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Pulse transit time in the analysis of autonomic nervous system effects on the cardiovascular system.

The purpose of this study was the development of a simple method for assessing autonomic nervous system (ANS) effects on the cardiovascular system. Pulse transit time (PTT) is the interval between ventricular electrical activity and the peripheral appearance of the pulse (here measured by ear densitography). Six normal subjects were studied with six drugs which either enhanced or blocked activity of one of the three major divisions of the ANS: parasympathetic, beta-sympathetic, alpha-sympathetic. Data analysis revealed characteristic patterns of change in PTT and heart rate (HR) which permitted differentiation of five of the six drugs' effects. Vagal enhancement (edrophonium) and alpha-sympathetic enhancement (phenylephrine)—which reflexly also increases vagal tone to the heart—could not be distinguished from one another unless blood pressure also was monitored. Monitoring of PTT and HR offers a simple, non-invasive method which can be used on-line to evaluate ANS effects on the cardiovascular system.