Airspace configuration at different transpulmonary pressures in normal and paraquat-induced lung injury in rats.

The aim of this study is to evaluate histoarchitecture of airspaces at different positive transpulmonary pressures, both during inflation and deflation of excised normal and paraquat-damaged rat lungs. Freshly excised lungs were placed in a plethysmograph connected to a graded pipette. Immediately after the achievement of the desired pressure level (5, 15, 25 cm H2O during inflation, and 15 and 5 cm H2O during deflation), the tracheal cannula was occluded and lungs were quick-frozen by immersion in liquid nitrogen, and fixed using Carnoy's solution. Sections representing the central and peripheral areas of the lungs were sampled and processed for paraffin embedding and stained with hematoxylin-eosin. By means of stereological techniques, surface-to-volume ratio (S/V) and the fraction of large-volume gas-exchanging airspaces (LVGEAS) were determined. We observed in paraquat-treated animals evidence of alveolar instability close to the resting volume. Structural unevenness was minimized by massive recruitment followed by alveolar pressurization. In conclusion, this work demonstrates that morphological evidence of uneven distribution of inspired air may be partially reversed by applying larger alveolar pressures. These larger pressures applied at the end-expiration in vivo (positive end-expiratory pressure, PEEP) can minimize the distortion of lung microarchitecture during ventilation.