Surface Adsorption of Pulmonary Surfactant in Relation to Bulk-Phase Concentration and Presence of CaCl2

Abstract

The adsorption rate of natural surfactant lipids was studied with a surface balance at 37 °C, with particular reference to the influence of various bulk-phase concentrations and to the presence of CaCl₂. On a hypophase of 0.9% NaCl, natural surfactant had rapid adsorption (1–5 s) in concentrations ≥ 0.5 mg/ml, whereas lipids extracted from the same surfactant showed a comparable adsorption rate only in concentrations ≥ 3.5 mg/ml. This indicates that natural surfactant contains some not yet identified nonlipid component enhancing the adsorption rate. On a hypophase of 0.9% NaCl +0.05% CaCl₂, the adsorption rate of extracted surfactant lipids was similar to that of natural surfactant on 0.9% NaCl. The concentration of surfactant phospholipids in fetal pulmonary fluid at term is about 0.6 mg/ml; our data suggest that at this concentration the adsorption of natural surfactant does not require the presence of bivalent cations to spread effectively in an air-liquid interface