Gender-based differences in the cardiovascular response to standing

Reduced tolerance to orthostatic stress is a recognized consequence of spaceflight. Both men and women serve as astronauts and are staying longer in space. While there are recognized cardiovascular differences in baseline function based on gender, little is known about any gender-based differences in cardiovascular responses to orthostatic stress. The purpose of this study was to compare the cardiovascular responses of men and women to the stand test. The subjects were 10 men and 10 women, 20-30 years of age. Heart rate, blood pressure, stroke volume, cardiac output, and total peripheral resistance were monitored during 5 min supine and 5 min standing. Men responded similarly in heart rate (39 vs. 35%); but had significantly greater decreases in stroke volume (-53 vs. -40%), cardiac output (-36 vs. -21%), and pulse pressure (-19 vs. -12%); and greater increases in blood pressure (11 vs. 6%) and total peripheral resistance (77 vs. 34%) than did the women. Men and women demonstrated fundamental differences in cardiovascular responses during standing. Differences in the height of the subjects did not account for these differing cardiovascular responses. The mechanisms for these differences are not yet clear. Men and women should be studied as separate groups until these differences are understood.