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Comparison of hemodynamic determinants for myocardial oxygen consumption under different contractile states in human
H Takaoka1, M Takeuchi, M Odake
1First Department of Medicine, Kobe University School of Medicine, Japan.
Background:
Recently, several indexes such as tension-time index (TTI), tension-time or force-time integral (FTI), rate-pressure product (RPP), pressure-work index (PWI), and systolic pressure-volume area (PVA) have been developed as predictors of myocardial oxygen consumption in experimental and clinical studies. However, it is still unclear whether these indexes are reliable predictors of myocardial oxygen consumption under various contractile states in human hearts.
Methods And Results:
We assessed the relation between TTI, FTI, RPP, PWI, and PVA and myocardial oxygen consumption per beat (VO2) in 13 patients with heart disease during volume loading. Left ventricular (LV) volume and pressure were measured simultaneously by the conductance catheter with the tipped micromanometer technique. VO2 was calculated from arterial coronary sinus oxygen content difference, and coronary sinus blood flow was measured by the thermodilution method. After z transformation of the correlation coefficients, mean z value for the VO2-PVA relation (1.83 +/- 0.60) was greater than those for the VO2-TTI relation (1.22 +/- 0.66; p < 0.005), VO2-FTI relation (1.18 +/- 0.61; p < 0.05), VO2-RPP relation (0.95 +/- 0.65; p < 0.05), and VO2-PWI relation (1.24 +/- 0.58; p < 0.05). During dobutamine infusion (5 micrograms.kg-1.min-1) in five of the 13 patients, VO2 also correlated best with PVA (z = 1.70 +/- 0.89) compared with TTI (z = 1.43 +/- 0.86), FTI (z = 1.48 +/- 0.95), RPP (z = 1.00 +/- 0.53), and PWI (z = 0.88 +/- 0.80). The contractile efficiency (38 +/- 14% to 38 +/- 20%), the reciprocal of the slope of the VO2-PVA relation, remained unchanged, whereas the VO2,PVA 0.8 (VO2 at PVA = 0.8 J per beat/100 g LV) increased from 1.48 +/- 1.16 to 2.06 +/- 1.13 J per beat/100 g LV (p < 0.05). These results show the parallel upward shift of the VO2-PVA relation during dobutamine infusion. Because increases in the VO2-intercept represent the VO2 for the increased excitation-contraction (E-C) coupling associated with the augmented contractile state, the parallelism of the VO2-PVA relation could discriminate between VO2 for mechanical work (PVA-dependent VO2) and VO2 for E-C coupling (PVA-independent VO2).
Conclusions:
The results of the present study indicate that PVA is a reliable and valuable predictor of myocardial oxygen consumption under different contractile states in human hearts. The VO2-PVA relation could provide useful information about mechanoenergetics in diseased human hearts.