| The long term patency of surgical bypass grafts is reduced by the development of distal anastomotic intimal hyperplasia (DAIH), which can lead to stenosis or thrombosis of the graft-artery junction. The non-physiological structural mechanics of the vascular reconstruction are thought to promote DAIH, however, the exact mechanism of DAIH formation has not yet been elucidated, and is the subject of this thesis.;Even though arterial behaviour is nonlinear and anisotropic, and arteries are subject to large strains and deformations in vivo, most analyses of vascular mechanics in complex three dimensional geometries use linear, isotropic, small strain models. In the present study, a strain energy density function (SEDF) r0W=12aI 2E-bIIE is used to describe the large strain mechanics of blood vessels. This model is shown to predict the nonlinear stress stiffening behaviour of blood vessels as well as the role of residual stresses in reducing stress gradients through the vessel wall. The applicability of this model to describing the behaviour of blood vessels subjected to physiological axial stretches, inflation pressures and torsion is also demonstrated. The above SEDF is incorporated into an efficient finite element model of vascular mechanics so that the stress distribution in complex 3-D graft-artery anastomoses can be calculated.;Stress analyses of graft-artery junctions, which include suture-induced stress concentrations, are presented. These analyses demonstrate that, in the first few months following implantation, large stress concentrations exist around the suture-line. Histological examination of coronary artery bypass grafts (CABG) shows that during this time, DAIH develops mostly around the suture-line. Together, these findings suggest that early hyperplasia development in CABGs is promoted by high suture-induced stresses. A further analysis of the influence of graft-artery compliance mismatch on suture-induced stresses demonstrates that increased compliance mismatch at end-to-end anastomoses does not increase anastomotic stress concentrations, however, in end-to-side anastomoses, it does lead to a substantial increase in anastomotic stresses. This combination of results explains previous experimental findings that increased compliance mismatch does not lead to increased DAIH in end-to-end anastomoses, but in end-to-side anastomoses, it does lead to a profound increase in DAIH. Finally, since high suture-line stresses are found in both end-to-end and end-to-side junctions, elevated intramural stresses may be an important proliferative stimulus for DAIH in all vascular reconstructions. |
