Physical and physiological properties of dry lung surfactant

THE phospholipids of pulmonary surfactant1 cover the respiratory epithelium and because of their unique properties of lowering surface tension, spreading rapidly and sustaining high surface pressures, allow the lungs to expand easily and prevent their collapse. Deficiency of lung surfactant is the major cause of respiratory distress syndrome in premature babies and also contributes to the respiratory problems of paraquat poisoning and cardiac bypass surgery. It has generally been assumed that surfactant, whether in the lamellar bodies or alveoli, is in an aqueous environment and must, therefore, be hydrated. We show here, however, that fully hydrated surfactant is apparently inactive and that surfactant can only be effective as a surface monolayer if the source of the material is 'dry'. © 1978 Nature Publishing Group.