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(Circulation. 2003;107:1770.)
© 2003 American Heart Association, Inc.

Clinical Investigation and Reports

Baroreflex Buffering Is Reduced With Age in Healthy Men

From the Department of Kinesiology and Applied Physiology, University of Colorado, Boulder (P.P.J., D.D.C., D.R.S.); the Department of Medicine, University of Colorado Health Sciences Center, Denver (D.R.S.); and the Franz-Volhard Clinical Research Center and Helios Klinikum, Medical Faculty of the Charite, Humboldt University, Berlin, Germany (J.J.).

Correspondence to Pamela Parker Jones, PhD, Department of Kinesiology and Applied Physiology, University of Colorado at Boulder, UCB 354, Boulder, CO 80309. E-mail pamela{at}spot.colorado.edu

Background— Baroreflex buffering is an important mechanism in arterial blood pressure control. The effect of healthy (physiological) aging on tonic baroreflex buffering in humans is unknown.

Methods and Results— Baroreflex buffering was determined in 27 young (aged 25±1 years) and 16 older (aged 65±1 years) healthy normotensive men by measuring the potentiation of the systolic blood pressure (SBP) responses to a phenylephrine bolus (BRB_bolus) and incremental infusion (BRB_slope) during compared with before ganglionic blockade with trimethaphan. The SBP responses to phenylephrine either were not different or greater in the older men before ganglionic blockade, but smaller during ganglionic blockade. BRB_bolus (2.1±0.4 versus 5.1±0.7, P<0.001) and BRB_slope (1.6±0.2 versus 3.5±0.4, P<0.0001) were 115% smaller in the older men. Baroreflex buffering was not consistently related to mean levels or variability of blood pressure or heart rate, or to cardiovagal baroreflex sensitivity, but correlated with muscle sympathetic nerve activity (BRB_bolus: r=-0.55, BRB_slope: r=-0.69, P<0.005) and the SBP responses to phenylephrine during ganglionic blockade (BRB_bolus: r=0.53; BRB_slope: r=0.98, P<0.0001). BRB_bolus was also inversely related to the SBP response to phenylephrine before ganglionic blockade (r=-0.78, P<0.0001).

Conclusions— Physiological aging in men is associated with a marked reduction in baroreflex buffering. The decrease in baroreflex buffering with aging is related to increases in basal sympathetic nerve activity and reductions in systemic ₁–adrenergic vascular responsiveness. These findings are helpful for interpreting changes in baroreflex buffering in older patients with cardiovascular disease, as well as changes in responsiveness to vasoactive drugs with aging.

Key Words: autonomic • sympathetic activity • vascular responsiveness

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