Influence of age on cardiac baroreflex function during dynamic exercise in humans

Abstract

We investigated the influence of aging on cardiac baroreflex function during dynamic exercise in seven young (22 Ϯ 1 yr) and eight older middle-aged (59 Ϯ 2 yr) healthy subjects. Carotid-cardiac baroreflex function was assessed at rest and during moderate-intensity steadystate cycling performed at 50% heart rate reserve (HRR). Five-second pulses of neck pressure and neck suction from ϩ40 to Ϫ80 Torr were applied to determine the operating point gain (GOP) and maximal gain (GMAX) of the full carotid-cardiac baroreflex function curve and examine baroreflex resetting during exercise. At rest, mean arterial pressure (MAP) and heart rate were similar between the younger and older subjects. In contrast, the resting GOP and GMAX were significantly lower in the older subjects. The increase in MAP from rest to exercise was greater in the older subjects (⌬ ϩ20 Ϯ 2 older vs. ⌬ ϩ6 Ϯ 3 younger mmHg; P Ͻ 0.001). However, the GOP was similar in both groups during exercise because of a reduction in the younger subjects. In contrast, GMAX was unchanged from rest and therefore remained lower in older subjects (Ϫ0.19 Ϯ 0.05 older vs. Ϫ0.42 Ϯ 0.05 younger beats ⅐ min Ϫ1 ⅐ mmHg Ϫ1 ; 50% HRR; P Ͻ 0.001). Furthermore, exercise resulted in an upward and rightward resetting of the cardiac baroreflex function curve in both groups. Collectively, these findings suggest that the cardiac baroreflex function curve appropriately resets during exercise in older subjects but operates at a reduced GMAX primarily because of age-related reductions in carotidcardiac control manifest at rest. arterial baroreceptors; aging; heart rate HEALTHY AGING HAS BEEN associated with impaired arterial baroreflex control of heart rate (HR; see Refs. 10,17,25,33), vasomotor tone (8), and blood pressure (23) under resting conditions. However, little is known about how aging alters baroreflex function during dynamic exercise. Importantly, alterations noted at rest cannot simply be extrapolated to exercise because peripheral feedback from skeletal muscle (i.e., exercise pressor reflex; EPR) and feedforward central neural inputs (i.e., central command) modulate arterial baroreflex control during exercise, influencing reflex sensitivity and also contributing to the resetting of the baroreflex function curve (13,27). Moreover, EPR function may be attenuated in older subjects (24), thereby leading to decreases in input from the EPR to the baroreflex, potentially altering baroreflex sensitivity and resetting characteristics. In addition, it is possible that an agerelated enhancement of central command may also modify the baroreflex during exercise (5). Thus it is important to consider the influence of healthy aging on baroreflex function and resetting during dynamic exercise. This is particularly relevant from a clinical standpoint since older subjects are increasingly being encouraged to exercise and decreases in baroreflex control of HR can increase the occurrence of ventricular arrhythmias during physical activity (1,38).Limited studies have attempted to investigate ag...

Carotid baroreflex control of arterial blood pressure at rest and during dynamic exercise in aging humans

“…hypothesized that older individuals would have reductions in ABR control of BP during exercise. Our rationale was that impairments in ABR function with increased age may contribute to the augmented BP often observed in older individuals during exercise (9,19,34,45). However, the results suggest that although the carotid baroreflex BP function curve was reset further upward and rightward during exercise in the older group, no age-related differences in the maximal gain were observed.…”

“…However, previous studies examining the influence of age on vascular responses to sympathetic activation have reported both blunted (10) and preserved (14) responses in older individuals. In addition, the reduced BP response to carotid baroreceptor unloading may also be related to an attenuated tachycardic response (18,19). Further work is required to examine the influence of aging on the ABR-regulation of vascular conductance and the relative contribution of central hemodynamics to overall ABR control of BP.…”

“…All subjects performed a continuous incremental exercise test to ascertain peak HR for the determination of steady-state exercise workloads, as previously described (19). Briefly, subjects were seated in a semirecumbent position on a medical exam table equipped with an electrically braked cycle ergometer (Angio V2; Lode, Groningen, The Netherlands), while HR (12-lead ECG) and BP (automated sphygmomanometer) were measured.…”

“…cardiovascular control; autonomic nervous system; baroreflex sensitivity; arterial baroreceptors; total vascular conductance THE ARTERIAL BAROREFLEX (ABR) plays a critical role in the moment-to-moment regulation of arterial blood pressure (BP) via modulation of autonomic neural activity to the heart and vasculature. Although a wealth of data has indicated that aging is associated with impairments in resting cardiac baroreflex function (3,14,19,29), studies examining ABR control of muscle sympathetic nerve activity (SNA) have reported equivocal results demonstrating impaired, preserved, or augmented responsiveness in older healthy adults (11,14,24,29,30,46). Moreover, regarding overall ABR regulation of BP and aging, limited studies have been performed suggesting either reduced (24, 27) or unchanged (4, 41) control with advanced age.…”

“…In exercising dogs, acute baro-denervation leads to an exaggerated increase in BP (49, 50), while in humans who have surgically denervated carotid baroreceptors, not only is resting BP variability elevated but the BP response to exercise is greater (42, 47). Such observations raise the possibility that age-related impairments in ABR function may contribute to the augmented BP often observed in older individuals during exercise (9,19,34,45). However, whether aging affects the resetting, sensitivity, and general parameters for the ABR control of BP during dynamic exercise is presently unknown.…”