Chronic nonpulsatile blood flow. II. Hemodynamic responses to progressive exercise in calves with chronic...

We investigated the effects of stepwise treadmill exercise on animal (calf) hemodynamic variables during chronic nonpulsatile biventricular bypass with ventricular fibrillation. Seven days was allowed for recovery from the effects of anesthesia and surgery; each animal's natural heart was then fibrillated. The pump flows were maintained at nominal rates of 90, 100, and 120 ml.kg-1.min-1 for 1 week each, with the order varying from experiment to experiment. A total of 30 incremental exercise tests were performed on five animals. No significant changes in mean aortic pressure were observed during nonpulsatile perfusion at the three nominal flow rates of nonpulsatile flow either before or during exercise. The systemic vascular resistance decreased significantly during exercise (from 705 +/- 22 to 547 +/- 81 dyne.sec.cm-5, p < 0.01, and from 604 +/- 25 to 510 +/- 15 dyne.sec.cm-5, p < 0.05, at nominal flow rates of 100 and 120 ml.kg-1.min-1, respectively). There were also significant (analysis of variance, Scheffe test, p < 0.05) differences in systemic vascular resistance among three nominal flow rates both before and during exercise. These results suggest that the autonomic nerve reflex control of the cardiovascular system in physical exercise was functioning normally in animals with chronic nonpulsatile blood flow.