Figure 4.

Percent change from baseline for cerebral oxygen saturation (ScO₂; A) and oxygenated hemoglobin (Oxy-hemoglobin; 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 ScO₂ and Oxy-hemoglobin responses between the sexes. Deoxygenated hemoglobin (Deoxy-hemoglobin; C) progressively increased from −30 mmHg LBNP in males (dashed line, open circle) and females (solid line, closed circle), however, was higher in males than females at −45 mmHg, −60 mmHg LBNP, and at the PS-1 time point. Mean ± SE. *Difference from baseline, P < 0.08. †Sex differences, P range from 0.01 to 0.08. 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.