Faclors ioncreasing the energy conversion efficiency of myocardial contractile machinery

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The aim of this project was to search for factors which can increase the energy conversion efficiency of the contractile machinery of myocardium. We used excised, cross-circulated dog left ventricles and analyzed the relationship belween left ventricular oxygen consumption (V02) and systolic pressure-volume area (PVA) as a measure of the total mechanical energy of ventricular contraction. The slope of the V05-PVA relation which is virtually linear indicales the reciprocal of the overall efficiency of the contractile machinery. We studied this efficiency 1) under cooling myocardium from 37C to 29C, 2) under global ischemia by lowering coronary perfusion pressure from 80 to 50 and to 30 mmhg, and 3) in quick release contractions in which release time was varied during systole. We found virtually no change in the slope of the V02-PVA relation under cooling and ischemia. However, quick release decreased the slope, suggesting an increased efficiency. However, We interpreted this result to reflect that the maintenance of PVA is energy-dependent and abbreviation of the maintenance saved V02. All these results help us better understand the coupling between mechanics and energetics of myocardium.