Cardiovascular and respiratory effects of isoproterenol before and after artificial heart implantation.
Quantitation of peripheral vascular versus direct cardiac effects of isoproterenol (0.002 mg/kg) was attempted in a new pharmacologic animal model, the unanesthetized calf, before and after replacement of its natural heart with a pneumatically driven artificial heart (AH). Isoproterenol significantly increased (rho less then 0.01) cardiac output and pulmonary shunt and decreased aortic blood pressure before and after AH replacment. Elevation of cardiac output and pulmonary shunt was greater (rho less than 0.05) and depression of aortic pressure less (rho less than 0.05) before AH replacement than after. Isoproterenol did not change pulmonary artery (PA) or right atrial (RA) blood pressures before AH implantation but did reduce (rho less than 0.05) PA diastolic and mean pressures and increase mean RA pressures after. Systemic vascular resistance was significantly (rho less than 0.01) reduced by isoproterenol before and after AH implantation. Heart rate, 02 uptake, respiratory rate, tidal volume, and minute volume were all markedly increased before AH implantation but unchanged after. These findings demonstrate that approximately half the increase in output and pulmonary shunt and all changes in 02 uptake and respiratory dynamics after administration of isoproterenol are related to cardiac effects of the drug. Our data also suggest that the unanesthetized bovine before and after AH replacement is a unique model for study of the differential pharmacology of drugs with respiratory, cardiac, and peripheral vascular effects.