zijing zeng - Academia.edu (original) (raw)
Papers by zijing zeng
An impeller for a pump disclosed herein. The impeller may comprise a hub having a fixed end and a... more An impeller for a pump disclosed herein. The impeller may comprise a hub having a fixed end and a free end. The impeller may also include a plurality of sheets, which are supported by the hub. Each sheet can have a fixed end which is coupled to the hub, and a free end. The impeller may have a stowed configuration and a deployed configuration, with the blades in the deployed configuration of the hub and extend away from the sheets being compressed in the stowed configuration to the hub.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2009
ASME 2011 Summer Bioengineering Conference, Parts A and B, 2011
An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by l... more An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by local enlargements of the arterial wall, typically into a saccular shape. Rupture of the aneurysm sac can result in devastating cerebral hemorrhage. Hemodynamic factors are believed to play an important role in initiation, development and rupture of IAs [1–3]. However, the coupling between hemodynamics and aneurysm pathophysiology is complex and remains poorly understood. Patient specific diagnostics regarding risk of rupture can be substantially advanced by improving our understanding of the in-vivo response of the aneurysm wall to intra-saccular hemodynamic stresses. A mechanism for fundamental studies of the impact of chronically altered WSS on the intact vascular wall is provided by animal models. However, cerebral aneurysms have not been shown to occur naturally in animals. Thus, a number of animal models have been created for studying aneurysm pathogenesis including those in mice, rats, rabbits, canines, swine and primates. To make meaningful use of these models, it is important to evaluate their relevance to human biomechanics and pathophysiology.Copyright © 2011 by ASME
Advances in Mathematical Fluid Mechanics, 2010
ABSTRACT
ASME 2008 Summer Bioengineering Conference, Parts A and B, 2008
ABSTRACT Hemodynamic factors are thought to play an important role in the initiation, growth, and... more ABSTRACT Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. In-vitro studies have demonstrated a correlation between the magnitude and distribution of wall shear stress (WSS) and biological response of both endothelial cells and smooth muscle cells [1–3]. In elastase induced saccular aneurysms, low WSS (below 0.5 Pa) was found to have a correlation with altered expression of biological markers [4]. Localized regions of rapid aneurysm growth in-vivo have been shown to be associated with regions where WSS is below a critical value of 0.1 Pa [5]. Further, aspect ratio (AR), the ratio of the maximum diameter of the aneurysm to the width of the aneurysm neck, has been correlated with elevated risk of rupture [6]. The purpose of the current study is to explore the possibility of creating elastase induced aneurysms in rabbits with a range of aspect ratios (ratio of aneurysm height/neck) and evaluate the existence of a correlation between aspect ratio and WSS distribution. Aneurysms with ARs from 0.98 to 2.8 were created at the origin of the right common carotid artery (n = 30). Qualitative differences in WSS distribution were found in the high AR aneurysms (HARA) (AR>1.6) and low AR aneurysms (LARA) (AR
Journal of Biomechanical Engineering, 2010
Computational fluid dynamics (CFD) studies provide a valuable tool for evaluating the role of hem... more Computational fluid dynamics (CFD) studies provide a valuable tool for evaluating the role of hemodynamics in vascular diseases such as cerebral aneurysms and atherosclerosis. However, such models necessarily only include isolated segments of the vasculature. In this work, we evaluate the influence of geometric approximations in vascular anatomy on hemodynamics in elastase induced saccular aneurysms in rabbits. One representative high aspect ratio (AR—height/neck width) aneurysm and one low AR aneurysm were created at the origin of the right common carotid artery in two New Zealand white rabbits. Three-dimensional (3D) reconstructions of the aneurysm and surrounding arteries were created using 3D rotational angiographic data. Five models with varying extents of neighboring vasculature were created for both the high and low AR cases. A reference model included the aneurysm sac, left common carotid artery (LCCA), aortic arch, and downstream trifurcation/quadrification. Three-dimension...
Journal of Biomechanics, 2011
Clinical studies suggest aneurysm aspect ratio (AR) is an important indicator of rupture likeliho... more Clinical studies suggest aneurysm aspect ratio (AR) is an important indicator of rupture likelihood. The importance of AR is hypothesized to arise from its influence on intra-aneurysmal hemodynamics. It has been conjectured that the flow in the domes of high AR sacs is slower than in low AR sacs and some aspect and leads to a cascade of enzymatic activities that weaken the aneurysm wall. However, the connection between AR, hemodynamics and wall weakening has never been proven. Animal models of saccular aneurysms provide a venue for evaluating this conjecture. The focus of this work was to evaluate whether a commonly used elastase induced aneurysm model in rabbits is suitable for a study of this kind from a hemodynamic perspective. In particular, to assess whether hemodynamic factors in low and high AR sacs are statistically different. To achieve this objective, saccular aneurysms were created in 51 rabbits and pulsatile computational fluid dynamics (CFD) studies were performed using rabbit specific inflows. Distinct hemodynamics were found in the low AR (AR<1.8, n=25), and high AR (AR>2.2, n=18) models. A single, stable recirculation zone was present in all low AR aneurysms, whereas a
An intracranial aneurysm (IA) is a pathological state of a cerebral artery in which the elastin a... more An intracranial aneurysm (IA) is a pathological state of a cerebral artery in which the elastin and smooth muscle cells found in the healthy arterial wall are absent. Rupture of an IA is a major cause of subarachnoid hemorrhage. Hemodynamics is believed to play an important role in initiation, development and rupture of the IA. However, the coupling between hemodynamics and aneurysm pathophysiology remains poorly understood. The initiation of cerebral aneurysms is believed to be caused by a breakdown in the homeostatic mechanism of healthy arteries, leading to destructive wall remodeling and damage. Due to its complex nature, there is a need for both controlled in vitro and in vivo studies of IA initiation. We have designed an in vitro flow chamber that can be used to reproduce specific magnitudes of wall shear stress and wall shear stress gradients found at the apices of arterial bifurcations, where aneurysms tend to form. Animal models provide a mechanism for fundamental studies of the coupling between hemodynamics and pathophysiology in cerebral aneurysms. We conducted a sensitivity study to develop an accurate CFD model for an elastase-induced rabbit aneurysm model. We then used this computational model to evaluate the capability of the rabbit model to reproduce hemodynamic features typical of human IAs. Geometric and hemodynamic features of 51 rabbit aneurysm models were analyzed and shown to fall within the range reported for human IAs. This model was also used to study the relationship between aspect ratio and hemodynamics in the v aneurysm sac. An-in silico design‖ approach was then used to explore the possibility of extending the rabbit model to capture more of the flow categories identified in human IAs. Based on a previously developed parametric model for human arterial bifurcations, we created and validated a parametric model for IAs. This parametric model captures important geometric and flow features of both the aneurysm and neighboring vasculature. The model is currently being used for studies of the coupling between geometry and hemodynamics in IAs. It can also be used to guide 3D reconstruction of poor quality clinical data or construct in vitro experimental models. vi TABLE OF CONTENTS
An impeller for a pump disclosed herein. The impeller may comprise a hub having a fixed end and a... more An impeller for a pump disclosed herein. The impeller may comprise a hub having a fixed end and a free end. The impeller may also include a plurality of sheets, which are supported by the hub. Each sheet can have a fixed end which is coupled to the hub, and a free end. The impeller may have a stowed configuration and a deployed configuration, with the blades in the deployed configuration of the hub and extend away from the sheets being compressed in the stowed configuration to the hub.
IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 2009
ASME 2011 Summer Bioengineering Conference, Parts A and B, 2011
An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by l... more An intracranial aneurysm (IA) is a pathological condition of cerebral arteries characterized by local enlargements of the arterial wall, typically into a saccular shape. Rupture of the aneurysm sac can result in devastating cerebral hemorrhage. Hemodynamic factors are believed to play an important role in initiation, development and rupture of IAs [1–3]. However, the coupling between hemodynamics and aneurysm pathophysiology is complex and remains poorly understood. Patient specific diagnostics regarding risk of rupture can be substantially advanced by improving our understanding of the in-vivo response of the aneurysm wall to intra-saccular hemodynamic stresses. A mechanism for fundamental studies of the impact of chronically altered WSS on the intact vascular wall is provided by animal models. However, cerebral aneurysms have not been shown to occur naturally in animals. Thus, a number of animal models have been created for studying aneurysm pathogenesis including those in mice, rats, rabbits, canines, swine and primates. To make meaningful use of these models, it is important to evaluate their relevance to human biomechanics and pathophysiology.Copyright © 2011 by ASME
Advances in Mathematical Fluid Mechanics, 2010
ABSTRACT
ASME 2008 Summer Bioengineering Conference, Parts A and B, 2008
ABSTRACT Hemodynamic factors are thought to play an important role in the initiation, growth, and... more ABSTRACT Hemodynamic factors are thought to play an important role in the initiation, growth, and rupture of cerebral aneurysms. In-vitro studies have demonstrated a correlation between the magnitude and distribution of wall shear stress (WSS) and biological response of both endothelial cells and smooth muscle cells [1–3]. In elastase induced saccular aneurysms, low WSS (below 0.5 Pa) was found to have a correlation with altered expression of biological markers [4]. Localized regions of rapid aneurysm growth in-vivo have been shown to be associated with regions where WSS is below a critical value of 0.1 Pa [5]. Further, aspect ratio (AR), the ratio of the maximum diameter of the aneurysm to the width of the aneurysm neck, has been correlated with elevated risk of rupture [6]. The purpose of the current study is to explore the possibility of creating elastase induced aneurysms in rabbits with a range of aspect ratios (ratio of aneurysm height/neck) and evaluate the existence of a correlation between aspect ratio and WSS distribution. Aneurysms with ARs from 0.98 to 2.8 were created at the origin of the right common carotid artery (n = 30). Qualitative differences in WSS distribution were found in the high AR aneurysms (HARA) (AR>1.6) and low AR aneurysms (LARA) (AR
Journal of Biomechanical Engineering, 2010
Computational fluid dynamics (CFD) studies provide a valuable tool for evaluating the role of hem... more Computational fluid dynamics (CFD) studies provide a valuable tool for evaluating the role of hemodynamics in vascular diseases such as cerebral aneurysms and atherosclerosis. However, such models necessarily only include isolated segments of the vasculature. In this work, we evaluate the influence of geometric approximations in vascular anatomy on hemodynamics in elastase induced saccular aneurysms in rabbits. One representative high aspect ratio (AR—height/neck width) aneurysm and one low AR aneurysm were created at the origin of the right common carotid artery in two New Zealand white rabbits. Three-dimensional (3D) reconstructions of the aneurysm and surrounding arteries were created using 3D rotational angiographic data. Five models with varying extents of neighboring vasculature were created for both the high and low AR cases. A reference model included the aneurysm sac, left common carotid artery (LCCA), aortic arch, and downstream trifurcation/quadrification. Three-dimension...
Journal of Biomechanics, 2011
Clinical studies suggest aneurysm aspect ratio (AR) is an important indicator of rupture likeliho... more Clinical studies suggest aneurysm aspect ratio (AR) is an important indicator of rupture likelihood. The importance of AR is hypothesized to arise from its influence on intra-aneurysmal hemodynamics. It has been conjectured that the flow in the domes of high AR sacs is slower than in low AR sacs and some aspect and leads to a cascade of enzymatic activities that weaken the aneurysm wall. However, the connection between AR, hemodynamics and wall weakening has never been proven. Animal models of saccular aneurysms provide a venue for evaluating this conjecture. The focus of this work was to evaluate whether a commonly used elastase induced aneurysm model in rabbits is suitable for a study of this kind from a hemodynamic perspective. In particular, to assess whether hemodynamic factors in low and high AR sacs are statistically different. To achieve this objective, saccular aneurysms were created in 51 rabbits and pulsatile computational fluid dynamics (CFD) studies were performed using rabbit specific inflows. Distinct hemodynamics were found in the low AR (AR<1.8, n=25), and high AR (AR>2.2, n=18) models. A single, stable recirculation zone was present in all low AR aneurysms, whereas a
An intracranial aneurysm (IA) is a pathological state of a cerebral artery in which the elastin a... more An intracranial aneurysm (IA) is a pathological state of a cerebral artery in which the elastin and smooth muscle cells found in the healthy arterial wall are absent. Rupture of an IA is a major cause of subarachnoid hemorrhage. Hemodynamics is believed to play an important role in initiation, development and rupture of the IA. However, the coupling between hemodynamics and aneurysm pathophysiology remains poorly understood. The initiation of cerebral aneurysms is believed to be caused by a breakdown in the homeostatic mechanism of healthy arteries, leading to destructive wall remodeling and damage. Due to its complex nature, there is a need for both controlled in vitro and in vivo studies of IA initiation. We have designed an in vitro flow chamber that can be used to reproduce specific magnitudes of wall shear stress and wall shear stress gradients found at the apices of arterial bifurcations, where aneurysms tend to form. Animal models provide a mechanism for fundamental studies of the coupling between hemodynamics and pathophysiology in cerebral aneurysms. We conducted a sensitivity study to develop an accurate CFD model for an elastase-induced rabbit aneurysm model. We then used this computational model to evaluate the capability of the rabbit model to reproduce hemodynamic features typical of human IAs. Geometric and hemodynamic features of 51 rabbit aneurysm models were analyzed and shown to fall within the range reported for human IAs. This model was also used to study the relationship between aspect ratio and hemodynamics in the v aneurysm sac. An-in silico design‖ approach was then used to explore the possibility of extending the rabbit model to capture more of the flow categories identified in human IAs. Based on a previously developed parametric model for human arterial bifurcations, we created and validated a parametric model for IAs. This parametric model captures important geometric and flow features of both the aneurysm and neighboring vasculature. The model is currently being used for studies of the coupling between geometry and hemodynamics in IAs. It can also be used to guide 3D reconstruction of poor quality clinical data or construct in vitro experimental models. vi TABLE OF CONTENTS