Peripheral artery endothelial function responses to altered shear stress patterns in humans

New findings: What is the central question of this study? What is the effect of altered shear stress pattern, with or without concurrent neurohumoral and metabolic activation, on the acute endothelial function response assessed via brachial artery flow-mediated dilatation? What is the main finding and its importance? Despite generating distinctive shear stress patterns (i.e. increases in anterograde only, anterograde only with neurohumoral and metabolic activation, and both anterograde and retrograde), similar acute improvements were observed in the brachial artery flow-mediated dilatation response in all conditions, indicating that anterograde and/or turbulent shear stress might be the essential element to induce acute increases in endothelial function.

Abstract: Endothelial function is influenced by both the direction and the magnitude of shear stress. Acute improvements in endothelial function have mostly been attributed to increased anterograde shear, whereas results from many interventional models in humans suggest that enhancing shear stress in an oscillatory manner (anterograde and retrograde) might be optimal. Here, we determined the acute brachial artery shear stress (SS) and flow-mediated dilatation (FMD) responses to three shear-altering interventions [passive heat stress (HEAT), mechanical forearm compression (CUFF) and handgrip exercise (HGEX)] and examined the relationship between changes in oscillatory shear index (OSI) and changes in FMD. During separate visits, 10 young healthy men (22 ± 3 years old) underwent 10 min of HEAT, CUFF or HGEX in their left forearm. Anterograde and retrograde SS, Reynolds number, OSI and FMD were assessed at rest and during/after each intervention. Anterograde SS increased during all interventions in a stepwise manner (P < 0.05 between interventions), with the change in HGEX (∆37.7 ± 12.2 dyn cm^-2 , P < 0.05) > CUFF (∆25.1 ± 11.9 dyn cm^-2 , P < 0.05) > HEAT (∆14.5 ± 7.9 dyn cm^-2 , P < 0.05). Retrograde SS increased during CUFF (∆-19.6 ± 4.3 dyn cm^-2 , P < 0.05). Anterograde blood flow was turbulent (i.e. Reynolds number ≥ |2000|) during all interventions (P < 0.05). The relative FMD improved after all interventions (P = 0.01), and there was no relationship between ∆OSI and ∆FMD. We elicited changes in SS profiles including increased anterograde SS (HEAT and HGEX) and both increased anterograde and retrograde SS (CUFF); regardless of the SS pattern, FMD improved to the same extent. These findings suggest that the presence of anterograde and/or turbulent SS might be the key to optimizing endothelial function in acute assessment protocols.