SIMULATION OF ANEURYSM HEMODYNAMICS TO PREDICT INTRALUMINAL THROMBUS FORMATION REGION

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Burcu Ramazanlı Ph.D. Thesis.pdf

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2022-12-02

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RAMAZANLI, BURCU

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Intraluminal thrombus (ILT) is a fibrin structure which might affect rupture characteristics and be observed 80% of abdominal aortic aneurysms (AAA). Disturbed hemodynamics inside AAA might affect ILT formation, that are generally quantified by wall shear stress (WSS) parameters in literature. Together with WSS parameters, vortex structures observed inside arterial systems can also be counted as indicators of disturbed hemodynamics, and might contribute the generation of ILT. To understand the effect of disturbed hemodynamics on ILT formation, blood flow through AAAs can be simulated by using computational methods. In computational models, setting up inlet boundary conditions (BC) and fluid properties are very important steps which affect the reliability and accuracy of the hemodynamic assessment. The aim of this study is understanding the effect of inlet boundary conditions and rheology model selection on predicting the WSS parameters and vortex structures, and determining a correlation between those hemodynamic parameters. To understand the effect of inlet different BCs on hemodynamic parameters, Womersley, Parabolic and Plug velocity profiles, with different entrance lengths, L_(ent )=D,3D and 11D, are examined. Results reveal that Parabolic profile even with a short entrance length can be utilized instead of complex Womersley profile. To investigate the effect of inlet flow waveform pattern on rheology model selection, three waveform patterns, Base, Case 1 and 2, are tested for eight viscous shear thinning models, along with the viscoelastic Oldroyd-B and Newtonian models. Newtonian model might obtain different OSI and ECAP distributions from shear-thinning models even for high mean flow rates, albeit the differences introduced by elasticity might be negligible. Also, vortex transport mechanism might affect the rheology model selection. To observe the correlation between WSS parameters and vortex structures, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), endothelial cell activation potential (ECAP) and relative residence time (RRT) distributions and contours of time-averaged (λ_ci ) ̅-criterion, Q ̅-criterion and (λ_2 ) ̅-criterion are plotted. Regions with high |(λ_ci ) ̅ |,|(λ_2 ) ̅ | and |Q ̅ | are correlated with high TAWSS and low OSI, ECAP and RRT. To conclude, vortex identification methods have the potential to be utilized to predict ILT accumulation and rupture sites.

Subject Keywords

Intraluminal thrombus formation, Womersley profile, Blood rheology, Wall shear stress parameters, Vortex identification methods

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https://hdl.handle.net/11511/101144

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

B. RAMAZANLI, “SIMULATION OF ANEURYSM HEMODYNAMICS TO PREDICT INTRALUMINAL THROMBUS FORMATION REGION,” Ph.D. - Doctoral Program, Middle East Technical University, 2022.