Stroke volume in conscious dogs; effect of respiration, posture, and vascular occlusion

Abstract

Right and left ventricular stroke volumes were measured beat by beat in tranquil, conscious, healthy dogs by electromagnetic flowmeter transducers implanted around the roots of the aorta and main pulmonary artery. The onset and time courses of stroke volume changes of each ventricle differed in response to respiration, passive change of posture, application and release of positive pressure, and occlusion of the inferior cava; the two ventricles were always out of phase and balance, and only appeared to be in phase when changes of heart rate dominated the picture. The immediate response to these events was probably determined by alterations in systemic venous return which changed end-diastolic fiber length and so altered stroke volume by the Frank-Starling mechanism. Changes of vagal tone might have played a small part by altering atrial contractility but sympathetic activity did not seem to be involved. The initial backflow in the pulmonary artery was taken as an index of the level of pulmonary vascular impedance and increased only when the transpulmonary pressure increased. ventricular stroke volume; electromagnetic flowmeter; Frank-Starling mechanism; autonomic tone; backflow pulmonary vascular impedance Submitted on December 3, 1964