Isotropy and homogeneity of lung tissue deformation

Triaxial force-extension tests on lung tissue cubes taken from excised dog lungs were performed to examine relative directional-dependent deformation behavior (isotropy) and locational-dependent deformation behavior (homogeneity). Four types of speciments were used: parenchyma tissue cubes from relatively young dogs (group A), parenchyma cubes from older aging dogs (group B), tissue cubes with intact pleural membranes on the cube surfaces (group C), and tissue cubes with one relatively large airway oriented along one of the principal axes (group D). The effects of aging and the presence of a pleural membrane and an airway on the deformation of lung tissue were also examined. Results indicate that mild anisotropic parenchymal deformation (less than 10% of the mean deformation) exists in relatively young lungs and to a lesser degree in older dogs. No significant locational dependence of deformation was found between upper and lower lobes. The pleural membrane slightly affected the directional deformation behavior pattern of the parenchyma tissue. The presence of an airway caused considerable data scatter with possible deformation characteristic change. It is concluded that the assumption of an intially isotropic and homogeneous parenchyma in gross modeling of lung deformation is reasonable.