Modelling nasal airflow using a Fourier descriptor representation of geometry

Gambaruto, Alberto; Taylor, D; Doorly, D. J.

doi:10.1002/fld.1866

Cited by 25 publications

(38 citation statements)

References 46 publications

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“…Openings (ostia) to the sinuses were omitted as they presented minimal cross-sectional area and were deemed to have a negligible impact on the gross airflow patterns. In-house bi-Laplacian smoothing techniques were implemented to remove pixellation artefacts and to provide a more realistic, smooth surface finish to the geometries, as discussed by Gambaruto et al (2008). Inflow and outflow extensions were attached to the replica geometry definitions at this stage to allow manufactured physical models to be connected to a flow loop for experimental studies.…”

Section: Methodsmentioning

confidence: 99%

Inflow boundary profile prescription for numerical simulation of nasal airflow

Taylor

Doorly

Schroter

2009

J. R. Soc. Interface.

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Knowledge of how air flows through the nasal passages relies heavily on model studies, as the complexity and relative inaccessibility of the anatomy prevents detailed in vivo measurement. Almost all models to date fail to incorporate the geometry of the external nose, instead employing a truncated inflow. Typically, flow is specified to enter the model domain either directly at the nares (nostrils), or via an artificial pipe inflow tract attached to the nares. This study investigates the effect of the inflow geometry on flow predictions during steady nasal inspiration. Models that fully replicate the internal and external nasal airways of two anatomically distinct subjects are used as a reference to compare the effects of common inflow treatments on physiologically relevant quantities including regional wall shear stress and particle residence time distributions. Inflow geometry truncation is found to affect flow predictions significantly, though slightly less so for the subject displaying more pronounced passage area contraction up to the internal nasal valve. For both subject geometries, a tapered pipe inflow provides a better approximation to the natural inflow than a blunt velocity profile applied to the nares. Computational modelling issues are also briefly outlined, by comparing quantities predicted using different surface tessellations, and by evaluation of domain-splitting techniques.

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Section: Methodsmentioning

confidence: 99%

Inflow boundary profile prescription for numerical simulation of nasal airflow

Taylor

Doorly

Schroter

2009

J. R. Soc. Interface.

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“…Even worse, some fully-automatic segmentation methods used in image analysis often lead to even larger deviations (Huang et al 2016) and are thus unsuitable for reconstructing nasal cavities. Moreover, smoothing procedures, which are often employed to prepare the surface for the generation of the computation mesh, can move boundaries by up to one pixel (Gambaruto et al 2009). In the case of a pixel size of h≈0.4 mm and ℓ≈3 mm, this implies that the resistance changes by a factor of 2.…”

Section: Discussionmentioning

confidence: 99%

“…In these methods, the computation mesh needs to conform to the boundary, which often requires additional smoothing of the surface ( Gabory et al 2018), e.g. using the bi-Laplacian iterative method (Gambaruto et al 2009). This smoothing alters the surface, degrades the effective resolution, and might thus introduce additional errors in the simulation (Gambaruto et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Validated reconstructions of geometries of nasal cavities from CT scans

Zwicker

Yang

Melchionna

et al. 2018

Biomed. Phys. Eng. Express

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Developing validated objective measures of nasal airflow is paramount for improving the management of nasal obstruction. Nasal airflow can be studied objectively by simulating the flow in the computer. This requires a faithful reconstruction of the nasal geometry since the simulated airflow is sensitive to small variations of the complex shape of the nasal cavity. We here show that altering the geometry by less than 1 mm can change the airflow two-fold. We also show that a faithful reconstruction of the nasal geometry is possible with a threshold-based segmentation. Utilizing the known geometry of a CT phantom, we determine an optimal segmentation threshold of −450 HU. Changing this threshold by 100 HU alters the geometry by only about 0.1 mm. We use this verified segmentation to extract nasal geometries of three patients and simulate the respective airflows using the Lattice Boltzmann method. Using a simple model, we can predict how the reconstruction threshold affects the resistance to airflow. Since the segmentation and the simulation can be automated completely, this is an important step toward an objective analysis of nasal airflow based on CT scans.

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“…The first stage of the smoothing is an explicit scheme where the severity of smoothing increases with the number of iterations performed, using the 'projected mean curvature flow' method [27,50] which involves moving the mesh nodes using the local mesh connectivity information in order to minimise the surface roughness (curvature variation). In the second stage of the smoothing method, the surface area and volume alterations brought about in the first stage are reduced by an iterative uniform inflation of the surface along the local normal, until the distance between the smoothed and the original surface representations is minimised [27,51].…”

Section: B Virtual Model Reconstructionmentioning

confidence: 99%

Wall shear stress and near-wall convective transport: Comparisons with vascular remodelling in a peripheral graft anastomosis

Gambaruto

Doorly

Yamaguchi

2010

Journal of Computational Physics

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General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. AbstractFluid dynamic properties of blood flow are implicated in cardiovascular diseases. The interaction between the blood flow and the wall occurs through the direct transmission of forces, and through the dominating influence of the flow on convective transport processes. Controlled, in-vitro testing in simple geometric configurations has provided much data on the cellular-level responses of the vascular walls to flow, but a complete, mechanistic explanation of the pathogenic process is lacking. In the interim, mapping the association between local haemodynamics and the vascular response is important to improve understanding of the disease process and may be of use for prognosis. Moreover establishing the haemodynamic environment in the regions of disease provides data on flow conditions to guide investigations of cellular-level responses.This work describes techniques to facilitate comparison between the temporal alteration in the geometry of the vascular conduit, as determined by in-vivo imaging, with local flow parameters. Procedures to reconstruct virtual models from images by means of a partition-of-unity implicit function formulation, and to align virtual models of follow-up scans to a common coordinate system, are outlined. A simple Taylor series expansion of the Lagrangian dynamics of the near-wall flow is shown to provide both a physical meaning to the directional components of the flow, as well as demonstrating the relation between near-wall convection in the wall-normal direction and spatial gradients of the wall shear stress.A series of post-operative follow-up MRI scans of two patient cases with bypass grafts in the peripheral vasculature are presented. These are used to assess how local haemodynamic parameters relate to vascular remodelling at the location of the distal end-to-side anastomosis, i.e. where the graft rejoins the host artery. Results indicate that regions of both low wall shear stress and convective transport towards the wall tend to be more associated with regions of inward remodelling. A strong point-wise correlation was not found to exist however between local changes in wall location and either quantity.

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Modelling nasal airflow using a Fourier descriptor representation of geometry

Cited by 25 publications

References 46 publications

Inflow boundary profile prescription for numerical simulation of nasal airflow

Inflow boundary profile prescription for numerical simulation of nasal airflow

Validated reconstructions of geometries of nasal cavities from CT scans

Wall shear stress and near-wall convective transport: Comparisons with vascular remodelling in a peripheral graft anastomosis

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