Effects of size and elasticity on the relation between flow velocity and wall shear stress in side-wall aneurysms: A lattice Boltzmann-based computer simulation study

Abstract

Blood flow in an artery is a fluid-structure interaction problem. It is widely accepted that aneurysm formation, enlargement and failure are associated with wall shear stress (WSS) which is exerted by flowing blood on the aneurysmal wall. To date, the combined effect of aneurysm size and wall elasticity on intra-aneurysm (IA) flow characteristics, particularly in the case of side-wall aneurysms, is poorly understood. Here we propose a model of threedimensional viscous flow in a compliant artery containing an aneurysm by employing the immersed boundary-lattice Boltzmann-finite element method. This model allows to adequately account for the elastic deformation of both the blood vessel and aneurysm walls. Using this model, we perform a detailed investigation of the flow through aneurysm under different conditions with a focus on the parameters which may influence the wall shear stress. Most importantly, it is shown in this work that the use of flow velocity as a proxy for wall shear stress is well justified only in those sections of the vessel which are close to the ideal cylindrical geometry. Within the aneurysm domain, however, the correlation between wall shear stress and flow velocity is largely lost due to the complexity of the geometry and the resulting flow pattern. Moreover, the correlations weaken further with the phase shift between flow velocity and transmural pressure. These findings have important implications for medical applications since wall shear stress is believed to play a crucial role in aneurysm rupture.

Geometry and Flow Properties Affect the Phase Shift between Pressure and Shear Stress Waves in Blood Vessels

“…The effect of the mesh size on the numerical accuracy of the present model was already addressed in [47]. Based on the experience gained from this work and a more recent study [50], we found that, within given constraints on the computation time, a mean effective spatial resolution (mesh size) of approximately 0.087 mm provides very good results. As will be shown below (see Section 4), with this choice, the simulations reproduced the predicted phase shift within an error of less than 2%.…”

“…The method and the underlying in-house software were tested versus semi-analytic results by Krüger et al [47]. Further applications of the software include suspensions of deformable red blood cells [36,48,49] and compliant blood vessels [50].…”

“…The limit of a quasi-rigid tube wall was achieved by assigning stiff springs on the entire wall, together with making all elastic moduli as large as possible; this is the same treatment as in [50].…”

On the Potential Self-Amplification of Aneurysms Due to Tissue Degradation and Blood Flow Revealed From FSI Simulations

“…Aneurysms are vascular diseases characterized by excessive tissue degradation and chronic inflammation (Frösen, 2014). There are relations among aneurysmal geometry, intra-aneurysmal hemodynamics (flow), and aneurysm pathobiology (Meng et al, 2014): Geometry instantaneously alters flow conditions (short-term effect) (Wang et al, 2020(Wang et al, , 2021a; abnormal-flow-induced hemodynamic-biomechanical triggers are transduced into biological signals and lead to the degradation, growth and/or remodeling of aneurysms via pathobiology (Meng et al, 2014); the interplay between the local flow environment and aneurysm pathobiology dominates the growth and geometric changes of the aneurysm (longterm effect) (Tarbell et al, 2014). Within an aneurysm wall, constructive (eutrophic) changes (cell proliferation and extracellular matrix production) and destructive (degradative) changes (cell death and extracellular matrix degradation) are ongoing concurrently (Frösen et al, 2012;Frösen, 2014;Meng et al, 2014).…”

Axisymmetric Peristaltic Flow of a Non-Newtonian Fluid in a Channel with Elastic Walls

“…In view of the effect of variable viscosity. Wang et al [30] proposed a model of three dimensional viscous flow in a compliant artery containing an aneurysm by employing the immersed boundary-lattice Boltzmann-finite element method which allows to adequately account for the elastic deformation of both the blood vessel and aneurysm walls.…”