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133 results on '"Doorly, Denis"'

1. Random walk diffusion simulations in semi-permeable layered media with varying diffusivity

Author

Alemany, Ignasi, Rose, Jan N., Garnier-Brun, Jérôme, Scott, Andrew D., and Doorly, Denis J.

Subjects
Physics - Biological Physics, Physics - Medical Physics
Abstract

In this paper we present analytical and random walk based solutions to diffusion in semi-permeable layered media with varying diffusivity. We propose a new random walk transit model (hybrid model) based on treating the membrane permeability and the change in diffusion as two infinitesimal separate phenomena. By conducting an extensive analytical flux analysis, the performance of our hybrid model is compared with a commonly used membrane model (reference model). We numerically demonstrate the limitations of the reference model and show the capability of our new model to overcome these restrictions. The suitability of both random walk transit models for the application to simulations of the diffusion tensor cardiovascular magnetic resonance (DT-CMR) is assessed in a histology-based domain. We consider a larger range of permeabilities to show the potential of our model to other possible applications beyond biological tissue.

Published
2022

2. The Effect of Temporal Variations in Myocardial Perfusion on Diffusion Tensor Measurements

Author

Alemany, Ignasi, Ferreira, Pedro F., Nielles-Vallespin, Sonia, Scott, Andrew D., Doorly, Denis J., Goos, Gerhard, Founding Editor, Hartmanis, Juris, Founding Editor, Bertino, Elisa, Editorial Board Member, Gao, Wen, Editorial Board Member, Steffen, Bernhard, Editorial Board Member, Yung, Moti, Editorial Board Member, Bernard, Olivier, editor, Clarysse, Patrick, editor, Duchateau, Nicolas, editor, Ohayon, Jacques, editor, and Viallon, Magalie, editor

Published
2023
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4. Dynamics of airflow in a short inhalation

Author

Bates, Alister, Doorly, Denis, Cetto, Raul, Calmet, Hadrien, Gambaruto, Alberto, Tolley, Neil, Houzeaux, Guillaume, and Schroter, Robert

Subjects
Physics - Fluid Dynamics
Abstract

During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective trans- port 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 litre per second 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 20ms, 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., Comment: 15 pages

Published
2015
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10. Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

Author

Stettler, Marc EJ, Nishida, Robert T, De Oliveira, Pedro M, Mesquita, Léo CC, Johnson, Tyler J, Galea, Edwin R, Grandison, Angus, Ewer, John, Carruthers, David, Sykes, David, Kumar, Prashant, Avital, Eldad, Obeysekara, Asiri IB, Doorly, Denis, Hardalupas, Yannis, Green, David C, Coldrick, Simon, Parker, Simon, Boies, Adam M, Stettler, Marc EJ [0000-0002-2066-9380], Nishida, Robert T [0000-0002-9820-1569], de Oliveira, Pedro M [0000-0002-5527-8128], Mesquita, Léo CC [0000-0001-5086-696X], Johnson, Tyler J [0000-0002-3641-0381], Galea, Edwin R [0000-0002-0001-6665], Grandison, Angus [0000-0002-9714-1605], Ewer, John [0000-0003-0609-272X], Carruthers, David [0000-0003-3363-0992], Sykes, David [0000-0002-7578-890X], Kumar, Prashant [0000-0002-2462-4411], Avital, Eldad [0000-0003-4411-1493], Doorly, Denis [0000-0002-5372-4702], Hardalupas, Yannis [0000-0002-8306-5429], Green, David C [0000-0002-0695-4660], Boies, Adam M [0000-0003-2915-3273], Apollo - University of Cambridge Repository, Stettler, Marc E. J. [0000-0002-2066-9380], Nishida, Robert T. [0000-0002-9820-1569], de Oliveira, Pedro M. [0000-0002-5527-8128], Mesquita, Léo C. C. [0000-0001-5086-696X], Johnson, Tyler J. [0000-0002-3641-0381], Galea, Edwin R. [0000-0002-0001-6665], Green, David C. [0000-0002-0695-4660], and Boies, Adam M. [0000-0003-2915-3273]

Subjects
Physics and biophysics, disease transmission, QR355, source terms, Multidisciplinary, SARS-CoV-2, exhaled aerosols, Review articles, model benchmarking, Q1
Abstract

There is ongoing and rapid advancement in approaches to modelling the fate of exhaled particles in different environments relevant to disease transmission. It is important that models are verified by comparison with each other using a common set of input parameters to ensure that model differences can be interpreted in terms of model physics rather than unspecified differences in model input parameters. In this paper, we define parameters necessary for such benchmarking of models of airborne particles exhaled by humans and transported in the environment during breathing and speaking.

Published
2022

11. Geometry and flow

Author

Doorly, Denis, Sherwin, Spencer, Quarteroni, Alfio, editor, Hou, Tom, editor, Le Bris, Claude, editor, Patera, Anthony T., editor, Zuazua, Enrique, editor, Formaggia, Luca, editor, and Veneziani, Alessandro, editor

Published
2009
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12. Applications and test cases

Author

Arimon, J. Alastruey, Doorly, Denis, Giordana, Sergio, Peiró, Joaquim, Sherwin, Spencer, Quarteroni, Alfio, editor, Hou, Tom, editor, Le Bris, Claude, editor, Patera, Anthony T., editor, Zuazua, Enrique, editor, Formaggia, Luca, editor, and Veneziani, Alessandro, editor

Published
2009
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14. Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

Author

Stettler, Marc E. J., primary, Nishida, Robert T., additional, de Oliveira, Pedro M., additional, Mesquita, Léo C. C., additional, Johnson, Tyler J., additional, Galea, Edwin R., additional, Grandison, Angus, additional, Ewer, John, additional, Carruthers, David, additional, Sykes, David, additional, Kumar, Prashant, additional, Avital, Eldad, additional, Obeysekara, Asiri I. B., additional, Doorly, Denis, additional, Hardalupas, Yannis, additional, Green, David C., additional, Coldrick, Simon, additional, Parker, Simon, additional, and Boies, Adam M., additional

Published
2022
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16. Supplementary Information from Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

Author

Stettler, Marc E.J., Nishida, Robert T., de Oliveira, Pedro M., Mesquita, Léo C.C., Johnson, Tyler J., Galea, Edwin R., Grandison, Angus, Ewer, John, Carruthers, David, Sykes, David, Kumar, Prashant, Avital, Eldad, Obeysekara, Asiri I.B., Doorly, Denis, Hardalupas, Yannis, Green, David C., Coldrick, Simon, Parker, Simon, and Boies, Adam M.

Subjects
viruses, digestive, oral, and skin physiology
Abstract

Additional material on breathing rates, exhaled particle size distributions and relative viral loads

Published
2022
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17. Source terms for benchmarking models of SARS-CoV-2 transmission via aerosols and droplets

Author

Stettler, Marc E.J., primary, Nishida, Robert T., additional, de Oliveira, Pedro M., additional, Mesquita, Léo C.C., additional, Johnson, Tyler J., additional, Galea, Edwin R., additional, Grandison, Angus, additional, Ewer, John, additional, Carruthers, David, additional, Sykes, David, additional, Kumar, Prashant, additional, Avital, Eldad, additional, Obeysekara, Asiri I.B., additional, Doorly, Denis, additional, Hardalupas, Yannis, additional, Green, David C., additional, Coldrick, Simon, additional, Parker, Simon, additional, and Boies, Adam M., additional

Published
2022
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18. Development of a cardiovascular magnetic resonance‐compatible large animal isolated heart model for direct comparison of beating and arrested hearts

Author

Scott, Andrew D., primary, Jackson, Tim, additional, Khalique, Zohya, additional, Gorodezky, Margarita, additional, Pardoe, Ben, additional, Begum, Lale, additional, Bruno, V. Domenico, additional, Chowdhury, Rasheda A., additional, Ferreira, Pedro F., additional, Nielles‐Vallespin, Sonia, additional, Roehl, Malte, additional, McCarthy, Karen P., additional, Sarathchandra, Padmini, additional, Rose, Jan N., additional, Doorly, Denis J., additional, Pennell, Dudley J., additional, Ascione, Raimondo, additional, de Silva, Ranil, additional, and Firmin, David N., additional

Published
2022
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20. See attached description of supplementary materials file from A simulated single ventilator/dual patient ventilation strategy for acute respiratory distress syndrome during the COVID-19 pandemic

Author

Solís-Lemus, José A., Costar, Edward, Doorly, Denis, Kerrigan, Eric C., Kennedy, Caroline H., Tait, Frances, Niederer, Steven, Vincent, Peter E., and Williams, Steven E.

Abstract

The potential for acute shortages of ventilators at the peak of the COVID-19 pandemic has raised the possibility of needing to support two patients from a single ventilator. To provide a system for understanding and prototyping designs, we have developed a mathematical model of two patients supported by a mechanical ventilator. We propose a standard set-up where we simulate the introduction of T-splitters to supply air to two patients and a modified set-up where we introduce a variable resistance in each inhalation pathway and one-way valves in each exhalation pathway. Using the standard set-up, we demonstrate that ventilating two patients with mismatched lung compliances from a single ventilator will lead to clinically significant reductions in tidal volume in the patient with the lowest respiratory compliance. Using the modified set-up, we demonstrate that it could be possible to achieve the same tidal volumes in two patients with mismatched lung compliances, and we show that the tidal volume of one patient can be manipulated independently of the other. The results indicate that, with appropriate modifications, two patients could be supported from a single ventilator with independent control of tidal volumes.

Published
2020
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21. A Simulated Single Ventilator / Dual Patient Ventilation Strategy for Acute Respiratory Distress Syndrome During the COVID-19 Pandemic

Author

Solís-Lemus, José A., Costar, Edward, Doorly, Denis, Kerrigan, Eric C., Kennedy, Caroline H., Tait, Frances, Niederer, Steven, Vincent, Peter E., and Williams, Steven E.

Subjects
Ventilator splitting Ventilator sharing Covid-19 Coronavirus Acute respiratory distress syndrome ARDS
Abstract

The potential for acute shortages of ventilators at the peak of the Covid-19 pandemic has raised the possibility of needing to support two patients from a single ventilator. To provide a system for understanding and prototyping designs we have developed a mathematical model of two patients supported by a mechanical ventilator. We propose a standard setup where we simulate the introduction of T-splitters to supply air to two patients and a modified setup where we introduce a variable resistance in each inhalation pathway and one-way valves in each exhalation pathway. Using the standard setup, we demonstrate that ventilating two patients with mismatched lung compliances from a single ventilator will lead to clinically-significant reductions in tidal volume in the patient with the lowest respiratory compliance. Using the modified setup, we demonstrate that it could be possible to achieve the same tidal volumes in two patients with mismatched lung compliances, and we show that the tidal volume of one patient can be manipulated independently of the other. The results indicate that, with appropriate modifications, two patients could be supported from a single ventilator with independent control of tidal volumes.Data, code and materials:The Simulink models used in this research have been uploaded to a Git repository at the following address: https://github.com/splitvent/splitvent.

Published
2020

32. Voxel-based simulation of flow and temperature in the human nasal cavity.

Author

Kimura, Shinya, Miura, Shuta, Sera, Toshihiro, Yokota, Hideo, Ono, Kenji, Doorly, Denis J., Schroter, Robert C., and Tanaka, Gaku

Subjects
FLOW simulations, NASAL cavity, AIR flow, NEUMANN boundary conditions, VOXEL-based morphometry, TEMPERATURE distribution, COMPUTED tomography
Abstract

The nasal airway is an extremely complex structure, therefore grid generation for numerical prediction of airflow in the nasal cavity is time-consuming. This paper describes the development of a voxel-based model with a Cartesian structured grid, which is characterized by robust and automatic grid generation, and the simulation of the airflow and air-conditioning in an individual human nasal airway. Computed tomography images of a healthy adult nose were used to reconstruct a virtual three-dimensional model of the nasal airway. Simulations of quiet restful inspiratory flow were then performed using a Neumann boundary condition for the energy equation to adequately resolve the flow and heat transfer. General agreements of airflow patterns, which were a high-speed jet posterior to the nasal valve and recirculating flow that occupied the anterior part of the upper cavity, and temperature distributions of the airflow and septum wall were confirmed by comparing in-vivo measurements with numerical simulation results. [ABSTRACT FROM AUTHOR]

Published
2021
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33. Oxford Abstracts

Author

Qiwei Xiao, Doorly, Denis, Bates, Alister, Ritchie, Lulu, Cetto, Raul, Schroter, Robert, and Tolley, Neil

Published
2017
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34. Novel insights into in‐vivo diffusion tensor cardiovascular magnetic resonance using computational modeling and a histology‐based virtual microstructure.

Author

Rose, Jan N., Nielles‐Vallespin, Sonia, Ferreira, Pedro F., Firmin, David N., Scott, Andrew D., and Doorly, Denis J.

Abstract

Purpose : To 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. Methods : We 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. Results : The 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. Conclusions : We 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. [ABSTRACT FROM AUTHOR]

Published
2019
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36. Applications and test cases

Author

Fernandez, Miguel, Dubini, Gabriele, Doorly, Denis, D'Angelo, Carlo, Balossino, Rossella, Arimon, Alastruey, Gerbeau, JEAN FREDERIC, Giordana, Sergio, Migliavacca, Francesco, Pennati, Giancarlo, Peiro', Joaquim, Prosi, Martin, Sherwin, Spencer, Vergara, Christian, Vidrascu, Marina, and Zunino, Paolo

Subjects
Test case, Three vessels, Computer science, Medical imaging, Distal bypass, Drug release, Bypass grafts, Arterial wall, Settore MED/11 - Malattie dell'Apparato Cardiovascolare, Biomedical engineering
Abstract

Although medical imaging can provide relatively accurate geometric data of in vivo bypass grafts, as will be discussed in Section 12.1.2, to obtain an understanding of the general flow features it is instructive to consider an idealisation of a distal bypass graft. In this example we therefore consider the problem shown in Fig. 12.1, which consists of three vessels, all of the same diameter D, where the bypass (connecting) vessel has a centreline length of 3D and the host vessel is represented by two co-aligned vessels of lengths 5D (distal) and 10D (proximal) from the junction.

Published
2009

37. Arteries and algorithms : multiple scale modelling of flow in the cardiovascular system

Author

Sherwin, Spencer, Alastruey, Jordi, Cookson, Andrew, Doorly, Denis, Kazakidi, Asimina, Parker, Kim, Peiro, Jaoquim, and Weinberg, Peter

Subjects
TA164
Abstract

This review outlines some of the different scales involved in computationally modelling arterial networks. Starting at the largest O(1m) scale we highlight current activities in reduced modelling of the pulse waves. We then focus on the O(10-1m) scale and provide an example of how CFD can be applied to understand the role of mixing in small amplitude helical pipes at physiologically relevant flow conditions. Finally we motivate the interaction at O(10-3m) scale by considering how localised flow features are suggestive of different types of arterial disease patterns.

Published
2008

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