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Research Papers

Development of a CFD Boundary Condition to Model Transient Vapor Absorption in the Respiratory Airways

[+] Author and Article Information
Geng Tian

Department of Mechanical Engineering, Virginia Commonwealth University, Richmond, VA 23284

P. Worth Longest1

Department of Mechanical Engineering, and Department of Pharmaceutics, Virginia Commonwealth University, Richmond, VA 23284pwlongest@vcu.edu

1

Corresponding author.

J Biomech Eng 132(5), 051003 (Mar 25, 2010) (13 pages) doi:10.1115/1.4001045 History: Received November 24, 2009; Revised January 14, 2010; Posted January 19, 2010; Published March 25, 2010; Online March 25, 2010

The absorption of moderately and highly soluble vapors into the walls of the conducting airways was previously shown to be a transient process over the timescale of an inhalation cycle. However, a boundary condition to predict the transient wall absorption of vapors in CFD simulations does not exist. The objective of this study was to develop and test a boundary condition that can be used to predict the transient absorption of vapors in CFD simulations of transport in the respiratory airways. To develop the boundary condition, an analytical expression for the concentration of an absorbed vapor in an air-mucus-tissue-blood (AMTB) model of the respiratory wall was developed for transient and variable air-phase concentrations. Based on the analytical expression, a flux boundary condition was developed at the air-mucus interface as a function of the far-field air-phase concentration. The new transient boundary condition was then implemented to predict absorption in a realistic model of the extrathoracic nasal airways through the larynx (nasal-laryngeal geometry). The results of the AMTB wall model verified that absorption was highly time dependent over the timescale of an inhalation cycle (approximately 1–2 s). At 1 s, transient conditions resulted in approximately 2–3 times more uptake in tissue and 20–25 times less uptake in blood than steady state conditions for both acetaldehyde and benzene. Application of this boundary condition to computational fluid dynamics simulations of the nasal-laryngeal geometry showed, as expected, that transient absorption significantly affected total deposition fractions in the mucus, tissue, and blood. Moreover, transient absorption was also shown to significantly affect the local deposition patterns of acetaldehyde and benzene. In conclusion, it is recommended that future analyses of vapors in the conducting airways consider time-dependent wall absorption based on the transient flux boundary condition developed in this study. Alternatively, a steady state absorption condition may be applied in conjunction with correction factors determined from the AMTB wall model.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 3

Boundary conditions at the air-mucus interface

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Figure 4

System setup for the (a) numerical solution and (b) hybrid analytical-numerical solution in the multilayer AMTB wall model

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Figure 5

Comparison of transient numerical and hybrid solutions for acetaldehyde and benzene concentrations in the mucus and tissue layers

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Figure 6

Acetaldehyde and benzene concentrations at the air-mucus and mucus-tissue interfaces

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Figure 7

Flux of acetaldehyde and benzene into the mucus, tissue, and blood layers

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Figure 8

Uptake of acetaldehyde and benzene for transient and steady state conditions

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Figure 9

Uptake of acetaldehyde and benzene for transient conditions including reactivity in the (a) mucus, (b) tissue, and (c) blood layers

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Figure 11

DEF contours of acetaldehyde for both (a) case 1 (S:S) and (b) case 2 (S:T) conditions over a 2 s inhalation period

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Figure 12

DEF contours of benzene for both (a) case 1 (S:S) and (b) case 2 (S:T) conditions over a 2 s inhalation period

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Figure 1

(a) The AMTB system and (b) nasal-laryngeal airway model

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Figure 2

System setup for analytic solutions in the mucus and tissue layers

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Figure 10

Deposition fraction of acetaldehyde and benzene vapors in mucus, tissue, and blood in the nasal-laryngeal airway model for case 1 (S:S) and case 2 (S:T) over a 2 s inhalation period

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