Biaxial elastic properties of rat arteries in vivo: influence of vascular wall cells on anisotropy.

There is no consensus as to the degree of arterial anisotropy or to its relationship to vascular cell function. Given the relevance of the isotropic assumption in formulating elasticity models, reliable measures of biaxial displacements are needed. In this study, a video motion analyzer (VMA) was used to describe the biaxial in vivo dynamic elasticity of 22 carotid arteries and 5 abdominal aortas in 27 rats. The influence of vascular cell function was also examined by subjecting six rats to a photosensitive drug, chloroaluminum sulfonated phthalocyanine (CASPc), which is focally cytotoxic on activation by laser. Circumferential compliance (Ccirc) was greater than longitudinal compliance (Clong) for all vessels. Compliance pressure curves were nonlinear, and biaxial displacements were in phase. The circumferential elastic modulus was less than the longitudinal modulus at common stresses. CASPc + laser reduced Ccirc but not Clong, thus altering Poisson's ratio. In conclusion, rat arteries are biaxially, nonlinearly elastic and anisotropic in vivo. Vascular cells modulate Poisson's ratio by influencing Ccirc.