Two-Dimensional in-Vitro Studies of Femoral Arterial Walls of the Dog

Analyses of the vascular system have characteristically been based on assumptions that the vessel wall is isotropic and that its properties and behavior can be linearized. To test the validity of these assumptions, excised arteries of dogs were submitted to stepwise strains tangentially and longitudinally during conditions of control, vasoconstriction, and inhibition of muscle metabolism. These strains were recorded simultaneously with the associated stresses, and the relations between stress and strain were studied during both dynamic-and steady-strain states. The vessels were anisotropic within most of the physiological ranges of tangential and longitudinal stress and strain. During control conditions the tangential modulus of elasticity was higher than the longitudinal; during vasoconstriction the situation was reversed for wall tensions corresponding to a blood pressure equal to or smaller than 190 mm Hg; however, above this value isotropic behavior prevailed. Vasoconstriction increased the non-linearity of the stress-strain relation, and decreased the modulus of elasticity of the arterial wall. The viscoelastic properties of the femoral artery were found to be different tangentially and longitudinally, as evidenced by a much larger amount of stress relaxation in the former direction than in the latter.