Cardiac vagal efferent activity and heart period in the carotid sinus reflex.

KATONA, PETER G., JAMES W. POITRAS, G. OCTO BARNETT, AND BRIAN S. TERRY. Cardiac vagal eferent activity and heart period in the carotidsinus reflex. Am. J. Physiol. 218(4): 1030-1037. 1970. -The activity of single and multiple cardiac vagal efferent (CVE) fibers was recorded in anesthetized dogs under a variety of conditions. During the inspiratory phase of natural respiration the activity of CVE fibers always stopped or greatly decreased regardless of the value of blood pressure. When spontaneous respiratory activity was suppressed by producing a slight hyperventilation during artificial respiration, the following attributes of variation of CVE activity with blood pressure were observed: a) an increase in blood pressure increased vagal activity, whereas a decrease in pressure caused the vagal activity to decrease, b) variations in blood pressure affected CVE firing with a delay that depended on the blood pressure, c) sudden changes in baroreceptor activity were reflected as more gradual changes in CVE firing frequency, and d) under certain experimental conditions CVE fibers were inactive even though the baroreceptors were firing. A simple dynamic model, consisting of an ideal delay and an integrator with a singIe time constant, successfully described moderate changes in heart period due to changes in vagal activity. This model should aid the quantitative characterization of the dynamics of the cardiovascular control system. Techniques similar to those that were successfully used to record CVE activity in the dog seldom yielded positive results in the cat.