Gender differences in baroreflex response and heart rate variability in anaesthetized humans.

BACKGROUND: In conscious humans, men have a greater cardiovagal baroreflex gain than women. We studied gender-related differences in baroreflex function during general anaesthesia.
METHODS: Sixty healthy patients (30 male and 30 female) were anaesthetized with sevoflurane 2% end-tidal in air and oxygen, and their lungs were mechanically ventilated. We recorded the ECG and invasive arterial pressure. Baroreflex gain was measured as the linear relationship of R-R interval with systolic arterial pressure changes caused by doses of phenylephrine i.v., and also the spontaneous changes in R-R interval and arterial pressure. In addition, consecutive R-R intervals were analysed using a fast Fourier transformation.
RESULTS: Baroreflex gains (mean (sd)) assessed by the pharmacological method in men (7.98 (5.12) ms x mm x Hg(-1)) was significantly greater than that in women (4.89 (3.87) ms x mm x Hg(-1)). Similarly, spontaneous baroreflex gains were significantly greater in men than in women, and correlated well with high-frequency power, but not with low-frequency power or low/high ratio, of heart rate variability in both genders.
CONCLUSIONS: Our results extend findings in conscious humans to sevoflurane anaesthesia. Men have greater cardiovagal reflex gains than women, which may reflect differences in parasympathetic action on heart rate.