Comparison of cardiovascular responses and left ventricular work during exercise before and after artificial heart...

Cardiovascular dynamics and left ventricular work were evaluated in 15 resting, standing, and treadmill-exercised calves before and at periodic intervals after their natural hearts (NH) were replaced with an artificial heart (AH). Standing produced increases in heart rate, cardiac output, oxygen uptake, and left ventricular work and decreases in mean aortic pressure and systemic vascular resistance in NH calves which were more marked with exercise. AH calves had higher aortic pressures, cardiac output, systemic vascular resistance, oxygen uptake, and left ventricular work during resting conditions in the first 2 postoperative weeks than did NH calves, which gradually returned to values similar to the latter by the fifth week after operation. Exercise was not tolerated early after AH implantation, but was after 5 to 6 weeks. Our results indicate that AH calves increase cardiac output with exercise by reducing systemic vascular resistance, whereas NH animals respond similarly, but also increase heart rate. The data suggest that a marked elevation in systemic vascular resistance early after AH implantation increases left ventricular work and prevents adequate rises in cardiac output to all but minor increases in metabolic requirements.