Paradoxical rise in left ventricular filling pressure in the dog during positive end-expiratory pressure ventilation. A reversed Bernheim effect.

Controversy exists whether positive end-expiratory pressure (PEEP) ventilation lowers cardiac output by reducing left ventricular preload, or by a combination of mechanisms. Sixteen open-chest dogs were instrumented for measurement of left and right ventricular pressure, aortic flow, and left ventricular dimensions. With the pericardium intact, PEEP caused the interventricular septum to bulge toward the left ventricular chamber, increased right and left ventricular end-diastolic pressures, but decreased the average of the three left ventricular dimensions. When right ventricular filling pressure was suddenly reduced, the interventricular septum moved back toward the right ventricle, and left ventricular filling pressure fell. With the pericardium removed, PEEP was associated with a decrease in all three left ventricular end-diastolic dimensions but no significant change in left ventricular filling pressure. Although several indices of contractility were decreased during PEEP, all returned to baseline values when left ventricular preload was normalized during PEEP by a rapid infusion of heparinized blood into the left atrium. In conclusion, PEEP decreases preload and significantly alters the shape and compliance of the left ventricle with the pericardium intact. With the pericardium removed, PEEP produces proportional decreased in major and minor axis dimensions, does not appear to affect left ventricular contractility independent of preload, and alters left ventricular compliance to only a small degree.