Baroreflex sensitivity and blood pressure transients in postmenopausal women

      Regulation of arterial blood pressure is altered after menopause. The purpose of the present study was to evaluate whether sympathetic and/or cardiac baroreflex sensitivities relate to the extent of change in blood pressure seen during vasoactive drug boluses (modified Oxford) in postmenopausal women. We hypothesized that both sympathetic and cardiac baroreflex sensitivities would be related to the magnitude of these transients. Fourteen healthy postmenopausal women (58±6 y) completed the study. Heart rate, arterial pressure, and muscle sympathetic nerve activity (MSNA) were monitored. Sympathetic baroreflex sensitivity was analyzed using the slope of the MSNA–diastolic blood pressure (DBP) relationship and cardiac baroreflex sensitivity was analyzed using the R–R interval (RRI)–systolic blood pressure (SBP) relationship. MSNA burst incidence (62±4 bursts/100 hb) and burst frequency (38±2 bursts/min) were measured under resting conditions. Mean sympathetic baroreflex sensitivity slope was −8±1 (AU/beat/mm Hg) and the cardiac baroreflex sensitivity slope was 7±1 (ms/mm Hg). The magnitudes of the acute drops in SBP, DBP, mean arterial pressure (MAP), and pulse pressure (PP) were associated with cardiac baroreflex sensitivity (r=0.54, r=0.54, r=0.67, and r=0.50, respectively; p<0.05), but not sympathetic baroreflex sensitivity (p>0.05). Similarly, the return of SBP, DBP, MAP, and PP to near baseline values was related to cardiac baroreflex sensitivity slopes (r=0.64, r=0.77, r=0.79, and r=0.53, respectively; p<0.05). The relationship between cardiac baroreflex sensitivity and the magnitude of change in blood pressure indicates that older women with low cardiac baroreflex sensitivity have larger transients in blood pressure during vasoactive drug boluses. This suggests a more prominent role for cardiac (as opposed to sympathetic) baroreflex sensitivity in responding to acute blood pressure changes in older women. However, further measurements during situations that simulate orthostasis are needed to evaluate the applicability of these findings to normal daily activities.
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