REMODELING OF THE CONSTITUTIVE EQUATION WHILE A BLOOD-VESSEL REMODELSITSELF UNDER STRESS

Changes in the mechanical properties of a blood vessel when it remodel s itself under stress are reviewed. One of the recent findings about b lood vessels is the rapidity of tissue remodeling when the blood press ure is changed. When the tissue structure and material composition rem odel, the zero-stress state of the vessel changes. The mechanical prop erties change also in the remodeling process. If the elastic behavior is expressed in terms of a pseudo-elastic strain-energy function, then the constants in the function will change in the course of the remode ling. With all these changes taking place, the scope of constitutive e quations broadens: it should now include a mass-and-structure growth-s tress relationship as well as a stress-strain-relationship. To obtain the mass-and-structure growth-stress relationship, one must be able to determine the mechanical properties of the different layers of the ve ssel wall, as well as the chemical composition and morphology. For the blood vessels, new methods of mechanical testing must be introduced. A key thought is to use bending of the blood vessel wall. By bending, different layers of the vessel wall are subjected to different stresse s, leading to equations that can be used to solve the inverse problem of determining the stress-strain law from measured stress and strain. In vitro and in vivo experiments and theoretical prospectives are pres ented.