Abstract
The dynamic behavior of changes in heart period in response to changes in frequency of supramaximal electrical stimulation of either pre- or postganglionic cardiac sympathetic nerves in five chloralosed cats pretreated with methyl atropine was investigated using time domain techniques. The typical response to step changes in frequency of stimulation (range 1–10 Hz) was found to be a decrease in heart period which reached a steady value after a short delay and was followed, after the stimulus was removed, by a slower return to prestimulus values. No significant difference was found between the responses to pre- and postganglionic stimulation although the strength of the stimuli required to achieve the same response was greater for postganglionic stimulation. Both the observed dynamic and steadystate responses were described to a good approximation by a first-order nonlinear system. The asymmetry in the response was accounted for by including in the model a second-order chemical reaction. The observed delay was accounted for by including a pure time delay. These results suggest that models proposed by previous investigators were unnecessarily complex.
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