Baroreflex Regulation of Heart Rate and Sympathetic Vasomotor Tone in Women and Men

Gender has been reported to influence baroreflex heart rate regulation and baroreflex blood pressure buffering. We tested the hypothesis that gender influences baroreflex regulation of heart rate and sympathetic vasomotor tone. We recruited 32 normal-weight healthy subjects (17 men and 15 women). ECGs for heart rate, brachial and finger blood pressure, and muscle sympathetic nerve activity (MSNA) were measured. Baroreflex heart rate and MSNA regulation were assessed using incremental phenylephrine and nitroprusside infusions. Baseline blood pressure was similar in men and women. MSNA was 21+/-2.5 bursts/min in women and 19+/-2.8 bursts/min in men (NS). The gain of the baroreflex MSNA curves was similar in women and men (-1.9+/-0.2 bursts/min per mm Hg in men and -2.0+/-0.3 bursts/min per mm Hg in women). Baroreflex gain for heart rate regulation was 17+/-3.2 ms/mm Hg in women and 19+/-1.9 ms/mm Hg in men (NS). We conclude that baroreflex gains for heart rate and sympathetic MSNA regulation are similar in women and men. However, the probability for congruence between men and women in terms of the MSNA baroreflex curves was 0.06% for burst rate, 0.4% for burst incidence, and 0.01% for burst area. In women, the MSNA baroreflex curve may be shifted to slightly lower blood pressure such that at a given blood pressure MSNA tends to be lower.