1
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Wang X, Carpenter HJ, Ghayesh MH, Kotousov A, Zander AC, Amabili M, Psaltis PJ. A review on the biomechanical behaviour of the aorta. J Mech Behav Biomed Mater 2023; 144:105922. [PMID: 37320894 DOI: 10.1016/j.jmbbm.2023.105922] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 05/14/2023] [Accepted: 05/20/2023] [Indexed: 06/17/2023]
Abstract
Large aortic aneurysm and acute and chronic aortic dissection are pathologies of the aorta requiring surgery. Recent advances in medical intervention have improved patient outcomes; however, a clear understanding of the mechanisms leading to aortic failure and, hence, a better understanding of failure risk, is still missing. Biomechanical analysis of the aorta could provide insights into the development and progression of aortic abnormalities, giving clinicians a powerful tool in risk stratification. The complexity of the aortic system presents significant challenges for a biomechanical study and requires various approaches to analyse the aorta. To address this, here we present a holistic review of the biomechanical studies of the aorta by categorising articles into four broad approaches, namely theoretical, in vivo, experimental and combined investigations. Experimental studies that focus on identifying mechanical properties of the aortic tissue are also included. By reviewing the literature and discussing drawbacks, limitations and future challenges in each area, we hope to present a more complete picture of the state-of-the-art of aortic biomechanics to stimulate research on critical topics. Combining experimental modalities and computational approaches could lead to more comprehensive results in risk prediction for the aortic system.
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Affiliation(s)
- Xiaochen Wang
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Harry J Carpenter
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Mergen H Ghayesh
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia.
| | - Andrei Kotousov
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Anthony C Zander
- School of Electrical and Mechanical Engineering, The University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Marco Amabili
- Department of Mechanical Engineering, McGill University, Montreal H3A 0C3, Canada
| | - Peter J Psaltis
- Adelaide Medical School, The University of Adelaide, Adelaide, South Australia 5005, Australia; Department of Cardiology, Central Adelaide Local Health Network, Adelaide, South Australia 5000, Australia; Vascular Research Centre, Heart Health Theme, South Australian Health & Medical Research Institute (SAHMRI), Adelaide, South Australia 5000, Australia
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2
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Aggarwal A, Mortensen P, Hao J, Kaczmarczyk Ł, Cheung AT, Al Ghofaily L, Gorman RC, Desai ND, Bavaria JE, Pouch AM. Strain estimation in aortic roots from 4D echocardiographic images using medial modeling and deformable registration. Med Image Anal 2023; 87:102804. [PMID: 37060701 PMCID: PMC10358753 DOI: 10.1016/j.media.2023.102804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 01/30/2023] [Accepted: 03/29/2023] [Indexed: 04/03/2023]
Abstract
Even though the central role of mechanics in the cardiovascular system is widely recognized, estimating mechanical deformation and strains in-vivo remains an ongoing practical challenge. Herein, we present a semi-automated framework to estimate strains from four-dimensional (4D) echocardiographic images and apply it to the aortic roots of patients with normal trileaflet aortic valves (TAV) and congenital bicuspid aortic valves (BAV). The method is based on fully nonlinear shell-based kinematics, which divides the strains into in-plane (shear and dilatational) and out-of-plane components. The results indicate that, even for size-matched non-aneurysmal aortic roots, BAV patients experience larger regional shear strains in their aortic roots. This elevated strains might be a contributing factor to the higher risk of aneurysm development in BAV patients. The proposed framework is openly available and applicable to any tubular structures.
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Affiliation(s)
- Ankush Aggarwal
- Glasgow Computational Engineering Centre, James Watt School of Engineering, University of Glasgow, Glasgow, G12 8LT, Scotland, United Kingdom
| | - Peter Mortensen
- Glasgow Computational Engineering Centre, James Watt School of Engineering, University of Glasgow, Glasgow, G12 8LT, Scotland, United Kingdom
| | - Jilei Hao
- Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA
| | - Łukasz Kaczmarczyk
- Glasgow Computational Engineering Centre, James Watt School of Engineering, University of Glasgow, Glasgow, G12 8LT, Scotland, United Kingdom
| | - Albert T Cheung
- Department of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Stanford, CA, USA
| | - Lourdes Al Ghofaily
- Department of Anesthesiology, University of Pennsylvania, Philadelphia, PA, USA
| | - Robert C Gorman
- Department of Surgery, University of Pennsylvania, Philadelphia, PA, USA
| | - Nimesh D Desai
- Department of Surgery, University of Pennsylvania, Philadelphia, PA, USA
| | - Joseph E Bavaria
- Department of Surgery, University of Pennsylvania, Philadelphia, PA, USA
| | - Alison M Pouch
- Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA; Department of Bioengineering, University of Pennsylvania, Philadelphia, PA, USA.
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3
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Celi S, Gasparotti E, Capellini K, Bardi F, Scarpolini MA, Cavaliere C, Cademartiri F, Vignali E. An image-based approach for the estimation of arterial local stiffness in vivo. Front Bioeng Biotechnol 2023; 11:1096196. [PMID: 36793441 PMCID: PMC9923115 DOI: 10.3389/fbioe.2023.1096196] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 01/19/2023] [Indexed: 01/31/2023] Open
Abstract
The analysis of mechanobiology of arterial tissues remains an important topic of research for cardiovascular pathologies evaluation. In the current state of the art, the gold standard to characterize the tissue mechanical behavior is represented by experimental tests, requiring the harvesting of ex-vivo specimens. In recent years though, image-based techniques for the in vivo estimation of arterial tissue stiffness were presented. The aim of this study is to define a new approach to provide local distribution of arterial stiffness, estimated as the linearized Young's Modulus, based on the knowledge of in vivo patient-specific imaging data. In particular, the strain and stress are estimated with sectional contour length ratios and a Laplace hypothesis/inverse engineering approach, respectively, and then used to calculate the Young's Modulus. After describing the method, this was validated by using a set of Finite Element simulations as input. In particular, idealized cylinder and elbow shapes plus a single patient-specific geometry were simulated. Different stiffness distributions were tested for the simulated patient-specific case. After the validation from Finite Element data, the method was then applied to patient-specific ECG-gated Computed Tomography data by also introducing a mesh morphing approach to map the aortic surface along the cardiac phases. The validation process revealed satisfactory results. In the simulated patient-specific case, root mean square percentage errors below 10% for the homogeneous distribution and below 20% for proximal/distal distribution of stiffness. The method was then successfully used on the three ECG-gated patient-specific cases. The resulting distributions of stiffness exhibited significant heterogeneity, nevertheless the resulting Young's moduli were always contained within the 1-3 MPa range, which is in line with literature.
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Affiliation(s)
- Simona Celi
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy,*Correspondence: Simona Celi,
| | - Emanuele Gasparotti
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy
| | - Katia Capellini
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy
| | - Francesco Bardi
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy,Mines Saint-Etienne, Universit’e de Lyon, INSERM, SaInBioSE U1059, Lyon, France
| | - Martino Andrea Scarpolini
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy,Dipartimento di Ingegneria Industriale, Università “Tor Vergata”, Roma, Italy
| | | | | | - Emanuele Vignali
- BioCardioLab, UOC Bioingegneria, Fondazione Toscana G Monasterio, Massa, Italy
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4
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Han HC, Liu Q, Baek S. Numerical simulations of the nonsymmetric growth and remodeling of arteries under axial twisting. J Biomech 2022; 140:111165. [PMID: 35667148 PMCID: PMC10782577 DOI: 10.1016/j.jbiomech.2022.111165] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Revised: 05/02/2022] [Accepted: 05/23/2022] [Indexed: 11/23/2022]
Abstract
Blood vessels are often subjected to axial twisting during body movement or surgery. Sustained twisting may lead to blood vessel growth and remodeling, however, it remains unclear how the extracellular matrix in the blood vessels remodel under sustained axial twisting. This study aimed to develop a computational model to simulate stress-induced growth and remodeling (G&R) of thin-walled blood vessels under axial twisting. Cylindrical vessels were subjected to a step increase in axial torque while the axial stretch and lumen pressure remained constant. The vessel walls were modeled based on the constrained mixture theory given as microstructure-based discrete fiber families with isotropic matrix structure models. Simulation results demonstrated that in response to a constant twist angle loading, arterial wall thickness, mass, and twisting torque gradually increase towards a new steady state. However, the stress and mass decrease in one diagonal fiber family while increasing in the other diagonal fiber family before reaching plateaus. A novel finding was that the two helical collagen fiber families showed different growth rates and patterns during remodeling, driven by the different fiber stresses generated by the twisting, and led to non-symmetric material properties. This study sheds new light on arterial wall remodeling under axial twisting.
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Affiliation(s)
- Hai-Chao Han
- Department of Mechanical Engineering, The University of Texas at San Antonio, TX 78249, United States.
| | - Qin Liu
- Department of Mechanical Engineering, The University of Texas at San Antonio, TX 78249, United States
| | - Seungik Baek
- Department of Mechanical Engineering, Michigan State University, East Lansing, MI 48824, United States
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5
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Laubrie JD, Mousavi SJ, Avril S. About prestretch in homogenized constrained mixture models simulating growth and remodeling in patient-specific aortic geometries. Biomech Model Mechanobiol 2022; 21:455-469. [PMID: 35067825 PMCID: PMC8940846 DOI: 10.1007/s10237-021-01544-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 10/01/2021] [Indexed: 11/10/2022]
Abstract
Evolution of mechanical and structural properties in the Ascending Thoracic Aorta (ATA) is the results of complex mechanobiological processes. In this work, we address some numerical challenges in order to elaborate computational models of these processes. For that, we extend the state of the art of homogenized constrained mixture (hCM) models. In these models, prestretches are assigned to the mixed constituents in order to ensure local mechanical equilibrium macroscopically, and to maintain a homeostatic level of tension in collagen fibers microscopically. Although the initial prestretches were assumed as homogeneous in idealized straight tubes, more elaborate prestretch distributions need to be considered for curved geometrical models such as patient-specific ATA. Therefore, we introduce prestretches having a three-dimensional gradient across the ATA geometry in the homeostatic reference state. We test different schemes with the objective to ensure stable growth and remodeling (G&R) simulations on patient-specific curved vessels. In these simulations, aneurysm progression is triggered by tissue changes in the constituents such as mass degradation of intramural elastin. The results show that the initial prestretches are not only critical for the stability of numerical simulations, but they also affect the G&R response. Eventually, we submit that initial conditions required for G&R simulations need to be identified regionally for ensuring realistic patient-specific predictions of aneurysm progression.
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6
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Rego BV, Weiss D, Bersi MR, Humphrey JD. Uncertainty quantification in subject-specific estimation of local vessel mechanical properties. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2021; 37:e3535. [PMID: 34605615 PMCID: PMC9019846 DOI: 10.1002/cnm.3535] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/24/2021] [Accepted: 09/26/2021] [Indexed: 05/08/2023]
Abstract
Quantitative estimation of local mechanical properties remains critically important in the ongoing effort to elucidate how blood vessels establish, maintain, or lose mechanical homeostasis. Recent advances based on panoramic digital image correlation (pDIC) have made high-fidelity 3D reconstructions of small-animal (e.g., murine) vessels possible when imaged in a variety of quasi-statically loaded configurations. While we have previously developed and validated inverse modeling approaches to translate pDIC-measured surface deformations into biomechanical metrics of interest, our workflow did not heretofore include a methodology to quantify uncertainties associated with local point estimates of mechanical properties. This limitation has compromised our ability to infer biomechanical properties on a subject-specific basis, such as whether stiffness differs significantly between multiple material locations on the same vessel or whether stiffness differs significantly between multiple vessels at a corresponding material location. In the present study, we have integrated a novel uncertainty quantification and propagation pipeline within our inverse modeling approach, relying on empirical and analytic Bayesian techniques. To demonstrate the approach, we present illustrative results for the ascending thoracic aorta from three mouse models, quantifying uncertainties in constitutive model parameters as well as circumferential and axial tangent stiffness. Our extended workflow not only allows parameter uncertainties to be systematically reported, but also facilitates both subject-specific and group-level statistical analyses of the mechanics of the vessel wall.
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Affiliation(s)
- Bruno V. Rego
- Department of Biomedical Engineering, School of Engineering & Applied Science, Yale University, New Haven, CT, USA
| | - Dar Weiss
- Department of Biomedical Engineering, School of Engineering & Applied Science, Yale University, New Haven, CT, USA
| | - Matthew R. Bersi
- Department of Mechanical Engineering & Materials Science, McKelvey School of Engineering, Washington University in St. Louis, St. Louis, MO, USA
| | - Jay D. Humphrey
- Department of Biomedical Engineering, School of Engineering & Applied Science, Yale University, New Haven, CT, USA
- Correspondence Jay D. Humphrey, Department of Biomedical Engineering, Malone Engineering Center, Yale University, New Haven, CT, USA.
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7
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Zhang L, Jiang Z, Choi J, Lim CY, Maiti T, Baek S. Patient-Specific Prediction of Abdominal Aortic Aneurysm Expansion Using Bayesian Calibration. IEEE J Biomed Health Inform 2019; 23:2537-2550. [PMID: 30714936 DOI: 10.1109/jbhi.2019.2896034] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Translating recent advances in abdominal aortic aneurysm (AAA) growth and remodeling (G&R) knowledge into a predictive, patient-specific clinical treatment tool requires a major paradigm shift in computational modeling. The objectives of this study are to develop a prediction framework that first calibrates the physical AAA G&R model using patient-specific serial computed tomography (CT) scan images, predicts the expansion of an AAA in the future, and quantifies the associated uncertainty in the prediction. We adopt a Bayesian calibration method to calibrate parameters in the G&R computational model and predict the magnitude of AAA expansion. The proposed Bayesian approach can take different sources of uncertainty; therefore, it is well suited to achieve our aims in predicting the AAA expansion process as well as in computing the propagated uncertainty. We demonstrate how to achieve the proposed aims by solving the formulated Bayesian calibration problems for cases with the synthetic G&R model output data and real medical patient-specific CT data. We compare and discuss the performance of predictions and computation time under different sampling cases of the model output data and patient data, both of which are simulated by the G&R computation. Furthermore, we apply our Bayesian calibration to real patient-specific serial CT data and validate our prediction. The accuracy and efficiency of the proposed method is promising, which appeals to computational and medical communities.
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8
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A modular inverse elastostatics approach to resolve the pressure-induced stress state for in vivo imaging based cardiovascular modeling. J Mech Behav Biomed Mater 2018; 85:124-133. [DOI: 10.1016/j.jmbbm.2018.05.032] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Revised: 03/28/2018] [Accepted: 05/22/2018] [Indexed: 01/18/2023]
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9
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Bosi GM, Capelli C, Cheang MH, Delahunty N, Mullen M, Taylor AM, Schievano S. Population-specific material properties of the implantation site for transcatheter aortic valve replacement finite element simulations. J Biomech 2018; 71:236-244. [PMID: 29482928 PMCID: PMC5889787 DOI: 10.1016/j.jbiomech.2018.02.017] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2017] [Revised: 02/07/2018] [Accepted: 02/09/2018] [Indexed: 10/31/2022]
Abstract
Patient-specific computational models are an established tool to support device development and test under clinically relevant boundary conditions. Potentially, such models could be used to aid the clinical decision-making process for percutaneous valve selection; however, their adoption in clinical practice is still limited to individual cases. To be fully informative, they should include patient-specific data on both anatomy and mechanics of the implantation site. In this work, fourteen patient-specific computational models for transcatheter aortic valve replacement (TAVR) with balloon-expandable Sapien XT devices were retrospectively developed to tune the material parameters of the implantation site mechanical model for the average TAVR population. Pre-procedural computed tomography (CT) images were post-processed to create the 3D patient-specific anatomy of the implantation site. Balloon valvuloplasty and device deployment were simulated with finite element (FE) analysis. Valve leaflets and aortic root were modelled as linear elastic materials, while calcification as elastoplastic. Material properties were initially selected from literature; then, a statistical analysis was designed to investigate the effect of each implantation site material parameter on the implanted stent diameter and thus identify the combination of material parameters for TAVR patients. These numerical models were validated against clinical data. The comparison between stent diameters measured from post-procedural fluoroscopy images and final computational results showed a mean difference of 2.5 ± 3.9%. Moreover, the numerical model detected the presence of paravalvular leakage (PVL) in 79% of cases, as assessed by post-TAVR echocardiographic examination. The final aim was to increase accuracy and reliability of such computational tools for prospective clinical applications.
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Affiliation(s)
- Giorgia M Bosi
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK; Cardiovascular Engineering Laboratory, UCL Mechanical Engineering, London, UK.
| | - Claudio Capelli
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Mun Hong Cheang
- Barts Health NHS Trust, University College London Hospital, London, UK
| | - Nicola Delahunty
- Barts Health NHS Trust, University College London Hospital, London, UK
| | - Michael Mullen
- Barts Health NHS Trust, University College London Hospital, London, UK
| | - Andrew M Taylor
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Silvia Schievano
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
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10
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Schroeder F, Polzer S, Slažanský M, Man V, Skácel P. Predictive capabilities of various constitutive models for arterial tissue. J Mech Behav Biomed Mater 2018; 78:369-380. [DOI: 10.1016/j.jmbbm.2017.11.035] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2017] [Revised: 11/09/2017] [Accepted: 11/20/2017] [Indexed: 11/16/2022]
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11
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Cheng CP, Zhu YD, Suh GY. Optimization of three-dimensional modeling for geometric precision and efficiency for healthy and diseased aortas. Comput Methods Biomech Biomed Engin 2018; 21:65-74. [DOI: 10.1080/10255842.2017.1423291] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
| | - Yufei D. Zhu
- Department of Surgery, Stanford University, Stanford, CA, USA
| | - Ga-Young Suh
- Department of Surgery, Stanford University, Stanford, CA, USA
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12
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Bersi MR, Bellini C, Di Achille P, Humphrey JD, Genovese K, Avril S. Novel Methodology for Characterizing Regional Variations in the Material Properties of Murine Aortas. J Biomech Eng 2017; 138:2525708. [PMID: 27210500 DOI: 10.1115/1.4033674] [Citation(s) in RCA: 50] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Indexed: 01/06/2023]
Abstract
Many vascular disorders, including aortic aneurysms and dissections, are characterized by localized changes in wall composition and structure. Notwithstanding the importance of histopathologic changes that occur at the microstructural level, macroscopic manifestations ultimately dictate the mechanical functionality and structural integrity of the aortic wall. Understanding structure-function relationships locally is thus critical for gaining increased insight into conditions that render a vessel susceptible to disease or failure. Given the scarcity of human data, mouse models are increasingly useful in this regard. In this paper, we present a novel inverse characterization of regional, nonlinear, anisotropic properties of the murine aorta. Full-field biaxial data are collected using a panoramic-digital image correlation (p-DIC) system. An inverse method, based on the principle of virtual power (PVP), is used to estimate values of material parameters regionally for a microstructurally motivated constitutive relation. We validate our experimental-computational approach by comparing results to those from standard biaxial testing. The results for the nondiseased suprarenal abdominal aorta from apolipoprotein-E null mice reveal material heterogeneities, with significant differences between dorsal and ventral as well as between proximal and distal locations, which may arise in part due to differential perivascular support and localized branches. Overall results were validated for both a membrane and a thick-wall model that delineated medial and adventitial properties. Whereas full-field characterization can be useful in the study of normal arteries, we submit that it will be particularly useful for studying complex lesions such as aneurysms, which can now be pursued with confidence given the present validation.
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13
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Liu M, Liang L, Sun W. Estimation of in vivo mechanical properties of the aortic wall: A multi-resolution direct search approach. J Mech Behav Biomed Mater 2017; 77:649-659. [PMID: 29101897 DOI: 10.1016/j.jmbbm.2017.10.022] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2017] [Revised: 10/02/2017] [Accepted: 10/16/2017] [Indexed: 11/18/2022]
Abstract
The patient-specific biomechanical analysis of the aorta requires in vivo mechanical properties of individual patients. Existing approaches for estimating in vivo material properties often demand high computational cost and mesh correspondence of the aortic wall between different cardiac phases. In this paper, we propose a novel multi-resolution direct search (MRDS) approach for estimation of the nonlinear, anisotropic constitutive parameters of the aortic wall. Based on the finite element (FE) updating scheme, the MRDS approach consists of the following three steps: (1) representing constitutive parameters with multiple resolutions using principal component analysis (PCA), (2) building links between the discretized PCA spaces at different resolutions, and (3) searching the PCA spaces in a 'coarse to fine' fashion following the links. The estimation of material parameters is achieved by minimizing a node-to-surface error function, which does not need mesh correspondence. The method was validated through a numerical experiment by using the in vivo data from a patient with ascending thoracic aortic aneurysm (ATAA), the results show that the number of FE iterations was significantly reduced compared to previous methods. The approach was also applied to the in vivo CT data from an aged healthy human patient, and using the estimated material parameters, the FE-computed geometry was well matched with the image-derived geometry. This novel MRDS approach may facilitate the personalized biomechanical analysis of aortic tissues, such as the rupture risk analysis of ATAA, which requires fast feedback to clinicians.
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MESH Headings
- Aged
- Algorithms
- Anisotropy
- Aorta/diagnostic imaging
- Aorta/physiology
- Aorta, Abdominal/diagnostic imaging
- Aorta, Abdominal/physiology
- Aorta, Thoracic/diagnostic imaging
- Aorta, Thoracic/physiology
- Aortic Aneurysm, Thoracic/diagnostic imaging
- Aortic Aneurysm, Thoracic/pathology
- Blood Pressure
- Computer Simulation
- Elasticity
- Endothelium, Vascular/pathology
- Finite Element Analysis
- Humans
- Models, Cardiovascular
- Principal Component Analysis
- Software
- Stress, Mechanical
- Tomography, X-Ray Computed
- Ultrasonography
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Affiliation(s)
- Minliang Liu
- Tissue Mechanics Laboratory, The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| | - Liang Liang
- Tissue Mechanics Laboratory, The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States
| | - Wei Sun
- Tissue Mechanics Laboratory, The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, United States.
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14
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A new inverse method for estimation of in vivo mechanical properties of the aortic wall. J Mech Behav Biomed Mater 2017; 72:148-158. [PMID: 28494272 DOI: 10.1016/j.jmbbm.2017.05.001] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 04/20/2017] [Accepted: 05/01/2017] [Indexed: 01/02/2023]
Abstract
The aortic wall is always loaded in vivo, which makes it challenging to estimate the material parameters of its nonlinear, anisotropic constitutive equation from in vivo image data. Previous approaches largely relied on either computationally expensive finite element models or simplifications of the geometry or material models. In this study, we investigated a new inverse method based on aortic wall stress computation. This approach consists of the following two steps: (1) computing an "almost true" stress field from the in vivo geometries and loading conditions, (2) building an objective function based on the "almost true" stress fields, constitutive equations and deformation relations, and estimating the material parameters by minimizing the objective function. The method was validated through numerical experiments by using the in vivo data from four ascending aortic aneurysm (AsAA) patients. The results demonstrated that the method is computationally efficient. This novel approach may facilitate the personalized biomechanical analysis of aortic tissues in clinical applications, such as in the rupture risk analysis of ascending aortic aneurysms.
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15
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Bosi GM, Biffi B, Biglino G, Lintas V, Jones R, Tzamtzis S, Burriesci G, Migliavacca F, Khambadkone S, Taylor AM, Schievano S. Can finite element models of ballooning procedures yield mechanical response of the cardiovascular site to overexpansion? J Biomech 2016; 49:2778-2784. [PMID: 27395759 PMCID: PMC5522534 DOI: 10.1016/j.jbiomech.2016.06.021] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2015] [Revised: 06/09/2016] [Accepted: 06/13/2016] [Indexed: 11/23/2022]
Abstract
Patient-specific numerical models could aid the decision-making process for percutaneous valve selection; in order to be fully informative, they should include patient-specific data of both anatomy and mechanics of the implantation site. This information can be derived from routine clinical imaging during the cardiac cycle, but data on the implantation site mechanical response to device expansion are not routinely available. We aim to derive the implantation site response to overexpansion by monitoring pressure/dimensional changes during balloon sizing procedures and by applying a reverse engineering approach using a validated computational balloon model. This study presents the proof of concept for such computational framework tested in-vitro. A finite element (FE) model of a PTS-X405 sizing balloon (NuMed, Inc., USA) was created and validated against bench tests carried out on an ad hoc experimental apparatus: first on the balloon alone to replicate free expansion; second on the inflation of the balloon in a rapid prototyped cylinder with material deemed suitable for replicating pulmonary arteries in order to validate balloon/implantation site interaction algorithm. Finally, the balloon was inflated inside a compliant rapid prototyped patient-specific right ventricular outflow tract to test the validity of the approach. The corresponding FE simulation was set up to iteratively infer the mechanical response of the anatomical model. The test in this simplified condition confirmed the feasibility of the proposed approach and the potential for this methodology to provide patient-specific information on mechanical response of the implantation site when overexpanded, ultimately for more realistic computational simulations in patient-specific settings.
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Affiliation(s)
- Giorgia M Bosi
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK.
| | - Benedetta Biffi
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK; Department of Medical Physics & Biomedical Engineering, UCL, London, UK
| | - Giovanni Biglino
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Valentina Lintas
- Laboratory of Biological Structure Mechanics (LaBS), Chemistry, Materials and Chemical Engineering Department "Giulio Natta", Politecnico di Milano, Italy
| | - Rod Jones
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Spyros Tzamtzis
- UCL Mechanical Engineering, Cardiovascular Engineering Laboratory, University College London, UK
| | - Gaetano Burriesci
- UCL Mechanical Engineering, Cardiovascular Engineering Laboratory, University College London, UK
| | - Francesco Migliavacca
- Laboratory of Biological Structure Mechanics (LaBS), Chemistry, Materials and Chemical Engineering Department "Giulio Natta", Politecnico di Milano, Italy
| | - Sachin Khambadkone
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Andrew M Taylor
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
| | - Silvia Schievano
- Centre for Cardiovascular Imaging, UCL Institute of Cardiovascular Science & Great Ormond Street Hospital for Children, London, UK
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16
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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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17
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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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18
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Zeinali-Davarani S, Wang Y, Chow MJ, Turcotte R, Zhang Y. Contribution of collagen fiber undulation to regional biomechanical properties along porcine thoracic aorta. J Biomech Eng 2015; 137:051001. [PMID: 25612301 DOI: 10.1115/1.4029637] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2014] [Indexed: 01/15/2023]
Abstract
As major extracellular matrix components, elastin, and collagen play crucial roles in regulating the mechanical properties of the aortic wall and, thus, the normal cardiovascular function. The mechanical properties of aorta, known to vary with age and multitude of diseases as well as the proximity to the heart, have been attributed to the variations in the content and architecture of wall constituents. This study is focused on the role of layer-specific collagen undulation in the variation of mechanical properties along the porcine descending thoracic aorta. Planar biaxial tensile tests are performed to characterize the hyperelastic anisotropic mechanical behavior of tissues dissected from four locations along the thoracic aorta. Multiphoton microscopy is used to image the associated regional microstructure. Exponential-based and recruitment-based constitutive models are used to account for the observed mechanical behavior while considering the aortic wall as a composite of two layers with independent properties. An elevated stiffness is observed in distal regions compared to proximal regions of thoracic aorta, consistent with sharper and earlier collagen recruitment estimated for medial and adventitial layers in the models. Multiphoton images further support our prediction that higher stiffness in distal regions is associated with less undulation in collagen fibers. Recruitment-based models further reveal that regardless of the location, collagen in the media is recruited from the onset of stretching, whereas adventitial collagen starts to engage with a delay. A parameter sensitivity analysis is performed to discriminate between the models in terms of the confidence in the estimated model parameters.
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19
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Aparício P, Mandaltsi A, Boamah J, Chen H, Selimovic A, Bratby M, Uberoi R, Ventikos Y, Watton PN. Modelling the influence of endothelial heterogeneity on the progression of arterial disease: application to abdominal aortic aneurysm evolution. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2014; 30:563-586. [PMID: 24424963 DOI: 10.1002/cnm.2620] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2013] [Revised: 09/19/2013] [Accepted: 11/18/2013] [Indexed: 06/03/2023]
Abstract
We sophisticate a fluid-solid growth computational framework for modelling aneurysm evolution. A realistic structural model of the arterial wall is integrated into a patient-specific geometry of the vasculature. This enables physiologically representative distributions of haemodynamic stimuli, obtained from a rigid-wall computational fluid dynamics analysis, to be linked to growth and remodelling algorithms. Additionally, a quasistatic structural analysis quantifies the cyclic deformation of the arterial wall so that collagen growth and remodelling can be explicitly linked to the cyclic deformation of vascular cells. To simulate aneurysm evolution, degradation of elastin is driven by reductions in wall shear stress (WSS) below homeostatic thresholds. Given that the endothelium exhibits spatial and temporal heterogeneity, we propose a novel approach to define the homeostatic WSS thresholds: We allow them to be spatially and temporally heterogeneous. We illustrate the application of this novel fluid-solid growth framework to model abdominal aortic aneurysm (AAA) evolution and to examine how the influence of the definition of the WSS homeostatic threshold influences AAA progression. We conclude that improved understanding and modelling of the endothelial heterogeneity is important for modelling aneurysm evolution and, more generally, other vascular diseases where haemodynamic stimuli play an important role.
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Affiliation(s)
- P Aparício
- Systems Biology Doctoral Training Centre, University of Oxford, Oxford, UK
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20
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Grytz R, Fazio MA, Girard MJA, Libertiaux V, Bruno L, Gardiner S, Girkin CA, Downs JC. Material properties of the posterior human sclera. J Mech Behav Biomed Mater 2013; 29:602-17. [PMID: 23684352 DOI: 10.1016/j.jmbbm.2013.03.027] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2013] [Accepted: 03/26/2013] [Indexed: 11/17/2022]
Abstract
To characterize the material properties of posterior and peripapillary sclera from human donors, and to investigate the macro- and micro-scale strains as potential control mechanisms governing mechanical homeostasis. Posterior scleral shells from 9 human donors aged 57-90 years were subjected to IOP elevations from 5 to 45mmHg and the resulting full-field displacements were recorded using laser speckle interferometry. Eye-specific finite element models were generated based on experimentally measured scleral shell surface geometry and thickness. Inverse numerical analyses were performed to identify material parameters for each eye by matching experimental deformation measurements to model predictions using a microstructure-based constitutive formulation that incorporates the crimp response and anisotropic architecture of scleral collagen fibrils. The material property fitting produced models that fit both the overall and local deformation responses of posterior scleral shells very well. The nonlinear stiffening of the sclera with increasing IOP was well reproduced by the uncrimping of scleral collagen fibrils, and a circumferentially aligned ring of collagen fibrils around the scleral canal was predicted in all eyes. Macroscopic in-plane strains were significantly higher in peripapillary region then in the mid-periphery. In contrast, the meso- and micro-scale strains at the collagen network and collagen fibril level were not significantly different between regions. The elastic response of the posterior human sclera can be characterized by the anisotropic architecture and crimp response of scleral collagen fibrils. The similar collagen fibril strains in the peripapillary and mid-peripheral regions support the notion that the scleral collagen architecture including the circumpapillary ring of collagen fibrils evolved to establish optimal load bearing conditions at the collagen fibril level.
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Affiliation(s)
- Rafael Grytz
- Ophthalmology, University of Alabama at Birmingham, Birmingham, AL, USA.
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21
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Measuring and modeling patient-specific distributions of material properties in abdominal aortic aneurysm wall. Biomech Model Mechanobiol 2012; 12:717-33. [PMID: 22955570 DOI: 10.1007/s10237-012-0436-1] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Accepted: 08/22/2012] [Indexed: 10/27/2022]
Abstract
Both the clinically established diameter criterion and novel approaches of computational finite element (FE) analyses for rupture risk stratification of abdominal aortic aneurysms (AAA) are based on assumptions of population-averaged, uniform material properties for the AAA wall. The presence of inter-patient and intra-patient variations in material properties is known, but has so far not been addressed sufficiently. In order to enable the preoperative estimation of patient-specific AAA wall properties in the future, we investigated the relationship between non-invasively assessable clinical parameters and experimentally measured AAA wall properties. We harvested n = 163 AAA wall specimens (n = 50 patients) during open surgery and recorded the exact excision sites. Specimens were tested for their thickness, elastic properties, and failure loads using uniaxial tensile tests. In addition, 43 non-invasively assessable patient-specific or specimen-specific parameters were obtained from recordings made during surgery and patient charts. Experimental results were correlated with the non-invasively assessable parameters and simple regression models were created to mathematically describe the relationships. Wall thickness was most significantly correlated with the metabolic activity at the excision site assessed by PET/CT (ρ = 0.499, P = 4 × 10(-7)) and to thrombocyte counts from laboratory blood analyses (ρ = 0.445, P = 3 × 10(-9)). Wall thickness was increased in patients suffering from diabetes mellitus, while it was significantly thinner in patients suffering from chronic kidney disease (CKD). Elastic AAA wall properties had significant correlations with the metabolic activity at the excision site (PET/CT), with existent calcifications, and with the diameter of the non-dilated aorta proximal to the AAA. Failure properties (wall strength and failure tension) had correlations with the patient's medical history and with results from laboratory blood analyses. Interestingly, AAA wall failure tension was significantly reduced for patients with CKD and elevated blood levels of potassium and urea, respectively, both of which are associated with kidney disease. This study is a first step to a future preoperative estimation of AAA wall properties. Results can be conveyed to both the diameter criterion and FE analyses to refine rupture risk prediction. The fact that AAA wall from patients suffering from CKD featured reduced failure tension implies an increased AAA rupture risk for this patient group at comparably smaller AAA diameters.
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22
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Grytz R, Girkin CA, Libertiaux V, Downs JC. Perspectives on biomechanical growth and remodeling mechanisms in glaucoma(). MECHANICS RESEARCH COMMUNICATIONS 2012; 42:92-106. [PMID: 23109748 PMCID: PMC3482120 DOI: 10.1016/j.mechrescom.2012.01.007] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Glaucoma is a blinding diseases in which damage to the axons results in loss of retinal ganglion cells. Experimental evidence indicates that chronic intraocular pressure elevation initiates axonal insult at the level of the lamina cribrosa. The lamina cribrosa is a porous collagen structure through which the axons pass on their path from the retina to the brain. Recent experimental studies revealed the extensive structural changes of the lamina cribrosa and its surrounding tissues during the development and progression of glaucoma. In this perspective paper we review the experimental evidence for growth and remodeling mechanisms in glaucoma including adaptation of tissue anisotropy, tissue thickening/thinning, tissue elongation/shortening and tissue migration. We discuss the existing predictive computational approaches that try to elucidate the potential biomechanical basis of theses growth and remodeling mechanisms and highlight open questions, challenges, and avenues for further development.
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Affiliation(s)
- Rafael Grytz
- Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, OR, United States
| | - Christopher A. Girkin
- Department of Ophthalmology, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Vincent Libertiaux
- Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, OR, United States
| | - J. Crawford Downs
- Ocular Biomechanics Laboratory, Devers Eye Institute, Portland, OR, United States
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23
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Humphrey JD, Holzapfel GA. Mechanics, mechanobiology, and modeling of human abdominal aorta and aneurysms. J Biomech 2012; 45:805-14. [PMID: 22189249 PMCID: PMC3294195 DOI: 10.1016/j.jbiomech.2011.11.021] [Citation(s) in RCA: 185] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/10/2011] [Indexed: 12/25/2022]
Abstract
Biomechanical factors play fundamental roles in the natural history of abdominal aortic aneurysms (AAAs) and their responses to treatment. Advances during the past two decades have increased our understanding of the mechanics and biology of the human abdominal aorta and AAAs, yet there remains a pressing need for considerable new data and resulting patient-specific computational models that can better describe the current status of a lesion and better predict the evolution of lesion geometry, composition, and material properties and thereby improve interventional planning. In this paper, we briefly review data on the structure and function of the human abdominal aorta and aneurysmal wall, past models of the mechanics, and recent growth and remodeling models. We conclude by identifying open problems that we hope will motivate studies to improve our computational modeling and thus general understanding of AAAs.
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Affiliation(s)
- J D Humphrey
- Department of Biomedical Engineering and Vascular Biology and Therapeutics Program, Malone Engineering Center, Yale University, New Haven, CT 06520-8260, USA.
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24
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Kwon ST, Rectenwald JE, Baek S. Intrasac pressure changes and vascular remodeling after endovascular repair of abdominal aortic aneurysms: review and biomechanical model simulation. J Biomech Eng 2011; 133:011011. [PMID: 21186901 DOI: 10.1115/1.4003134] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In this paper, we review existing clinical research data on post-endovascular repair (EVAR) intrasac pressure and relation with abdominal aortic aneurysm (AAA) size changes. Based on the review, we hypothesize that intrasac pressure has a significant impact on post-EVAR AAA size changes, and post-EVAR remodeling depends also on how the pressure has changed over a period of time. The previously developed model of an AAA based on a constrained mixture approach is extended to include vascular adaptation after EVAR using an idealized geometry. Computational simulation shows that the same mechanism of collagen stress-mediated remodeling in AAA expansion induces the aneurysm wall to shrink in a reduced sac-pressure after post-EVAR. Computational simulation suggests that the intrasac pressure of 60 mm Hg is a critical value. At this value, the AAA remains stable, while values above cause the AAA to expand and values below cause the AAA to shrink. There are, however, variations between individuals due to different cellular sensitivities in stress-mediated adaptation. Computer simulation also indicates that an initial decrease in intrasac pressure helps the AAA shrink even if the pressure increases after some time. The presented study suggests that biomechanics has a major effect on initial adaptation after EVAR and also illustrates the utility of a computational model of vascular growth and remodeling in predicting diameter changes during the progression and after the treatment of AAAs.
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Affiliation(s)
- S T Kwon
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD 21218, USA
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