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You searched for +publisher:"Georgia Tech" +contributor:("Stephen R. Hanson"). Showing records 1 – 2 of 2 total matches.

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Georgia Tech

1. Costello, James Robert. Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons.

Degree: PhD, Biomedical Engineering, 2004, Georgia Tech

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. Advisors/Committee Members: Don P. Giddens (Committee Co-Chair), Stephen R. Hanson (Committee Co-Chair), Changyi Chen (Committee Member), Hanjoong Jo (Committee Member), Robert Nerem (Committee Member).

Subjects/Keywords: CFD; MRI imaging; Hemodynamics; ePTFE; Prosthetic vascular grafts

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APA (6th Edition):

Costello, J. R. (2004). Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/5226

Chicago Manual of Style (16th Edition):

Costello, James Robert. “Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons.” 2004. Doctoral Dissertation, Georgia Tech. Accessed March 03, 2021. http://hdl.handle.net/1853/5226.

MLA Handbook (7th Edition):

Costello, James Robert. “Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons.” 2004. Web. 03 Mar 2021.

Vancouver:

Costello JR. Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons. [Internet] [Doctoral dissertation]. Georgia Tech; 2004. [cited 2021 Mar 03]. Available from: http://hdl.handle.net/1853/5226.

Council of Science Editors:

Costello JR. Effect of Material Properties and Hemodynamics on the Healing of Vascular Grafts in baboons. [Doctoral Dissertation]. Georgia Tech; 2004. Available from: http://hdl.handle.net/1853/5226


Georgia Tech

2. Fallon, Anna Marie. The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets.

Degree: PhD, Chemical Engineering, 2006, Georgia Tech

Bileaflet mechanical heart valves (BMHVs) are prone to thrombus formation in the hinge region due to high shear stress combined with stagnation regions. This thesis research addresses the hypothesis that models that isolate and mimic BMHV hinge geometries can be used to quantitatively characterize procoagulant potential using a novel in vitro blood flow system. Furthermore, these results can be correlated with digital particle image velocimetry (DPIV) measurements detailing flow fields for the same models. The significant findings were that: 1) recalcification of recirculating citrated blood markedly increases the magnitude of thrombus forming reactions and the sensitivity for their detection; 2) platelet activation, and the presence of adequate platelet numbers are essential for the activation of coagulation under conditions of high shear; and 3) thrombin formation can be inhibited by blocking the platelet receptors that facilitate platelet aggregation. The DPIV studies give some insight into why different channel geometries resulted in varying propensities for coagulation. The channel geometries with abrupt changes in diameter induced significantly higher levels of TAT and also formed jets that were subject to increased entrainment of the stagnant fluid in the chamber. This entrainment enables more mixing of the shear-activated platelets with the surrounding flow, which can propagate the coagulation cascade, thus increasing the chance for thrombus formation. The influence of abrupt changes in diameter was also evident in the BMHV human blood studies. The MP valve, which has a tortuous hinge pathway, induced significantly more TAT formation than the SJM Standard valve with a smoother hinge channel. Thus, BMHV hinge geometry should be as smooth and free of diameter changes as possible to eliminate stagnation regions that enable activated platelets to congregate and propagate the coagulation cascade. Leakage gap width also had a significant effect not only on procoagulant potential but also on platelet activation. Both the low and high leaker prototype valves had significantly higher levels of platelet activation compared to the SJM Standard valve, but only the low leaker valve demonstrated a higher propensity for coagulation. Thus, to minimize both platelet activation and thromboemboli formation, an optimal gap width should be maintained for BMHVs. Advisors/Committee Members: Ajit P. Yoganathan (Committee Chair), Dale E. Edmondson (Committee Member), Peter J. Ludovice (Committee Member), Stephen R. Hanson (Committee Member), Timothy M. Wick (Committee Member).

Subjects/Keywords: Blood; Thrombosis; Mechanical heart valves; Platelets; Shear stress

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Fallon, A. M. (2006). The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/10451

Chicago Manual of Style (16th Edition):

Fallon, Anna Marie. “The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets.” 2006. Doctoral Dissertation, Georgia Tech. Accessed March 03, 2021. http://hdl.handle.net/1853/10451.

MLA Handbook (7th Edition):

Fallon, Anna Marie. “The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets.” 2006. Web. 03 Mar 2021.

Vancouver:

Fallon AM. The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets. [Internet] [Doctoral dissertation]. Georgia Tech; 2006. [cited 2021 Mar 03]. Available from: http://hdl.handle.net/1853/10451.

Council of Science Editors:

Fallon AM. The Development of a Novel in vitro Flow System to Evaluate Platelet Activation and Procoagulant Potential Induced by Bileaflet Mechanical Heart Valve Leakage Jets. [Doctoral Dissertation]. Georgia Tech; 2006. Available from: http://hdl.handle.net/1853/10451

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