Estimation of fibrous aerosol deposition in upper bronchi based on experimental data with model bifurcation

Our plain-English summary of Estimation of fibrous aerosol deposition in upper bronchi based on experimental data with model bifurcation, by T. Myojo, M. Takaya (Industrial Health, 2001).

The study

• Authors: T. Myojo, M. Takaya
• Journal: Industrial Health
• Published: 2001;39(2):141-9
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Lung deposition of fibrous aerosol was studied by using a model of the lung bifurcation with dimensions based on the symmetric model A of Weibel. The fibrous aerosols were introduced to the model under steady inspiratory flow conditions. Glass fibers depositing in the daughter tubes and these escaping from them were observed under a scanning electron microscope (SEM). The deposited fractions were calculated for each length and diameter using a bivariate lognormal distribution. In this study the authors propose empirical equations to estimate total deposited fractions of fibrous aerosol at upper bronchi. The dimensionless relationship among deposited fractions Fd, Stokes number St for randomly-oriented fibers and interception parameter I were used to estimate the deposited fraction at arbitrary position in the upper bronchi. The calculation procedure for Fd(St,I) consists of two steps: the determination of the four deposited fractions, Fdn for each In (n=1-4) followed by interpolation or extrapolation from Fdn to find the deposited fraction Fd at a given I. With this procedure, it is possible to determine the deposited fraction Fd in the range of 2 x 10(-3)<St<5 x 10(-2) and 5 x 10(-4)<I<5 x 10(-2). Penetration from the trachea to the 10th generation of lung bifurcation was calculated for several cases of fiber diameter, length and flow rate. In the case corresponding to an inspiration of 500 cm3 air at a constant rate for 2 s, more than half of the fibers with a length of 100 microm and diameter of 3 microm are deposited at upper bronchi but more than 90% of fibers of the same length and 1 microm in diameter pass through the region.

In plain English

This laboratory study passed glass fibers, not asbestos, through brass models of a single airway branching point. The models were sized to match the 2nd-to-3rd or 3rd-to-4th branchings of a standard human lung model (Weibel's model A). Air flowed steadily at rates matching a 500 or 1000 cm3 breath drawn in over 2 seconds. Fibers stuck to the tube wall and fibers that escaped were measured under a scanning electron microscope. One new run was combined with three runs from earlier published work. The share of fibers deposited rose with flow rate and fiber length. The authors built equations from these data and estimated how many fibers travel from the windpipe to the 10th branching. For a 500 cm3 breath, more than half of fibers 100 µm long and 3 µm thick were deposited in the upper bronchi, while more than 90% of 1 µm-thick fibers of that length passed through. The authors concluded that almost all fibers thinner than 1 µm pass the upper bronchi and reach the alveolar region. They noted that true deposition is likely much larger, because only a short stretch of wall was examined and the flow was steady rather than cyclic.

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 (brass) models of a lung airway bifurcation under steady inspiratory flow, with empirical equations and calculated estimates of fiber penetration
• Who was studied: No people or animals. Two brass airway models matching the 2nd–3rd and 3rd–4th generation bifurcations of Weibel's lung model A. Four experimental runs: runs 1–3 came from previous work (ref. 19) and run 4 was new in this work.
• Exposure: Glass fibers from a binderless HEPA filter, sheared in a mill and dispersed as an aerosol. Flow in each daughter tube was 15.6 or 31.2 cm3 per second, corresponding to a 500 or 1000 cm3 breath inspired at a constant rate for 2 s. No asbestos was used.
• Main results:
  • In the model bifurcations, the measured deposited fraction rose with both flow rate and fiber length.
  • The deposited fraction rose sharply with both the Stokes number and the interception parameter. At small Stokes numbers, deposition was strongly influenced by interception.
  • The authors' procedure can estimate deposited fraction for Stokes numbers between 2 × 10^-3 and 5 × 10^-2, and interception parameters between 5 × 10^-4 and 5 × 10^-2.
  • Calculated estimate for a 500 cm3 breath over 2 s, fibers 100 µm long: more than half of 3 µm-diameter fibers were deposited in the upper bronchi, while more than 90% of 1 µm-diameter fibers passed through that region.
  • Calculated estimate for fibers 20 µm long under the same conditions: only 20% of 3 µm-diameter fibers were deposited in the upper bronchi.
• The authors' conclusion: The authors concluded that their model predicts almost all fine fibers thinner than 1 µm pass through the upper bronchi and enter the alveolar region.
• Limitations the authors state:
  • Deposited fibers were counted only on the daughter-tube wall from the carina to 4 or 6 mm downstream, so the authors state that true deposited fractions should be much larger.
  • Experiments used steady rather than cyclic (breathing-like) flow. Citing their earlier data, the authors suggest twice or more fibers may deposit at each bifurcation.
  • There were few long fibers, so two of the fiber length groups overlapped.
  • The penetration calculations assumed every bifurcation has a 45-degree branch angle.

Topics

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

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