EFFECTS OF CHRONIC ESTROGEN REPLACEMENT THERAPY ON BEAT-TO-BEAT BLOOD-PRESSURE DYNAMICS IN HEALTHY POSTMENOPAUSAL WOMEN

Recent data showing gender differences in autonomic control of heart r ate and acute estrogen effects on vasodilatation suggest that estrogen may influence autonomic regulation of heart rate and blood pressure. We aimed to determine the effect of postmenopausal estrogen replacemen t therapy on autonomic control of beat-to-beat heart rate and blood pr essure dynamics. Subjects included 20 healthy post menopausal women ag ed 60 to 75 years with normal exercise tolerance tests, 10 of whom wer e taking oral estrogen for 13+/-3 (+/-SEM) years. Six healthy premenop ausal women were also studied. Continuous electrocardiographic and non invasive radial artery blood pressure measurements and intermittent fo rearm blood flow recordings (by venous-occlusion plethysmography were obtained before and after a 20-minute, 60 degrees head-up tilt and a 4 20-kcal meal during periods of spontaneous and metronomic breathing (a t 0.25 Hz). Low-frequency (0.01- to 0.15-Hz) and high-frequency (0.15- to 0.50-Hz) heart rate and blood pressure spectral powers were comput ed with a fast Fourier transform. Cardiovascular and heart rate spectr al power responses to upright tilt and meal digestion were the same in postmenopausal estrogen users and nonusers. However, during spontaneo us breathing the blood pressure spectral power responses to upright ti lt and meal ingestion were significantly different between the two gro ups of women. The low-frequency systolic pressure power response to up right tilt was smaller in estrogen users than nonusers (P=.01). After meal ingestion nonusers had an early postprandial fall (20 to 30 minut es after the meal) and late rise (50 to 60 minutes) in low-frequency s ystolic and diastolic pressure powers, which were significantly attenu ated in estrogen users (P<.02). Healthy premenopausal women had a resp onse similar to that of postmenopausal estrogen users. Estrogen may at tenuate the low-frequency vasomotor response to posture change and mea l digestion in healthy postmenopausal women. This effect of estrogen m ay represent damping of vasomotor instability after menopause.