. METHODS: Two aortic models were constructed from medical images using the SimVascular software. FEM blood flow modelling of cardiac cycle was performed using CFD and CMM-FSI at different vascular wall parameters. RESULTS: The results showed that highest blood velocity was 1.18 m/s in aorta with the aneurysm and 1.9 m/s in healthy aorta model. The largest displacements ware in the aorta with the aneurysm (0.73 mm). In the aorta with the aneurysm, time averaged WSS values throughout the artery range from 0 Pa to 1 Pa. In the healthy aorta, distribution of WSS values changes from 0.3 Pa to 0.6 Pa. CONCLUSIONS: In the case of an ascending aortic aneurysm, the maximum blood velocity was found to be 1.6 times lower than in the healthy aorta. The aneurysm-based model demonstrates a 45% greater wall displacement, while the oscillatory shear index decreased by 30% compared to healthy aortic results.

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