Sex differences in limb vasoconstriction responses to increases in transmural pressures.

Women compared with men are more likely to have orthostatic intolerance. The purpose of this study was to examine whether sex affects limb vasoconstrictor response to increases in transmural pressure. Brachial and femoral mean blood velocity (MBV) and diameter (Doppler Ultrasound) were measured in 10 women and 10 men as transmural pressure was altered by applying local suction (-25, -50, -75, and -100 mmHg) via pressurized-limb tanks for 1 min to a single arm and leg. With the abrupt application of forearm suction (-75 and -100 mmHg), women compared with men had a greater initial rise in MBV (peak), followed by a quicker dynamic rate of velocity reduction. In the leg, women had a tendency for higher peak MBV but had similar dynamic velocity reductions compared with men. After 60 s of suction, women compared with men had attenuated reductions in brachial flow and conductance (-8.05 +/- 1.71 vs. -16.25 +/- 1.71 ml/min; -0.12 +/- 0.03 vs. -0.20 +/- 0.03 ml x min(-1) x mmHg(-1); main effect, P < 0.05), as well as attenuated femoral flow and conductance to sustained leg negative pressure at -100 mmHg (P < 0.05). When the data were expressed as percent change, women compared with men continued to have attenuated brachial flow responses (-24 +/- 2 vs. -36 +/- 2%, main effect, P < 0.05), with a trend toward attenuation at the highest leg pressure (-25 +/- 11 vs. -46 +/- 4%; P = 0.08). These sex differences remained after normalizing the flow responses by limb volume (percent change). Our findings suggest that young women compared with men have attenuated brachial and femoral vasoconstrictor responses to increases in transmural pressure, which may have implications for the greater incidence of orthostatic intolerance in women.