Evaluation of some alternative mechanisms for interface-related stress relaxation in lung.

Lung surfactant might exchange reversibly between the alveolar gas-liquid interface and the liquid lining layer. This solubilization process could then contribute to time-dependent pulmonary mechanical phenomena. Theoretical analysis of a model alveolus shows how solubilization can produce recoil pressure relaxation of the lung. The analysis shows that for most experimental observations reported the solubilization kinetics probably could not have been determined by the actual fitting in, or squeezing out, of surfactant in the surface film. Most data are consistent with a solubilization rate controlled by diffusion in the liquid sublayer. However, in order for a diffusion-controlled mechanism to be significant the diffusing substance should be large, such as a micelle, and the alveolar liquid layer should be at least 1 micrometer thick. These conditions are quite realistic for slightly edematous lungs and thus might apply to many experimental, or pathological, situations.