Brachial and carotid hemodynamic response to hot water immersion in men and women.

This study sought to compare the brachial and carotid hemodynamic response to hot water immersion (HWI) between healthy young men and women. Ten women (W) and 11 men (M) (24 ± 4 yr) completed a 60-min HWI session immersed to the level of the sternum in 40°C water. Brachial and carotid artery hemodynamics (Doppler ultrasound) were measured at baseline (seated rest) and every 15 min throughout HWI. Within the brachial artery, total shear rate was elevated to a greater extent in women [+479 (+364, +594) s-1] than in men [+292 (+222, +361) s-1] during HWI (P = 0.005). As shear rate is inversely proportional to blood vessel diameter and directly proportional to blood flow velocity, the sex difference in brachial shear response to HWI was the result of a smaller brachial diameter among women at baseline (P < 0.0001) and throughout HWI (main effect of sex, P < 0.0001) and a greater increase in brachial velocity seen in women [+48 (+36, +61) cm/s] compared with men [+35 (+27, +43) cm/s] with HWI (P = 0.047) which allowed for a similar increase in brachial blood flow between sexes [M: +369 (+287, +451) mL/min, W: +364 (+243, +486) mL/min, P = 0.943]. In contrast, no differences were seen between sexes in carotid total shear rate, flow, velocity, or diameter at baseline or throughout HWI. These data indicate the presence of an artery-specific sex difference in the hemodynamic response to a single bout of HWI.