Time course of lung inflammatory and fibrogenic responses during protective mechanical ventilation in healthy rats

This study aimed to assess pulmonary inflammatory and fibrogenic responses and their impact on lung mechanics and histology in healthy rats submitted to protective mechanical ventilation for different experimental periods. Eighteen Wistar rats were randomized to undergo open lung-mechanical ventilation (OL-MV) for 1, 6 or 12 h. Following a recruitment maneuver, a decremental PEEP trial was performed and PEEP set according to the minimal respiratory system static elastance. Respiratory system, lung, and chest-wall elastance and gas-exchange were maintained throughout the 12 h experimental period. Histological lung injury score remained low at 1 and 6 h, but was higher at 12 h due to overinflation. A moderate inflammatory response was observed with a distinct peak at 6 h. Compared to unventilated controls, type I procollagen mRNA expression was decreased at 1 and 12 h, while type III procollagen expression decreased throughout the 12 h experimental period. In conclusion, OL-MV in healthy rats yielded overinflation after 6 h even though respiratory elastance and gas-exchange were preserved for up to 12 h.