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 mm Hg-1) was significantly greater than that in women (4.89 (3.87) ms mm 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.