Tissue remodeling of rat pulmonary artery in hypoxic breathing. II. Courseof change of mechanical properties

When cells and the matrix of a tissue remodel, the mechanical properties of the tissue do change. The mechanical properties are expressed by constitut ive equations. In this article the remodeling of the constitutive equation of the pulmonary artery is studied. The remodeling was induced in a rat bre athing a gas whose oxygen concentration was suddenly decreased as a step fu nction of time and maintained constant (17.2%, 13.6%, or 10%) afterwards. S ince the mathematical form of the constitutive equation has been identified in earlier papers, we need to determine only the elastic constants that ch ange in the process of tissue remodeling. We consider arteries subjected to blood pressure and longitudinal stretch, and limit ourselves to two-dimens ional problems involving only circumferential and longitudinal stress and s train. In the neighborhood of an in vivo state, the perturbations of stress es and strains are related by linear, anisotropic, tensor equations involvi ng three elastic constants: the incremental Young's modulus in the circumfe rential direction Y-theta theta, that in the longitudinal direction Y-zz, a nd the cross modulus Y-thetaz. Over a 24 h period, changes of Y-theta theta between 164 and 187 kN/m(2), Y-zz between 64 and 92 kN/m(2), and Y-thetaz between 61 and 88 kN/m(2) are statistically insignificant. (C) 2001 Biomedi cal Engineering Society.