Barotrauma susceptibility in hamster lungs following elastase exposure

The hypothesis that reduced lung compliance increases barotrauma susceptibility was tested in isolated hamster lungs. Elastase, instilled intratracheally in some hamsters from 4 h up to 8 days prior to testing, caused a patchy distribution of acute suppurative bronchiolitis and pneumonia. Airway blockage and decreased compliance were the anticipated results. For testing, anesthetized animals were ventilated with positive end-expiratory pressure prior to opening of the chest wall; this minimum pressure was maintained throughout testing. Transpulmonary pressure and lung volume changes, determined plethysmographically, were used to calculate quasi-static (C) and dynamic compliance (Cdyn) over a 2-ml tidal volume at frequencies up to 120 breaths/min. Some lungs were exposed, airway open, to a vacuum to stimulate a rapid ascent to the surface. All lungs were eventually pressurized through the trachea to determine rupture pressure (Pr). Rupture pressure exhibited an unexpected dichotomy apparently unrelated to elastase exposure. Statistically C did not differ between the elastase-treated and nontreated animals. Compliance correlated with Pr in a well-defined group (elastase-treated, nonevacuated lungs), but compliance had no value in predicting Pr for the group as a whole.