Figure 1.

Tolerance time (in seconds; A) to lower body negative pressure (LBNP) in male and female subjects. Mean (bars) and individual subject data (circles) are presented. P = 0.15, assessed via unpaired t test. Stroke volume index (B) decreased in both males (dashed line, open circle) and females (solid line, closed circle) during lower body negative pressure (LBNP). Over the 1 min prior to presyncope (PS-1), there were no differences in these responses between the sexes. Mean ± SE. *Difference from baseline, P ≤ 0.002. A two-factor (sex, time) linear mixed model analysis with Holm-corrected post hoc tests run on the least squared means (within and between males and females up to −60 mmHg LBNP), and unpaired t tests (between males and females at PS-1) were used for analysis. PS, presyncope.