Oxygen conservation by propranolol and intra-aortic balloon pumping in the normal canine heart

Abstract

This study examines the effects of myocardial-depressant doses of propranolol (PROP) on myocardial oxygen consumption (MVO 2) during intra-aortic balloon pumping (IABP). The objective was synergistic reduction of MVO 2 with support of cardiac output (CO) by IABP as a model for myocardial preservation during ischemia. Accordingly, conventional hemo-dynamics, MVO 2, and plasma catecholamines were measured in seven open-chest dogs during IABP and administration of 2 mg/kg of PROP. compared with appropriate controls, MVO 2 decreased from 5.83 ± 0.49 (SE) to 3.47 ± 0.27 ml/min/100 g of LV ( P < 0.01), and LV dp/dt decreased from 1795 ± 114 to 1012 ± 64 ( P < 0.01) mm Hg/sec. However, CO decreased from 2.7 ± 0.5 to 2.1 ± 0.3 liters/min ( P < 0.05). In general, CO was linearly related to MVO 2; it was not possible to reduce MVO 2 without similar decreases in CO. The principal effect of IABP in the PROP-depressed circulation was to increase LV contractility by raising coronary perfusion pressure, with a resultant increase in both CO and MVO 2 when compared to the effects of PROP alone. The results indicate that while myocardial-depressant doses of PROP can provide dramatic reductions in MVO 2 in the canine model, large reductions in CO are unavoidable, even with IABP. Measurements of plasma catecholamines indicate that an important mechanism of action of IABP is reflex-induced reduction of circulating catecholamines.