Determination of arterial behavior through material testing, numerical and finite element modeling.

摘要

Coronary artery atherosclerosis often is clinically silent or results in chronic stable angina due to chronic coronary luminal encroachment. The transition from this stable condition to an acute coronary syndrome is thought to reflect the transition from a stable to an unstable plaque, resulting in plaque rupture. This work was conducted in order to gain a better understanding of them solid mechanics involved in plaque rupture through three distinct studies.; Introduction. The purpose of initial study was to determine elastic and visco-elastic coronary artery wall material properties ex vivo using intravascular ultrasound (IVUS). Methods. The IVUS system was used to monitor the geometry of 17 vessels as a function of internal pressure load and time. Results. Arteries were found to have non-linear stress/strain behavior. The total tissue creep strain was epsiloncreep = 0.082 +/- 0.018 mm/mm with a tau creep = 1.85 +/- 0.54 seconds. Conclusions. IVUS can be used to determine both the viscoelastic and elastic material behavior of coronary arteries.; Introduction. The second study looked at what constitutive relations could accurately reproduce the porcine arterial behavior found in the first study. Methods. The equilibrium compatibility, and constitutive equations are applied at N discretized points in the arterial wall, in an efficient scheme using Mathcad software on a desktop computer. Results. The model reproduces experimental stress relaxation data with a correlation coefficient of 0.985 and can reproduce quasi-static stress strain data with equal accuracy. Conclusion. The program can reproduce the time dependent and steady-state responses seen in arterial tissue.; Introduction. The third study used non-linear finite element analysis to determine what factors influenced the stress distribution in a plaque. A sensitivity study was conducted on the effects of anisotrophy, changes in cap and lipid properties and changes in the cap and lipid geometries on plaque cap stress in the developing lesion. Results. The sensitivity study revealed that the models were sensitive to changes in geometry and changes in the material properties of the plaque cap and lipid pool. They were relatively insensitive to anisotropic changes in the cap material properties. Conclusion. Modeling of atherosclerotic lesions can provide researchers with valuable information that would not be available through other means. The use of linear elasticity is unacceptable for the modeling of atherosclerotic lesions. (Abstract shortened by UMI.)