Research Article A Feasible Computational Fluid Dynamics Study for Relationships of Structural and Functional Alterations with Particle Depositions in Severe Asthmatic Lungs Sanghun Choi , 1 Shinjiro Miyawaki, 2,3 and Ching-Long Lin 3 1 School of Mechanical Engineering, Kyungpook National University, Daegu, Republic of Korea 2 Jacobs, 1100 NE Circle Blvd., Suite 300, Corvallis, Oregon 97330, USA 3 Department of Mechanical and Industrial Engineering, IIHR-Hydroscience and Engineering, University of Iowa, Iowa City, Iowa, USA Correspondence should be addressed to Ching-Long Lin; ching-long-lin@uiowa.edu Received 2 February 2018; Accepted 26 March 2018; Published 22 July 2018 Academic Editor: Yu Feng Copyright © 2018 Sanghun Choi et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Tis study aims to investigate the efect of altered structures and functions in severe asthma on particle deposition by using computational fuid dynamics (CFD) models. Airway geometrical models of two healthy subjects and two severe asthmatics were reconstructed from computed tomography (CT) images. Subject-specifc fow 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 fows was applied to simulate airfows, and particle transport simulations were then performed for 2.5, 5, and 10 m particles using CFD-predicted fow felds. 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 signifcant reduction of hydraulic diameter ( h ). 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 m particles. Te structural alterations measured by Cr and  h were associated with a higher particle deposition.  h was found to be the most important metric which afects the specifc location of particle deposition. Tis study demonstrates the relationship of CT-based structural and functional alterations in severe asthma with fow and particle dynamics. 1. Introduction Asthma is pathologically characterized by combined pheno- types of airfow obstruction, bronchial hyperresponsiveness, and airway infammation [1]. However, how structural and functional alterations of asthma afect fow structure and particle deposition is yet to be investigated. In imaging stud- ies 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– 4]. In addition, via quantitative computed tomography (QCT) imaging, several studies [5–8] have demonstrated sig- nifcant alterations such as reduced airway diameter as well as increased wall thickness and air trapping. Although QCT can provide structural measurements of the airways up to seg- mental airways (∼2 mm), quantifcation of local functional variables is still limited. Image registration technique has been utilized to provide functional information by matching images at diferent infa- tion levels [9]. Te registration derived-variables were vali- dated by comparing ventilation maps from diferent imaging modalities [10]. Furthermore, this technique has shown strengths when characterizing functional alterations of dis- eased lungs [11, 12]. For instance, a study used the technique to diferentiate airway vs. parenchymal phenotypes in a chronic obstructive pulmonary disease (COPD) [11]. We have recent- ly demonstrated that volume changes of severe asthmatic lungs are preferentially smaller near basal regions and the smaller volume changes are compensated with air-volume Hindawi Computational and Mathematical Methods in Medicine Volume 2018, Article ID 6564854, 12 pages https://doi.org/10.1155/2018/6564854