Data are mean ± SE. Statistical analysis was done using two-way analysis of variance (ANOVA) and followed, if significant, by Duncans test for multiple comparisons. In comparing results obtained at PEEP with those at ZEEP, the paired t test as modified by Dunnett was used. Significance was defined as p<0.05.
At ZEEP, the initial values (ie, before run 1) of PEEPi and Cst,rs of the ten patients were 1.6±1.1 cm H20 (range, 0.3 to 5.0 cm HaO) and 60 ±2 ml/cm HaO (range, 48 to 78 ml/cm H20), respectively. Figure 1 depicts the changes in EELV, Cst,rs, and PEEPi measured at ZEEP after the three subsequent inflation-deflation runs with PEEP All increased progressively after runs 1 and 2 with no further change after run 3. While Cst,rs increased significantly already after run 1, EELV and PEEPi increased significantly only after run 2. In line with the classic study of Mead and Collier, it is likely that the parallel increase of EELV and Cst,rs after runs 1 and 2 reflects recruitment of previously atelectatic alveoli. Thus, in this case, AEELV should reflect recruited lung volume (Vrec). The increase of PEEPi after runs 1 and 2 probably reflects the concomitant increase in Cst,rs and hence a decrease in expiratory driving pressure.
Figure 1. Effects of the three repeated stepwise inflation-deflation runs with PEEP (1,11,111) on end-expiratory lung volume (AEELV), static compliance of respiratory system (Cst,rs), and intrinsic PEEP (PEEPi).