Surface-active Material in Fetal Lung Fluid Concentrated by Foaming.

A fluid has been demonstrated to flow from the trachea of fetal lambs1,2). By studies with the modified Wilhelmy balance the fluid has been found to have a very low surface tension when the surface area is compressed to 20% of its maximal size3). These findings are of particular interest since the fluid originates from the lungs and is aspirated with initial aeration. It is likely that the surface activity of this fluid may be of importance in stabilizing the alveoli. The surface-active material in the lung is thought to be a lipoprotein with a phospholipid as the major active component4.5,6). It has been demonstrated that fetal lung fluid contains an appreciable amount of phospholipids3). It has also been shown that the active components of this material are lecithin and sphingomyelin7). According to Gibb's law, a surface-active material is concentrated in an air liquid interfaces). The foam produced by bubbling nitrogen through crude lung fluid is therefore likely to contain a greater concentration of surface-active material. The results of concentrating surface-active material from fetal lung fluid according to this principle are presented here. Crude fetal lung fluid, the foam obtained from it, and the residuum have been analyzed for active phospho lipid components and surface properties.