Numerical simulation of pulsatile non-Newtonian flow in the carotid artery bifurcation

Both clinical and post mortem studies indicate that, in humans, the carotid sinus of the carotid artery bifurcation is one of the favored sites for the genesis and development of atherosclerotic lesions. Hemodynamic factors have been suggested to be important in atherogenesis. To understand the correlation between atherogenesis and fluid dynamics in the carotid sinus, the blood flow in artery was simulated numerically. In those studies, the property of blood was treated as an incompressible, Newtonian fluid. In fact, however, the blood is a complicated non-Newtonian fluid with shear thinning and viscoelastic properties, especially when the shear rate is low. A variety of non-Newtonian models have been applied in the numerical studies. Among them, the Casson equation was widely used. However, the Casson equation agrees well only when the shear rate is less than 10 s-1. The flow field of the carotid bifurcation usually covers a wide range of shear rate. We therefore believe that it may not be sufficient to describe the property of blood only using the Casson equation in the whole flow field of the carotid bifurcation. In the present study, three different blood constitutive models, namely, the Newtonian, the Casson and the hybrid fluid constitutive models were used in the flow simulation of the human carotid bifurcation. The results were compared among the three models. The results showed that the Newtonian model and the hybrid model had verysimilar distributions of the axial velocity, secondary flow and wall shear stress, but the Casson model resulted in significant differences in these distributions from the other two models. This study suggests that it is not appropriate to only use the Casson equation to simulate the whole flow field of the carotid bifurcation, and on the other hand, Newtonian fluid is a good approximation to blood for flow simulations in the carotid artery bifurcation.

Multidimensional modeling of the stenosed carotid artery: A novel CAD approach accompanied by an extensive lumped model

This study describes a multidimensional 3D/lumped parameter（LP） model which contains appropriate inflow/outflow boundary conditions in order to model the entire human arterial trees. A new extensive LP model of the entire arterial network（48 arteries） was developed including the effect of vessel diameter tapering and the parameterization of resistance, conductor and inductor variables. A computer aided-design（CAD） algorithm was proposed to effciently handle the coupling of two or more 3D models with the LP model, and substantially lessen the coupling processing time. Realistic boundary conditions and Navier-Stokes equations in healthy and stenosed models of carotid artery bifurcation（CAB） were used to investigate the unsteady Newtonian blood flow velocity distribution in the internal carotid artery（ICA）. The present simulation results agree well with previous experimental and numerical studies. The outcomes of a pure LP model and those of the coupled 3D healthy model were found to be nearly the same in both cases. Concerning the various analyzed 3D zones, the stenosis growth in the ICA was not found as a crucial factor in determining the absorbing boundary conditions.This paper demonstrates the advantages of coupling local and systemic models to comprehend physiological diseases of the cardiovascular system.

A Case Summary of the Application of a Drug-eluting Stent Combined with a Drug-Coated Balloon in Left Main Coronary Artery Disease

Objective:To evaluate the clinical efficacy of a drug-eluting stent(DES)combined with a drug-coated balloon(DCB)in the treatment of left main coronary artery bifurcation lesions.Methods:A retrospective analysis was conducted on the clinical data of eight patients with left main coronary artery bifurcation lesions treated with a DES combined with a DCB who were admitted to our hospital from July 2016 to July 2017.These eight patients all underwent DES treatment for their left main coronary artery and left anterior descending coronary artery lesions,and DCB treatment at the ostium of the left circumflex artery;six of the patients underwent surgical procedures under the guidance of intravascular ultrasonography.Immediate postoperative angiography was used to evaluate the patency of the diseased vessels,and the restenosis rate at the 6-month follow-up after the operation and the incidence of serious clinical events within 6 months were assessed as well.Results:The use of a DES combined with a DCB in the treatment of left main coronary artery bifurcation lesions had a low restenosis rate(left main coronary artery(8.4±5.3)%,left anterior descending coronary artery(18.2±5.0)%,left circumflex artery(30.5±16.5)%).No serious clinical events occurred in any patients.Conclusion:A DES combined with a DCB is a safe and effective interventional treatment for left main artery coro-nary bifurcation lesions.

Non-Newtonian biomagnetic fluid flow through a stenosed bifurcated artery with a slip boundary condition

The effects of a velocity slip and an external magnetic field on the flow of biomagnetic fluid(blood)through a stenosed bifurcated artery are investigated by using ANSYS FLUENT.Blood is regarded as a non-Newtonian power-law fluid,and the magnetization and electrical conductivity are considered in the mathematical model.The no-slip condition is replaced by the first-order slip condition.The slip boundary condition and magnetic force are compiled in the solver by the user-defined function(UDF).Numerical solutions are obtained by the finite volume method based on a nonuniform grid structure.The accuracy and efficiency of the solver are verified through a comparison with the literature.The results are presented graphically for different parameter values,and the effects of the magnetic number,the magnetic source position,the vascular obstruction ratio,the slip parameter,and the power-law index on the flow and temperature fields are illustrated.

A Computational Study on the Effect of Bifurcation Lesions with DifferentStructures on Blood Velocity and Temperature

Treating coronary bifurcation stenosis is still a challenging task. Existing procedures still display a relatively smallrate of success. This paper aims to investigate numerically the effect of bifurcation lesions with different structureson the dynamics of blood flow and related temperature. The problem geometry is parametrically varied by changing the bifurcation angle and radius. A finite volume method is used to simulate the three-dimensional flow. Theeffects induced by the structure of the stenosis, the artery bifurcation angle and radius, and the inlet velocity ofblood are discussed in terms of flow pattern, pressure distribution, and shear stress at the blood wall. The heattransfer from the solid tissue is also determined for different stenosis configurations. The present study has beenconducted with the explicit intention to generate useful data for the development of methods curing the vascularstenosis with thermal ablation.

Couple stress nanofluid flow through a bifurcated artery—Application of catheterization process

In this article,we are exploring the hemodynamics of nanofluid,flowing through a bifurcated artery with atherosclerosis in the presence of a catheter.For treating obstruction in the artery,one can use the catheter whose outer surface is carrying the drug coated with nano-particles.The resultant solvent is considered as blood nano-fluid.Blood being a complex fluid,is modeled by couple stress fluid.In the presence of nano-particles,the temperature and the concentration distribution are understood in a bifurcated stenotic artery.The concluded mathematical model is governed by coupled non-linear equations,and are solved by using the homotopy perturbation method.Consequently,we have explored is the effects of fluid and the embedded geometric parameters on the hemodynamics characteristics.It is also realized that high wall shear stress exists for couple stress nano-fluid when compared to Newtonian nano-fluid.which is computed at a location corresponding to maximum constriction(z=12.5)of the artery.

Non-Newtonian Flow of Blood in a Catheterized Bifurcated Stenosed Artery

The paper is devoted to study the non-Newtonian behavior of blood flowing in an artery having a stenosis, in a situation when a catheter has been inserted into it. The blood rheology is described by Herschel-Bulkley fluid model. The flow configuration is con- structed by choosing suitable curvature at the lateral junction, where the flow separation is initiated. The effects of insertion of catheter and that of yield stress of blood on the velocity distribution, rate of flow and flow resistance of blood, distribution of shear stress at the arterial wall and the location of yield plane are investigated. The results provide some useful information for the prediction/treatment of some arterial diseases and circulatory disorders of the cardiovascular system, in a situation, when a stenosis is developed on the endothelium of the daughter artery / bifurcated artery. The study reveals that if the ratio between the radii of the catheter and the artery is increased, the shear stress at the arterial wall diminishes. However, when the bifurcation angle is increased, the wall shear stress is enhanced.