抄録
Mechanical instabilities of canine arterial walls were theoretically analyzed. The unstable conditions of arterial walls were determined on the basis of the solutions of differential equations which described the equilibrium conditions of membrane forces both in the radial and axial directions under the condition of small deformation superimposed on the deformed cylindrical membrane. It was assumed that the blood vessel wall was represented as a cylinder of constant thin wall-thickness and of circular cross section, and also was composed of homogeneous, isotropic, incompressible material.
With canine abdominal aorta, common carotid and femoral arteries having normal tissue properties the unstable conditions never emerged. However, when the mechanical properties of the tissue were changed and it became more deformable, the likelihood of the cylindrical vessel having unstable conditions and of inducing the blow-out phenomena or vibration of the wall could be presumed. This unstable conditions depended also on the aspect ratio of the cylinder, i. e., the ratio of length to the radius. The mechanism described above was proposed as a new theory on the formation of abdominal aortic aneurysm. In view of the experimental evidence reported by Newman et al. to the effect that the incremental elastic modulus of aortic tissues of atherosclerotic cockrels had much lower values than normal ones in the early stages of atherogenesis, it could be pointed out that the elastic modulus was a dominant factor in early atherogenesis and that the localized dilatation of abdominal aorta might have occurred by the mechanical instability of aortic tissue if the elastic modulus fell to the level lower than some critical value in this early stage.
