Numerical study of the influence of wall compliance on the haemodynamics in a patient-specific arteriovenous fistula

Total cavopulmonary connection (TCPC) hemodynamics has been hypothesized to be associated with long-term complications in single ventricle heart defect patients. Rigid wall assumption has been commonly used when evaluating TCPC hemodynamics using computational fluid dynamics (CFD) simulation. Previous study has evaluated impact of wall compliance on extra-cardiac TCPC hemodynamics using fluid-structure interaction (FSI) simulation. However, the impact of ignoring wall compliance on the presumably more compliant intra-atrial TCPC hemodynamics is not fully understood. To narrow this knowledge gap, this study aims to investigate impact of wall compliance on an intra-atrial TCPC hemodynamics. A patient-specific model of an intra-atrial TCPC is simulated with an FSI model. Patient-specific 3D TCPC anatomies were reconstructed from transverse cardiovascular magnetic resonance images. Patient-specific vessel flow rate from phase-contrast magnetic resonance imaging (MRI) at the Fontan pathway and the superior vena cava under resting condition were prescribed at the inlets. From the FSI simulation, the degree of wall deformation was compared with in vivo wall deformation from phase-contrast MRI data as validation of the FSI model. Then, TCPC flow structure, power loss and hepatic flow distribution (HFD) were compared between rigid wall and FSI simulation. There were differences in instantaneous pressure drop, power loss and HFD between rigid wall and FSI simulations, but no difference in the time-averaged quantities. The findings of this study support the use of a rigid wall assumption on evaluation of time-averaged intra-atrial TCPC hemodynamic metric under resting breath-held condition.

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Determination of a Pressure Drop in the Arteriovenous Fistula With Fluid Structure Interaction Simulations and In Vitro Methods

Volume 3: Biomedical and Biotechnology Engineering ◽

10.1115/imece2017-70402 ◽

2017 ◽

Author(s):

Daniel Jodko ◽

Tomasz Palczynski ◽

Piotr Reorowicz ◽

Kacper Miazga ◽

Damian Obidowski ◽

...

Keyword(s):

Pressure Drop ◽

Blood Vessel ◽

Arteriovenous Fistula ◽

In Vitro Model ◽

Experimental Methods ◽

Measurement Methods ◽

Patient Specific ◽

Vessel Walls ◽

Vitro Model

A pressure drop and its oscillations occurring in the arteriovenous fistula due to sudden changes in the velocity vector direction or the transitional or turbulent flow, related to its complicated geometry, can exert a significant impact on the blood vessel wall behaviour. On the other hand, the pressure drop cannot be precisely measured in vivo with non-invasive measurement methods. The aim of this study is to assess the pressure drop with numerical and experimental methods in the patient-specific fistula model taking into account a pulsating nature of the flow and the elasticity of blood vessel walls. An additional target is to find a correlation between these two methods. FSI and in vitro simulations of the blood flow were performed for a patient-specific model of the fistula. Basic geometrical data of the correctly functioning mature fistula were obtained with angio-computed tomography. Those data were applied to develop a spatial CAD model of the fistula, which allowed for creating a virtual model for computer simulations and an analogous in vitro model made with rapid prototyping techniques. The material used to build the in vitro model is characterised by mechanical properties similar to the arterial tissue. A non-stationary computer simulation was carried out with an ANSYS software package, keeping as many flow similarities to the experiments carried out on the test stand as possible, and where the blood mimicking fluid was a water solution of glycerine. During the experiments, the static pressure was measured downstream and upstream of the anastomosis with precise pressure transducers. The pressure drop was determined with the numerical and experimental methods, which take into account the elasticity of blood vessels. This is a novel approach, since most of similar studies were conducted on the assumption of rigid blood vessel walls. The obtained results show that the pressure drop within the fistula is not so high as reported in the literature, which is correlated with the precision of measurement methods and the fact that a large portion of the fluid energy is accumulated by the elastic walls.

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Tomographic PIV analysis of physiological flow conditions in a patient-specific arteriovenous fistula

Experiments in Fluids ◽

10.1007/s00348-020-03085-4 ◽

2020 ◽

Vol 61 (12) ◽

Author(s):

Sanjiv Gunasekera ◽

Olivia Ng ◽

Shannon Thomas ◽

Ramon Varcoe ◽

Charitha de Silva ◽

...

Keyword(s):

Arteriovenous Fistula ◽

Patient Specific ◽

Flow Conditions ◽

Tomographic Piv ◽

Physiological Flow ◽

Piv Analysis

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Numerical Simulation of the Dispersion and Deposition of a Spray Carried by a Pulsating Airflow in a Patient-Specific Human Nasal Cavity

Proceedings ILASS–Europe 2017. 28th Conference on Liquid Atomization and Spray Systems ◽

10.4995/ilass2017.2017.4628 ◽

2017 ◽

Author(s):

Ali Farnoud ◽

Xinguang Cui ◽

Ingo Baumann ◽

Eva Gutheil

Keyword(s):

Nasal Cavity ◽

High Performance ◽

Numerical Study ◽

Three Dimensional ◽

Flow Simulation ◽

Patient Specific ◽

Process Time ◽

Nasal Valve ◽

Time Step ◽

Real Process

The present numerical study concerns the dispersion and deposition of a nasal spray in a patient-specific human nose. The realistic three-dimensional geometry of the nasal cavity is reconstructed from computer tomography (CT) scans. Identification of the region of interest, removal of artifacts, segmentation, generation of the .STL file and the triangulated surface grid are performed using the software packages ImageJ, meshLab, and NeuRA2. An unstructured computational volume grid with approximately 15 million tetrahedral grid cells is generated using the software Ansys ICEM-CFD 11.0. An unsteady Eulerian-Lagrangian formulation is used to describe the airflow and the spray dispersion and deposition in the realistic human nasal airway using two-way coupling. A new solver called pimpleParcelFoam is developed, which combines the lagrangianParcel libraries with the pimpleFoam solver within the software package OpenFOAM 3.0.0. A large eddy simulation (LES) with the dynamic sub-grid scale (SGS) model is performed to study the spray in both a steady and a pulsating airflow with an inflow rate of 7.5 L/min (or maximum value in case of the pulsating spray) and a frequency of 45 Hz for pulsation as used in commercial inhalation devices. 10,000 mono-disperse particles with the diameters of 2.4 µm and 10 µm are uniformly injected at the nostrils. In order to fulfil the stability conditions for the numerical solution, a constant time-step of 10−5 s is implemented. The simulations are performed for a real process time of 1 s, since after the first second of the process, all particles have escaped through the pharynx or they are deposited at the surface of the nasal cavity. The numerical computations are performed on the high-performance computer bwForCluster MLS&WISO Production using 256 processors, which take around 32 and 75 hours for steady and pulsating flow simulation, respectively. The study shows that the airflow velocity reaches its maximum values in the nasal valve, in parts of the septum and in the nasopharynx. A complex airflow is observed in the vestibule and in the nasopharynx region, which may directly affect the dispersion and deposition pattern of the spray. The results reveal that the spray tends to deposit in the nasal valve, the septum and in the nasopharynx due to the change in the direction of the airflow in these regions. Moreover, it is found that due to the pulsating airflow, the aerosols are more dispersed and penetrate deeper into the posterior regions and the meatuses where the connections to the sinuses reside.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4628

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Numerical Study of Lymph Mechanics

10.23889/suthesis.58474 ◽

2021 ◽

Author(s):

◽

Daniel J. Watson

Keyword(s):

Lymphatic System ◽

Numerical Study ◽

Patient Specific ◽

Single Subject ◽

3D Analysis ◽

Large Network ◽

Lumped Model ◽

Biphasic Model ◽

Lymphatic Valve ◽

Scale Modelling

Methods taken from engineering and computer science were applied to the lymphatic system. Starting with a 3D analysis of a single subject-speciﬁc lymphatic valve. A mechanism was presented to explain previous experimental results showing the eﬀect of trans-mural pressure on the pressure required to close lymphatic valves. The impor-tance of wall motion in future FSI studies of lymphatic valve dynamics were identiﬁed. Previous approaches to lumped modelling of the lymphatic system were considered and modiﬁcations were proposed. A less-idealised valve model, incorporating trans-mural dependent bias, was proposed as well as a method of allowing self-organised contrac-tion through a stretch-dependent frequency of contraction. A network of the superﬁcial lymphatics of the upper-limb was reconstructed from an anatomical sketch. The net-work was used in conjunction with the lumped model to produce a 421 vessel lymphatic model consisting of 17,706 lymphangions. Several issues which impede large network scale modelling of the lymphatic system are identiﬁed. A simpliﬁed patient-speciﬁc biphasic model of lymphoedema was proposed and used to develop a novel shape-based metric for lymphoedema. A statistically signiﬁcant relationship between the metric and the presence of lymphoedema was found.

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Disturbed flow in a patient-specific arteriovenous fistula for hemodialysis: Multidirectional and reciprocating near-wall flow patterns

Journal of Biomechanics ◽

10.1016/j.jbiomech.2015.04.013 ◽

2015 ◽

Vol 48 (10) ◽

pp. 2195-2200 ◽

Cited By ~ 25

Author(s):

Bogdan Ene-Iordache ◽

Cristina Semperboni ◽

Gabriele Dubini ◽

Andrea Remuzzi

Keyword(s):

Arteriovenous Fistula ◽

Flow Patterns ◽

Patient Specific ◽

Disturbed Flow ◽

Wall Flow ◽

Near Wall

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Computational Analysis of Self-Expanding and Balloon-Expandable Transcatheter Heart Valves

Biomechanics ◽

10.3390/biomechanics1010004 ◽

2021 ◽

Vol 1 (1) ◽

pp. 43-52

Author(s):

Salvatore Pasta ◽

Caterina Gandolfo

Keyword(s):

Aortic Valve ◽

Heart Valves ◽

Numerical Study ◽

Flow Analysis ◽

Patient Specific ◽

Area At Risk ◽

Virtual Planning ◽

Local Maxima ◽

Transcatheter Aortic Valve ◽

Transcatheter Heart Valve

Bicuspid aortic valve (BAV) patients are usually excluded from transcatheter aortic valve implantation (TAVI) as this valve anatomy likely leads to oval expansion. This study presents a numerical study of TAVI using both self-expanding and balloon expandable transcatheter heart valve (THV) in bicuspid patients with severe stenosis. The simulation framework included a patient-specific anatomy of the aortic root, calcifications and BAV leaflets extracted from medical imaging analysis as well as a realistic crimping and deployment of the THV. Tissue stress analysis highlighted local maxima in the contact area between the inner aortic lumen and the THV stent frame. Flow analysis based on the smoothed particle hydrodynamics (SPH) technique displayed the area at risk of paravalvular leakage (PVL). These findings provide insights on the TAVI in BAV and thus represents a further step towards the use of in-silico for the virtual planning of TAVI, aiming at improving not only the efficacy of the implantation but also the exploration of borderline anatomy as the case of TAVI in BAVs.

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Numerical Study of Non-Newtonian Blood Behavior in the Abdominal Aortic Bifurcation of a Patient-Specific at Rest

The Open Sports Sciences Journal ◽

10.2174/1875399x01710010279 ◽

2017 ◽

Vol 10 (1) ◽

pp. 279-285 ◽

Cited By ~ 1

Author(s):

Carlos Oliveira ◽

Armando A. Soares ◽

André Simões ◽

Sílvia Gonzaga ◽

Abel Rouboa

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Cardiovascular Health ◽

Numerical Study ◽

Shear Thinning ◽

Patient Specific ◽

Aortic Bifurcation ◽

Low Velocity ◽

Abdominal Aortic ◽

Wall Shear

Background:The interaction of blood flow with walls of blood vessels is central for the development and maintenance of cardiovascular health. The analysis of wall shear stress is, therefore, fundamental in hemodynamic studies.Objective:The aim of this work is to study numerically the influence of the shear thinning blood properties on the hemodynamics in the abdominal aortic bifurcation for a patient-specific at rest.Methods:Were tested two models for the blood dynamic viscosity, one Newtonian and other non-Newtonian, with dependence on hematocrit and total protein minus albumin.Results and Conclusion:The results show the shear thinning behavior influence on the velocity distribution and wall shear stress. Furthermore, wall shear stress values are globally lower for non-Newtonian blood model at high velocity values than those for the Newtonian blood model. However, for low velocity values this behavior is inverted.

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