Instantaneous pressure-volume relationship of the canine right ventricle

The instantaneous isovolumic and ejecting pressure-volume relationship of the right ventricle was studied in 11 cross-circulated, isolated canine hearts to characterize the right ventricular contractile state. Accurate measurement of volume was achieved by the use of a water-filled, thin latex balloon in the right ventricle connected to a special volume loading and transducing chamber. Pressure was measured with a miniature pressure transducer mounted within the balloon. Wide variations in loading conditions were achieved by changing the volume of air above the volumetric chamber. The pressure and volume data were collected from multiple beats under a constant contractile state in the same mode of contraction while the left ventricle was vented to air. Linear regression analysis applied to each of the isochronal pressure-volume data sets at 20-msec intervals from the onset of contraction showed a highly linear correlation between the pressure and the volume. Both the slope and the volume intercept of the regression lines changed with time throughout the cardiac cycle. The maximal slope of the regression line (Emax) averaged 2.50 ± 0.49 mm Hg/ml (mean ± SD) for ejecting beats and 2.68 ± 0.55 mm Hg/ml for isovolumic beats. Epinephrine infusions of 12.5 μg/min and 25.0 μg/min increased Emax by 31% and 62%, respectively (P<0.005). Authors conclude that: The instantaneous pressure-volume relationship of the right ventricle in the isovolumic and ejecting modes can be regarded as linear, at least within the physiological range; however, these two modes of contraction did not yield an identical relationship. The slope of these pressure-volume relationship curves changes with a change in the contractile state.