Predictive changes in ventricular interdependence

Based on the balance of forces across the interventricular septum, we developed a theoretical analysis to explain how one ventricle can directly influence the filling characteristics of the other ventricle. The analysis indicated that the pressure and volume transfer were related to the relative compliances of the interventricular septum and ventricular free walls. The present study examined whether the theoretical analysis could be used to predict changes in ventricular interdependence caused by altering regional compliance. To examine this hypothesis, hearts were removed from 18 dogs and placed in cool cardioplegic solution. Balloons were inserted into each ventricle, and the left and right pressure (δP₁, δP_r) and volume (δV₁, δV_r) changes caused by changing the pressure and volume of the other ventricle were recorded. After the initial measurements, acute changes in left ventricular free wall compliance (n=6), septal compliance (n=6), and right ventricular free wall compliance (n=6) were induced by glutaraldehyde injections. As predicted by the theoretical analysis, decreasing left ventricular free wall compliance increased δP₁/δP_r, δP₁/δV_r, δP_r/δV₁, and δV_r/δV₁ significantly (P<0.05) by 89±15, 155±33, 282±65, and 112±22% (mean±SEM), respectively. Decreasing septal compliance decreases δP₁/δP_r, δV₁/δP_r, δV₁/δV_r, δP_r/δP₁, and δV_r/δV₁ significantly (P<0.05) by 48±7, 71±10, 69±14, 48±7, 62±8, and 57±13%, respectively. Decreasing right ventricular free wall compliance increased δP₁/δV_r, δV₁/δV_r, δP_r/δP₁, and δP_r/δV₁ significantly (P<0.05) by 97±25, 79±20, 57±18, and 59±23%, respectively. Furthermore, these alterations in ventricular coupling were predictable: The actual and predicted percentage changes in the transfer functions were in close agreement. The results of these studies show predictable alterations in the mechanical coupling between the ventricles following changes in right ventricular septal, and left ventricular free wall compliances.