Baroreflex Buffering Is Reduced With Age in Healthy Men

Abstract

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 α 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.