In all runs AEELV increased significantly with PEEP of 5 and 10 cm H20 (p<0.001), w hereas Vrec increased significantly only at PEEP of 10 cm ILO (p<0.001) for all runs. In the three patients studied at PEEP of 15 cm H20, the values of both Vrec and AEELV’ were consistently much higher than those observed at PEEP of 10 cm H20 (Fig 3).
Figure 4 shows the average values ( + SE) of Cst,rs at ZEEP and at PEEP of 5 and 10 cm H20 obtained during the three inflation runs with PEEP in the ten patients. During run 1, Cst,rs increased slightly but significantly (p<0.()01) with PEEP of 5 and 10 cm ILO. During inflation runs 2 and 3, the changes in Cst,rs with PEEP were not significant. At ZEEP and PEEP of 5 cm ILO, the values of Cst,rs during inflation runs 2 and 3 were significantly higher than the corresponding values obtained in run 1. The changes in Cst,rs at ZEEP following the three consecutive inflation-deflation runs with PEEP are also depicted in Figure 1.
The values of Cst,rs, Vrec, and AEELV during stepwise PEEP decrease were significantly higher at all levels of PEEP compared with those obtained during PEEP increase, as shown in Figure 5 for PEEP of 5 cm H20. At this level of PEEP, the values of Cst,rs, Vrec, and AEELV obtained in the three runs with decreasing PEEP were not significantly different, although AEELV and Vrec tended to be higher during run 1.

Figure 4. Average values of static compliance of the respiratory system (Cst,rs) during stepwise inflation runs I, II, and III at three levels of PEEP in ten patients, Bars=l SE. Asterisk = p<0.05 versus run 1.

Figure 5. Average values of static compliance of the respiratory system (Cst,rs), recruited alveolar volume (Vrec), and changes in end-expiratory lung volume (AEELV) obtained at PEEP of 5 cm H20 during inflation (filled bars) and deflation (open bars) runs I, II, and III in ten subjects. Bars= 1 SE. P values refer to comparisons between inflation and deflation. Asterisk = p<0.05; two asterisks = p<0.01.