Lung volume and pleural pressure effects on ventricular function

To investigate the changes in ventricular function that occur during continuous positive-pressure ventilation, we studied the effects of separate increases in lung volume, pleural pressure, and right ventricular afterload in 15 dogs. Isovolume increases of pleural pressure caused changes in right and left ventricular hemodynamics indistinguishable from those induced by preload reduction. Lung distension with the chest open to atmosphere caused both right and left atrial intracavitary pressures to rise as cardiac output fell, suggesting altered function of both ventricles. Raising right ventricular afterload by pulmonary artery constriction did not reproduce the hemodynamic changes observed during increases of lung volume. These data indicate that the apparent alteration of ventricular function that occurs during continuous positive-pressure ventilation is produced by the associated increase in lung volume and that a right ventricular afterload-ventricular interdependence effect is not the responsible mechanism.