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A variety of circulatory disorders can be brought on by stenosis, which restricts a bodily passage artery or orifice. It may cause of brain disorders, heart diseases and legs disabilities. With the assistance of the Prandtl fluid model, the present investigation proposes an analytical strategy for monitoring blood flow through a stenosed artery. The artery is depicted as a tube with a cross-sectional view of an ellipse form. The flow-regulating equations are derived in the dimensionless form under the assumption of mild stenosis. The solution of mathematical equations is obtained by employing the perturbation technique via polynomial of degree four. It is analyzed graphically how flow-related parameters such as artery length L, stenosis height δ l , fluid parameters α , and K influence the velocity distribution, wall shear stress, and flow resistance. It is observed that the non-Newtonian effects dominate in the surrounding stenosed wall of the artery along the minor axis. The wall shear stress is found to attain its maximum value at the peak of stenosis. The height of stenosis considerably impacts the flow resistance, and as it increases, so does the opposition, which develops the disorder in the confined area. The streamlines are also plotted to analyze the flow behavior, and it is observed that the contours are produced in the constricted zone. [ABSTRACT FROM AUTHOR]

How do vessels find optimal radii? Capillaries are known to adapt their radii to maintain the shear stress of blood flow at the vessel wall at a set point, yet models of adaptation purely based on average shear stress have not been able to produce complex loopy networks that resemble real microvascular systems. For narrow vessels where red blood cells travel in a single file, the shear stress on vessel endothelium peaks sharply when a red blood cell passes through. We show that stable shear-stress-based adaptation is possible if vessel shear stress set points are cued to the stress peaks. Model networks that respond to peak stresses alone can quantitatively reproduce the observed zebrafish trunk microcirculation, including its adaptive trajectory when hematocrit changes or parts of the network are amputated. Our work reveals the potential for mechanotransduction alone to generate stable hydraulically tuned microvascular networks. [ABSTRACT FROM AUTHOR]

Abdominal aortic aneurysm (AAA) is a serious dilated vascular disease. The risk factors of aneurysm rupture and postoperative blood pressure are the major clinical concerns. The purpose of this work is to analyze the hemodynamic difference between preoperative and postoperative AAA using patient-specific boundary conditions and explore the rupture risk of AAA with different torsion and to simulate the blood flow of different degrees of hypertension. A three-element Windkessel model is utilized as the outlet boundary condition. 20-sim software and self-developed user-defined functions are used to calibrate the parameters. To analyze the influence of aortic tortuosity on hemodynamics, five AAA geometries with different torsion degrees are modified and obtained. We also grade the hypertension and explore the effect of hypertension after operation. The analysis results are consistent with the patient-specific situation. The results show that stent implantation for aneurysms reduces the pressure at the lesion site and increase the speed and wall shear stress. Vessels with high torsion have lower time-averaged wall shear stress (TAWSS), higher oscillatory shear stress index (OSI) and relative retention time, and more disordered blood flow. After stent implantation, with the increase in blood pressure, TAWSS and OSI continue to increase, and the blood flow speed is also faster. AAA with high torsion is more likely to rupture. In clinical practice, attention should be paid to the degree of torsion of the lesion site. Furthermore, blood pressure should be monitored and controlled in time to prevent postoperative complications. [ABSTRACT FROM AUTHOR]

The analysis of blood flow in the stenotic artery is imperative as the existence and progression of stenosis effectively disturbs the blood flow in the artery, which may cause vascular disease. In this study, we considered the linearized Phan-Thien–Tanner (PTT) fluid model to study the non-Newtonian nature of blood flow in the stenosed artery inclined at an angle γ. The artery is considered to have multiple stenoses and a cross-section of elliptical shape. The PTT model is appropriate for this analysis as viscoelastic properties and shear-thinning characteristics characterize it. The elliptical cross-section of the artery raises the nonlinearity of the mathematical model and makes it effortful to solve the equations analytically. The mathematical equations of the model are processed to non-dimensional form under the assumptions of mild stenosis, which help us to get the exact solutions of the equations in the elliptical domain. The analytically acquired solutions are investigated in detail by their graphical interpretation. It is analyzed that progressive height of stenosis generates the more significant disorder in the narrowed part of the channel as the velocity reverses its behavior in that region. The advancing values of the Weissenberg number, Grashof number and extensional and heat source parameters cause to lessen the axial velocity and slow the fluid flow. The rising Grashof number has nearly no impact on the velocity in the center of the channel. The wall shear stress aggrandizes with the growth of stenosis height, and its behavior for other physical constraints is similar to the flow velocity. It also has a practical enhancement in the stenotic region of the conduit. It is observed that fluid velocity and wall shear stress have larger values for zero angles of inclination than the inclination angle of 9 0 ∘ . The streamlined examination indicates the generation of the vortices in the stenotic part of the artery. Moreover, the flow velocity and wall shear stress have lower values for the nonuniform shape than for the uniform form of stenosis. [ABSTRACT FROM AUTHOR]

Blood is a sophisticated biological fluid with components like erythrocytes that give it non-Newtonian behavior. Hemodynamic factors such as velocity magnitude, pressure, and wall shear stress descriptors are the most important factors in the development of atherosclerosis. The wall shear stress descriptors are regulated not only by flow geometry but also by blood rheological properties. In the current study, we carried out a numerical analysis of the non-Newtonian pulsatile blood flow while taking into account a patient-specific geometry and transient boundary conditions. Non-Newtonian blood flow is modeled using the four non-Newtonian models: the power-law model, the Carreau model, the Casson model, and the Quemada model, and compared with the Newtonian model. Streamline analysis vividly illustrates velocity patterns, revealing the presence of recirculation zones near sinus regions. The study suggests the significance of selecting appropriate viscosity models for accurate assessments, particularly in regions with low time-average wall shear stress values, such as those associated with atherosclerotic plaques. The differences in the time-averaged wall shear stress between the four non-Newtonian models were found to be the highest in the Quemada model. The study concluded that the non-Newtonian model is required when the focus is on the low-time-averaged wall shear stress area. [ABSTRACT FROM AUTHOR]

The stenosis and non-Newtonian property of the uid in the blood ow represent the behavior of Herschel-Buckley uid. In a tapered tube model all the vessels which carry blood towards the tissues are considered as long, slowly tapering cones rather than cylinders. Since the blood ow consist of two regions in which one is central region, consist of concentrated blood cells and its behavior is non-Newtonian and other region is peripheral layer of plasma which represent the Newtonian behavior of uid motion. In present paper, we have considered the ow of blood through a uniform tapered tube which obeys the Bingham uid model and obtained the condition for the wall shear stress and pressure gradient. Further in various graphs we represent the variation of shear stress at the wall and pressure gradient with respect to suspension concentration and tapered angle over the ow rate range 0.01 to 0.1 cc/sec. [ABSTRACT FROM AUTHOR]

We present a microfluidic cell culture platform for studying the responses of Endothelial Cells (ECs) under pulsatile flow conditions of blood plasma. Through numerical investigations, we explore the dynamic behaviors of the Endothelial Cell Monolayer under both physiological and extreme conditions, including the formation of recirculation zones. Furthermore, we conduct a quantitative analysis of the Wall Shear Stress (WSS) magnitude on the EC surface and evaluate the Oscillatory Shear Index (OSI) to gain insights into the extent of WSS reversal within a single cycle across different spatial locations. Our findings reveal that the ECs deform in the direction of the flow, periodically returning to their initial position, with slight vertical deformation in the nanometer scale. In contrast to our previous observations for startup rheometry, cell membrane thinning is found to be more prominent at the lateral points of the cell protrusion, where fluid detachment from the cell surface initiates, rather than at the top. We further note that negative shear stresses emerge within the cytoplasm. Moreover, the shear stresses within the nucleus remain consistent for both rheometric protocols, while the normal stresses are slightly lower during pulsatile experiments. Finally, the model provides insight into the actual phenomena that arise in vivo as well as the expected behaviors in the vicinity of the endothelium of a vessel. [ABSTRACT FROM AUTHOR]

The present study analyzes the theoretical consequences of slip effects in a complex stenosed region. The flow of blood in a stenosed region is incorporated with hybrid nanofluid features which are being prepared with copper and copper oxide nanoparticles. The flow is also intensified by applying an electric field in the axial direction. The governing equations for the proposed paradigm are solved and the corresponding closed-form solutions are obtained for the cases of mild stenosis. Parameters such as Electro-osmotic, velocity slip and Helmholtz–Smoluchowski are specially focused in this study. The heat transfer, hemodynamic velocity, wall shear stress and resistance impedance for the flow are precisely determined. The various parameters that influence the physical characteristics of flow are plotted, and their effects are discussed in detail. The present model has the potential application in medical pumps for drug delivery systems. [ABSTRACT FROM AUTHOR]

Hemodynamics is crucial for the activation and aggregation of platelets in response to flow-induced shear. In this paper, a novel image-based computational model simulating blood flow through and around platelet aggregates is presented. The microstructure of aggregates was captured by two different modalities of microscopy images of in vitro whole blood perfusion experiments in microfluidic chambers coated with collagen. One set of images captured the geometry of the aggregate outline, while the other employed platelet labelling to infer the internal density. The platelet aggregates were modelled as a porous medium, the permeability of which was calculated with the Kozeny-Carman equation. The computational model was subsequently applied to study hemodynamics inside and around the platelet aggregates. The blood flow velocity, shear stress and kinetic force exerted on the aggregates were investigated and compared under 800 s−1, 1600 s−1 and 4000 s−1 wall shear rates. The advection-diffusion balance of agonist transport inside the platelet aggregates was also evaluated by local Péclet number. The findings show that the transport of agonists is not only affected by the shear rate but also significantly influenced by the microstructure of the aggregates. Moreover, large kinetic forces were found at the transition zone from shell to core of the aggregates, which could contribute to identifying the boundary between the shell and the core. The shear rate and the rate of elongation flow were investigated as well. The results imply that the emerging shapes of aggregates are highly correlated to the shear rate and the rate of elongation. The framework provides a way to incorporate the internal microstructure of the aggregates into the computational model and yields a better understanding of the hemodynamics and physiology of platelet aggregates, hence laying the foundation for predicting aggregation and deformation under different flow conditions. Author summary: The initial step in the formation of an arterial thrombus is the rapid aggregation of the tiny blood particles called platelets. This process significantly influences the formation and structure of the resulting thrombi. The mechanical properties of the aggregates depend on their microstructure, which in turn is dictated by their interaction with the flow during formation. However, due to currently existing technological limitations, it is not possible to measure these interactions in sufficient detail experimentally. In this paper, an image-based computational model is proposed based on two different modalities of experimental images, that can complement the experiments and give detailed information on hemodynamics during the aggregation. The image sets are captured from whole blood perfused microfluidic chambers coated with collagen. One modality of images captured the shape of the aggregate outline with high contrast, while the other employed platelet labeling to infer the internal density. The platelet aggregates are considered as porous media in the simulations, informed by the images. This framework incorporates the internal microstructure of the aggregates into the computational model and yields a better understanding of the hemodynamics and physiology of platelet aggregates, hence laying the foundation for predicting aggregation and deformation under different flow conditions. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases have been a leading cause of death for the past several decades. A comparison of blood flow patterns through diseased and treated arteries can be beneficial in diagnosis and treatment. The computational fluid dynamic (CFD) analysis was utilized to numerically simulate the blood flow dynamics of stenosed and stented carotid artery bifurcation. Two lumen models were generated: first with the stenosis and then a stent was introduced to remove the abnormality. The control volume method was implemented to discretize the blood domain, and then the steady-state velocity inlet was used based on the measured blood flow rate. The transitional flow was observed in the post-stenotic region due to the high Reynold's number near peak systole; however, the flow exhibited laminar characteristics at the peak diastole. Four distinct locations downstream of the stenosis were used to compare the results. The internal carotid artery (ICA) stenosis resulted in high wall shear stresses, irregular flow patterns, and low-pressure areas. The velocity and pressure profiles oscillated in the immediate vicinity downstream of the stenosis. The stented model showed minimal pressure and velocity fluctuations, as well as minimal wall shear stresses. Additionally, for the stented model, the flow could not enter the transitional regime under both conditions. The proposed simulation methodology can be utilized until the abnormalities in the carotid artery geometry are removed and normal blood flow characteristics are achieved, which then become the basis for an optimal design of a carotid artery stent. [ABSTRACT FROM AUTHOR]

In this study, a patient-specific carotid artery model was analyzed with an open source program foam-extend. The research includes the effect of arterial wall deformation by fluid-structure analysis. Pulsatile velocity cycle is trained for 144 patients with different hemodynamic parameters, by machine learning algorithm using blood flow velocity measured from 337 points of the carotid artery. Data used for training is obtained from an open source in the literature. Here, the machine learning algorithm was created by the help of an open source code Phyton. Then, using trained values of machine learning, and the known systole and diastole blood pressures for a specific chosen patient, the patient-specific pulsatile velocity cycle was estimated. The estimated pulsatile velocity cycle was then fitted to Fourier series. This pulsatile velocity cycle is used as the input boundary condition for the model analyzed in foam-extend. The outlet boundary condition, pulsatile pressure cycle is found by 4-Element Windkessel algorithm. Wall shear stresses and time averaged wall shear stresses were obtained for both the rigid and fluid structure interaction models, and variation of displacement throughout the pulsatile cycle was found for the FSI model. Wall shear stresses, velocity, and displacements were obtained high at peak systole, consistent with pulsatile cycles. Like the wall shear stresses, the time averaged wall shear stresses for the FSI model were also found lower than the rigid model. The wall shear stresses showed an increase towards the exit of internal and external carotid artery. [ABSTRACT FROM AUTHOR]

We study the steady hemodynamics in physiological elastic microvessels proposing an advanced fluid–structure interaction model. The arteriolar tissue is modeled as a two-layer fiber-reinforced hyperelastic material representing its Media and Adventitia layers. The constitutive model employed (Holzapfel et al. in J Elast 61:1–48, 2000) is parametrized via available data on stress–strain experiments for arterioles. The model is completed by simulating the blood/plasma flow in the lumen, using the thixotropic elasto-viscoplastic model in its core, and the linear Phan-Thien and Tanner viscoelastic model in its annular part. The Cell-Free Layer (CFL) and the Fåhraeus and Fåhraeus-Lindqvist effects are considered via analytical expressions based on experimental data (Giannokostas et al. in Materials (Basel) 14:367, 2021b). The coupling between tissue deformation and blood flow is achieved through the experimentally verified pressure-shear hypothesis (Pries et al. Circ Res 77:1017–1023, 1995). Our calculations confirm that the increase in the reference inner radius produces larger expansion. Also, by increasing the intraluminal pressure, the thinning of the walls is more pronounced and it may reach 40% of the initial thickness. Comparing our predictions with those in rigid-wall microtubes, we conclude that apart from the vital importance of vasodilation, there is an up to 25% reduction in wall shear stress. The passive vasodilation contributes to the decrease in the tissue stress fields and affects the hemodynamic features such as the CFL thickness, reducing the plasma layer when blood flows in vessels with elastic walls, in quantitative agreement with previous experiments. Our calculations verify the correctness of the pressure-shear hypothesis but not that of the Laplace law. [ABSTRACT FROM AUTHOR]

Blood flow within the vasculature of the retina has been found to influence the progression of diabetic retinopathy. In this research cell resolved blood flow simulations are used to study the pulsatile flow of whole blood through a segmented retinal microaneurysm. Images were collected using adaptive optics optical coherence tomography of the retina of a patient with diabetic retinopathy, and a sidewall (sacciform) microaneurysm was segmented from the volumetric data. The original microaneurysm neck width was varied to produce two additional aneurysm geometries in order to probe the influence of neck width on the transport of red blood cells and platelets into the aneurysm. Red blood cell membrane stiffness was also increased to resolve the impact of rigid red blood cells, as a result of diabetes, in blood flow. Wall shear stress and wall shear stress gradients were calculated throughout the aneurysm domains, and the quantification of the influence of the red blood cells is presented. Average wall shear stress and wall shear stress gradients increased due to the increase of red blood cell membrane stiffness. Stiffened red blood cells were also found to induce higher local wall shear stress and wall shear stress gradients as they passed through the leading and draining parental vessels. Stiffened red blood cells were found to penetrate the aneurysm sac more than healthy red blood cells, as well as decreasing the margination of platelets to the vessel walls of the parental vessel, which caused a decrease in platelet penetration into the aneurysm sac. [ABSTRACT FROM AUTHOR]

Endothelial cells (ECs) are the primary cellular constituent of blood vessels that are in direct contact with hemodynamic forces over their lifetime. Throughout the body, vessels experience different blood flow patterns and rates that alter vascular architecture and cellular behavior. Because of the complexities of studying blood flow in an intact organism, particularly during development, the field has increasingly relied on in vitro modeling of blood flow as a powerful technique for studying hemodynamic-dependent signaling mechanisms in ECs. While commercial flow systems that recirculate fluids exist, many commercially available pumps are peristaltic and best model pulsatile flow conditions. However, there are many important situations in which ECs experience laminar flow conditions in vivo, such as along long straight stretches of the vasculature. To understand EC function under these contexts, it is important to be able to reproducibly model laminar flow conditions in vitro. Here, we outline a method to reliably adapt commercially available peristaltic pumps to study laminar flow conditions. Our proof-of-concept study focuses on 2D models but could be further adapted to 3D environments to better model in vivo scenarios, such as organ development. Our studies make significant inroads into solving technical challenges associated with flow modeling and allow us to conduct functional studies toward understanding the mechanistic role of shear forces on vascular architecture, cellular behavior, and remodeling in diverse physiological contexts. [ABSTRACT FROM AUTHOR]

Tissue degradation plays a crucial role in vascular diseases such as atherosclerosis and aneurysms. Computational modeling of vascular hemodynamics incorporating both arterial wall mechanics and tissue degradation has been a challenging task. In this study, we propose a novel finite element method-based approach to model the microscopic degradation of arterial walls and its interaction with blood flow. The model is applied to study the combined effects of pulsatile flow and tissue degradation on the deformation and intra-aneurysm hemodynamics. Our computational analysis reveals that tissue degradation leads to a weakening of the aneurysmal wall, which manifests itself in a larger deformation and a smaller von Mises stress. Moreover, simulation results for different heart rates, blood pressures and aneurysm geometries indicate consistently that, upon tissue degradation, wall shear stress increases near the flow-impingement region and decreases away from it. These findings are discussed in the context of recent reports regarding the role of both high and low wall shear stress for the progression and rupture of aneurysms. [ABSTRACT FROM AUTHOR]

In the current problem, we aim to discuss the heat transfer of pulsatile unsteady fractional Maxwell fluid (blood) flow through a vertical stenosed artery with body acceleration. The concept of fractional Cattaneo model will modify the energy equation. We will get the solutions using Laplace and finite Hankel transformations. The inverse of the transformed functions will be calculated numerically. It is observed that, the heat relaxation time causes a delay in the heat transfer until a critical time. In addition, the heat transfer increases sharply to take its maximum value at a critical value of time then it decreases to reach the steady state. Moreover, the blood velocity, the flow rate, and the shear stress continue to fluctuate during the time period due to the pulsatile phenomenon and body acceleration. [ABSTRACT FROM AUTHOR]

The current work analyzes the effects of concentric ballooned catheterization and heat transfer on the hybrid nano blood flow through diseased arterial segment having both stenosis and aneurysm along its boundary. A fractional second-grade fluid model is considered which describes the non-Newtonian characteristics of the blood. Governing equations are linearized under mild stenosis and mild aneurysm assumptions. Precise articulations for various important flow characteristics such as heat transfer, hemodynamic velocity, wall shear stress, and resistance impedance are attained. Graphical portrayals for the impact of the significant parameters on the flow attributes have been devised. The streamlines of blood flow have been examined as well. The present finding is useful for drug conveyance system and biomedicines. [ABSTRACT FROM AUTHOR]

BACKGROUND: Coronary artery disease is reported as one of the most common sources of death all over the world. The presence of stenosis (plaque) in the coronary arteries results in the restriction of blood supply, which leads to myocardial infarction. OBJECTIVE: The aim of this study was to investigate the effect of multi stenosis on hemodynamics parameters in idealized coronary artery models with varying degrees of stenosis and interspace distance between the stenosis. METHODS: A finite volume-based software package (Ansys CFX version 17.2) was employed to model the blood flow. The hemodynamic stenosis parameters of blood, such as the pressure, velocity, and wall shear stress were obtained. RESULTS: The computed results showed that the pressure drop is maximum across the 90% area stenosis (AS). The pressure drop is increased as the distance between the proximal and distal stenosis is decreased across the proximal stenosis for the model P70_D70 during the systolic period of the cardiac cycle. A recirculation zone is formed behind the stenosis and is restricted by the occurrence of distal stenosis as the interspacing distance decreases, which could lead to further progression of stenosis in the flow-disturbed area. The wall shear stress was found to increase as the distance between the proximal and distal stenosis is increased across the distal stenosis. The maximum wall shear stress was found at 90% AS. CONCLUSIONS: In the clinical diagnosis, an overestimation of distal stenosis severity could be possible. Furthermore, the low wall shear stress zone in between the proximal and distal stenosis may help atherosclerotic growth or merge adjacent stenosis. [ABSTRACT FROM AUTHOR]

The motion of the blood inside an artery is investigated under the transverse magnetic field. The velocity and temperature variation of the blood flow motion are solved by perturbation technique. We considered the magnetic field is constant and viscosity of the fluid distribution depends on temperature. We derived flow rate and wall shear stress during the flow of blood through the human artery. We analyzed the effect of temperature profiles, flow rate and wall shear stress during the propagation of blood. It is observed that the human will die with respect to the increase temperature in the blood flow distribution. [ABSTRACT FROM AUTHOR]

Wall shear stress (WSS) has been suggested as a potential biomarker in various cardiovascular diseases and it can be estimated from phase-contrast Magnetic Resonance Imaging (PC-MRI) velocity measurements. We present a parametric sequential method for MRI-based WSS quantification consisting of a geometry identification and a subsequent approximation of the velocity field. This work focuses on its validation, investigating well controlled high-resolution in vitro measurements of turbulent stationary flows and physiological pulsatile flows in phantoms. Initial tests for in vivo 2D PC-MRI data of the ascending aorta of three volunteers demonstrate basic applicability of the method to in vivo. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases are among the most important causes of global mortality. Computational Fluid Dynamics (CFD) is a powerful research tool that analyzes the hemodynamics of artery and blood flow patterns. In this study, CFD simulations are performed to assess the patient-specific healthy aorta, fusiform, and saccular aneurysm with various mesh types, including tetrahedral, polyhedral, and poly-hexacore. The aim of this study is to explore how different mesh types and grid densities impact the hemodynamic properties of physiological flows, with the goal of identifying the most cost-effective meshing approach. A mesh independence study is carried out to ensure the precision of the results, considering the wall shear stress distribution. For this, five different mesh resolutions are generated for each geometry. The uncertainties of the simulations associated with the discretization techniques and solutions are evaluated using the Grid Convergence Index (GCI) method. The findings showed that increasing the mesh density provides smaller uncertainty. GCI values for the wall shear stress are in the range of convergence, indicating that the results are reliable and accurate. Mesh type selection affects the accuracy and computational cost of our simulations. The polyhedral and poly-hexacore meshes lead to a good compromise between precision and computational cost, while the tetrahedral mesh style gives the most precise results with fluctuation. This work provides a systematic approach based on the Grid Convergence Index method in order to select the most appropriate mesh type for evaluating uncertainties in CFD simulations of patient-specific healthy aortas and aortas with abdominal aneurysms. According to the findings and GCI analysis, the polyhedral mesh type was chosen for all patient-specific aorta models. The study clearly demonstrated its superiority over other mesh types, considering uncertainties and computational costs associated with different mesh styles. • Mesh Independence analyses are performed for patient-specific aorta models. • Uncertainty of numerical simulations is determined using the grid convergence index (GCI) method. • The computational performance of three different discretization techniques is compared for cost efficiency. • Wall shear stress over the aorta walls is evaluated by considering different aorta models. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Endothelial cells (EC) in vivo are continuously exposed to a mechanical microenvironment from blood flow, and fluidic shear stress plays an important role in EC behavior. New approaches to generate physiologically and pathologically relevant pulsatile flows are needed to understand EC behavior under different shear stress regimes. Here, we demonstrate an adaptable pump (Adapt-Pump) platform for generating pulsatile flows from human pluripotent stem cell-derived cardiac spheroids (CS) via quantitative imaging-based signal transduction. Pulsatile flows generated from the Adapt-Pump system can recapitulate unique CS contraction characteristics, accurately model responses to clinically relevant drugs, and simulate CS contraction changes in response to fluidic mechanical stimulation. We discovered that ECs differentiated under a long QT syndrome derived pathological pulsatile flow exhibit abnormal EC monolayer organization. This Adapt-Pump platform provides a powerful tool for modeling the cardiovascular system and improving our understanding of EC behavior under different mechanical microenvironments. [ABSTRACT FROM AUTHOR]

An analytic solution for the two-layered model of pulsatile blood flow in stenotic arteries is discussed. The blood flow in narrow arteries is assumed to obey the two-fluid model: non-Newtonian viscoelastic as Jeffrey fluid in core region, and Newtonian as plasma fluid in peripheral region. The present study is aimed to develop an oscillatory viscoelastic model of blood flow and obtain the analytic expressions for velocity of pulsatile blood flow in a stenotic artery. The velocity of pulsatile blood flow is used to discuss the wall shear stress and volume flow rate through stenotic artery and to relate relaxation time, retardation time, height of the stenosis with the velocity, volume flow rate and wall shear stress. The solution of the model boundary value problem is obtained by the method of special functions under the assumption of steady oscillations. It is found that the velocity is directly proportional to relaxation time and on the other hand retardation time is inversely proportional. For non-zero time period, the wall shear stress increases as relaxation time increases and decreases as retardation time increases. It reveals a significant influence of relaxation and retardation time on oscillatory blood flow in stenotic artery under the pathological state of cardiovascular disease. [ABSTRACT FROM AUTHOR]

Abnormal accumulation of macromolecules such as low‐density lipoproteins (LDLs) in the arterial wall causes narrowing and blockage of vessels, which leads to atherosclerosis. Effects of pulsatile nature of blood flows as well as the initial length on transport of the LDL species in the arterial boundary layer region are analyzed numerically in the present work. The set of governing equations consisting of continuity, Navier‐Stokes, and species transport is solved using a projection method based on the second‐order central difference discretization. The obtained results are in excellent agreement with the pertinent data. The computational results imply that the flow field and concentration distribution are time dependent but the variation of the filtration velocity can be ignored. The LDL concentration boundary layer thickness decreases in the outer part and increases in the inner part for both with or without straight length. Presence of initial straight length generates about 26% growth in the boundary layer thickness, although its effect on the LDL surface concentration (LSC) is negligible. The maximum LSC is related to the regions with minimum wall shear stress in the inner part of the curved artery, which have more potential for formation of atherosclerosis. A new numerical correlation between the LSC and boundary layer thickness is proposed and examined. [ABSTRACT FROM AUTHOR]

Flow behavior at the arterial bifurcations has significant implications on the plaque formation. It depends on the vessel size, two bifurcation angles, i.e. angle between the mother and daughter vessels and their relative magnitudes. In this study, hemodynamics for steady and pulsatile flow of blood has been investigated in an idealized carotid artery bifurcation having all the vessels in the same plane for a range of bifurcation angles for symmetric and asymmetric bifurcation. The simulations reveal the presence of a pair of helical vortices, symmetric about the bifurcation plane, in each daughter tube near the bifurcation. [ABSTRACT FROM AUTHOR]

Blood is a non-Newtonian suspension of red and white cells, platelets, fibrinogen, and cholesterols in Newtonian plasma. To assess its non-Newtonian behaviors, this work considers a newly proposed blood test, unidirectional large-amplitude oscillatory shear flow (udLAOS). In the laboratory, we generate this experiment by superposing LAOS onto steady shear flow in such a way that the shear rate never changes sign. It is thus intended to best represent the unidirectional pulsatile flow in veins and arteries. To model human blood, we consider the simplest model that can predict infinite-shear viscosity, the corotational Jeffreys fluid. We arrive at an exact analytical expression for the shear stress response of this model fluid. We discover fractional harmonics comprising the transient part of the shear stress response and both integer and fractional harmonics, the alternant part. By fractional, we mean that these occur at frequencies other than integer multiples of the superposed oscillation frequency. We generalize the corotational Jeffreys fluid to multimode to best represent three blood samples from three healthy but different donors. To further improve our model predictions, we consider the multimode Oldroyd 8-constant framework, which contains the corotational Jeffreys fluid as a special case. In other words, by advancing from the multimode corotational Jeffreys fluid to the multimode Oldroyd 8-constant framework, five more model parameters are added, yielding better predictions. We find that the multimode corotational Jeffreys fluid adequately describes the steady shear viscosity functions measured for three different healthy donors. We further find that adding two more specific nonlinear constants to the multimode corotational Jeffreys fluid also adequately describes the behaviors of these same bloods in udLAOS. This new Oldroyd 5-constant model may find usefulness in monitoring health through udLAOS. [ABSTRACT FROM AUTHOR]

Highlights • Molecular Resonance Velocimetry was implemented with a 180° curved artery model. • In the straight inlet section, a Womersley flow-based analysis was performed. • Pulsatile pressure drop, vorticity and wall shear stress estimates were determined. • In the curved tube, a material volume-based circulation analysis was done. • Analysis led to assessment of vortex-splitting in pulsatile, arterial flow. Abstract The purpose of this study was to gain an understanding of the formation of arterial secondary flow structures due to physiological parameters such as geometry (curvature), pulsatility and harmonics of inflow conditions. The variation of the unsteady pressure gradient, inflow vorticity and wall shear stress, and its concomitant effect on the secondary flow morphology during the pulsatile flow cycle was investigated. In vitro experimental investigation of arterial secondary flow structures was performed using the magnetic resonance velocimetry (MRV) technique in a 180° curved artery model at Stanford University. MRV benefits include its being a tracer- particle-free technique and its ability to resolve a full, three-dimensional flow field. In this paper, we discuss the kinematics of vorticity in the following two regions of a 180° curved artery model; (i) the entrance- (or straight-inlet pipe) and (ii) the 180° curved pipe-region. We applied the Womersley solution in the entrance-region to ascertain the time-dependent pressure drop per unit length, in-plane vorticity and wall shear stress for a pulsatile, carotid artery-based flow rate waveform. We hypothesize that in the 180° curved pipe region, the time rate of change of circulation will discern the propensity of large-scale, deformed Dean-type vortices to separate into two vortices in pulsatile arterial flows. [ABSTRACT FROM AUTHOR]

Aneurysm or stenosis in an artery is not very common, but it is becoming increasingly recognized due to its high incidence in pediatric and young adult patient. In the present study, a fractional second-grade fluid model with ternary nano-particles (Cu, Ag, CuO) is implemented to investigate the effects of electroosmotic forces (EMHD) through an oblique stenosed aneurysmal artery. The mild stenotic supposition is used to normalize and reduce the two directional momentum equations to the unidirectional flow. Closed-form solutions are calculated for the situation of mild stenosis and aneurysm by solving the governing equations for the suggested paradigm. Graphs are used to illustrate the effects of nanoparticles and aneurysm on blood flow rate, wall shear stress, and impedance. The results of ternary nanoparticles (Cu-Ag-CuO /blood), hybrid nanoparticles (Cu-Ag/blood), and copper (Cu) nanoparticles have also been compared, and this comparison suggests that ternary nanoparticles (Cu-Ag-CuO/blood) are more effective at attenuating hemodynamic factors (such as wall shear stress and impedance) than hybrid and copper (Cu) nanoparticles. Through the streamlines for various emerging parameters, the general behaviour of the blood flow patterns is also seen. The present study findings are particularly helpful for drug transportation and biomedical research. • The fractional second-grade, EMHD, ternary (modified) nanofluid model is utilized in this paper to investigate blood flow characteristics in stenosed and aneurysmal arterial segments. Exact solutions are found, and the impact of the important parameters is investigated. Comparisons are made for aneurysm and stenosis instances. The highlights of the paper are described as follows. • Ternary nanofluid has a higher hemodynamic velocity than hybrid nanofluid. • Resistance impedance is lower in aneurysm segments than in stenosis segments. • This model is appropriate to the drug dispersal system and also effective for physiological conversion in which nanoparticles have an important role. [ABSTRACT FROM AUTHOR]

• Application of a hemorheological TEVP model in an aneurysmal geometry. • Development of WSS spatial oscillation around the mouth of the sack. • The curvature of the parent vessel affects the stress dynamics and the onset of the instability. In recent years, significant progress in hemorheological modeling has occurred after the development of constitutive models able to represent the major physical mechanisms that govern the interaction, deformation, and motion of blood cells and plasma. Only a few of them have a tensorial form and can be applied in complex multidimensional flows, allowing a better understanding of hemodynamics and the evolution of biological processes in tissues. In this research, the pulsatile blood flow in 3D rigid aneurysmal geometries is studied in silico , employing our integrated elasto-viscoplastic constitutive model with thixotropy (TEVP), the parameters of which have been evaluated for normal blood subjects. Blood flow is investigated under sinusoidal waveforms with different frequencies and amplitudes, providing a thorough parametric study. As pulse frequency increases, the variation of the structure parameter decreases, and a recirculation is formed inside the aneurysmal dome. Moreover, a significantly higher value of the wall shear stress (W S S) develops around the mouth of the aneurysm, potentially leading to a progressive increase in the size of a real sack. Interestingly, W S S exhibits spatial oscillations and attains higher amplitudes along the part of the tube wall beside the aneurysm, where an instability is developed. With an increase in the pulse amplitude, blood gets softer and flows more easily. At the same time, the W S S inside the aneurysm remains low enough to potentially promote a growth or rupture, since low wall-stresses have been related to these processes. The curvature of the parent vessel of the aneurysm affects the flow dynamics throughout the cycle. In contrast to the W S S , the magnitude of the total stress for the curved vessel is higher than that for the straight vessel. [ABSTRACT FROM AUTHOR]

The purpose of this study was to identify the characteristics of blood flow in aortic coarctation based on stenotic shape structure, stenosis rate, and the distribution of the wall load delivered into the blood vessels and to predict the impact on aneurysm formation and rupture of blood vessels by using a computational fluid dynamics modeling method. It was applied on the blood flow in abdominal aortic blood vessels in which stenosis occurred by using the commercial finite element software ADINA on fluid-solid interactions. The results of modeling, with an increasing stenosis rate and Reynolds number, showed the pressure drop was increased and the velocity was greatly changed. When the stenosis rate was the same, the pressure drop and the velocity change were larger in the stenosis with a symmetric structure than in the stenosis with an asymmetric one. Maximal changes in wall shear stress were observed in the area before stenosis and minimal changes were shown in stenosis areas. The minimal shear stress occurred at different locations depending on the stenosis shape models. With an increasing stenosis rate and Reynolds number, the maximal wall shear stress was increased and the minimal wall shear stress was decreased. Through such studies, it is thought that the characteristics of blood flow in the abdominal aorta where a stenosis is formed will be helpful in understanding the mechanism of growth of atherosclerosis and the occurrence and rupture of the abdominal aortic flow. [ABSTRACT FROM AUTHOR]

An acousto-optic modulator (AOM) was used in combination with two-beam multipoint laser Doppler velocimetry (MLDV) to achieve advanced blood flow observation for simultaneous determination of the magnitude and direction of the blood flow velocity. To measure the shear stress around the blood vessel wall, especially in regions near obstructions, the shear rate (velocity gradient) in a pulsatile blood flow was measured using the AOM in combination with two-beam MLDV (AOM–MLDV). In addition, the blood viscosity was measured using a rotating viscometer for the estimation of shear stress. Based on the measurement results, the shear stress could be estimated as the product of the viscosity and the shear rate, which was identified determined from the velocity distribution. The blood flow velocity was found to increase in the region around the obstruction in the flow channel. Complex flows formed as a result of the obstruction, and the shear stress was observed to reach a peak value around the obstruction based on the AOM–MLDV results. This paper presents a novel blood flow detection system that provides real-time state determination capabilities using acousto-optic modulation and LDV. • Our original two beam multipoint laser Doppler (MLDV) was supposed. • An acousto-optic modulator (AOM) was used in combination with MLDV. • The shear stress could be estimated as the product of the viscosity and shear rate. • The shear stress distribution was observed in a narrow flow channel. [ABSTRACT FROM AUTHOR]

• Using Sisko model, blood flow is simulated inside an artery with cone shape of stenosis. • An artery radius of 0.002 m was fixed to study the effects of stenosis on the flow behavior. • With increasing stenosis angle, maximum blood flow velocity is sharply increased. • Effect of increasing artery radius versus the influences of stenosis angle, is affected by the stress tension. In this work, using Sisko model, blood flow is simulated inside an artery which have cone shape of stenosis with different angles of φ = 0.25, φ = 0.5, φ = 0.75, φ = 1 and φ = 1.25 degree, respectively. In the first step, an artery radius of 0.002 m is fixed to study the effects of cone shape of arterial stenosis on the flow behavior. Then, stenosis angle of φ = 0.5 degree is fixed to study the effects of different Artery radii of 0.002 m, 0.0025 m, 0.003m, and 0.0035 m orderly on the flow behavior. For simulation the blood flow, Sisko model is used. Afterward, stenosis angle of φ = 0.5 degrees with a radius of 0.002m is fixed for investigating the influences of different behavior of blood fluid by manipulation of constant parameters of the Sisko model. It is reported that with increasing arterial stenosis angle, maximum blood flow velocity is sharply increased in central region of artery from 0.12 m/s to 0.16 m/s, 0.25 m/s, 0.36 m/s and 0.56 m/s in order of increasing stenosis angles from φ = 0.25 to φ = 0.5, φ = 0.75, φ = 1 and φ = 1.25 degree, respectively. Also, maximum shear stress of artery wall are as much as 64 Pa, 42 Pa, 24 Pa, 18 Pa and 16Pa respectively in order of stenosis angles of φ = 0.25, φ = 0.5, φ = 0.75, φ = 1 and φ = 1.25 degree. On the other side, the effect of increasing artery radius is against the influences of stenosis angle, and contradiction of these parameters is affected by the stress tension and viscosity of blood. Variations of blood behavior from non-Newtonian to Newtonian shows that shear stress in blood stream in the stenosis artery with non-Newtonian blood is higher than that of Newtonian blood due to differences in their viscous behaviors and reactions in exposure of stenosis and artery wall effects. [ABSTRACT FROM AUTHOR]

With establishment of uteroplacental blood flow, the perfused fetal chorionic tissue has to deal with fluid shear stress that is produced by hemodynamic forces across different trophoblast subtypes. Amongst many other cell types, trophoblasts are able to sense fluid shear stress through mechanotransduction. Failure in the adaption of trophoblasts to fluid shear stress is suggested to contribute to pregnancy disorders. Thus, in the past twenty years, a significant body of work has been devoted to human- and animal-derived trophoblast culture under microfluidic conditions, using a rather broad range of different fluid shear stress values as well as various different flow systems, ranging from commercially 2D to customized 3D flow culture systems. The great variations in the experimental setup reflect the general heterogeneity in blood flow through different segments of the uteroplacental circulation. While fluid shear stress is moderate in invaded uterine spiral arteries, it drastically declines after entrance of the maternal blood into the wide cavity of the intervillous space. Here, we provide an overview of the increasing body of evidence that substantiates an important influence of maternal blood flow on several aspects of trophoblast physiology, including cellular turnover and differentiation, trophoblast metabolism, as well as endocrine activity, and motility. Future trends in trophoblast flow culture will incorporate the physiological low oxygen conditions in human placental tissue and pulsatile blood flow in the experimental setup. Investigation of trophoblast mechanotransduction and development of mechanosome modulators will be another intriguing future direction. [ABSTRACT FROM AUTHOR]

Article presents results of the numerical study concerning nature of blood flow in the post-surgical artery. The research focuses on the development of geometric variants of patches sewn into the common carotid artery during surgery of the atherosclerotic plaque removal. Based on analytical methods, the geometry of the patch described by the polynomial function has been developed. The simulations of blood flow in the arteries with the sewn patch were performed. The study includes the influence of the patient's diameter, the width and length of the chosen patch on blood flow disorders. The study results comprise the development of software that with the use on input data related to arterial geometry, patch length and patient's blood parameters (affecting the fluid density and viscosity), shall generate an accurate contour of the patch of width in the selected range. [ABSTRACT FROM AUTHOR]

We propose a hemodynamic reduced‐order model bridging macroscopic and mesoscopic blood flow circulation scales from arteries to capillaries. In silico tree‐like vascular geometries, mathematically described by graphs, are synthetically generated by means of stochastic growth algorithms constrained by statistical morphological and topological principles. Scale‐specific pruning gradation of the tree is then proposed in order to fit computational budget requirement. Different compliant structural models with respect to pressure loads are used depending on vessel walls thicknesses and structures, which vary considerably from macroscopic to mesoscopic circulation scales. Nonlinear rheological properties of blood are also included, and microcirculation network responses are computed for different rheologies. Numerical results are in very good agreement with available experimental measurements. The computational model captures the dynamic transition between large‐ to small‐scale flow pulsatility speeds and magnitudes and wall shear stresses, which have wide‐ranging physiological influences. [ABSTRACT FROM AUTHOR]

Thrombus formation in hemostasis or thrombotic disease is initiated by the rapid adhesion, activation, and aggregation of circulating platelets in flowing blood. At arterial or pathological shear rates, for example due to vascular stenosis or circulatory support devices, platelets may be exposed to highly pulsatile blood flow, while even under constant flow platelets are exposed to pulsation due to thrombus growth or changes in vessel geometry. The aim of this study is to investigate platelet thrombus formation dynamics within flow conditions consisting of either constant or variable shear. Human platelets in anticoagulated whole blood were exposed ex vivo to collagen type I-coated microchannels subjected to constant shear in straight channels or variable shear gradients using different stenosis geometries (50%, 70%, and 90% by area). Base wall shears between 1800 and 6600 s−1, and peak wall shears of 3700 to 29,000 s−1 within stenoses were investigated, representing arterial-pathological shear conditions. Computational flow-field simulations and stenosis platelet thrombi total volume, average volume, and surface coverage were analysed. Interestingly, shear gradients dramatically changed platelet thrombi formation compared to constant base shear alone. Such shear gradients extended the range of shear at which thrombi were formed, that is, platelets became hyperthrombotic within shear gradients. Furthermore, individual healthy donors displayed quantifiable differences in extent/formation of thrombi within shear gradients, with implications for future development and testing of antiplatelet agents. In conclusion, here, we demonstrate a specific contribution of blood flow shear gradients to thrombus formation, and provide a novel platform for platelet functional testing under shear conditions. [ABSTRACT FROM AUTHOR]