Numerical analysis of non‐Newtonian blood flow and wall shear stress in realistic single, double and triple aorto‐coronary bypasses

Abstract

Considering the fact that hemodynamics plays an important role in the patency and overall performance of implanted bypass grafts, this work presents a numerical investigation of pulsatile non-Newtonian blood flow in three different patient-specific aorto-coronary bypasses. The three bypass models are distinguished from each other by the number of distal side-to-side and end-to-side anastomoses and denoted as single, double and triple bypasses. The mathematical model in the form of time-dependent nonlinear system of incompressible Navier-Stokes equations is coupled with the Carreau-Yasuda model describing the shear-thinning property of human blood and numerically solved using the principle of the SIMPLE algorithm and cell-centred finite volume method formulated for hybrid unstructured tetrahedral grids. The numerical results computed for non-Newtonian and Newtonian blood flow in the three aorto-coronary bypasses are compared and analysed with emphasis placed on the distribution of cycle-averaged wall shear stress and oscillatory shear index. As shown in this study, the non-Newtonian blood flow in all of the considered bypass models does not significantly differ from the Newtonian one. Our observations further suggest that, especially in the case of sequential grafts, the resulting flow field and shear stimulation are strongly influenced by the diameter of the vessels involved in the bypassing.

On the relevance of boundary conditions and viscosity models in blood flow simulations in patient‐specific aorto‐coronary bypass models

“…Additionally to the analysis of different boundary conditions, the paper also aims to reassess conclusions drawn in the previous study 17 regarding the occurrence of shear‐thinning non‐Newtonian effects in coronary bypasses. The motivation for this part of the paper is the fact that the prospective change in haemodynamics computed for each of the coronary artery outlets will naturally lead to a change in shear‐dependent blood viscosity, which was previously deemed negligible and which now with altered flow conditions will require a re‐evaluation.…”

“…As mentioned in the Introduction, the present haemodynamic study is a follow‐up of an earlier work 17 conducted by the authors of this article, which was oriented towards non‐Newtonian blood flow modelling in three patient‐specific aorto‐coronary bypasses. Now with the intent to assess the extent to which the choice of coronary boundary condition can affect the numerical results, let us re‐introduce the three vascular geometries (Figure 3) as representatives of the most often performed standard techniques of coronary artery bypass grafting with the saphenous vein graft.…”

“…Although this form of boundary condition may seem simple and straightforward with regard to its implementation, it cannot reproduce the unique coronary haemodynamics and, more often than not, yields physiologically unrealistic results, as it significantly restricts the local pressure field 16 . For an example illustrating this issue in aorto‐coronary bypasses, it is possible to refer the readers to one of the previous studies 17 conducted by the authors of this article, where a non‐physiological phenomenon of back flow, induced by a short‐term reversal in pressure drop between the ascending aorta and the coronary artery outlets, was encountered.…”

Investigating the impact of non‐Newtonian blood models within a heart pump

“…The authors observed that the Newtonian model returned lower values of wall shear stress and also noted that the use of a non‐Newtonian blood model tended to reduce the predicted peak values of strain rate in the vicinity of the aneurysm. In contrast, Vimmr's study in 2013 of pulsatile non‐Newtonian blood flow in three different patient‐specific aorta‐coronary bypasses indicated that results from the Carreau–Yasuda did not significantly differ from the Newtonian model.…”

Computational mechanics and electro‐mechanics in cardiovascular physiology and disease

“…However, the deployed device caused substantial strains and stresses in the arterial wall and plaque that, although not critical in terms of rupture risk, may lead to intimal hyperplasia and restenosis. A treatment option for coronary artery disease typically required once endovascular interventions become insufficient, namely, coronary artery bypass grafting, was the focus of a study presented by Vimmr et al . The long‐term patency of coronary bypass grafts is known to be significantly affected by local haemodynamics.…”