Surface tension properties of lung alveolar surfactant obtained by alveolar micropuncture

Abstract

A bubble method was used to record dynamic area/surface-tension diagrams (ASD's) both for lung alveolar surfactant (LAS) obtained by micropuncture of rat lung alveoli, and for pulmonary surfactant (PS) obtained by rinsing the bronchi. These ASD's are fundamentally like those characteristic of films of mixed lecithin and cholesterol. After lipid fractionation of the LAS material, typical lecithin and cholesterol films are obtained. At the end of the compression phase, the minimal surface tension of the LAS films and the PS films is 18–20 dyn/cm; this value is independent both of the amplitude of the area oscillation and of the absolute value of the area. The difference between maximal and minimal surface tension is dependent on the amplitude of oscillation of area or of radius, up to maximal surface tensions equal to the surface tension of the hypophase. These findings suggest that at least at the end of expiration, and presumably at other times as well, the difference in surface tension between alveoli of differing radii is not sufficient to guarantee the pressure compensation required to stabilize the alveolar structure of the lungs. ASD's of synthetic and alveolar lecithin films, as well as those both of synthetic and alveolar cholesterol films and of blood plasma films from the rat, clearly have properties other than those for LAS or PS films. Some consequences for respiratory mechanics are discussed.