Effects of Coronary Blood Flow and Perfusion Pressure on Left Ventricular Contractility in Dogs

Abstract

The effects of changes in coronary blood flow and coronary artery pressure on left ventricular (LV) contractility were determined in 18 animals. Dogs on cardiopulmonary bypass provided isovolumetric LV contractions during controlled perfusion of the coronary circulation. Coronary venous efflux, myocardial oxygen consumption, peak LV pressure, LV dp/dt, and the force-velocity relations of the LV were determined at normal and at "supernormal" levels of flow and pressure. Coronary vasodilatation was obtained with nitroglycerine, permitting independent variation of flow and pressure. Augmenting flow by increasing pressure increased LV contractility, as reflected by increases in peak LV pressure, dp/dt max, peak wall tension, and maximal measured contractile element velocity. Increased contractility appeared to be primarily due to increased flow, rather than to pressure, as an increase in flow without an increase in pressure produced similar changes, and decreases in pressure at constant flow did not change maximal measured contractile element velocity or dp/dt max, although some decrease in peak LV pressure and wall tension did occur. These data suggest that coronary flow is an independent determinant of the contractile state of myocardium, and that an increase in flow in excess of that required to supply metabolic demands augments myocardial contractility.