43 research outputs found

    Numerical approach for the evaluation of hemodynamic behaviour in peripheral arterial disease : A systematic review

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    Reduced blood flow to the lower extremities causes peripheral arterial disease (PAD), which is caused by atherosclerotic plaque in the arterial wall. If this impairment is not treated, it will result in severe vascular diseases like ulceration and gangrene. Previous research has shown that while evaluating the pathology of the peripheral artery, the assumption of the model geometry significantly impacts the uncertainty of the stenosis area. However, more work needs to be done to understand the interaction between mechanical better and flow conditions in the peripheral artery using a separate computer model of the cardiovascular system. This paper reviews the numerical approach on pre and post-treatment of hemodynamic behavior in peripheral arterial disease (PAD). The goal of this study was to thoroughly examine the most recent developments with the application of computational studies in PAD from 2017 to 2022. While FSI investigation highlights the behavior of both the fluid and structure domains (blood and artery) during the numerical analysis of blood flow, CFD simulations primarily focus on the fluid domain (blood) behavior. Out of 92 research publications, 19 were appropriate for this assignment. This thorough study divides the publications into the categories of CFD, and FSI approaches. The results were then reviewed in accordance with the wall characteristic, analytical method, geometry, viscosity models, and validation. This paper summarizes the parameters of geometrical construction, viscosity models, analysis methods, and wall characteristics taken into consideration by the researchers to identify and simulate the blood flood flow in the stenosis area. These parameters are summarised in this study. Additionally, it could offer systematic data to help future studies produce better computational analyse

    The Impact of Myocardial Bridging on Fractional Flow Reserve

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    Arterial stenosis is a problem of immediate significance, as cardiovascular disease is the number one leading cause of death worldwide. Fractional flow reserve (FFR) was proposed to evaluate the functional severity of coronary plaque-induced stenosis more accurately. FFR relies on invasive pressure measurements, while computational fluid dynamics (CFD) studies have been demonstrated to be useful tools to predict FFR less invasively. Myocardial bridging (MB) is an abnormality of the epicardial coronary artery where a segment of artery tunnels through the myocardium. MB presents as a ‘dynamic’ stenosis, in contrast to the ‘fixed’ stenosis caused by plaque: in systole, the artery is compressed due to the heart compression force, while in diastole the compression is non-significant. The objective of the project is to replicate the MB compression phenomenon via fluid-structure interaction (FSI) analysis and identify its impact on FFR. The relationship between ‘fixed’ stenosis and FFR was analyzed as a reference firstly, followed by the introduction of a pressure wire and surface roughness, to determine their impacts on CFD-derived FFR. Secondly, both commercial software and in-house code solver were used to perform FSI study and investigate the mechanism of bridging. With increasing severity of the ‘fixed’ stenosis – 0% to 70% diameter reduction, FFR decreased from 0.96 to 0.55. The presence of the pressure wire led to an overestimation of FFR by 3%-38% in various degrees of stenosis model, while the impact of the surface roughness on FFR was not apparent. Mild MB was studied via COMSOL simulations, while moderate and severe MB models were computed with the in-house code solver. The combination effect of the pressure wire and the upstream plaque in the mild MB was not additive, which was larger than the separate effect caused by each factor. With the increasing of the compression of MB – 44% to 60% diameter reduction, FFR decreased slightly, where the values were larger than 0.92. However, FFR dropped noticeably from 0.84 to 0.75 when the compression of MB increased from 72% to 87%. Furthermore, an expansion was observed in the severe MB model due to a greater inner pressure than outer compression pressure. In conclusion, the flow dynamics of MB were quite different compared to the plaqueinduced or ‘fixed’ stenosis. The use of traditional FFR to evaluate the functional severity of MB should be applied carefully and the cut-off value needs to be amended accordingly

    The Haemodynamics of a Stented Arteriovenous Fistula through Experiments and Flow Modelling

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    The arteriovenous fistula (AVF) is a vasculature created for end-stage renal disease patients who undergo haemodialysis. This vasculature is often affected by stenosis in the juxta-anastomotic (JXA) region and the presence of disturbed haemodynamics within the vessel is known to initiate such diseased conditions. A novel treatment involving the implantation of a flexible stent in the JXA region has shown potential for retaining healthy AVFs. Only a limited number of experimental studies have been conducted to understand the disturbed flow conditions, while the impact of stent implantation on the haemodynamics within the AVF is yet to be explored. The study was initiated by developing a benchtop patient-specific AVF model to conduct a Tomographic Particle Image Velocimetry (Tomo-PIV) measurement. The subsequent temporally resolved volumetric velocity field was phase-averaged to quantify fluctuations occurring over the inlet pulsatile conditions. It was noted that high turbulent kinetic energy (TKE) was generated at the JXA region. To study the effects of the stent implantation, Large Eddy Simulations (LES) comparing the AVF geometry with and without the presence of the stent implantation were conducted. The trajectory of the flow in the stented case was funnelled within the stent encapsulated region which in turn, contained the disturbed flow within the stent lumen while mitigating the generation of turbulence. Consequently, the distribution of adverse wall shear stress (WSS) in the stented region was much lower compared to that of the `stent-absent' case. Simulations were also conducted on the diseased patient AVF, before the stent implantation, to make an overall assessment of the effect of treatment. Larger and persistent regions of high TKE were noted in the vessel downstream of the stenosis despite the lower velocity of flow in the diseased model. In summary, the stent implantation in the patient AVF showed the ability to funnel flow disturbances away from the vessel wall, thereby leading to lower adverse WSS distributions. The presence of the stent also mitigated turbulence generation. These findings provide valuable insight into the favourable haemodynamic effects of this novel endovascular procedure, thus, substantiating this treatment strategy to treat vascular disease in AVFs

    Numerical Simulation in Biomechanics and Biomedical Engineering

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    In the first contribution, Morbiducci and co-workers discuss the theoretical and methodological bases supporting the Lagrangian- and Euler-based methods, highlighting their application to cardiovascular flows. The second contribution, by the Ansón and van Lenthe groups, proposes an automated virtual bench test for evaluating the stability of custom shoulder implants without the necessity of mechanical testing. Urdeitx and Doweidar, in the third paper, also adopt the finite element method for developing a computational model aim to study cardiac cell behavior under mechano-electric stimulation. In the fourth contribution, Ayensa-Jiménez et al. develop a methodology to approximate the multidimensional probability density function of the parametric analysis obtained developing a mathematical model of the cancer evolution. The fifth paper is oriented to the topological data analysis; the group of Cueto and Chinesta designs a predictive model capable of estimating the state of drivers using the data collected from motion sensors. In the sixth contribution, the Ohayon and Finet group uses wall shear stress-derived descriptors to study the role of recirculation in the arterial restenosis due to different malapposed and overlapping stent conditions. In the seventh contribution, the research group of Antón demonstrates that the simulation time can be reduced for cardiovascular numerical analysis considering an adequate geometry-reduction strategy applicable to truncated patient specific artery. In the eighth paper, Grasa and Calvo present a numerical model based on the finite element method for simulating extraocular muscle dynamics. The ninth paper, authored by Kahla et al., presents a mathematical mechano-pharmaco-biological model for bone remodeling. Martínez, Peña, and co-workers propose in the tenth paper a methodology to calibrate the dissection properties of aorta layer, with the aim of providing useful information for reliable numerical tools. In the eleventh contribution, Martínez-Bocanegra et al. present the structural behavior of a foot model using a detailed finite element model. The twelfth contribution is centered on the methodology to perform a finite, element-based, numerical model of a hydroxyapatite 3D printed bone scaffold. In the thirteenth paper, Talygin and Gorodkov present analytical expressions describing swirling jets for cardiovascular applications. In the fourteenth contribution, Schenkel and Halliday propose a novel non-Newtonian particle transport model for red blood cells. Finally, Zurita et al. propose a parametric numerical tool for analyzing a silicone customized 3D printable trachea-bronchial prosthesis

    Evaluating the haemodynamic performance of endografts for complex aortic arch repair

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    Thoracic endovascular aortic repair (TEVAR) of aortic aneurysms and dissections involving the arch has evolved over the last two decades. Compared to conventional surgical methods, endovascular repair offers a less invasive treatment option with lower risk and faster recovery. Endografts used in TEVAR vary in design depending on the procedure and application. Novel endografts (e.g., branched stent-graft) were developed to ensure perfusion of blood to the supra-aortic vessels, but their haemodynamic performance and long-term durability have not been adequately studied. This review focuses on the use of computational modelling to study haemodynamics in commercially available endografts designed for complex aortic arch repair. First, we summarise the currently adopted workflow for computational fluid dynamics (CFD) modelling, including geometry reconstruction, boundary conditions, flow models, and haemodynamic metrics of interest. This is followed by a review of recently (2010-present) published CFD studies on complex aortic arch repair, using both idealized and patient-specific models. Finally, we introduce some of the promising techniques that can be potentially applied to predict post-operative outcomes

    Etiology, Pathogenesis and Pathophysiology of Aortic Aneurysms and Aneurysm Rupture

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    This book considers mainly etiology, pathogenesis, and pathophysiology of aortic aneurysms (AA) and aneurysm rupture and addresses anyone engaged in treatment and prevention of AA. Multiple factors are implicated in AA pathogenesis, and are outlined here in detail by a team of specialist researchers. Initial pathological events in AA involve recruitment and infiltration of leukocytes into the aortic adventitia and media, which are associated with the production of inflammatory cytokines, chemokine, and reactive oxygen species. AA development is characterized by elastin fragmentation. As the aorta dilates due to loss of elastin and attenuation of the media, the arterial wall thickens as a result of remodeling. Collagen synthesis increases during the early stages of aneurysm formation, suggesting a repair process, but resulting in a less distensible vessel. Proteases identified in excess in AA and other aortic diseases include matrix metalloproteinases (MMPs), cathepsins, chymase and others. The elucidation of these issues will identify new targets for prophylactic and therapeutic intervention

    The use of patient-specific modelling in the assessment of a clinical indicator for arteriovenous fistula failure

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    The arteriovenous fistula (AVF) is a surgically-made vascular structure connecting an artery to a vein. It is the optimal form of vascular access for haemodialysis-dependent end-stage renal disease patients. However, AVF are prone to access dysfunction through the formation of stenoses, which compromise the structure’s utility. To date, a plethora of clinical models are used to predict AVF formation failure based on patient factors and other models predicting late AVF failure by assessing haemodynamics and quantifying disturbed flow behaviours and wall shear stress metrics with stenosis formation. That said, inconsistencies were identified in the correlation between these metrics and diseased AVFs. This thesis aims to assess the suitability of another haemodynamic-related metric, resistance, derived from pressure drop and flow rates through patient-specific CFD modelling, for diagnosing and predicting AVF failure. A three-dimensional ultrasound scanning system was used to obtain patient-specific geometry and flow profiles, used for CFD models which were then analysed, with resistance calculated for each patient. The significance of patient-specific CFD modelling was demonstrated in its usefulness to generate a patient-targeted indicator of diseased AVF. To study the effectiveness of resistance as a metric, the relationship between CFD-derived resistance and the potential for AVF failure was evaluated, starting with classification of resistance results among patients who had undergone treatment for stenosis. An exploratory study into the suitability of CFD-derived resistance and its association with patients’ AVF conditions was further conducted by classifying data from a larger patient dataset and fitting the classified data to a multilevel regression model. CFD-derived resistance was found to be higher at the proximal vein of problematic AVF, however this figure was 76% lower among patients who had undergone stenosis treatment. Meanwhile, no correlation was found between resistance at the proximal artery and patency status. An area under curve of 92.1% was found from the receiver operating characteristic analysis, noting an outstanding discrimination of the classification. CFD-derived resistance appears to be a promising metric in the assessment of a suitable diagnostic marker for AVF failure. This research concludes with aspirations for clinical implementation of a related system, alongside routine surveillance of AVF
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