Autonomic Function in Hypertensive and Normotensive Subjects

Abstract

Abstract-Baroreceptor reflex sensitivity (BRS) has been found lower and heart rate variability (HRV) parasympathetic markers have been found higher in healthy women than in healthy men. Thus, in the present study we hypothesized gender differences in the autonomic function among hypertensive subjects. Forty-one hypertensive patients and 34 normotensive subjects, age 53Ϯ1 years, were examined. Four weeks after cessation of antihypertensive therapy, HRV was assessed in 24-hour Holter ECGs, and BRS was calculated with the transfer technique. A t test was performed after log transformation of spectral values. Resting blood pressure and heart rate in the hypertensive and the normotensive groups were 150Ϯ2/100Ϯ1 (meanϮSEM) and 121Ϯ2/81Ϯ1 mm Hg, respectively, and 68Ϯ1 and 60Ϯ1 bpm, respectively (PϽ0.0005). Compared with normotensive controls, hypertensive patients had lower total power (1224Ϯ116 versus 1797Ϯ241 ms 2 ; Pϭ0.03), lower low frequency power (550Ϯ57 versus 813Ϯ115 ms 2 ; Pϭ0.04), lower high frequency power (141Ϯ23 versus 215Ϯ38 ms 2 ; Pϭ0.06), lower root mean square successive difference (28.7Ϯ2.7 versus 35.7Ϯ3.0 ms; Pϭ0.03), and PNN50 (4.9Ϯ0.6% versus 9.8Ϯ1.5%; Pϭ0.003). BRS was also lower in the hypertensive subjects (7.6Ϯ0.6 versus 10.4Ϯ0.8 ms/mm Hg; Pϭ0.005). When comparing the same parameters between normotensive subjects and hypertensive subjects within the same gender group, we found significant reduction (PϽ0.05) only within the female group. The difference in BRS within the female group was twice that within the male group. Stepwise multiple regression analysis revealed gender, age, HDL cholesterol, and blood pressure as independent explanatory variables of BRS and HRV. Our results suggest that gender is an important determinant of BRS and HRV. Autonomic function parameters were especially impaired in hypertensive women compared with hypertensive men. Key Words: hypertension Ⅲ gender Ⅲ baroreflex Ⅲ catecholamines Ⅲ heart rate T he autonomic nervous system plays a crucial role in blood pressure (BP) and heart rate (HR) control and may thus be an important pathophysiological factor in the development of hypertension. There have been numerous studies on plasma catecholamines in essential hypertension, 1 most of which have shown increased levels in hypertensive subjects. Moreover, disturbed autonomic HR and BP control has been demonstrated in several studies by means of HR variability (HRV) and baroreceptor reflex sensitivity (BRS). [2][3][4][5][6][7][8][9][10] HRV, which estimates the tonic HR control, 11-13 is generally reduced (standard deviation of all R-R intervals [SDNN] and total power [energy in the heart period spectrum between 0.0033 and 0.40 Hz] [TP]) in hypertensive patients. 2,4 -6 Markers of sympathetic predominance are increased in some 3 but not all studies. 4 -6 BRS, which estimates the reflex vagal HR control, 11-13 is reduced in hypertensive subjects. 6 -10 Both BRS and HRV parameters (except low frequency power [energy in the heart period spectrum between 0.04 and 0.15 Hz] [LF]/h...

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