Differential cell count in the BAL fluid. The only cell types found in BAL fluid of unventilated control mice were monocytes and macrophages. In contrast, all samples from ventilated mice also contained neutrophils (Fig. 6) . Numbers of neutrophils were highest in mice ventilated with high V T . Considerably less neutrophils were recruited to alveoli of lowV T mice, whereof the group lowV T RM5 had the lowest neutrophil count. Histopathology. Histopathological samples revealed that no severe lung injury was induced by the ventilation strategies applied (Fig. 7) . Nonetheless, significant histopathological alterations were present in all ventilated lungs and were most obvious in mice ventilated with high V T (Fig. 8) . Alveolar septal thickening was observed in most of the ventilated lungs, resulting in a score of one. A score of two was given, when neutrophils were observed additionally, as in most lungs from highV T mice. This is in line with the results from the differential cell count in the BAL fluid. Only some highV T noRM mice showed alveolar congestion, bringing the lung injury score up to three. Hyaline membranes were not observed in any sections, indicating that the applied ventilation strategies induced only moderate injury in the healthy lungs.