Ventricular Performance Modified by Elastic Properties of Outflow System

Abstract

Left ventricular and atrial pressures, left ventricular circumference and longitudinal meridional segment length, coronary flow, and cardiac oxygen consumption were measured under conditions which permitted intentional variation of the elasticity of the left ventricular outflow system and comparison of cardiac performance during steady states in which heart rate, stroke work, and stroke volume were identical, but the outflow elastic storage capacity was varied. When ejecting through a rigid (as compared with a distensible) system, the left ventricle generated a larger fraction of the contractile tension under auxotonic conditions (i.e., during the ejection phase), and left ventricular systolic peak pressure was increased. Ejections through rigid tubes proceeded from higher diastolic ventricular pressures and larger external dimensions. The effort of hearts which ejected through rigid outflow conduits was associated with a reduced myocardial oxygen consumption. Studies of left ventricular performance in isolated hearts are physiologically significant only when the experimental arrangement comprises an outflow system with distensibility characteristics similar to that of the arterial tree.