Abstract: Elastic compression stockings (ECSs) have been widely applied in prophylaxis and treatment of chronic venous insufficiency of lower extremities. The medical function of ECS is to improve venous return and increase muscular pumping action to facilitate blood circulation, which is largely determined by the complex interaction between the ECS and lower limb tissues. Understanding the mechanical transmission of ECS along the skin surface, deeper tissues, and vascular system is essential to assess the effectiveness of the ECSs. In this study, a three-dimensional (3D) finite element (FE) model of the leg-ECS system integrated with a 3D fluid-solid interaction (FSI) model of the leg-vein system was constructed to analyze the biomechanical properties of veins and soft tissues under different ECS compression. The Magnetic Resonance Imaging (MRI) of the human leg was divided into three regions, including soft tissues, bones (tibia and fibula) and veins (peroneal vein, great saphenous vein, and small saphenous vein). The ECSs with pressure ranges from 15 to 26 mmHg (Classes I and II) were adopted in the developed FE-FSI model. The soft tissue was assumed as a Neo-Hookean hyperelastic model with the fixed bones, and the ECSs were regarded as an orthotropic elastic shell. The interfacial pressure and stress transmission were simulated by the FE model, and venous hemodynamics properties were simulated by the FSI model. The experimental validation indicated that the simulated interfacial pressure distributions were in accordance with the pressure measurement results. The developed model can be used to predict interfacial pressure, stress transmission, and venous hemodynamics exerted by ECSs and optimize the structure and materials properties of ECSs design, thus improving the efficiency of compression therapy.
Abstract: The aim of this study is to estimate the effect of blood flow through the coronary artery in human heart so as to assess the coronary artery disease.Velocity, wall shear stress (WSS), strain rate and wall pressure distribution are some of the important hemodynamic parameters that are non-invasively assessed with computational fluid dynamics (CFD). These parameters are used to identify the mechanical factors responsible for the plaque progression and/or rupture in left coronary arteries (LCA) in coronary arteries.The initial step for CFD simulations was the construction of a geometrical model of the LCA. Patient specific artery model is constructed using computed tomography (CT) scan data with the help of MIMICS Research 19.0. For CFD analysis ANSYS FLUENT-14.5 is used.Hemodynamic parameters were quantified and flow patterns were visualized both in the absence and presence of coronary plaques. The wall pressure continuously decreased towards distal segments and showed pressure drops in stenotic segments. Areas of high WSS and high flow velocities were found adjacent to plaques deposition.
Abstract: The aim of this investigation was to validate the fluid-structure interaction (FSI) model of type B aortic dissection with our experimental results from a bench-top-model. Another objective was to study the relationship between the size of a septectomy that increases the outflow of the false lumen and its effect on the values of the differential of pressure between true lumen and false lumen. FSI analysis based on Galerkin’s formulation was used in this investigation to study flow pattern and hemodynamics within a flexible type B aortic dissection model using boundary conditions from our experimental data. The numerical results of our model were verified against the experimental data for various tear size and location. Thus, CFD tools have a potential role in evaluating different scenarios and aortic dissection configurations.
Abstract: In this work, the hemodynamics in the sinuses of
Valsalva after Transcatheter Aortic Valve Implantation is numerically
examined. We focus on the physical results in the two-dimensional
case. We use a finite element methodology based on a Lagrange
multiplier technique that enables to couple the dynamics of blood
flow and the leaflets’ movement. A massively parallel implementation
of a monolithic and fully implicit solver allows more accuracy and
significant computational savings. The elastic properties of the aortic
valve are disregarded, and the numerical computations are performed
under physiologically correct pressure loads. Computational results
depict that blood flow may be subject to stagnation in the lower
domain of the sinuses of Valsalva after Transcatheter Aortic Valve
Implantation.
Abstract: The aim of the present study is to computationally evaluate the hemodynamic factors which affect the formation of atherosclerosis and plaque rupture in the human artery. An increase of atherosclerosis disease in the artery causes geometry changes, which results in hemodynamic changes such as flow separation, reattachment, and adhesion of new cells (chemotactic) in the artery. Hence, geometry plays an important role in the determining the nature of hemodynamic patterns. Influence of stenosis in the non-bifurcating artery, under pulsatile flow condition, has been studied on an idealized geometry. Analysis of flow through symmetric and asymmetric stenosis in the artery revealed the significance of oscillating shear index (OSI), flow separation, low WSS zones and secondary flow patterns on plaque formation. The observed characteristic of flow in the post-stenotic region highlight the importance of plaque eccentricity on the formation of secondary stenosis on the arterial wall.
Abstract: The numerical simulation has made tremendous
advances in investigating the blood flow phenomenon through elastic
arteries. Such study can be useful in demonstrating the disease
progression and hemodynamics of cardiovascular diseases such as
atherosclerosis. In the present study, patient specific case diagnosed
with partially stenosed complete right ICA and normal left carotid
bifurcation without any atherosclerotic plaque formation is
considered. 3D patient specific carotid bifurcation model is generated
based on CT scan data using MIMICS-4.0 and numerical analysis is
performed using FSI solver in ANSYS-14.5. The blood flow is
assumed to be incompressible, homogenous and Newtonian, while
the artery wall is assumed to be linearly elastic. The two-way
sequentially coupled transient FSI analysis is performed using FSI
solver for three pulse cycles. The hemodynamic parameters such as
flow pattern, Wall Shear Stress, pressure contours and arterial wall
deformation are studied at the bifurcation and critical zones such as
stenosis. The variation in flow behavior is studied throughout the
pulse cycle. Also, the simulation results reveal that there is a
considerable increase in the flow behavior in stenosed carotid in
contrast to the normal carotid bifurcation system. The investigation
also demonstrates the disturbed flow pattern especially at the
bifurcation and stenosed zone elevating the hemodynamics,
particularly during peak systole and later part of the pulse cycle. The
results obtained agree well with the clinical observation and
demonstrates the potential of patient specific numerical studies in
prognosis of disease progression and plaque rupture.
Abstract: The characteristics of physiological blood flow in human carotid arterial bifurcation model have been numerically studied using a fully coupled fluid-structure interaction (FSI) analysis. This computational model with the fluid-structure interaction is constructed to investigate the flow characteristics and wall shear stress in the carotid artery. As the flow begins to decelerate after the peak flow, a large recirculation zone develops at the non-divider wall of both internal carotid artery (ICA) and external carotid artery (ECA) in FSI model due to the elastic energy stored in the expanding compliant wall. The calculated difference in wall shear stress (WSS) in both Non-FSI and FSI models is a range of between 5 and 11% at the mean WSS. The low WSS corresponds to regions of carotid artery that are more susceptible to atherosclerosis.
Abstract: Human heart valves diseased by congenital heart
defects, rheumatic fever, bacterial infection, cancer may cause stenosis
or insufficiency in the valves. Treatment may be with medication but
often involves valve repair or replacement (insertion of an artificial
heart valve). Bileaflet mechanical heart valves (BMHVs) are widely
implanted to replace the diseased heart valves, but still suffer from
complications such as hemolysis, platelet activation, tissue
overgrowth and device failure. These complications are closely related
to both flow characteristics through the valves and leaflet dynamics. In
this study, the physiological flow interacting with the moving leaflets
in a bileaflet mechanical heart valve (BMHV) is simulated with a
strongly coupled implicit fluid-structure interaction (FSI) method
which is newly organized based on the Arbitrary-Lagrangian-Eulerian
(ALE) approach and the dynamic mesh method (remeshing) of
FLUENT. The simulated results are in good agreement with previous
experimental studies. This study shows the applicability of the present
FSI model to the complicated physics interacting between fluid flow
and moving boundary.
Abstract: Brain Computer Interface (BCI) has been recently
increased in research. Functional Near Infrared Spectroscope (fNIRs)
is one the latest technologies which utilize light in the near-infrared
range to determine brain activities. Because near infrared technology
allows design of safe, portable, wearable, non-invasive and wireless
qualities monitoring systems, fNIRs monitoring of brain
hemodynamics can be value in helping to understand brain tasks. In
this paper, we present results of fNIRs signal analysis indicating that
there exist distinct patterns of hemodynamic responses which
recognize brain tasks toward developing a BCI. We applied two
different mathematics tools separately, Wavelets analysis for
preprocessing as signal filters and feature extractions and Neural
networks for cognition brain tasks as a classification module. We
also discuss and compare with other methods while our proposals
perform better with an average accuracy of 99.9% for classification.
Abstract: In this study, numerical simulations on laminar flow in
sinusoidal wavy shaped tubes were conducted for mean Reynolds
number of 250, which is in the range of physiological flow-rate and
investigated flow structures, pressure distribution and particle
trajectories both in steady and periodic inflow conditions. For
extensive comparisons, various wave lengths and amplitudes of sine
function for geometry of tube models were employed. The results
showed that small amplitude secondary curvature has significant
influence on the nature of flow patterns and particle mixing
mechanism. This implies that characterizing accurate geometry is
essential in accurate predicting of in vivo hemodynamics and may
motivate further study on any possibility of reflection of secondary
flow on vascular remodeling and pathophysiology.
Abstract: The recent advances in computational fluid dynamics
(CFD) can be useful in observing the detailed hemodynamics in
cerebral aneurysms for understanding not only their formation and
rupture but also for clinical evaluation and treatment. However,
important hemodynamic quantities are difficult to measure in vivo. In
the present study, an approximate model of normal middle cerebral
artery (MCA) along with two cases consisting broad and narrow
saccular aneurysms are analyzed. The models are generated in
ANSYS WORKBENCH and transient analysis is performed in
ANSYS-CFX. The results obtained are compared for three cases and
agree well with the available literature.
Abstract: Recurrence of aneurysm rupture can be attributed to
coil migration and compaction. In order to verify the effects of
hemodynamics on coil compaction and migration, we analyze the
forces and displacements on the coil bundle using a computational
method. Lateral aneurysms partially filled coils are modeled, and
blood flow fields and coil deformations are simulated considering
fluid and solid interaction. Effects of aneurysm neck size and parent
vessel geometry are also investigated. The results showed that coil
deformation was larger in the aneurysms with a wider neck. Parent
vessel geometry and aneurysm neck size also affected mean pressure
force profiles on the coil surface. Pressure forces were higher in wide
neck models with curved parent vessel geometry. Simulation results
showed that coils in the wide neck aneurysm with a curved parent
vessel may be displaced and compacted more easily.