131 results found
Calmet H, Bertomeu PF, McIntyre C, et al., 2022, Computational modelling of an aerosol extraction device for use in COVID-19 surgical tracheotomy, Journal of Aerosol Science, Vol: 159, ISSN: 0021-8502
In view of the ongoing COVID-19 pandemic and its effects on global health, understanding and accurately modelling the propagation of human biological aerosols has become crucial. Worldwide, health professionals have been one of the most affected demographics, representing approximately 20% of all cases in Spain, 10% in Italy and 4% in China and US. Methods to contain and remove potentially infected aerosols during Aerosol Generating Procedures (AGPs) near source offer advantages in reducing the contamination of protective clothing and the surrounding theatre equipment and space. In this work we describe the application of computational fluid dynamics in assessing the performance of a prototype extraction hood as a means to contain a high speed aerosol jet. Whilst the particular prototype device is intended to be used during tracheotomies, which are increasingly common in the wake of COVID-19, the underlying physics can be adapted to design similar machines for other AGPs. Computational modelling aspect of this study was largely carried out by Barcelona Supercomputing Center using the high performance computational mechanics code Alya. Based on the high fidelity LES coupled with Lagrangian frameworks the results demonstrate high containment efficiency of generated particles is feasible with achievable air extraction rates.
Doorly D, Xiao Q, Bates A, et al., 2021, The effect of decongestion on nasal airway patency and airflow, Nature Scientific Reports, Vol: 11, Pages: 1-13, ISSN: 2045-2322
Nasal decongestant reduces blood flow to the nasal turbinates, reducing tissue volume and increasing nasal airway patency. This study maps the changes in nasal anatomy and measures how these changes affect nasal resistance, flow partitioning between superior and inferior cavity, flow patterns and wall shear stress. High-resolution MRI was applied to capture nasal anatomy in 10 healthy subjects before and after application of a topical decongestant. Computational fluid dynamics simulated nasal airflow at steady inspiratory flow rates of 15 L.min−1 and 30 L.min−1. The results show decongestion mainly increases the cross-sectional area in the turbinate region and SAVR is reduced (median approximately 40% reduction) in middle and lower parts of the cavity. Decongestion reduces nasal resistance by 50% on average, while in the posterior cavity, nasal resistance decreases by a median factor of approximately 3 after decongestion. We also find decongestant regularises nasal airflow and alters the partitioning of flow, significantly decreasing flow through the superior portions of the nasal cavity. By comparing nasal anatomies and airflow in their normal state with that when pharmacologically decongested, this study provides data for a broad range of anatomy and airflow conditions, which may help characterize the extent of nasal variability.
Kimura S, Miura S, Sera T, et al., 2020, Voxel-based simulation of flow and temperature in the human nasal cavity, COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING, Vol: 24, Pages: 459-466, ISSN: 1025-5842
Solis-Lemus JA, Costar E, Doorly D, et al., 2020, A simulated single ventilator/dual patient ventilation strategy for acute respiratory distress syndrome during the COVID-19 pandemic, ROYAL SOCIETY OPEN SCIENCE, Vol: 7, ISSN: 2054-5703
Xiao Q, Cetto R, Doorly D, et al., 2019, Assessing changes in airflow and energy loss in a progressive tracheal compression before and after surgical correction, Annals of Biomedical Engineering, Vol: 48, Pages: 822-833, ISSN: 0090-6964
The energy needed to drive airflow through the trachea normally constitutes a minor component of the work ofbreathing. However, with progressive tracheal compression, patient subjective symptoms can include severe breathingdifficulties. Many patients suffer multiple respiratory co-morbidities and so it is important to assess compression effectswhen evaluating the need for surgery. This work describes the use of computational prediction to determine airflowresistance in compressed tracheal geometries reconstructed from a series of CT scans. Using energy flux analysis, theregions that contribute the most to airway resistance during inhalation are identified. The principal such region is where flowemerging from the zone of maximum constriction undergoes breakup and turbulent mixing. Secondary regions are alsofound below the tongue base and around the glottis, with overall airway resistance scaling nearly quadratically with flowrate. Since the anatomical extent of the imaged airway varied between scans - as commonly occurs with clinical data andwhen assessing reported differences between research studies - the effect of sub-glottic inflow truncation is considered.Analysis shows truncation alters the location of jet breakup and weakly influences the pattern of pressure recovery. Testsalso show that placing a simple artificial glottis in the inflow to a truncated model can replicate patterns of energy loss inmore extensive models, suggesting a means to assess sensitivity to domain truncation in tracheal airflow simulations.
Cookson AN, Doorly DJ, Sherwin SJ, 2019, Efficiently Generating Mixing by Combining Differing Small Amplitude Helical Geometries, FLUIDS, Vol: 4, ISSN: 2311-5521
Rose JN, Nielles-Vallespin S, Ferreira PF, et al., 2019, Novel insights into in-vivo diffusion tensor cardiovascular magnetic resonance using computational modelling and a histology-based virtual microstructure, Magnetic Resonance in Medicine, Vol: 81, Pages: 2759-2773, ISSN: 0740-3194
PurposeTo develop histology‐informed simulations of diffusion tensor cardiovascular magnetic resonance (DT‐CMR) for typical in‐vivo pulse sequences and determine their sensitivity to changes in extra‐cellular space (ECS) and other microstructural parameters.MethodsWe synthesised the DT‐CMR signal from Monte Carlo random walk simulations. The virtual tissue was based on porcine histology. The cells were thickened and then shrunk to modify ECS. We also created idealised geometries using cuboids in regular arrangement, matching the extra‐cellular volume fraction (ECV) of 16–40%. The simulated voxel size was 2.8 × 2.8 × 8.0 mm3 for pulse sequences covering short and long diffusion times: Stejskal–Tanner pulsed‐gradient spin echo, second‐order motion‐compensated spin echo, and stimulated echo acquisition mode (STEAM), with clinically available gradient strengths.ResultsThe primary diffusion tensor eigenvalue increases linearly with ECV at a similar rate for all simulated geometries. Mean diffusivity (MD) varies linearly, too, but is higher for the substrates with more uniformly distributed ECS. Fractional anisotropy (FA) for the histology‐based geometry is higher than the idealised geometry with low sensitivity to ECV, except for the long mixing time of the STEAM sequence. Varying the intra‐cellular diffusivity (DIC) results in large changes of MD and FA. Varying extra‐cellular diffusivity or using stronger gradients has minor effects on FA. Uncertainties of the primary eigenvector orientation are reduced using STEAM.ConclusionsWe found that the distribution of ECS has a measurable impact on DT‐CMR parameters. The observed sensitivity of MD and FA to ECV and DIC has potentially interesting applications for interpreting in‐vivo DT‐CMR parameters.
Doorly D, Kimura S, Sakamoto T, et al., 2019, Voxel-based modeling of airflow in the human nasal cavity, Computer Methods in Biomechanics and Biomedical Engineering, ISSN: 1025-5842
Kimura S, Sakamoto T, Sera T, et al., 2019, Voxel-based modeling of airflow in the human nasal cavity, Computer Methods in Biomechanics and Biomedical Engineering, Vol: 22, Pages: 331-339, ISSN: 1025-5842
This paper describes the simulation of airflow in human nasal airways using voxel-based modeling characterized by robust, automatic, and objective grid generation. Computed tomography scans of a healthy adult nose are used to reconstruct 3D virtual models of the nasal airways. Voxel-based simulations of restful inspiratory flow are then performed using various mesh sizes to determine the level of granularity required to adequately resolve the airflow. For meshes with close voxel spacings, the model successfully reconstructs the nasal structure and predicts the overall pressure drop through the nasal cavity.
Calmet H, Houzeaux G, Vazquez M, et al., 2018, Flow features and micro-particle deposition in a human respiratory system during sniffing, Journal of Aerosol Science, Vol: 123, Pages: 171-184, ISSN: 0021-8502
As we inhale, the air drawn through our nose undergoes successive accelerations and decelerations as it is turned, split and recombined before splitting again at the end of the trachea as it enters the bronchi. Fully describing the dynamic behaviour of the airflow and how it transports inhaled particles poses a severe challenge to computational simulations. In this paper we explore two aspects: the dynamic behaviour of airflow during a rapid inhalation (or sniff) and the transport of inhaled aerosols. The development of flow unsteadiness from a laminar state at entry to the nose through to the turbulent character of tracheal flow is resolved using accurate numerical models with high performance computing-based large scale simulations. Combining the flow solution with a Lagrangian computation reveals the effects of flow behaviour and airway geometry on the deposition of inhaled microparticles. Improved modelling of airflow and delivery of therapeutic aerosols could be applied to improve diagnosis and treatment.
Bates AJ, Cetto R, Doorly DJ, et al., 2016, The effects of curvature and constriction on airflow and energy loss in pathological tracheas, Respiratory Physiology & Neurobiology, Vol: 234, Pages: 69-78, ISSN: 1569-9048
This paper considers factors that play a significant role in determining inspiratory pressure and energy losses in the human trachea. Previous characterisations of pathological geometry changes have focussed on relating airway constriction and subsequent pressure loss, however many pathologies that affect the trachea cause deviation, increased curvature, constriction or a combination of these. This study investigates the effects of these measures on tracheal flow mechanics, using compressive goitre (a thyroid gland enlargement) as an example. Computational fluid dynamics simulations were performed in airways affected by goitres (with differing geometric consequences) and a normal geometry for comparison. Realistic airways, derived from medical images, were used because idealised geometries often oversimplify the complex anatomy of the larynx and its effects on the flow. Two mechanisms, distinct from stenosis, were found to strongly affect airflow energy dissipation in the pathological tracheas. The jet emanating from the glottis displayed different impingement and breakdown patterns in pathological geometries and increased loss was associated with curvature.
Doorly DJ, Bates A, Comerford A, et al., 2016, Computational fluid dynamics benchmark dataset of airflow in tracheas, Data in Brief, Vol: 10, Pages: 101-107, ISSN: 2352-3409
Computational Fluid Dynamics (CFD) is fast becoming a useful tool to aid clinicians in pre-surgical planning through the ability to provide information that could otherwise be extremely difficult if not impossible to obtain. However, in order to provide clinically relevant metrics, the accuracy of the computational method must be sufficiently high. There are many alternative methods employedin the process of performing CFD simulations within the airways, including different segmentation and meshing strategies, as well as alternative approaches to solving the Navier-Stokes equations.However, as in vivovalidation of the simulated flow patterns within the airways is not possible, little exists in the way of validation of the various simulation techniques. The data presented here consists of very highly resolved flow data. The degree of resolution is compared to the highest necessary resolutions of the Kolmogorov length and timescales. Therefore this data is ideally suited to act as a benchmark case to which cheaper computational methods may be compared.A dataset and solution setup for one such more efficient method, large eddy simulation (LES), is also presented.
The effort required to inhale a breath of air is a critically important measure in assessing airway function. Although the contribution of the trachea to the total flow resistance of the airways is generally modest, pathological alterations in tracheal geometry can have a significant negative effect. This study investigates the mechanisms of flow energy loss in a healthy trachea and in four geometries affected by retrosternal goitre which can cause significant distortions of tracheal geometry including constriction and deviation with abnormal curvature. By separating out the component of energy loss related to the wall shear (frictional loss), striking differences are found between the patterns of energy dissipation in the normal and pathological tracheas. Furthermore the ratio of frictional to total loss is dramatically reduced in the pathological geometries.
Doorly DJ, Calmet H, Gambaruto AM, et al., 2015, Large-scale CFD simulations of the transitional and turbulent regime for the large human airways during rapid inhalation, Computers in Biology and Medicine, Vol: 69, Pages: 166-180, ISSN: 0010-4825
The dynamics of unsteady flow in the human large airways during a rapid inhalation were investigated using highly detailed large-scale computational fluid dynamics on a subject-specific geometry. The simulations were performed to resolve all the spatial and temporal scales of the flow, thanks to the use of massive computational resources. A highly parallel finite element code was used, running on two supercomputers, solving the transient incompressible Navier–Stokes equations on unstructured meshes. Given that the finest mesh contained 350 million elements, the study sets a precedent for large-scale simulations of the respiratory system, proposing an analysis strategy for mean flow, fluctuations and wall shear stresses on a rapid and short inhalation (a so-called sniff). The geometry used encompasses the exterior face and the airways from the nasal cavity, through the trachea and up to the third lung bifurcation; it was derived from a contrast-enhanced computed tomography (CT) scan of a 48-year-old male. The transient inflow produces complex flows over a wide range of Reynolds numbers (Re). Thanks to the high fidelity simulations, many features involving the flow transition were observed, with the level of turbulence clearly higher in the throat than in the nose. Spectral analysis revealed turbulent characteristics persisting downstream of the glottis, and were captured even with a medium mesh resolution. However a fine mesh resolution was found necessary in the nasal cavity to observe transitional features. This work indicates the potential of large-scale simulations to further understanding of airway physiological mechanics, which is essential to guide clinical diagnosis; better understanding of the flow also has implications for the design of interventions such as aerosol drug delivery.
During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective transport of an inhaled gas were investigated in a subject geometry extending from the nose to the bronchi. The progress of flow transition and the advance of an inhaled non-absorbed gas were determined using highly resolved simulations of a sniff 0.5 s long, 1 l s⁻¹ peak flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved through three phases: (i) an initial transient of about 50 ms, roughly the filling time for a nasal volume, (ii) quasi-equilibrium over the majority of the inhalation, and (iii) a terminating phase. Flow transition commenced in the supraglottic region within 20 ms, resulting in large-amplitude fluctuations persisting throughout the inhalation; in the nose, fluctuations that arose nearer peak flow were of much reduced intensity and diminished in the flow decay phase. Measures of gas concentration showed non-uniform build-up and wash-out of the inhaled gas in the nose. At the carina, the form of the temporal concentration profile reflected both shear dispersion and airway filling defects owing to recirculation regions.
Rossi L, Doorly D, Kustrin D, 2013, Lamination, stretching, and mixing in cat's eyes flip sequences with varying periods, PHYSICS OF FLUIDS, Vol: 25, ISSN: 1070-6631
This paper presents a gluing method for composite meshes. Different meshes are generated independently and are glued together using some extension elements to connect them. The resulting global mesh is non-conforming and consists of connected overlapping meshes. The method is inherently implicit, parallel and versatile, in the sense that it is PDE independent. The most cited gluing method is probably the Chimera method, used for overset grids, where patch meshes are superimposed onto a background mesh. The method employed here was originally devised for such situations and is now applied to disjoint or overlapping meshes. One of the advantages of the method is that the meshes do not have to coincide and can present a gap between them. The method is illustrated through some simple examples to demonstrate the mesh convergence and finally applied to the solution of the airflow in the complete respiratory system, by joining independent meshes for the large and small airways. © 2013 The Authors.
Rossi L, Doorly D, Kustrin D, 2012, Lamination and mixing in three fundamental flow sequences driven by electromagnetic body forces, PHYSICAL REVIEW E, Vol: 86, ISSN: 1539-3755
Objective: We present a study investigating the effect of a decongestant on the nasal mucosa, showing results in terms of the change in erectile tissue volume (ETV) in normal subjects using high resolution 3T-MRI scanning. Method: Seven volunteers with no nasal complaints (SNOT-22) or obvious rhinoscopic abnormalities were studied. Each subject underwent 2 MRI scans producing a series of 120 contiguous 1.2 mm sections pre- and postdecongestion. Patients were decongested with xylometazoline-HCL, remaining immobilized following the first scan. The scans were segmented using ITK-Snap and analyzed using MATLAB. Results: Subject age ranged from 21-38 years (mean = 28). The SNOT-22 scores ranged from 1-10 (mean = 4.8). Decongestion had the greatest effect in 3 sites: the inferior turbinates, middle turbinates, and septum. The greatest change in ETV was observed in the inferior turbinates (P <.005), reducing by up to 1/3 at the posterior aspect of the inferior turbinate following decongestion. Changes were also seen in ETV of the middle turbinate and septal mucosa to a lesser extent. Conclusion: The effect of decongestion on ETV has been investigated here in far greater detail than previously studied, and at higher spatial resolution. 3T-MRI was found to be an excellent modality for mapping changes in nasal mucosa. Our results demonstrate the significant effect of decongestion on ETV of the inferior turbinates.
Gambaruto AM, Taylor DJ, Doorly DJ, 2012, Decomposition and Description of the Nasal Cavity Form, ANNALS OF BIOMEDICAL ENGINEERING, Vol: 40, Pages: 1142-1159, ISSN: 0090-6964
Alastruey J, Siggers JH, Peiffer V, et al., 2012, Reducing the data: Analysis of the role of vascular geometry on blood flow patterns in curved vessels, PHYSICS OF FLUIDS, Vol: 24, ISSN: 1070-6631
Rossi L, Doorly D, Kustrin D, 2012, Lamination and mixing in laminar flows driven by Lorentz body forces, EPL, Vol: 97, ISSN: 0295-5075
Rennie CE, Hood CM, Blenke EJSM, et al., 2011, Physical and computational modelling of ventilation of the maxillary sinus, Otolaryngology-Head and Neck Surgery, Vol: 145, ISSN: 0194-5998
BackgroundThis study quantifies the time-varying flow rate during inspiration at rest and in sniffing, both predecongestion and postdecongestion. It aims to provide a better understanding of nasal airflow mechanics, for application to the physiological modeling of nasal respiration and to therapeutic drug delivery.MethodsThe temporal profiles of nasal inspiration were measured at high fidelity in 14 healthy individuals using simultaneous bilateral hot-wire anemometry. Peak nasal inspiratory flow (PNIF) rate, acoustic rhinometry (AR), and the sinonasal outcome test (SNOT) provided complementary clinical measurements. The impact of decongestion was also investigated.ResultsIn the initial phase of inspiration, a rapid rise in flow rate was observed. Flow first exceeded 150 mL/second in either passage within a median time of approximately 120 ms for inspiration at rest and approximately 60 ms in sniffing (∼20 ms in the fastest sniffs). The mean sustained flow rate attained and the overall period of each measured inspiratory profile were analyzed. AR showed a significant change in nasal volume with decongestion, although these change were not manifest in the temporal profiles of inspiratory flow (barring a weak effect associated with the most vigorous sniffs).ConclusionNovel methods were applied to investigate the temporal profiles of nasal inspiration. Characteristic features of the profile were identified and found to be significantly different between inspiration at rest and sniffing. Decongestion was found to have little effect on the temporal profiles for the flow regimes studied.
Rossi L, Doorly D, Durant A, et al., 2011, Lamination and mixing in canonical and turbulent flows
Lamination and mixing properties are characterised for a canonical flow (cat's eyes flip) at low Reynolds number (~13) and a turbulent flow. The cat's eyes flow is experimentally driven by electromagnetic forces while the turbulent flow is generated using 2D DNS. It is shown that lamination and stretching grow exponentially for both flows with an exponent higher for the stretching than for the lamination. Noticeably, the difference between the stretching and lamination exponents is higher for the turbulent flow than for the low Reynolds number flow with ratios respectively about 1.32 and 1.12. Moreover, lamination enhances mixing locally by reducing the distance over which diffusion needs to act to finalise mixing. The difference in the mixing properties of the flows is related to the distribution of lamination. The turbulent flow saturates locally, i.e. it reaches locally high lamination values where diffusion can act swiftly over short distances to finalise mixing while most of the flow is still with low values of lamination. This leads to an algebraic growth of the mixing coefficient. The cat's eyes flip flow globally increases lamination with a better space filling than the turbulent flow. This delays the saturation of mixing and leads to an initial exponential growth of the mixing coefficient.
Cookson AN, Doorly DJ, Sherwin SJ, 2010, Using coordinate transformation of Navier–Stokes equations to solve flow in multiple helical geometries, Journal of Computational and Applied Mathematics, Vol: 234, Pages: 2069-2079
Recent research on small amplitude helical pipes for use as bypass grafts and arterio-venous shunts, suggests that mixing may help prevent occlusion by thrombosis. It is proposed here that joining together two helical geometries, of different helical radii, will enhance mixing, with only a small increase in pressure loss. To determine the velocity field, a coordinate transformation of the Navier–Stokes equations is used, which is then solved using a 2-D high-order mesh combined with a Fourier decomposition in the periodic direction. The results show that the velocity fields in each component geometry differ strongly from the corresponding solution for a single helical geometry. The results suggest that, although the mixing behaviour will be weaker than an idealised prediction indicates, it will be improved from that generated in a single helical geometry.
Gambaruto AM, Doorly DJ, Yamaguchi T, 2010, Wall shear stress and near-wall convective transport: Comparisons with vascular remodelling in a peripheral graft anastomosis, JOURNAL OF COMPUTATIONAL PHYSICS, Vol: 229, Pages: 5339-5356, ISSN: 0021-9991
Taylor DJ, Doorly DJ, Schroter RC, 2010, Inflow boundary profile prescription for numerical simulation of nasal airflow, JOURNAL OF THE ROYAL SOCIETY INTERFACE, Vol: 7, Pages: 515-527, ISSN: 1742-5689
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