Fig. 4. Percentages of all microscopic fields present in histological sections of tissue blocks sampled from apical, middle, and diaphragmatic lobes of all animals in each of the six groups (n = 6,267) and characterized by inflammation, alveolar wall disruption, hemorrhage, and edema. Lung samples were obtained in three groups of pigs without ALI (A, C, E, G ) and three groups of pigs with acid aspiration ALI (B, D, F, H ). 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. ALI – PEEP 5 = pigs with ALI and ventilated with PEEP 5 cm H2O for 1 h. ALI – PT = pigs with ALI and treated with PEEP titration. ALI – PT + RM = pigs with ALI and treated with PEEP titration plus three consecutive recruitment maneuvers during each PEEP level. P value less than 0.001 at the top of the figures indicates statistically significant difference existing among 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 maneuver.