Computational fluid dynamics in the development of novel vascular grafts
1
$284 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Oral Presentations Financial Support: NSERC Operating (CRE); Canadian Foundation for Inno- and hemodynamic models needed to investigate specific clinical questions vation (MH), CIHR (MH), and ORDCF (MH). about cerebral aneurysms and their endovascular treatment. 5876 Tu, 16:45-17:00 (P24) Computational fluid dynamics in the development of novel vascular grafts T.M. McGIoughlin, M.T. Walsh, T.P. O'Brien. Centre for Applied Biomedical Engineering Research and Materials and Surface Science Institute, Department of Mechanical and Aeronautical Engineering, University of Limerick, Limerick, Ireland Introduction: The restoration of blood supply to diseased limb extremities is possible using vascular bypass grafts. However, such procedures have moderate patency rates. Intimal hyperplasia causing stenosis at the distal anastomosis is a major cause of failure of infrainguinal vascular bypass grafts. It is characterised by the proliferation of vascular smooth muscle cells which migrate to cause intimal hyperplasia. Anastomotic restenoses occur predominantly at the heel and toe of the anastomosis and on the artery bed, opposite the anastomosis. Disease formation on the bed of the junction is thought to be largely due to the abnormal flow patterns created as the blood flows from the graft into the artery, impinging on the bed of the junction. Such flow behaviour which give rise to stagnation regions is not commonly found in the arterial system. Thus, hemodynamic flow patterns in distal end-to-side anastomoses are widely implicated in the initiation of the disease formation processes. Materials and Methods: A range of studies have been conducted which have examined the flow mechanics using Computational Fluid Dynamics (CFD). Studies have been conducted on a range of currently used end-to-side graft configurations as well as on two novel concept configurations. The CFD results have have led to the development of two novel, patented, vascular graft concepts, namely Prolong I and Prolong II for use in the treatment of peripheral vascular disease. Results: In the Prolong 1 device, the bed of the junction is eliminated and in the Distal Outflow Section (DOS) the wall shear stress (WSS) was found to return to a more normal value over a much shorter distance. In the second device Prolong 2, again normal fully developed flow was restored at a distance 25% shorter than in the conventional bypass case. In terms of peak WSS a reduction of more than 50% is achieved over conventional bypass grafts within the host artery. Thus, the computational modelling indicated that the novel grafts may have improved hemodynamic performance over currently used devices and this may lead to improved clinical outcomes. 6400 Tu, 17:00-17:15 (P24) Computational framework for the study of cerebral aneurysms and their endovascular treatment A. Frangi 1, C.M. Putman 2, J.R. Cebral3. 1Dept. of Technology, Pompeu Fabra University, Barcelona, Spain, 21nterventional Neuroradiology, Inova Farifax Hospital, Virginia, USA, 3School of Computational Sciences, George Mason University, Virginia, USA In this article we describe a computational framework for studying the hemo- dynamics of cerebral aneurysms. This framework is composed of an efficient computational modeling pipeline for constructing patient-specific computational fluid dynamics models of cerebral aneurysms from 3D medical images, a searchable database that archives clinical information, medical images and computational models, and novel techniques for personalized simulation of endovascular treatments. The computational modeling pipeline consists in a streamlined set of semi-automatic tools for: a) vessel reconstruction from anatomical images such as 3D rotational angiography, computed tomogra- phy angiography or magnetic resonance angiography, b) geometry modeling, c) unstructured grid generation, d) finite element solution of the fluid flow equations, e) visualization and characterization of aneurysm geometry and hemodynamics. The database stores in a consistent manner, for each patient: a) clinical information consisting of patient data, history of clinical events such as subarachnoid hemorrhage, symptoms, treatment information, etc., b) medical images obtained during various examinations of the patient, c) ge- ometrical models constructed from the anatomical images, d) hemodynamics models constructed from the geometrical models, and e) visualizations of the intraaneurysmal flow patterns and distributions of hemodynamic forces on the aneurysm sac. The simulation of blood flows in the presence of endovascular devices such as stents and coils is carried out using adaptive embedded unstructured grid methods. This approach allows the analysis of the alterations of the aneurysmal flow patterns induced by the deployment of endovascular devices typically used to block or divert the blood flow away from the aneurysm. The combination of body conforming and embedded unstructured grids makes this analysis possible for the first time on a patient- specific base. In summary, this computational framework allows the efficient construction, archival and analysis of the numerous patient-specific anatomical 14.3.5. Hemodynamics (General) 6202 We, 14:00-14:15 (P34) Flow and deformation in initially curved stenosis model of arterial disease S. Kobayashi1, '~ Ayama 1, H. Morikawa1, D. Tang 2, D.N. Ku3. 1Department of Functional Machinery and Mechanics, Shinshu University, Ueda, Nagano, Japan, 2Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, USA, 3 GVW/VSchool of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA High grade stenoses can limit blood flow and produce conditions in which the artery may collapse. The resultant compression may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization. We have developed curved stenosis models made of hydrogel that closely approximate the coronary disease situation, and performed flow experiments. Pulsatile flow was produced using a gear pump controlled by a digitized physiologic waveform. The stenosis model was bent on a rubber support with ends that are pulled by a wire to change its curvature corresponding to curvature of the epicardial surface cyclically. The phase difference between flow rate and pressure between upstream and downstream of the stenosis occurred due to the compliance of the model and the stenosis resistance. For a 70% nominal stenosis by diameter, stiffness parameter 15 = 10 of straight portion of model, and 100±30mmHg upstream pressure, the first outbreak of collapse occurred at the end of systole with pulsatile pressure drops of 76mmHg, on average. The magnitude of the required pressure drop was reduced with an increase in the stiffness and curvature of the stenosis model. There was no great difference in flow rate between cyclic changes of curvature and fixed curvatures, but the average downstream pressure for the first outbreak of collapse during cyclic changes of curvature was smaller than that for the maximum fixed curvature in the range of cyclic change of curvature. The results indicate that collapse was influenced by the degree of curvature and the cyclic change of curvature. 6652 We, 14:15-14:30 (P34) Impedance pump as a cardiovascular assist device L. Waisman 1, M. Rosenfeld 2, S. Einav 1. 1Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv Israel, 2School of Mechanical Engineering, Faculty of Engineering, TeI-Aviv University, Tel Aviv, Israel Pumping blood in one direction is the main function of the heart, which is equipped with valves to ensure unidirectional flow. Generating the net flow may be facilitated by impedance pumping (IP) effects, through a careful matching of the heart's compliance and beating characteristics to the compliance of the entire circulation system. IP generates net flow without using valves and therefore the understanding of its characteristics may also be a key factor in developing of novel designs of valveless Ventricular Assist Devices (VADs). An IP is a flexible, valveless vessel filled with fluid connected to other vessel with heterogynous elastic properties. By pinching the vessel periodically at an asymmetric location, a complex pattern of waves is established, which generates a net flow. The magnitude and direction of the net flow depends on the IP characteristics (compression amplitude and frequency, vessels elasticity). Any flow system consisting of connected vessels of different elastic properties, such as the cardiovascular system, exhibits similar characteristics. A multiscale approach, containing a continuum model for the vascular segment and a lumped model for the remaining systemic circulation, is used for modeling the cardiovascular system and its IP characteristics. The mathematical model of a single segment is based on one-dimensional Navier-Stokes approximation. The resulting non-linear hyperbolic system is solved numerically based on a hybrid approach. The two-step Lax-Wendroff finite-difference scheme is used to compute the flow and cross section area along the vascular segment, while the characteristics method is employed for the computation of boundary condition of the vascular segment. A pulsatile pressure is assigned at the inlet and a 3-element Windkessel model for the termination is employed. The results present the effect of the pinching properties (amplitude, frequency and location) on the total mass flow rate of a healthy as well as dysfunctional heart to evaluate the IP characteristics. Knowing those characteristics will provide accomplishment of a unique VAD.
Transcript of Computational fluid dynamics in the development of novel vascular grafts
$284 Journal of Biomechanics 2006, Vol. 39 (Suppl 1) Oral Presentations
Financial Support: NSERC Operating (CRE); Canadian Foundation for Inno- and hemodynamic models needed to investigate specific clinical questions vation (MH), CIHR (MH), and ORDCF (MH). about cerebral aneurysms and their endovascular treatment.
5876 Tu, 16:45-17:00 (P24) Computational fluid dynamics in the development of novel vascular grafts T.M. McGIoughlin, M.T. Walsh, T.P. O'Brien. Centre for Applied Biomedical Engineering Research and Materials and Surface Science Institute, Department of Mechanical and Aeronautical Engineering, University of Limerick, Limerick, Ireland
Introduction: The restoration of blood supply to diseased limb extremities is possible using vascular bypass grafts. However, such procedures have moderate patency rates. Intimal hyperplasia causing stenosis at the distal anastomosis is a major cause of failure of infrainguinal vascular bypass grafts. It is characterised by the proliferation of vascular smooth muscle cells which migrate to cause intimal hyperplasia. Anastomotic restenoses occur predominantly at the heel and toe of the anastomosis and on the artery bed, opposite the anastomosis. Disease formation on the bed of the junction is thought to be largely due to the abnormal flow patterns created as the blood flows from the graft into the artery, impinging on the bed of the junction. Such flow behaviour which give rise to stagnation regions is not commonly found in the arterial system. Thus, hemodynamic flow patterns in distal end-to-side anastomoses are widely implicated in the initiation of the disease formation processes. Materials and Methods: A range of studies have been conducted which have examined the flow mechanics using Computational Fluid Dynamics (CFD). Studies have been conducted on a range of currently used end-to-side graft configurations as well as on two novel concept configurations. The CFD results have have led to the development of two novel, patented, vascular graft concepts, namely Prolong I and Prolong II for use in the treatment of peripheral vascular disease. Results: In the Prolong 1 device, the bed of the junction is eliminated and in the Distal Outflow Section (DOS) the wall shear stress (WSS) was found to return to a more normal value over a much shorter distance. In the second device Prolong 2, again normal fully developed flow was restored at a distance 25% shorter than in the conventional bypass case. In terms of peak WSS a reduction of more than 50% is achieved over conventional bypass grafts within the host artery. Thus, the computational modelling indicated that the novel grafts may have improved hemodynamic performance over currently used devices and this may lead to improved clinical outcomes.
6400 Tu, 17:00-17:15 (P24) Computational framework for the study of cerebral aneurysms and their endovascular treatment A. Frangi 1 , C.M. Putman 2, J.R. Cebral 3. 1Dept. of Technology, Pompeu Fabra University, Barcelona, Spain, 21nterventional Neuroradiology, Inova Farifax Hospital, Virginia, USA, 3School of Computational Sciences, George Mason University, Virginia, USA
In this article we describe a computational framework for studying the hemo- dynamics of cerebral aneurysms. This framework is composed of an efficient computational modeling pipeline for constructing patient-specific computational fluid dynamics models of cerebral aneurysms from 3D medical images, a searchable database that archives clinical information, medical images and computational models, and novel techniques for personalized simulation of endovascular treatments. The computational modeling pipeline consists in a streamlined set of semi-automatic tools for: a) vessel reconstruction from anatomical images such as 3D rotational angiography, computed tomogra- phy angiography or magnetic resonance angiography, b) geometry modeling, c) unstructured grid generation, d) finite element solution of the fluid flow equations, e) visualization and characterization of aneurysm geometry and hemodynamics. The database stores in a consistent manner, for each patient: a) clinical information consisting of patient data, history of clinical events such as subarachnoid hemorrhage, symptoms, treatment information, etc., b) medical images obtained during various examinations of the patient, c) ge- ometrical models constructed from the anatomical images, d) hemodynamics models constructed from the geometrical models, and e) visualizations of the intraaneurysmal flow patterns and distributions of hemodynamic forces on the aneurysm sac. The simulation of blood flows in the presence of endovascular devices such as stents and coils is carried out using adaptive embedded unstructured grid methods. This approach allows the analysis of the alterations of the aneurysmal flow patterns induced by the deployment of endovascular devices typically used to block or divert the blood flow away from the aneurysm. The combination of body conforming and embedded unstructured grids makes this analysis possible for the first time on a patient- specific base. In summary, this computational framework allows the efficient construction, archival and analysis of the numerous patient-specific anatomical
14.3.5. Hemodynamics (General)
6202 We, 14:00-14:15 (P34) Flow and deformation in initially curved stenosis model of arterial disease S. Kobayashi 1 , '~ Ayama 1 , H. Morikawa 1 , D. Tang 2, D.N. Ku 3. 1Department of Functional Machinery and Mechanics, Shinshu University, Ueda, Nagano, Japan, 2Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA, USA, 3 GVW/V School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, USA
High grade stenoses can limit blood flow and produce conditions in which the artery may collapse. The resultant compression may be important in the development of atherosclerotic plaque fracture and subsequent thrombosis or distal embolization. We have developed curved stenosis models made of hydrogel that closely approximate the coronary disease situation, and performed flow experiments. Pulsatile flow was produced using a gear pump controlled by a digitized physiologic waveform. The stenosis model was bent on a rubber support with ends that are pulled by a wire to change its curvature corresponding to curvature of the epicardial surface cyclically. The phase difference between flow rate and pressure between upstream and downstream of the stenosis occurred due to the compliance of the model and the stenosis resistance. For a 70% nominal stenosis by diameter, stiffness parameter 15 = 10 of straight portion of model, and 100±30mmHg upstream pressure, the first outbreak of collapse occurred at the end of systole with pulsatile pressure drops of 76mmHg, on average. The magnitude of the required pressure drop was reduced with an increase in the stiffness and curvature of the stenosis model. There was no great difference in flow rate between cyclic changes of curvature and fixed curvatures, but the average downstream pressure for the first outbreak of collapse during cyclic changes of curvature was smaller than that for the maximum fixed curvature in the range of cyclic change of curvature. The results indicate that collapse was influenced by the degree of curvature and the cyclic change of curvature.
6652 We, 14:15-14:30 (P34) Impedance pump as a cardiovascular assist device
L. Waisman 1 , M. Rosenfeld 2, S. Einav 1 . 1Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv Israel, 2School of Mechanical Engineering, Faculty of Engineering, TeI-Aviv University, Tel Aviv, Israel
Pumping blood in one direction is the main function of the heart, which is equipped with valves to ensure unidirectional flow. Generating the net flow may be facilitated by impedance pumping (IP) effects, through a careful matching of the heart's compliance and beating characteristics to the compliance of the entire circulation system. IP generates net flow without using valves and therefore the understanding of its characteristics may also be a key factor in developing of novel designs of valveless Ventricular Assist Devices (VADs). An IP is a flexible, valveless vessel filled with fluid connected to other vessel with heterogynous elastic properties. By pinching the vessel periodically at an asymmetric location, a complex pattern of waves is established, which generates a net flow. The magnitude and direction of the net flow depends on the IP characteristics (compression amplitude and frequency, vessels elasticity). Any flow system consisting of connected vessels of different elastic properties, such as the cardiovascular system, exhibits similar characteristics. A multiscale approach, containing a continuum model for the vascular segment and a lumped model for the remaining systemic circulation, is used for modeling the cardiovascular system and its IP characteristics. The mathematical model of a single segment is based on one-dimensional Navier-Stokes approximation. The resulting non-linear hyperbolic system is solved numerically based on a hybrid approach. The two-step Lax-Wendroff finite-difference scheme is used to compute the flow and cross section area along the vascular segment, while the characteristics method is employed for the computation of boundary condition of the vascular segment. A pulsatile pressure is assigned at the inlet and a 3-element Windkessel model for the termination is employed. The results present the effect of the pinching properties (amplitude, frequency and location) on the total mass flow rate of a healthy as well as dysfunctional heart to evaluate the IP characteristics. Knowing those characteristics will provide accomplishment of a unique VAD.
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