Elasticity of excised dog lung parenchyma.

An experimental procedure was developed to measure the stress-strain relationship on rectangular slabs (5.0 X 5.0 X 0.5 cm) of excised dog's lung. The slabs were subjected to biaxial loading and the resulting triaxial deformations were measured. Deformations were measured in the central portion of the specimen by video dimension analysers in order to minimize boundary effects. Specimen thickness was measured with a magnetic reluctance proximeter system. The data were sampled and stored on-line by a PDP-8E computer. An electromechanical servo system was used to control the lateral force. Tests were performed at several pH values and at 20 and 37 degrees C. The tissue exhibited a highly nonlinear stress-strain relationship, compliant at low stress levels and stiff when the stress was high. Hysteresis was observed to be about 28% and was unaffected by a 250-fold change in strain rate. Biaxial loading revealed a new characteristic: there is a change in elastic behavior when the tissue undergoes a compressive strain. When the tissue was in tension increasing the lateral load decreased the compliance, but the opposite was true when compressive strain was present.