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1 Department of Medical Pharmacology & Physiology, University of Missouri, Columbia, Missouri, United States; Department of Veterans Affairs Medical Center, Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri, United States
2 Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas, United States
3 Department of Internal Medicine, University of Missouri, Columbia, Missouri, United States
4 Department of Radiology, University of Missouri, Columbia, Missouri, United States
5 Department of Medical Pharmacology & Physiology, University of Missouri, Columbia, Missouri, United States; Dalton Cardiovascular Research Center, University of Missouri, Columbia, Missouri, United States; Department of Veterans Affairs Medical Center, Harry S. Truman Memorial Veterans Hospital, Columbia, Missouri, United States
* To whom correspondence should be addressed. E-mail: fadelp{at}health.missouri.edu.
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 (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 (
+20±2 older vs. +6±3 younger mmHg; P<0.001). However, the GOP was similar in both groups during exercise due to a reduction in the younger subjects. In contrast, GMAX was unchanged from rest, and therefore remained lower in older subjects (-0.19±0.05 older vs. -0.42±0.05 younger bpm/mmHg; 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 maximal gain primarily due to age-related reductions in carotid-cardiac control manifest at rest.
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