Effect of positive end-expiratory pressure on lung compliance in dogs after acute alveolar injury.

We studied the effect of positive end-expiratory pressure (PEEP) on lung compliance (CL) in 17 dogs during the early phase of acute alveolar injury induced by the subcutaneous administration of N-nitroso-N-methylurethane (NNNMU). The acute phase of this injury is characterized by necrosis of the alveolar epithelium and by decreased CL, which is caused by abnormal surface forces and which correlates with decreased alveolar surfactant lipids. During the control period and after NNNMU both CL decreased significantly with increments of PEEP (p less than 0.001) and plots of FRC versus PEEP had a rising curve with a decreasing slope. Static volume-pressure curves obtained in vivo in 6 dogs showed a rightward shift of the curve without increase of hysteresis after NNNMU. these data suggest that in the surfactant-deficient lung, PEEP predominantly causes overdistention of patent alveoli rather than recruitment of closed air spaces. The physiologic response of the NNNMU-injured lung to PEEP differs from that of severely edematous lungs but is similar to that of surfactant-deficient lungs of premature lambs.