There are no differences in brachial artery endothelial shear stress and blood flow patterns between males and females during exercise

Abstract

Premenopausal females have a lower cardiovascular risk than males. Sex differences on exercise-induced endothelial shear stress (ESS) and blood flow patterns may explain part of this risk reduction. The purpose of this cross-sectional study was to determine the differences in brachial artery exercise-induced ESS and blood flow patterns between males and females. Thirty subjects (13 females) were recruited to perform a three-workload steady-state exercise test based on blood lactate levels (i.e. <2.0, 2.0-4.0, >4.0 mmol/l). ESS and blood flow patterns were estimated at rest and during each workload using Womersley's approximation and Reynolds number, respectively. Both males and females showed an exercise intensity-dependent increase in antegrade and retrograde ESS. There was no significant sex effect or interaction for antegrade ESS (F_{(1, 30)} = 0.715, p = 0.405 and F_{(1·672, 60)} = 1.511, p = 0.232, respectively) or retrograde ESS (F_{(1, 30)} = 0.794, p = 0.380 and F_{(1·810, 60)} = 1.022, p = 0.361, respectively). Additionally, antegrade blood flow was turbulent during all bouts of exercise while retrograde blood flow became disturbed at moderate and high exercise intensities in both groups. There are no differences in exercise-induced ESS and blood flow patterns between males and females when the exercise load is equivalent. This suggests that the vascular benefits of exercise training are similar in both sexes from a haemodynamic standpoint.

Keywords: blood lactate; exercise intensity; imaging ultrasound; sex.