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TWO WAY FSI ANALYSIS OF CABG WITH PHYSIOLOGICALLY REALISTIC PULSATILE FLOW AND NONLINEAR ARTERY STRUCTURE
Biofluids II: CFD and Modelling Approaches
Presentation O-241
S245
TWO WAY FSI ANALYSIS OF CABG WITH PHYSIOLOGICALLY REALISTIC PULSATILE FLOW AND NONLINEAR ARTERY STRUCTURE Esfandyar Kouhi, Yos Morsi, Syed Hassan Masood
Swinburne University of Technology Faculty of Engineering & Industrial Sciences Mail 66, P.O Box 218, Hawthorn, Victoria 3122, Australia
Introduction The presence of hemodynamic factors could localize vascular disease in regions of complex flow, occurred due to branching, bifurcations, and curvature of the arteries in the coronary, carotid, abdominal, and femoral arteries. These factors could produce severely atherosclerotic regions in the mentioned arteries. For instance, in the carotid artery, atherosclerotic lesions localize along the outer wall of the carotid sinus region where the wall shear stress is low [Zarins et al., 1983]. The bypass graft implantation surgery is a common procedure for patients with significant stenosis in their arteries. However the patency of such a surgery strongly depends on the choice of blood vessel(s) used for the revascularization [Lytle et al., 1985]. Various experimental and numerical investigations have been performed trying to reveal the contribution of different hemodynamic factors in the long term success of arterial bypass surgery such as recirculation, vortex motions, and shear stress distributions on the artery wall. For example, an intimal hyperplasia at arterial bypass graft anastomoses has been stated as the major factor responsible for the graft failure [Cole et al., 2002]. However, the exact nature of the two way interaction between the dominant pulsing flow and the deformable structure of the arteries has not been fully investigated numerically.
Methods This work presents the results of symmetrical Twoway fluid structure interaction analysis of the left interior mammary artery (LIMA) anastomosed with the angel of 60° on the left anterior descending artery (LAD) with 80% occlusion using the code ANSYS CFX Multi-field solver version11. For the a fluid region, a three-dimensional, unsteady, pastille, laminar, Newtonian, and compressible blood rheology has been considered [Johnston et al., 2006, Tang et al., 2004, Valencia and Villanueva, 2006]. The flow measurements with pulsed Doppler ultrasound acquired in the right internal carotid were used to impose the physiologically flow conditions before the proximal anastomosis. Meanwhile, the arteries wall which is assumed to be hyper-elastic, isotropic, incompressible, and homogeneous, behaves as soft tissue with two degrees of freedom moving in axial 16th ESB Congress, Oral Presentations, Wednesday 9 July 2008
and radial directions. A nonlinear Young’s modulus E relation with increasing strain presented in [Olufsen, 1999] was used to predict the realistic behaviour of arteries elasticity.
Results and discussions Fully converged transient solutions were computed using the graft and the host artery boundary conditions for governing equations over the big systole. The solution procedure was started for the first time step of the solid region in the ANSYS package at the rest condition. The convergence target of 1e-3 under relaxation factor of 0.75 was reached. Simultaneously, the fluid region solution was initialized in the CFX package. A fully implicit second order backward Euler differencing scheme was adopted for all equations during the pulsatile simulations. The RMS residual for each solved equation was held at or below 1e-05 taking a maximum of 35 coefficient iterations at each timestep. The results were recorded each 0.01 seconds for both regions. The results of fluid and solid regions were evaluated in the terms of flow patterns and distributions of time-averaged wall shear stress, Total Mesh Displacement, Equivalent Stress and Von Misses Stress. The results then compared with some available published data. These results provide helpful information for further attacking the exact factors to cause the restenosis in the host artery with bypass graft implantation.
References COLE, J. S. et al. Medical Engineering and Physics, 24, 393-401, 2002 JOHNSTON, B. et al. Journal of Biomechanics, 39, 1116-1128, 2006 LYTLE, B. W. et al. Journal of Thoracic and Cardiovascular Surgery, 89, 248-258, 1985 OLUFSEN, M. S. Am J Physiol Heart Circ Physiol, 276, H257-268, 1999. TANG, D. et al. Annals of Biomedical Engineering, 32, 947-960, 2004. VALENCIA, A. et al. International Communications in Heat and Mass Transfer, 33, 966-975, 2006. ZARINS, C. et al. (1983). Circulation Research, 53, 502-514.
Journal of Biomechanics 41(S1)
Presentation O-241
S245
TWO WAY FSI ANALYSIS OF CABG WITH PHYSIOLOGICALLY REALISTIC PULSATILE FLOW AND NONLINEAR ARTERY STRUCTURE Esfandyar Kouhi, Yos Morsi, Syed Hassan Masood
Swinburne University of Technology Faculty of Engineering & Industrial Sciences Mail 66, P.O Box 218, Hawthorn, Victoria 3122, Australia
Introduction The presence of hemodynamic factors could localize vascular disease in regions of complex flow, occurred due to branching, bifurcations, and curvature of the arteries in the coronary, carotid, abdominal, and femoral arteries. These factors could produce severely atherosclerotic regions in the mentioned arteries. For instance, in the carotid artery, atherosclerotic lesions localize along the outer wall of the carotid sinus region where the wall shear stress is low [Zarins et al., 1983]. The bypass graft implantation surgery is a common procedure for patients with significant stenosis in their arteries. However the patency of such a surgery strongly depends on the choice of blood vessel(s) used for the revascularization [Lytle et al., 1985]. Various experimental and numerical investigations have been performed trying to reveal the contribution of different hemodynamic factors in the long term success of arterial bypass surgery such as recirculation, vortex motions, and shear stress distributions on the artery wall. For example, an intimal hyperplasia at arterial bypass graft anastomoses has been stated as the major factor responsible for the graft failure [Cole et al., 2002]. However, the exact nature of the two way interaction between the dominant pulsing flow and the deformable structure of the arteries has not been fully investigated numerically.
Methods This work presents the results of symmetrical Twoway fluid structure interaction analysis of the left interior mammary artery (LIMA) anastomosed with the angel of 60° on the left anterior descending artery (LAD) with 80% occlusion using the code ANSYS CFX Multi-field solver version11. For the a fluid region, a three-dimensional, unsteady, pastille, laminar, Newtonian, and compressible blood rheology has been considered [Johnston et al., 2006, Tang et al., 2004, Valencia and Villanueva, 2006]. The flow measurements with pulsed Doppler ultrasound acquired in the right internal carotid were used to impose the physiologically flow conditions before the proximal anastomosis. Meanwhile, the arteries wall which is assumed to be hyper-elastic, isotropic, incompressible, and homogeneous, behaves as soft tissue with two degrees of freedom moving in axial 16th ESB Congress, Oral Presentations, Wednesday 9 July 2008
and radial directions. A nonlinear Young’s modulus E relation with increasing strain presented in [Olufsen, 1999] was used to predict the realistic behaviour of arteries elasticity.
Results and discussions Fully converged transient solutions were computed using the graft and the host artery boundary conditions for governing equations over the big systole. The solution procedure was started for the first time step of the solid region in the ANSYS package at the rest condition. The convergence target of 1e-3 under relaxation factor of 0.75 was reached. Simultaneously, the fluid region solution was initialized in the CFX package. A fully implicit second order backward Euler differencing scheme was adopted for all equations during the pulsatile simulations. The RMS residual for each solved equation was held at or below 1e-05 taking a maximum of 35 coefficient iterations at each timestep. The results were recorded each 0.01 seconds for both regions. The results of fluid and solid regions were evaluated in the terms of flow patterns and distributions of time-averaged wall shear stress, Total Mesh Displacement, Equivalent Stress and Von Misses Stress. The results then compared with some available published data. These results provide helpful information for further attacking the exact factors to cause the restenosis in the host artery with bypass graft implantation.
References COLE, J. S. et al. Medical Engineering and Physics, 24, 393-401, 2002 JOHNSTON, B. et al. Journal of Biomechanics, 39, 1116-1128, 2006 LYTLE, B. W. et al. Journal of Thoracic and Cardiovascular Surgery, 89, 248-258, 1985 OLUFSEN, M. S. Am J Physiol Heart Circ Physiol, 276, H257-268, 1999. TANG, D. et al. Annals of Biomedical Engineering, 32, 947-960, 2004. VALENCIA, A. et al. International Communications in Heat and Mass Transfer, 33, 966-975, 2006. ZARINS, C. et al. (1983). Circulation Research, 53, 502-514.
Journal of Biomechanics 41(S1)