101
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Conlisk N, Forsythe RO, Hollis L, Doyle BJ, McBride OMB, Robson JMJ, Wang C, Gray CD, Semple SIK, MacGillivray T, van Beek EJR, Newby DE, Hoskins PR. Exploring the Biological and Mechanical Properties of Abdominal Aortic Aneurysms Using USPIO MRI and Peak Tissue Stress: A Combined Clinical and Finite Element Study. J Cardiovasc Transl Res 2017; 10:489-498. [PMID: 28808955 PMCID: PMC5722953 DOI: 10.1007/s12265-017-9766-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2017] [Accepted: 08/04/2017] [Indexed: 01/15/2023]
Abstract
Inflammation detected through the uptake of ultrasmall superparamagnetic particles of iron oxide (USPIO) on magnetic resonance imaging (MRI) and finite element (FE) modelling of tissue stress both hold potential in the assessment of abdominal aortic aneurysm (AAA) rupture risk. This study aimed to examine the spatial relationship between these two biomarkers. Patients (n = 50) > 40 years with AAA maximum diameters > = 40 mm underwent USPIO-enhanced MRI and computed tomography angiogram (CTA). USPIO uptake was compared with wall stress predictions from CTA-based patient-specific FE models of each aneurysm. Elevated stress was commonly observed in areas vulnerable to rupture (e.g. posterior wall and shoulder). Only 16% of aneurysms exhibited co-localisation of elevated stress and mural USPIO enhancement. Globally, no correlation was observed between stress and other measures of USPIO uptake (i.e. mean or peak). It is suggested that cellular inflammation and stress may represent different but complimentary aspects of AAA disease progression.
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Affiliation(s)
- Noel Conlisk
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK. .,School of Clinical Sciences, The University of Edinburgh, Edinburgh, UK. .,Institute for Bioengineering, The University of Edinburgh, Faraday Building, The King's Buildings, Mayfield Road, Edinburgh, EH9 3JL, UK.
| | - Rachael O Forsythe
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,School of Clinical Sciences, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Lyam Hollis
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK
| | - Barry J Doyle
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Vascular Engineering Laboratory, Harry Perkins Institute of Medical Research, Perth, Australia.,School of Mechanical and Chemical Engineering, The University of Western Australia, Perth, Australia
| | - Olivia M B McBride
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,School of Clinical Sciences, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Jennifer M J Robson
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,School of Clinical Sciences, The University of Edinburgh, Edinburgh, UK
| | - Chengjia Wang
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Calum D Gray
- Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Scott I K Semple
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Tom MacGillivray
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Centre for Clinical Brain Sciences, The University of Edinburgh, Edinburgh, UK
| | - Edwin J R van Beek
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - David E Newby
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, UK
| | - Peter R Hoskins
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, UK.,Institute for Bioengineering, The University of Edinburgh, Faraday Building, The King's Buildings, Mayfield Road, Edinburgh, EH9 3JL, UK
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102
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Yan P, Chen K, Wang Q, Yang D, Li D, Yang Y. UCP-2 is involved in angiotensin-II-induced abdominal aortic aneurysm in apolipoprotein E-knockout mice. PLoS One 2017; 12:e0179743. [PMID: 28683125 PMCID: PMC5500278 DOI: 10.1371/journal.pone.0179743] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2017] [Accepted: 06/02/2017] [Indexed: 02/07/2023] Open
Abstract
UCP-2 shows an important role in modulating of mitochondrial membrane potential and cell apoptosis. Whether or not UCP-2 could been a critical factor in preventing AAA formation is not known. We report that UCP-2 protein and mRNA expression were significantly higher in Ang-Ⅱ-induced AAA of mice. The incident rate of AAA in UCP-2-/-ApoE-/- mice after Ang-Ⅱtreatment was higher than the rate in the UCP-2+/+ApoE-/- mice. The abdominal aorta from UCP-2-/-ApoE-/- mice showed the medial hypertrophy, fragmentation of elastic lamellas and depletion of α-SMA. The NADPH oxidase activity and level of MDA was significantly higher in UCP-2-/-ApoE-/- mice than UCP-2+/+ApoE-/- or WT mice. Besides, the SOD activity is increased in UCP-2+/+ApoE-/- mice as compared with WT mice, whereas deficiency of UCP-2 decreased the increasing SOD activity in Ang-Ⅱ treated ApoE-/- mice. UCP-2 knockout up-regulated the MMP2 and MMP9 expression in aortic aneurysm. Ang-Ⅱ induced apoptosis of VSMCs was increased in UCP-2-/-ApoE-/- mice. And the expression of eNOS in vascular tissue from UCP-2-/-ApoE-/- mice is lower than WT and UCP-2+/+ApoE-/- mice. This study provides a mechanism by which UCP-2, via anti-oxidants and anti-apoptosis, participates in the preventing of AAA formation.
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MESH Headings
- Actins/genetics
- Actins/metabolism
- Angiotensin II/pharmacology
- Animals
- Aorta, Abdominal/drug effects
- Aorta, Abdominal/metabolism
- Aorta, Abdominal/pathology
- Aortic Aneurysm, Abdominal/chemically induced
- Aortic Aneurysm, Abdominal/genetics
- Aortic Aneurysm, Abdominal/metabolism
- Aortic Aneurysm, Abdominal/pathology
- Apolipoproteins E/deficiency
- Apolipoproteins E/genetics
- Apoptosis/drug effects
- Endothelial Cells/drug effects
- Endothelial Cells/metabolism
- Endothelial Cells/pathology
- Gene Expression Regulation
- Malondialdehyde/metabolism
- Matrix Metalloproteinase 2/genetics
- Matrix Metalloproteinase 2/metabolism
- Matrix Metalloproteinase 9/genetics
- Matrix Metalloproteinase 9/metabolism
- Membrane Potential, Mitochondrial/drug effects
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- NADPH Oxidases/genetics
- NADPH Oxidases/metabolism
- Nitric Oxide Synthase Type III/genetics
- Nitric Oxide Synthase Type III/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Signal Transduction
- Superoxide Dismutase/genetics
- Superoxide Dismutase/metabolism
- Uncoupling Protein 2/deficiency
- Uncoupling Protein 2/genetics
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Affiliation(s)
- Peng Yan
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
| | - Ken Chen
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
| | - Qiang Wang
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
| | - Dachun Yang
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
| | - De Li
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
| | - Yongjian Yang
- Department of Cardiology, Chengdu Military General Hospital, Chengdu, Sichuan, P.R. China
- * E-mail:
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103
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de Gelidi S, Tozzi G, Bucchi A. The effect of thickness measurement on numerical arterial models. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2017; 76:1205-1215. [DOI: 10.1016/j.msec.2017.02.123] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Revised: 02/03/2017] [Accepted: 02/24/2017] [Indexed: 10/20/2022]
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104
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Astaneh AV, Urban MW, Aquino W, Greenleaf JF, Guddati MN. Arterial waveguide model for shear wave elastography: implementation andin vitrovalidation. Phys Med Biol 2017; 62:5473-5494. [DOI: 10.1088/1361-6560/aa6ee3] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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105
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Kehl S, Gee MW. Calibration of parameters for cardiovascular models with application to arterial growth. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017; 33:e2822. [PMID: 27501849 DOI: 10.1002/cnm.2822] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 07/31/2016] [Accepted: 08/01/2016] [Indexed: 06/06/2023]
Abstract
We present a computational framework for the calibration of parameters describing cardiovascular models with a focus on the application of growth of abdominal aortic aneurysms (AAA). The growth rate in this sort of pathology is considered a critical parameter in the risk management and is an essential indicator for the assessment of surveillance intervals. Parameters describing growth of AAAs are not measurable directly and need to be estimated from available data often given by medical imaging technologies. Registration procedures often applied in standard workflows of parameter identification to extract the image encoded information are a source of significant systematic error. The concept of surface currents provides means to effectively avoid this source of errors by establishing a mathematical framework to compare surface information, directly accessible from image data. By utilizing this concept it is possible to inversely estimate growth parameters using sophisticated numerical models of AAAs from measurements available as surface information. In this work we present a framework to obtain spatial distributions of parameters governing growth of arterial tissue, and we show how the use of surface currents can significantly improve the results. We further present the application to patient specific follow-up data resulting in a spatial map of volumetric growth rates enabling, for the first time, prediction of further AAA expansion.
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Affiliation(s)
- Sebastian Kehl
- Mechanics and High Performance Computing Group, Technische Universität München, Parkring 35, Garching bei, 85748, München
| | - Michael W Gee
- Mechanics and High Performance Computing Group, Technische Universität München, Parkring 35, Garching bei, 85748, München
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106
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Nauta FJH, de Beaufort HWL, Conti M, Marconi S, Kamman AV, Ferrara A, van Herwaarden JA, Moll FL, Auricchio F, Trimarchi S. Impact of thoracic endovascular aortic repair on radial strain in an ex vivo porcine model. Eur J Cardiothorac Surg 2017; 51:783-789. [PMID: 28043989 DOI: 10.1093/ejcts/ezw393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 11/01/2016] [Indexed: 11/14/2022] Open
Abstract
Objectives To quantify the impact of thoracic endovascular aortic repair (TEVAR) on radial aortic strain with the aim of elucidating stent-graft-induced stiffening and complications. Methods Twenty fresh thoracic porcine aortas were connected to a mock circulatory loop driven by a centrifugal flow pump. A high-definition camera captured diameters at five different pressure levels (100, 120, 140, 160, and 180 mmHg), before and after TEVAR. Three oversizing groups were created: 0-9% ( n = 7), 10-19% ( n = 6), and 20-29% ( n = 6). Radial strain (or deformation) derived from diameter amplitude divided by baseline diameter at 100 mmHg. Uniaxial tensile testing evaluated Young's moduli of the specimens. Results Radial strain was reduced after TEVAR within the stented segment by 49.4 ± 24.0% ( P < 0.001). As result, a strain mismatch was observed between the stented segment and the proximal non-stented segment (7.0 ± 2.5% vs 11.8 ± 3.9%, P < 0.001), whereas the distal non-stented segment was unaffected ( P = 0.99). Stent-graft oversizing did not significantly affect the amount of strain reduction ( P = 0.30). Tensile testing showed that the thoracic aortas tended to be more elastic proximally than distally ( P = 0.11). Conclusions TEVAR stiffened the thoracic aorta by 2-fold. Such segmental stiffening may diminish the Windkessel function considerably and might be associated with TEVAR-related complications, including stent-graft-induced dissection and aneurysmal dilatation. These data may have implications for future stent-graft design, in particular for TEVAR of the highly compliant proximal thoracic aorta.
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Affiliation(s)
- Foeke J H Nauta
- Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy.,Department of Vascular Surgery, University Medical Center Utrecht, The Netherlands
| | - Hector W L de Beaufort
- Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy.,Department of Vascular Surgery, University Medical Center Utrecht, The Netherlands
| | - Michele Conti
- Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy
| | - Stefania Marconi
- Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy
| | - Arnoud V Kamman
- Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy.,Department of Vascular Surgery, University Medical Center Utrecht, The Netherlands
| | - Anna Ferrara
- Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy
| | | | - Frans L Moll
- Department of Vascular Surgery, University Medical Center Utrecht, The Netherlands
| | - Ferdinando Auricchio
- Department of Civil Engineering and Architecture, Beta-lab, University of Pavia, Italy
| | - Santi Trimarchi
- Thoracic Aortic Research Center, Policlinico San Donato IRCCS, University of Milan, Italy
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107
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Subramaniam DR, Stoddard WA, Mortensen KH, Ringgaard S, Trolle C, Gravholt CH, Gutmark EJ, Mylavarapu G, Backeljauw PF, Gutmark-Little I. Continuous measurement of aortic dimensions in Turner syndrome: a cardiovascular magnetic resonance study. J Cardiovasc Magn Reson 2017; 19:20. [PMID: 28231838 PMCID: PMC5324249 DOI: 10.1186/s12968-017-0336-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2017] [Accepted: 02/02/2017] [Indexed: 01/15/2023] Open
Abstract
BACKGROUND Severity of thoracic aortic disease in Turner syndrome (TS) patients is currently described through measures of aorta size and geometry at discrete locations. The objective of this study is to develop an improved measurement tool that quantifies changes in size and geometry over time, continuously along the length of the thoracic aorta. METHODS Cardiovascular magnetic resonance (CMR) scans for 15 TS patients [41 ± 9 years (mean age ± standard deviation (SD))] were acquired over a 10-year period and compared with ten healthy gender and age-matched controls. Three-dimensional aortic geometries were reconstructed, smoothed and clipped, which was followed by identification of centerlines and planes normal to the centerlines. Geometric variables, including maximum diameter and cross-sectional area, were evaluated continuously along the thoracic aorta. Distance maps were computed for TS and compared to the corresponding maps for controls, to highlight any asymmetry and dimensional differences between diseased and normal aortae. Furthermore, a registration scheme was proposed to estimate localized changes in aorta geometry between visits. The estimated maximum diameter from the continuous method was then compared with corresponding manual measurements at 7 discrete locations for each visit and for changes between visits. RESULTS Manual measures at the seven positions and the corresponding continuous measurements of maximum diameter for all visits considered, correlated highly (R-value = 0.77, P < 0.01). There was good agreement between manual and continuous measurement methods for visit-to-visit changes in maximum diameter. The continuous method was less sensitive to inter-user variability [0.2 ± 2.3 mm (mean difference in diameters ± SD)] and choice of smoothing software [0.3 ± 1.3 mm]. Aortic diameters were larger in TS than controls in the ascending [TS: 13.4 ± 2.1 mm (mean distance ± SD), Controls: 12.6 ± 1 mm] and descending [TS: 10.2 ± 1.3 mm (mean distance ± SD), Controls: 9.5 ± 0.9 mm] thoracic aorta as observed from the distance maps. CONCLUSIONS An automated methodology is presented that enables rapid and precise three-dimensional measurement of thoracic aortic geometry, which can serve as an improved tool to define disease severity and monitor disease progression. TRIAL REGISTRATION ClinicalTrials.gov Identifier - NCT01678274 . Registered - 08.30.2012.
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Affiliation(s)
| | - William A. Stoddard
- Department of Aerospace Engineering and Engineering Mechanics, CEAS, University of Cincinnati, Cincinnati, OH USA
| | - Kristian H. Mortensen
- Cardio-respiratory Unit, Great Ormond Street Hospital for Children NHS Foundation Trust, London, UK
| | - Steffen Ringgaard
- Institute for Clinical Medicine, Aarhus University, Aarhus N, Denmark
| | - Christian Trolle
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus C, Denmark
| | - Claus H. Gravholt
- Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus C, Denmark
- Department of Molecular Medicine, Aarhus University Hospital, Aarhus N, Denmark
| | - Ephraim J. Gutmark
- Department of Aerospace Engineering and Engineering Mechanics, CEAS, University of Cincinnati, Cincinnati, OH USA
- UC Department of Otolaryngology, Head and Neck Surgery, Cincinnati, OH USA
| | - Goutham Mylavarapu
- Division of Pulmonary Medicine, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH USA
| | - Philippe F. Backeljauw
- Division of Endocrinology, Department of Pediatrics, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229 USA
| | - Iris Gutmark-Little
- Division of Endocrinology, Department of Pediatrics, Cincinnati Children’s Hospital Medical Center, Cincinnati, OH 45229 USA
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108
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Rausch MK, Zöllner AM, Genet M, Baillargeon B, Bothe W, Kuhl E. A virtual sizing tool for mitral valve annuloplasty. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2017; 33:10.1002/cnm.2788. [PMID: 27028496 PMCID: PMC5289896 DOI: 10.1002/cnm.2788] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Revised: 02/16/2016] [Accepted: 03/19/2016] [Indexed: 05/08/2023]
Abstract
Functional mitral regurgitation, a backward leakage of the mitral valve, is a result of left ventricular growth and mitral annular dilatation. Its gold standard treatment is mitral annuloplasty, the surgical reduction in mitral annular area through the implantation of annuloplasty rings. Recurrent regurgitation rates may, however, be as high as 30% and more. While the degree of annular downsizing has been linked to improved long-term outcomes, too aggressive downsizing increases the risk of ring dehiscences and significantly impairs repair durability. Here, we prototype a virtual sizing tool to quantify changes in annular dimensions, surgically induced tissue strains, mitral annular stretches, and suture forces in response to mitral annuloplasty. We create a computational model of dilated cardiomyopathy onto which we virtually implant annuloplasty rings of different sizes. Our simulations confirm the common intuition that smaller rings are more invasive to the surrounding tissue, induce higher strains, and require larger suture forces than larger rings: The total suture force was 2.2 N for a 24-mm ring, 1.9 N for a 28-mm ring, and 0.8 N for a 32-mm ring. Our model predicts the highest risk of dehiscence in the septal and postero-lateral annulus where suture forces are maximal. These regions co-localize with regional peaks in myocardial strain and annular stretch. Our study illustrates the potential of realistic predictive simulations in cardiac surgery to identify areas at risk for dehiscence, guide the selection of ring size and shape, rationalize the design of smart annuloplasty rings and, ultimately, improve long-term outcomes after surgical mitral annuloplasty. Copyright © 2016 John Wiley & Sons, Ltd.
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Affiliation(s)
- Manuel K. Rausch
- Department of Biomedical Engineering, Yale University, New Haven, CT 06511, USA
| | - Alexander M. Zöllner
- Department of Mechanical Engineering, Stanford University, Stanford, CA 94305, USA
| | - Martin Genet
- Laboratoire de Mécanique des Solides CNRS-UMR 7649, Ecole Polytechnique, 91128 Palaiseau, France
| | | | - Wolfgang Bothe
- University Heart Center Freiburg, 79106 Freiburg, Germany
| | - E. Kuhl
- Departments of Mechanical Engineering, Bioengineering and Cardiothoracic Surgery, Stanford University, Stanford, CA 94305, USA
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109
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Cyron CJ, Humphrey JD. Growth and Remodeling of Load-Bearing Biological Soft Tissues. MECCANICA 2017; 52:645-664. [PMID: 28286348 PMCID: PMC5342900 DOI: 10.1007/s11012-016-0472-5] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The past two decades reveal a growing role of continuum biomechanics in understanding homeostasis, adaptation, and disease progression in soft tissues. In this paper, we briefly review the two primary theoretical approaches for describing mechano-regulated soft tissue growth and remodeling on the continuum level as well as hybrid approaches that attempt to combine the advantages of these two approaches while avoiding their disadvantages. We also discuss emerging concepts, including that of mechanobiological stability. Moreover, to motivate and put into context the different theoretical approaches, we briefly review findings from mechanobiology that show the importance of mass turnover and the prestressing of both extant and new extracellular matrix in most cases of growth and remodeling. For illustrative purposes, these concepts and findings are discussed, in large part, within the context of two load-bearing, collagen dominated soft tissues - tendons/ligaments and blood vessels. We conclude by emphasizing further examples, needs, and opportunities in this exciting field of modeling soft tissues.
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Affiliation(s)
- C J Cyron
- Institute for Computational Mechanics, Technische Universität München, Garching, Germany
| | - J D Humphrey
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA; Vascular Biology and Therapeutics Program, Yale School of Medicine, New Haven, CT, USA
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110
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Long Ko JK, Liu RW, Ma D, Shi L, Ho Yu SC, Wang D. Pulsatile hemodynamics in patient-specific thoracic aortic dissection models constructed from computed tomography angiography. JOURNAL OF X-RAY SCIENCE AND TECHNOLOGY 2017; 25:233-245. [PMID: 28234275 DOI: 10.3233/xst-17256] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
PURPOSE Thoracic aortic dissection (TAD) is considered one of the most catastrophic and non-traumatic cardiovascular diseases associated with high morbidity and mortality rates in clinical treatment. The purpose of this paper is to investigate the pulsatile hemodynamics changes throughout a cardiac cycle in a Stanford Type B TAD model with the aid of computational fluid dynamics (CFD) method. METHODS A patient-specific dissected aorta geometry was reconstructed from the three-dimensional (3D) computed tomography angiography (CTA) scanning. The realistic time-dependent pulsatile boundary conditions were prescribed for our 3D patient-specific TAD model. Blood was considered to be an incompressible, Newtonian fluid. The aortic wall was assumed to be rigid, and a no-slip boundary condition was applied at the wall. CFD simulations were processed using the finite volume (FV) method to investigate the pulsatile hemodynamics in terms of blood flow velocity, aortic wall pressure, wall shear stress and flow vorticity. In the experiments, blood velocity, pressure, wall shear stress and vorticity distributions were analyzed qualitatively and quantitatively. RESULTS The experimental results demonstrated a high wall shear stress and strong vertical flow at dissection initiation. The results also indicated that wall shear progressed along the false lumen, which is a possible cause of blood flow between aortic wall layers.
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Affiliation(s)
- Jacky Ka Long Ko
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
| | - Ryan Wen Liu
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
| | - Diya Ma
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
| | - Lin Shi
- Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
- Chow Yuk Ho Technology Center for Innovative Medicine, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
| | - Simon Chun Ho Yu
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
| | - Defeng Wang
- Department of Imaging and Interventional Radiology, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
- Research Center for Medical Image Computing, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong
- Shenzhen Research Institute, The Chinese University of Hong Kong, Shenzhen, China
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111
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Comellas E, Gasser TC, Bellomo FJ, Oller S. A homeostatic-driven turnover remodelling constitutive model for healing in soft tissues. J R Soc Interface 2016; 13:rsif.2015.1081. [PMID: 27009177 DOI: 10.1098/rsif.2015.1081] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Accepted: 03/01/2016] [Indexed: 01/08/2023] Open
Abstract
Remodelling of soft biological tissue is characterized by interacting biochemical and biomechanical events, which change the tissue's microstructure, and, consequently, its macroscopic mechanical properties. Remodelling is a well-defined stage of the healing process, and aims at recovering or repairing the injured extracellular matrix. Like other physiological processes, remodelling is thought to be driven by homeostasis, i.e. it tends to re-establish the properties of the uninjured tissue. However, homeostasis may never be reached, such that remodelling may also appear as a continuous pathological transformation of diseased tissues during aneurysm expansion, for example. A simple constitutive model for soft biological tissues that regards remodelling as homeostatic-driven turnover is developed. Specifically, the recoverable effective tissue damage, whose rate is the sum of a mechanical damage rate and a healing rate, serves as a scalar internal thermodynamic variable. In order to integrate the biochemical and biomechanical aspects of remodelling, the healing rate is, on the one hand, driven by mechanical stimuli, but, on the other hand, subjected to simple metabolic constraints. The proposed model is formulated in accordance with continuum damage mechanics within an open-system thermodynamics framework. The numerical implementation in an in-house finite-element code is described, particularized for Ogden hyperelasticity. Numerical examples illustrate the basic constitutive characteristics of the model and demonstrate its potential in representing aspects of remodelling of soft tissues. Simulation results are verified for their plausibility, but also validated against reported experimental data.
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Affiliation(s)
- Ester Comellas
- International Center for Numerical Methods in Engineering (CIMNE), Campus Nord UPC, Building C1, c/Gran Capita s/n, 08034 Barcelona, Spain Department of Strength of Materials and Structural Engineering, ETSECCPB, Universitat Politcnica de Catalunya, Barcelona Tech (UPC), Campus Nord, Building C1, c/Jordi Girona 1-3, 08034 Barcelona, Spain
| | - T Christian Gasser
- Department of Solid Mechanics, School of Engineering Sciences, KTH Royal Institute of Technology, Teknikringen 8, 100 44 Stockholm, Sweden
| | - Facundo J Bellomo
- INIQUI (CONICET), Faculty of Engineering, National University of Salta, Av. Bolivia 5150, 4400 Salta, Argentina
| | - Sergio Oller
- International Center for Numerical Methods in Engineering (CIMNE), Campus Nord UPC, Building C1, c/Gran Capita s/n, 08034 Barcelona, Spain Department of Strength of Materials and Structural Engineering, ETSECCPB, Universitat Politcnica de Catalunya, Barcelona Tech (UPC), Campus Nord, Building C1, c/Jordi Girona 1-3, 08034 Barcelona, Spain
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112
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Gültekin O, Dal H, Holzapfel GA. A phase-field approach to model fracture of arterial walls: Theory and finite element analysis. COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING 2016; 312:542-566. [PMID: 31649409 PMCID: PMC6812523 DOI: 10.1016/j.cma.2016.04.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
This study uses a recently developed phase-field approach to model fracture of arterial walls with an emphasis on aortic tissues. We start by deriving the regularized crack surface to overcome complexities inherent in sharp crack discontinuities, thereby relaxing the acute crack surface topology into a diffusive one. In fact, the regularized crack surface possesses the property of Gamma-Convergence, i.e. the sharp crack topology is restored with a vanishing length-scale parameter. Next, we deal with the continuous formulation of the variational principle for the multi-field problem manifested through the deformation map and the crack phase-field at finite strains which leads to the Euler-Lagrange equations of the coupled problem. In particular, the coupled balance equations derived render the evolution of the crack phase-field and the balance of linear momentum. As an important aspect of the continuum formulation we consider an invariant-based anisotropic constitutive model which is additively decomposed into an isotropic part for the ground matrix and an exponential anisotropic part for the two families of collagen fibers embedded in the ground matrix. In addition we propose a novel energy-based anisotropic failure criterion which regulates the evolution of the crack phase-field. The coupled problem is solved using a one-pass operator-splitting algorithm composed of a mechanical predictor step (solved for the frozen crack phase-field parameter) and a crack evolution step (solved for the frozen deformation map); a history field governed by the failure criterion is successively updated. Subsequently, a conventional Galerkin procedure leads to the weak forms of the governing differential equations for the physical problem. Accordingly, we provide the discrete residual vectors and a corresponding linearization yields the element matrices for the two sub-problems. Finally, we demonstrate the numerical performance of the crack phase-field model by simulating uniaxial extension and simple shear fracture tests performed on specimens obtained from a human aneurysmatic thoracic aorta. Model parameters are obtained by fitting the set of novel experimental data to the predicted model response; the finite element results agree favorably with the experimental findings.
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Affiliation(s)
- Osman Gültekin
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/II, 8010, Graz, Austria
| | - Hüsnü Dal
- Department of Mechanical Engineering, Middle East Technical University, Dumlupınar Bulvarı No. 1, Çankaya, 06800, Ankara, Turkey
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16/II, 8010, Graz, Austria
- Corresponding author. (G.A. Holzapfel)
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113
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Cook DD, Robertson DJ. The generic modeling fallacy: Average biomechanical models often produce non-average results! J Biomech 2016; 49:3609-3615. [PMID: 27770999 DOI: 10.1016/j.jbiomech.2016.10.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Revised: 09/29/2016] [Accepted: 10/02/2016] [Indexed: 12/17/2022]
Abstract
Computational biomechanics models constructed using nominal or average input parameters are often assumed to produce average results that are representative of a target population of interest. To investigate this assumption a stochastic Monte Carlo analysis of two common biomechanical models was conducted. Consistent discrepancies were found between the behavior of average models and the average behavior of the population from which the average models׳ input parameters were derived. More interestingly, broadly distributed sets of non-average input parameters were found to produce average or near average model behaviors. In other words, average models did not produce average results, and models that did produce average results possessed non-average input parameters. These findings have implications on the prevalent practice of employing average input parameters in computational models. To facilitate further discussion on the topic, the authors have termed this phenomenon the "Generic Modeling Fallacy". The mathematical explanation of the Generic Modeling Fallacy is presented and suggestions for avoiding it are provided. Analytical and empirical examples of the Generic Modeling Fallacy are also given.
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Affiliation(s)
- Douglas D Cook
- Division of Engineering, New York University - Abu Dhabi, Abu Dhabi, United Arab Emirates
| | - Daniel J Robertson
- Division of Engineering, New York University - Abu Dhabi, Abu Dhabi, United Arab Emirates.
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Luo Y, Duprey A, Avril S, Lu J. Characteristics of thoracic aortic aneurysm rupture in vitro. Acta Biomater 2016; 42:286-295. [PMID: 27395826 DOI: 10.1016/j.actbio.2016.06.036] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 06/13/2016] [Accepted: 06/28/2016] [Indexed: 10/21/2022]
Abstract
UNLABELLED Ascending thoracic aortic aneurysms (ATAAs) are focal dilatations in the aorta that are prone to rupture or dissection. To accurately evaluate the rupture risk, one must know the local mechanical conditions at the rupture site and understand how rupture is triggered in a layered fibrous media. A challenge facing experimental studies of ATAA rupture is that the ATAA tissue is highly heterogeneous; experimental protocols that operate under the premise of tissue homogeneity will have difficulty delineating the location conditions. In this work, we employed a previously established pointwise identification method to characterize wall stress, strain, and property distributions to a sub-millimeter resolution. Based on the acquired field data, we obtained the local mechanical properties at the rupture site in nine ATAA tissue samples. The rupture stress, ultimate strain, energy density, and the toughness of the tested samples were also reported. Our results show that the direction of the rupture is aligned with the direction of maximum stiffness, indicating that higher stiffness is not always related to higher strength. It was also found that the rupture generally occurs at a location of highest stored energy. As a higher stiffness and higher strain energy indicate a larger recruitment of collagen fibers in the tissue at the location and along the direction of rupture, the recruitment of collagen fibers in the deformation of the tissue is probably essential in ATAA rupture. STATEMENT OF SIGNIFICANCE A major challenge in the experimental study of aneurysm properties is that the tissues are heterogeneous. When the specimens are not reasonably homogeneous, traditional tests that work under the premise of tissue homogeneity cannot reliably delineate the local conditions at the rupture site. In this work, we investigated the local characteristics of rupture of human ascending aortic aneurysm tissue. We identified the stress, strain, and elastic properties to a submillimeter resolution. Based on the field values, we determined the local conditions - elastic properties, direction of maximum stiffness, stress, strain, energy consumption - at the rupture site. It was found that the tissues consistently cleave in the direction of the maximum stiffness, and generally occurs at the location of highest energy. Since a higher stiffness and higher strain energy indicate a larger recruitment of collagen fibers in the tissue at the location and along the direction of rupture, the work suggests that the recruitment of collagen fibers in the deformation of the tissue is probably essential in aneurysm rupture.
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116
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Dabiri Y, Ronsky J, Ali I, Basha A, Bhanji A, Narine K. Effects of Leaflet Design on Transvalvular Gradients of Bioprosthetic Heart Valves. Cardiovasc Eng Technol 2016; 7:363-373. [PMID: 27573761 DOI: 10.1007/s13239-016-0279-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 08/17/2016] [Indexed: 11/25/2022]
Abstract
Bioprosthetic aortic valves (BAVs) are becoming the prostheses of choice in heart valve replacement. The objective of this paper is to assess the effects of leaflet geometry on the mechanics and hemodynamics of BAVs in a fluid structure interaction model. The curvature and angle of leaflets were varied in 10 case studies whereby the following design parameters were altered: a circular arch, a line, and a parabola for the radial curvature, and a circular arch, a spline, and a parabola for the circumferential curvature. Six different leaflet angles (representative of the inclination of the leaflets toward the surrounding aortic wall) were analyzed. The 3-dimensional geometry of the models were created using SolidWorks, Pointwise was used for meshing, and Comsol Multiphysics was used for implicit finite element calculations. Realistic loading was enforced by considering the time-dependent strongly-coupled interaction between blood flow and leaflets. Higher mean pressure gradients as well as von Mises stresses were obtained with a parabolic or circular curvature for radial curvature or a parabolic or spline curvature for the circumferential curvature. A smaller leaflet angle was associated with a lower pressure gradient, and, a lower von Mises stress. The leaflet curvature and angle noticeably affected the speed of valve opening, and closing. When a parabola was used for circumferential or radial curvature, leaflets displacements were asymmetric, and they opened and closed more slowly. A circular circumferential leaflet curvature, a linear leaflet radial curvature, and leaflet inclination toward the surrounding aortic wall were associated with superior BAVs mechanics.
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Affiliation(s)
- Yaghoub Dabiri
- Libin Cardiovascular Institute of Alberta, Health Research Innovation Centre (HRIC), University of Calgary, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada
| | - Janet Ronsky
- Schulich School of Engineering, University of Calgary, Calgary, Canada
| | - Imtiaz Ali
- Libin Cardiovascular Institute of Alberta, Health Research Innovation Centre (HRIC), University of Calgary, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada
| | - Ameen Basha
- Cummings School of Medicine Health Sciences, University of Calgary, Calgary, Canada
| | - Alisha Bhanji
- Nanotechnology Engineering, University of Waterloo, Waterloo, Canada
| | - Kishan Narine
- Libin Cardiovascular Institute of Alberta, Health Research Innovation Centre (HRIC), University of Calgary, 3280 Hospital Drive NW, Calgary, AB, T2N 4Z6, Canada.
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117
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Modelling of residually stressed materials with application to AAA. J Mech Behav Biomed Mater 2016; 61:221-234. [DOI: 10.1016/j.jmbbm.2016.01.012] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/07/2016] [Accepted: 01/19/2016] [Indexed: 12/19/2022]
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118
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Li H, Lin K, Shahmirzadi D. FSI Simulations of Pulse Wave Propagation in Human Abdominal Aortic Aneurysm: The Effects of Sac Geometry and Stiffness. Biomed Eng Comput Biol 2016; 7:25-36. [PMID: 27478394 PMCID: PMC4951115 DOI: 10.4137/becb.s40094] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Revised: 06/28/2016] [Accepted: 07/02/2016] [Indexed: 11/21/2022] Open
Abstract
This study aims to quantify the effects of geometry and stiffness of aneurysms on the pulse wave velocity (PWV) and propagation in fluid–solid interaction (FSI) simulations of arterial pulsatile flow. Spatiotemporal maps of both the wall displacement and fluid velocity were generated in order to obtain the pulse wave propagation through fluid and solid media, and to examine the interactions between the two waves. The results indicate that the presence of abdominal aortic aneurysm (AAA) sac and variations in the sac modulus affect the propagation of the pulse waves both qualitatively (eg, patterns of change of forward and reflective waves) and quantitatively (eg, decreasing of PWV within the sac and its increase beyond the sac as the sac stiffness increases). The sac region is particularly identified on the spatiotemporal maps with a region of disruption in the wave propagation with multiple short-traveling forward/reflected waves, which is caused by the change in boundary conditions within the saccular region. The change in sac stiffness, however, is more pronounced on the wall displacement spatiotemporal maps compared to those of fluid velocity. We conclude that the existence of the sac can be identified based on the solid and fluid pulse waves, while the sac properties can also be estimated. This study demonstrates the initial findings in numerical simulations of FSI dynamics during arterial pulsations that can be used as reference for experimental and in vivo studies. Future studies are needed to demonstrate the feasibility of the method in identifying very mild sacs, which cannot be detected from medical imaging, where the material property degradation exists under early disease initiation.
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Affiliation(s)
- Han Li
- Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ, USA
| | - Kexin Lin
- Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ, USA
| | - Danial Shahmirzadi
- Department of Mechanical Engineering, Stevens Institute of Technology, Hoboken, NJ, USA
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119
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Courtial EJ, Fanton L, Orkisz M, Douek P, Huet L, Fulchiron R. Hyper-Viscoelastic Behavior of Healthy Abdominal Aorta. Ing Rech Biomed 2016. [DOI: 10.1016/j.irbm.2016.03.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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120
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Seyedsalehi S, Zhang L, Choi J, Baek S. Prior Distributions of Material Parameters for Bayesian Calibration of Growth and Remodeling Computational Model of Abdominal Aortic Wall. J Biomech Eng 2016. [PMID: 26201289 DOI: 10.1115/1.4031116] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
For the accurate prediction of the vascular disease progression, there is a crucial need for developing a systematic tool aimed toward patient-specific modeling. Considering the interpatient variations, a prior distribution of model parameters has a strong influence on computational results for arterial mechanics. One crucial step toward patient-specific computational modeling is to identify parameters of prior distributions that reflect existing knowledge. In this paper, we present a new systematic method to estimate the prior distribution for the parameters of a constrained mixture model using previous biaxial tests of healthy abdominal aortas (AAs). We investigate the correlation between the estimated parameters for each constituent and the patient's age and gender; however, the results indicate that the parameters are correlated with age only. The parameters are classified into two groups: Group-I in which the parameters ce, ck1, ck2, cm2,Ghc, and ϕe are correlated with age, and Group-II in which the parameters cm1, Ghm, G1e, G2e, and α are not correlated with age. For the parameters in Group-I, we used regression associated with age via linear or inverse relations, in which their prior distributions provide conditional distributions with confidence intervals. For Group-II, the parameter estimated values were subjected to multiple transformations and chosen if the transformed data had a better fit to the normal distribution than the original. This information improves the prior distribution of a subject-specific model by specifying parameters that are correlated with age and their transformed distributions. Therefore, this study is a necessary first step in our group's approach toward a Bayesian calibration of an aortic model. The results from this study will be used as the prior information necessary for the initialization of Bayesian calibration of a computational model for future applications.
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121
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Tonar Z, Tomášek P, Loskot P, Janáček J, Králíčková M, Witter K. Vasa vasorum in the tunica media and tunica adventitia of the porcine aorta. Ann Anat 2016; 205:22-36. [DOI: 10.1016/j.aanat.2016.01.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 11/14/2015] [Accepted: 01/05/2016] [Indexed: 02/07/2023]
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123
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Conlisk N, Geers AJ, McBride OMB, Newby DE, Hoskins PR. Patient-specific modelling of abdominal aortic aneurysms: The influence of wall thickness on predicted clinical outcomes. Med Eng Phys 2016; 38:526-37. [PMID: 27056256 DOI: 10.1016/j.medengphy.2016.03.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Revised: 01/04/2016] [Accepted: 03/06/2016] [Indexed: 10/22/2022]
Abstract
Rupture of abdominal aortic aneurysms (AAAs) is linked to aneurysm morphology. This study investigates the influence of patient-specific (PS) AAA wall thickness on predicted clinical outcomes. Eight patients under surveillance for AAAs were selected from the MA(3)RS clinical trial based on the complete absence of intraluminal thrombus. Two finite element (FE) models per patient were constructed; the first incorporated variable wall thickness from CT (PS_wall), and the second employed a 1.9mm uniform wall (Uni_wall). Mean PS wall thickness across all patients was 1.77±0.42mm. Peak wall stress (PWS) for PS_wall and Uni_wall models was 0.6761±0.3406N/mm(2) and 0.4905±0.0850N/mm(2), respectively. In 4 out of 8 patients the Uni_wall underestimated stress by as much as 55%; in the remaining cases it overestimated stress by up to 40%. Rupture risk more than doubled in 3 out of 8 patients when PS_wall was considered. Wall thickness influenced the location and magnitude of PWS as well as its correlation with curvature. Furthermore, the volume of the AAA under elevated stress increased significantly in AAAs with higher rupture risk indices. This highlights the sensitivity of standard rupture risk markers to the specific wall thickness strategy employed.
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Affiliation(s)
- Noel Conlisk
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, EH16 4TJ, UK; Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, EH16 4TJ, UK.
| | - Arjan J Geers
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, EH16 4TJ, UK
| | - Olivia M B McBride
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, EH16 4TJ, UK
| | - David E Newby
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, EH16 4TJ, UK; Clinical Research Imaging Centre, The University of Edinburgh, Edinburgh, EH16 4TJ, UK
| | - Peter R Hoskins
- Centre for Cardiovascular Science, The University of Edinburgh, Edinburgh, EH16 4TJ, UK
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Phan L, Courchaine K, Azarbal A, Vorp D, Grimm C, Rugonyi S. A Geodesics-Based Surface Parameterization to Assess Aneurysm Progression. J Biomech Eng 2016; 138:054503. [PMID: 27003915 DOI: 10.1115/1.4033082] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Indexed: 12/15/2022]
Abstract
Abdominal aortic aneurysm (AAA) intervention and surveillance is currently based on maximum transverse diameter, even though it is recognized that this might not be the best strategy. About 10% of patients with small AAA transverse diameters, for whom intervention is not considered, still rupture; while patients with large AAA transverse diameters, for whom intervention would have been recommended, have stable aneurysms that do not rupture. While maximum transverse diameter is easy to measure and track in clinical practice, one of its main drawbacks is that it does not represent the whole AAA and rupture seldom occurs in the region of maximum transverse diameter. By following maximum transverse diameter alone clinicians are missing information on the shape change dynamics of the AAA, and clues that could lead to better patient care. We propose here a method to register AAA surfaces that were obtained from the same patient at different time points. Our registration method could be used to track the local changes of the patient-specific AAA. To achieve registration, our procedure uses a consistent parameterization of the AAA surfaces followed by strain relaxation. The main assumption of our procedure is that growth of the AAA occurs in such a way that surface strains are smoothly distributed, while regions of small and large surface growth can be differentiated. The proposed methodology has the potential to unravel different patterns of AAA growth that could be used to stratify patient risks.
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125
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Valentin A, Notaro D, Zunino P, Allen R, Ambrosi D, Wang Y, Robertson AM. Theory and application of arterial tissue in-host remodelling. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2016; 2015:1869-72. [PMID: 26736646 DOI: 10.1109/embc.2015.7318746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A central therapeutic goal in many applications of modern Biomedicine is the reconstruction of the diseased arterial sections via robust and viable tissue equivalents. In-host remodelling is an emerging technology that exploits the remodelling ability of the host to regenerate tissue. We develop a general theoretical framework of growth and remodeling of arterial tissue starting from a synthetic, degradable, acellularized graft and we demonstrate the potential of mechanistic models to guide the development and assisting in the design of arterial tissue engineered constructs.
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126
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Nicolás M, Peña E, Malvè M, Martínez M. Mathematical modeling of the fibrosis process in the implantation of inferior vena cava filters. J Theor Biol 2015; 387:228-40. [DOI: 10.1016/j.jtbi.2015.09.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2015] [Revised: 09/13/2015] [Accepted: 09/17/2015] [Indexed: 11/26/2022]
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127
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Farías JG, Herrera EA, Carrasco-Pozo C, Sotomayor-Zárate R, Cruz G, Morales P, Castillo RL. Pharmacological models and approaches for pathophysiological conditions associated with hypoxia and oxidative stress. Pharmacol Ther 2015; 158:1-23. [PMID: 26617218 DOI: 10.1016/j.pharmthera.2015.11.006] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hypoxia is the failure of oxygenation at the tissue level, where the reduced oxygen delivered is not enough to satisfy tissue demands. Metabolic depression is the physiological adaptation associated with reduced oxygen consumption, which evidently does not cause any harm to organs that are exposed to acute and short hypoxic insults. Oxidative stress (OS) refers to the imbalance between the generation of reactive oxygen species (ROS) and the ability of endogenous antioxidant systems to scavenge ROS, where ROS overwhelms the antioxidant capacity. Oxidative stress plays a crucial role in the pathogenesis of diseases related to hypoxia during intrauterine development and postnatal life. Thus, excessive ROS are implicated in the irreversible damage to cell membranes, DNA, and other cellular structures by oxidizing lipids, proteins, and nucleic acids. Here, we describe several pathophysiological conditions and in vivo and ex vivo models developed for the study of hypoxic and oxidative stress injury. We reviewed existing literature on the responses to hypoxia and oxidative stress of the cardiovascular, renal, reproductive, and central nervous systems, and discussed paradigms of chronic and intermittent hypobaric hypoxia. This systematic review is a critical analysis of the advantages in the application of some experimental strategies and their contributions leading to novel pharmacological therapies.
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Affiliation(s)
- Jorge G Farías
- Facultad de Ingeniería y Ciencias, Departamento de Ingeniería Química, Universidad de la Frontera, Casilla 54-D, Temuco, Chile
| | - Emilio A Herrera
- Programa de Fisiopatología, ICBM, Facultad de Medicina, Universidad de Chile, Chile; International Center for Andean Studies (INCAS), Universidad de Chile, Chile
| | | | - Ramón Sotomayor-Zárate
- Centro de Neurobiología y Plasticidad Cerebral (CNPC), Instituto de Fisiología, Facultad de Ciencias, Universidad de Valparaíso, Chile
| | - Gonzalo Cruz
- Centro de Neurobiología y Plasticidad Cerebral (CNPC), Instituto de Fisiología, Facultad de Ciencias, Universidad de Valparaíso, Chile
| | - Paola Morales
- Programa de Farmacología Molecular y Clínica, ICBM, Facultad de Medicina, Universidad de Chile, Chile
| | - Rodrigo L Castillo
- Programa de Fisiopatología, ICBM, Facultad de Medicina, Universidad de Chile, Chile.
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128
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Volokh KY, Aboudi J. Aneurysm strength can decrease under calcification. J Mech Behav Biomed Mater 2015; 57:164-74. [PMID: 26717251 DOI: 10.1016/j.jmbbm.2015.11.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 11/04/2015] [Accepted: 11/11/2015] [Indexed: 12/18/2022]
Abstract
Aneurysms are abnormal dilatations of vessels in the vascular system that are prone to rupture. Prediction of the aneurysm rupture is a challenging and unsolved problem. Various factors can lead to the aneurysm rupture and, in the present study, we examine the effect of calcification on the aneurysm strength by using micromechanical modeling. The calcified tissue is considered as a composite material in which hard calcium particles are embedded in a hyperelastic soft matrix. Three experimentally calibrated constitutive models incorporating a failure description are used for the matrix representation. Two constitutive models describe the aneurysmal arterial wall and the third one - the intraluminal thrombus. The stiffness and strength of the calcified tissue are simulated in uniaxial tension under the varying amount of calcification, i.e. the relative volume of the hard inclusion within the periodic unit cell. In addition, the triaxiality of the stress state, which can be a trigger for the cavitation instability, is tracked. Results of the micromechanical simulation show an increase of the stiffness and a possible decrease of the strength of the calcified tissue as compared to the non-calcified one. The obtained results suggest that calcification (i.e. the presence of hard particles) can significantly affect the stiffness and strength of soft tissue. The development of refined experimental techniques that will allow for the accurate quantitative assessment of calcification is desirable.
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Affiliation(s)
| | - Jacob Aboudi
- Faculty of Engineering, Tel Aviv University, Israel.
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129
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Berg P, Roloff C, Beuing O, Voss S, Sugiyama SI, Aristokleous N, Anayiotos AS, Ashton N, Revell A, Bressloff NW, Brown AG, Jae Chung B, Cebral JR, Copelli G, Fu W, Qiao A, Geers AJ, Hodis S, Dragomir-Daescu D, Nordahl E, Bora Suzen Y, Owais Khan M, Valen-Sendstad K, Kono K, Menon PG, Albal PG, Mierka O, Münster R, Morales HG, Bonnefous O, Osman J, Goubergrits L, Pallares J, Cito S, Passalacqua A, Piskin S, Pekkan K, Ramalho S, Marques N, Sanchi S, Schumacher KR, Sturgeon J, Švihlová H, Hron J, Usera G, Mendina M, Xiang J, Meng H, Steinman DA, Janiga G. The Computational Fluid Dynamics Rupture Challenge 2013—Phase II: Variability of Hemodynamic Simulations in Two Intracranial Aneurysms. J Biomech Eng 2015; 137:121008. [DOI: 10.1115/1.4031794] [Citation(s) in RCA: 67] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Indexed: 11/08/2022]
Abstract
With the increased availability of computational resources, the past decade has seen a rise in the use of computational fluid dynamics (CFD) for medical applications. There has been an increase in the application of CFD to attempt to predict the rupture of intracranial aneurysms, however, while many hemodynamic parameters can be obtained from these computations, to date, no consistent methodology for the prediction of the rupture has been identified. One particular challenge to CFD is that many factors contribute to its accuracy; the mesh resolution and spatial/temporal discretization can alone contribute to a variation in accuracy. This failure to identify the importance of these factors and identify a methodology for the prediction of ruptures has limited the acceptance of CFD among physicians for rupture prediction. The International CFD Rupture Challenge 2013 seeks to comment on the sensitivity of these various CFD assumptions to predict the rupture by undertaking a comparison of the rupture and blood-flow predictions from a wide range of independent participants utilizing a range of CFD approaches. Twenty-six groups from 15 countries took part in the challenge. Participants were provided with surface models of two intracranial aneurysms and asked to carry out the corresponding hemodynamics simulations, free to choose their own mesh, solver, and temporal discretization. They were requested to submit velocity and pressure predictions along the centerline and on specified planes. The first phase of the challenge, described in a separate paper, was aimed at predicting which of the two aneurysms had previously ruptured and where the rupture site was located. The second phase, described in this paper, aims to assess the variability of the solutions and the sensitivity to the modeling assumptions. Participants were free to choose boundary conditions in the first phase, whereas they were prescribed in the second phase but all other CFD modeling parameters were not prescribed. In order to compare the computational results of one representative group with experimental results, steady-flow measurements using particle image velocimetry (PIV) were carried out in a silicone model of one of the provided aneurysms. Approximately 80% of the participating groups generated similar results. Both velocity and pressure computations were in good agreement with each other for cycle-averaged and peak-systolic predictions. Most apparent “outliers” (results that stand out of the collective) were observed to have underestimated velocity levels compared to the majority of solutions, but nevertheless identified comparable flow structures. In only two cases, the results deviate by over 35% from the mean solution of all the participants. Results of steady CFD simulations of the representative group and PIV experiments were in good agreement. The study demonstrated that while a range of numerical schemes, mesh resolution, and solvers was used, similar flow predictions were observed in the majority of cases. To further validate the computational results, it is suggested that time-dependent measurements should be conducted in the future. However, it is recognized that this study does not include the biological aspects of the aneurysm, which needs to be considered to be able to more precisely identify the specific rupture risk of an intracranial aneurysm.
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Affiliation(s)
- Philipp Berg
- University of Magdeburg, Magdeburg 39106, Germany
| | | | - Oliver Beuing
- University Hospital of Magdeburg, Magdeburg 39120, Germany
| | - Samuel Voss
- University of Magdeburg, Magdeburg 39106, Germany
| | | | | | | | - Neil Ashton
- The University of Manchester, Manchester M60 1QD, UK
| | | | | | | | | | | | | | - Wenyu Fu
- Beijing University of Technology, Beijing 100124, China
| | - Aike Qiao
- Beijing University of Technology, Beijing 100124, China
| | | | - Simona Hodis
- Texas A&M University, Kingsville, TX 78363
- Mayo Clinic, Rochester, MN 55905
| | | | | | | | | | | | - Kenichi Kono
- Wakayama Rosai Hospital, Wakayama 640-8505, Japan
| | - Prahlad G. Menon
- Sun Yat-sen University—Carnegie Mellon University Joint Institute of Engineering, Pittsburgh, PA 15219
| | - Priti G. Albal
- Sun Yat-sen University—Carnegie Mellon University Joint Institute of Engineering, Pittsburgh, PA 15219
| | - Otto Mierka
- University of Dortmund, Dortmund 44227, Germany
| | | | | | | | - Jan Osman
- Charité-Universitätsmedizin Berlin, Berlin 13353, Germany
| | | | | | | | | | | | | | - Susana Ramalho
- blueCAPE Lda—CAE Solutions, Milharado 2665-305, Portugal
| | - Nelson Marques
- blueCAPE Lda—CAE Solutions, Milharado 2665-305, Portugal
| | | | | | | | | | | | - Gabriel Usera
- Universidad de la República, Montevideo 11300, Uruguay
| | | | - Jianping Xiang
- University at Buffalo—State University of New York, Buffalo, NY 14203
| | - Hui Meng
- University at Buffalo—State University of New York, Buffalo, NY 14203
| | | | - Gábor Janiga
- University of Magdeburg, Magdeburg 39106, Germany
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130
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Wittek A, Derwich W, Karatolios K, Fritzen CP, Vogt S, Schmitz-Rixen T, Blase C. A finite element updating approach for identification of the anisotropic hyperelastic properties of normal and diseased aortic walls from 4D ultrasound strain imaging. J Mech Behav Biomed Mater 2015; 58:122-138. [PMID: 26455809 DOI: 10.1016/j.jmbbm.2015.09.022] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2015] [Revised: 09/15/2015] [Accepted: 09/18/2015] [Indexed: 10/23/2022]
Abstract
Computational analysis of the biomechanics of the vascular system aims at a better understanding of its physiology and pathophysiology and eventually at diagnostic clinical use. Because of great inter-individual variations, such computational models have to be patient-specific with regard to geometry, material properties and applied loads and boundary conditions. Full-field measurements of heterogeneous displacement or strain fields can be used to improve the reliability of parameter identification based on a reduced number of observed load cases as is usually given in an in vivo setting. Time resolved 3D ultrasound combined with speckle tracking (4D US) is an imaging technique that provides full field information of heterogeneous aortic wall strain distributions in vivo. In a numerical verification experiment, we have shown the feasibility of identifying nonlinear and orthotropic constitutive behaviour based on the observation of just two load cases, even though the load free geometry is unknown, if heterogeneous strain fields are available. Only clinically available 4D US measurements of wall motion and diastolic and systolic blood pressure are required as input for the inverse FE updating approach. Application of the developed inverse approach to 4D US data sets of three aortic wall segments from volunteers of different age and pathology resulted in the reproducible identification of three distinct and (patho-) physiologically reasonable constitutive behaviours. The use of patient-individual material properties in biomechanical modelling of AAAs is a step towards more personalized rupture risk assessment.
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Affiliation(s)
- Andreas Wittek
- Department of Biological Sciences, Goethe University Frankfurt am Main, Germany; Department of Mechanical Engineering, University Siegen, Germany
| | - Wojciech Derwich
- Department of Vascular and Endovascular Surgery, Goethe University Frankfurt am Main, Germany
| | | | | | - Sebastian Vogt
- University Heart Centre, Philipps University Marburg, Germany
| | - Thomas Schmitz-Rixen
- Department of Vascular and Endovascular Surgery, Goethe University Frankfurt am Main, Germany
| | - Christopher Blase
- Department of Biological Sciences, Goethe University Frankfurt am Main, Germany.
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131
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Tonar Z, Kubíková T, Prior C, Demjén E, Liška V, Králíčková M, Witter K. Segmental and age differences in the elastin network, collagen, and smooth muscle phenotype in the tunica media of the porcine aorta. Ann Anat 2015; 201:79-90. [DOI: 10.1016/j.aanat.2015.05.005] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 05/26/2015] [Accepted: 05/26/2015] [Indexed: 12/18/2022]
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132
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Sassani SG, Kakisis J, Tsangaris S, Sokolis DP. Layer-dependent wall properties of abdominal aortic aneurysms: Experimental study and material characterization. J Mech Behav Biomed Mater 2015; 49:141-61. [DOI: 10.1016/j.jmbbm.2015.04.027] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2015] [Revised: 04/21/2015] [Accepted: 04/27/2015] [Indexed: 12/11/2022]
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133
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Farsad M, Zeinali-Davarani S, Choi J, Baek S. Computational Growth and Remodeling of Abdominal Aortic Aneurysms Constrained by the Spine. J Biomech Eng 2015; 137:2397298. [PMID: 26158885 PMCID: PMC4574855 DOI: 10.1115/1.4031019] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 06/27/2015] [Indexed: 01/01/2023]
Abstract
Abdominal aortic aneurysms (AAAs) evolve over time, and the vertebral column, which acts as an external barrier, affects their biomechanical properties. Mechanical interaction between AAAs and the spine is believed to alter the geometry, wall stress distribution, and blood flow, although the degree of this interaction may depend on AAAs specific configurations. In this study, we use a growth and remodeling (G&R) model, which is able to trace alterations of the geometry, thus allowing us to computationally investigate the effect of the spine for progression of the AAA. Medical image-based geometry of an aorta is constructed along with the spine surface, which is incorporated into the computational model as a cloud of points. The G&R simulation is initiated by local elastin degradation with different spatial distributions. The AAA-spine interaction is accounted for using a penalty method when the AAA surface meets the spine surface. The simulation results show that, while the radial growth of the AAA wall is prevented on the posterior side due to the spine acting as a constraint, the AAA expands faster on the anterior side, leading to higher curvature and asymmetry in the AAA configuration compared to the simulation excluding the spine. Accordingly, the AAA wall stress increases on the lateral, posterolateral, and the shoulder regions of the anterior side due to the AAA-spine contact. In addition, more collagen is deposited on the regions with a maximum diameter. We show that an image-based computational G&R model not only enhances the prediction of the geometry, wall stress, and strength distributions of AAAs but also provides a framework to account for the interactions between an enlarging AAA and the spine for a better rupture potential assessment and management of AAA patients.
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Affiliation(s)
- Mehdi Farsad
- Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail:
| | | | - Jongeun Choi
- Associate Professor
Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
- Department of Electrical and
Computer Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail:
| | - Seungik Baek
- Associate Professor
Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail:
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134
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Rao J, Brown BN, Weinbaum JS, Ofstun EL, Makaroun MS, Humphrey JD, Vorp DA. Distinct macrophage phenotype and collagen organization within the intraluminal thrombus of abdominal aortic aneurysm. J Vasc Surg 2015. [PMID: 26206580 DOI: 10.1016/j.jvs.2014.11.086] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
OBJECTIVE Little is known about the etiologic factors that lead to the occurrence of intraluminal thrombus (ILT) during abdominal aortic aneurysm (AAA) development. Recent work has suggested that macrophages may play an important role in progression of a number of other vascular diseases, including atherosclerosis; however, whether these cells are present within the ILT of a progressing AAA is unknown. The purpose of this work was to define the presence, phenotype, and spatial distribution of macrophages within the ILT excised from six patients. We hypothesized that the ILT contains a population of activated macrophages with a distinct, nonclassical phenotypic profile. METHODS ILT samples were examined using histologic staining and immunofluorescent labeling for multiple markers of activated macrophages (cluster of differentiation [CD]45, CD68, human leukocyte antigen-DR, matrix metalloproteinase 9) and the additional markers α-smooth muscle actin, CD34, CD105, fetal liver kinase-1, and collagen I and III. RESULTS Histologic staining revealed a distinct laminar organization of collagen within the shoulder region of the ILT lumen and a spatially heterogeneous cell composition within the ILT. Most of the cellular constituents of the ILT were in the luminal region and predominantly expressed markers of activated macrophages but also concurrently expressed α-smooth muscle actin, CD105, and synthesized collagen I and III. CONCLUSIONS This report presents evidence for the presence of a distinct macrophage population within the luminal region of AAA ILT. These cells express a set of markers indicative of a unique population of activated macrophages. The exact contributions of these previously unrecognized cells to ILT formation and AAA pathobiology remains unknown.
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Affiliation(s)
- Jayashree Rao
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pa
| | - Bryan N Brown
- Department of Bioengineering, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pa
| | - Justin S Weinbaum
- Department of Bioengineering, and McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pa
| | - Emily L Ofstun
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pa
| | - Michel S Makaroun
- Department of Surgery, Division of Vascular Surgery, Center for Vascular Remodeling and Regeneration, University of Pittsburgh, Pittsburgh, Pa
| | - Jay D Humphrey
- Department of Biomedical Engineering, Yale University, New Haven, Conn
| | - David A Vorp
- Department of Bioengineering, Department of Cardiothoracic Surgery, Department of Surgery, Center for Vascular Remodeling and Regeneration, McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, Pa.
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135
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Volokh K. Thrombus rupture via cavitation. J Biomech 2015; 48:2186-8. [DOI: 10.1016/j.jbiomech.2015.04.044] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 04/30/2015] [Accepted: 04/30/2015] [Indexed: 11/17/2022]
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136
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Wu J, Shadden SC. Coupled Simulation of Hemodynamics and Vascular Growth and Remodeling in a Subject-Specific Geometry. Ann Biomed Eng 2015; 43:1543-54. [PMID: 25731141 PMCID: PMC4497867 DOI: 10.1007/s10439-015-1287-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2014] [Accepted: 02/19/2015] [Indexed: 01/20/2023]
Abstract
A computational framework to couple vascular growth and remodeling (G&R) with blood flow simulation in a 3D patient-specific geometry is presented. Hyperelastic and anisotropic properties are considered for the vessel wall material and a constrained mixture model is used to represent multiple constituents in the vessel wall, which was modeled as a membrane. The coupled simulation is divided into two time scales-a longer time scale for G&R and a shorter time scale for fluid dynamics simulation. G&R is simulated to evolve the boundary of the fluid domain, and fluid simulation is in turn used to generate wall shear stress and transmural pressure data that regulates G&R. To minimize required computation cost, the fluid dynamics are only simulated when G&R causes significant vascular geometric change. For demonstration, this coupled model was used to study the influence of stress-mediated growth parameters, and blood flow mechanics, on the behavior of the vascular tissue growth in a model of the infrarenal aorta derived from medical image data.
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Affiliation(s)
- Jiacheng Wu
- Mechanical Engineering, University of California, 5126 Etcheverry Hall, Berkeley, CA, 94720-1740, USA
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137
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Virag L, Wilson JS, Humphrey JD, Karšaj I. A Computational Model of Biochemomechanical Effects of Intraluminal Thrombus on the Enlargement of Abdominal Aortic Aneurysms. Ann Biomed Eng 2015; 43:2852-2867. [PMID: 26070724 DOI: 10.1007/s10439-015-1354-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2015] [Accepted: 06/03/2015] [Indexed: 10/23/2022]
Abstract
Abdominal aortic aneurysms (AAAs) typically develop an intraluminal thrombus (ILT), yet most computational models of AAAs have focused on either the mechanics of the wall or the hemodynamics within the lesion, both in the absence of ILT. In the few cases wherein ILT has been modeled directly, as, for example, in static models that focus on the state of stress in the aortic wall and the associated rupture risk, thrombus has been modeled as an inert, homogeneous, load-bearing material. Given the biochemomechanical complexity of an ILT, there is a pressing need to consider its diverse effects on the evolving aneurysmal wall. Herein, we present the first growth and remodeling model that addresses together the biomechanics, mechanobiology, and biochemistry of thrombus-laden AAAs. Whereas it has been shown that aneurysmal enlargement in the absence of ILT depends primarily on the stiffness and turnover of fibrillar collagen, we show that the presence of a thrombus within lesions having otherwise the same initial wall composition and properties can lead to either arrest or rupture depending on the biochemical effects (e.g., release of proteases) and biomechanical properties (e.g., stiffness of fibrin) of the ILT. These computational results suggest that ILT should be accounted for when predicting the potential enlargement or rupture risk of AAAs and highlight specific needs for further experimental and computational research.
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Affiliation(s)
- Lana Virag
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
| | - John S Wilson
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA
| | - Jay D Humphrey
- Department of Biomedical Engineering, Yale University, New Haven, CT, USA.,Vascular Biology and Therapeutics Program, Yale University, New Haven, CT, USA
| | - Igor Karšaj
- Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Zagreb, Croatia
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138
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Tong J, Holzapfel GA. Structure, Mechanics, and Histology of Intraluminal Thrombi in Abdominal Aortic Aneurysms. Ann Biomed Eng 2015; 43:1488-501. [DOI: 10.1007/s10439-015-1332-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2015] [Accepted: 05/06/2015] [Indexed: 01/08/2023]
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139
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Rahmani S, Alagheband M, Karimi A, Alizadeh M, Navidbakhsh M. Wall stress in media layer of stented three-layered aortic aneurysm at different intraluminal thrombus locations with pulsatile heart cycle. J Med Eng Technol 2015; 39:239-45. [PMID: 25906361 DOI: 10.3109/03091902.2015.1040173] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
At the point when the aorta ruptures suddenly, as opposed to as the after-effect of injury, it is for the most part in aortic aneurysm. Aortic aneurysm rupture happens when the wall stress surpasses the strength of the vascular tissue. Intraluminal thrombus (ILT) may have advantages as it can absorb tension and decrease aortic aneurysm wall stress. This study aims to investigate the presence and growth effects of ILT on the wall stress in a stented aneurysm in one heart cycle. A virtual stented aneurysm model with ILT was made to study the flow and wall dynamics using fluid-structure interaction (FSI) analysis. Wall stresses at the center line of media layer of aorta thickness were calculated by two-dimensional axisymmetric finite element analysis. Calculations were executed as thrombus elastic modulus increased from 0.1 to 2 MPa and calculations were repeated as thrombus depth was increased in 10% increment until thrombus filled the whole aneurysm cavity. The von Mises stresses were compared in three sections, namely proximal, aneurysm and distal sections in the abdominal aorta. The wall stress showed its maximum value during a peak flow and pressure and gradually decreased as the pressure and velocity of blood reduced in all three aforementioned sections. As the intraluminal thrombus depth increased from 10% to 100%, the wall stress in distal, proximal and centre of aneurysm during one heart cycle was decreased. Furthermore, increasing the elastic modulus of thrombus from 10% to 100% triggered a reduction in wall stress in proximal, centre of intraluminal thrombus and distal regions during one heart cycle. The achievements of this study may have implications not only for understanding the wall stress in ILT, but also for providing more detailed information about aortic aneurysm with intraluminal thrombus and can help surgeons to do their best.
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Affiliation(s)
- Shahrokh Rahmani
- School of Mechanical Engineering, Iran University of Science and Technology , Tehran , Iran
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140
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Raaz U, Zöllner AM, Schellinger IN, Toh R, Nakagami F, Brandt M, Emrich FC, Kayama Y, Eken S, Adam M, Maegdefessel L, Hertel T, Deng A, Jagger A, Buerke M, Dalman RL, Spin JM, Kuhl E, Tsao PS. Segmental aortic stiffening contributes to experimental abdominal aortic aneurysm development. Circulation 2015; 131:1783-95. [PMID: 25904646 DOI: 10.1161/circulationaha.114.012377] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 03/05/2015] [Indexed: 01/19/2023]
Abstract
BACKGROUND Stiffening of the aortic wall is a phenomenon consistently observed in age and in abdominal aortic aneurysm (AAA). However, its role in AAA pathophysiology is largely undefined. METHODS AND RESULTS Using an established murine elastase-induced AAA model, we demonstrate that segmental aortic stiffening precedes aneurysm growth. Finite-element analysis reveals that early stiffening of the aneurysm-prone aortic segment leads to axial (longitudinal) wall stress generated by cyclic (systolic) tethering of adjacent, more compliant wall segments. Interventional stiffening of AAA-adjacent aortic segments (via external application of surgical adhesive) significantly reduces aneurysm growth. These changes correlate with the reduced segmental stiffness of the AAA-prone aorta (attributable to equalized stiffness in adjacent segments), reduced axial wall stress, decreased production of reactive oxygen species, attenuated elastin breakdown, and decreased expression of inflammatory cytokines and macrophage infiltration, and attenuated apoptosis within the aortic wall, as well. Cyclic pressurization of segmentally stiffened aortic segments ex vivo increases the expression of genes related to inflammation and extracellular matrix remodeling. Finally, human ultrasound studies reveal that aging, a significant AAA risk factor, is accompanied by segmental infrarenal aortic stiffening. CONCLUSIONS The present study introduces the novel concept of segmental aortic stiffening as an early pathomechanism generating aortic wall stress and triggering aneurysmal growth, thereby delineating potential underlying molecular mechanisms and therapeutic targets. In addition, monitoring segmental aortic stiffening may aid the identification of patients at risk for AAA.
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Affiliation(s)
- Uwe Raaz
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Alexander M Zöllner
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Isabel N Schellinger
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Ryuji Toh
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Futoshi Nakagami
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Moritz Brandt
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Fabian C Emrich
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Yosuke Kayama
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Suzanne Eken
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Matti Adam
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Lars Maegdefessel
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Thomas Hertel
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Alicia Deng
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Ann Jagger
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Michael Buerke
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Ronald L Dalman
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Joshua M Spin
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Ellen Kuhl
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.)
| | - Philip S Tsao
- From Division of Cardiovascular Medicine, Stanford University School of Medicine, CA (U.R., I.N.S., R.T., F.N., Y.K., M.A., A.D., A.J., J.MS., P.S.T.); Cardiovascular Institute, Stanford University School of Medicine, CA (U.R., A.M.Z., F.N., M.B., F.C.E., Y.K., M.A., R.L.D., J.M.S., P.S.T.); VA Palo Alto Health Care System, CA (U.R., I.N.S., Y.K., M.A., A.D., A.J., J.M.S., P.S.T.); Department of Mechanical Engineering, Stanford University School of Medicine, CA (A.M.Z., E.K.); Department of Cardiothoracic Surgery, Stanford University School of Medicine, CA (F.C.E., E.K.); Department of Medicine, Karolinska Institute, Stockholm, Sweden (S.E., L.M.); Center for Vascular Medicine, Zwickau, Germany (T.H.); Division of Cardiovascular Medicine and Intensive Care Medicine, Saint Mary's Hospital, Siegen, Germany (M.B.); Division of Vascular Surgery, Stanford University School of Medicine, CA (R.L.D.); and Department of Bioengineering, Stanford University School of Medicine, CA (E.K.).
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141
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A method for incorporating three-dimensional residual stretches/stresses into patient-specific finite element simulations of arteries. J Mech Behav Biomed Mater 2015; 47:147-164. [PMID: 25931035 DOI: 10.1016/j.jmbbm.2015.03.024] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 03/24/2015] [Accepted: 03/25/2015] [Indexed: 11/21/2022]
Abstract
The existence of residual stresses in human arteries has long been shown experimentally. Researchers have also demonstrated that residual stresses have a significant effect on the distribution of physiological stresses within arterial tissues, and hence on their development, e.g., stress-modulated remodeling. Through progress in medical imaging, image analysis and finite element (FE) meshing tools it is now possible to construct in vivo patient-specific geometries and thus to study specific, clinically relevant problems in arterial mechanics via FE simulations. Classical continuum mechanics and FE methods assume that constitutive models and the corresponding simulations start from unloaded, stress-free reference configurations while the boundary-value problem of interest represents a loaded geometry and includes residual stresses. We present a pragmatic methodology to simultaneously account for both (i) the three-dimensional (3-D) residual stress distributions in the arterial tissue layers, and (ii) the equilibrium of the in vivo patient-specific geometry with the known boundary conditions. We base our methodology on analytically determined residual stress distributions (Holzapfel and Ogden, 2010, J. R. Soc. Interface 7, 787-799) and calibrate it using data on residual deformations (Holzapfel et al., 2007, Ann. Biomed. Eng. 35, 530-545). We demonstrate our methodology on three patient-specific FE simulations calibrated using experimental data. All data employed here are generated from human tissues - both the aorta and thrombus, and their respective layers - including the geometries determined from magnetic resonance images, and material properties and 3-D residual stretches determined from mechanical experiments. We study the effect of 3-D residual stresses on the distribution of physiological stresses in the aortic layers (intima, media, adventitia) and the layers of the intraluminal thrombus (luminal, medial, abluminal) by comparing three types of FE simulations: (i) conventional calculations; (ii) calculations accounting only for prestresses; (iii) calculations including both 3-D residual stresses and prestresses. Our results show that including residual stresses in patient-specific simulations of arterial tissues significantly impacts both the global (organ-level) deformations and the stress distributions within the arterial tissue (and its layers). Our method produces circumferential Cauchy stress distributions that are more uniform through the tissue thickness (i.e., smaller stress gradients in the local radial directions) compared to both the conventional and prestressing calculations. Such methods, combined with appropriate experimental data, aim at increasing the accuracy of classical FE analyses for patient-specific studies in computational biomechanics and may lead to increased clinical application of simulation tools.
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142
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Genovese K, Humphrey JD. Multimodal optical measurement in vitro of surface deformations and wall thickness of the pressurized aortic arch. JOURNAL OF BIOMEDICAL OPTICS 2015; 20:046005. [PMID: 25867620 DOI: 10.1117/1.jbo.20.4.046005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 03/18/2015] [Indexed: 06/04/2023]
Abstract
Computational modeling of arterial mechanics continues to progress, even to the point of allowing the study of complex regions such as the aortic arch. Nevertheless, most prior studies assign homogeneous and isotropic material properties and constant wall thickness even when implementing patient-specific luminal geometries obtained from medical imaging. These assumptions are not due to computational limitations, but rather to the lack of spatially dense sets of experimental data that describe regional variations in mechanical properties and wall thickness in such complex arterial regions. In this work, we addressed technical challenges associated with in vitro measurement of overall geometry, full-field surface deformations, and regional wall thickness of the porcine aortic arch in its native anatomical configuration. Specifically, we combined two digital image correlation-based approaches, standard and panoramic, to track surface geometry and finite deformations during pressurization, with a 360-deg fringe projection system to contour the outer and inner geometry. The latter provided, for the first time, information on heterogeneous distributions of wall thickness of the arch and associated branches in the unloaded state. Results showed that mechanical responses vary significantly with orientation and location (e.g., less extensible in the circumferential direction and with increasing distance from the heart) and that the arch exhibits a nearly linear increase in pressure-induced strain up to 40%, consistent with other findings on proximal porcine aortas. Thickness measurements revealed strong regional differences, thus emphasizing the need to include nonuniform thicknesses in theoretical and computational studies of complex arterial geometries.
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Affiliation(s)
- Katia Genovese
- University of Basilicata, School of Engineering, Potenza 85100, Italy
| | - Jay D Humphrey
- Yale University, Department of Biomedical Engineering, New Haven, Connecticut 06520, United States
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143
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Schriefl AJ, Schmidt T, Balzani D, Sommer G, Holzapfel GA. Selective enzymatic removal of elastin and collagen from human abdominal aortas: uniaxial mechanical response and constitutive modeling. Acta Biomater 2015; 17:125-36. [PMID: 25623592 DOI: 10.1016/j.actbio.2015.01.003] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2014] [Revised: 10/31/2014] [Accepted: 01/05/2015] [Indexed: 02/01/2023]
Abstract
The ability to selectively remove the structurally most relevant components of arterial wall tissues such as collagen and elastin enables ex vivo biomechanical testing of the remaining tissues, with the aim of assessing their individual mechanical contributions. Resulting passive material parameters can be utilized in mathematical models of the cardiovascular system. Using eighteen wall specimens from non-atherosclerotic human abdominal aortas (55 ± 11 years; 9 female, 9 male), we tested enzymatic approaches for the selective digestion of collagen and elastin, focusing on their application to human abdominal aortic wall tissues from different patients with varying sample morphologies. The study resulted in an improved protocol for elastin removal, showing how the enzymatic process is affected by inadequate addition of trypsin inhibitor. We applied the resulting protocol to circumferential and axial specimens from the media and the adventitia, and performed cyclic uniaxial extension tests in the physiological and supra-physiological loading domain. The collagenase-treated samples showed a (linear) response without distinct softening behavior, while the elastase-treated samples exhibited a nonlinear, anisotropic response with pronounced remanent deformations (continuous softening), presumably caused by some sliding of collagen fibers within the damaged regions of the collagen network. In addition, our data showed that the stiffness in the initial linear stress-stretch regime at low loads is lower in elastin-free tissue compared to control samples (i.e. collagen uncrimping requires less force than the stretching of elastin), experimentally confirming that elastin is responsible for the initial stiffness in elastic arteries. Utilizing a continuum mechanical description to mathematically capture the experimental results we concluded that the inclusion of a damage model for the non-collagenous matrix material is, in general, not necessary. To model the softening behavior, continuous damage was included in the fibers by adding a damage variable which led to remanent strains through the consideration of damage.
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Affiliation(s)
| | - Thomas Schmidt
- University of Duisburg-Essen, Institute of Mechanics, Germany
| | - Daniel Balzani
- Dresden University of Technology, Faculty of Civil Engineering, Germany
| | - Gerhard Sommer
- Graz University of Technology, Institute of Biomechanics, Austria
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144
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Modeling of human artery tissue with probabilistic approach. Comput Biol Med 2015; 59:152-159. [PMID: 25748681 DOI: 10.1016/j.compbiomed.2015.01.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Revised: 01/26/2015] [Accepted: 01/28/2015] [Indexed: 11/21/2022]
Abstract
Accurate modeling of biological soft tissue properties is vital for realistic medical simulation. Mechanical response of biological soft tissue always exhibits a strong variability due to the complex microstructure and different loading conditions. The inhomogeneity in human artery tissue is modeled with a computational probabilistic approach by assuming that the instantaneous stress at a specific strain varies according to normal distribution. Material parameters of the artery tissue which are modeled with a combined logarithmic and polynomial energy equation are represented by a statistical function with normal distribution. Mean and standard deviation of the material parameters are determined using genetic algorithm (GA) and inverse mean-value first-order second-moment (IMVFOSM) method, respectively. This nondeterministic approach was verified using computer simulation based on the Monte-Carlo (MC) method. Cumulative distribution function (CDF) of the MC simulation corresponds well with that of the experimental stress-strain data and the probabilistic approach is further validated using data from other studies. By taking into account the inhomogeneous mechanical properties of human biological tissue, the proposed method is suitable for realistic virtual simulation as well as an accurate computational approach for medical device validation.
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145
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Diameter-Related Variations of Geometrical, Mechanical, and Mass Fraction Data in the Anterior Portion of Abdominal Aortic Aneurysms. Eur J Vasc Endovasc Surg 2015; 49:262-70. [DOI: 10.1016/j.ejvs.2014.12.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 12/08/2014] [Indexed: 11/21/2022]
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146
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Grytsan A, Watton PN, Holzapfel GA. A Thick-Walled Fluid–Solid-Growth Model of Abdominal Aortic Aneurysm Evolution: Application to a Patient-Specific Geometry. J Biomech Eng 2015; 137:2020812. [DOI: 10.1115/1.4029279] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Indexed: 11/08/2022]
Abstract
We propose a novel thick-walled fluid–solid-growth (FSG) computational framework for modeling vascular disease evolution. The arterial wall is modeled as a thick-walled nonlinearly elastic cylindrical tube consisting of two layers corresponding to the media-intima and adventitia, where each layer is treated as a fiber-reinforced material with the fibers corresponding to the collagenous component. Blood is modeled as a Newtonian fluid with constant density and viscosity; no slip and no-flux conditions are applied at the arterial wall. Disease progression is simulated by growth and remodeling (G&R) of the load bearing constituents of the wall. Adaptions of the natural reference configurations and mass densities of constituents are driven by deviations of mechanical stimuli from homeostatic levels. We apply the novel framework to model abdominal aortic aneurysm (AAA) evolution. Elastin degradation is initially prescribed to create a perturbation to the geometry which results in a local decrease in wall shear stress (WSS). Subsequent degradation of elastin is driven by low WSS and an aneurysm evolves as the elastin degrades and the collagen adapts. The influence of transmural G&R of constituents on the aneurysm development is analyzed. We observe that elastin and collagen strains evolve to be transmurally heterogeneous and this may facilitate the development of tortuosity. This multiphysics framework provides the basis for exploring the influence of transmural metabolic activity on the progression of vascular disease.
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Affiliation(s)
- Andrii Grytsan
- Department of Solid Mechanics, Royal Institute of Technology (KTH), Teknikringen 8d, Stockholm 10044, Sweden
| | - Paul N. Watton
- Department of Computer Science, University of Sheffield, Sheffield, UK
- INSIGNEO Institute of In Silico Medicine, University of Sheffield, Sheffield, UK
| | - Gerhard A. Holzapfel
- Institute of Biomechanics, Graz University of Technology, Kronesgasse 5-I, Graz 8010, Austria e-mail:
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147
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Volokh KY. Cavitation instability as a trigger of aneurysm rupture. Biomech Model Mechanobiol 2015; 14:1071-9. [PMID: 25637515 DOI: 10.1007/s10237-015-0655-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2014] [Accepted: 01/22/2015] [Indexed: 11/26/2022]
Abstract
Aneurysm formation and growth is accompanied by microstructural alterations in the arterial wall. Particularly, the loss of elastin may lead to tissue disintegration and appearance of voids or cavities at the micron scale. Unstable growth and coalescence of voids may be a predecessor and trigger for the onset of macroscopic cracks. In the present work, we analyze the instability of membrane (2D) and bulk (3D) voids under hydrostatic tension by using two experimentally calibrated constitutive models of abdominal aortic aneurysm enhanced with energy limiters. The limiters provide the saturation value for the strain energy, which indicates the maximum energy that can be stored and dissipated by an infinitesimal material volume. We find that the unstable growth of voids can start when the critical stress is considerably less than the aneurysm strength. Moreover, this critical stress may even approach the arterial wall stress in the physiological range. This finding suggests that cavitation instability can be a rational indicator of the aneurysm rupture.
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Affiliation(s)
- K Y Volokh
- Faculty of Civil and Environmental Engineering, Technion - I.I.T., Haifa, Israel,
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148
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Simsek FG, Kwon YW. Investigation of material modeling in fluid-structure interaction analysis of an idealized three-layered abdominal aorta: aneurysm initiation and fully developed aneurysms. J Biol Phys 2015; 41:173-201. [PMID: 25624113 DOI: 10.1007/s10867-014-9372-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 11/06/2014] [Indexed: 01/26/2023] Open
Abstract
Different material models for an idealized three-layered abdominal aorta are compared using computational techniques to study aneurysm initiation and fully developed aneurysms. The computational model includes fluid-structure interaction (FSI) between the blood vessel and the blood. In order to model aneurysm initiation, the medial region was degenerated to mimic the medial loss occurring in the inception of an aneurysm. Various cases are considered in order to understand their effects on the initiation of an abdominal aortic aneurysm. The layers of the blood vessel were modeled using either linear elastic materials or Mooney-Rivlin (otherwise known as hyperelastic) type materials. The degenerated medial region was also modeled in either linear elastic or hyperelastic-type materials and assumed to be in the shape of an arc with a thin width or a circular ring with different widths. The blood viscosity effect was also considered in the initiation mechanism. In addition, dynamic analysis of the blood vessel was performed without interaction with the blood flow by applying time-dependent pressure inside the lumen in a three-layered abdominal aorta. The stresses, strains, and displacements were compared for a healthy aorta, an initiated aneurysm and a fully developed aneurysm. The study shows that the material modeling of the vessel has a sizable effect on aneurysm initiation and fully developed aneurysms. Different material modeling of degeneration regions also affects the stress-strain response of aneurysm initiation. Additionally, the structural analysis without considering FSI (called noFSI) overestimates the peak von Mises stress by 52% at the interfaces of the layers.
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Affiliation(s)
- Fatma Gulden Simsek
- Institute of Biomedical Engineering, Bogazici University, Kandilli Camp, Istanbul, Turkey,
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149
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Xenos M, Labropoulos N, Rambhia S, Alemu Y, Einav S, Tassiopoulos A, Sakalihasan N, Bluestein D. Progression of abdominal aortic aneurysm towards rupture: refining clinical risk assessment using a fully coupled fluid-structure interaction method. Ann Biomed Eng 2014; 43:139-53. [PMID: 25527320 DOI: 10.1007/s10439-014-1224-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 12/09/2014] [Indexed: 01/12/2023]
Abstract
Rupture of abdominal aortic aneurysm (AAA) is associated with high mortality rates. Risk of rupture is multi-factorial involving AAA geometric configuration, vessel tortuosity, and the presence of intraluminal pathology. Fluid structure interaction (FSI) simulations were conducted in patient based computed tomography scans reconstructed geometries in order to monitor aneurysmal disease progression from normal aortas to non-ruptured and contained ruptured AAA (rAAA), and the AAA risk of rupture was assessed. Three groups of 8 subjects each were studied: 8 normal and 16 pathological (8 non-ruptured and 8 rAAA). The AAA anatomical structures segmented included the blood lumen, intraluminal thrombus (ILT), vessel wall, and embedded calcifications. The vessel wall was described with anisotropic material model that was matched to experimental measurements of AAA tissue specimens. A statistical model for estimating the local wall strength distribution was employed to generate a map of a rupture potential index (RPI), representing the ratio between the local stress and local strength distribution. The FSI simulations followed a clear trend of increasing wall stresses from normal to pathological cases. The maximal stresses were observed in the areas where the ILT was not present, indicating a potential protective effect of the ILT. Statistically significant differences were observed between the peak systolic stress and the peak stress at the mean arterial pressure between the three groups. For the ruptured aneurysms, where the geometry of intact aneurysm was reconstructed, results of the FSI simulations clearly depicted maximum wall stress at the a priori known location of rupture. The RPI mapping indicated several distinct regions of high RPI coinciding with the actual location of rupture. The FSI methodology demonstrates that the aneurysmal disease can be described by numerical simulations, as indicated by a clear trend of increasing aortic wall stresses in the studied groups, (normal aortas, AAAs and rAAAs). Ultimately, the results demonstrate that FSI wall stress mapping and RPI can be used as a tool for predicting the potential rupture of an AAA by predicting the actual rupture location, complementing current clinical practice by offering a predictive diagnostic tool for deciding whether to intervene surgically or spare the patient from an unnecessary risky operation.
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Affiliation(s)
- Michalis Xenos
- Department of Mathematics, University of Ioannina, Ioannina, Greece
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English SJ, Diaz JA, Shao X, Gordon D, Bevard M, Su G, Henke PK, Rogers VE, Upchurch GR, Piert M. Utility of (18) F-FDG and (11)C-PBR28 microPET for the assessment of rat aortic aneurysm inflammation. EJNMMI Res 2014; 4:20. [PMID: 26055934 PMCID: PMC4593011 DOI: 10.1186/s13550-014-0020-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2013] [Accepted: 03/21/2014] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND The utility of (18) F-FDG and (11)C-PBR28 to identify aortic wall inflammation associated with abdominal aortic aneurysm (AAA) development was assessed. METHODS Utilizing the porcine pancreatic elastase (PPE) perfusion model, abdominal aortas of male Sprague-Dawley rats were infused with active PPE (APPE, AAA; N = 24) or heat-inactivated PPE (IPPE, controls; N = 16). Aortic diameter increases were monitored by ultrasound (US). Three, 7, and 14 days after induction, APPE and IPPE rats were imaged using (18) F-FDG microPET (approximately 37 MBq IV) and compared with (18) F-FDG autoradiography (approximately 185 MBq IV) performed at day 14. A subset of APPE (N = 5) and IPPE (N = 6) animals were imaged with both (11)C-PBR28 (approximately 19 MBq IV) and subsequent (18) F-FDG (approximately 37 MBq IV) microPET on the same day 14 days post PPE exposure. In addition, autoradiography of the retroperitoneal torso was performed after (11)C-PBR28 (approximately 1,480 MBq IV) or (18) F-FDG (approximately 185 MBq IV) administration at 14 days post PPE exposure. Aortic wall-to-muscle ratios (AMRs) were determined for microPET and autoradiography. CD68 and translocator protein (TSPO) immunohistochemistry (IHC), as well as TSPO gene expression assays, were performed for validation. RESULTS Mean 3 (p = 0.009), 7 (p < 0.0001) and 14 (p < 0.0001) days aortic diameter increases were significantly greater for APPE AAAs compared to IPPE controls. No significant differences in (18) F-FDG AMR were determined at days 3 and 7 post PPE exposure; however, at day 14, the mean (18) F-FDG AMR was significantly elevated in APPE AAAs compared to IPPE controls on both microPET (p = 0.0002) and autoradiography (p = 0.02). Similarly, mean (11)C-PBR28 AMR was significantly increased at day 14 in APPE AAAs compared to IPPE controls on both microPET (p = 0.04) and autoradiography (p = 0.02). For APPE AAAs, inhomogeneously increased (18) F-FDG and (11)C-PBR28 uptake was noted preferentially at the anterolateral aspect of the AAA. Compared to controls, APPE AAAs demonstrated significantly increased macrophage cell counts by CD68 IHC (p = 0.001) as well as increased TSPO staining (p = 0.004). Mean TSPO gene expression for APPE AAAs was also significantly elevated compared to IPPE controls (p = 0.0002). CONCLUSION Rat AAA wall inflammation can be visualized using (18) F-FDG and (11)C-PBR28 microPET revealing regional differences of radiotracer uptake on microPET and autoradiography. These results support further investigation of (18) F-FDG and (11)C-PBR28 in the noninvasive assessment of human AAA development.
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Affiliation(s)
- Sean J English
- />Conrad Jobst Vascular Research Laboratories, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - Jose A Diaz
- />Conrad Jobst Vascular Research Laboratories, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - Xia Shao
- />Division of Nuclear Medicine, Department of Radiology, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - David Gordon
- />Department of Pathology, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - Melissa Bevard
- />Division of Vascular and Endovascular Surgery, University of Virginia Health System, Charlottesville, VA 22903 USA
| | - Gang Su
- />Division of Vascular and Endovascular Surgery, University of Virginia Health System, Charlottesville, VA 22903 USA
| | - Peter K Henke
- />Conrad Jobst Vascular Research Laboratories, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - Virginia E Rogers
- />Division of Nuclear Medicine, Department of Radiology, University of Michigan Health System, Ann Arbor, MI 48109 USA
| | - Gilbert R Upchurch
- />Division of Vascular and Endovascular Surgery, University of Virginia Health System, Charlottesville, VA 22903 USA
| | - Morand Piert
- />Division of Nuclear Medicine, Department of Radiology, University of Michigan Health System, Ann Arbor, MI 48109 USA
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