Similar normalized Emax and O2 consumption-pressure-volume area relation in rabbit and dog

The end-systolic pressure-volume relation (ESPVR), a measure of ventricular contractile state, and systolic pressure-volume area (PVA), a primary determinant of cardiac oxygen consumption per beat (VO2), have been derived from the pressure-volume diagram of the cross-circulated dog left ventricle. The slope of the PVA-VO2 relation represents the efficiency of chemomechanical energy transduction of the contractile machinery. To see whether these relationships were similar in other animals, we studied the isovolumic ESPVR and the VO2-PVA relation in nine excised, cross-circulated rabbit left ventricles. The base-line ESPVR was linear (r = 0.94-0.99) with the slope (Emax) and volume-axis intercept (V0) equal to 83.4 +/- 18.3 mmHg/ml and 0.43 +/- 0.17 ml, respectively. When normalized for left ventricular weight, Emax (4.1 +/- 1.1 mmHg.ml-1.100 g) and V0 (8.9 +/- 3.7 ml/100 g) were similar to values reported for the dog left ventricle. The correlation between PVA and VO2 was linear (r = 0.93-1.00), and the slope (1.90 X 10(-5) +/- 0.44 X 10(-5) ml O2.mmHg-1.ml-1) and VO2-axis intercept (0.040 +/- 0.009 ml O2.beat-1.100 g-1) were similar to values found in the dog left ventricle. Hence, despite the greatly different heart size, the base-line contractile state and chemomechanical energy conversion efficiency of the excised, cross-circulated rabbit left ventricle are similar to those of the dog left ventricle.