DYNAMICS OF LUNG COLLAPSE AND RECRUITMENT DURING PROLONGED BREATHING IN PORCINE LUNG INJURY

Oleic acid (OA) injection, lung lavage, and endotoxin infusion are thr ee commonly used methods to induce experimental lung injury. The dynam ics of lung collapse and recruitment in these models have not been stu died, although knowledge of this is desirable to establish ventilatory techniques that keep the lungs open. We measured lung density by comp uted tomography during breath-holding procedures. Lung injury was indu ced with OA, lung lavage, or endotoxin in groups of six mechanically v entilated pigs. After a stabilization period, repetitive computed tomo graphy scans of the same slice were obtained during prolonged expirati ons with and without positive end-expiratory pressure and during prolo nged inspirations after 5 and 30 s of expiration. Lung collapse and re cruitment occurred mainly within the first 4 s of breath-holding proce dures in all three lung injury models, and some collapse and recruitme nt occurred even within 0.6 s. OA-injured lungs were significantly mor e unstable than lungs injured by bronchoalveolar lavage or endotoxin i nfusion. In this experimental setting, expiration times <0.6 s are req uired to avoid cyclic alveolar collapse during mechanical ventilation without extrinsic positive end-expiratory pressure.