Surfactant dysfunction makes lungs vulnerable to repetitive collapse and reexpansion.

Reexpansion of collapsed lung creates intrapulmonary shear forces. In an earlier study we showed that application of a negative end-expiratory airway pressure (NEEP) to normal rabbit lungs in vivo produced tidal collapse and reexpansion with transient changes in compliance and gas exchange but no histologic damage. In the present study we examined NEEP in a model of surfactant perturbation produced by an inhaled aerosol of 2% and 5% dioctyl sodium sulfosuccinate (DOSS). DOSS increased alveolocapillary permeability without affecting compliance or oxygenation. Repeated collapse and reexpansion (RECOREX), caused by NEEP for 3 h was compared with ventilation with positive-end expiratory pressure (PEEP). Groups ventilated with PEEP maintained normal lung mechanics and morphology even if pretreated with DOSS. NEEP disturbed lung mechanics and gas exchange with persistent dose-related histologic damage in animals pretreated with DOSS. Lungs subjected to NEEP without DOSS had normal morphology. We conclude that perturbation of the surfactant system makes lungs vulnerable to injury by RECOREX. The combination of DOSS and NEEP might lead to leakage of plasma proteins into alveoli, causing inactivation of surfactants and increased shear forces with resulting lung damage. Similar mechanisms may accelerate lung damage in the respiratory distress syndrome.