Effects of Age and Gender on Autonomic Control of Blood Pressure Dynamics

Abstract

Abstract-Both age and gender influence cardiovascular autonomic control, which in turn may influence the ability to withstand adverse cardiac events and respond to orthostatic stress. The purpose of this study was (1) to quantify age-and gender-related alterations in autonomic control of blood pressure (BP) and (2) to examine the impact of these autonomic alterations on BP response to orthostatic stress. We measured continuous BP and R-R intervals and vasoactive peptide levels in the supine and 60°head-up tilt positions during paced respiration (0.25 Hz) in 89 carefully screened healthy subjects (41 men, 48 women, aged 20 to 83 years). Data were analyzed by gender (age adjusted) and by age group (gender adjusted). During tilt, women had greater decreases in systolic BP than men (Ϫ10.2Ϯ2 versus Ϫ1.2Ϯ3 mm Hg; Pϭ0.02) and smaller increases in low-frequency (sympathetically mediated) BP power (Pϭ0.02). Upright plasma norepinephrine was lower in women (Pϭ0.02). Women had greater supine high-frequency R-R interval power than men (Pϭ0.0001). In elderly subjects, the tilt-induced increase in low-frequency BP power was also diminished (Pϭ0.01), despite higher supine (Pϭ0.02) and similar upright norepinephrine levels compared with younger subjects. Thus, healthy women have less sympathetic influence on BP and greater parasympathetic influence on R-R interval than men. Elderly subjects also have reduced sympathetic influence on BP, but this appears to be more consistent with a reduction in vasomotor sympathetic responsiveness. (Hypertension. 1999;33:1195-1200.)Key Words: sympathetic nervous system Ⅲ norepinephrine Ⅲ spectral analysis Ⅲ hypotension A nalyses of the beat-to-beat variability of cardiac R-R intervals have been used to quantify alterations in autonomic function and predict adverse clinical events. 1,2 Since both age and gender have a profound influence on the risk of cardiovascular disease and death, it is important to understand the effects of healthy aging and gender on autonomic control of cardiovascular function. Previous studies have shown reductions in heart rate (HR) variability with aging 3,4 and increases in high-frequency HR variability in women compared with men. [5][6][7] Since many studies did not rigorously screen subjects to exclude occult cardiovascular disease, it is not known whether abnormalities in short-term autonomic control of HR reflect subclinical cardiovascular disease or whether they represent "normal" age-or gender-related alterations in autonomic function.The effects of age and gender on beat-to-beat blood pressure (BP) dynamics have been less well studied, and it is not known whether changes in the autonomic regulation of beat-to-beat BP are associated with hemodynamic impairment. Therefore, we asked the following questions: (1) Are there specific age-and gender-related alterations in the autonomic control of beat-tobeat BP dynamics in healthy individuals free of cardiovascular disease? (2) If so, what are the hemodynamic consequences of these changes during orthostatic stress?We u...

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.…”

Women Have Lower Tonic Autonomic Support of Arterial Blood Pressure and Less Effective Baroreflex Buffering Than Men

“…The ability of baroreflexes to "buffer" acute changes in BP under such conditions (ie, baroreflex buffering [BRB]) is reduced in certain physiological 9 and disease 10 states associated with impaired short-term BP regulation and/or altered responsiveness to vasoactive medications. In light of previous reports of less effective short-term regulation of BP in women than in men, 1,2,6,[11][12][13][14] we also hypothesized that premenopausal women have lower BRB of BP than men of similar age.…”

“…[1][2][3][4] The autonomic nervous system (ANS) plays a critical role in BP regulation. Surprisingly, however, little or no direct evidence exists regarding possible gender-related differences in ANS control of BP in humans.…”

“…1,5,6 The ANS provides tonic support for resting BP, and we recently established that basal sympathetic nervous system activity is a key physiological determinant of the amount of tonic BP support provided by the ANS. 7 Because premenopausal women tend to have lower resting sympathetic activity than men, [2][3][4]8 we hypothesized that women have lower tonic ANS support of BP than men.…”

Reduced alpha adrenergic mediated contraction of renal preglomerular blood vessels as a function of gender and aging

“…Examples of decreased renal vasoconstrictor effectiveness in aging are demonstrated by the fact that young men undergo a reduction of approximately 45% in renal blood flow during exercise while healthy, elderly men undergo a significantly smaller decrease of only 12% to a similar exercise challenge [Kenny and Zappe, 1994]. In addition, elderly subjects have a reduction in sympathetic neural control of blood pressure during tilting from supine to the upright posture [Barnett et al, 1999]. Similarly, senescent Fischer 344 rats have been reported to have sustained a shorter duration of elevated renal resistance compared to their younger male counterparts as a function of air-jet stress tests [Stauss et al, 1996].…”