Sharif Digital Repository

In this paper, it is shown that the main source of mechanical energy of cardiovascular (CV) system i.e., rhythmic heart contraction is transformed to the oscillations of the CV walls and blood flow, and finally CV acoustical waves. These waves propagate through both blood flow (hemodynamical pathways) and tissues (viscoelastical pathways) toward the skin. Nonetheless, the CV walls could be assumed as the source of acoustical waves, since they act as the interface between blood flows and other tissues including skin. After obtaining the approximate accelerations of CV walls from pressure-flow (PF) models, we also needed to model the viscoelastical pathways until the skin. Some improvements on... 

A one dimensional model of the pulmonary arterial network along with systemic circulation was introduced to quantify the human pulmonary artery hemodynamics. A lumped parameter model of the right ventricle was used as the inlet boundary condition. A time varying elastance related the volume and pressure of the right ventricle was imposed in the model. By using a four element Windkessel model, blood flow rate throughout the right ventricle was in hand. An asymmetric structured tree was chosen as the outlet boundary conditions. Simulation was based on solving one-dimensional equations of conservation of mass and momentum by using finite volume method. Blood flow rate, pressure and velocity... 

In an effort to identify a useful noninvasive screening tool for cardiovascular diseases (CVD) screening, photoplethysmograph (PPG) signals were acquired and analyzed. These PPG signals were recorded during reactive hyperemia experiments consisting of a 4-minute blood flow blockage of the right arm (RA) brachial artery (BA) using a blood pressure cuff inflator. This procedure is usually done for the assessment of endothelial dysfunction which is a risk factor for developing CVD. In this study, signals of the infrared (IR) and red (R) LED's of the PPG sensor were analyzed. These signals were preprocessed, normalized and slow varying component of the signal (DC values) and the pulsatile... 

The problem of removing white zero-mean Gaussian noise from an image is an interesting inverse problem to be investigated in this paper through sparse and redundant representations. However, finding the sparsest possible solution in the noise scenario was of great debate among the researchers. In this paper we make use of new approach to solve this problem and show that it is comparable with the state-of-art denoising approaches. © Springer-Verlag Berlin Heidelberg 2009  

In this paper a new method for face virtual pose generation is presented. The proposed method uses subspace image representation. The general problem of blurring is addressed by introducing a multi resolution time-frequency analysis to subspace image representation. The training gallery contains face images in two different poses. Undecimated Wavelet Transform is applied on all training face images in first pose and the corresponding images in the second pose to produce image subbands. Then, a new subspace is constructed for each subband in both poses. The mapping between two corresponding subbands of two poses is learnt using linear regression. The resulted mapping matrix is used to... 

In some diseases there is a focal pattern of velocity in regions of bifurcation, and thus the dynamics of bifurcation has been investigated in this work. A computational model of blood flow through branching geometries has been used to investigate the influence of bifurcation on blood flow distribution. The flow analysis applies the time-dependent, three-dimensional, incompressible Navier-Stokes equations for Newtonian fluids. The governing equations of mass and momentum conservation were solved to calculate the pressure and velocity fields. Movement of blood flow from an arteriole to a venule via a capillary has been simulated using the volume of fluid (VOF) method. The proposed simulation... 

Atherosclerosis as a common cardiovascular disease is a result of both adverse hemodynamics conditions and monocyte deposition within coronary arteries. It is known that the adhesion of monocytes on the arterial wall and their interaction with the vascular surface are one of the main parameters in the initiation and progression of atherosclerosis. In this work, hemodynamic parameters and monocyte deposition have been investigated in a 3D computational model of the Left Anterior Descending coronary artery (LAD) and its first diagonal branch (D1) under the heart motion. A one-way Lagrangian approach is performed to trace the monocyte particles under different blood flow regimes and heart motion... 

Ageing is one of the main contributing factors towards increasing arterial stiffness, leading to changes in peripheral pulses propagation. Therefore the characteristics of the photoplethysmogram (PPG) pulse, especially the rising edge and peak position, are greatly affected. In this study, the PPG pulse rising edge and corresponding peak position have been investigated non-invasively in human subjects as a function of age. Fifteen healthy subjects were selected and grouped in five age intervals, from 20 to 59 years, based on their comparable systolic-diastolic blood pressure and PPG amplitude. As expected, the peripheral pulse shows a steep rise and early peak in younger subjects. With age,... 

This study considers blood flow in total cavopulmonary connection (TCPC) morphology created in Fontan surgical procedure in patients with a single ventricle heart disease. Ordinary process of TCPC operation reduces pulmonary blood flow pulsatility since the right ventricle being bypassed. This reduction may limit the long term outcome of Fontan circulation. There is an idea of increasing pulmonary flow pulsations by keeping Main Pulmonary Artery (MPA) partially open while it was closed in ordinary TCPC operation. The purpose of the present study is to verify the effects of Antegrade Flow (AF) coming through stenosed MPA on pulmonary flow pulsations. The 3D geometry is reconstructed from CT... 

The main goal of this study is to investigate the effects of plaque structure on its stress distribution. Rupture of plaque causes cerebrovascular diseases which lead to high mortality rates all over the world. Computers are powerful tools to understand the mechanism of plaque rupture. In this study, 3D fluid structure interaction simulation is constructed in ABAQUS 6.13 to clarify the relation between stress distribution of plaque and its structure. A model of common carotid artery with distributed stenosis was chosen for the simulation. To investigate the effects of plaque structure on stress distribution, thickness of fibrous cap and lipid core size were varied in the stenosis.... 

The Fontan surgery is performed on patients with a single ventricle heart defect to prevent the combination of highlyoxygenated and poorly-oxygenated blood. Blood flow in total cavopulmonary connection (TCPC) which culminates an ordinary Fontan operation is practically steady-state but this flow is not appropriate for respiratory systems. This article investigates an approach in Fontan surgery that has been recently proposed in order to make the pulmonary blood flow pulsating. Moreover, for investigating the compliance of vessels and its effects on blood flow in TCPC, we have used the FSI (Fluid Structure Interaction) method as well as rigid wall assumption for comparison purposes. Our TCPC... 

The brain is one of the vital organs in the body. The main cerebral distribution center of blood flow in the brain is the circle of Willis (CoW). In more than 50% of healthy brains and in more than 80% of dysfunctional ones, at least one artery of the circle of Willis is absent or underdeveloped. These variations reduce the collateral flow availability and increase the risk of stroke and transient ischemic attack in patients with atherosclerosis. Thus it is essential to simulate the circle of Willis and investigate the effects of stenosis. In this work the systemic arteries along with the circle of Willis are simulated using the finite volume method and one-dimensional equations of... 

Cardiovascular diseases are one of the major causes of death in the world; atherosclerosis being one aspect. Carotid bifurcation is one of the sites that are vulnerable to this disease. Wall Shear Stress (WSS) is known to be responsible for the process of atherogenesis. In this study, we have simulated the blood flow for Newtonian and non-Newtonian, steady and unsteady, flow conditions in three idealistic and five realistic geometries. A risk factor has been presented based on the results of wall shear stress and, then, a relation was found between geometrical features and the wall shear stress risk factor. Our main conclusions are: 1) The non-Newtonian behavior of blood elevates the value... 

The function and morphology of Endothelial Cells (ECs) play a key role in atherosclerosis. The mechanical stimuli of ECs, such as Wall Shear Stress (WSS) and arterial wall strain, greatly inuence the function and morphology of these cells. The present article deals with computations of these stimuli for a 3D model of a healthy coronary artery bifurcation. The focus of the study is to propose an accurate method for computations of WSS and strains. Two approaches are considered: Coupled simultaneous simulation of arterial wall and blood flow, called fluid-Structure Interaction (FSI) simulation, and decoupled, which simulates each domain (fluid and solid domain) separately. The study... 

Stress concentration in carotid stenosis has been proven to assist plaque morphology in disease diagnosis and vulnerability. This work focuses on numerical analysis of stress and strain distribution in the cross-section of internal carotid artery using a 2D structure-only method. The influence of four different idealized plaque geometries (circle, ellipse, oval and wedge) is investigated. Numerical simulations are implemented utilizing linear elastic model along with four hyperelastic constitutive laws named neo-Hookean, Ogden, Yeoh and Mooney-Rivlin. Each case is compared to the real geometry. Results show significant strength of oval and wedged geometries in predicting stress and strain... 

The objective of this paper is to apply computational fluid dynamic (CFD) as a complementary tool for clinical tests to not only predict the present and future status of left coronary artery stenosis but also to evaluate some clinical hypotheses. In order to assess the present status of the coronary artery stenosis severity, and thereby selecting the most appropriate type of treatment for each patient, fractional flow reserve (FFR), instantaneous wave free-ratio (iFR), and coronary flow reserve (CFR) are calculated. To examine FFR, iFR, and CFR results, the effect of geometric features of stenoses, including diameter reduction (%), lesion length (LL), and minimum lumen diameter (MLD), is...