The effect of positive end-expiratory pressure ventilation on atrial filling.

As a measure of atrial filling, left and right auricular diameter and free wall segment length were recorded by sonomicrometry during incremental positive end-expiratory pressure (PEEP) in eight acutely instrumented closed chest dogs. The effect of PEEP was assessed with the pericardium open (n = 6) and closed (n = 8). On both occasions, PEEP decreased left auricular diameter (P less than 0.05). PEEP also caused a reduction in right auricular diameter with the pericardium open (P less than 0.05), while the variable was unchanged with the pericardium closed. PEEP did not cause any changes in either left or right free wall segment lengths. Both left and right auricular pressure-diameter relationships were progressively shifted leftwards with incremental PEEP. These observations suggest that PEEP may reduce left ventricular output not only by interfering with passive ventricular filling, but also by reducing atrial dimensions.