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

Background-Primary aging is associated with changes in the autonomic nervou s system (ANS), but the functional significance of these changes for system ic circulatory control of arterial blood pressure (BP) is unknown. We teste d 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/diast olic 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 mea n BP (radial artery catheter) with trimethaphan was almost twice as great i n the older men (-33 +/-2 versus -19 +/-2 mm Hg; -40% versus -22% of baseli ne; 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 differe nt. 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 w ith trimethaphan correlated with the standard deviation of the R-R interval s (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 re lated to measures of sympathetic activity (r=0.58 to 0.67, P <0.005), chang e 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 les s cardiac vagal inhibition of heart rate and cardiac output. Basal sympathe tic activity and a-adrenergic vascular sensitivity are also key physiologic al correlates of ANS support of BP in healthy men.