Gender differences in wall shear-mediated brachial artery vasoconstrictionand vasodilation

OBJECTIVES We sought to investigate wall shear rate (WSR) and brachial arte ry diameter (BAD) changes simultaneously and to determine whether any gende r differences exist in arterial reactivity. BACKGROUND Wall shear rate/stress and arterial reactivity are rarely assess ed at the same time, Furthermore, flow-mediated vasoconstriction has receiv ed less attention than flow-mediated vasodilation in humans. METHODS A new noninvasive evaluation of WSR in the brachial artery, using m ultigated, pulsed Doppler velocimeter and a double-transducer probe moved a nd fixed by a robotic system, was developed. RESULTS The validity of the system was tested in vitro with calibrated tube s and showed a high correlation (r = 0.98, p < 0.001). In 10 men and 10 wom en of similar age, induction of low and high shear rates by, forearm occlus ion produced significant vasoconstriction and vasodilation, respectively. T he time lag for maximal BAD changes was 3 min for vasoconstriction and 1 mi n for vasodilation. A greater half-time for vasodilation (96 +/- 6 for men and 86 +/- 12 s for women) than for shear rate (31 +/- 5 s for men and 34 /- 4 s for women) was observed after discontinuation of occlusion. Relative BAD was correlated with WSR changes, showing a significantly higher slope in women than in men (p < 0.01). Moreover, a larger normalized arterial dia meter per shear rate was observed for vasoconstriction (p < 0.01) and vasod ilation (p < 0.01) in women than in men. CONCLUSIONS Shear-mediated arterial vasodilation and vasoconstriction were more pronounced in women than in men, suggesting different gender-related s ensitivity, in the regulation of large-artery vascular tone. (C) 2001 by th e American College of Cardiology.