Instantaneous pressure-volume relationship of the canine right ventricle.

Abstract

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. Volume was measured by 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. Variations in loading conditions were made 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 ms intervals from the onset of contraction showed a linear correlation between pressure and volume. 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 .mu.g/min and 25.0 .mu.g/min increased Emax by 31 and 62%, respectively (P < 0.005). Apparently the instantaneous pressure-volume relationships of the right ventricle in the isovolumic and ejecting modes are linear within the physiological range; the 2 modes of contraction do not have an identical relationship. The slope of these pressure-volume relationship curves changes with a change in the contractile state.