Episodic bouts of hyperaemia and shear stress improve arterial blood flow and endothelial function

Exercise and heat stress lead to systemic improvements in arterial endothelial function, vascular stiffness, and cardiopulmonary capacity. The improvements in endothelial function may be primarily mediated via increases in shear stress. This study examined whether improvements in arterial function may be achieved in the absence of systemic vascular adaptations. Specifically, we hypothesized that repeated bouts of brief occlusion would improve arterial endothelial function via shear stress-dependent mechanisms. Eleven healthy males underwent a shear stress intervention (5 s brachial occlusion, 10 s rest) for 30 min, five times weekly for 6 weeks on one arm while the other acted as an untreated control. Ultrasound was used to assess brachial arterial forearm blood flow (FBF) and vascular conductance (FVC), diameter, and shear rate (SR), while endothelial function was assessed by flow-mediated dilatation (FMD). Post-occlusive reactive hyperaemia and pulse wave velocity (PWV) were also measured. There were no changes in any of the measures in the control arm (all d < 0.2, p > 0.05). After 3 weeks of the intervention, FMD was increased from baseline (7.6 +/- 0.6 vs. 5.9 +/- 0.9%; d = 1.3, p = 0.038) and further increased after 6 weeks to 9.5 +/- 2.6% (d = 1.7, p < 0.001). SR was also increased following the 6-week intervention (all d >= 0.6, p < 0.001). Resting and peak FBF and FVC were also increased in response to the intervention (all d >= 0.6, p < 0.001) and PWV was reduced. These data demonstrate that episodic increases in shear stress elicit marked increases in arterial endothelial function and vascular reactivity.