Cardiovascular changes from expiration to inspiration during IPPV.

In vitro studies indicated that one ventricle can influence diastolic distensibility and systolic function of the opposite ventricle. Based on these in vitro observations, ventricular interdependence was examined in 12 anesthetized dogs. Right (RV) and left (LV) ventricular volumes and pressures and esophageal pressure (EP) were simultaneously measured during intermittent positive-pressure ventilation (IPPV) at zero end-expiratory pressure. Volumes were calculated from cineradiographic positions of endocardial, radiopaque markers. A comparison of the data obtained at end expiration with the data obtained at peak inspiration shows that EP decreased (4.6 +/- 0.3 to -2.1 +/- 0.2 mmHg, P less than 0.05) and RV end-diastolic volume increased (31.0 +/- 1.3 to 36.3 +/- 1.6 ml, P less than 0.05), whereas LV end-diastolic pressure increased (6.8 +/- 1.6 to 8.3 +/- 1.5 mmHg, P less than 0.05) and LV end-diastolic volume decreased (33.6 +/- 1.3 to 32.9 +/- 1.3 ml). The data indicate decreased LV distensibility as RV diastolic volume increased. As for systolic function, a comparison of end-expiration and peak inspiration data shows that RV ejection fraction increased (0.48 +/- 0.03 to 0.55 +/- 0.03 P less than 0.05) and RV stroke volume increased 5.6 +/- 1.0 ml, whereas LV ejection fraction decreased (0.54 +/- 0.03 to 0.52 +/- 0.03, P less than 0.05) and LV stroke volume decreased 0.8 +/- 0.6 ml. The decreased LV ejection fraction and stroke volume may suggest systolic interaction between the ventricles. The data indicate that the cardiovascular response to IPPV is complex, with ventricular interdependence being an important element.