Cardiac oxygen consumption and systolic pressure volume area

Since we found that the total mechanical energy generated by ventricular contraction could be represented by a specific area (PVA) in the pressure-volume diagram, we have been studying the correlation between myocardial oxygen consumption (VO2) per beat and PVA in dog left ventricles. VO2 was found to be closely and linearly correlated with PVA under a variety of loading, heart rate, and contractile conditions. The regression of VO2 on PVA was given by VO2 = A X PVA + B.A was 1.8 X 10(-5) ml O2/(mm Hg ml) on the average and was relatively constant despite the changes in loading, heart rate, and contractile conditions. B was 0.02 ml O2/beat/100 g on the average in control contractile state and was relatively constant despite the changes in loading and heart rate conditions. However, B increased by 50-80% with 70-80% increases in Emax by epinephrine or calcium infused into the coronary circulation. After both VO2 and PVA were expressed in J/beat/100 g, the inverse of the slope coefficient A indicated that the energy conversion efficiency of PVA from the excess VO2 above the VO2 of the mechanically unloaded contraction was relatively constant at 40%, independent of the loading, heart rate, and contractile conditions.