A Gender comparison of Cardiovascular Responses to Lower Body Negative Pressure Exposure

The purpose of this study was to compare the LBNP tolerance between genders. Twenty healthy subjects (8 men, 12 women) were exposed to 10 min of 45mmHg LBNP. Baseline was taken in the sitting and supine positions. Finger blood pressure and heart rate (HR) were recorded continuously. Stroke volume (SV), cardiac output (CO) and total peripheral resistance (TPR) were calculated by a pulse contour method. Baseline cardiovascular variables were similar in all females, independently of the menstrual cycle phase and they were considered as one group. Seven of 8 men and 7 of 12 women completed the 10 min of LBNP. Non-finishers (n=6) increased heart rate, decreased systolic blood pressure, mean blood pressure, calculated SV and CO in comparison with the Finisher (n=14) group (p<0.05). Both groups, however, maintained TPR unchanged during the exposure to LBNP. This suggests the tolerance to LBNP is related to the capability of both avoiding too large a decrease in SV, and inducing an adequate vasoconstriction response.