Strain and Stress of Pulmonary Tissues

Abstract

A function in the form of F=A(e^ax-1) was proposed to predict the stress of pulmonary tissues over a wide range of strain. The expression could likewise be applied to a number of different tissues. In the expression, x was the strain, F the corresponding stress, A a constant determined by the quantity of the elastic system and a indicated the elastic property of the system. The latter constant was designated as elasticity constant. Its importance in the stress function consisted in its exclusive role to determine the pattern of the strain-stress relation. The elasticity constant was estimated around 4.0 with tissues composed mainly of elastic fibers. It was about 10 or more in tissues of predominantly collagenous type. As pulmonary tissues had values about 5.0 for a, it was concluded that the pulmonary elastic system was mainly constituted by elastic, not by collagenous, fibers. The possible influence of non-parallel orientation of fibers on the above stress function was analytically discussed. It was practically negligible so far as the estimation of elasticity constant was concerned. An attempt was made theoretically to derive the function on a hypothetical molecular model for the fiber.