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Am J Physiol Heart Circ Physiol 276: H1339-H1345, 1999;
0363-6135/99 $5.00
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Vol. 276, Issue 4, H1339-H1345, April 1999

Oxygen-wasting effect of inotropy  in the "virtual work model"

Christian Korvald, Odd P. Elvenes, Lars M. Ytrebø, Dag G. Sørlie, and Truls Myrmel

Department of Thoracic and Cardiovascular Surgery, University Hospital of Tromsø, N-9038 Tromsø, Norway

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 × 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.

left ventricle; myocardial oxygen consumption; myocardial energetics; pressure-volume area; total mechanical energy


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