AbstractDynamics of the chronotropic action of the efferent vagus on the heart has been studied in rabbits anesthetized by urethan. The analysis has been carried out in the manner used in the examination of technical control systems. The system of the efferent vagus and cardiac pacemaker was considered as a control element the input variable being the frequency of stimuli applied to the nerve and the output being the heart rate. A special stimulator was used enabling the sinusoidal modulation of the frequency of rectangular stimulating pulses. The sinusoidal modulating signal had constant amplitude but variable frequency. The frequency-modulated stimulation elicited oscillatory variations of the heart rate whose amplitude and phase shift against the driving signal could be precisely estimated. The relation of the amplitude and phase of these oscillations to their frequency was determined and the resulting values plotted in the form of a frequency-response characteristic and a Nyquist diagram both being th...
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