New investigations of autonomic nervous system function.

Sensitive noninvasive techniques are available for beat-to-beat measurement of heart rate, blood pressure, and stroke volume. These allow for the assessment of the dynamic response capacity of the autonomic nervous system to stimuli that perturb baseline activity. In this review, the accuracy of volume clamp photoplethysmography for the measurement of finger arterial pressure and impedance cardiography for the measurement of cardiac output is critically evaluated. The utility of spectral analysis of blood pressure and heart rate for the routine assessment of autonomic function is discussed. It is suggested that these techniques will afford valuable information concerning central autonomic regulatory mechanisms and their dysfunction.