Assessment of surface roughness and blood rheology on local coronary haemodynamics: a multi-scale computational fluid dynamics study

Abstract

The surface roughness of the coronary artery is associated with the onset of atherosclerosis. The study applies, for the first time, the micro-scale variation of the artery surface to a 3D coronary model, investigating the impact on haemodynamic parameters which are indicators for atherosclerosis. The surface roughness of porcine coronary arteries have been detailed based on optical microscopy and implemented into a cylindrical section of coronary artery. Several approaches to rheology are compared to determine the benefits/limitations of both single and multiphase models for multi-scale geometry. Haemodynamic parameters averaged over the rough/smooth sections are similar; however, the rough surface experiences a much wider range, with maximum wall shear stress greater than 6 Pa compared to the approximately 3 Pa on the smooth segment. This suggests the smooth-walled assumption may neglect important near-wall haemodynamics. While rheological models lack sufficient definition to truly encompass the micro-scale effects occurring over the rough surface, single-phase models (Newtonian and non-Newtonian) provide numerically stable and comparable results to other coronary simulations. Multiphase models allow for phase interactions between plasma and red blood cells which is more suited to such multi-scale models. These models require additional physical laws to govern advection/aggregation of particulates in the near-wall region.

Computational fluid dynamics of the right atrium: Assessment of modelling criteria for the evaluation of dialysis catheters

“…Given the importance of using non-Newtonian models for the study of local haemodynamics [ 30 ], and similarly to the recent paper by Owen et al (2020) [ 31 ], blood was considered a Non-Newtonian fluid [ 32 ] and modelled using the Bird-Carreau model: where μ is the blood viscosity, μ ∞ is the high shear viscosity, μ 0 is the low shear viscosity, λ is the time constant, is the shear rate and n is the Power law index [ 33 ]. As per previous studies, the following values were used: λ = 3.313 s, n = 0.3568, μ 0 = 0.056 Pa s and μ ∞ = 0.00345 Pa s [ 33 , 34 ] and a blood density of 1060 kg/m 3 .…”

“…Given the importance of using non-Newtonian models for the study of local haemodynamics [30], and similarly to the recent paper by Owen et al (2020) [31], blood was considered a Non-Newtonian fluid [32] and modelled using the Bird-Carreau model:…”

Numerical modelling of blood rheology and platelet activation through a stenosed left coronary artery bifurcation

“…Despite both multiphase models utilising the same velocity and hematocrit boundary conditions, predictions in RBC transport and hematocrit vary extensively in both the healthy and stenosed arteries ( Fig 9 ). The non-Newtonian behaviour of RBC in the MKM5 model is most significant in the near-wall region due to the wide range of shear rates and hematocrit occurring near the surface [ 30 ]. These fluctuations in hematocrit close to the surface will not only impact WSS magnitudes due to increased viscosity, but also affect platelet transport [ 71 ] which is strongly linked to interaction/collisions with RBC [ 72 ], hence the limited RBC transport of the multiphase Newtonian model is a significant limitation in accurately modelling blood rheology.…”

“…The single-phase models assumed blood to be incompressible with a density [ 37 ] of ρ = 1060 kg/m 3 . The transport and phase interactions of the multiphase models were implemented using an Eulerian-Eulerian mixture model similar to other cardiovascular models [ 38 ], which considers RBC as a dilute suspension within a Newtonian plasma continuum, with a comprehensive overview of this technique available elsewhere [ 30 ].…”

“…Many of the studies that focus on the impact of different types of rheology in coronary artery hemodynamics employ healthy geometries, and assume blood as a single-phase fluid [ 27 – 29 ], with fewer studies assessing the effects of multiphase models in coronary hemodynamics [ 30 , 31 ]. Despite significant evidence on the non-Newtonian effects occurring around the coronary bifurcation, and the importance of hematocrit on the properties of blood, to date there is no conclusive study comparing these effects on parameters associated with the progression of atherosclerosis, and the subsequent impact on atherothrombosis/platelet activation.…”