non-Newtonian Blood Viscosity Research Articles

Hemodynamic analysis of hybrid treatment for thoracoabdominal aortic aneurysm based on Newtonian and non-Newtonian models in a patient-specific model

The accuracy of the Newtonian model used in retrograde visceral revascularization (RVR) of hybrid surgery for thoracoabdominal aortic aneurysm (TAAA) hemodynamic simulation remains unclear. Noting that an appropriate blood viscosity model is a significant factor to capture hemodynamic changes in numerical studies. Therefore, both Newtonian and non-Newtonian blood viscosity models were adopted in this study to investigate the importance of hemodynamics when non-Newtonian blood property was accounted for in a patient-specific RVR simulation. The results revealed that disturbed flow and unfavorable WSS distribution can be observed in the anastomosis region under both blood viscosity models due to the retrograde flow pattern in the RVR model. However, although the non-Newtonian blood model has negligible effect on flow pattern and pressure drop, there were of significance quantitative and qualitative difference of local normalized helicity and wall shear stress distribution under pulsatile flow condition. In particular, the unfavorable WSS indicators distribution was better matched with a patient-specific follow-up report when non-Newtonian blood viscosity was accounted for. To conclude, the use of a Newtonian blood model is a reasonable approximation to obtain the general features of the flow field under steady flow condition. However, to study the hemodynamic parameters within retrograde flow under pulsatile flow condition, a non-Newtonian model may be more appropriate.

Ramifications of Vorticity on Aggregation and Activation of Platelets in Bi-Leaflet Mechanical Heart Valve: Fluid-Structure-Interaction Study.

Bileaflet mechanical heart valves (BMHV) are widely implanted to replace diseased heart valves. Despite many improvements in design, these valves still suffer from various complications, such as valve dysfunction, tissue overgrowth, hemolysis, and thromboembolism. Thrombosis and thromboembolism are believed to be initiated by platelet activation due to contact with foreign surfaces and nonphysiological flow patterns. The implantation of the valve causes nonphysiological patterns of vortex shedding behind the leaflets. This study signifies the importance of vorticity in platelet activation and aggregation in BMHV implants. A two-phase model with the first Eulerian phase for blood and the second discrete phase for platelets is used here. The generalized cross model of viscosity has been used to simulate the non-Newtonian viscosity of blood. A fluid-structure-interaction model has been used to simulate the motion of leaflets. This study has also estimated the platelet activation state (PAS), which is the mathematical estimation of the degree of activation of platelets due to flow-induced shear stresses that cause thrombus formation. The regions in the fluid domain with a higher vorticity field have been found to contain platelets with relatively higher PAS than regions with relatively lower vorticity fields. Also, this study has quantitatively reported the effect of vorticity on platelet aggregation. Platelet densities in fluid areas with higher vorticity are higher than densities in fluid areas with lower vorticity, indicating that highly activated platelets aggregate in areas with stronger vorticity.

Effect of stenosis and dilatation on the hemodynamic parameters associated with left coronary artery

Background and Objective: The main objective of the work is to examine the curvature effects of stenosis/dilatation region pertaining to left coronary artery. The hemodymamic features during the cardiac cycle is thoroughly examined.Methods: A numerical fluid structure interaction model incorporating multi- layered elastic artery wall, non-Newtonian blood viscosity and pulsating boundary conditions is developed. The composite arterial wall consists of a thin layer tunica intima, atheroma and a thick wall. Higher stiffness of atheroma is captured by using higher Young’s modulus. The CFD and FSI models are validated with available experimental and analytical data. Computations are done with five different non-Newtonian models and arterial wall with various elasticity levels. The local and time averaged WSS, velocity contours downstream of stenosis, wall pressure and pressure drop during various phases of cardiac cycle are provided in detail.Results: The influence of non-Newtonian effects of blood viscosity is found to be significant especially at stenosis regions. The flexible wall caused wall deformation and the associated flow and pressure wave propagation affecting WSS and pressure drop compared to the rigid wall. Flow recirculation is noticed at stenosis downstream locations and its strength increases with increased severity of the stenosis. A stenosis is characterised by a sudden drop in wall pressure and a slower two stage recovery during peak velocity periods of the cardiac cycle.Conclusions: The pressure drop, local WSS at stenosis centre, and radial velocity increase are significantly higher for stenosis cases and the effect is severe during peak diastole. The variation in hemodynamic parameters is found to be less significant for dilatation. Significantly lower WSS is noticed for the recirculation regions downstream of stenosis which can enhance the tendency for monocytes to attach to the endothelium. The radius of curvature of the stenosis is found to be the most sensitive parameter affecting the hemodynamic characteristics rather than the detailed geometry of the stenosis. The main effect of variation of artery wall stiffness is noted at recirculation regions present downstream of stenosis. The results from the study may be useful for predicting wall shear stress signatures associated with stenosis/dilatation changes and the management of specific cases.

On the significance of blood flow shear-rate-dependency in modeling of Fontan hemodynamics

For univentricular heart patients, the Fontan operation creates a unique non-physiologic circulation where the pulmonary arteries are directly supplied from the systemic venous blood return, leading to chronic non-pulsatile low-shear-rate pulmonary blood flow. Computational fluid dynamic (CFD) simulations are widely used in cardiovascular biofluid studies and a Newtonian fluid assumption is common since blood acts as a Newtonian fluid in large arteries. Although blood viscosity increases exponentially in low-shear-rate flow environments, a Newtonian assumption is still conventionally used in both experimental and CFD studies of the low-shear-rate Fontan circulation. The error introduced by a Newtonian assumption in this setting has not been thoroughly evaluated. Recent in vitro studies have demonstrated that non-Newtonian effects are substantial in the Fontan circulation. However, no previous studies have used CFD to systemically investigate non-Newtonian effects in Fontan simulations. Thus the role of shear-rate-dependent non-Newtonian blood viscosity in this pathophysiology is still unclear. In this study we used a computational approach to compare flow behavior between a non-Newtonian fluid and a Newtonian fluid in a simplified model of the Fontan circulation over a wide range of experimental conditions. We examined important clinical metrics in Fontan hemodynamics: shear stress, power loss, pulmonary flow distribution, viscous dissipation, and non-Newtonian importance factors. Our results suggest that the Newtonian fluid assumption for blood introduces considerable error into the simulations of the Fontan circulation, where the fluid environment is predominated by low-shear-rate flow.

Size-Dependent Distribution of Patient-Specific Hemodynamic Factors in Unruptured Cerebral Aneurysms Using Computational Fluid Dynamics.

Purpose: To analyze size-dependent hemodynamic factors [velocity, shear rate, blood viscosity, wall shear stress (WSS)] in unruptured cerebral aneurysms using computational fluid dynamics (CFD) based on the measured non-Newtonian model of viscosity. Methods: Twenty-one patients with unruptured aneurysms formed the study cohort. Patient-specific geometric models were reconstructed for CFD analyses. Aneurysms were divided into small and large groups based on a cutoff size of 5 mm. For comparison between small and large aneurysms, 5 morphologic variables were measured. Patient-specific non-Newtonian blood viscosity was applied for more detailed CFD simulation. Quantitative and qualitative analyses of velocity, shear rate, blood viscosity, and WSS were conducted to compare small and large aneurysms. Results: Complex flow patterns were found in large aneurysms. Large aneurysms had a significantly lower shear rate (235 ± 341 s−1) than small aneurysms (915 ± 432 s−1) at peak-systole. Two times higher blood viscosity was observed in large aneurysms compared with small aneurysms. Lower WSS was found in large aneurysms (1.38 ± 1.36 Pa) than in small aneurysms (3.53 ± 1.22 Pa). All the differences in hemodynamic factors between small and large aneurysms were statistically significant. Conclusions: Large aneurysms tended to have complex flow patterns, low shear rate, high blood viscosity, and low WSS. The hemodynamic factors that we analyzed might be useful for decision making before surgical treatment of aneurysms.

Patient-Specific Computational Fluid Dynamics in Ruptured Posterior Communicating Aneurysms Using Measured Non-Newtonian Viscosity : A Preliminary Study.

ObjectiveThe objective of this study was to analyze patient-specific blood flow in ruptured aneurysms using obtained non-Newtonian viscosity and to observe associated hemodynamic features and morphological effects. MethodsFive patients with acute subarachnoid hemorrhage caused by ruptured posterior communicating artery aneurysms were included in the study. Patients’ blood samples were measured immediately after enrollment. Computational fluid dynamics (CFD) was conducted to evaluate viscosity distributions and wall shear stress (WSS) distributions using a patient-specific geometric model and shear-thinning viscosity properties. ResultsSubstantial viscosity change was found at the dome of the aneurysms studied when applying non-Newtonian blood viscosity measured at peak-systole and end-diastole. The maximal WSS of the non-Newtonian model on an aneurysm at peaksystole was approximately 16% lower compared to Newtonian fluid, and most of the hemodynamic features of Newtonian flow at the aneurysms were higher, except for minimal WSS value. However, the differences between the Newtonian and non-Newtonian flow were not statistically significant. Rupture point of an aneurysm showed low WSS regardless of Newtonian or non-Newtonian CFD analyses. ConclusionBy using measured non-Newtonian viscosity and geometry on patient-specific CFD analysis, morphologic differences in hemodynamic features, such as changes in whole blood viscosity and WSS, were observed. Therefore, measured non-Newtonian viscosity might be possibly useful to obtain patient-specific hemodynamic and morphologic result.

An impact of non-Newtonian blood viscosity on hemodynamics in a patient-specific model of a cerebral aneurysm

Despite of the recent achievements in the research of blood rheology, the effect of non-Newtonian blood viscosity on hemodynamic parameters in cerebral aneurysms is not clarified. The purpose of this study is to investigate the role of different rheological models for prediction of hemodynamic parameters in the patient-specific model of a saccular aneurysm. Transient flow simulations were conducted using OpenFOAM CFD Toolbox. The simulations employed different viscosity models: Newtonian, Power Law, Bird-Carreau, Casson and Local viscosity model. The similar flow patterns were observed both for Newtonian and non- Newtonian fluids in the patient-specific model of the aneurysm. The average difference between Newtonian and non-Newtonian models was about 12%. However for some specific points in the region of recirculating flow the difference was significantly higher - from 20% to 63%. The non-Newtonian blood behaviour influenced the streamlines distribution in the aneurysm region, producing a larger recirculating zone in the center of the aneurysm. The results showed that the major differences between Newtonian and non-Newtonian fluids were found in regions of low velocities and recirculating zones.

Red blood cell aggregates and their effect on non-Newtonian blood viscosity at low hematocrit in a two-fluid low shear rate microfluidic system.

Red blood cells (RBCs) are the most abundant cells in human blood. Remarkably RBCs deform and bridge together to form aggregates under very low shear rates. The theory and mechanics behind aggregation are, however, not yet completely understood. The main objective of this work is to quantify and characterize RBC aggregates in order to enhance the current understanding of the non-Newtonian behaviour of blood in microcirculation. Suspensions of human blood were flowed and observed in vitro in poly-di-methyl-siloxane (PDMS) microchannels to characterize RBC aggregates. These microchannels were fabricated using standard photolithography methods. Experiments were performed using a micro particle image velocimetry (μPIV) system for shear rate measurements, coupled with a high-speed camera for flow visualization. RBC aggregate sizes were quantified in controlled and measurable shear rate environments for 5, 10 and 15% hematocrit. Aggregate sizes were determined using image processing techniques, while apparent viscosity was measured using optical viscometry. For the samples suspended at 5% H, aggregate size was not strongly correlated with shear rate. For the 10% H suspensions, in contrast, lowering the shear rate below 10 s-1 resulted in a significant increase of RBC aggregate sizes. The viscosity was found to increase with decreasing shear rate and increasing hematocrit, exemplifying the established non-Newtonian shear-thinning behaviour of blood. Increase in aggregation size did not translate into a linear increase of the blood viscosity. Temperature was shown to affect blood viscosity as expected, however, no correlation for aggregate size with temperature was observed. Non-Newtonian parameters associated with power law and Carreau models were determined by fitting the experimental data and can be used towards the simple modeling of blood’s non-Newtonian behaviour in microcirculation. This work establishes a relationship between RBC aggregate sizes and corresponding shear rates and one between RBC aggregate sizes and apparent blood viscosity at body and room temperatures, in a microfluidic environment for low hematocrit. Effects of hematocrit, shear rate, viscosity and temperature on RBC aggregate sizes have been quantified.

Pore-Scale Modeling of Non-Newtonian Shear-Thinning Fluids in Blood Oxygenator Design.

This paper reviews and further develops pore-scale computational flow modeling techniques used for creeping flow through orthotropic fiber bundles used in blood oxygenators. Porous model significantly reduces geometrical complexity by taking a homogenization approach to model the fiber bundles. This significantly simplifies meshing and can avoid large time-consuming simulations. Analytical relationships between permeability and porosity exist for Newtonian flow through regular arrangements of fibers and are commonly used in macroscale porous models by introducing a Darcy viscous term in the flow momentum equations. To this extent, verification of analytical Newtonian permeability-porosity relationships has been conducted for parallel and transverse flow through square and staggered arrangements of fibers. Similar procedures are then used to determine the permeability-porosity relationship for non-Newtonian blood. The results demonstrate that modeling non-Newtonian shear-thinning fluids in porous media can be performed via a generalized Darcy equation with a porous medium viscosity decomposed into a constant term and a directional expression through least squares fitting. This concept is then investigated for various non-Newtonian blood viscosity models. The proposed methodology is conducted with two different porous model approaches, homogeneous and heterogeneous, and validated against a high-fidelity model. The results of the heterogeneous porous model approach yield improved pressure and velocity distribution which highlights the importance of wall effects.

Effects of Non-Newtonian Viscosity on the Hemodynamics of Cerebral Aneurysms

The purpose of this study is to present a comparative study between Newtonian and non-Newtonian blood viscosity models for simulating the hemodynamic wall shear stress (WSS) of cerebral aneurysms. The non-Newtonian blood viscosity was modeled using the Carreau-Yasuda nonlinear model. Two realistic cerebral aneurysm models, derived from 3D angiography imaging, were studied and simulated via computational fluid dynamics solver based on finite volume method, with a pulsating sinusoidal waveform boundary conditions. The maximum wall shear stresses were found at the aneurysm’s neck and apex, the inlet arteriole recorded an average wall shear stress and as for the blebs and tips the wall shear stress values were remarkably low. The comparison indicated that non-Newtonian blood viscosity model predicted a lower range of WSS than of the Newtonian model, which provides more accuracy for simulating aneurysm hemodynamics.

Realistic non-Newtonian viscosity modelling highlights hemodynamic differences between intracranial aneurysms with and without surface blebs

Most computational fluid dynamic (CFD) simulations of aneurysm hemodynamics assume constant (Newtonian) viscosity, even though blood demonstrates shear-thinning (non-Newtonian) behavior. We sought to evaluate the effect of this simplifying assumption on hemodynamic forces within cerebral aneurysms, especially in regions of low wall shear stress, which are associated with rupture. CFD analysis was performed for both viscosity models using 3D rotational angiography volumes obtained for 26 sidewall aneurysms (12 with blebs, 12 ruptured), and parametric models incorporating blebs at different locations (inflow/outflow zone). Mean and lowest 5% values of time averaged wall shear stress (TAWSS) computed over the dome were compared using Wilcoxon rank-sum test. Newtonian modeling not only resulted in higher aneurysmal TAWSS, specifically in areas of low flow and blebs, but also showed no difference between aneurysms with or without blebs. In contrast, for non-Newtonian analysis, bleb-bearing aneurysms showed significantly lower 5% TAWSS compared to those without (p=0.005), despite no significant difference in mean dome TAWSS (p=0.32). Non-Newtonian modeling also accentuated the differences in dome TAWSS between ruptured and unruptured aneurysms (p<0.001). Parametric models further confirmed that realistic non-Newtonian viscosity resulted in lower bleb TAWSS and higher focal viscosity, especially when located in the outflow zone. The results show that adopting shear-thinning non-Newtonian blood viscosity in CFD simulations of intracranial aneurysms uncovered hemodynamic differences induced by bleb presence on aneurysmal surfaces, and significantly improved discriminant statistics used in risk stratification. These findings underline the possible implications of using a realistic model of blood viscosity in predictive computational hemodynamics.

Flow and mixing analysis of non-Newtonian fluids in straight and serpentine microchannels

Numerical simulations were carried out to investigate the flow dynamics and mixing behavior in T-shaped and serpentine microchannels with non-Newtonian working fluids using shear-dependent viscosity models. As an illustrative case study, the microfluidic transport of blood was considered. The Carreau–Yasuda and Casson non-Newtonian blood viscosity models were used to capture the non-Newtonian characteristics. Steady Navier–Stokes equations with a diffusion-convection model for species concentration were solved in flow and mixing analyses. Under similar operating conditions, flow dynamics and mixing were compared between the working fluids: water (a Newtonian fluid), and blood using the Carreau–Yasuda non-Newtonian model. For a mass flow rate of ṁ<10−2kg/h, the mixing performances of both the fluids were found to be nearly equivalent, and decreased with flow rate. With increased flow rate, the mixing with water was significantly improved. However, a negligible change in mixing performance was observed using the Carreau–Yasuda model for blood. Also, the pumping power needed was considerably higher for the blood sample (~1bar) than for water (~0.40bar) at the same flow rate. The mixing behavior with the Carreau–Yasuda blood model was compared for T-shaped and serpentine channels over a fixed mixing length. The serpentine channel showed better mixing performance over the flow rate range considered.

Numerical simulation of non-Newtonian blood flow dynamics in human thoracic aorta

Three non-Newtonian blood viscosity models plus the Newtonian one are analysed for a patient-specific thoracic aorta anatomical model under steady-state flow conditions via wall shear stress (WSS) distribution, non-Newtonian importance factors, blood viscosity and shear rate. All blood viscosity models yield a consistent WSS distribution pattern. The WSS magnitude, however, is influenced by the model used. WSS is found to be the lowest in the vicinity of the three arch branches and along the distal walls of the branches themselves. In this region, the local non-Newtonian importance factor and the blood viscosity are elevated, and the shear rate is low. The present study revealed that the Newtonian assumption is a good approximation at mid-and-high flow velocities, as the greater the blood flow, the higher the shear rate near the arterial wall. Furthermore, the capabilities of the applied non-Newtonian models appeared at low-flow velocities. It is concluded that, while the non-Newtonian power-law model approximates the blood viscosity and WSS calculations in a more satisfactory way than the other non-Newtonian models at low shear rates, a cautious approach is given in the use of this blood viscosity model. Finally, some preliminary transient results are presented.

Influence of non-Newtonian viscosity of blood on microvascular impairment

The present research investigated the role of blood viscosity on flow within a microvascular network to identify the conditions of blood flow stagnation. When the yield stress of blood was less than 0.005 Pa, there were no stagnant regions in the microvasculature. However, when the yield stress increased to 0.05 Pa, stagnant or reduced flow areas began to appear, which grew and expanded rapidly with further increase in the yield stress. Thus, the yield stress determined from blood viscosity profile of a patient can be utilized to evaluate the risk of circulatory impairment.

Numerical Simulation of the blood flow behavior in the circle of Willis.

Introduction: This paper represents the numerical simulation of blood flow in the circle of Willis (CoW). Circle of Willis is responsible for the oxygenated blood distribution into the cerebral mass. To investigate the blood behavior, two Newtonian and non-Newtonian viscosity models were considered and the results were compared under steady state conditions. Methods: Methodologically, the arterial geometry was obtained using 3D magnetic resonance angiography (MRA) data. The blood flow through the cerebral vasculature was considered to be steady and laminar, and the Galerkin’s finite element method was applied to solve the systems of non-linear Navier-Stokes equations. Results: Flow patterns including flow rates and shear rates were obtained through the simulation. The minimal magnitude of shear rates was much greater than 100 s-1 through the larger arteries; thus, the non-Newtonian blood viscosity tended to approach the constant limit of infinite shear viscosity through the CoW. So, in larger arteries the non-Newtonian nature of blood was less dominant and it would be treated as a Newtonian fluid. The only exception was the anterior communicating artery (ACoA) in which the blood flow showed different behavior for the Newtonian and non-Newtonian cases. Conclusion By comparing the results it was concluded that the Newtonian viscosity assumption of blood flow through the healthy, complete circle of Willis under the normal and steady conditions would be acceptably accurate.

A Case Study on Non-Newtonian Viscosity of Blood through Atherosclerotic Artery

Presented herein the study of rheological character of blood flow and investigate the significance of non-Newtonian viscosity of blood through stenosed artery by assuming blood as Bingham Plastic and Casson’s fluid models. The results show that blood pressure increases very significantly in the upstream zone of the stenotic artery as the degree of the stenosis area severity increases. It is also shown that the non-Newtonian behaviour of blood has significant effects on the velocity profile of the blood flow and the magnitude of the wall shear stresses. It has been concluded in this paper that the Casson’s fluid model is more realistic in comparison to Bingham Plastic fluid model.

Patient based computational fluid dynamic characterization of carotid bifurcation stenosis before and after endovascular revascularization

IntroductionHemodynamic forces play a critical role in determining the molecular phenotype of the endothelial cell and in influencing vascular remodeling. A lesion based computational fluid dynamic (CFD) modeling approach is...

Simulation of Flow Field for Pulsatile Blood Flow in a Femoral Artery Based on Cosserat Continua

This investigation describes unsteady, pulsatile, laminar, and locally fully developed blood flow velocity and rotation fields during cardiac cycle in the femoral artery using Cosserat continuum mechanics approach. After solving the continuity, linear momentum, and angular momentum equations for flow of blood through artery, the time and position dependent velocity and rotation fields have been calculated. It is shown that the maximum values of velocity occur at the inlet core, while the maximum values of rotation occur on the arterial boundary. It is also demonstrated that the flow of blood in artery is laminar and a good agreement with existing data is established. A time dependent Gaussian equation for non-Newtonian blood viscosity coefficient γv has also been found.

A comparison between non-Newtonian and Newtonian blood viscosity models

In this study the effects of some non-Newtonian viscosity and Newtonian viscosity models on the Wall Shear Stress and velocity distributions in carotid artery are investigated. Three distinct non-Newtonian viscosity models named Carreua, Casson and Generalised Power Method and Newtonian model are employed in the simulations. 3D Navier–Stokes equations is solved numerically on anatomically realistic geometry which is obtained from CT data. At the inlet of the numerical model experimental flow data which is measured at a real common carotid artery is imposed. The WSS and velocity distributions which are calculated using different viscosity models are compared. Results show that the differences between non-Newtonian models and Newtonian model are important at the regions having low velocity.

Critical Influence of Framing Coil Orientation on Intra-Aneurysmal and Neck Region Hemodynamics in a Sidewall Aneurysm Model

Although coiling of intracranial aneurysms is thought to rely on obstruction of blood flow into the aneurysm and induction of intra-aneurysmal thrombosis, little data exist regarding the effect of coil deployment on hemodynamics. To evaluate the effects of simulated coiling of a model aneurysm on flow and wall shear stress in the dome and neck regions using computational fluid dynamic analysis. A spherical sidewall aneurysm on a curved parent vessel underwent simulated embolization with 1 or more computer-designed helical coils. The coils' axes had parallel, orthogonal, or transverse orientation with respect to blood flow. Pulsatile laminar flow computational fluid dynamic analysis was performed on high-resolution conformal meshes of the aneurysm-coil complex using realistic non-Newtonian blood viscosity. Intra-aneurysmal flow and energy flux into the dome were significantly reduced by coil insertion, with little effect on pressure distribution. Coiling increased viscosity in the distal dome with progressive spread toward the neck with greater coil packing. Coiling also decreased wall shear stress and its gradient both in the inflow zone and the downstream parent vessel. These alterations were dependent on coil orientation, with effectiveness rank order of parallel>transverse>orthogonal. We successfully modeled the hemodynamic effects of aneurysm coil embolization and uncovered a framing coil orientation dependence of dome and parent vessel hemodynamics. In addition to suggesting a pathophysiological link among coil configuration, protection from rupture, and aneurysm regrowth, these results pave the way for the analysis of aneurysm-coil complex interactions on a patient lesion-specific basis.