The surface properties of the lung in rats with alveolar lipo-proteinosis.

The physical behaviour of the intact lungs and of lung extracts from rats affected by alveolar lipo-proteinsosis as a consequence of silica inhalation, was studied by means of pressure volume relations and surface tension area loops. Air inflation of diseased lungs occurred at a lower pressure and collapse was less on deflation than in control specimens, although there appeared to be little change in elastic forces. When saline was used dusted rat lungs showed at higher lung volumes a peculiar hysteresis effect which is attributable to consolidation of alveoli by the lipid material. Extracts from affected lungs showed differences from controls in respect of maximum and minimum surface tensions and stability index but all the values fell within the accepted limits of normal. However, with extracts from pathological lungs the area of the hysteresis loop increased, the shape of the surface tension area curve was abnormal and the percentage compression required to reduce the surface tension to 120 muN/cm fell. Extracts from diseased lungs depressed the maximum surface tension of normal lung extracts and increased the hysteresis area but had little effect on the minimum tension, the stability index or the % compression to achieve 120 muN/cm. The response was thus mainly that of an extract from a dusted rat. The surface activity of phospholipids may be affected by neutral lipid, cholesterol and the products of cell breakdown, all of which occur in the alveolar material. The occurrence within the same lung of compunds which reduce surface tension and others which modify the same lung of compounds which reduce surface tension and others which modify this property suggests that their relative concentrations may determine the overall effectiveness of the lung lining.