Stress and Strain in the Lung

The stress-strain relationship of the lung tissue is described. There are two sources of stresses in the lung: that due to elasticity of the material, and that due to surface tension on the interfaces between the moist interalveolar wall and the air. A theoretical formula is derived for the stress-strain relationship on the basis of an idealized alveolar structure. Evidences supporting the validity of the formula are quoted. This formula is then used as the basis for analyzing the stress and strain distribution in the lung. An exact solution is obtained for a vertical lung supporting its own weight by hydrostatic pressure distributed on the pleura (the outer surface of the lung).