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Approximating near-wall mass transport in human arteries with wall shear stress topological skeleton analysis

Giulia Ingrami Bianchini

Approximating near-wall mass transport in human arteries with wall shear stress topological skeleton analysis.

Rel. Umberto Morbiducci, Diego Gallo, Giuseppe De Nisco. Politecnico di Torino, Corso di laurea magistrale in Ingegneria Biomedica, 2020

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Local hemodynamics plays a major role in promoting atherosclerosis development in arteries. Despite low/oscillatory wall shear stress (WSS) is widely recognized as marker of deranged hemodynamic, recent evidences suggested its weak ability to predict plaque localization and endothelial disfunction at the early stage. In this contest, a marked interest recently emerged on the topological skeleton (TS) of WSS vector field. The WSS TS consists in: WSS fixed points, where the WSS vanishes, and WSS manifolds, identifying WSS contraction/expansion regions at the luminal surface, linking fixed points. WSS TS features allow the identification of biomechanical events linked to “aggravating” biological events. Among aggravating biological events, mass transport processes are markedly involved by mediating, e.g., the lipids accumulation at the arterial wall. Mass transport mechanisms are influenced by local hemodynamics, which may promote, e.g., low-density lipoproteins (LDL) receptor expression on the endothelium. These mechanisms are causally related to the disease development. For this reason, Lagrangian-based features of WSS TS has been suggested to provide a template of near-wall mass transport. However, their complexity requires high computational costs. To overcome this limitation, a Eulerian method to analyze WSS TS has been recently proposed by Mazzi and co-workers. The aim of this work was to test the ability of Eulerian-based features of WSS TS to provide a template of blood-to-wall LDL transfer, in patient-specific computational models of human arteries. Starting from medical images, the lumen geometry of one carotid bifurcation and one right coronary artery were reconstructed. High-quality meshes were built with 30 prismatic layers in the boundary layer to properly simulate the blood-to-wall LDL transfer. The finite volume method was applied to solve the Navier-Stokes equations coupled with the advection-diffusion equation. A constant LDL concentration was applied at the inlet section, and the stress-free condition was set at the outlets. Measured flow rates were prescribed as inflow and outflow condition. Near-wall hemodynamics was analyzed in terms of (a) classical WSS-based descriptors (i.e., TAWSS, OSI, RRT) and (b) WSS TS, where WSS manifolds were identified by the divergence of the normalized WSS vector field. Finally, the ability of each hemodynamic descriptor to identify local LDL uptake was assessed in terms of Similarity Index. A marked co-localization between WSS contraction regions and LDL polarization clearly emerged. WSS contraction action and LDL polarization mainly occurred at the basis of carotid bifurcation and along the inner curvature of the right coronary artery. The similarity analysis confirmed that WSS contraction regions co-localized with LDL polarization from 60% to 85% more than classical WSS-based descriptors. These findings indicate that: (a) recently proposed Eulerian-based WSS TS features provide an effective template of the LDL blood-to-wall transfer; (b) WSS contraction regions co-localize with LDL luminal polarization (better than classical WSS-based descriptors of deranged hemodynamics). The latter suggests that WSS contraction action may promote near-wall mass transfer. All these evidences stimulate further investigation on the effects of WSS TS on vascular pathophysiology, suggesting its contribution to a deeper understanding of the hemodynamics-driven processes.

Relators: Umberto Morbiducci, Diego Gallo, Giuseppe De Nisco
Academic year: 2020/21
Publication type: Electronic
Number of Pages: 101
Corso di laurea: Corso di laurea magistrale in Ingegneria Biomedica
Classe di laurea: New organization > Master science > LM-21 - BIOMEDICAL ENGINEERING
Aziende collaboratrici: Politecnico di Torino
URI: http://webthesis.biblio.polito.it/id/eprint/15837
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