Hemodynamic Characteristics Of Blood Flow Research Articles

Hemodynamic characteristics of blood flow in an inclined overlapped stenosed arterial section

This work presents a theoretical analysis of the non-linear behavior of blood flow along an angled arterial section with overlapping stenosis. An elastic cylindrical tube with a moving wall is used to represent the artery, and a Casson liquid is used to simulate blood flowing through it. The nonlinear equations that govern blood flow are taken into account. The influence of the pulsatile pressure gradient caused by the regular heartbeat on the flow process in the stenosed artery is demonstrated mathematically. The current analytical method can compute the wall shear stress, flow resistivity, and velocity profiles with mild stenosis assumption by applying the boundary conditions. Numerical calculations of the desired quantities are carried out systematically. They provide an overview of how the degree of stenosis and the malleability of the artery wall influence blood flow abnormalities. Concerning the height of stenosis, the surface shear stress and the resistivity to flow increase together with an increase in the proclivity angle.

Advanced cross-sectional imaging of cerebral aneurysms.

While the rupture rate of cerebral aneurysms is only 1% per year, ruptured aneurysms are associated with significant morbidity and mortality, while aneurysm treatments have their own associated risk of morbidity and mortality. Conventional markers for aneurysm rupture include patient-specific and aneurysm-specific characteristics, with the development of scoring systems to better assess rupture risk. These scores, however, rely heavily on aneurysm size, and their accuracy in assessing risk in smaller aneurysms is limited. While the individual risk of rupture of small aneurysms is low, due to their sheer number, the largest proportion of ruptured aneurysms are small aneurysms. Conventional imaging techniques are valuable in characterizing aneurysm morphology; however, advanced imaging techniques assessing the presence of inflammatory changes within the aneurysm wall, hemodynamic characteristics of blood flow within aneurysm sacs, and imaging visualization of irregular aneurysm wall motion have been used to further determine aneurysm instability that otherwise cannot be characterized by conventional imaging techniques. The current manuscript reviews conventional imaging techniques and their value and limitations in cerebral aneurysm characterization, and evaluates the applications, value and limitations of advanced aneurysm imaging and post-processing techniques including intracranial vessel wall MRA, 4D-flow, 4D-CTA, and computational fluid dynamic simulations.

Aneurysm geometric features effect on the hemodynamic characteristics of blood flow in coronary artery: CFD simulation on CT angiography-based model.

The main purpose of the present numerical study is to evaluate the influences of aneurysm geometric features on the hemodynamic conditions within the left coronary arteries (LCA). Simulations have been conducted in two major parts: Section (I)encompassing three different cases(case 1, case 2, and case 3), in which three various sizes of the bifurcation region ([Formula: see text], [Formula: see text], and [Formula: see text]) were considered for each case, and Section (II)also consists of three distinct cases (case 4, case 5, and case 6) which two different positions (P1 and P2; proximal and distal to the main bifurcation, respectively) were taken into account for a fusiform aneurysm located on their left circumflex branch. Prediction and assessment of the correlation between morphological characteristics of an aneurysm with atherosclerosisandthrombosis were performed using quantitative and qualitative results including streamline and velocity contours, wall shear stress, oscillatory shear index, and relative residence time.Depending on the various cases, the time-averaged wall shear stress (TAWSS) of the bifurcation region for models of [Formula: see text] was nearly 18-24% fewer than [Formula: see text], and around 74-81% fewer than intact models. Moreover, the smaller size of the LCA dilation results in less flow recirculation and, accordingly, the lower risk of blood clotting. Additionally, the TAWSS of the aneurysm in the P1 model of case 4 was found 16.4% lower than in P2; however, the values for P1 models of case 5 and case 6 were higher than in P2 by close to 16.3% and 12.5%, respectively. Furthermore, it was concluded that the intricate geometry of LCAs, especially pre-aneurysm curvatures, have remarkable effects on the hemodynamics within the aneurysms. Even though a limited number of cases were used in this study, due to the scarcity of similar works, the outcomes of this computational evaluation can positively contribute to clinical decision-making in the assessment of coronary aneurysms.

Lattice Boltzmann Method for Simulating Disturbed Hemodynamic Characteristics of Blood Flow in Stenosed Human Carotid Bifurcation

The local hemodynamic factor plays a vital role in the formation and progression of atherosclerosis. In this study, we simulated pulsatile flow patterns in the three-dimensional stenosed and normal carotid artery bifurcations throughout a cardiac cycle using the multiple-relaxation-time lattice Boltzmann (MRT-LB) method. Additionally, we investigated the time-varied flow rate and its division ratios between the parent and daughter branches, the multidirectionality of the stress field, and the averaged local energy dissipation rate. The results can be used in computational modeling of carotid artery hemodynamics and further investigation of the relationship between hemodynamics and cardiovascular diseases.

Evaluation of the presence of endothelial dysfunction in children with Henoch-Schonlein purpura in terms of doppler ultrasound

Purpose - to assess the presence of endothelial dysfunction in children with Henoch-Schonlein purpura in terms of Doppler ultrasound. Material and methods. We examined 123 children with Henoch - Schonlein purpura from 1 to 18 years old. Assessment of functional status and vasoregulatory vascular endothelial function was performed using Doppler ultrasound using ultrasound scanner "Philips HDII XE" B-mode sensor linear format in the frequency range from 5 MHz to 15 MHz at rest. The Results. Using doppler ultrasound, we found that the endothelial dysfunction observed in all children with at Henoch - Schonlein purpura. In patients with maximum disease activity index of structural and functional state of the endothelium of the carotid and brachial arteries were 1.3 - 1.5 times more than in healthy children. Also, more severe violations of hemodynamic characteristics of blood flow in the brachial artery (speed reduction) were observed at the III degree of activity and accounted for - Vsp 34,59 ± 3,18 mm / sec, Ved 2,72 ± 0,57 mm / sec, S / D 10 15 ± 0,82.

Hemodynamic features and platelet aggregation in a stenosed microchannel

Platelet aggregation has been known to be closely influenced by the surrounding hemodynamic environments. Especially, platelet activation, aggregation, and thrombus formation frequently occur at the locally stenosed blood vessel where recirculation and stagnation flow regions are developed. However, the relationship between hemodynamic feature and platelet aggregation is not fully understood yet. The main objective of this study is to investigate the hemodynamic characteristics of blood flow in a stenosis channel and their effects on platelet aggregation. Whole blood was injected into a stenosed microchannel with 85% severity at various flow rates, ranging from 10 to 50mLhr−1. The velocity vector field of the blood flow in the stenosed microchannel was measured using newly developed LED (light emitting diode)-illumination microparticle image velocimetry (micro-PIV). The blood flow is highly disturbed by the micro-stenosis, and a recirculation flow region is formed at the post-stenosis region. The occurring site and the shape of the platelet aggregation are highly influenced by the hemodynamic characteristics of blood flow around the stenosis. Especially, the platelet aggregation is found to occur at the interface where the downward momentum of the central jet at the post-stenosis region and the upward momentum of the recirculation flow are balanced. These experimental results would be helpful to understand the platelet aggregation under disturbed blood flow conditions.

SIMULATION OF PULSATILE BLOOD FLOW THROUGH STENOTIC ARTERY CONSIDERING DIFFERENT BLOOD RHEOLOGIES: COMPARISON OF 3D AND 2D-AXISYMMETRIC MODELS

Hemodynamic factors such as velocity distribution, pressure gradient and wall shear stress are thought to play an important role in the prognosis of symptomatic carotid occlusion. Although there are many studies about modeling the blood flow behavior in carotid, hemodynamic characteristics of blood flow in a stenosed carotid artery is still debatable. In this study a three-dimensional (3D) model of a symmetric stenosed common carotid artery (CCA) is developed and the simulation results of it are compared to the experimental data where subsequent agreement is confirmed. To study the accuracy of two-dimensional (2D) axisymmetric model, the result of it is compared to the result of the 3D model. Two non-Newtonian rheological models, namely Carreau and modified Power-law, as well as Newtonian model are used to realize the hemodynamical differences of 2D-axisymmetric and 3D models in pulsatile blood flow. Comparing the 3D simulated results with 2D-axisymmetric modeling results that were published in recent years indicates that the assumption of 2D-axisymmetric model cannot adequately predict the velocity profiles even for a symmetric stenotic artery. Although a symmetric stenotic artery is considered, the results indicate a nonsymmetric flow in poststenosis region that is detected by the presence of extensive secondary flows particularly at diastole. The existence of secondary flows that can only be detected in 3D modeling is the main reason for the differences in hemodynamic factors in 3D and 2D results.

Non-Newtonian Effect on Hemodynamic Characteristics of Blood Flow in Stented Cerebral Aneurysm

AbstractStent placement is considered as a promising and minimally invasive technique to prevent rupture of aneurysm and favor coagulation mechanism inside the aneurysm. Many scholars study the effect of the stent on blood flow in cerebral aneurysm by numerical simulations, and usually regard blood as the Newtonian fluid, blood, however, is a kind of non-Newtonian fluid in practice. The main purpose of the present paper is to investigate the effect of non-Newtonian behavior on the hemodynamic characteristics of blood flow in stented cerebral aneurysm with lattice Boltzmann method. The Casson model is used to describe the blood non-Newtonian character, which is one of the most popular models in depicting blood fluid. In particular, hemodynamic characteristics derived with Newtonian and non-Newtonian models are studied, and compared in detail. The results show that the non-Newtonian effect gives a great influence on hemodynamic characteristics of blood flow in stented cerebral aneurysm, especially in small necked ones.

Velocity field measurements of valvular blood flow in a human superficial vein using high-frequency ultrasound speckle image velocimetry

This study aims to investigate the blood flow around the perivalvular area in a human superficial vein using high-frequency ultrasound (HFUS) speckle image velocimetry. HFUS B-mode images were captured from the superficial veins of human lower extremity with a 35-MHz transducer. To measure the instantaneous velocity fields of blood flow, a cross-correlation particle image velocimetry (PIV) algorithm was applied to two B-mode images that were captured consecutively. The echo speckles of red blood cells (RBCs) were used as flow tracers. In the vicinity of the venous valve, the opening and closing motions of valve cusps were simultaneously visualized with the phasic variation of velocity fields. Large-scale vortices were observed behind the sinus pockets while the main bloodstream was directed proximally. This measurement technique combining PIV algorithm and HFUS B-mode imaging was found to be unique and useful for investigating the hemodynamic characteristics of blood flow in the perivalvular area and for diagnosing venous insufficiency and valve abnormality in superficial blood vessels.

Micro-PIV measurements of blood flow in extraembryonic blood vessels of chicken embryos

The hemodynamic characteristics of blood flow are important in the diagnosis of circulatory diseases, since such diseases are related to wall shear stress of cardiovascular vessels. In chicken embryos at early stages of development, it is possible to directly visualize blood flow inside blood vessels. We therefore employed a micro-PIV technique to assess blood flow in extraembryonic venous and arterial blood vessels of chicken embryos, using red blood cells (RBCs) as tracers and obtaining flow images of RBCs using a high-speed CMOS camera. The mean velocity field showed non-Newtonian flow characteristics. The blood flow in two venous vessels merged smoothly into the Y-shaped downstream vein without any flow separation or secondary flow. Vorticity was high in the inner regions, where the radius of curvature varied greatly. A periodic variation of temporally resolved velocity signals, due to beating of the heart, was observed in arterial blood vessels. The pulsating frequency was obtained by fast Fourier transform analysis using the measured velocity data. The measurement technique used here was useful in analyzing the hemodynamic characteristics of in vivo blood flow in chicken embryos.

Performance Study on Newly Developed Impellers for a Left Ventricular Assist Device

Our research develops a performance study on newly developed impellers for a left ventricular assist device. In order to analyze the hemodynamic characteristics of blood flow through the ventricular assist device, the CFX-TASCflow software is adopted to investigate the flow-field characteristics. The numerical results provide not only the flow characteristics for the overall field, but also the data of relationship for flow rate and pressure head. In the conceptual design process, hemodynamic study for an initial impeller design is presented first and a geometry change is recommended. Two design models are developed and the associated flow rate and pressure head performances are evaluated as well. According to design criteria, the most efficient design is the one with a smooth flow passage and with a low possibility for vortex generation. We suggest the superior design be chosen for further in vitro testing and be prepared for the new design generation. It has been shown that the design can provide a flow rate of 3.0 l/min with a pressure head of 127.09 mmHg. Both the flow rate and pressure head can meet requirements for the left ventricular assist device to work normally.

Effects of elastic property of the wall on flow characteristics through arterial stenoses

Hemodynamic characteristics of blood flow through arterial stenoses are numerically investigated in this work. The blood is assumed as a Newtonian fluid and the pulsatile nature of flow is modeled by using measured values of the flowrate and pressure for the canine femoral artery. An isotropic elastic and incompressible material is assumed for the wall at each axial section, but a non-uniform distribution of the shear modulus in axial direction is used to model the high stiffness of the wall at the stenosis location. Full Navier equations for a thick wall are used as the governing equations for the wall displacements. A continuous grid extending over the flow field and the wall is considered and governing equations are transformed for use in the computational domain. Discretized forms of the transformed wall and flow equations, which are coupled through the boundary conditions at their interface, are obtained by control volume method and simultaneously solved using the well-known SIMPLER algorithm. To study the effects of wall deformability, solutions are obtained for both rigid and elastic walls. The results indicate that deformability of the wall causes an increase in the time average of pressure drop, but a decrease in the maximum wall shear stress. Displacement and stress distributions in the wall are presented.

Influence Of Blood Flow On The LongitudinalImpedance In Arteries: A Simulation Study

Longitudinal impedance is an important parameter in determining local hemodynamic characteristics of blood flow in arteries. It is usually calculated through formulas based on linearized models for blood flow, which are deduced omitting the convective terms in the Navier-Stokes equations. The role of fluid motion nonlinearities in main arteries has been demonstrated both experimentally and computationally in the last two decades. In this paper the attention is focused on the influence of these nonlinearities on the longitudinal impedance when flow rate undergoes to large variations, as may occur in physiological conditions. The study is performed by using a mathematical model previously proposed, which takes into account all the nonlinear terms of the fluid motion and which is solved numerically. The results obtained in the simulated cases show that longitudinal impedance and in particular its resistive component, is highly affected by flow rate.