Altered autonomic support of arterial blood pressure with age in healthy men

Background-Primary aging is associated with changes in the autonomic nervous system (ANS), but the functional significance of these changes for systemic circulatory control of arterial blood pressure (BP) is unknown. We tested the hypothesis that ANS support of BP is altered in healthy older humans. Methods and Results-A total of 23 young (aged 24 +/-1 years; systolic/diastolic BP, 126 +/-2/66 +/-1 mm Hg) and 16 older (aged 65 +/-1 years; systolic/diastolic BP, 125 +/-3/62 +/-2 mm Hg) healthy men were studied before and during ganglionic blockade (intravenous trimethaphan). The reduction in mean BP (radial artery catheter) with trimethaphan was almost twice as great in the older men (-33 +/-2 versus -19 +/-2 mm Hg; -40% versus -22% of baseline; P <0.01) due to a lack of increase in heart rate (3 +/-2 versus 25 +/-2 bpm; P <0.001) and cardiac output (-0.42 +/-0.19 versus 1.01 +/-0.26 L/min; P <0.001); the decreases in systemic vascular resistance were not different. The absence of tachycardia in the older men was associated with reduced baseline heart rate variability (HRV, P <0.05); the change in heart rate with trimethaphan correlated with the standard deviation of the R-R intervals (HRVSD R.R interval; r=0.57, P <0.001). Among individual subjects (pooled groups), the reductions in mean BP with trimethaphan were most strongly related to measures of sympathetic activity (r=0.58 to 0.67, P <0.005), change in mean BP with intravenous phenylephrine (r=0.57, P <0.001), and HRVSD (R.R interval) (r=-0.40, P <0.01). Conclusions-ANS support of BP is altered with age in healthy men due to less cardiac vagal inhibition of heart rate and cardiac output. Basal sympathetic activity and a-adrenergic vascular sensitivity are also key physiological correlates of ANS support of BP in healthy men.