THE EFFECT OF GEOMETRY, HEMODYNAMICS, AND TISSUE FACTOR ON CLOT FORMATION IN ANEURYSM MODELS
Open Access
- Author:
- Saravanan, Pratima
- Graduate Program:
- Bioengineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 13, 2018
- Committee Members:
- Keefe B Manning, Thesis Advisor/Co-Advisor
Jian Yang, Committee Member
William O Hancock, Committee Member - Keywords:
- aneurysm
hemodynamics
tissue factor
thrombus
wall shear stress
poly (1
8 - octane diol citrate) - Abstract:
- According to a statistical report by The Centers for Disease Control and Prevention (CDC), aortic aneurysms alone constitutes 9,845 deaths in 2013, where men of age 55 and older being the most affected population. The National Institutes of Health (NIH) reported that 2 to 5% of the United States population suffers from cerebral aneurysm. An aneurysm forms a region for recirculation of blood, which eventually leads to clot formation and rupture. This study was done to mainly explore the relationship between the geometry of an aneurysm, varying flow speed of blood, and influence of tissue factor towards clot formation. To achieve this, aneurysm models of two different sizes, 10x10 mm and 20x10 mm, and also straight tubes as controls were synthesized using a biocompatible polymer, poly (1,8 - octane diol citrate). A computational study was performed to develop an understanding of the flow dynamics in the aneurysms and for studying the effect of laminar and turbulent flows, and to optimize the experimental setup. A steady-state flow loop with bovine blood was used to represent the blood flow through a vessel, as in a human circulatory system. The blood flow rate through the loop was adjusted for both laminar (Re = 1000) and turbulent (Re = 3000) flows. The effect of tissue factor (TF) on clot formation was also studied by infusing it in an aneurysm while running the steady flow loop. To study the characteristics of the intraluminal thrombi formed in an aneurysm magnetic resonance imaging was performed. The results showed that the TF flow rate of 20 µL/min through a needle inserted in the center plane of the defect with an angle of 10° facing downward was optimal to imitate slow release of TF from the endothelial cells. The wall shear stress (WSS) was found to be high at the downstream of an aneurysm and low at the upstream. Turbulence leads to increase in WSS in both aneurysm sizes. The experimental results showed that clot formation is higher under turbulent flow than in laminar since the WSS is higher in turbulence. This was proved by comparing the simulated WSS with the 3D reconstructed clot obtained from MR imaging. The clots formed in 10x10 aneurysms had a higher volume than 20x10s under all the experimental conditions. However, the weight and surface area of the clots in 20x10 aneurysms exceeds the 10x10s under the influence of TF. The TF has proved to increase clot formation in both the aneurysm sizes under Re 1000 and Re 3000. Therefore, this study demonstrated that TF increases the size of the clot formation, and the size of an aneurysm affected the hemodynamics, and also influenced the clot formation.