Hemodynamic dependence of myocardial oxygen consumption indexes

We tested the afterload and contractile state dependency of three indexes of myocardial oxygen consumption (MVO2): total energy requirement (Et), pressure work index (PWI), and pressure-volume area (PVA). MVO2 was measured in seven isolated canine hearts at four or five different end-diastolic volumes at each of three settings of afterload resistance and with the hearts contracting isovolumically. In several hearts, contractility was also varied by dobutamine infusion. Measured MVO2 (MMVO2) was compared with values predicted (PMVO2) by each index. There was always a high degree of correlation between MMVO2 and PMVO2 for each of the indexes. However, there was a large degree of variability in the coefficients of the MMVO2-PMVO2 relation from one heart to another. We also observed a statistically significant influence of both afterload and contractile state on the predictive power of each of the indexes. Thus each index that we tested had shortcomings in being able to predict MVO2 accurately over a wide range of hemodynamic conditions.