Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons
Costello, James Robert
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Each year, more than one million prosthetic vascular grafts are implanted. Well-over 50 % of these artificial vessels are of the small caliber variety with an inner diameter less than or equal to 10 mm. The challenge rests in implanting these synthetic substitutes into a hemodynamic environment with a high downstream resistance and low rates of flow. Over the course of four interrelated studies, we investigated the healing properties of small caliber prosthetic vascular grafts. All of these studies were conducted using baboons. First, we documented the difference in healing response between three different types of vascular grafts: (1) autologous artery (2) allogeneic vessel (3) prosthetic ePTFE. This comparison furnished an important model of graft healing. Proliferating endothelial cells were localized to the top 10 % of the neointima, while the proliferating smooth muscle cells were identified within the lower 10 % of the neointima. Secondly, we examined the effects of changing a prosthetic grafts material properties and how that change impacts healing of the grafts surface. These ultrastructural changes were introduced by radially stretching a porous 60 mm ePTFE vascular graft. Radially stretching the graft material decreased the void fraction, reduced the potential for transmural ingrowth, and changed the healing characteristics of the implanted vessels. Thirdly, we investigated the effect of a changing hemodynamic environment upon the healing of a vascular graft with uniform material properties. The changing hemodynamics were generated with a stenotic model. Under sub-acute conditions, an inverse relationship failed to exist between intimal thickening and wall shear stress. Lastly, the details of this hemodynamic environment were documented with computational fluid dynamics (CFD). The computational grids were constructed using three sets of geometric information: (1) incorporating the ideal material dimensions of the implanted vessel (2) utilizing contour information from pressure-perfused histologic cross-sections (3) applying geometric information form detailed MRI imaging. MRI imaging information provided the best description of the vessels hemodynamic environment. With this computational information, correlations were made between the intimal thickening and hemodynamic parameters.