Patient-specific analysis of flow and stress patterns in thoracoabdominal aneurysms
1
Track 14. Cardiovascular Mechanics 5003 Mo-Tu, no. 7 (P65) Endovascular stenting of an intimal lesion with acute limb ischemia of the upper extremity after shoulder hemiarthroplasty: a case report S. Schmitt 1, R. Gareis 2, G. Schmidt 2, H. Eichst~dt 3, Th. St6rk 2. 1Karl- Olga-Krankenhaus, Baumann-Klinik, Dep. of Orthopaedic Surgery, Stuttgart, Germany, 2Karl-Olga-Krankenhaus, Dep. of Cardiology, Stuttgart, Germany, 3 Charit& Campus Virchow, Dep. of Cardiology, Berlin, Germany Intimal ruptures with limb ischemia of the upper extremity after joint replace- ment are very rare. However, they are described in cases of traumatic joint dislocation and direct open surgical repair has been the indicated treatment. We report a case of a 60 year old male patient presenting with pain, paraes- thesia in the fingers, and a cold, pulseless hand 14 hours after shoulder hemiarthroplasty. Immediate angiographic examination showed the subtotal occlusion of the axillary artery due to an intimal rupture that occurred probably either with joint dislocation or with positioning of an instrument intra-operatively. Direct surgical repair could be avoided by percutaneous angioplasty and primary stenting of the axillary artery using a 6.0 30mm Bard Luminex self expanding Nitinol stent. Follow-up color duplex ultrasonography was performed immediately after intervention and again at three months follow-up. It showed a complete and persistent revascularisation of the artery. Lingering adverse physical symptoms have not been noted in this patient. He recovered with a restored pulse and normal skin color immediately post-intervention, his paraesthetic sensations are ongoing to improve. Endovasular stenting is a minimal invasive therapy and an attractive option for treatment of postoperative limb ischemia due to intimal disruption after joint replacement, even in unusual sites. 7635 Mo-Tu, no. 8 (P65) Biomechanics of the aortic wall: developing a method to predict aneurysm rupture M. Tenholt 1, R Remek 1, G. Benderoth 2, G. Silber 2, Th. Schmitz-Rixen 1. Center of Biomedical Engineering (CBME), 1Department of Vascular and Endovascular Surgery, Johann Wolfgang Goethe University, and 2Institute of Material Science, University of Applied Sciences, Frankfurt~Main, Germany Introduction: The third most common cause for sudden death is abdominal aortic aneurysm rupture. The only valid parameter to estimate the risk of rupture is the transversal diameter of the aneurysm. To develop a more valid predictor for rupture we investigated the material properties of the aneurys- matic aortic wall. ACT scan was used to obtain the geometric data of the aortic specimen and tensile tests were applied to evaluate material properties for a finite element model. Material and Methods: Twenty 4 2cm strips from the infrarenal abdominal aorta of pigs and ten 3x2cm strips from infrarenal aneurysms of patients, requiring surgical treatment for their aneurysms, were compared in this study. The aortic strips were inserted into a specially constructed holding device and then investigated in a CT for 3D-geometric reconstruction. Via these images a volume-body was generated for an FE-model. The strips were then stretched with a traversal speed of 1 mm/s until rupture. The tensile test was simulated in the FE-Tool (ABAQUS). The stress-strain data were predicted by a hyperelastic constitutive equation (strain energy function of Ogden type). A non linear optimization procedure (Simplex; Nelder and Mead) was used to generate optimal parameters of the mathematical model. To calculate the quality function in the optimization algorithm, the FE-Tool was used to solve the boundary value problem. Results: This methodology can be used to describe the elastic behaviour of the aortic wall. The pig aortic wall showed anisotropic behavior in longitudinal and transversal directions, being transversally more elastic. In contrast, the human aneurysmatic wall was isotropic in both directions and more rigid. Conclusion: Characterizing the elastic behaviour of nonaneurysmatic and aneurysmatic aortic wall, as described in this method, is a first step towards being able to more precisely predict aneurysm rupture. 7347 Mo-Tu, no. 9 (P65) Analysis of biomechamical properties of abdominal aorta and abdominal aortic aneurysm M. Kobielarz 1, R. Bgdzir~ski 1, S. Szotek 1, J. Gnus 2, W. Hauzer 2, P. Kuropka 3. 1Biomedical Engineering and Experimental Mechanics Division, Wroctaw University of Technology, Wroctaw, Poland, 2Regional Specialistic Hospital in Wroclaw, Wroclaw, Poland, 3Department of Anatomy and Histology, Agricultural University of Wroctaw, Wroctaw, Poland The aorta must withstand the huge load imposed by arterial blood pressure. Aorta weakens with age and induces gradual dilatations of diameter of aorta, it causes a formation of abdominal aortic aneurysm. Abdominal aortic aneurysm is a disease, which consists in disorder of the structural composition of vessels' walls. The knowledge of mechanical behavior and structural composition of abdominal aortic aneurysm in comparison to nonaneurysmal abdominal aorta 14.1. Aneurysms S605 may provide information on natural history of this disease i.e. onest of the disease and its progression. With this end in view uniaxial tensile tests and microscopic analysises of abdominal aortic aneurysms' walls and abdominal aortas' walls were per- formed. On the basis of mechanical tests, the stress-strain relationships were calculated for each specimen. On the basis histological analysises, a quantity of load-bearing fibers were determined. Loss of quantity of load-bearing fibers in aortic wall induce alterations of vascular elasticity. The comparison of an average value of the mechanical properties of abdominal aortic aneurysms' walls and abdominal aortas' wall can confirm an increased stiffness of the tissue in the case of abdominal aortic aneurysms, particularly in circumferential direction. References [1] Holzapfel G.A. Biomechanics of soft tissue. In: J. Lemaitre (Ed.), The Hand- book of Materials Behavior Models. 2001; Academic Press, Boston, ch. 10.11, pp. 1049-1063. [2] Kobielarz M., Filipiak J., Bedzinski R., Gnus J., Hauser W., Plawski P., Witkiewicz W. Comparison of the mechanical properties of the abdominal aortic aneurysm and normal abdominal aorta's wall. Presented at 14th Conference of the European Society of Biomechanics, 's-Hertogenbosch, July 4-7, 2004. [3] Raghavan M., Webster M., Vorp D. Ex vivo biomechanical behaviour of abdom- inal aortic aneurysm: assessment using a new mathematical model. Annals of Biomedical Engineering 1996. 4522 Mo-Tu, no. 10 (P65) Patient-specific analysis of flow and stress patterns in thoracoabdominal aneurysms A. Borghi 1, N.B. Wood 1, R.H. Mohiaddin 2, X.'~ Xu 1. 1Department ef Chemical Engineering, Imperial College London, London, UK, 2Royal Brompton & Harefield NHS Trust, London, UK A thoracoabdominal anerusym (TA) involves an abnormal enlargement of the aorta that extends from the descending aorta to the abdomen; type I TAs originate just below the left subclavian artery and involve most or all of the descending aorta [1]. Two patients with type I TA were examined using a magnetic resonance (MR) scanner and the geometries were reconstructed from the MR images using in house segmentation techniques. Computational models were created for the two aneurysms, differentiating the wall, lumen and thrombus domains, and the models were imported into ADINA, a finite element program. Fluid-solid interaction simulations were performed under patient- specific flow conditions, for which MR velocity measurements were made at the upstream boundaries of the aneurysms. A typical pressure waveform obtained from the literature was imposed at the model outlet. Hyperelastic properties for the wall and thrombus materials were based on literature values [2,3].The results show similar stress patterns in the two aneurysms with the maximum stress located in the wall opposite to the thrombus. The wall shear stress pattern reveals that the aneurysm with larger amount of thrombus presents lower values over all of the lumen area. The analysis of a larger group of patients is expected to lead to a better understanding of this pathology, including the importance of the biomechanical factors in its progression and in determining possible rupture criteria. References [1] Webb T.H., Williams G.M. Thoracoabdominal aneurysm repair. Cardiovasc Surg 1999; 7(6): 573-85. [2] Vorp D.A., et al. Effect of aneurysm on the tensile strength and biomechanical behavior of the ascending thoracic aorta. Ann Thorac Surg 2003; 75(4): 1210-4. [3] Wang D.H., et al. Effect of intraluminal thrombus on wall stress in patient-specific models of abdominal aortic aneurysm. J Vasc Surg 2002; 36(3): 598~04. 6602 Mo-Tu, no. 11 (P65) Fluid-structure interactions in abdominal aortic aneurysms K.H. Fraser 1, M. Li 2, W.J. Easson 2, P.R. Hoskins 1. 1Medical Physics and 2School of Engineering and Electronics, The University of Edinburgh, Edinburgh, UK Abdominal aortic aneurysm (AAA) is a vascular disease involving a focal dilation of the aorta, the largest of the arteries. AAA may be present in up to 5.9% of the population aged 80 years [1]. Without treatment an AAA gradually expands until rupture, an event with a mortality rate of 90% [2]. Peak wall stress may affect the risk of AAA rupture. Disturbed flows are associated with atherosclerosis and the development of clotted blood, or thrombosis [3]. Fluid-structure interaction (FSI) models of aneurysms have the potential to predict both flow patterns and wall stress more accurately than rigid walled models or static pressure models respectively. However, FSI models are computationally demanding, and the improvement on the estimation of flow and wall stress compared with uncoupled models is unclear. The aim of this study is to compare blood flow and wall stress in idealised aneurysms in order to inform the selection of the model type in future studies of patient specific aneurysms.
Transcript of Patient-specific analysis of flow and stress patterns in thoracoabdominal aneurysms
Track 14. Cardiovascular Mechanics
5003 Mo-Tu, no. 7 (P65) Endovascular stenting of an intimal lesion with acute limb ischemia of the upper extremity after shoulder hemiarthroplasty: a case report
S. Schmitt 1 , R. Gareis 2, G. Schmidt 2, H. Eichst~dt 3, Th. St6rk 2. 1Karl- Olga-Krankenhaus, Baumann-Klinik, Dep. of Orthopaedic Surgery, Stuttgart, Germany, 2 Karl-Olga-Krankenhaus, Dep. of Cardiology, Stuttgart, Germany, 3 Charit& Campus Virchow, Dep. of Cardiology, Berlin, Germany
Intimal ruptures with limb ischemia of the upper extremity after joint replace- ment are very rare. However, they are described in cases of traumatic joint dislocation and direct open surgical repair has been the indicated treatment. We report a case of a 60 year old male patient presenting with pain, paraes- thesia in the fingers, and a cold, pulseless hand 14 hours after shoulder hemiarthroplasty. Immediate angiographic examination showed the subtotal occlusion of the axillary artery due to an intimal rupture that occurred probably either with joint dislocation or with positioning of an instrument intra-operatively. Direct surgical repair could be avoided by percutaneous angioplasty and primary stenting of the axillary artery using a 6.0 30mm Bard Luminex self expanding Nitinol stent. Follow-up color duplex ultrasonography was performed immediately after intervention and again at three months follow-up. It showed a complete and persistent revascularisation of the artery. Lingering adverse physical symptoms have not been noted in this patient. He recovered with a restored pulse and normal skin color immediately post-intervention, his paraesthetic sensations are ongoing to improve. Endovasular stenting is a minimal invasive therapy and an attractive option for treatment of postoperative limb ischemia due to intimal disruption after joint replacement, even in unusual sites.
7635 Mo-Tu, no. 8 (P65) Biomechanics of the aortic wall: developing a method to predict aneurysm rupture
M. Tenholt 1 , R Remek 1 , G. Benderoth 2, G. Silber 2, Th. Schmitz-Rixen 1 . Center of Biomedical Engineering (CBME), 1Department of Vascular and Endovascular Surgery, Johann Wolfgang Goethe University, and 2Institute of Material Science, University of Applied Sciences, Frankfurt~Main, Germany
Introduction: The third most common cause for sudden death is abdominal aortic aneurysm rupture. The only valid parameter to estimate the risk of rupture is the transversal diameter of the aneurysm. To develop a more valid predictor for rupture we investigated the material properties of the aneurys- matic aortic wall. A C T scan was used to obtain the geometric data of the aortic specimen and tensile tests were applied to evaluate material properties for a finite element model. Material and Methods: Twenty 4 2cm strips from the infrarenal abdominal aorta of pigs and ten 3x2cm strips from infrarenal aneurysms of patients, requiring surgical treatment for their aneurysms, were compared in this study. The aortic strips were inserted into a specially constructed holding device and then investigated in a CT for 3D-geometric reconstruction. Via these images a volume-body was generated for an FE-model. The strips were then stretched with a traversal speed of 1 mm/s until rupture. The tensile test was simulated in the FE-Tool (ABAQUS). The stress-strain data were predicted by a hyperelastic constitutive equation (strain energy function of Ogden type). A non linear optimization procedure (Simplex; Nelder and Mead) was used to generate optimal parameters of the mathematical model. To calculate the quality function in the optimization algorithm, the FE-Tool was used to solve the boundary value problem. Results: This methodology can be used to describe the elastic behaviour of the aortic wall. The pig aortic wall showed anisotropic behavior in longitudinal and transversal directions, being transversally more elastic. In contrast, the human aneurysmatic wall was isotropic in both directions and more rigid. Conclusion: Characterizing the elastic behaviour of nonaneurysmatic and aneurysmatic aortic wall, as described in this method, is a first step towards being able to more precisely predict aneurysm rupture.
7347 Mo-Tu, no. 9 (P65) Analysis of biomechamical properties of abdominal aorta and abdominal aortic aneurysm
M. Kobielarz 1 , R. Bgdzir~ski 1 , S. Szotek 1 , J. Gnus 2, W. Hauzer 2, P. Kuropka 3. 1Biomedical Engineering and Experimental Mechanics Division, Wroctaw University of Technology, Wroctaw, Poland, 2Regional Specialistic Hospital in Wroclaw, Wroclaw, Poland, 3Department of Anatomy and Histology, Agricultural University of Wroctaw, Wroctaw, Poland
The aorta must withstand the huge load imposed by arterial blood pressure. Aorta weakens with age and induces gradual dilatations of diameter of aorta, it causes a formation of abdominal aortic aneurysm. Abdominal aortic aneurysm is a disease, which consists in disorder of the structural composition of vessels' walls. The knowledge of mechanical behavior and structural composition of abdominal aortic aneurysm in comparison to nonaneurysmal abdominal aorta
14.1. Aneurysms S605
may provide information on natural history of this disease i.e. onest of the disease and its progression. With this end in view uniaxial tensile tests and microscopic analysises of abdominal aortic aneurysms' walls and abdominal aortas' walls were per- formed. On the basis of mechanical tests, the stress-strain relationships were calculated for each specimen. On the basis histological analysises, a quantity of load-bearing fibers were determined. Loss of quantity of load-bearing fibers in aortic wall induce alterations of vascular elasticity. The comparison of an average value of the mechanical properties of abdominal aortic aneurysms' walls and abdominal aortas' wall can confirm an increased stiffness of the tissue in the case of abdominal aortic aneurysms, particularly in circumferential direction.
References [1] Holzapfel G.A. Biomechanics of soft tissue. In: J. Lemaitre (Ed.), The Hand-
book of Materials Behavior Models. 2001; Academic Press, Boston, ch. 10.11, pp. 1049-1063.
[2] Kobielarz M., Filipiak J., Bedzinski R., Gnus J., Hauser W., Plawski P., Witkiewicz W. Comparison of the mechanical properties of the abdominal aortic aneurysm and normal abdominal aorta's wall. Presented at 14th Conference of the European Society of Biomechanics, 's-Hertogenbosch, July 4-7, 2004.
[3] Raghavan M., Webster M., Vorp D. Ex vivo biomechanical behaviour of abdom- inal aortic aneurysm: assessment using a new mathematical model. Annals of Biomedical Engineering 1996.
4522 Mo-Tu, no. 10 (P65) Patient-specific analysis of flow and stress patterns in thoracoabdominal aneurysms
A. Borghi 1 , N.B. Wood 1 , R.H. Mohiaddin 2, X.'~ Xu 1 . 1Department ef Chemical Engineering, Imperial College London, London, UK, 2Royal Brompton & Harefield NHS Trust, London, UK
A thoracoabdominal anerusym (TA) involves an abnormal enlargement of the aorta that extends from the descending aorta to the abdomen; type I TAs originate just below the left subclavian artery and involve most or all of the descending aorta [1]. Two patients with type I TA were examined using a magnetic resonance (MR) scanner and the geometries were reconstructed from the MR images using in house segmentation techniques. Computational models were created for the two aneurysms, differentiating the wall, lumen and thrombus domains, and the models were imported into ADINA, a finite element program. Fluid-solid interaction simulations were performed under patient- specific flow conditions, for which MR velocity measurements were made at the upstream boundaries of the aneurysms. A typical pressure waveform obtained from the literature was imposed at the model outlet. Hyperelastic properties for the wall and thrombus materials were based on literature values [2,3].The results show similar stress patterns in the two aneurysms with the maximum stress located in the wall opposite to the thrombus. The wall shear stress pattern reveals that the aneurysm with larger amount of thrombus presents lower values over all of the lumen area. The analysis of a larger group of patients is expected to lead to a better understanding of this pathology, including the importance of the biomechanical factors in its progression and in determining possible rupture criteria.
References [1] Webb T.H., Williams G.M. Thoracoabdominal aneurysm repair. Cardiovasc Surg
1999; 7(6): 573-85. [2] Vorp D.A., et al. Effect of aneurysm on the tensile strength and biomechanical
behavior of the ascending thoracic aorta. Ann Thorac Surg 2003; 75(4): 1210-4. [3] Wang D.H., et al. Effect of intraluminal thrombus on wall stress in patient-specific
models of abdominal aortic aneurysm. J Vasc Surg 2002; 36(3): 598~04.
6602 Mo-Tu, no. 11 (P65) Fluid-structure interactions in abdominal aortic aneurysms
K.H. Fraser 1 , M. Li 2, W.J. Easson 2, P.R. Hoskins 1 . 1Medical Physics and 2School of Engineering and Electronics, The University of Edinburgh, Edinburgh, UK
Abdominal aortic aneurysm (AAA) is a vascular disease involving a focal dilation of the aorta, the largest of the arteries. AAA may be present in up to 5.9% of the population aged 80 years [1]. Without treatment an AAA gradually expands until rupture, an event with a mortality rate of 90% [2]. Peak wall stress may affect the risk of AAA rupture. Disturbed flows are associated with atherosclerosis and the development of clotted blood, or thrombosis [3]. Fluid-structure interaction (FSI) models of aneurysms have the potential to predict both flow patterns and wall stress more accurately than rigid walled models or static pressure models respectively. However, FSI models are computationally demanding, and the improvement on the estimation of flow and wall stress compared with uncoupled models is unclear. The aim of this study is to compare blood flow and wall stress in idealised aneurysms in order to inform the selection of the model type in future studies of patient specific aneurysms.
