Fig. 6. Mean alveolar area and mean linear intercept in pigs with (A , C ) and without (B, D ) acid aspiration acALI. PEEP 5 = animals ventilated with PEEP 5 cm H2O for 1 h, PT = PEEP titration, pigs treated with incremental and decremental values of PEEP, PT + RM = pigs treated with PEEP titration plus three consecutive recruitment maneuvers during each PEEP level. Dashed line indicates the median value of control pigs without mechanical ventilation. P value less than 0.001 at the top of the figures indicates statistically significant difference existing between the three groups using linear mixed models. Comparisons between two groups were performed using Tukey tests. *P < 0.01, PEEP 5 versus PT, §P < 0.01, PEEP 5 versus PT + RM. ALI = acute lung injury; PEEP = positive end-expiratory pressure; RM = recruitment maneuvers.