Cardiac changes during behavioral stress in dogs.

Alterations in heart rate (HR), left ventricular systolic pressure (LVP), and maximum rate of left ventricular pressure development (LV dP/dtmax) during a Sidman avoidance task were studied in eight chronically prepared dogs. Four of these animals comprised a nonstressed control group. In the experimental group, in addition to phasic increases in HR, LVP, and LV dP/dtmax during the avoidance period of each day, tonic increases in these measures were also observed over the 13 days of the experiment. Left ventricular systolic pressure was found to be least sensitive to the stress procedure inasmuch as the phasic changes were no longer present after the 10th day and tonic levels were within base-line values by the 13th day. When alterations in cardiac activity were observed in the nonstressed animals, there were decreases in function. It was concluded that controlled behavioral stress produces increased cardiac performance without increased bodily activity. It was also hypothesized that preavoidance increases in heart rate in experimental animals were the result of vagal influences on the heart, whereas avoidance increases in HR, LV dP/dtmax, and LVP were functions of increased beta-sympathetic activity on the heart and adaptive peripheral vascular changes.