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ORIGINAL RESEARCH ARTICLE

Physically Active Lifestyle Enhances Vagal-Cardiac Function but Not Central Autonomic Neural Interaction in Elderly Humans

Xiangrong Shi^*,1, Frederick A. Schaller, Nancy Tierney, Patrick Chanthavong^*, Shande Chen, Peter B. Raven^* and Michael L. Smith^*

^* Department of Integrative Physiology, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107; Department of Internal Medicine, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107; and Department of Biostatistics, University of North Texas Health Science Center at Fort Worth, Fort Worth, Texas 76107

To whom requests for reprints should be addressed at ¹ Department of Integrative Physiology, UNT Health Science Center, Fort Worth, TX 76107. E-mail: xshi{at}hsc.unt.edu

The cause of the age-related impairment of arterial baroreflex function remains ill-defined; moreover, it is unknown whether this impairment results from aging per se or from an inactive lifestyle associated with aging. In this study, we sought to: 1) determine whether elderly individuals who maintained an active lifestyle had an enhanced carotid baroreflex function as compared with their sedentary counterparts; and 2) determine whether this difference was due in part to altered function of the arterial baroreceptor and/or altered central modulation. Eight healthy, sedentary (SED, 68 ± 2 yr) and eight physically active (ACT, 68 ± 1 yr) elderly men with peak O₂ consumption 25.5 ± 1.2 vs 35.7 ± 2.4 ml/min/kg (P < 0.01), respectively, were assessed with carotid baroreceptor (CBR) function using 5s pulses of neck pressure or suction (ranging from +40 to –80 Torr) delivered to the carotid sinus region at rest and during lower body negative pressure (LBNP) of –15 and –40 Torr. Changes in heart rate (HR) and mean arterial pressure (MAP) were assessed for CBR-HR and CBR-MAP gains, respectively. Overall CBR-HR gains in a range of 120 mmHg of carotid sinus pressure were greater (P < 0.01) in ACT than SED at rest and during LBNP. The derived peak CBR-HR slopes between ACT and SED at rest were –0.32 ± 0.07 vs –0.11 ± 0.02 bpm/mmHg (P = 0.007), respectively. However, there was no statistical difference (P = 0.37) in CBR-MAP gains between the groups. Neither CBR-MAP (P = 0.08) nor CBR-HR (P = 0.41) gain was augmented by LBNP in the elderly. Conclusion: Active lifestyle enhances the CBR-HR reflex sensitivity as a result of the improved vagal-cardiac function in elderly people. Aging is associated with an absence of central autonomic interaction in the control of blood pressure regardless of physical fitness.

Key Words: aging • arterial baroreflex gain • carotid sinus pressure • central autonomic dysfunction • lower body negative pressure