Influence of Aging on Carotid-Baroreflex Peak Response Latency at Rest and During Dynamic Exercise in Humans

Abstract

The stability of a physiological control system, such as the arterial baroreflex, depends critically upon both the magnitude (i.e., gain or sensitivity) and time delay (i.e., latency) of the effector response. Although studies have examined resting arterial baroreflex sensitivity in older subjects, little attention has been given to the influence of aging on the latency to peak baroreflex responses. Furthermore, how baroreflex latency is altered by dynamic exercise in young and older subjects has not been fully elucidated. PURPOSE: We sought to determine how aging influences the temporal pattern of beat-to-beat heart rate and blood pressure responses elicited by acute activation of the carotid baroreceptors at rest and during dynamic exercise. METHODS: Heart rate (HR) and mean arterial pressure (MAP) were continuously measured at rest and during leg cycling performed at 50% heart rate reserve in six young (23 ± 2 yrs) and four older (66 ± 2 yrs) healthy subjects. Five second pulses of neck suction (NS, -80 Torr) were applied to activate carotid baroreceptors at rest and during exercise. RESULTS: Under resting conditions the time to the peak change in HR in response to NS was delayed in older (4.8 ± 1.1s) compared to the younger subjects (2.1 ± 0.2s; P<0.05). Likewise, the time to the peak change in MAP was also significantly slower in the older individuals (9.5 ± 0.3s) compared to the younger subjects (6.5 ± 1.0s). During exercise the latency of the peak reflex tachycardia was similar between groups (4.8 ± 0.3s vs. 4.8 ± 0.4s, for the young and older groups, P>0.05) due to a significantly prolonged peak response latency in the young subjects (135 ± 20%; P<0.05), whereas the MAP response latencies remained slower in the older subjects. CONCLUSIONS: In summary, these preliminary data suggest that healthy aging is associated with a delayed peak HR response to acute carotid baroreceptor stimulation at rest, and a delayed peak MAP (i.e., vasomotor) response both at rest and during exercise. We speculate that the sluggish baroreflex responses observed in older individuals may lead to instabilities in baroreflex-mediated blood pressure regulation with age both at rest and during exercise.