Effects of PEEP on inspiratory and expiratory mechanics in adult respiratory distress syndrome

The purpose of the present study was to assess the mechanical behavior of the respiratory system separately during inspiration and expiration in adult respiratory distress syndrome (ARDS) and the influence of PEEP on any phasic variations of the mechanical respiratory parameters. Airways pressure (P), flow (V), and volume (V) signals were recorded in nine patients with ARDS and 10 patients without known respiratory disorder (control group). All patients were artificially ventilated at three levels of positive end-expiratory pressure (PEEP): 0, 5, and 10 hPa. Data were analyzed separately for inspiratory and expiratory records using multiple linear regression analysis (MLRA) according to the equation: P=Ers V + Rrs V' + P-0, where Ers and Rrs represent, respectively, the intubated respiratory system elastance and resistance, and P-0 the end-expiratory pressure. In the ARDS group expiratory Ers (Ers(EXP)=45.58 +/- 4.24 hPa/L) was substantially higher (p < 0.01) than inspiratory Ers (Ers(INSP)=36.76 +/- 2.55) with a marked effect of applied PEEP in diminishing the difference between Ers(EXP) and Ers(INSP) (P < 0.01). For the ARDS group inspiratory Rrs (Rrs(INSP)) decreased significantly with increasing PEEP (PEEP=0: Rrs(INSP)=1643, PEEP=10: Rrs(INSP)=13.28, p < 0.01). The found differences between Ers(EXP) and Ers(INSP) could be attributable to an influence of mechanical ventilation by positive airway pressure on pulmonary edema and interstitial fluid during the inspiratory phase of the respiratory cycle. (C) 2002 Elsevier Science Ltd, All rights reserved.