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

Abstract

Abstract-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 21Ϯ2.5 bursts/min in women and 19Ϯ2.8 bursts/min in men (NS). The gain of the baroreflex MSNA curves was similar in women and men (Ϫ1.9Ϯ0.2 bursts/min per mm Hg in men and Ϫ2.0Ϯ0.3 bursts/min per mm Hg in women). Baroreflex gain for heart rate regulation was 17Ϯ3.2 ms/mm Hg in women and 19Ϯ1.9 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. Key Words: autonomic nervous system Ⅲ baroreflex Ⅲ gender Ⅲ nervous system, sympathetic T he autonomic nervous system influences blood pressure and heart rate through adjustments in parasympathetic and sympathetic activity. Parasympathetic and sympathetic activities are tightly regulated through baroreflex mechanisms. Therefore, baroreflexes have a pivotal role in shortterm cardiovascular regulation and buffer-excessive blood pressure swings. 1,2 Among numerous other variables, baroreflexes are also involved in long-term blood pressure maintenance. [3][4][5] Even when overall blood pressure regulation is functioning properly, the balance between baroreflex regulation of heart rate and vascular tone may be perturbed. Imbalance between sympathetic activation of the heart and the vasculature has been described in heart failure patients, 6 postural tachycardia syndrome patients, 7,8 and in healthy subjects treated with norepinephrine transporter inhibitors. 9,10 Factors influencing baroreflex function may have an important bearing on human cardiovascular disease. Gender may be such a variable. Previous studies suggest that baroreflex blood pressure buffering is less effective in women than in men. 11 The balance between baroreflex-mediated heart rate and muscle sympathetic nerve activity (MSNA) changes may also be influenced by gender. The idea is supported by the observation that resting sympathetic vasomotor tone tends to be decreased in women, 12,13 whereas resting heart rate is increased. 14 -16 Furthermore, with standing, women showed an exaggerated heart rate and an attenuated sympathetic vasomotor response. 17 Moreover, previous studies suggested that baroreflex heart rate regulati...

Squatting test: a dynamic postural manoeuvre to study baroreflex sensitivity

“…Baroreflex gain was similar in men and women, confirming previous observations obtained with the pharmacological reference test [42]. However, baroreflex gain was slightly but significantly decreased in overweight/obese subjects versus lean subjects and markedly decreased in elderly versus young individuals, also in agreement with data obtained from the pharmacological test using sequential nitroprusside-phenylephrine infusions [29] (Table 1).…”

The effect of gender on the sympathetic nerve hyperactivity of essential hypertension

“…48 In that report, the baroreceptor reflex sensitivity controlling MSNA was found to be increased in relation to increased plasma levels of oestrogen and progesterone. 48 Although we did not examine the mechanisms underlying the observed gender-related differences, taking the above considerations together with previously published reports, 20,41,49,50 it is reasonable to raise the possibility that the lower sympathetic activity in women could be related to their greater sympatho-inhibitory baroreceptor reflexes than those in men. This normal genderrelated difference would then affect the level of the central sympathetic hyperactivity attained in women and men with hypertension.…”

“…4,14 On the other hand, previously reported findings in normotensive populations have not been consistent as to whether MSNA levels are different between men and women. Young women may have a lower [15][16][17][18][19] or similar 20,21 level of resting MSNA relative to young men. Also, older women may have a lower 15 or similar 17,19 level of resting MSNA relative to older men.…”

A Study of Relationship Between Arterial Blood Pressure and Body Mass Index in Young Adults

“…[8,9] This figure shows that all parameters are higher in male subjects as compared to female subjects.…”