Impact of shear rate modulation on vascular function in humans

Abstract

Shear stress is an important stimulus to arterial adaptation in response to exercise and training in humans. We recently observed significant reverse arterial flow and shear during exercise and different antegrade/retrograde patterns of shear and flow in response to different types of exercise. The purpose of this study was to simultaneously examine flow-mediated dilation, a largely NO-mediated vasodilator response, in both brachial arteries of healthy young men before and after 30-minute interventions consisting of bilateral forearm heating, recumbent leg cycling, and bilateral handgrip exercise. During each intervention, a cuff inflated to 60 mm Hg was placed on 1 arm to unilaterally manipulate the shear rate stimulus. In the noncuffed arm, antegrade flow and shear increased similarly in response to each intervention (ANOVA; P<0.001, no interaction between interventions; P=0.71). Baseline flow-mediated dilation (4.6%, 6.9%, and 6.7%) increased similarly in response to heating, handgrip, and cycling (8.1%, 10.4%, and 8.9%, ANOVA; P<0.001, no interaction; P=0.89). In contrast, cuffed arm antegrade shear rate was lower than in the noncuffed arm for all of the conditions (P<0.05), and the increase in flow-mediated dilation was abolished in this arm (4.7%, 6.7%, and 6.1%; 2-way ANOVA: all conditions interacted P<0.05). These results suggest that differences in the magnitude of antegrade shear rate transduce differences in endothelial vasodilator function in humans, a finding that may have relevance for the impact of different exercise interventions on vascular adaptation in humans.

Conflict of interest statement

Disclosures:

None of the authors have conflict to disclosure

Figures

FIGURE 1

Shear rate pattern (SR; mean, antegrade and retrograde shear rate) during heating (black bars), handgrip (white bars) and recumbent leg cycling (grey bars) in healthy young men (n=10) in the non cuffed arm. A 1-way ANOVA was used to examine differences between the 3 interventions for mean SR, while a 2-way ANOVA was utilized to examine the differences in blood flow pattern (antegrade – retrograde SR) between the 3 interventions. *Post hoc significantly different from forearm heating. Error bars represent SE.

FIGURE 2

Flow-mediated dilation (FMD) before (black) and after (grey) heating, handgrip and recumbent leg cycling in healthy young men (n=10) in the non cuffed arm. A 2-way repeated measures ANOVA was used to examine the impact of the interventions on FMD (main effect) and whether the change in FMD differed among the 3 interventions (interaction). *Post-hoc significant from pre-intervention. Error bars represent SE.

FIGURE 3

Mean shear rate and shear rate pattern during the intervention (+ve; antegrade shear rate, −ve; retrograde shear rate) and flow-mediated dilation (FMD) before and after the intervention is presented for the non cuffed (grey bars) and cuffed arms (white bars). Data is presented for forearm heating (A), handgrip (B) and recumbent leg cycling (C) in healthy young men (n=10). Mean and pattern of shear between the non cuffed and cuffed arm during each intervention is tested with a paired t-test (*P<0.05). A 2-way ANOVA is used to examine whether cuff placement influenced the change in FMD upon the 30-min intervention (*Post-hoc significant between pre- and post-intervention). Error bars represent SE.

FIGURE 4

Endothelium-independent vasodilation examined using glyceryl trinitrate (GTN) before and after the intervention is presented for the non cuffed (black bars) and cuffed arms (white bars). Data is presented for forearm heating (A), handgrip (B) and recumbent leg cycling (C) in healthy young men (n=6). A 2-way ANOVA did not find an effect of the intervention of the GTN-response in the non cuffed or cuffed arm. Error bars represent SE.