INCREASE IN CIRCUMFERENTIAL STRESS IN ARTERIAL WALL BY LOSS OF FUNCTION OF ELASTIN

Increased mechanical stress in the arterial wall leads to an altered arterial function and structural degeneration. This investigation aimed to determine changing arterial wall circumferential stress due to altered elastic properties (e.g. by aging). Finite element modelling was used to evaluate circumferential stress profile in a typical model of abdominal aorta with lemellarstructure with a non-liner incremental stress-strain relationship tor the media. Results were obtained for a variety of interlamellar/lamellar stiffness rations. An increased interlamellar/lamellar elastic moduli ratio ( ζ ) indicates functional loss of elastin network and consequently a relative stiffening of the media. Maximum circumferential stress occurred at the lumen and increased by increase in ζ. By increse of ζ from 10 to 100, the maximum circumferential stress was evaluated from 0.73 MPa to 1.34 MPa for a luminal pressure of 110 mm Hg. The opening angle values of sheep aortic rings were evaluated to investigate effects of functional loss of elastin on the arterial circumferential residual stress. The opening angle (the angle which determines the opening of an aortic ring after cutting in radial direction) indicates the residual stress. The larger the opening angle the more residual stress. The opening angle values of aortic rings from 20 sheep aortic after treating with elastase and calcium chloride were compared to control group samples from the same arteral site. Results showed a statistically significant decrease in opening angle value after treatment. Treatments with elastase and calcium chloride result in the removal of elastin fibres and calcium binding to elastin fibres respectively, and consequently loss of function of elastin. The experimental results showed a decrease in circumferential residual stress due to functional loss of elastin. Residual stress in component compensates some part of maximum tensile stress caused by blood pressure on luminal edge. Any decrease in residual stress reduces effects of that compensation.