A Feasible Computational Fluid Dynamics Study for Relationships of Structural and Functional Alterations with Particle Depositions in Severe Asthmatic Lungs.

Sanghun Choi,Shinjiro Miyawaki,Ching-Long Lin

doi:10.1155/2018/6564854

Sanghun Choi, Shinjiro Miyawaki + Show 1 more

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https://doi.org/10.1155/2018/6564854

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Abstract

This study aims to investigate the effect of altered structures and functions in severe asthma on particle deposition by using computational fluid dynamics (CFD) models. Airway geometrical models of two healthy subjects and two severe asthmatics were reconstructed from computed tomography (CT) images. Subject-specific flow boundary conditions were obtained by image registration to account for regional functional alterations of severe asthmatics. A large eddy simulation (LES) model for transitional and turbulent flows was applied to simulate airflows, and particle transport simulations were then performed for 2.5, 5, and 10 μm particles using CFD-predicted flow fields. Compared to the healthy subjects, the severe asthmatics had a smaller air-volume change in the lower lobes and a larger air-volume change in the upper lobes. Both severe asthmatics had smaller airway circularity (Cr), but one of them had a significant reduction of hydraulic diameter (Dh). In severe asthmatics, the larger air-volume change in the upper lobes resulted in more particles in the upper lobes, especially for the small 2.5 μm particles. The structural alterations measured by Cr and Dh were associated with a higher particle deposition. Dh was found to be the most important metric which affects the specific location of particle deposition. This study demonstrates the relationship of CT-based structural and functional alterations in severe asthma with flow and particle dynamics.

Highlights

Asthma is pathologically characterized by combined phenotypes of airflow obstruction, bronchial hyperresponsiveness, and airway inflammation [1]
Bronchodilator was performed for both healthy subjects and severe asthmatics to obtain maximal lung functions, and computed tomography (CT) scans were acquired after bronchodilator because the aim of Severe Asthma Research Program (SARP) study was to assess lung function of stable asthma [33]
According to baseline and maximal Pulmonary Function Test (PFT), Severe asthmatics (SA) 2 is likely to have significant airway narrowing despite bronchodilator, whereas airways of SA 1 might have dilated with the aid of bronchodilator

Summary

Introduction

Asthma is pathologically characterized by combined phenotypes of airflow obstruction, bronchial hyperresponsiveness, and airway inflammation [1]. In imaging studies of asthma, ventilation defects and airway structural changes have been investigated by using magnetic resonance image (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT) [2,3,4]. Via quantitative computed tomography (QCT) imaging, several studies [5,6,7,8] have demonstrated significant alterations such as reduced airway diameter as well as increased wall thickness and air trapping. The registration derived-variables were validated by comparing ventilation maps from different imaging modalities [10]. This technique has shown strengths when characterizing functional alterations of diseased lungs [11, 12]. We have recently demonstrated that volume changes of severe asthmatic lungs are preferentially smaller near basal regions and the smaller volume changes are compensated with air-volume

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