Lung compliance and lung morphology following artificial ventilation in the premature and full-term rabbit neonate.

Rabbit neonates delivered on day 27--30 of gestation were subjected to intermittent positive pressure ventilation (IPPV) for 60 min. Tidal volume was standardized to 10 ml/kg, and the insufflation pressure required to maintain this tidal volume was recorded. The quasistatic compliance of the lung-thorax system, corrected for variations in body weight, was significantly lower in animals delivered on day 27--28 than in those delivered on day 29--30. Immature animals with low lung-thorax compliance (less than 0.40 ml/cm H2O.kg) regularly developed widespread necrosis of bronchiolar epithelium following IPPV, whereas no such lesions were observed in mature animals. It seems probable that these lesions are secondary to overdistension of bronchioles during IPPV and that this abnormal expansion pattern is related to a deficiency of surfactant in the lungs of immature newborn animals.