Mechanical behavior of lung parenchyma as a compressible continuum: a theoretical analysis

The mechanical behavior of bronchial volume with respect to parenchymal properties, and to both the intrabronchial and pleural pressure, was investigated utilizing a theory of finite elasticity. Treating the lung parenchyma as a compressible continuum, we derived a simple strain-energy density function from pressure-volume curves of saline-filled lungs. On the basis of this function, large deformations of the fluid-filled excised dog lobe could be analyzed by numerical procedures. For the purpose of obtaining peribronchial stress, the lung was represented by a hollow thick-walled cylinder corresponding to an axial bronchus with surrounding parenchyma. In general, we found that the theoretical results corresponded well to previous experimental results, being able to predict quantitatively the stress and strain around the bronchus during collapse previously demonstrated by Nakamura et al. Peribronchial radial and circumferential stresses were shown to be concentrated at the bronchial wall, but dissipated rapidly within 1-2 bronchial radii away from the wall. We conclude that the magnitude of regional lung recoil around bronchi during collapse can be plausibly estimated by a theoretical analysis of total lung pressure-volume relationships.