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      Effects of Variations of Flow and Heart Rate on Intra-Aneurysmal Hemodynamics in a Ruptured Internal Carotid Artery Aneurysm During Exercise

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          Abstract

          Background:

          Hemodynamics is thought to play an important role in the mechanisms responsible for initiation, growth, and rupture of intracranial aneurysms. Computational fluid dynamic (CFD) analysis is used to assess intra-aneurysmal hemodynamics.

          Objectives:

          This study aimed to investigate the effects of variations in heart rate and internal carotid artery (ICA) flow rate on intra-aneurysmal hemodynamics, in an ICA aneurysm, by using computational fluid dynamics.

          Patients and Methods:

          Computed tomography angiography (CTA) was performed in a 55 years old female case, with a saccular ICA aneurysm, to create a patient-specific geometrical anatomic model of the aneurysm. The intra-aneurysmal hemodynamic environments for three states with different flow and heart rates were analyzed using patient-specific image-based CFD modeling.

          Results:

          Results showed significant changes for the three simulated states. For a proportion of the states examined, results were counterintuitive. Systolic and time-averaged wall shear stress and pressure on the aneurysm wall showed a proportional evolution with the mainstream flow rate.

          Conclusion:

          Results reinforced the pivotal role of vascular geometry, with respect to hemodynamics, together with the importance of performing patient-specific CFD analyses, through which the effect of different blood flow conditions on the aneurysm hemodynamics could be evaluated.

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          Magnitude and role of wall shear stress on cerebral aneurysm: computational fluid dynamic study of 20 middle cerebral artery aneurysms.

          Masaaki Shojima, Marie Oshima, Kiyoshi Takagi … (2004)
          Wall shear stress (WSS) is one of the main pathogenic factors in the development of saccular cerebral aneurysms. The magnitude and distribution of the WSS in and around human middle cerebral artery (MCA) aneurysms were analyzed using the method of computed fluid dynamics (CFD). Twenty mathematical models of MCA vessels with aneurysms were created by 3-dimensional computed tomographic angiography. CFD calculations were performed by using our original finite-element solver with the assumption of Newtonian fluid property for blood and the rigid wall property for the vessel and the aneurysm. The maximum WSS in the calculated region tended to occur near the neck of the aneurysm, not in its tip or bleb. The magnitude of the maximum WSS was 14.39+/-6.21 N/m2, which was 4-times higher than the average WSS in the vessel region (3.64+/-1.25 N/m2). The average WSS of the aneurysm region (1.64+/-1.16 N/m2) was significantly lower than that of the vessel region (P<0.05). The WSSs at the tip of ruptured aneurysms were markedly low. These results suggest that in contrast to the pathogenic effect of a high WSS in the initiating phase, a low WSS may facilitate the growing phase and may trigger the rupture of a cerebral aneurysm by causing degenerative changes in the aneurysm wall. The WSS of the aneurysm region may be of some help for the prediction of rupture.
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            Quantitative characterization of the hemodynamic environment in ruptured and unruptured brain aneurysms.

            J Cebral, F Mut, J. Weir … (2011)
            Hemodynamics are thought to play an important role in the mechanisms of aneurysm pathogenesis, progression, and rupture. The purpose of this study was to define quantitative measures related to qualitative flow characteristics previously analyzed and to investigate their relationship to aneurysm rupture. The hemodynamic environments in 210 cerebral aneurysms were analyzed by using image-based CFD under different flow conditions. Quantitative hemodynamic variables were defined and extracted from the simulation results. A statistical analysis of the relationship to the previous history of aneurysm rupture was performed, and the variability with flow conditions was assessed. Ruptured aneurysms were more likely to have larger inflow concentrations, larger MWSS, larger shear concentrations, and lower viscous dissipation ratios than unruptured aneurysms. Areas under low WSS and measures of abnormally low shear force distributions of ruptured and unruptured aneurysms were not statistically different. Although the values of hemodynamic quantities changed with different flow conditions, the statistical differences or ratios between their mean values over the ruptured and unruptured groups were maintained, for both pulsatile and steady flows. Concentrated inflow streams and WSS distributions with elevated levels of MWSS and low aneurysmal viscous dissipation are statistically associated with a clinical history of prior aneurysm rupture. In contrast, the area and total viscous shear force applied in the aneurysm region subjected to abnormally low WSS levels are not. This study highlights the potential for image-based CFD for investigating aneurysm-evolution mechanisms and for clinical assessment of aneurysm risks.
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              Aneurysm growth occurs at region of low wall shear stress: patient-specific correlation of hemodynamics and growth in a longitudinal study.

              Nancy Young, R T Higashida, Loic Boussel … (2008)
              Evolution of intracranial aneurysmal disease is known to be related to hemodynamic forces acting on the vessel wall. Low wall shear stress (WSS) has been reported to have a negative effect on endothelial cells normal physiology and may be an important contributor to local remodeling of the arterial wall and to aneurysm growth and rupture. Seven patient-specific models of intracranial aneurysms were constructed using MR angiography data acquired at two different time points (mean 16.4+/-7.4 months between the two time points). Numeric simulations of the flow in the baseline geometries were performed to compute WSS distributions. The lumenal geometries constructed from the two time points were manually coregistered, and the radial displacement of the wall was calculated on a pixel-by-pixel basis. This displacement, corresponding to the local growth of the aneurysm, was compared to the time-averaged wall shear stress (WSS TA) through the cardiac cycle at that location. For statistical analysis, radial displacement was considered to be significant if it was larger than half of the MR pixel resolution (0.3 mm). Mean WSS TA values obtained for the areas with a displacement smaller and greater than 0.3 mm were 2.55+/-3.6 and 0.76+/-1.5 Pa, respectively (P<0.001). A linear correlation analysis demonstrated a significant relationship between WSS TA and surface displacement (P<0.001). These results indicate that aneurysm growth is likely to occur in regions where the endothelial layer lining the vessel wall is exposed to abnormally low wall shear stress.
              Article 0 comments Cited 106 times – based on 0 reviews     Review now
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                Author and article information

                Journal
                Journal ID (nlm-ta): Iran J Radiol
                Journal ID (iso-abbrev): Iran J Radiol
                Journal ID (doi): 10.5812/iranjradiol
                Journal ID (publisher-id): Kowsar
                Title: Iranian Journal of Radiology
                Publisher: Kowsar
                ISSN (Print): 1735-1065
                ISSN (Electronic): 2008-2711
                Publication date (Electronic): 02 January 2016
                Publication date Collection: January 2016
                Volume: 13
                Issue: 1
                Electronic Location Identifier: e18217
                Affiliations
                [1 ]Department of Chemical Engineering, Isfahan University of Technology, Isfahan, Iran
                [2 ]Medical Physics and Biomedical Engineering, Tehran University of Medical Sciences, Tehran, Iran
                [3 ]Advanced Diagnostic and Interventional Radiology Research Center (ADIR), Tehran University of Medical Sciences, Tehran, Iran
                Author notes
                [* ]Corresponding author: Mohsen Nasr Esfahany, Department of Chemical Engineering, Isfahan University of Technology, Isfahan, Iran. Tel: +98-3133915631, Fax: +98-3113912677, E-mail: mnasr@ 123456cc.iut.ac.ir
                Article
                DOI: 10.5812/iranjradiol.18217
                PMC ID: 4837368
                PubMed ID: 27110332
                SO-VID: 7ed21c3e-bd1b-43e4-a9d4-14b45bf52272
                Copyright © Copyright © 2016, Tehran University of Medical Sciences and Iranian Society of Radiology.
                License:

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License ( http://creativecommons.org/licenses/by-nc/4.0/) which permits copy and redistribute the material just in noncommercial usages, provided the original work is properly cited.

                History
                Date received : 13 February 2014
                Date revision received : 18 June 2014
                Date accepted : 20 July 2014
                Categories
                Subject: Physics

                ScienceOpen disciplines: Radiology & Imaging
                Keywords: fluid dynamics,internal carotid artery,aneurysm,heart rate
                Data availability:
                ScienceOpen disciplines: Radiology & Imaging
                Keywords: fluid dynamics, internal carotid artery, aneurysm, heart rate

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