Thirty minutes of handgrip exercise potentiates flow-mediated dilatation in response to sustained and transient shear stress stimuli to a similar extent.

Abstract

What is the central question of this study? This study sought to determine whether enhancement of brachial artery flow-mediated dilatation (FMD) after acute exposure to a sustained elevation in shear stress is greater when the shear stress stimulus for FMD is also sustained. What is the main finding and its importance? Brachial artery FMD in response to a sustained (handgrip exercise) and transient (reactive hyperaemia) shear stress stimulus was enhanced to a similar extent 10min after a 30min handgrip exercise intervention. This suggests that prior exposure to a sustained elevation in shear stress results in a similar acute augmentation of the ability of the endothelium to transduce sustained and transient shear stress stimuli. Brief (30min) exposure of the brachial artery (BA) to a sustained elevation in shear stress has been shown to potentiate subsequent BA flow-mediated dilatation (FMD) in response to a transient shear stress stimulus [reactive hyperaemia (RH) FMD]. It is unknown whether matching the sustained shear stress exposure to a subsequent sustained shear stress stimulus for FMD [via handgrip exercise (SS-FMD)] might enhance the potentiation of FMD. The purpose of the study, therefore, was to assess the impact of a 30min handgrip exercise intervention-induced elevation in shear stress on subsequent BA SS-FMD versus RH-FMD. Nineteen healthy men (22±3years) preformed a 30min rhythmic handgrip exercise intervention on two experimental days. BA-FMD was assessed using either an RH or a 6min sustained shear stress stimulus created via handgrip exercise (order of visits counterbalanced) at three time points: pre-intervention and 10 and 60min post-intervention. The FMD was assessed using duplex ultrasound. Shear stress was estimated as shear rate (SR=BA blood velocity/BA diameter). Data are mean±SD. Both SS and RH-FMD increased from pre-intervention to 10min post-intervention [SS-FMD (6min average), from 0.11±0.05 to 0.16±0.08mm; P=0.008; Cohen's d = 0.66; and RH-FMD, from 0.25±0.1 to 0.32±0.11mm; P=0.013; Cohen's d = 0.68]. The magnitude of enhancement in RH and SS-FMD did not differ (change in RH versus SS-FMD pre- versus 10min post-intervention, P=0.344). These findings suggest that exposure to elevated shear stress via 30min of handgrip exercise potentiates subsequent FMD in response to sustained and transient elevations in shear stress to a similar extent.