Effect of PEEP on respiratory mechanics in anesthetized paralyzed humans

With the use of the technique of rapid airway occlusion during constant flow inflation, respiratory mechanics were studied in eight anesthetized paralyzed supine normal humans during zero (ZEEP) and positive end-expiratory pressure (PEEP) ventilation. PEEP increased the end-expiratory lung volume by 0.49 liter. The changes in transpulmonary and esophageal pressure after flow interruption were analyzed in terms of a seven-parameter "viscoelastic" model. This allowed assessment of static lung and chest wall elastance (Est,L and Est,W), partitioning of overall resistance into airway interrupter (Rint,L) and tissue resistances (delta RL and delta RW), and computation of lung and chest wall "viscoelastic constants." With increasing flow, Rint,L increased, whereas delta RL and delta RW decreased, as predicted by the model. Est,L, Est,W, and Rint,L decreased significantly with PEEP because of increased lung volume, whereas delta R and viscoelastic constants of lung and chest wall were independent of PEEP. The results indicate that PEEP caused a significant decrease in Rint,L, Est,L, and Est,W, whereas the dynamic tissue behavior, as reflected by delta RL and delta RW, did not change.