INFLUENCE OF BRETYLIUM ON RESPONSES OF THE HEART-LUNG PREPARATION: DMPP AND PARTIAL OCCLUSION OF THE PULMONARY ARTERY

The results derived from 12 canine heart-lung preparations show that DMPP elicits a biphasic response with an initial period of cardiac inhibition followed by stimulation. The former effect can be blocked by atropine and both are blocked by large doses of bretylium. Partial occlusion of the pulmonary artery does not cause an increase in systemic flow because of the loss of a functional sympathetic cardiac reflex. One heartlung preparation responded initially to DMPP by marked cardiac inhibition but the administration of epinephrine converted the response to that of cardiac stimulation. Such a procedure also resulted in an increase in systemic flow during partial occlusion of the pulmonary artery.