Abstract
In animal and in-vitro models, increased oscillatory shear stress characterized by increased retrograde shear-rate (SR) is associated with acutely decreased endothelial cell function. While previous research suggests a possible detrimental role of elevated retrograde SR on endothelial-function in the brachial artery in humans, little research has been conducted examining arteries in the leg. Examinations of altered shear pattern in the superficial femoral artery (SFA) are important, as this vessel is both prone to atherosclerosis and leg exercise is a common form of activity in humans. Seven healthy men participated; bilateral endothelial-function was assessed via flow-mediated-dilation (FMD) before and after 30-minute unilateral inflations of a thigh blood pressure cuff to either 75 mmHg or 100 mmHg on two separate visits. Inflation of the cuff induced increases in maximum anterograde (p<0.05), maximum retrograde (p<0.01), and oscillatory shear index (OSI) (p<0.001) in the cuffed leg at both inflation pressures. At 100 mmHg the increases in SR were larger in the retrograde than the anterograde direction evidenced by a decrease in mean SR (p<0.01). There was an acute decrease in relative FMD in the cuffed leg alone following inflation to both pressures. These results indicate that in the SFA, altered SR profiles incorporating increased retrograde and OSI influence the attenuation in FMD after a 30-minute unilateral thigh-cuff inflation intervention. Novel information highlighting the importance of OSI calculations and assessments of flow profiles add to current body of knowledge regarding the influence of changes in SR patterns on FMD. Findings from the current study may provide additional insight when designing strategies to combat impaired vascular function in the lower extremity where blood vessels are more prone to atherosclerosis in comparison to the upper extremity.
Highlights
Endothelial dysfunction is widely accepted as a precursor to the development of atherosclerosis, may contribute to later stage cardiovascular disease (CVD) [1], and is predictive of cardiovascular events in healthy individuals as well as in those with existing CVD [2]
A recent study in humans examined the shape of anterograde and retrograde blood velocity profiles through the femoral artery using the relationship between mean (MBV) and peak (PBV) blood velocity across the vessel lumen; they defined a parabolic velocity when mean velocity is half the peak velocity (MBV/PBV 50.5) [9]
They found mean, anterograde, and retrograde profiles were parabolic in shape at rest (i.e. MBV/PBV ratio not different from 0.5). These findings suggest calculations of mean, anterograde, and retrograde SR are acceptable approximations when evaluating endothelial function via flowmediated dilation (FMD), and when examining resting SR patterns
Summary
Endothelial dysfunction is widely accepted as a precursor to the development of atherosclerosis, may contribute to later stage cardiovascular disease (CVD) [1], and is predictive of cardiovascular events in healthy individuals as well as in those with existing CVD [2]. A recent study in humans examined the shape of anterograde and retrograde blood velocity profiles through the femoral artery using the relationship between mean (MBV) and peak (PBV) blood velocity across the vessel lumen; they defined a parabolic velocity when mean velocity is half the peak velocity (MBV/PBV 50.5) [9]. They found mean, anterograde, and retrograde profiles were parabolic in shape at rest (i.e. MBV/PBV ratio not different from 0.5) These findings suggest calculations of mean, anterograde, and retrograde SR are acceptable approximations when evaluating endothelial function via flowmediated dilation (FMD), and when examining resting SR patterns
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