Surface spreading of lung alveolar surfactant

Abstract

Surfactants tend to spread over and reduce equally the surface tension of a surface. Indications were sought of the rate of spreading of lung alveolar surfactant in the presence of known differentials of surface tension. It was found to spread and abolish surface tension differences at a rate measured in centimeters/second whether the initial surface tension differential was relatively high (35 dynes/cm) or low (15 dynes/cm). Alveolar lung has been thought to be stabilized by maintenance of surface tensions at values which remain directly proportional to alveolar size. However, groups of alveoli of varying sizes are contiguous and, forming a single surface, possibly act as a unit with respect to surface tension because of rapid equalization of differences in surface tension. On the other hand, the equilibrium surface tension of lung alveolar surfactant is less than the equilibrium surface tension of material found elsewhere in the lung. Combining this fact with the tendency of surfactants to spread from areas of lower to areas of higher surface tension indicates that lung alveolar surfactant does originate in the alveoli and could act as an agent to remove substances from lung alveoli to the ciliated part of the lung structure.