Figure 3.

Percent change from baseline for middle cerebral artery velocity (MCAv; A), posterior cerebral artery velocity (PCAv; B), and end-tidal CO₂ (etCO₂; C) 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 MCAv and PCAv responses between the sexes; however, etCO₂ was lower in males (open triangle) compared to females (closed triangle). Mean ± SE. *Difference from baseline, P < 0.05. 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.