Autonomic nervous control of the heart in exercising man

Effects of pharmacological denervation with propranolol (0.2 mg.kg-1) and/or atropine (0.04 mg.kg-1) on the control system of heart rate during exercise were studied using a frequency domain analysis, to evaluate the cardiac control function of autonomic nervous systems in man. Propranolol decreased the gain of the system in low frequency range and increased the gain slightly in middle and high frequency ranges. The phase angle of the system was advanced over the whole frequency range observed. Atropine decreased and delayed the gain and phase angle, respectively, especially in high frequency range. The combined administration of blockades significantly decreased the gain and delayed the phase angle in the whole and high frequency ranges, respectively. These findings suggest that sympathetic and parasympathetic nervous systems act nearly independently in controlling heart rate during exercise; that they act in different manners; and that the characteristics of the systems can feasibly be used to estimate clinically the cardiac control function of autonomic nerves in man.