Autonomic function in hypertensive and normotensive subjects: the importance of gender

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 53+/-1 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 150+/-2/100+/-1 (mean+/-SEM) and 121+/-2/81+/-1 mm Hg, respectively, and 68+/-1 and 60+/-1 bpm, respectively (P<0.0005). Compared with normotensive controls, hypertensive patients had lower total power (1224+/-116 versus 1797+/-241 ms(2); P=0.03), lower low frequency power (550+/-57 versus 813+/-115 ms(2); P=0.04), lower high frequency power (141+/-23 versus 215+/-38 ms(2); P=0.06), lower root mean square successive difference (28.7+/-2.7 versus 35.7+/-3.0 ms; P=0.03), and PNN50 (4.9+/-0.6% versus 9.8+/-1.5%; P=0.003). BRS was also lower in the hypertensive subjects (7.6+/-0.6 versus 10.4+/-0.8 ms/mm Hg; P=0.005). When comparing the same parameters between normotensive subjects and hypertensive subjects within the same gender group, we found significant reduction (P<0.05) 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.