Pulmonary Surfactant in Health and Disease.

towards the unless a distending surface tensions are alway more than 20 prasure were maintained to the dynes 'cm.'" .\ lung extract can be inacsurface forces. It is remarkable, however, tivated b! the following means: that the distending pressure necessary to ( 1 ) Addition of oleic acid or cholamaintain the inflation of an alveolus is terol to the surface. extremely low. apparently hecause the lung ( 2 ) Preparing the extract with distilled contains an extreniel) surface-active subwater instead of saline solution (presumstance. This surface-active substance, or pulably the cells are damaged and release inrnonary surfactant, can lower the surface hibiting substances). tension almost to zero and reduce the dis( 3 ) ~~~~i~~ above 40" to 4 2 " ~ . tending presure required. It cannot, how~h~ degree to which inactivation of the ever, maintain veq low surface tensions for surfactant occun in z,iz,o has not been adeprolonged periods time without a change quately determined, a l t h o u g h elevated of surface area. temperature can apparently inactivate the During this presentation. I will discuss surfactant reversibly in excised rat lungs.' the followine aspects of surface phenom~h~ studier indicated that if a low surena within the lung: face tension developed one could conclude 1. Current evidence of the nature of the that a highly surface active substance was pulmonan surfactant. present in the extract, but if low surface 2. Current concepts of the role of the tension did not develop, a deficiency of surpulmonary surfactant in maintaining alfactant could not be assured. veolar stability. It now appears that specific phospho3. The changinx compliance and evenlipids must he present in lung extracts if tual atelectasis that occurs with shallow surface tensions less than 10 dynes/cm. are breathing. which may be related to the to develop.' T h w phospholipids include time-dependent characteristics of the pulthe saturated lecithins and po~sibly sphinmonary surfactant. gomyelin. Cnsaturated fatty acids in the C l e m e n ~ and a%%oriates1 obtained pullecithin molecule greatly alter the surface monar) surfactant hyrinsing saline through tension so tha t a t 20°C.