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Objective: The aim was to examine how regional variations in pericardial pressure affect the mechanical coupling between the ventricles., Methods: Canine hearts from 14 dogs (14.5-18 kg) were removed and placed in cold cardioplegia solution. Balloons were inserted into the left and right ventricles and the atria. Pericardial pressure over the left ventricle (Pclv) and the right ventricle (Pcrv) was measured with thin balloon catheters. Ventricular and pericardial pressures were measured, and ventricular and pericardial coupling was calculated, under control conditions and with increases in pericardial tension and fluid., Results: At baseline, regional differences in pericardial pressure occurred [Pclv > Pcrv, 4.0(SD 0.9) v 2.9(0.6) mm Hg, p < 0.05]. Ventricular coupling via the pericardium was defined as delta Pclv/delta Pcrv for right ventricular volume increases and delta Pcrv/delta Pclv for left ventricular volume increases. This ratio increased more after increasing right ventricular volume than after increasing left ventricular volume [delta Pclv/delta Pcrv > delta Pcrv/delta Pclv, 1.14(0.33) v 0.51(0.15), p < 0.05]. Increasing the pericardial tension by clamping the pericardium increased pericardial pressures, yet did not alter the regional variations in pressure [Pclv > Pcrv, 8.4(2.2) v 6.4(2.5) mm Hg, p < 0.05] or pericardial coupling [delta Pclv/delta Pcrv > delta Pclv/delta Pcrv, 1.18(0.46) v 0.54(0.16), p < 0.05]. In contrast, creating a mild tamponade increased pericardial pressures, eliminated regional differences in pressure, and altered the coupling between ventricles [delta Pclv/delta Pcrv approximately delta Pclv/delta Pcrv, 0.95(0.11) v 1.05(0.08), p = NS]. These regional differences in pericardial pressure might have a geometrical basis. In four in vivo canine experiments using cine magnetic resonance, the short axis radius of curvature for the right ventricle was greater than for the left ventricle [38.3(4.4) mm v 29.2(3.8) mm, p < 0.05]., Conclusions: The pericardium partially protects right ventricular filling: regional differences in pericardial pressure normally occurred with lower pericardial pressure over the right ventricle, and left to right ventricular coupling was less. This protection of right ventricular filling was lost with even a small pericardial effusion.

Objective: The aim was to determine if rapid changes in left ventricular pressure can acutely alter right ventricular systolic pressure and thus influence the length of right ventricular ejection., Methods: The experiments were performed in six open chest anaesthetised dogs, weight 18-25.5 kg. Left and right ventricular pressures and pulmonary blood flow were recorded continuously as left ventricular pressure was abruptly decreased by opening a shunt in systole. From these data, the pressure and flow changes and the duration of right ventricular ejection were determined., Results: Opening the left ventricular shunt caused left ventricular pressure to fall from 94.1(SD 10.5) to 62.6(11.3) mm Hg (p < 0.01), right ventricular pressure to fall from 30.3(4.6) to 27.0(3.6) mm Hg (p < 0.01), and pulmonary flow to fall from 69.5(14.2) to 57.5(13.9) ml.s-1. The duration of right ventricular ejection, determined from pulmonary flow, also decreased from 192.7(22.7) to 157.2(18.7) ms (p < 0.05) and was significantly related to the length of left ventricular systole. Time between end diastole and peak negative dP/dt decreased for both left and right ventricle. Left and right ventricular time intervals were related before (r = 0.99) and after (r = 0.75) opening the shunt., Conclusions: The duration of right ventricular ejection was decreased by a sudden decrease in left ventricular afterload and was significantly related to the length of left ventricular systole. The duration of right ventricular ejection may be coupled with left ventricular contraction through ventricular interdependence.

Study Objective: The aim was to measure the systolic coupling between the ventricles and to determine the relative importance of ventricular interaction in the pressure development of each ventricle., Design: Acute studies were done in dogs to measure the changes in right and left ventricular pressures (dPr, dPl) caused by sudden changes in left ventricular pressure (dPl') with release of an aortic constriction, and sudden changes in right ventricular pressure (dPr') with release of a pulmonary artery constriction, respectively. The instantaneous cross talk gain [dPr/dPl' (Klr) or dPl/dPr' (Krl)] was calculated during the ejection phase. The potential systolic pressure generated by the contralateral ventricle was evaluated as the cross talk gain multiplied by the contralateral systolic developed pressure., Experimental Material: Studies were done in eight random source dogs (12-18 kg), anaesthetised with sodium pentobarbitone., Measurements and Main Results: The maximal Klr was lower than the maximal Krl, at 0.09 (SD 0.05) v 0.25 (0.06), and the mean Klr also was lower than the mean Krl, at 0.04 (0.02) v 0.10 (0.03), p less than 0.05. The potential right ventricular pressures developed by the left ventricle [maximum 10.3(5.6), mean 4.8(2.7) mm Hg] were not significantly different from the potential left ventricular pressures developed by the right ventricle [maximum 8.8(2.7), mean 3.4(0.7) mm Hg]. However, the ratio between the potential transmitted pressure and the measured developed pressure was greater in the right ventricle [maximum 39.0(21.1), mean 17.8(8.9)%] than in the left ventricle [maximum 11.1(7.1)%, p less than 0.05; mean 3.9(1.5)%, p less than 0.01]. This suggests that about 20-40% of the right ventricular systolic pressure may result from the left ventricle and about 4-10% of the left ventricular systolic pressure may result from right ventricle., Conclusions: Although the pressure coupling was greater in right to left ventricular interaction, right ventricular pressure generation may be more dependent on the left ventricle. Systolic ventricular interaction may be more important for right ventricular systolic function. Further, the parameters of right ventricular systolic function currently used may be considerably affected by the left ventricle.