Prediction of shear stress imposed on alveolar epithelium of healthy and diseased lungs.

Lung alveoli are modeled as spherical caps, lined internally by a thin surfactant-laden liquid film, and the periodic wall shear stress exerted along the epithelium during small-amplitude radial oscillations of their wall is computed. A novel set of boundary conditions, applied at the rim, reveals the dominant role of Marangoni stresses. These stresses develop along the air/liquid interface due to spatial gradients of interfacial surfactant concentration and are transported to the wall by the action of viscosity. The effect of a variety of geometric and functional characteristics, including rim interstitial thickness, alveolar opening angle and liquid film thickness and viscosity, is interrogated, and the results are discussed in relation to the onset and evolution of acute and chronic lung diseases, such as asthmatic attacks, pulmonary emphysema and pulmonary fibrosis.