Fiber deposition in the tracheobronchial region: experimental measurements

Our plain-English summary of Fiber deposition in the tracheobronchial region: experimental measurements, by Y. Zhou, W.C. Su, Y.S. Cheng (Inhalation Toxicology, 2007).

The study

• Authors: Y. Zhou, W.C. Su, Y.S. Cheng
• Journal: Inhalation Toxicology
• Published: 2007;19(13):1071-8
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fiber deposition efficiency in the tracheobronchial region was studied by using two human airway replicas. Carbon fibers with a monodisperse diameter of 3.66 mu were delivered into lung casts at the flow rates of 15, 45, and 60 L/min. Deposition efficiencies in each airway bifurcation were obtained individually. Even though the data shows large variability among the bifurcations within the same generation, there is a general trend for the data obtained in these two replicas. Our results show that fiber deposition for carbon fibers increases with the Stokes number, indicating that inertial impaction is the dominant mechanism. Also, fiber deposition in the tracheobronchial region is lower than that of spherical particles at a given Stokes number, and is similar to the deposition found in the nasal and oral airways as reported previously. This finding implies that it is easier for fibers to penetrate the upper respiratory tract and to reach the lower airways as compared to spherical particles. Our measurements are in general agreement with data obtained with asbestos fiber as reported in another study using a hollow airway replica. Our study appears to give a higher deposition efficiency than the results obtained using idealized single symmetrical bifurcation models. This demonstrates, again, the importance of using a realistic airway model, including larynx, to simulate the airway geometry and flow pattern of the human respiratory tract.

In plain English

This laboratory study measured fiber deposition in two replicas of the human airway. The replicas were made from dental impressions of the mouth and from cadavers for the windpipe and three to four generations of bronchi. No asbestos was used. Carbon fibers 3.66 µm in diameter, of varying lengths, were passed through the replicas at 15, 43.5 and 60 L/min, and the deposited fibers were counted at each branch point. Deposition rose with the Stokes number (a measure combining particle size, air speed and tube size), which the authors took to mean that inertial impaction was the main mechanism. Results varied widely between branches of the same generation. In the trachea, fiber deposition was lower than earlier measurements for spherical particles in one replica. For the bronchial branches, the results section said fiber deposition appeared higher, while the conclusions describe it as lower. The data broadly agreed with an earlier asbestos-fiber study by Sussman and coworkers, though the authors said the tracheal comparison was difficult. The authors concluded that fibers may reach the lower airways more easily than spherical particles.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory experiment using physical replicas (casts) of the human airway
• Who was studied: No people or animals. Two human airway replicas (casts A and B) including the oral cavity, pharynx, larynx, trachea and three to four generations of bronchi, made from dental impressions and cadavers, at Lovelace Respiratory Research Institute, Albuquerque, New Mexico
• Exposure: Conductive carbon fibers with a uniform diameter of 3.66 µm and varying lengths, delivered at inspiratory flow rates of 15, 43.5 and 60 L/min (rest to moderate exercise). Asbestos was not tested; asbestos data came from an earlier study used for comparison.
• Main results:
  • Across the first to fourth bronchial generations of both casts, carbon fiber deposition generally increased as the Stokes number increased
  • In the trachea, fiber deposition was lower than that of spherical particles (measured previously in cast A) at a given Stokes number
  • Deposition varied widely among bronchial branches, even within the same generation
  • In the bronchial airways, the results section described fiber deposition as appearing higher than that of spherical particles
  • In the first generation, most fibers deposited at the carina (the ridge where an airway splits)
  • At the fourth generation of cast A, deposition was higher than in earlier glass-fiber experiments by Myojo using idealized bifurcation models
  • The carbon fiber data were in general agreement with the asbestos fiber data of Sussman et al. (1991) obtained in a hollow human tracheobronchial cast
• The authors' conclusion: The authors concluded that inertial impaction dominates carbon fiber deposition. They also concluded that fiber deposition in the tracheobronchial region is lower than for spherical particles at a given Stokes number, implying that fibers penetrate the upper respiratory tract and reach the lower airways more easily. They added that realistic airway models including the larynx are important.
• Limitations the authors state:
  • The Stokes number used included only the parent tube diameter, so other geometry differences between branches could also have affected deposition
  • For the trachea, the Stokes number ranges of this study and the asbestos study did not overlap well, making agreement hard to judge
  • Data are needed for fibers about 1 µm in diameter
  • The comparison with Myojo's glass fiber data was limited to a narrow Stokes number range

Topics

Medical terms in this study, explained in our Lexicon: Deposition.

Related studies

• Ozone enhances the uptake of mineral particles by tracheobronchial epithelial cells in organ culture — A. Churg, M. Brauer, et al. (1996)
• Mechanisms of asbestos-induced squamous metaplasia in tracheobronchial epithelial cells — G. Cameron, C.D. Woodworth, et al. (1989)
• In vitro activity of silicon carbide whiskers in comparison to other industrial fibers using four cell culture systems — N.F. Johnson, M.D. Hoover, et al. (1992)
• Estimation of fibrous aerosol deposition in upper bronchi based on experimental data with model bifurcation — T. Myojo, M. Takaya (2001)
• Experimental asbestosis with four types of fibers: importance of small particles — P.F. Holt, J. Mills, et al. (1965)
• Hydrolysis of inositol phospholipids precedes cellular proliferation in asbestos-stimulated tracheobronchial epithelial cells — A. Sesko, M. Cabot, et al. (1990)

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