Surface Properties of Lung Extracts

AbstractExtracts of rabbit lungs from adult animals as well as from fetuses near term were studied with a dynamic alveolar model and with a modified Wilhelmy balance. With both methods the minimal value of surface tension was significantly higher in the fetal extracts, probably because they have a lower concentration of surface active material. With no change in surface area the extracts from adult lungs after 30 min had a mean surface tension of 41 ± 5 dyn/min. When surface area was compressed the tension decreased and when the surface area was expanded the tension increased. The difference between the mean value and the minimal or the maximal value was a function of change in surface area as well as time. The change in surface area and the rate with which it occurs in the lungs is more closely simulated with the dynamic alveolar model than with the modified Wilhelmy balance. The minimal value of surface tension was recorded at minimal surface area. It increased if surface area was maintained at minimal size. This demonstrates viscosity of the surface film. For alveolar stability the outlining film should probably have high viscosity as well as low surface tension. In the newborn these properties have to develop rapidly to prevent alveolar collapse.