Steady Blood Flow Research Articles

Numerical simulation of radiative flow with magnetized micropolar nanofluid along a curved stretched surface involving blood silica nanoparticles

Silicon nanoparticles can be used as contrast agents in medical imaging procedures such as computed tomography (CT), magnetic resonance imaging (MRI), and fluorescence imaging. They can aid in the early identification and diagnosis of illnesses by enhancing image sensitivity and resolution through adjustable optical and magnetic properties. Additionally, the knowledge gathered from this research might help create cooling systems for electronics and thermal management applications that are more effective. The focus of current research is on the steady two-dimensional radiative flow of blood with silicon dioxide particles along a curved, stretched surface using a magnetized micropolar nanofluid. Furthermore, the effect of radiation is mentioned. Formulating a mathematical representation of flow equations requires the use of variables in curvilinear form. The leading PDEs are converted into nonlinear ODEs using the non-similarity approach. A bvp4c based on a three-stage Lobatto approach is used to solve the modified nonlinear ODEs. Numerical results for skin factor, couple stress, and local Nusselt number are presented in tabular form, and velocity, microrotation, and temperature fields are presented in graphs. The micro-rotation and temperature field exhibits a declining tendency with rising material parameters, whereas the velocity profile shows the opposite pattern. In addition, the significance of various physical characteristics under various parametric assumptions for a curved, stretched channel is reviewed and emphasized.

Modeling the mechanisms of non-neurogenic dynamic cerebral autoregulation.

Dynamic cerebral autoregulation (dCA) refers to a collection of mechanisms that act to maintain steady state cerebral blood flow (CBF) near constant despite changes in arterial blood pressure (ABP), but which is known to become impaired in various cerebrovascular diseases. Currently, the mechanisms of dCA and how they are affected in different physiological conditions are poorly understood. The objective of this study was to disentangle the magnitudes and time scales of the myogenic and metabolic responses of dCA, in order to investigate how each mechanism is affected in impaired dCA. A physiological model of dCA was developed, where both the myogenic and metabolic responses were represented by a gain and time constant. Model parameters were optimized with pressure-flow impulse responses under normocapnia, thigh cuff, and hypercapnia conditions. The impulse responses were derived by applying transfer function analysis (TFA) to experimental recordings of ABP (Finapres), end-tidal CO2 (capnograph), and CBF velocity (transcranial doppler ultrasound in bilateral middle cerebral arteries). The myogenic gain to time constant ratio was significantly smaller (p-values < 0.001 using both univariate and multivariate TFA), and the metabolic time constant was significantly larger (p-values < 0.001 using both univariate and multivariate TFA) in hypercapnia compared to normocapnia. Both the myogenic and metabolic responses were shown to be affected in impaired dCA, and the metabolic response was shown to be slowed down. This study contributes to the understanding of the complexities of dCA and how it is affected in different physiological conditions.

Influence of Wavy Arteries and Veins on Hemodynamic Characteristics: A Numerical Study.

The present work is focused on the study of hemodynamic characteristics for tortuous arteries/veins. Tortuosity in arteries/veins is defined by introducing waviness in the wall of the tube. Analysis is further extended for bifurcated veins with and without wavy walls. Waviness is defined by two geometric parameters; pitch and depth of the wave. Four different combinations of pitch and depth are studied and compared with a plain straight wall. The present study is carried out numerically by using a computational fluid dynamics tool. Hemodynamics for a steady flow of blood is investigated through pressure, velocity, and wall shear stress distribution. Waviness in the wall of arteries/veins creates a recirculation zone at the crest and trough of the wall. Occurrence of the recirculation zone leads to reduction in velocity which in turn reduces wall shear stress. Variation in the magnitude of the velocity and corresponding wall shear stress at the crest and trough of the wavy wall depends on the pitch and depth of the artery/veins (tube).

Microfluidic viscometer using capillary pressure sensing

Blood viscosity is considered as a vital determinant of the efficiency of blood flow in blood-vessel networks. The coflowing method is considered as a promising technique for measuring blood viscosity. However, it requires two precise syringe pumps to supply two fluids (i.e., the reference fluid and blood), calibration in advance, and long waiting time for securing steady blood flow. To solve these problems, a single syringe pump is adopted to supply blood into a microfluidic device without requiring a reference fluid. Two key parameters—fluidic resistance and compliance coefficient—are suggested and obtained by analyzing the fluid velocities in a microfluidic channel and calculating the air pressure in the air compliance unit. Using a discrete fluidic circuit model, the pressure difference is analytically derived and utilized as the nonlinear regression formula. The two key parameters are then obtained through nonlinear regression analysis. According to experimental results, the air cavity and flow rate contribute to increasing the compliance coefficient. The fluidic resistance increases significantly at higher concentrations of glycerin solution ranging from 20% to 50%. The proposed method underestimates the values by approximately 27.5% compared with the previous method. Finally, the proposed method is adopted to detect the effects of hematocrit and red blood cell sedimentation in the driving syringe based on two vital parameters. Regarding the fluidic resistance, the normalized difference between the proposed and previous methods is less than 10%. Therefore, two key parameters can be considered as effective for quantitatively monitoring the hematocrit variation in blood flow. In conclusion, from a biomechanical perspective, the proposed method is highly promising for quantifying blood flow in a microfluidic channel.

Experimental and numerical study of flow structure in a model of distal anastomosis of femoral artery

Physical and numerical simulation of the steady blood flow was carried out focusing on the distal end-to-side anastomosis of a graft to the femoral artery. The angle between the graft and the artery was 60°. Two Reynolds numbers were considered that corresponded to the physiological range when estimated using the average (Re = 240) and maximum (Re = 1640) blood flow through the human femoral artery over a single cardiac cycle. The experiment included flow visualization and measurements of instantaneous vector fields of velocity using an optical SIV (Smoke Image Velocimetry) technique. Direct numerical simulation (DNS) was employed for numerical study. The distribution of blood flows through the branches of the main artery was 80 % in the antegrade and 20 % in the retrograde direction. Main patterns in the distribution of velocity and its root-mean-square fluctuations in both branches of the main artery were revealed. Flow separation regions were observed in the branching area. Additionally, secondary flows (Prandtl’s vortices of the first kind) were revealed. The flow in the branching area was still laminar Re = 240, while the signs of transition to turbulence were documented within separation regions at Re = 1640. Distributions of streamwise and circumferential components of skin friction vector were estimated. In some regions of flow, these components were shown to be comparable in size. The location of regions was revealed in which the friction magnitude in the considered flow regimes was lower than the one in an unimpaired artery (developed laminar flow in a circular pipe) at appropriate Reynolds numbers.

Adjoint shape sensitivities of blood flows considering non‐Newtonian properties

AbstractThis article discusses the derivation and numerical implementation of an adjoint system, to the primal Navier–Stokes equations, for the computation of shape sensitivities of ducted blood flows considering non‐Newtonian fluid properties. The ever‐growing advancements in blood flow simulations are, naturally, accompanied by an increased interest in the optimization of related medical devices. In the majority of the computational studies, the Newtonian assumption is used to describe the rheology of blood. While this assumption has been shown to satisfactorily capture the flow when it is governed by high shear rates, it falls short at low shear rates. A rich variety of viscosity models has been proposed to tackle this shortcoming. In this article we show how such models can be incorporated into an adjoint system targeting to produce the shape sensitivity which can be used by a gradient‐based optimization method for the minimization of an objective functional. A general formulation of the adjoint equations is proposed, in which contributions of the non‐Newtonian properties explicitly occur. The numerical implementation is discussed and the validity of the method is assessed by means of numerical experiments of steady blood flows in a 2D stenosed duct, where results are compared against second‐order finite‐difference (FD) studies. The proposed methodology is then applied to CAD‐free, gradient‐based shape optimizations of an idealized 3D arterial bypass‐graft operating at three relevant Reynolds numbers. It is observed that the impact of the adjoint viscosity treatment is amplified in low shear‐rate flow regimes while fades for higher shear‐rates, analogous to its primal counterpart.

Vascular function: a key player in hypertension.

The major functions of the arterial system are to "efficiently deliver blood to the peripheral organs and maintain vascular homeostasis". Both the endothelial and medial layer contribute to the three major functions, namely, conversion of pulsatile to steady blood flow, appropriate distribution of blood flow to the target organs, and vascular protection and homeostasis. Vascular dysfunction contributes to the development of cardiovascular diseases through a combination of several mechanisms, including impaired coronary perfusion, cardiac systolic/diastolic dysfunction, microvascular damage, and abnormal hemodynamics in the arterial tree. The representative marker of endothelial function is flow-mediated vasodilatation and that of the medial layer function is pulse wave velocity, and that of the blood supply function of the arterial tree is the ankle-brachial pressure index. In hypertension, vascular dysfunction could also lead to the development of isolated systolic hypertension, isolated diastolic hypertension, and systolic/diastolic hypertension. Vascular dysfunction is involved in a vicious cycle with abnormal blood pressure variability. Furthermore, a vicious cycle may also exist between vascular dysfunction and hypertension. While the significances of vascular function tests to predict future cardiovascular events has been established in cases of hypertension, their usefulness in assessing the effectiveness of management of the vascular functions in hypertension on the cardiovascular outcomes has not yet been fully clarified. Thus, vascular dysfunction plays crucial roles in the pathophysiology of hypertension, and further research is warranted to establish strategies to improve vascular dysfunction in cases of hypertension. Vascular functions in the pathophysiology of hypertension. Vascular dysfunction and elevation of blood pressure are components of a vicious cycle even from their early stages, which including abnormal blood pressure variabilities. This vicious cycle is associated with hypertensive organ damage and also adverse cardiovascular outcomes. Strategies to break this vicious cycle have not yet been fully established.

Steady blood flow through a porous microchannel with the influence of an inclined magnetic field

This research deals with steady blood flow through a porous microchannel with the influence of an inclined magnetic field. In the research, we formulate time-independent differential equations which represent the blood momentum, energy equation, and mass concentration in the flood governing the flow. The governing equations were scaled to be dimensionless using some prescribed dimensionless parameters in the work. The reduced dimensionless governing equations were further solved using the Frobenius method (FM), where the blood velocity, mass concentration and blood temperature profiles were obtained. Numerical simulation was carried out using Wolfram Mathematica, version 12, to investigate the effect of the variation of the values of pertinent parameters on the flow profiles. In the investigation, it was revealed that the variation of Grashof number, Schmidt number, and porosity parameters increased the blood velocity before decreasing to zero when the boundary layer thickness was at its peak, while the variation of magnetic field and Prandtl number reduced blood velocity. However, the magnetic field angle of inclination initially increased the blood velocity before decreasing. In a similar vein, as the Schmidt number and chemical reaction parameters decrease the mass concentration level in the fluid, the blood temperature increases for the variation of the Schmidt number. In conclusion, the problem was formulated, solved, and simulation was done successfully, where various pertinent parameters were checked. These results are very useful for clinicians and scientists who are interested in investigating the role of some pertinent factors in understanding blood circulation problems theoretically.

Solitonic Windkessel Model for Intracranial Aneurysm.

The Windkessel model, which is known as a successful model for explaining the hemodynamic circulation, is a mathematical model with a direct correspondence with the electric circuit. We propose a theoretical model for the intracranial aneurysm based on the Windkessel-type steady blood flow. Intracranial aneurysms are well known vascular lesions, which cause subarachnoid hemorrhages. Since an aneurysm is an end-sack formed on the blood vessel, it functions as an unusual blood path that has characteristic features such as a reservoir and bottle neck orifice. We simulate an aneurysm by an electric circuit consisting of three different impedances, resistance, capacitance and inductance. A dumbbell-shaped aneurysm is the most dangerous aneurysm to easily rupture. Our aneurysmal model is created as a two-story aneurysm model for this point, thus namely the five-element Windkessel. Then, the mathematical formula was solved in numerical simulations by changing the size of the aneurysm and the elasticity of the aneurysm wall. An analysis of this model provided that the presence of the daughter aneurysm and the thinning of the aneurysm wall are positively correlated with a sharp increase in blood pressure in the aneurysm dome. Our mathematic aneurysm model proposes a good analogue to the real aneurysm and proved that this model includes soliton that is a non-decreasing wave propagation.

Taylor dispersion in non-Darcy porous media with bulk chemical reaction: a model for drug transport in impeded blood vessels

The present article discusses the solute transport process in steady laminar blood flow through a non-Darcy porous medium, as a model for drug movement in blood vessels containing deposits. The Darcy–Brinkman–Forchheimer drag force formulation is adopted to mimic a sparsely packed porous domain, and the vessel is approximated as an impermeable cylindrical conduit. The conservation equations are implemented in an axisymmetric system (R, Z) with suitable boundary conditions, assuming constant tortuosity and porosity of the medium. Newtonian flow is assumed, which is physically realistic for large vessels at high shear rates. The velocity field is expanded asymptotically, and the concentration field decomposed. Advection and dispersion coefficient expressions are rigorously derived. Extensive visualization of the influence of effective Péclet number, Forchheimer number, reaction parameter on velocity, asymptotic dispersion coefficient, mean concentration, and transverse concentration at different axial locations and times is provided. Increasing reaction parameter and Forchheimer number both decrease the dispersion coefficient, although the latter exhibits a linear decay. The maximum mean concentration is enhanced with greater Forchheimer numbers, although the centre of the solute cloud is displaced in the backward direction. Peak mean concentration is suppressed with the reaction parameter, although the centroid of the solute cloud remains unchanged. Peak mean concentration deteriorates over time since the dispersion process is largely controlled by diffusion at the large time, and therefore the breakthrough curve is more dispersed. A similar trend is computed with increasing Péclet number (large Péclet numbers imply diffusion-controlled transport). The computations provide some insight into a drug (pharmacological agents) reacting linearly with blood.

Modelling the leptomeningeal collateral circulation during acute ischaemic stroke

A novel model of the leptomeningeal collateral circulation is created by combining data from multiple sources with statistical scaling laws. The extent of the collateral circulation is varied by defining a collateral vessel probability. Blood flow and pressure are simulated using a one-dimensional steady state blood flow model. The leptomeningeal collateral vessels provide significant flow during a stroke. The pressure drop over an occlusion predicted by the model ranges between 60 and 85 mmHg depending on the extent of the collateral circulation. The linear transport of contrast material was simulated in the circulatory network. The time delay of peak contrast over an occlusion is 3.3 s in the model, and 2.1 s (IQR 0.8–4.0 s) when measured in dynamic CTA data of acute ischaemic stroke patients. Modelling the leptomeningeal collateral circulation could lead to better estimates of infarct volume and patient outcome.

Cerebral arterial architectonics and CFD simulation in mice with type 1 diabetes mellitus of different duration

Type 1 diabetes is a chronic autoimmune disease that affects tens of millions of people. Diabetes mellitus is one of the strongest factors in the development of cerebrovascular diseases. In this study we used NOD.CB17 Prkdcscid mice and the pharmacological model of type 1 diabetes mellitus of different duration to study changes in the cerebral vasculature. We used two combined approaches using magnetic resonance angiography both steady and transient CFD blood flow modeling. We identified the influence of type 1 diabetes on the architectonics and hemodynamics of the large blood vessels of the brain as the disease progresses. For the first time, we detected a statistically significant change in angioarchitectonics (the angles between the vessels of the circle of Willis, cross-sections areas of vessels) and hemodynamic (maximum blood flow rate, hydraulic resistance) in animals with diabetes duration of 2 months, that is manifested by the development of asymmetry of cerebral blood flow. The result shows the negative effect of diabetes on cerebral circulation as well as the practicability of CFD modeling. This may be of extensive interest, in pharmacological and preclinical studies.

Prostaglandin E1 Is an Efficient Molecular Tool for Forest Leech Blood Sucking.

From a survival perspective, it is hypothesized that leech saliva exhibits certain physiological effects to ensure fast blood-feeding, including analgesia, anesthesia, and anti-inflammation to stay undetected by the host and vasodilatation and anti-hemostasis to ensure a steady, rapid, and sustained blood flow to the feeding site. Many anti-hemostatic compounds have been identified in leech saliva, such as hirudin, calin, and bdellin A. However, no specific substance with direct vasodilatory and anti-inflammatory function has been reported from forest leech saliva. Herein, using activity-guided analysis, prostaglandin E1 (PGE1) was identified for the first time as an efficient molecular tool for forest leech blood sucking. The structure of PGE1 was analyzed by nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectroscopy. PGE1 was found to be primarily distributed in the leech salivary gland (1228.36 ng/g body weight). We also analyzed how forest leech PGE1 affects platelet aggregation, skin vascular permeability, bleeding time, and pain. Results indicated that PGE1 efficiently inhibited platelet aggregation induced by adenosine diphosphate (ADP) (5 μM) with an IC50 of 21.81 ± 2.24 nM. At doses of 10, 100 nM, and 1 μM, PGE1 increased vascular permeability by 1.18, 5.8, and 9.2 times. It also prolonged bleeding time in a concentration-independent manner. In the formalin-induced mouse paw pain model, PGE1 suppressed acute pain. To the best of our knowledge, this is the first report on PGE1 in invertebrates. The functions of PGE1, such as vasodilation, platelet aggregation inhibition, anti-inflammation, and pain alleviation, may facilitate the ingestion of host blood by leeches.

Newtonian and Non-Newtonian Blood Rheology Inside a Model of Stenosis

In order to imitate the atherosclerosis artery disease and determine the key issues, Computational Fluid Dynamics (CFD) is able to play a leading rule in the analysis of flow physics within the clogged arteries, in particular the stenosis artery. The problem of blood flow blockage through the blood vessel has been investigated numerically within a stenosis artery. In this work, a CFD technique was employed to solve the three-dimensional, steady, laminar and non-Newtonian Carreau model blood flow through a stenosis artery using Star-CCM+ software. The shape of stenosis that has been selected is a trapezoidal with two cases (70% and 90% blockage). Shear rate, streamlines, vorticity and importance factor are examined to assess the influence of non-Newtonian model through the test section, the Carreau model was compared with Newtonian model. The clinical significance of the shear rate is reported for the examined cases, observing that the levels of non-Newtonian model are predicted to be higher in the 90% blockage than that observed within the 70%; the same finding as related with the axial velocity and vorticity. The levels of re-circulation areas and vorticity are showed to be enlarged in the Carreau model compared with the case of Newtonian.

Hemodynamic study in 3D printed stenotic coronary artery models: experimental validation and transient simulation

Atherosclerosis is a progressive disease that can significantly reduce blood supply to vital organs, being one of the main causes of death worldwide. In this work, a numerical and experimental study in 3D printed stenotic coronary arteries, considering both steady and pulsatile blood flow conditions, is presented. The results revealed that a degree of stenosis superior to 50% creates disturbed flows downstream of the contraction, with an accented increase in the wall shear stress measurements at the stenosis throat. Finally, the multiphase mixture was investigated and compared with a single-phase modelling, and only slight differences were observed right after the stenosis throat.

Racial Differences In Exercising Limb Blood Flow During Elevated Sympathetic Activity

PURPOSE: Young, healthy African Americans (AA) exhibit lower vascular conductance during an exercise bout compared to Caucasian Americans (CA). This disparity may be due to greater sympathetic vasoconstriction and an impairment in functional sympatholysis during exercise in AA. Thus, the purpose of this study is to examine racial differences in vascular conductance during lower limb exercise in the presence of elevated sympathetic activity administered via cold pressor test (CPT). METHODS: A total of 5 African American (AA) and 4 Caucasian (CA) young (24 ± 2 yrs), healthy males were recruited. Subjects then underwent 6 minutes of rhythmic plantar flexion (PF) exercise at 30% of their previously determine maximum voluntary contraction (MVC). Doppler ultrasonography was utilized to measure superficial femoral artery blood flow on the exercising leg while simultaneous measures of mean arterial pressure (MAP) were obtained via finger plethysmography. Subjects underwent the CPT (minutes 4-6) during which the hand was placed in cold water (4 °C) during PF exercise. Measures were obtained during steady state exercise blood flow (measured at minutes 3-4) and during the CPT (measured at minute 5-6) to determine differences in vascular conductance with and without the presence of elevated sympathetic activity. RESULTS: The CPT resulted in similar increases in MAP in both AA (+24.8 ± 3 mmHg) and CA (+25.56 ± 13 mmHg) (p = 0.95) when compared to PF exercise alone. Exercising leg blood flow [AA (-38.89 ± 62 mL/min); CA (+137.97 ± 62 mL/min) (p = .09)] or leg vascular conductance [AA (-1.00 ± .6 mL/min/mmHg); CA (-0.28 ± .4 ml/min/mmHg) (p = .35)] was not different between groups when evaluated during the CPT and expressed as change from PF exercise alone. CONCLUSIONS: This study suggests that during lower limb exercise, young AA males, when compared to CA, are similarly resistant to reductions in lower limb vascular conductance in response to elevated sympathetic activity.

Investigation of Newtonian and Power-Law Blood Flow Models in a 180° Curved Pipe at Low to Medium Shear Rate

The purpose of this brief paper is to obtain quantitative information on mean velocity profile in ideal vasculature (i.e. straight and toroidal pipes) at low to medium shear rates. To shed the light on the significance of considering blood shear-thinning properties, the power-law model is compared to the commonly used Newtonian viscosity hypothesis. Validated CFD models of blood flow were established and parameterized to solve steady incompressible blood flow under Reynolds number of 50~200. The calculations of the Reynolds number and boundary conditions adopted the shear-thinning index of the power-law models to provide physically correct benchmark for the comparison presented herein. Velocity profiles for Newtonian and non-Newtonian fluid flow are described and sketched. Shear rate values had a range of 20~200 s-1 which represents the physiological range found in cerebral vasculature. This study provides the means to estimate the effect of the non-Newtonian properties of the blood on the flow patterns. It is clearly shown that the difference between Newtonian and power-law blood flow models is not significantly affected by Reynolds number for the current range of shear rate. The differences identified in the pressuredrop per unit length and average wall-shear stress were found to be of significant values. The difference between the Newtonian and power-law model (case1) in the pressure drop per unit length for the straight pipe was 386 while for the curved pipe was 371. These differences increased to 538 at Re=200 for the straight pipe and reached 603 for the curved pipe. This research suggests that the non-Newtonian effects of cerebral blood flow should be considered in the respective CFD models.

Numerical treatment of slip velocity and catheterization on the gravity flow of non-Newtonian fluid model through a uniform blood vessel

The aim of the present article is to investigate the influence of gravity and slip velocity on the steady flow of blood through an inclined catheterized blood vessel. The constitutive relation of Herschel–Bulkley fluid is utilized to capture the non-Newtonian characteristics of the blood. The effects of catheter radius, yield stress, slip velocity and the inclination angle on the velocity, flow rate, wall shear stress and resistance to the flow are analyzed in detail. The expression of velocity is evaluated numerically by using Regula falsi method. The variation of different flow variables corresponding to the involved geometric and rheologic parameters is shown through graphs. It is shown that the velocity decreases as the yield stress attains higher values. The yield stress enhances the impedance and wall shear stress. Increase in the catheter radius reduces the wall shear stress and resistive impedance. The study also reveals that the impedance for horizontal blood vessel is higher as compared to the vertical blood vessel.

Effect of asymmetry on the flow behavior in an idealized arterial bifurcation

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.

A Long “Biotube” Vascular Graft for Hemodialysis Access: Evaluation in an Animal Model

Introduction - In patients receiving hemodialysis, autologous arteriovenous fistula (AVF) is first choice for vascular access. On the other hand, artificial vascular grafts are needed in an underlying disease or second surgery. However, they had any risk such as infectivity or low patency. In-body tissue architecture (iBTA) can prepare collagenous tubes, called Biotubes, by using a patient's body as a bioreactor. Previously, autologous Biotubes grown in patient’s subcutaneous pouches were successfully bypassed the venous stenosis region as the first-in-human study. In this study, long Biotubes were implanted as canine or goat AV hemodialysis access. Methods - Disk-like molds (1 in photos) having spiral cylinder were embedded in beagles or goats subcutaneously for 2 months. Biotubes with diameter of 4 or 5 mm and wall thickness of 1.5 mm were obtained after removing the mold harvested (2 in photos). The Biotubes were stored in an alcoholic solution at room temperature. Immediately before implantation Biotubes were immersed in a 0.6% glutaraldehyde solution for 2 min. AV shunts were prepared with allogenic Biotubes (straight shape, length 10 cm for beagles, U-shape, 50 cm for goats) between the carotid artery and jugular vein. Follow up was performed with Doppler echo and angiography. Results - Following placement of all Biotubes, continuous thrill was felt by palpation and Doppler echo showed turbulent blood flow. Angiography revealed that all three straight beagle Biotubes were patent for 6 months without any abnormal deformation in vascular shape (3 in photos). Percutaneous punctures and compression hemostasis within several minutes at every other day were possible after 1 month of implantation. All two U-shaped goat Biotubes were also patent up to 3 months until now even with the length of 50 cm (4 in photos). Conclusion - Long Biotubes successfully created an AV shunt that maintained steady blood flow, suggesting that Biotubes can have high potential clinical use as vascular access for hemodialysis.