Cell-resolved blood flow simulations of saccular aneurysms: effects of pulsatility and aspect ratio

Czaja, Benjamin; Závodszky, Gábor; Tarksalooyeh, V. Azizi; Hoekstra, Alfons G.

doi:10.1098/rsif.2018.0485

Cited by 18 publications

(8 citation statements)

References 56 publications

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“…The CFD simulations can overcome these limitations and deliver physiological information anywhere in the model such as velocity, viscosity or haematocrit level 7,11,13,20 . However, the success of the CFD simulation depends on the state-of-art of the mathematical model and its associated computational cost to solve it, which are the current limitations for whole blood simulation 27,28 . Moreover, the results are interpretive and need to be validated using in vivo or experimental data 28 .…”

Section: Discussionmentioning

confidence: 99%

The impact of arterial flow complexity on flow diverter outcomes in aneurysms

Chodzynski

Uzureau

Nuyens

et al. 2020

Sci Rep

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The flow diverter is becoming a standard device for treating cerebral aneurysms. The aim of this in vitro study was to evaluate the impact of flow complexity on the effectiveness of flow diverter stents in a cerebral aneurysm model. The flow pattern of a carotid artery was decomposed into harmonics to generate four flow patterns with different pulsatility indexes ranging from 0.72 to 1.44. The effect of flow diverters on the aneurysm was investigated by injecting red dye or erythrocytes as markers. The recorded images were postprocessed to evaluate the maximum filling of the aneurysm cavity and the washout time. There were significant differences in the cutoff flows between the markers, linked to the flow complexity. Increasing the pulsatility index altered the performance of the flow diverter. The red dye was more sensitive to changes in flow than the red blood cell markers. The flow cutoff depended on the diverter design and the diverter deployment step was crucial for reproducibility of the results. These results strongly suggest that flow complexity should be considered when selecting a flow diverter. Flow diverters are common devices for treating large or complex intracranial aneurysms. As the mechanisms underlying aneurysm occlusion are still not fully understood, the choice of flow diverter is mainly empirical and based on the physician's own experience 1,2. Outcomes range from complete or partial occlusion after varying periods to lack of thrombosis or even haemorrhage 3,4. The factors responsible for occlusion following flow diverter placement are still under debate 3,5. Analysis of the flow inside large aneurysms reveals that, by contrast with small aneurysms where flow is similar to the parent vessel, the flow pattern can be markedly altered 6. Recent studies show that flow complexity is a key factor in flow diverter performance. Computational fluid dynamics (CFD) simulations showed that flow reduction following flow diverter treatment was more noticeable during diastole than systole and that flow diverter performance was related to the flow pattern 7,8. Although blood flow complexity can be fully described using a Fourier decomposition into harmonics, these values are not commonly used in the medical field 9. Instead, the pulsatility index, which can be directly assessed from Doppler or magnetic resonance imaging (MRI) examinations, is more widely used to describe the complexity of patient blood flows 10. The pulsatility index varies within the cerebral arterial tree and within the same artery in different patients, reflecting the diversity of flow patterns that can be encountered within the vessels altered by aneurysms 11,12. Different outcomes are therefore observed when the same flow diverter is used in situations of different flow patterns associated with vessel geometry and position in the cerebral arterial tree, and the physiological state and activity of the patient 13,14. In addition, flow diverter design, including the number of layers, porosity, number of holes, weave angle, wire diameter, a...

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Section: Discussionmentioning

confidence: 99%

The impact of arterial flow complexity on flow diverter outcomes in aneurysms

Chodzynski

Uzureau

Nuyens

et al. 2020

Sci Rep

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“…The cellular flow is simulated with the HemoCell software. 40,49 It is based on a combination of the lattice Boltzmann method (LBM) which has been shown to reproduce accurate flow fields in vascular settings [50][51][52][53] and a high-performance implementation of the immersed boundary method (IBM). 54,55 The blood plasma is represented as an incompressible Newtonian fluid, and the cells are modelled as triangulated membrane meshes immersed in the plasma flow.…”

Section: A Numerical Methodsmentioning

confidence: 99%

Red blood cell and platelet diffusivity and margination in the presence of cross-stream gradients in blood flows

et al. 2019

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The radial distribution of cells in blood flow inside vessels is highly non-homogeneous. This leads to numerous important properties of blood, yet the mechanisms shaping these distributions are not fully understood. The motion of cells is governed by a variety of hydrodynamic interactions and cell-deformation mechanics. Properties, such as the effective cell diffusivity, are therefore difficult to investigate in flows other than pure shear flows. In this work, several single-cell, cell-pair, and large-scale many-cell simulations are performed using a validated numerical model. Apart from the single-cell mechanical validations, the arising flow profile, cell free layer widths, and cell drift velocities are compared to previous experimental findings. The motion of the cells at various radial positions and under different flow conditions is extracted, and evaluated through a statistical approach. An extended diffusive flux-type model is introduced which describes the cell diffusivities under a wide range of flow conditions and incorporates the effects of cell deformability through a shear dependent description of the cell collision cross sections. This model is applicable for both red blood cells and platelets. Further evaluation of particle trajectories shows that the margination of platelets cannot be the net result of gradients in diffusivity. However, the margination mechanism is strongly linked to the gradient of the hematocrit level. Finally, it shows that platelets marginate only until the edge of the red blood cell distribution and they do not fill the cell free layer.

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“…The immersed boundary method is used, which is a fluid-structure interaction method, so the RBC membrane exerts a force on the fluid and the RBC membrane feels the velocity of the fluid. The model implementation is described in detail in Czaja et al (2018). Step and chamber dimensions are not drawn to scale…”

Section: Cell-based Flowmentioning

confidence: 99%

A particle-based model for endothelial cell migration under flow conditions

Zun

Narracott

Evans

et al. 2019

Biomech Model Mechanobiol

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Endothelial cells (ECs) play a major role in the healing process following angioplasty to inhibit excessive neointima. This makes the process of EC healing after injury, in particular EC migration in a stented vessel, important for recovery of normal vessel function. In that context, we present a novel particle-based model of EC migration and validate it against in vitro experimental data. We have developed a particle-based model of EC migration under flow conditions in an in vitro vessel with obstacles. Cell movement in the model is a combination of random walks and directed movement along the local flow velocity vector. For model calibration, a set of experimental data for cell migration in a similarly shaped channel has been used. We have calibrated the model for a baseline case of a channel with no obstacles and then applied it to the case of a channel with ridges on the bottom surface, representative of stent strut geometry. We were able to closely reproduce the cell migration speed and angular distribution of their movement relative to the flow direction reported in vitro. The model also reproduces qualitative aspects of EC migration, such as entrapment of cells downstream from the flow-disturbing ridge. The model has the potential, after more extensive in vitro validation, to study the effect of variation in strut spacing and shape, through modification of the local flow, on EC migration. The results of this study support the hypothesis that EC migration is strongly affected by the direction and magnitude of local wall shear stress.

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Cell-resolved blood flow simulations of saccular aneurysms: effects of pulsatility and aspect ratio

Cited by 18 publications

References 56 publications

The impact of arterial flow complexity on flow diverter outcomes in aneurysms

The impact of arterial flow complexity on flow diverter outcomes in aneurysms

Red blood cell and platelet diffusivity and margination in the presence of cross-stream gradients in blood flows

A particle-based model for endothelial cell migration under flow conditions

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