The influence of lung volume during imaging on CFD within realistic airway models

Abstract

In this article, we address a fundamental question regarding computational fluid dynamics (CFD) modeling within lung airways: does the inhaled volume during imaging have a significant effect on CFD computations of aerosol deposition? High resolution computed tomography (HRCT) images taken at mean lung volume (MLV) and at total lung capacity (TLC) obtained as part of a previous study of ventilation and aerosol deposition using positron emission tomography (PET) in challenged asthmatics were utilized to construct two airway models for each subject, and the differences in CFD calculated deposition metrics were subsequently quantified. These models included all the airway generations that could be rendered from the HRCT images. CFD calculations for three inhalation flow rates and four monodisperse aerosol sizes used images at MLV and at TLC from 24 volunteer subjects. Both large scale and detailed measures of particle deposition distribution were used in the analysis. The influence of lung volume during imaging is to increase airway dimensions in realistic models and thus reduce flow velocity and deposition due to impaction in the upper airways as calculated by CFD. However, large-scale deposition measures are confounded when the TLC models include deeper generations in the lung that increase the total airway deposition. These trends are modulated by the flow and particle characteristics of the aerosol, making consistent quantifiable differences between MLV and TLC difficult to predict unless both models consider the same anatomical airways.

Particle Disposition in the Realistic Airway Tree Models of Subjects with Tracheal Bronchus and COPD

“…Alzahrany et al [ 27 ] found that the orientation of endotracheal tube determines the local and total deposition. Katz et al [ 28 ] considered the influence of lung volume during imaging on PD.…”

The effect of disease and respiration on airway shape in patients with moderate persistent asthma

“…This misconception has recently been recognized by researchers using such models of the lung. For example, in a CFD study on aerosol deposition in bronchial tree models extracted from HRCT images at MLV and TLC, Katz et al [ 27 ] concluded that lung volume should be explicitly considered when using deposition models. Bordas et al [ 21 ], lacking relevant information for a population of asthmatic patients, used the minimum inner diameters of the segmented airways in conjunction with a circular cross-section assumption to predict airflow in the lung.…”

“…Modeling of the lungs has become an important tool for both diagnostic [ 1 – 4 ] and research [ 5 – 11 ] purposes. Functional features of the lung such as airway compliance or distensibility [ 12 – 15 ], resistance [ 9 , 12 , 16 – 21 ], aerosol deposition [ 5 , 9 , 22 – 27 ] and ventilation distribution [ 10 , 19 , 26 , 28 – 32 ] computations are frequently made using a combination of medical images and the utilization of such models. Clearly, knowledge of the underlying lung morphologies is a key to these applications.…”

Anthropometry‐based generation of personalized and population‐specific human airway models

“…One possible explanation for the above might be due to the variation in the drug deposition due to (a) patient‐specific differences in the lung dimensions, (b) drug inhaler usage, (c) variability in liver/kidney clearances, and (d) change in the lung morphology, due to the severity and type of the disease (for instance, certain asthma attacks and Chronic obstructive pulmonary disease (COPD) conditions are characterized by highly localized blockages that heavily affect the flow of gas and drug particle deposition in these regions). To address the first source of variation, researchers have been developing tools, for the generation of the population‐ and subject‐specific virtual airway anatomical and computational aerosol inhalation and deposition models based on anthropometric data and physiological vitals . When combined with inhalation topography, such models are invaluable in respiratory diagnostics, personalized pulmonary pharmacology, and model‐based management of chronic respiratory diseases.…”

“…It is possible to develop 3D models for computational fluid dynamics (CFD) calculations of aerosol transport and deposition based on these morphometric models. The converse is also possible, that is, the use of 3D models acquired through medical imaging modalities for the development of morphometric models of the lung or the direct simulation of gas and aerosol transport and deposition on such models …”