Aging as a modulator of respiratory sinus arrhythmia.

Aging is associated with an accentuated shift toward sympathetic outflow. Evidence suggests that sympathetic and vagal-cardiac activity change reciprocally. If this hypothesis is correct, then aging would result in an attenuation of vagal-cardiac activity. The current cross-sectional investigation assessed the relationship between aging, vagal-cardiac activity, and arteriolar compliance (AC). Respiratory sinus arrhythmia (RSA) and finger plethysmography, noninvasive measures of vagal-cardiac activity and arteriolar compliance, respectively, were made on 70 normotensive male subjects (age range 15-81 years). Both RSA and AC decreased with age (r = .71 and .89, respectively, p < .001). Analysis of variance revealed significant differences between the six decade groups for RSA and AC (p < .05). These findings support the notion that there is an age-related loss of vagal-cardiac activity that could be partly explained by the loss of arteriolar compliance. These findings are consistent with the hypothesis that there is autonomic nervous system compensation of cardiovascular function in response to an age-related decrease in arteriolar compliance in a normotensive population.