An Integrated Fluid-Chemical Model Toward Modeling the Formation of Intra-Luminal Thrombus in Abdominal Aortic Aneurysms

Abstract

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence their evolution biochemically and biomechanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region.The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development.

A comparison of hemodynamic metrics and intraluminal thrombus burden in a common iliac artery aneurysm

“…This is supported by multiple anatomic studies of ILT, as it commonly occurs in the distal anterior region of AAA [23,[41][42][43]. In 2012, an integrated fluid-chemical approach for modelling ILT formation in AAA was introduced by Biasetti et al which showed agreement with the site specificity of ILT formation and the movement of vortex structures [44].…”

“…With this in mind, we approximated the blood flow as laminar and considered the blood to be an incompressible fluid with a density of 1050 kg/m 3 . The walls of the arteries were characterised by no-slip, rigid wall boundary conditions [5,6,32,35,54,55] and the viscosity was modelled using a non-Newtonian approximation (Carreau-Yasuda, as implemented by Biasetti et al [44]; [56]). By using a non-Newtonian model, as opposed Newtonian, we can capture the macro-scale shear-thinning of the blood, allowing a one-way Lagrangian particle transport model to provide a good prediction of individual blood-cell trajectories within the continuous phase (blood).…”

A coupled chemo-fluidic computational model for thrombogenesis in infarcted left ventricles

“…For the modeling of blood coagulation and thrombus formation in the infarcted LV, we adopt thrombosis biochemical reaction models employed in previous studies (4,28,32) of vascular thrombosis. It is assumed here that thrombus formation in the LVs with AMI is initiated by the exposure of blood to tissue factor (TF) (42) emanating from the damaged ventricle wall.…”

“…2) is coupled with the hemodynamic simulation through the flow velocity vector ¡ U. The diffusion coefficient D for the coagulation factors is set to 1.0e-8 m 2 /s following Biasetti et al (4). The detailed description of the reaction term R i and the initial concentrations of the species are given in APPENDIX C. At the wall, a zero diffusive flux boundary condition is applied except in the damaged region, where the TF is exposed and combined with factor VIIa.…”

“…Eighteen species are ordered as listed in Table C1, and the reaction coefficients k are given in Table C2. The detailed description for the reaction coefficient can be found in Biasetti et al (4) and Jones and Mann (21). The rate coefficients are determined by Jones and Mann (21) based on the experimental study of Lawson et al (26).…”