LUNG GAS VOLUMES AND EXPIRATORY TIME CONSTANT IN IMMATURE NEWBORN RABBITS TREATED WITH NATURAL OR SYNTHETIC SURFACTANT OR DETERGENTS

Immature newborn rabbits delivered at a gestational age of 27 days wer e tracheotomized and treated, via the tracheal cannula, with clinicall y recommended doses of natural or synthetic surfactant (Curosurf(R) an d Exosurf(R), respectively). Littermates received 0.1% tyloxapol, 5% T ween 20, or saline. The dose volume of Curosurf was 2.5 ml/kg, that of the other materials 5 ml/kg. Animals were kept in a multiplethysmogra ph system and ventilated for 30 min with a standardized sequence of in sufflation pressures. End-expiratory lung gas volume was calculated at the end of the experiment from measurements of lung weight and total lung volume. Tidal volumes were significantly improved in all groups o f animals receiving surfactant or detergents. However, expiratory time constant (determined from the tidal volume tracing) was significantly longer, and end-expiratory gas volume significantly larger, in animal s treated with Curosurf than in those receiving Exosurf or detergents. These differences were confirmed by semiquantitative evaluation of al veolar air expansion in histological sections. In addition, airway epi thelial necrosis was reduced in animals receiving Curosurf, Exosurf, o r Tween 20, but not in animals treated with tyloxapol. The discrepancy between improvements in tidal volume, expiratory time constant, and e nd-expiratory gas volume reflects failure of lung stabilization in ani mals treated with Exosurf or detergents, probably due to absence of sp ecific hydrophobic proteins in the synthetic products.