ELASTIC PROPERTIES OF HUMAN AORTAS IN RELATION TO AGE AND ATHEROSCLEROSIS - A STRUCTURAL MODEL

A new structural model is described for the tension-radius relationshi p of blood vessels, taking into account their mechanically important c onstituents: collagen, elastin and smooth muscle. The model has four c haracteristic parameters: E(C), the Young's modulus of the collagen fi bres; E(SE), the Young's modulus of the combined smooth-muscle/elastin network; epsilon(mu), the amount of strain at which the high stiffnes s region on the tension-radius curve is reached, and eta an indicator for the degree of collagen fibre stretching. The structural stiffness of the wall constituents is reflected by E(C) and E(SE) whereas the gl obal stiffness of the entire blood vessel is described by epsilon(mu) and eta. All these elasticity parameters are pressure independent, in contrast to generally quoted values for the incremental modulus or vas cular compliance which are stongly pressure dependent. Hence, an objec tive comparison of the mechanical properties for various types of bloo d vessel, based on the present model parameters, has been made possibl e. The model was successfully fitted to tension-radius data of 65 huma n aortas, age range 30-88 years, with moderate or severe atheroscleros is. The structural as well as the global stiffness changes with age, e .g. collagen stiffness shows a ninefold increase over 60 years. Global stiffness depends on atherosclerosis.