The distribution of Low density lipoprotein (LDL) within the arterial wall is helpful in understa... more The distribution of Low density lipoprotein (LDL) within the arterial wall is helpful in understanding the onset and development of atherosclerosis. The objective of the study is to study the transport and LDL distribution within patient-specific arterial wall using computational analysis under normal and hypertensive conditions. Patient specific model of the thoracic aorta is computationally examined. The arterial wall is treated macroscopically as homogeneous (one layered) porous media of variable thickness. The interfacial lumen-arterial wall (endothelium) coupling is achieved by the Kedem-Katchalsky equation. High values of LDL are located at areas where WSS values range from 0.4Â N/m(2) to 1.5Â N/m(2) for normal conditions. In this case the Pearson correlation coefficient r between LDL values and WSS is equal to -0.655 denoting a strong negative linear correlation. In the case that hypertension takes place, high LDL values are located at areas where WSS values range from 0.59Â N/m...
The three-dimensional wall pressure gradient (WPG) of the normal human left coronary artery (LCA)... more The three-dimensional wall pressure gradient (WPG) of the normal human left coronary artery (LCA) tree is quantitatively analysed. A model LCA tree, based on averaged human data set extracted from angiographies was adopted for finite-element analysis. The LCA tree includes the left main coronary artery (LMCA), the left anterior descending (LAD), the left circumflex artery (LCxA) and their major branches. The WPG is calculated using 44,452 nodes throughout the tree extension. The governing flow equations were solved using a validated numerical code. WPG as well as wall shear stress gradient (WSSG) were calculated at all available bifurcation regions. In proximal LCA tree regions where atherosclerosis frequently occurs, low WPG appears. At distal segments, WPG increases substantially due to increased velocity resulted from increased vessel tapering. Low WPG occurs at bifurcations in regions opposite the apexes, which are anatomic sites predisposed for atherosclerotic development. Endothelial cells respond to the combined effects of locally low WPG and low WSSG and provide a mechanism promoting atherosclerosis. This computational work determines probably for the first time the topography of the WPG in the normal human LCA tree. Spatial WPG differentiation indicates that locally low values of this physical parameter probably correlate to atherosclerosis localization.
On the basis of pathological, angiographical, intravascular ultrasound and computed tomography da... more On the basis of pathological, angiographical, intravascular ultrasound and computed tomography data coronary atherosclerosis appears to be more prevalent in the left coronary arterial system compared to the right. However, the pathophysiological mechanisms implicated in this discrepancy largely remain uncertain. The hemodynamic or anatomical differences between the right and left coronary artery might play a key role. Physiologically, the right coronary flow is more uniform during the cardiac cycle compared to the left, which experiences a remarkable systolic decline accompanied by a significant diastolic increment. Thus, the oscillatory shear stress, that constitutes a proved atherogenic factor, is more intense in regions with disturbed flow in the left coronary system. Likewise, the wall stress is more oscillatory during the cardiac cycle in the left coronary artery. On top of that, several differences regarding the anatomical configuration (3D geometry, branching) and the phasic motion between the right and the left arterial system appear to play a critical role in the modulation of the local atherogenic environment. Therefore, it could be assumed that the flow characteristics along with the geometrical and phasic motion patterns generate an intense oscillation of the imposed to the arterial wall stresses, especially in the left coronary artery. Over the long-term, these augmented oscillatory stresses, in combination with the effect of systemic risk factors, might modulate a more atherogenic environment in the atherosclerosis-prone regions of the left coronary system.
BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation... more BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation between blood flow physical parameters and the wall thickening in typical human coronary arteries. Digitized images of seven transparent arterial segments prepared post-mortem were adopted from a previous study in order to extract the geometry for numerical analysis. Using the exterior outline, reconstructed forms of the vessel geometries were used for subsequent computational fluid dynamic analysis. Data was input to a pre-processing code for unstructured mesh generation. The flow was assumed to be two-dimensional, steady, laminar with parabolic inlet velocity profile. The vessel walls were assumed to be smooth, inelastic and impermeable. Non-Newtonian power law was applied to model blood rheology. The arterial wall thickening was measured and correlated to the wall shear stress, static pressure, molecular viscosity, and near wall blood flow velocity. Wall shear stress, static pressure and near wall velocity magnitude exhibit negative correlation to wall thickening, while molecular viscosity exhibits positive correlation to wall thickening. There is a strong correlation between the development of vessel wall thickening and the blood flow physical parameters. Amongst these parameters the role of local low wall static pressure is predominant.
Wall shear stress gradient (WSSG) in vitro has shown its importance in atherogenesis, probably as... more Wall shear stress gradient (WSSG) in vitro has shown its importance in atherogenesis, probably as a local modulator of endothelial gene expression. The purpose of this study is to numerically analyse the WSSG distribution over the normal human left coronary artery (LCA) tree. A three-dimensional computer generated model of the LCA tree, based on an averaged human data set extracted from angiographies, was adopted for finite-element analysis. The LCA tree includes the left main coronary artery (LMCA), the left anterior descending (LAD), the left circumflex artery (LCxA) and their major branches. In proximal LCA tree regions where at bifurcations in regions opposite the flow atherosclerosis frequently occurs, low WSSG appears. At distal segments, the WSSG increases substantially due to increased velocity resulting from increased vessel tapering. Low WSSG occurs dividers, which are anatomic sites predisposed for atherosclerotic development. This computational work determines, probably for the first time, the topography of the WSSG in the normal human LCA tree. Spatial WSSG differentiation indicates that low values of this parameter probably correlate to atherosclerosis localization. However, further studies are needed to clarify the role of WSSG in atherogenesis.
The distribution of Low density lipoprotein (LDL) within the arterial wall is helpful in understa... more The distribution of Low density lipoprotein (LDL) within the arterial wall is helpful in understanding the onset and development of atherosclerosis. The objective of the study is to study the transport and LDL distribution within patient-specific arterial wall using computational analysis under normal and hypertensive conditions. Patient specific model of the thoracic aorta is computationally examined. The arterial wall is treated macroscopically as homogeneous (one layered) porous media of variable thickness. The interfacial lumen-arterial wall (endothelium) coupling is achieved by the Kedem-Katchalsky equation. High values of LDL are located at areas where WSS values range from 0.4Â N/m(2) to 1.5Â N/m(2) for normal conditions. In this case the Pearson correlation coefficient r between LDL values and WSS is equal to -0.655 denoting a strong negative linear correlation. In the case that hypertension takes place, high LDL values are located at areas where WSS values range from 0.59Â N/m...
The three-dimensional wall pressure gradient (WPG) of the normal human left coronary artery (LCA)... more The three-dimensional wall pressure gradient (WPG) of the normal human left coronary artery (LCA) tree is quantitatively analysed. A model LCA tree, based on averaged human data set extracted from angiographies was adopted for finite-element analysis. The LCA tree includes the left main coronary artery (LMCA), the left anterior descending (LAD), the left circumflex artery (LCxA) and their major branches. The WPG is calculated using 44,452 nodes throughout the tree extension. The governing flow equations were solved using a validated numerical code. WPG as well as wall shear stress gradient (WSSG) were calculated at all available bifurcation regions. In proximal LCA tree regions where atherosclerosis frequently occurs, low WPG appears. At distal segments, WPG increases substantially due to increased velocity resulted from increased vessel tapering. Low WPG occurs at bifurcations in regions opposite the apexes, which are anatomic sites predisposed for atherosclerotic development. Endothelial cells respond to the combined effects of locally low WPG and low WSSG and provide a mechanism promoting atherosclerosis. This computational work determines probably for the first time the topography of the WPG in the normal human LCA tree. Spatial WPG differentiation indicates that locally low values of this physical parameter probably correlate to atherosclerosis localization.
On the basis of pathological, angiographical, intravascular ultrasound and computed tomography da... more On the basis of pathological, angiographical, intravascular ultrasound and computed tomography data coronary atherosclerosis appears to be more prevalent in the left coronary arterial system compared to the right. However, the pathophysiological mechanisms implicated in this discrepancy largely remain uncertain. The hemodynamic or anatomical differences between the right and left coronary artery might play a key role. Physiologically, the right coronary flow is more uniform during the cardiac cycle compared to the left, which experiences a remarkable systolic decline accompanied by a significant diastolic increment. Thus, the oscillatory shear stress, that constitutes a proved atherogenic factor, is more intense in regions with disturbed flow in the left coronary system. Likewise, the wall stress is more oscillatory during the cardiac cycle in the left coronary artery. On top of that, several differences regarding the anatomical configuration (3D geometry, branching) and the phasic motion between the right and the left arterial system appear to play a critical role in the modulation of the local atherogenic environment. Therefore, it could be assumed that the flow characteristics along with the geometrical and phasic motion patterns generate an intense oscillation of the imposed to the arterial wall stresses, especially in the left coronary artery. Over the long-term, these augmented oscillatory stresses, in combination with the effect of systemic risk factors, might modulate a more atherogenic environment in the atherosclerosis-prone regions of the left coronary system.
BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation... more BACKGROUND/STUDY OBJECTIVES: The purpose of our study was to investigate the possible correlation between blood flow physical parameters and the wall thickening in typical human coronary arteries. Digitized images of seven transparent arterial segments prepared post-mortem were adopted from a previous study in order to extract the geometry for numerical analysis. Using the exterior outline, reconstructed forms of the vessel geometries were used for subsequent computational fluid dynamic analysis. Data was input to a pre-processing code for unstructured mesh generation. The flow was assumed to be two-dimensional, steady, laminar with parabolic inlet velocity profile. The vessel walls were assumed to be smooth, inelastic and impermeable. Non-Newtonian power law was applied to model blood rheology. The arterial wall thickening was measured and correlated to the wall shear stress, static pressure, molecular viscosity, and near wall blood flow velocity. Wall shear stress, static pressure and near wall velocity magnitude exhibit negative correlation to wall thickening, while molecular viscosity exhibits positive correlation to wall thickening. There is a strong correlation between the development of vessel wall thickening and the blood flow physical parameters. Amongst these parameters the role of local low wall static pressure is predominant.
Wall shear stress gradient (WSSG) in vitro has shown its importance in atherogenesis, probably as... more Wall shear stress gradient (WSSG) in vitro has shown its importance in atherogenesis, probably as a local modulator of endothelial gene expression. The purpose of this study is to numerically analyse the WSSG distribution over the normal human left coronary artery (LCA) tree. A three-dimensional computer generated model of the LCA tree, based on an averaged human data set extracted from angiographies, was adopted for finite-element analysis. The LCA tree includes the left main coronary artery (LMCA), the left anterior descending (LAD), the left circumflex artery (LCxA) and their major branches. In proximal LCA tree regions where at bifurcations in regions opposite the flow atherosclerosis frequently occurs, low WSSG appears. At distal segments, the WSSG increases substantially due to increased velocity resulting from increased vessel tapering. Low WSSG occurs dividers, which are anatomic sites predisposed for atherosclerotic development. This computational work determines, probably for the first time, the topography of the WSSG in the normal human LCA tree. Spatial WSSG differentiation indicates that low values of this parameter probably correlate to atherosclerosis localization. However, further studies are needed to clarify the role of WSSG in atherogenesis.
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Papers by George Giannoglou