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Effect of Pulsatility on the Transport of Thrombin in an Idealized Cerebral Aneurysm Geometry. Symmetry (Basel) 2022. [DOI: 10.3390/sym14010133] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Computational models of cerebral aneurysm thrombosis are designed for use in research and clinical applications. A steady flow assumption is applied in many of these models. To explore the accuracy of this assumption a pulsatile-flow thrombin-transport computational fluid dynamics (CFD) model, which uses a symmetrical idealized aneurysm geometry, was developed. First, a steady-flow computational model was developed and validated using data from an in vitro experiment, based on particle image velocimetry (PIV). The experimental data revealed an asymmetric flow pattern in the aneurysm. The validated computational model was subsequently altered to incorporate pulsatility, by applying a data-derived flow function at the inlet boundary. For both the steady and pulsatile computational models, a scalar function simulating thrombin generation was applied at the aneurysm wall. To determine the influence of pulsatility on thrombin transport, the outputs of the steady model were compared to the outputs of the pulsatile model. The comparison revealed that in the pulsatile case, an average of 10.2% less thrombin accumulates within the aneurysm than the steady case for any given time, due to periodic losses of a significant amount of thrombin-concentrated blood from the aneurysm into the parent vessel’s bloodstream. These findings demonstrate that pulsatility may change clotting outcomes in cerebral aneurysms.
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Pandey PK, Paul C, Das MK, Muralidhar K. Assessment and visualization of hemodynamic loading in aneurysm sac and neck: Effect of foam insertion. Proc Inst Mech Eng H 2021; 235:927-939. [PMID: 33971763 DOI: 10.1177/09544119211015569] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Shape memory polymer (SMP) foam is often proposed as the future alternative of coils in aneurysm treatment devices. Present work numerically investigates the unsteady, three-dimensional simulation of blood flow in a cerebral aneurysm filled with SMP foam. Simulations are conducted on patient-specific geometries with realistic blood velocity waveform imposed at the inlet while SMP foam is treated as a porous medium. The present study introduces a "loading risk map" that helps to visualize the hemodynamic effect of foam insertion on the aneurysm sac and neck. The loading risk maps suggest that while the SMP foam subdues the flow and wall shear pulsations in the aneurysm sac, the pressure distribution is minimally affected. The maps suggest that while the downstream lip is the most risk-prone site for both geometries, downstream vascular anatomy significantly influences foam efficiency in reducing pressure and wall shear stress loading.
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Affiliation(s)
- Pawan Kumar Pandey
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP, India
| | - Chandan Paul
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP, India
| | - Malay K Das
- Department of Mechanical Engineering, Indian Institute of Technology Kanpur, Kanpur, UP, India
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Stockle J, Romero DA, Amon CH. Optimization of porous stents for endovascular repair of abdominal aortic aneurysms. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2020; 36:e3336. [PMID: 32212322 DOI: 10.1002/cnm.3336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Revised: 01/21/2020] [Accepted: 03/17/2020] [Indexed: 06/10/2023]
Abstract
This study presents a simulation-based methodology to design porous stents to induce suitable hemodynamic environments inside abdominal aortic aneurysm (AAA) sacs. In the proposed methodology, an optimization algorithm iteratively modifies the porosity distribution of the stent and executes a computational fluid dynamics (CFD) simulation to determine the effect of these changes on the hemodynamic conditions inside the aneurysm sac. The optimization iterations proceed until relevant hemodynamic parameters are within ranges prescribed a priori by the user as desirable to control the progression of the AAA. The resulting porosity distribution uniquely describes the porous stent design that can control the hemodynamic environment (eg, shear stress at the aneurysm wall, pressure distribution, residence time), reducing AAA rupture risks and improving treatment efficacy. To demonstrate its potential, the proposed methodology is applied to idealized AAA geometry under steady-state flow conditions, though it may be easily applied to more complex AAA geometries under transient, pulsatile flow conditions. The proposed methodology has the potential to enable the design of a new generation of porous stents tailored to patient-specific geometries and flow conditions, to improve patient outcomes.
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Affiliation(s)
- Juan Stockle
- Escuela de Ingenieria Industrial, Universidad Diego Portales, Santiago, Chile
| | - David A Romero
- Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
| | - Cristina H Amon
- Mechanical and Industrial Engineering, University of Toronto, Toronto, Ontario, Canada
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
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Saqr KM. Computational fluid dynamics simulations of cerebral aneurysm using Newtonian, power-law and quasi-mechanistic blood viscosity models. Proc Inst Mech Eng H 2020; 234:711-719. [PMID: 32423286 DOI: 10.1177/0954411920917531] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Cerebral aneurysm is a fatal neurovascular disorder. Computational fluid dynamics simulation of aneurysm haemodynamics is one of the most important research tools which provide increasing potential for clinical applications. However, computational fluid dynamics modelling of such delicate neurovascular disorder involves physical complexities that cannot be easily simplified. Recently, it was shown that the Newtonian simplification used to close the shear stress tensor of the Navier-Stokes equation is not sufficient to explore aneurysm haemodynamics. This article explores the differences between the latter simplification, non-Newtonian power-law model and a newly proposed quasi-mechanistic model. The modified Krieger model, which treats blood as a suspension of plasma and particles, was implemented in computational fluid dynamics context here for the first time and is made available to the readers in a C# code in the supplementary material of this article. Two middle-cerebral artery and two anterior-communicating artery aneurysms, all ruptured, were utilized here as case studies. It was shown that the modified Krieger model had higher sensitivity for wall shear stress calculations in comparison with the other two models. The modified Krieger model yielded lower wall shear stress values consistently in comparison with the other two models. Moreover, the modified Krieger model has generally predicted higher pressure in the aneurysm models. Based on published aneurysm rupture studies, it is believed that ruptured aneurysms are usually correlated with lower wall shear stress values than unruptured ones. Therefore, this work concludes that the modified Krieger model is a potential candidate for providing better clinical relevance to aneurysm computational fluid dynamics simulations.
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Affiliation(s)
- Khalid M Saqr
- Mechanical Engineering Department, College of Engineering and Technology, Arab Academy for Science, Technology and Maritime Transport (AASTMT), Alexandria, Egypt
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Sarrami-Foroushani A, Lassila T, Frangi AF. Virtual endovascular treatment of intracranial aneurysms: models and uncertainty. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2017; 9. [PMID: 28488754 DOI: 10.1002/wsbm.1385] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 01/09/2017] [Accepted: 02/07/2017] [Indexed: 01/11/2023]
Abstract
Virtual endovascular treatment models (VETMs) have been developed with the view to aid interventional neuroradiologists and neurosurgeons to pre-operatively analyze the comparative efficacy and safety of endovascular treatments for intracranial aneurysms. Based on the current state of VETMs in aneurysm rupture risk stratification and in patient-specific prediction of treatment outcomes, we argue there is a need to go beyond personalized biomechanical flow modeling assuming deterministic parameters and error-free measurements. The mechanobiological effects associated with blood clot formation are important factors in therapeutic decision making and models of post-treatment intra-aneurysmal biology and biochemistry should be linked to the purely hemodynamic models to improve the predictive power of current VETMs. The influence of model and parameter uncertainties associated to each component of a VETM is, where feasible, quantified via a random-effects meta-analysis of the literature. This allows estimating the pooled effect size of these uncertainties on aneurysmal wall shear stress. From such meta-analyses, two main sources of uncertainty emerge where research efforts have so far been limited: (1) vascular wall distensibility, and (2) intra/intersubject systemic flow variations. In the future, we suggest that current deterministic computational simulations need to be extended with strategies for uncertainty mitigation, uncertainty exploration, and sensitivity reduction techniques. WIREs Syst Biol Med 2017, 9:e1385. doi: 10.1002/wsbm.1385 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Ali Sarrami-Foroushani
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
| | - Toni Lassila
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
| | - Alejandro F Frangi
- Center for Computational Imaging and Simulation Technologies in Biomedicine (CISTIB), The University of Sheffield, Sheffield, UK
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Carty G, Chatpun S, Espino DM. Modeling Blood Flow Through Intracranial Aneurysms: A Comparison of Newtonian and Non-Newtonian Viscosity. J Med Biol Eng 2016. [DOI: 10.1007/s40846-016-0142-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Larrabide I, Geers AJ, Morales HG, Bijlenga P, Rüfenacht DA. Change in aneurysmal flow pulsatility after flow diverter treatment. Comput Med Imaging Graph 2016; 50:2-8. [DOI: 10.1016/j.compmedimag.2015.01.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2014] [Revised: 12/16/2014] [Accepted: 01/19/2015] [Indexed: 11/30/2022]
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Chung B, Cebral JR. CFD for Evaluation and Treatment Planning of Aneurysms: Review of Proposed Clinical Uses and Their Challenges. Ann Biomed Eng 2014; 43:122-38. [DOI: 10.1007/s10439-014-1093-6] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Accepted: 08/08/2014] [Indexed: 11/29/2022]
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On the Characterization of a Non-Newtonian Blood Analog and Its Response to Pulsatile Flow Downstream of a Simplified Stenosis. Ann Biomed Eng 2013; 42:97-109. [DOI: 10.1007/s10439-013-0893-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Accepted: 08/10/2013] [Indexed: 11/25/2022]
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Bernabeu MO, Nash RW, Groen D, Carver HB, Hetherington J, Krüger T, Coveney PV. Impact of blood rheology on wall shear stress in a model of the middle cerebral artery. Interface Focus 2013; 3:20120094. [PMID: 24427534 PMCID: PMC3638489 DOI: 10.1098/rsfs.2012.0094] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Perturbations to the homeostatic distribution of mechanical forces exerted by blood on the endothelial layer have been correlated with vascular pathologies, including intracranial aneurysms and atherosclerosis. Recent computational work suggests that, in order to correctly characterize such forces, the shear-thinning properties of blood must be taken into account. To the best of our knowledge, these findings have never been compared against experimentally observed pathological thresholds. In this work, we apply the three-band diagram (TBD) analysis due to Gizzi et al. (Gizzi et al. 2011 Three-band decomposition analysis of wall shear stress in pulsatile flows. Phys. Rev. E 83, 031902. (doi:10.1103/PhysRevE.83.031902)) to assess the impact of the choice of blood rheology model on a computational model of the right middle cerebral artery. Our results show that, in the model under study, the differences between the wall shear stress predicted by a Newtonian model and the well-known Carreau-Yasuda generalized Newtonian model are only significant if the vascular pathology under study is associated with a pathological threshold in the range 0.94-1.56 Pa, where the results of the TBD analysis of the rheology models considered differs. Otherwise, we observe no significant differences.
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Affiliation(s)
- Miguel O. Bernabeu
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
- CoMPLEX, University College London, Physics Building, Gower Street, London WC1E 6BT, UK
| | - Rupert W. Nash
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Derek Groen
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Hywel B. Carver
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
- CoMPLEX, University College London, Physics Building, Gower Street, London WC1E 6BT, UK
| | - James Hetherington
- Research Software Development Team, Research Computing and Facilitating Services, University College London, Podium Building, 1st Floor, Gower Street, London WC1E 6BT, UK
| | - Timm Krüger
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
| | - Peter V. Coveney
- Centre for Computational Science, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK
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Walker AM, Johnston CR, Rival DE. The quantification of hemodynamic parameters downstream of a Gianturco Zenith stent wire using newtonian and non-newtonian analog fluids in a pulsatile flow environment. J Biomech Eng 2013; 134:111001. [PMID: 23387783 DOI: 10.1115/1.4007746] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Although deployed in the vasculature to expand vessel diameter and improve blood flow, protruding stent struts can create complex flow environments associated with flow separation and oscillating shear gradients. Given the association between magnitude and direction of wall shear stress (WSS) and endothelial phenotype expression, accurate representation of stent-induced flow patterns is critical if we are to predict sites susceptible to intimal hyperplasia. Despite the number of stents approved for clinical use, quantification on the alteration of hemodynamic flow parameters associated with the Gianturco Z-stent is limited in the literature. In using experimental and computational models to quantify strut-induced flow, the majority of past work has assumed blood or representative analogs to behave as Newtonian fluids. However, recent studies have challenged the validity of this assumption. We present here the experimental quantification of flow through a Gianturco Z-stent wire in representative Newtonian and non-Newtonian blood analog environments using particle image velocimetry (PIV). Fluid analogs were circulated through a closed flow loop at physiologically appropriate flow rates whereupon PIV snapshots were acquired downstream of the wire housed in an acrylic tube with a diameter characteristic of the carotid artery. Hemodynamic parameters including WSS, oscillatory shear index (OSI), and Reynolds shear stresses (RSS) were measured. Our findings show that the introduction of the stent wire altered downstream hemodynamic parameters through a reduction in WSS and increases in OSI and RSS from nonstented flow. The Newtonian analog solution of glycerol and water underestimated WSS while increasing the spatial coverage of flow reversal and oscillatory shear compared to a non-Newtonian fluid of glycerol, water, and xanthan gum. Peak RSS were increased with the Newtonian fluid, although peak values were similar upon a doubling of flow rate. The introduction of the stent wire promoted the development of flow patterns that are susceptible to intimal hyperplasia using both Newtonian and non-Newtonian analogs, although the magnitude of sites affected downstream was appreciably related to the rheological behavior of the analog. While the assumption of linear viscous behavior is often appropriate in quantifying flow in the largest arteries of the vasculature, the results presented here suggest this assumption overestimates sites susceptible to hyperplasia and restenosis in flow characterized by low and oscillatory shear.
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Affiliation(s)
- Andrew M Walker
- Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive N.W., Calgary, AB T2N 1N4, Canada.
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