Cardiac function and exercise training in conscious dogs.

Exercise training (T) was accomplished in 21 mongrel dogs. The animals were instrumented to measure ascending aortic flow, left ventricular pressure, and left atrial pressure. They were allowed to recover for 4 wk following surgery before accomplishing a standardized submaximal test (SMT). The exercise program alternated daily between sprint and endurance training. During T, the animals were tested while lying quietly on a laboratory table as well as during the SMT. In six animals, ventricular function curves (VFC) were obtained by rapid volume loading at similar time intervals as the SMT. Heart rate increased during the SMT but was found to be reduced in the T animals by an average of 20 beats/min. The maximum derivative of left ventricular pressure (P) increased during the SMT in T animals by an average of 2,200 Torr/s above the untrained animals. The VFC was lower in T animals than untrained animals because of a reduction in heart rate response. Results indicate a reflex adaptation of the nervous system with training to improve cardiac function.