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Ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery in clinical research.

ABSTRACT: The vascular endothelium is a monolayer of cells that cover the interior of blood vessels and provide both structural and functional roles. The endothelium acts as a barrier, preventing leukocyte adhesion and aggregation, as well as controlling permeability to plasma components. Functionally, the endothelium affects vessel tone. Endothelial dysfunction is an imbalance between the chemical species which regulate vessel tone, thombroresistance, cellular proliferation and mitosis. It is the first step in atherosclerosis and is associated with coronary artery disease, peripheral artery disease, heart failure, hypertension, and hyperlipidemia. The first demonstration of endothelial dysfunction involved direct infusion of acetylcholine and quantitative coronary angiography. Acetylcholine binds to muscarinic receptors on the endothelial cell surface, leading to an increase of intracellular calcium and increased nitric oxide (NO) production. In subjects with an intact endothelium, vasodilation was observed while subjects with endothelial damage experienced paradoxical vasoconstriction. There exists a non-invasive, in vivo method for measuring endothelial function in peripheral arteries using high-resolution B-mode ultrasound. The endothelial function of peripheral arteries is closely related to coronary artery function. This technique measures the percent diameter change in the brachial artery during a period of reactive hyperemia following limb ischemia. This technique, known as endothelium-dependent, flow-mediated vasodilation (FMD) has value in clinical research settings. However, a number of physiological and technical issues can affect the accuracy of the results and appropriate guidelines for the technique have been published. Despite the guidelines, FMD remains heavily operator dependent and presents a steep learning curve. This article presents a standardized method for measuring FMD in the brachial artery on the upper arm and offers suggestions to reduce intra-operator variability.

SUBMITTER: Alley H

PROVIDER: S-EPMC4353419 | biostudies-literature | 2014 Oct

REPOSITORIES: biostudies-literature

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Ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery in clinical research.

Alley Hugh H Owens Christopher D CD Gasper Warren J WJ Grenon S Marlene SM

Journal of visualized experiments : JoVE 20141022 92

The vascular endothelium is a monolayer of cells that cover the interior of blood vessels and provide both structural and functional roles. The endothelium acts as a barrier, preventing leukocyte adhesion and aggregation, as well as controlling permeability to plasma components. Functionally, the endothelium affects vessel tone. Endothelial dysfunction is an imbalance between the chemical species which regulate vessel tone, thombroresistance, cellular proliferation and mitosis. It is the first s ...[more]

PMID: 25406739

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Project description:Many stroke survivors have reduced cardiorespiratory fitness as a result of their stroke. Ischemic conditioning (IC) is a noninvasive, cost-effective, easy-to-administer intervention that can be performed at home and has been shown to improve both motor function in stroke survivors and vascular endothelial function in healthy individuals. In this study, we examined the effects of 2 wk of remote IC (RIC) on brachial artery flow mediated dilation (FMD) in chronic stroke survivors. We hypothesized that FMD would be improved following RIC compared with a sham RIC control group. This was a prospective, randomized, double-blinded, controlled study. Twenty-four chronic stroke survivors (>6 mo after stroke) were enrolled and randomized to receive either RIC or sham RIC on their affected thigh every other day for 2 wk. For the RIC group, a blood pressure cuff was inflated to 225 mmHg for 5 min, followed by 5 min of recovery, and repeated a total of five times per session. For the sham RIC group, the inflation pressure was 10 mmHg. Brachial artery FMD was assessed on the nonaffected arm at study enrollment and following the 2-wk intervention period. Nine men and fourteen women completed all study procedures. Brachial artery FMD increased from 5.4 ± 4.8 to 7.8 ± 4.4% (P = 0.030; n = 12) in the RIC group, while no significant change was observed in the sham RIC group (3.5 ± 3.9% pretreatment versus 2.4 ± 3.1% posttreatment; P = 0.281, n = 11). Two weeks of RIC increases brachial artery FMD in chronic stroke survivors.NEW & NOTEWORTHY In this study, we report that 2 wk of remote ischemic conditioning (RIC) improves brachial artery flow-mediated dilation in chronic stroke survivors. Because poor cardiovascular health puts stroke survivors at a heightened risk for recurrent stroke and other cardiovascular events, an intervention that is simple, cost-effective, and easy to perform like RIC holds promise as a means to improve cardiovascular health in this at-risk population.

Project description:ObjectiveTo investigate the association between sympathetic activity, reactive hyperemia and brachial artery flow-mediated dilation (FMD).BackgroundIt is claimed that major surgery has an impact on endothelial function, as observed by post-operative reduced brachial artery FMD response. However, another explanation for the observed reduced FMD response post-operatively may be sympathetic stress-induced reduction in blood flow.MethodsSeventeen healthy volunteers with a median age (25th-75th percentiles) of 23.5 (23-24.8) years were recruited. Participants' brachial blood flow and FMD response were measured (i) during normal non-stress conditions (Normal1); (ii) during exposure to ice water; and (iii) afterwards, under normal non-stress conditions (Normal2). We continuously measured arterial blood pressure (Finometer), heart rate (ECG), skin blood flow of the index finger (laser Doppler), and brachial artery blood flow and diameter (Ultrasound Doppler). Measurements were taken at baseline; before a 5-min suprasystolic forearm occlusion; and following a 3-min post-occlusion, to measure reactive hyperemia and FMD.ResultsMedian (25th-75th percentiles) FMD response after exposure to ice water was reduced compared to non-stress conditions [4.9 (2.9-8.4) % during ice water vs. 9.7 (7.6-12.2) % Normal1 and 9.7 (6.4-10.3) % Normal2, P < 0.001]. Blood flow 60 s after cuff-deflation during ice water exposure was significantly reduced to 328 (289-421) mL compared to non-stress conditions (both P < 0.05). No differences were observed between Normal1 [446 (359-506) mL] and Normal2 [455 (365-515) mL] (both P > 0.05). Heart rate significantly increased during ice water exposure [67 (59-69) beats/min)] compared to 55 (49-60) beats/min during Normal1 and 54 (47-60) beats/min during Normal2 (both P < 0.05). MAP did not change during Normal1 [72 (64-84)] or during Normal2 [71 (65-81) mm Hg] (both P > 0.05), but increased to 86 (75-98) mm Hg during ice water exposure (P < 0.05).ConclusionsIncreased sympathetic activity resulted in decreased blood flow and brachial artery FMD response in healthy volunteers, independent of endothelial dysfunction. Future studies should adjust for blood flow when interpreting the FMD response.

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Ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery in clinical research.

Publications

Ultrasound assessment of endothelial-dependent flow-mediated vasodilation of the brachial artery in clinical research.

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