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

¹Department of Medical Pharmacology and Physiology, ²Dalton Cardiovascular Research Center, ³Department of Internal Medicine, ⁴Department of Radiology, University of Missouri, Columbia, and ⁵Harry S. Truman Memorial Veterans Hospital, Department of Veterans Affairs Medical Center, Columbia, Missouri; and ⁶Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas

Submitted 14 February 2007 ; accepted in final form 20 April 2007

We investigated the influence of aging on cardiac baroreflex function during dynamic exercise in seven young (22 ± 1 yr) and eight older middle-aged (59 ± 2 yr) healthy subjects. Carotid-cardiac baroreflex function was assessed at rest and during moderate-intensity steady-state cycling performed at 50% heart rate reserve (HRR). Five-second pulses of neck pressure and neck suction from +40 to –80 Torr were applied to determine the operating point gain (G_OP) and maximal gain (G_MAX) 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 G_OP and G_MAX were significantly lower in the older subjects. The increase in MAP from rest to exercise was greater in the older subjects ( +20 ± 2 older vs. +6 ± 3 younger mmHg; P < 0.001). However, the G_OP was similar in both groups during exercise because of a reduction in the younger subjects. In contrast, G_MAX was unchanged from rest and therefore remained lower in older subjects (–0.19 ± 0.05 older vs. –0.42 ± 0.05 younger beats·min^–1·mmHg^–1; 50% HRR; P < 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 G_MAX primarily because of age-related reductions in carotid-cardiac control manifest at rest.

arterial baroreceptors; aging; heart rate

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