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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]

Due to their effect on aneurysm hemodynamics, flow diverters (FD) have become a routine endovascular therapy for intracranial aneurysms. Since over- and undersizing affect the device's hemodynamic abilities, selecting the correct device diameter and accurately simulating FD placement can improve patient-specific outcomes. The purpose of this study was to validate the accuracy of virtual flow diverter deployments in the novel Derivo® 2 device. We retrospectively analyzed blood flows in ten FD placements for which 3D DSA datasets were available pre- and post-intervention. All patients were treated with a second-generation FD Derivo® 2 (Acandis GmbH, Pforzheim, Germany) and post-interventional datasets were compared to virtual FD deployment at the implanted position for implanted stent length, stent diameters, and curvature analysis using ANKYRAS (Galgo Medical, Barcelona, Spain). Image-based blood flow simulations of pre- and post-interventional configurations were conducted. The mean length of implanted FD was 32.61 (±11.18 mm). Overall, ANKYRAS prediction was good with an average deviation of 8.4% (±5.8%) with a mean absolute difference in stent length of 3.13 mm. There was a difference of 0.24 mm in stent diameter amplitude toward ANKYRAS simulation. In vessels exhibiting a high degree of curvature, however, relevant differences between simulated and real-patient data were observed. The intrasaccular blood flow activity represented by the wall shear stress was qualitatively reduced in all cases. Inflow velocity decreased and the pulsatility over the cardiac cycle was weakened. Virtual stenting is an accurate tool for FD positioning, which may help facilitate flow FDs' individualization and assess their hemodynamic impact. Challenges posed by complex vessel anatomy and high curvatures must be addressed. [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]

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]

Arterial deformations arise in blood flow when surrounding tissue invades the space available for a blood vessel to maintain its circular cross section, the most immediate effects being a reduction in blood flow and redistribution of shear stress. Here we consider deformations from circular to elliptic cross sections. Solution of this problem in steady flow is fairly straightforward. The focus in the present paper is on pulsatile flow where the change from circular to elliptic cross sections is associated with a transition in the character of the equations governing the flow from Bessel to Mathieu equations. The main aim of our study is to examine the hemodynamic consequences of the change from circular to elliptic cross sections and on possible implications of this change in blood flow regulation. The study of this problem has been hampered in the past because of difficulties involved in the solution of the governing equations. In the present study we describe methods we have used to overcome some of these difficulties and present a comprehensive set of results based on these methods. In particular, vessel deformation is examined under two different conditions relevant to blood flow regulation: (i) keeping cross sectional area constant and (ii) keeping cross sectional circumference constant. The results provide an important context for the mechanism of neurovascular control of blood flow under the pathological conditions of vessel deformation. The difficulty which has characterized this problem is that it involves elements of mathematics which are well outside the scope of a clinical/physiological study, while it actually involves clinical/physiological elements which are well outside the scope of a mathematical study. We hope that the context which we provide in this paper helps resolve this difficulty. [ABSTRACT FROM AUTHOR]

Blood image intensity has been used to detect erythrocyte sedimentation rate (ESR). However, it does not give information on the biophysical properties of blood samples under continuous ESR. In this study, to quantify mechanical variations of blood under continuous ESR, blood shear stress and blood image intensity were obtained by analyzing blood flows in the capillary channel. A blood sample is loaded into a driving syringe to demonstrate the proposed method. The blood flow rate is set in a periodic on–off pattern. A blood sample is then supplied into a capillary chip, and microscopic blood images are captured at specific intervals. Blood shear stress is quantified from the interface of the bloodstream in the coflowing channel. τ0 is defined as the maximum shear stress obtained at the first period. Simultaneously, ESRτ is then obtained by analyzing temporal variations of blood shear stress for every on period. AII is evaluated by analyzing the temporal variation of blood image intensity for every off period. According to the experimental results, a shorter period of T = 4 min and no air cavity contributes to the high sensitivity of the two indices (ESRτ and AII). The τ0 exhibits substantial differences with respect to hematocrits (i.e., 30–50%) as well as diluents. The ESRτ and AII showed a reciprocal relationship with each other. Three suggested properties represented substantial differences for suspended blood samples (i.e., hardened red blood cells, different concentrations of dextran solution, and fibrinogen). In conclusion, the present method can detect variations in blood samples under continuous ESR effectively. [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]

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]

Femoral artery bypass surgery needs postoperative monitoring due to the high complication risks after bypass. Numerical simulation is an effective tool to help solve this task. This work presents the experience of patient-specific CFD simulation of blood flow in proximal anastomosis for femoral-popliteal bypass, including patient follow-up after bypass surgery. Six cases of proximal anastomosis of femoral-popliteal bypass 3–30 months after surgery were studied. A repeated study was performed for four patients to monitor geometric and hemodynamic changes. The blood flow structure variety in proximal anastomoses and the blood flow dynamics during the cardiac cycle are described in detail using CFD simulation. Special attention is paid to time-average wall shear stresses (TAWSS) and oscillatory shear index (OSI) distributions. Low and oscillatory wall shear stresses were registered in the graft downstream from the suture, especially in case of low inlet flow. It was shown that the postoperative geometry changes led to significant hemodynamic changes; thereby, neointima has grown in areas with initially low and oscillatory wall shear stresses. [ABSTRACT FROM AUTHOR]

Blood flow dynamics plays a crucial role in the growth and rupture of abdominal aortic aneurysms. The aim of this study was to analyze the possibility of predicting aneurysmal rupture by numerical investigations based on diagnostic images. The blood flow dynamics was analyzed in a patient-specific abdominal aortic aneurysm, reconstructed from CT images of an aneurysm while it was rupturing. The patient-specific geometry was virtually repaired in order to obtain a non-ruptured model representative of the geometry immediately preceding the rupture. To reproduce physiological conditions, numerical simulations were performed under pulsatile flow conditions, and blood was modelled as a non-Newtonian fluid, using the Carreau rheological model. Hemodynamic parameters that influence the rupture of the aneurysm were investigated, and their possible association with vascular disease was discussed. The results of the numerical simulations indicated regions of slow recirculation and low values of Time Averaged Wall Shear Stress (TAWSS) in the region of rupture. Unlike literature results, a high Oscillatory Shear Index (OSI) was not clearly found in this region. Nevertheless, just in the region where the rupture will occur, high values of Endothelial Cell Activation Potential index (ECAP) were found. This index is therefore extremely significant for assessing the vulnerability of the aortic wall and locating the critical rupture region. [ABSTRACT FROM AUTHOR]

In order to study the effects of active speed modulation on the internal flow field and blood damages in the blood pumps, the CFD method was adopted to simulate the full flowpath internal flow of a blood pump under speed modulations. The combined numerical simulation of the lumped cardiovascular system mathematical model and the rotary blood pump model was used to obtain the ventricular and aortic pressures under the assisting of the blood pump, which were then set as the inlet and outlet boundary conditions of the blood pump in CFD simulations. The flow fields of blood pump under the constant speed and three types of asynchronous speed modulation waveforms, including sine, square and triangle waves, were analyzed, and the velocity distribution and shear stress distribution of the rotary blood pumps were obtained. The results show that the flow pulsation of blood pump is enhanced under speed modulations, which is a feasible scheme to restore the pulsation of the blood flow. Among the three speed modulation waveforms, the blood pump flow pulsation index is high and the shear stress in the blood pump is small under the sinusoidal speed modulation, which is a relatively ideal speed modulation waveform. [ABSTRACT FROM AUTHOR]

This article explicates the blood flow across an artery with multiple stenosis at outer wall and a thrombus at the centre. The symmetric multiple stenosis and non-symmetric multiple stenosis shapes are both considered in this study. Entropy analysis is also taken into account for a detailed study of irreversibility. The governing equations are interpreted with provided boundary conditions and exact mathematical solutions are developed. Further, these exact solutions are elucidated graphically. Streamlines show that the closed contours are symmetric in shape for symmetric multiple stenosis but non-symmetric in shape for non-symmetric multiple stenosis shape. The increase in multiple stenosis heights, increases the shear stress at wall having multiple stenosis. [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]

The current study provides an analytical approach to analyze the blood flow through a stenosed artery by using the Carreau fluid model. The flow governing equations are derived under the consideration of mild stenosis. Mathematical analysis has been carried out by considering the blood as non-Newtonian nature. Then, the analytical solution has been investigated by using the regular perturbation technique. The solutions obtained by this perturbation are up to the second-order in dimensionless Weissenberg number We . The performed computations of various parameter values such as velocity, wall shear stress, shear stress, and resistance impedance at the stenotic throat are discussed in detail for different values of Weissenberg number We . The obtained results demonstrate that for shear-thinning fluid, the fluid velocity increases with the increasing parameter m while opposite behavior is observed with the increase in We. Hence, the presented numerical analysis reveals many aspects of the flow by considering the blood as a non-Newtonian Carreau fluid model, and the presented model can be equally applicable to other bio-mathematical studies. [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]

The effects of pulsatile pressure gradient in the presence of a transverse magnetic field on unsteady blood flow through an inclined tapered cylindrical tube of porous medium are discussed in this article. The fractional calculus technique is used to provide a mathematical model of blood flow with fractional derivatives. The solution of the governing equations is found using integral transformations (Laplace and finite Hankel transforms). For the semianalytical solution, the inverse Laplace transform is found by means of Stehfest's and Tzou's algorithms. The numerical calculations were performed by using Mathcad software. The flow is significantly affected by Hartmann number, inclination angle, fractional parameter, permeability parameter, and pulsatile pressure gradient frequency, according to the findings. It is deduced that there exists a significant difference in the velocity of the flow at higher time when the magnitude of Reynolds number is small and large. [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]

Background: The effects of arterial wall compliance on blood flow have been revealed using fluid-structure interaction in last decades. However, microcirculation is not considered in previous researches. In fact, microcirculation plays a key role in regulating blood flow. Therefore, it is very necessary to involve microcirculation in arterial hemodynamics. Objective: The main purpose of the present study is to investigate how wall compliance affects the flow characteristics and to establish the comparisons of these flow variables with rigid wall when microcirculation is considered. Methods: We present numerical modeling in arterial hemodynamics incorporating fluid-structure interaction and microcirculation. A novel outlet boundary condition is employed to prescribe microcirculation in an idealised model. Results: The novel finding in this work is that wall compliance under the consideration of microcirculation leads to the increase of wall shear stress in contrast to rigid wall, contrary to the traditional result that wall compliance makes wall shear stress decrease when a constant or time dependent pressure is specified at an outlet. Conclusions: This work provides the valuable study of hemodynamics under physiological and realistic boundary conditions and proves that wall compliance may have a positive impact on wall shear stress based on this model. This methodology in this paper could be used in real model simulations. [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]

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]

The pulsatile flow of blood in narrow arteries with multiple-stenoses under body acceleration is analyzed mathematically, treating blood as (i) single-phase Herschel-Bulkley fluid model and (ii) two-phase Herschel- Bulkley fluid model. The expressions for various flow quantities obtained by Sankar and Ismail (2010) for single-phase Herschel-Bulkley fluid model and Sankar (2010c) for two-phase Herschel-Bulkley fluid model are used to compute the data for comparing these fluid models in a new flow geometry. It is noted that the plug core radius, wall shear stress and longitudinal impedance to flow are marginally lower for two-phase HB fluid model than those of the single-phase H-B fluid model. It is found that the velocity decreases significantly with the increase yield stress of the fluid and the reverse behavior is noticed for longitudinal impedance to flow. It is also noticed that the velocity distribution and flow rate are higher for two-phase Herschel-Bulkley fluid model than those of the single-phase Herschel-Bulkley fluid model. It is also recorded that the estimates of the mean velocity increase with the increase of the body acceleration and this behavior is reversed when the stenosis depth increases. [ABSTRACT FROM AUTHOR]

A Mathematical model for the pulsatile blood flow through stenosed artery with the effect of body acceleration and slip velocity is proposed. Blood has been represented by casson fluid equation. Analytic expression for velocity, flow rate, wall shear stress and effective viscosity is derived. Flow variables with the change of parameters are represented graphically. The effect of pulsatility, stenosis, body acceleration, slip velocity, yield stress has been investigated. It is found that yield stress of the fluid and body acceleration highly influenced the velocity of the fluid, shear stress, flow rate in a stenosed artery. High blood viscosity is dangerous in the cardiovascular disorders; the present model may be used as a tool for reducing the blood viscosity by using slip velocity at the constricted wall. [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]

Introduction: Atherosclerosis is a focal disease that susceptibly forms near bifurcations, anastomotic joints, side branches, and curved vessels along the arterial tree. In this study, pulsatile blood flow in a bifurcation model with a non-planar branch is investigated. Methods: Wall shear stress (WSS) distributions along generating lines on vessels for different bifurcation angles are calculated during the pulse cycle. Results: The WSS at the outer side of the bifurcation plane vanishes especially for higher bifurcation angles but by increasing the bifurcation angle low WSS region squeezes. At the systolic phase there is a high possibility of formation of a separation region at the outer side of bifurcation plane for all the cases. WSS peaks exist on the inner side of bifurcation plane near the entry section of daughter vessels and these peaks drop as bifurcation angle is increased. Conclusion: It was found that non-planarity of the daughter vessel lowers the minimum WSS at the outer side of the bifurcation and increases the maximum WSS at the inner side. So it seems that the formation of atherosclerotic plaques at bifurcation region in direction of non-planar daughter vessel is more risky. [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]

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]