Effect of PEEP on left ventricular function in right-heart-bypassed dogs

Positive-pressure ventilation with positive end-expiratory pressure (PEEP) has been associated with elevation of left ventricular filling pressure for a stable or reduced cardiac output. To exclude the possibility that right ventricular distension due to increased pulmonary vascular resistance decreases left ventricular compliance (ventricular interdependence), we studied the effect of PEEP on left ventricular function in open-chest right-heart-bypassed dogs. A rightward shift of the left ventricular function curve was caused by 15 cmH2O PEEP without a change in the aortic pressure-flow relationship. The pericardial pressure, however, was found to exceed atmospheric pressure on 15 cmH2O even with the chest widely opened. This increase in the pressure surrounding the heart accounted for the increase in left ventricular filling pressure. We postulate, therefore, that the elevation in left ventricular filling pressure found with PEEP is due in part, if not entirely, to mechanical interaction of the heart and lungs by direct compression or pericardial traction.