The distribution of amosite asbestos in the periphery of the normal human lung

Our plain-English summary of The distribution of amosite asbestos in the periphery of the normal human lung, by A. Churg (British Journal of Industrial Medicine, 1990).

The study

• Author: A. Churg
• Journal: British Journal of Industrial Medicine
• Published: 1990;47(10):677-81
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 003766).

Abstract

Although theoretical models and experiments on animals exist that predict the distribution of asbestos fibres in the lung, there are few studies in man that relate to this question and they have generated contradictory results. To examine this distribution analytical electron microscopy was employed to determine the amosite fibre concentration, size, surface area, and mass in 29 circumferential sites around the periphery of a mid-sagittal slice from nine morphologically normal left lungs of heavily exposed shipyard workers and insulators. Fibre concentrations were heaviest in the apical segment of the upper lobe, and low concentrations were seen in the posterior basal portion of the lower lobe. Overall, the upper lung zones had significantly greater concentrations than the lower lung zones. Fibre length was shortest in the anterior portion of the upper lobe, greater in the lingula, and greatest in the posterior basal portion of the lower lobe; fibre length overall was significantly greater in the lower compared with the upper zones. Aspect ratio followed a similar pattern. Distinct geographic runs of high or low concentrations and long or short lengths and aspect ratios were present. No consistent distribution patterns for fibre width, surface area, or mass were found. It is concluded that: (1) in the periphery of the normal lung, concentration of amosite fibres is greatest in the apex and least in the peripheral lower lobe. This distribution is the opposite of what would be expected from the known distribution of asbestosis (peripheral lower zone); nor does it correlate with bronchial pathlength or branch number, contrary to predictions from studies on animals and theoretical models; (2) fibre length and related parameters show a distribution opposite to that of fibre concentration and again do not correlate with theoretical predictions.

In plain English

This study looked at how amosite asbestos fibres were spread around the outer edge of the human lung. The author used analytical electron microscopy on lungs obtained at necropsy from nine heavily exposed shipyard workers and insulators from the Pacific northwest. Only lungs close to normal were used, to rule out differences caused by diseases such as asbestosis, and only amosite fibres were counted. Tissue came from 29 sites around the edge of a mid-sagittal slice of the left lung. Fibre concentrations were highest in the apex and anterior upper lobe and much lower in the posterior and basal lower lobes. Overall, the upper zone had a significantly greater concentration than the lower zone. Longer fibres, and fibres with a higher length-to-width ratio (aspect ratio), were found in the lower zones. Fibre width, surface area and mass showed no obvious pattern. The author concluded that this concentration pattern is the opposite of what the lower-zone distribution of asbestosis would suggest, and that it does not match predictions from animal studies and theoretical models. The author noted that lungs with fibrosis might show a different pattern.

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: Pathology study of autopsy (necropsy) lung tissue, measuring fibres at multiple sites with analytical electron microscopy
• Who was studied: Nine morphologically near-normal left lungs obtained at necropsy from shipyard workers and insulators from the Pacific northwest, all with a history of heavy asbestos exposure. Mean age was 62 (SEM 5), mean pack-years of smoking 36 (13), and mean years of exposure 21 (6). Years of study not stated.
• Exposure: Amosite asbestos only. Lungs were included only if an initial sample showed at least 300 000 amosite fibres per g dry lung.
• Main results:
  • Amosite fibre concentrations were highest in the apex and anterior upper lobe (p less than 0.001 comparing these sites with the rest of the lung), with much lower concentrations in the posterior and basal lower lobes.
  • When the lung was arbitrarily divided into upper and lower zones, fibre concentration in the upper zone was significantly greater than in the lower zone. The printed p value is damaged by scanning.
  • The longest fibres and the fibres with the highest aspect ratio were found in the lower zones. The upper versus lower zone difference was significant (p less than 0.02 for length, p less than 0.01 for aspect ratio).
  • No obvious patterns were seen for fibre width, surface area or mass.
  • A runs test confirmed distinct runs of high or low values for concentration (p less than 0.004), length, and aspect ratio (p less than 0.004). No runs were seen for width, surface area or mass.
• The authors' conclusion: The author concluded that in the periphery of the normal lung, amosite concentration is greatest in the apex and least in the peripheral lower lobe. This is the opposite of what the known lower-zone distribution of asbestosis would suggest, and it does not correlate with bronchial pathlength or branch number as animal studies and theoretical models predict. Fibre length shows the opposite distribution to concentration. The author suggested the results are difficult to explain unless fibre length is considerably more important than fibre concentration in starting disease.
• Limitations the authors state:
  • The findings may represent the pattern in non-diseased lungs only; disease such as fibrosis might change the distribution of inhaled fibres.
  • Only the periphery of the lung was examined; showing whether fibres redistribute in humans would require examining the deep lung tissue as well.
  • At a few sites fibre concentration was extremely low, and fewer than about 50 fibres were counted.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Amosite, Insulator, Aspect Ratio (Length-to-diameter ratio).

Related studies

• Findings from high resolution computed tomography of the lung and pleura of symptom free workers exposed to amosite who had normal chest radiographs and pulmonary function tests — S. Neri, A. Antonelli, et al. (1994)
• Observations on the distribution of asbestos fibers in human lungs — A. Churg, P. Wood (1983)
• Mineralogic parameters related to amosite asbestos-induced fibrosis in humans — A. Churg, J. Wright, et al. (1990)
• Immunohistochemical distribution of tubulin beta II in human normal and neoplastic tissues — E. Oda, Y. Nakamura, et al. (2005)
• The distribution of amosite asbestos fibers in the lungs of workers with mesothelioma or carcinoma — A. Churg, B. Wiggs (1989)
• Long and short fiber amosite asbestos alters at a different extent the redox metabolism in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2003)

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