Cardiovascular Biomechanics
Hadi Taghizadeh; Faezeh Amini
Volume 16, Issue 1 , May 2022, , Pages 11-21
Abstract
Atherosclerosis, a common cardiovascular disease, is among the leading causes of death. Many of the heart attacks results from ruptured atherosclerotic lesion and emboli formation. Then, the susceptibility of the lesion is a key factor in preventing negative outcomes of the rupture. Mechanisms of plaque ...
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Atherosclerosis, a common cardiovascular disease, is among the leading causes of death. Many of the heart attacks results from ruptured atherosclerotic lesion and emboli formation. Then, the susceptibility of the lesion is a key factor in preventing negative outcomes of the rupture. Mechanisms of plaque rupture are under debate. However, a general agreement on the bold contribution of hemodynamic factors including the blood pressure is established. In the current study, biomechanical impacts of plaque calcification procedure and the changed thickness of fibrous cap were investigated. To do so, a cross-section of the constricted coronary artery is reconstructed from the histological images and extruded in the axial direction of the artery to produce the three dimensional configuration of the coronary model. Holzapfel strain energy density function is utilized for mechanical description of the arterial tissue and the fibrous cap which enables us to adopt collagen fiber orientation into the mechanical model. Furthermore, since the constricted vessel configuration is asymmetrical, instead of simplified cylindrical coordinates for collagen orientation, a discrete coordinate system is assigned to every element and respective circumferential, axial and radial directions were assigned. With calcification, plaque is more stable and produces monotonic stress patterns in its vicinity. Also, the fibrous cap thickness plays an important role as a barrier to inhibit stress concentration from soft lipid core and disturb the mechanical loads to the neighboring regions. These two parameters, provide useful insight on mechanical load distribution around an atherosclerotic lesion and the pathway of arterial tissue toward a new homeostasis.
Cardiovascular Biomechanics
Sara Barati; Nasser Fatouraee; Malikeh Nabaei
Volume 15, Issue 4 , March 2022, , Pages 355-366
Abstract
Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these ...
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Transcatheter aortic valves have become the standard procedure for high-risk patients with severe aortic valve stenosis. This minimally invasive procedure can expand to a wider range of patients with a lower risk of surgery. The complications after the implantation and the structural malfunction of these prostheses are the obstacles of this transition. Design optimization of the stents of these prostheses can improve their performance and reduce the post-operative complications associated with them. Since all prostheses are crimped before implantation, the designs should guarantee an acceptable structural performance after expansion, especially self-expandable stents for which the fatigue behavior strongly depends on the strain. This study applies a simple, cost-effective optimization framework to optimize the geometric parameters of these stents regarding the maximum strain during the crimping process. The design parameters include diameter profile, cell size, number of repeating components, and strut cross-section. The simplified models are evaluated and verified by the 3D simulations. The results show that the middle cells' height, number of cells, and strut width have the most prominent effect on the maximum crimping strain of the stent. The maximum strain of the optimized stent in the selected design space was 0.52. This stent had a width of 0.2 mm, thickness of 0.3 mm, the number of cells and patterns of 3 and 15, respectively, and the diameter profile associated with the diameter ratio of 1.05. This framework can be applied to a wide range of stent designs and tremendously reduce the cost of stent design and optimization.
Cardiovascular Biomechanics
Mosayeb Mobasheri; Manije Mokhtari Dizaji; Faride Roshanali
Volume 10, Issue 1 , May 2016, , Pages 11-23
Abstract
Heart torsion is one of the biomechanical parameters that are sensitive to changes in both regional and global left ventricular (LV) function. In this study, angle of myocardium’s trajectory in three dimensions (Ф) was estimated by simultaneous use of two dimensional long apical and short ...
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Heart torsion is one of the biomechanical parameters that are sensitive to changes in both regional and global left ventricular (LV) function. In this study, angle of myocardium’s trajectory in three dimensions (Ф) was estimated by simultaneous use of two dimensional long apical and short axis views of LV septum sequential images. Then correlation of 3D angle and 2D rotation angle from long (χ) and short (θ) axis views respectively was estimated and compared at three levels of base, mid and apex of interventricular septum wall. Sequential two dimensional echocardiography images of long and short axis views with minimum temporal resolution 14 ms of 19 healthy men was recorded and analyzed. Interventricular septum wall motion at three levels of base, mid and apex were estimated using sequential images processing of echocardiography in long and short axis views with block matching algorithm throughout three cardiac cycles. Then correlation of 2D angle of rotation from long (χ) and short (θ) axis views was analyzed with three dimentional angular of myocardium’s trajectory (Ф) at three levels of base, mid and apex of interventricular septum wall. Ф, θ and χ angles at base level 16.33±3.01, 10.61±3.38 and 15.11±3.30 degrees, mid level 22.77±4.95, 7.78±2.96 and 16.72±2.66 degrees and apex level of interventricular septum wall 14.60±5.81, 10.37±5.48 and 8.79±3.32 degrees were extracted respectively. Regard to sensitivity of 3D angle to variation of motion in each of three dimensions, it is suggested for examination of biomechanical behavior myocardium in different pathologic conditions.
Cardiovascular Biomechanics
Saeed Bahrami; Faramarz Firouzi
Volume 9, Issue 3 , December 2015, , Pages 293-303
Abstract
It is accepted that wall shear stress (WSS) and Oscillatory Shear index (OSI) are strong hemodynamic factors to development of atherosclerotic (AS) plaque. Sometimes, OSI has an important effect on AS plaque formation, because WSSdoesn't make it happenalone. Most computational fluid dynamic (CFD) simulations ...
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It is accepted that wall shear stress (WSS) and Oscillatory Shear index (OSI) are strong hemodynamic factors to development of atherosclerotic (AS) plaque. Sometimes, OSI has an important effect on AS plaque formation, because WSSdoesn't make it happenalone. Most computational fluid dynamic (CFD) simulations were performed on left main coronary bifurcation geometry, and whole left coronary artery tree has not been investigated by now. In this paper, a thorough three-dimensional model of left coronary artery tree was considered, including left main coronary, left anterior descending and its branches, left circumflex artery and its branches. Effects of cardiac motions on vessel wall of left coronary were considered. The governingNavier–Stokes equations for pulsatile flow and incompressible non-Newtonian blood was analyzed with finite element method. The study concentrates on shear stress distribution and OSI distribution on the vessel wall. Comparing the results of this study with previous clinical investigations shows that the regions with low wall shear stress (equal to and less than 1.5[Pa]) along with high OSI value (equal to and more than 0.3) have potential to development of AS plaque.So it can be predicted that the LAD region after D3 and the bifurcation of LCxA-OM have high potential to development of AS, in addition to the bifurcation of LCxA-LMCA which had been specified before.
Biomedical Image Processing / Medical Image Processing
Ali Kermani; Ahmad Ayatollahi; Sorour Mohajerani
Volume 8, Issue 4 , February 2015, , Pages 325-337
Abstract
IVUS imaging is a minimally invasive blood vessel cross-sectional imaging procedure in which accurate data is obtained from what is in there. Processing on these images or raw signals can provide wide range information for experts and practitioners, and can help them in making an accurate diagnosis and ...
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IVUS imaging is a minimally invasive blood vessel cross-sectional imaging procedure in which accurate data is obtained from what is in there. Processing on these images or raw signals can provide wide range information for experts and practitioners, and can help them in making an accurate diagnosis and appropriate treatment. Extraction of tissue boundaries in the blood vessels is one of the challenging parts as a first step in this direction. In this paper a new method was proposed based on the minimax technique and connected components for extracting Adventitia tissue boundary in intravascular ultrasound images. For this purpose, initial boundary will be extracted using improved minimax technique. Then final boundary is extracted with high precision using connected components. The method was tested on a set of real data with regard to the Hausdorff distance and Jaccard index to evaluate its performance. Mean of Hausdorff distance and mean of Jaccard index were obtained 95% and 0.45 millimeter, consequently. These results show that the proposed method in this paper can extract Adventitia tissue boundaries more accurately than existing methods with regard to the distance Hausdorff distance and Jaccard index.
Cardiovascular Biomechanics
Navid Soltani; Abbas Nasiraei Moghaddam; Nasser Faturaee; Saeed Seyri; Aisa Rassoli
Volume 8, Issue 4 , February 2015, , Pages 359-370
Abstract
Experimental tests and equations on the continuum mechanics are used in order to obtain the constitutive models of soft tissue using in predictive heart simulation. Considering the myocardium as one of the important tissues, in this paper first the morphology and structure of myocardium has been reviewed ...
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Experimental tests and equations on the continuum mechanics are used in order to obtain the constitutive models of soft tissue using in predictive heart simulation. Considering the myocardium as one of the important tissues, in this paper first the morphology and structure of myocardium has been reviewed and the mechanical response of passive form of this tissue has been investigated. The myocardium of left ventricle was considered as non linear elastic, in-compressible and non homogeneous material and using of bi-axial test in 3 lambs myocardium on fiber direction; a constitutive model of this tissue has been proposed. The model so constructed is then evaluated against the biaxial data, and values of the material constants have been obtained by curve fitting so the final model states the strain-energy function as cauchy's invariants which can be helpful in heart simulation.
Cardiovascular Biomechanics
Farzad Forouzandeh; Mahdie Haji-Bozorgi; Behrooz Meshkat; Nasser Fatouraee
Volume 8, Issue 3 , September 2014, , Pages 241-248
Abstract
Coronary Artery Diseases are one of the main reasonsof mortality. When these arteries occlude, usually a CoronaryArtery Bypass Graft (CABG) surgery is performed. Sine humanSaphenous Veins (SV) is used for CABG, they are of interest forresearchers. In this study human SV samples undergo inflationtest, ...
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Coronary Artery Diseases are one of the main reasonsof mortality. When these arteries occlude, usually a CoronaryArtery Bypass Graft (CABG) surgery is performed. Sine humanSaphenous Veins (SV) is used for CABG, they are of interest forresearchers. In this study human SV samples undergo inflationtest, using an inflation test device. Displacements of the samplesfor different pressures are analyzed, and average values are usedas input of a computational method. In the numerical simulationthe tissue is assumed as an elastic, isotropic, and homogenoussolid material, and its output is Young’s Modulus (E) ofthetissue. Results show that E of the SV increases linearly with thedistension pressure. Although simplifications were applied in thisstudy, it can be helpful for giving a basic insight aboutmechanical properties of human Saphenous Vein, which can befollowed by more realistic studies in the future.
Fluid-Structure Interaction in Biological Media / FSI
Saeed Nahidi; Alireza Hossein-Nezhad; Nasser Fatouraee; Zahra Heidari
Volume 7, Issue 2 , June 2013, , Pages 107-120
Abstract
Blood flow parameters are affected by position and shape of the accumulation of low density lipoprotein (LDL) in the layers of the arterial wall, and this phenomenon itself is influenced by infiltration flow of the blood. In this paper, in order to investigate the effect of wall flexibility on the infiltration ...
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Blood flow parameters are affected by position and shape of the accumulation of low density lipoprotein (LDL) in the layers of the arterial wall, and this phenomenon itself is influenced by infiltration flow of the blood. In this paper, in order to investigate the effect of wall flexibility on the infiltration flow in a pulsatile non-Newtonian blood flow in a symmetric carotid artery stenosis with a two flexible and porous layers, a finite element model with Porous Fluid Structure Interaction (PFSI) method was used and the results were compared to the porous rigid model. Study parameters were investigated in three different stenosis severities. Comparison of the presented results using PFSI model with those of Porous Rigid model showed about 22% decrease in wall shear stress in the stenosis region, about 20% increase in filtration velocity in the pre- and post-stenosis regions of the porous layer, but a slight difference in filtration velocity in the stenosis region.
Biomedical Image Processing / Medical Image Processing
Pedram Masaeli; Hamid Behnam; Zahra Alizadeh Sani; Ahmad Shalbaf
Volume 7, Issue 3 , June 2013, , Pages 237-254
Abstract
Coronary artery diseases cause more than half of all deaths in the world. Obviously, early identification is an important way to control coronary artery disease that is diagnosed by measurement and scoring general and regional movement of left ventricle of heart (Normal, Hypokinetic and Akinetic). The ...
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Coronary artery diseases cause more than half of all deaths in the world. Obviously, early identification is an important way to control coronary artery disease that is diagnosed by measurement and scoring general and regional movement of left ventricle of heart (Normal, Hypokinetic and Akinetic). The most common method of imaging the heart using ultrasound is called echocardiography. Using this method accurate view of the heart walls, valves and beginning of main arteries can be obtainbed. Due to the difficulty for the interpretation of these images, time consumption and errors in manual analysis methods, an automated analysis method is required. In this paper we calculate the displacement field in a cycle of heart motion from two-dimensional echocardiography images. To do this, a frame is usually chosen as the reference frame and then all images in a cycle are mapped to it with a mathematical equation. The main idea is to find a semi-local spatiotemporal parametric model for deformation created in a cardiac cycle with nonrigid registration using B-spline functions; as an optimization problem that effectively corrects differences due to movements by minimizing the difference between current frame and a reference frame. Motion estimation accuracy is measured using the sum of squares differences. We use gradient-descend algorithm and multiresolution method to acquire the coefficients in the motion model. The accuracy of the proposed method is assessed using a synthesis sequence of cardiac cycles produced with the simulation software Field II. This algorithm can be applied for the clinical analysis of regional left ventricle then movement parameters and threshold values for the scoring of each section can be extracted. The algorithm represents significant difference between a part of the normal heart and unhealthy heart that shows potential of clinical applications of the proposed method.
Fluid-Structure Interaction in Biological Media / FSI
Saeed Nahidi; Alireza Hossein-Nezhad; Nasser Fatouraee; Zahra Heidari
Volume 6, Issue 1 , June 2012, , Pages 71-79
Abstract
Hemodynamic parameters are always affected by stenosis severity of arterial and these parameters in their turn have influence on the development of atherosclerosis. In this paper, By considering three different stenosis severity, the effects of wall porosity assumption on the hemodynamic parameters of ...
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Hemodynamic parameters are always affected by stenosis severity of arterial and these parameters in their turn have influence on the development of atherosclerosis. In this paper, By considering three different stenosis severity, the effects of wall porosity assumption on the hemodynamic parameters of a stenosed artery with a two-layer flexible wall (intima-media, adventitia), in which inner layer (intima-media) assumed porous, is numerically investigated, using Porous Fluid Structure Interaction (PFSI) model. Blood is assumed as an incompressible non-Newtonian fluid with pulsatile flow condition. In this investigation, the results show that the permeability assumption has much influenced on the hemodynamic characteristics so that the comparison of the results using PFSI with those of a non-porous model show 6% decrease in shear stress, 30% increase in displacement and more than 72% increase in effective stress in the porous layer.
Fluid-Structure Interaction in Biological Media / FSI
Alireza Hashemi Fard; Nasser Fatouraee
Volume 5, Issue 1 , June 2011, , Pages 1-12
Abstract
The heart muscle is supplied via the coronary arteries. The coronary arteries are deformed in each cardiac cycle by the contraction of the myocardium. The aim of this work was to investigate the effects of physiologically idealized cardiac-induced motion on flow rate in human left coronary arteries. ...
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The heart muscle is supplied via the coronary arteries. The coronary arteries are deformed in each cardiac cycle by the contraction of the myocardium. The aim of this work was to investigate the effects of physiologically idealized cardiac-induced motion on flow rate in human left coronary arteries. The blood flow rate were numerically simulated in an elastic modeled left anterior descending coronary artery (LAD) having a uniform circular cross section. Blood was considered to be a non-Newtonian fluid and Arterial motion was specified based on monoplane physiologically idealized bending. Simulations were carried out with dynamic pressure difference conditions between inlet and outlet in both fixed and moving LAD models, to evaluate the relative importance of LAD motion, flow rate, and the interaction between motion and time-averaged flow rate. LAD motion was caused variations in time-averaged flow rate in the moving LAD models as compare as the fixed models. There was significant variability in the magnitude of this motion-induced flow variation. However, the magnification of time-averaged flow rate is depending to specification of the cardiac motion. Furthermore, the effects of pressure pulsatility dominated LAD motion induced effects; specifically, there were local flow variation and secondary flow in the simulations conducted in moving LAD models.
Cardiovascular Biomechanics
Mehdi Molaei; Mohammad Saeid Saeidi; Bahar Firoozabadi
Volume 5, Issue 4 , June 2011, , Pages 279-288
Abstract
Study of Physiological Parameters of the Cardiovascular System by One Dimensional and Numerical Simulation. Owning to important role of the cardiovascular system in the human body and increase of cardiovascular diseases from day to day, in this study, we try to simulate a system of arteries by using ...
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Study of Physiological Parameters of the Cardiovascular System by One Dimensional and Numerical Simulation. Owning to important role of the cardiovascular system in the human body and increase of cardiovascular diseases from day to day, in this study, we try to simulate a system of arteries by using one dimensional numerical modeling. For the first time in the one dimensional simulation, we use the finite volume method for discretization of Navier-Stocks equations coupled with the state equation. In order to develop the outflow boundary condition, we use a kind of lumped model called arteriole structure tree. Results of this study are verified by results of other one dimensional modeling such as the characteristic method and are showed that finite volume method is able to demonstrate characteristic of blood flow in arteries. Normal pressure and flow profiles in main systemic arteries are determined, and it is founded that the pressure profile becomes steeper with distance from the heart, which is in agreement with physiological patterns. Furthermore, we can show that when elasticity of arteries is increased in arterioscleroses disease, systolic pressure increases, yet diastolic pressure decreases. Finally, according to available results, it is clear that the finite volume method is useful to simulate numerically and one dimensionally the cardiovascular system.
Cardiovascular Biomechanics
Mohammad Shafigh; Nasser Fatouraee; Amir Saeed Seddighi
Volume 5, Issue 4 , June 2011, , Pages 297-304
Abstract
Understanding of mechanical properties of healthy brain arteries is a key element in the development of clinical diagnosis and prevention.For this reason we make biaxial measurements to have appropriate parameters for the underlying material models. To acquire these properties, eight samples were obtained ...
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Understanding of mechanical properties of healthy brain arteries is a key element in the development of clinical diagnosis and prevention.For this reason we make biaxial measurements to have appropriate parameters for the underlying material models. To acquire these properties, eight samples were obtained from middle cerebral arteries of human cadavers, whose death were not due to injuries or diseases of cerebral vessels, and tested within twelve hours after resection. The changes of force and deformation until the vessel rupture were recorded. Thereafter, the stress-strain curves were plotted and fitted with a hyperelastic five-parameter Fung model parameters, according to the best fit, were determined. It was found that the arteries were remarkably stiffer in circumferential than in axial direction. It was also found that the use of multi-parameter hyperelastic constitutive models is applicable for mathematical description of behavior of cerebral vessel tissue. The reported material properties can be a proper reference for numerical simulation of cerebral arteries of healthy or diseased intracranial arteries.
Cardiovascular Biomechanics
Vahid Abouie; Farzad Towhidkhah; Vahid Reza Nafisi; Hani Sharifian
Volume 5, Issue 4 , June 2011, , Pages 305-311
Abstract
Today, Dialysis hypotension during hemodialysis process is the most common problems for about 20 to 30 percent of dialysis patients. In order to avoid this hypotension, blood pressure should be measured during dialysis process continuously and noninvasively But it is practically impossible and few devices ...
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Today, Dialysis hypotension during hemodialysis process is the most common problems for about 20 to 30 percent of dialysis patients. In order to avoid this hypotension, blood pressure should be measured during dialysis process continuously and noninvasively But it is practically impossible and few devices for noninvasive and continuous blood pressure measurement are very expensive. Considering this subject, the parameters related to blood pressure should be used to reach this goal. The blood concentrations and heart rate changes are associated with blood pressure in dialysis patients, so in this study, we determined a model by these two parameters in order to predict the blood pressure of hemodialysis patients. After measuring blood concentration, Heart rate and blood pressure from 14 dialysis patients, using neural network model, we determined a new model that can predict blood pressure in dialysis patient by using blood concentration and heart rate data with 3.8 percent error between the real pressure and the pressure that predicted by the model.
Fluid-Structure Interaction in Biological Media / FSI
Borhan Alhoseini Hamedani; Mehdi Navidbakhsh; Hosein Ahmaditafti
Volume 5, Issue 1 , June 2011, , Pages 45-56
Abstract
In this paper, study of mechanical properties of human blood vessels is considered, especially those of related to the Coronary Artery Bypass Graft (CABG). Unfortunately more than 30% of saphenous grafts are re-occluded within 10 years while mammary artery shows better results. In this study elastomechanical ...
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In this paper, study of mechanical properties of human blood vessels is considered, especially those of related to the Coronary Artery Bypass Graft (CABG). Unfortunately more than 30% of saphenous grafts are re-occluded within 10 years while mammary artery shows better results. In this study elastomechanical properties of human saphenous vein, which is common in CABG, is studied. Stress-stretch behavior of these samples after a cyclic loading was obtained and large deformation formulation was used to obtain real stress and stretch ratio of these vessels. Then a fourth order polynomial was used to show nonlinear behavior of these results. Results show that blood vessel stiffness in longitudinal direction is two times greater than circumferential direction, while it is more than 74% stretchable in the circumferential direction. So modulus of elasticity in longitudinal direction is greater than circumferential direction. If we continue stretching until final rupture after maximum strength, longitudinal samples will be broken down faster than circumferential samples because of collagen fibers orientation.
Cardiovascular Biomechanics
Hamed Khalesi; Hanie Niroomand Oscuii; Farzan Ghalichi
Volume 5, Issue 2 , June 2011, , Pages 143-149
Abstract
Prediction of the relationship between different types of mechanical loading and the failure of the intervertebral disc is so important to identify the risk factors which are difficult to study in vivo and in vitro. On the basis of finite element methods some of these issues may be overcome enabling ...
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Prediction of the relationship between different types of mechanical loading and the failure of the intervertebral disc is so important to identify the risk factors which are difficult to study in vivo and in vitro. On the basis of finite element methods some of these issues may be overcome enabling more detailed assessment of the biomechanical behavior of the intervertebral disc. The objective of this paper is to develop a nonlinear axisymmetric poroelastic finite element model of lumbar motion segment and show its capability for studying the time-dependent response of disc. After comparison of the response of different models in quasi-static analysis, the poroelastic model of intervertebral disc is presented and the results of short-term, long-term creep tests and cyclic loading were investigated. The results of the poroelastic model are in agreement with experimental ones reported in the literature. Hence, this model can be used to study how different dynamic loading regimes are important as risk factors for initiation of intervertebral disc degeneration.
Fluid-Structure Interaction in Biological Media / FSI
Hamed Khalesi; Hanie Niroomand Oscuii; Farzan Ghalichi
Volume 5, Issue 1 , June 2011, , Pages 67-78
Abstract
Biomechanics believe that, the arteries are remodeled under the influence of hemodynamic and mechanical factors. Biomechanical factors such as Opening Angle and the Tethering could have important effects on this phenomenon. The effects of various Opening Angle and Tethering during thoracic aorta aging ...
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Biomechanics believe that, the arteries are remodeled under the influence of hemodynamic and mechanical factors. Biomechanical factors such as Opening Angle and the Tethering could have important effects on this phenomenon. The effects of various Opening Angle and Tethering during thoracic aorta aging on arterial wall stress have been studied. ADINA software is used for numerical simulation.In this study, for the first time, numerical methods of Fluid-Structure Interaction have been used to study and simulate effects of Opening Angle and the Tethering in elastic artery remodeling due to age. Large deformation theory has been used for modeling changes of arterial radius; furthermore, behavior of Newtonian fluid has been used for blood. Pulsatile pressure and physiological Pulsatile flow waveforms have been applied to simulate transient behavior of arterial system. The results show that opening angle has further effect on circumferential stress so smooth distribution of circumferential stress on the wall accrued. Also, increasing Opening Angle with age reverses the circumferential stress distribution slop across the arterial wall. Tethering has further effect on axial stress. Decreasing Tethering in remodeling process over age leads to increase stress levels in the aged artery. Also, arterial wall shear stress in remodeled artery shows significant reduction in maximum, mean and amplitude values that caused reduction of pathological effects of endothelial cells.
Cardiovascular Biomechanics
Ahmad Ramezani Saadatabadi; Majid Ahmadlouy Darab; Farzan Ghalichi; Ataollah Kamyabi
Volume 4, Issue 1 , June 2010, , Pages 65-72
Abstract
This study aimed to simulate three dimensional pulsatile Newtonian blood flow in End-to-Side anastomosis of Aorta-coronary bypass using ascending aorta velocity flow wave as graft inlet and left anterior descending coronary artery (LAD) velocity flow wave as coronary inlet for 50% symmetric stenosis. ...
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This study aimed to simulate three dimensional pulsatile Newtonian blood flow in End-to-Side anastomosis of Aorta-coronary bypass using ascending aorta velocity flow wave as graft inlet and left anterior descending coronary artery (LAD) velocity flow wave as coronary inlet for 50% symmetric stenosis. We have supposed that LAD walls were rigid and had no spatial mobility due to heart beats. In order to investigate the graft angles effects on blood flow, especially on the wall shear stress magnitudes, 20, 30 and 40 degrees graft angles were used. Using ascending aorta and LAD pulses simultaneously as boundary conditions for the first time is one of the important features of this study because already these boundary conditions have not been used simultaneously. We considered prograde flow effects. Appearance of recirculation flows in various degrees of grafting angles, existence of secondary flows and increased in their effects specially in pulses deceleration phase, existence of double core helical flows and increase in their intensify specially at the systole peak and the rise in the spatial wall shear stress gradient by increasing in the graft angle are some of important results of this study. Finally, according to our assumptions we suggest 20 to 30 degrees as desired angles for grafting.
Fluid-Structure Interaction in Biological Media / FSI
Hanie Niroomand Oscuii; Farzan Ghalichi; Mohammad Tafazzoli Shadpour
Volume 2, Issue 1 , June 2008, , Pages 1-8
Abstract
In this paper, we studied the effect of mechanical loading on remodeling process with aging in muscular arteries. Based on the gathered experimental data, the brachial artery was selected for simulation. In this simulation, pulsatile pressure and flow waves were considered as boundary conditions to study ...
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In this paper, we studied the effect of mechanical loading on remodeling process with aging in muscular arteries. Based on the gathered experimental data, the brachial artery was selected for simulation. In this simulation, pulsatile pressure and flow waves were considered as boundary conditions to study the effect of circumferential stress and wall shear stress on the remodeling process. FSI based transient numerical simulation was used to solve the fluid and solid equations. The results of three remodeling schemes showed that inward eutrophic scheme is an optimum algorithm for brachia! Artery remodeling with aging. Such remodeling scheme causes the most optimized outcome to keep circumferential stress with minimal alteration.
Fluid-Structure Interaction in Biological Media / FSI
Afsane Mojra; Mohammad Tafazzoli Shadpour; Ehsan Yakhshi Tafti
Volume 2, Issue 1 , June 2008, , Pages 9-20
Abstract
Arterial stenosis and the consequent cardiovascular diseases such as atherosclerosis remain the major cause of mortality in the world. In this study, blood flow was analyzed in a three-dimensional model of stenosed carotid artery with asymmetric stenosis utilizing fluid-structure interaction method. ...
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Arterial stenosis and the consequent cardiovascular diseases such as atherosclerosis remain the major cause of mortality in the world. In this study, blood flow was analyzed in a three-dimensional model of stenosed carotid artery with asymmetric stenosis utilizing fluid-structure interaction method. The modeling was performed by ANSYS finite element software. To overcome the software inconsistency in FSI mode, a new code was designed in ANSYS multi-physics environment for coupling of solid and fluid domains via incremental boundary iteration method. The results indicated a considerable variation of local blood pressure, velocity and shear stress in stenosed artery, high pressure drop along stenosis, compressive stress and larger flow separation zone in the post-stenotic region as the result of increased eccentricity of stenosis. The results might be applied in evaluation of plaque severity, progression of disease, plaque growth and vulnerable regions of plaque to fracture.
Fluid-Structure Interaction in Biological Media / FSI
Bahman Vahidi; Nasser Fatouraee
Volume 2, Issue 4 , June 2008, , Pages 285-296
Abstract
Arterial embolism is one of the major killers of the people who have heart diseases. In cerebral arteries, the danger of embolism is that the ruptured particles are carried into the brain, provoking neurological symptoms or a stroke. In this research, for the first time, we have presented a numerical ...
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Arterial embolism is one of the major killers of the people who have heart diseases. In cerebral arteries, the danger of embolism is that the ruptured particles are carried into the brain, provoking neurological symptoms or a stroke. In this research, for the first time, we have presented a numerical model to study the complete blockage of the human common carotid artery resulted from the physical motion of a blood clot bulk with spherical geometry in it. In the numerical model, a transient flow was assumed in an axisymmetric finite length tube. The incompressible Navier-Stokes equations were used as the governing equations for the fluid and a linear elastic model was utilized for the blood clot bulk. In order to model the contact conditions between the blood clot and arterial wall, an axisymmetric rigid contact model was used. The arbitrary Lagrangian-Eulerian formulation (ALE) was applied to analyze the solid large displacements inside fluid flow. The results indicated that during contact between stenosis and the clot, separation and reattachment regions were occurred on the stenosis extensively which are susceptible to thrombosis onset and growth. By abruption of the clot from the arterial wall during its passage through the stenosis, an extensive recirculation zone occurred downstream of the stenosis and beneath the moving clot bulk. Analysis of the clot motion and deformation have showed that when the clot passed the stenosis completely, the areas near the clot peak had a large tendency to expand which indicated the propensity of these areas to disperse.
Cardiovascular Biomechanics
Mansour Alizadeh; Iman Mohebbi Nejad
Volume 2, Issue 4 , June 2008, , Pages 317-324
Abstract
Mechanical characteristic of arteries is very important for stent producing and cardiovascular implants. In this study mechanical behavior of a piece of left anterior descending coronary artery with specified dimension and separated layers which was prepared by holtzapfel and tested under tensile test ...
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Mechanical characteristic of arteries is very important for stent producing and cardiovascular implants. In this study mechanical behavior of a piece of left anterior descending coronary artery with specified dimension and separated layers which was prepared by holtzapfel and tested under tensile test bas been considered. Ogden hyperelastic model has been implemented for the experimental data and related parameters were obtained. These parameters have been optimized. The obtained results showed that by using the same experimental data the Ogden model can be fitted well with holtzapfel model and the errors fall within acceptable range.
Cardiovascular Biomechanics
Nasser Fatouraee; Mojtaba Gholipour Samarghaveh
Volume 1, Issue 1 , June 2007, , Pages 9-17
Abstract
Blood is one of the vital fluids of the human body. Measurement of its viscosity and other properties is very important in detecting and understanding different cardiovascular diseases. In this study, the blood flow in a concentric cylinder viscometer was simulated numerically. The blood flow patterns ...
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Blood is one of the vital fluids of the human body. Measurement of its viscosity and other properties is very important in detecting and understanding different cardiovascular diseases. In this study, the blood flow in a concentric cylinder viscometer was simulated numerically. The blood flow patterns were analyzed by applying different rotational speed of inner cylinder. Creation of a Couette flow, end effects and suitable rotational speed limit were analyzed. The amount of the torque applied to the inner cylinder which prevents the generation of the Taylor vortices was also predicted. From the obtained results, one can conclude that these vortices were not as important as the end effects were. In order to keep the blood sample temperature within a constant and acceptable range a thermal bath was used. Heat removal rate with different inflow rates of coolant was also predicted numerically.
Cardiovascular Biomechanics
Mehdi Maerefat; Asghar Khoushkar Shalmani; Manije Mokhtari Dizaji
Volume 1, Issue 2 , June 2007, , Pages 95-104
Abstract
Modeling of blood flow and arterial wall in large arteries such as carotid artery, using ultrasonic measurements, allows non-invasive evaluation of clinically interesting homodynamic variables. In this study, a nonlinear mathematical model for the pulsatile arterial flow is proposed using the approximation ...
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Modeling of blood flow and arterial wall in large arteries such as carotid artery, using ultrasonic measurements, allows non-invasive evaluation of clinically interesting homodynamic variables. In this study, a nonlinear mathematical model for the pulsatile arterial flow is proposed using the approximation of “local flow” theory. The blood velocity profile, the pressure gradient and the elastic modulus can be calculated using the model by measuring instantaneous radius and center-line blood velocity. An original mathematical model of pressure gradient in a tapered and elastic tube, using center-line blood velocity, is presented. A Newtonian incompressible Navier-Stokes solver coupled with elastic or visco-elastic arterial wall model is developed to solve the equations of model. The results of modeling and simulation indicate that the approach can estimate the elastic modulus of arterial wall from ultrasonic data. There is a good agreement between the computed arterial wall elasticity and the measured one. The method presented is relatively simple to implement clinically and can be taken as a new diagnostic tool for detecting local vascular change.
Biomedical Image Processing / Medical Image Processing
Jamal Esmaeilpour; Sattar Mirzakouchaki; Jalil Seyfali Harsini; Abdorrahim Kadkhoda Mohammadi
Volume 1, Issue 3 , June 2007, , Pages 167-176
Abstract
In this paper, the role of Vector Quantizer Neural Network in classification of six types of ECG signals has been investigated using the features that extracted from Daubechies6 Wavelet transformation. The six types of signals are: normal beat, left bundle branch block beat, right bundle branch block ...
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In this paper, the role of Vector Quantizer Neural Network in classification of six types of ECG signals has been investigated using the features that extracted from Daubechies6 Wavelet transformation. The six types of signals are: normal beat, left bundle branch block beat, right bundle branch block beat, premature ventricular contraction paced beat and fusion of paced and normal beats. The required data were obtained from the MIT/BIH arrhythmia databases. By using the annotation files of the databases, the patterns of these six types of ECG signals were separated. Then, for better feature extraction, filtering and scaling on the patterns were applied. We used the energies of the last five detailed signals obtained from the exerting the Wavelet transformation in six levels, as the pattern features for Vector Quantizer Network training and testing. From each class, five hundred patterns were used for network training and one hundred patterns for testing. The results indicated %93.1 accuracy for six classes and above %94.3 for lesser than six classes. Then the rate of similarity and dissimilarity of the classes were considered. Finally, the results of this method were compared with some other methods in terms of accuracy.
