The optical and electron microscopic determination of pulmonary asbestos fibre concentration and its relation to the human pathological reaction

Our plain-English summary of The optical and electron microscopic determination of pulmonary asbestos fibre concentration and its relation to the human pathological reaction, by T. Ashcroft, A.G. Heppleston (Journal of Clinical Pathology, 1973).

The study

• Authors: T. Ashcroft, A.G. Heppleston
• Journal: Journal of Clinical Pathology
• Published: 1973;26(3):224-34
• Cited by: 134 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. 003635).

Abstract

The quantitative extraction of asbestos fibres from asbestotic lung by alkali digestion has been refined by maceration of the tissue without prior drying, the minimum use of centrifugation, and the adoption of phase contrast microscopy. Preliminary experiments suggested that, using this technique, asbestos fibre counts were accurate to within at least +/- 20% and in most instances to within +/- 10%. The method was used to assess asbestos concentrations in lung tissue showing various degrees and forms of fibrosis. The results, as determined by light microscopy, indicated that uncoated fibres generally outnumbered coated fibres. In mild and moderate asbestosis there was a progressive increase in concentration of asbestos fibres, both coated and uncoated, with increasing severity of fibrosis, whereas in severe asbestosis no correlation existed between the fibre concentration and the form or the extent of the pathological reaction. It is suggested that the severe fibrosis results from the supervention of non-specific inflammatory processes. Asbestos fibre diameter distributions, gauged by electron microscopy, were fairly constant irrespective of the degree of fibrosis. Optically visible fibres constituted between 12 and 30% of the total, so that an optical count may be said to give an approximate indication of the total asbestos concentration and, so far as asbestosis is concerned, may well serve for comparative purposes. The relation between asbestos and neoplasia will, however, require identification and quantitation of particular types of the mineral by microanalytical techniques.

In plain English

This laboratory study refined a method for counting asbestos fibres in human lung tissue. Lung samples were dissolved in strong alkali and fibres were counted with phase-contrast light microscopy. Fibre widths were measured by electron microscopy. The authors analysed lungs from 30 people who had died with diffuse malignant mesothelioma of the pleura or peritoneum, and from five people who had died with severe asbestosis without malignant disease. In the mesothelioma cases, uncoated fibres usually made up 60 to 80% of the count. Average fibre counts rose between cases with no, mild and moderate asbestosis, and these differences were statistically significant. In severe asbestosis, fibre counts showed no correlation with the form or severity of scarring. Most fibres looked like amphibole asbestos, with only occasional chrysotile. The authors suggested that mild or moderate fibrosis is directly related to the amount of asbestos retained. They suggested that severe fibrosis is instead due to secondary, possibly non-specific inflammatory, processes. They noted that expressing counts per gram of dried lung may introduce error, that few cases were examined by electron microscopy, and that detailed exposure histories were not available.

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 method study with analysis of lung tissue taken at necropsy (autopsy). Fibres were counted by light microscopy and fibre diameters were measured by electron microscopy.
• Who was studied: Lung tissue from 30 necropsy cases of diffuse malignant mesothelioma (25 pleural, 5 peritoneal). Of these, 13 had no asbestosis, 12 had mild asbestosis and 5 had moderately severe asbestosis. The study also used 15 lung samples from 5 necropsies on severe asbestosis without malignant disease. The work was done at the Department of Pathology, University of Newcastle upon Tyne. Dates of the cases are not given.
• Exposure: Asbestos dust. All but one of the mesothelioma cases had a history of definite or probable exposure. Detailed exposure information was not available. Fibres seen by electron microscopy were mostly of amphibole appearance, with occasional chrysotile.
• Main results:
  • In the mesothelioma cases, fibre concentrations ranged from 154 thousand to 684 million fibres per gram of dry lung.
  • In the mesothelioma cases, uncoated fibres usually made up 60 to 80% of the total count.
  • In the mesothelioma cases, mean coated, uncoated and total fibre counts differed significantly between the no, mild and moderate asbestosis grades. The mean counts showed six- to 10-fold increases between successive grades. The p values were printed with damaged decimals, as between 0.008 and 0.001.
  • The mean proportion of uncoated fibres rose slightly with increasing fibrosis, but the differences between grades were not statistically significant.
  • In the mesothelioma cases, no significant relationship was found between severity of asbestosis and either length of asbestos exposure or time from first exposure to death.
  • The mean proportion of uncoated fibres did not appear to differ between cases with long and short survival after last exposure.
  • In the five severe asbestosis cases, there was no correlation between fibre concentration or the proportion of uncoated fibres and the form or severity of the disease.
  • Total fibre counts in severe asbestosis cases 42, 43 and 44 lay mostly within the range for mild asbestosis in the mesothelioma cases. Counts in cases 45 and 46 lay within the range for moderate asbestosis.
  • Electron microscopy was done on six cases, two from each grade. Fibres 0.1 to 0.19 micrometres in diameter were most numerous in each. Less than a third, and usually less than a fifth, of fibres were wide enough to be seen by light microscopy (0.4 micrometres or over). There was no difference between grades.
  • By electron microscopy, the vast majority of fibres looked like amphibole asbestos. Only occasional chrysotile fibres were identified.
  • Method tests: repeated centrifugation lost uncoated fibres. Drying tissue before dissolving it gave higher coated fibre counts in all five specimens tested.
• The authors' conclusion: The authors suggested that mild or moderate fibrosis is directly related to the amount of asbestos dust retained. They suggested that the changes of severe asbestosis show no such relationship and are due to secondary pathological processes, possibly non-specific inflammatory ones. They also stated that an optical count could be held to give a reasonable indication of total asbestos concentration.
• Limitations the authors state:
  • Expressing counts per gram of dried lung may introduce error, because denser (scarred or pneumonic) tissue lowers fibres per unit weight. The authors said individual results must be regarded as approximations.
  • Using an estimated rather than measured dry weight introduced an error that the authors judged unlikely to exceed 20%.
  • Only a small number of cases were examined for fibre diameter by electron microscopy.
  • Detailed information on the cases' asbestos exposure was not available.
  • Fibre types were judged by appearance only. Diffraction studies were not done.
  • Fibres thinner than the light microscope's resolution would not be detected in the optical counts.

Topics

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

Medical terms in this study, explained in our Lexicon: phase contrast microscopy (PCM), Fibrosis.

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