Comparison between Bretschneider's total myocardial energy demand (Et) and our total mechanical energy (PVA) as a predictor of cardiac oxygen consumption in dogs.

We compared the predictive capability of two indexes of ventricular oxygen consumption (VO2) in excised cross-circulated dog hearts. One of the indexes was Bretschneider's Et, formulated as the sum of energies for 5 different mechanical and nonmechanical activities of myocardium. The other one was the left ventricular systolic pressure-volume area (PVA), originally proposed by Suga. PVA is a measure of total mechanical energy and has been combined with Emax (ventricular contractility index) to predict VO2 in different inotropic states. When all data sampled from different hearts under various loading and inotropic conditions were pooled, both VO2 (Bret) predicted from Bretschneider's index and VO2 (Suga) predicted from Suga's index correlated well with the measured VO2 (VO2 (Measured)). However, VO2 (Bret) was more affected by the contraction mode as compared with VO2 (Suga), because the former includes ejection period as a parameter. Among the 5 terms of VO2 (Bret), the major correlate of VO2 (Measured) was found to be tension development energy term E3 which includes dP/dtmax as a parameter. VO2(Suga), as a predictive index of VO2 (Measured), was more reliable in each heart than in pooled data from all the hearts because of the interindividual variations of the coefficients. We conclude that both indexes have usefulness and limitations, and should be chosen depending on the application.