Influence of prior anterograde shear rate exposure on exercise-induced brachial artery dilation

Abstract

Shear rate can elicit substantial adaptations to vascular endothelial function. Recent studies indicate that prior exposure to anterograde flow and shear increases endothelium-dependent flow-mediated dilation at rest and that anterograde shear can create an anti-atherosclerotic and provasodilatory state. The primary aim of the present study was therefore to determine the effects of prior exposure to anterograde shear on exercise-induced brachial artery dilation, total forearm blood flow (FBF), and vascular conductance (FVC) during dynamic handgrip exercise. Eight men completed a constant-load exercise test corresponding to 10% maximal voluntary contraction, prior to (baseline) and following a 40 min shear rate intervention (post-SRI) achieved via unilateral forearm heating, which has previously been shown to increase anterograde shear rate in the brachial artery. During the SRI, anterograde shear rate increased 60.9 ± 29.2 sec(-1) above baseline (P < 0.05). Post-SRI, the exercise-induced brachial artery vasodilation was significantly increased compared to baseline (4.1 ± 0.7 vs. 4.3 ± 0.6 mm, P < 0.05). Post-SRI FBF mean response time (33.2 ± 16.0 vs. 23.0 ± 11.8 sec, P < 0.05) and FVC mean response time (31.1 ± 12.8 20.2 ± 10.7 sec, P < 0.05) at exercise onset were accelerated compared to baseline. These findings demonstrate that prior exposure to anterograde shear rate increases the vascular responses to exercise and supports the possible beneficial effects of anterograde shear rate in vivo.

Keywords: Blood Flow; exercise; shear rate.

Figure 1

Mean, anterograde (+sr), retrograde (−sr) shear rates in the brachial artery prior to (pre-SRI), and during the shear rate intervention (SRI) elicited via unilateral limb heating. Mean and anterograde shear rate were significantly increased and retrograde shear rate significantly decreased compared to pre-SRI values. The*indicates significant difference versus pre-SRI, P < 0.05. Error bars represent SE.

Figure 2

Effects of the 40 min shear rate intervention (SRI) on exercise responses. (A)The post-SRI mean response time for forearm blood flow (MRT_FBF) and (B) forearm vascular conductance (MRT_FVC) were significantly faster compared to pre-SRI. (C) The exercise-induced brachial artery vasodilation was significantly greater post- SRI compared to pre-SRI. The *indicates significant difference versus pre-SRI, P < 0.05. Error bars represent SE.