THE EFFECTS OF DYNAMIC CARDIAC COMPRESSION ON VENTRICULAR MECHANICS AND ENERGETICS - ROLE OF VENTRICULAR SIZE AND CONTRACTILITY

The purpose of this study was to determine the role of ventricular siz e or contractility in the effectiveness of dynamic cardiac compression in terms of the pressure-volume relationship and myocardial oxygen co nsumption. In 10 isolated cross-circulated dog hearts, the ventricle,v as directly compressed during systole. For the volume run, measurement s for slope of the end-systolic pressure-volume relation, pressure-vol ume area, external work, coronary blood flow, and myocardial oxygen co nsumption were achieved before and during a fixed amount of dynamic ca rdiac compression. Left ventricular volume was then increased while st roke volume was kept constant, and measurements were repeated. For the contractility run, after the control measurements were taken, left ve ntricular contractility was significantly increased or decreased by in fusion of either dobutamine or propranolol into the coronary circulati on. Measurements were repeated before and during dynamic cardiac compr ession at the control level of end-diastolic and stroke volumes. Dynam ic cardiac compression significantly increased slope of the end-systol ic pressure-volume relation, pressure-volume area, and external work ( p < 0.01), whereas coronary blood flow and myocardial oxygen consumpti on were not affected. The increase in pressure-volume area caused by d ynamic cardiac compression was greater with the larger volume. Despite the significant differences in the native left ventricular contractil ity, the increases in slope of the end-systolic pressure-volume relati on, pressure-volume area, and external work did not differ among the t hree groups. We conclude that dynamic cardiac compression enhances lef t ventricular systolic function independent of ventricular contractili ty and without affecting coronary blood dow or myocardial oxygen consu mption. Mechanical enhancement is more effective in the dilated heart.