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Abstract
In the "virtual work model," left ventricular total mechanical energy (TME) is linearly related to myocardial oxygen consumption (MVO2). This relationship (MVO2-TME) is supposedly independent of inotropic stimulation, vascular loading, and heart rate variations. We reexamined the effect of inotropic stimulation (dopamine) on the metabolic to mechanical energy transfer in nine open-chest anesthetized pigs. Left ventricular mechanical energy was calculated using TME (mean ejection pressure x end-diastolic volume + stroke work), TMEW (end-diastolic volume reduced by unstressed ventricular volume), and the pressure-volume area (PVA). A highly linear relationship between MVO2 and mechanical energy was found for all three indexes during control and dopamine runs (r = 0.87-0.99). The slopes were unaltered by dopamine. y-Axis intercepts were (control vs. dopamine) as follows (in J. beat-1. 100 mg-1; means +/- SD): TME, 0.36 +/- 0.12 vs. 0.61 +/- 0.30 (P < 0.02); TMEW, 0.43 +/- 0.16 vs. 0.72 +/- 0.32 (P < 0.02); and PVA, 0.34 +/- 0.13 vs. 0.60 +/- 0.30 (P < 0.02). We conclude that the virtual work model is dependent on inotropic stimulation and that new insight into myocardial chemomechanical coupling is not added by this concept.
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