Follow-up respiratory measurements in Quebec chrysotile asbestos miners and millers

Our plain-English summary of Follow-up respiratory measurements in Quebec chrysotile asbestos miners and millers, by M.R. Becklake, D. Thomas, F. Liddell, et al (Scandinavian Journal of Work, Environment & Health, 1982).

The study

• Authors: M.R. Becklake, D. Thomas, F. Liddell, J.C. McDonald
• Journal: Scandinavian Journal of Work, Environment & Health
• Published: 1982;8 Suppl 1:105-10
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000660).

Abstract

In 1974 changes in dyspnea, lung function, and pneumoconiotic radiographic abnormalities were recorded among the 1,015 Quebec chrysotile miners and millers surveyed in 1967-1968. The aim was to relate these changes to dust exposure--age, smoking, and earlier health status being taken into account. Dyspnea and lung function were assessed in 722 men, and for 277 recent radiographs were read separately by three experts for changes in the parenchyma and pleura. Each measure was analyzed independently for men without any abnormality when first seen (eligible for "attack") and for others (eligible for progression/regression). Age significantly influenced the rate of attack of pleural abnormality and the rates of attack and progression of dyspnea and lung function decline. Smoking had comparatively minor effects. The only associations with exposure were for progression of parenchymal change (one reader), and for progression of dyspnea. These essentially negative findings are similar to those obtained in a previous longitudinal survey of radiographs from the same workforce.

In plain English

This study followed up 1,015 male workers from the chrysotile asbestos mines and mills of Quebec who had first been examined in 1967–1968. They had been chosen by random sampling weighted toward older men. In 1974, 722 of them repeated a breathlessness questionnaire and lung function tests. For 277 of these men, pairs of chest X-rays were also read separately by three experienced readers. Each man's past dust exposure was estimated from his employment records up to October 1966. The authors looked at new abnormalities, and at worsening or improvement of existing ones, taking age and smoking into account. Age was significantly related to new and worsening breathlessness, to lung function changes, and to new pleural abnormality. Smoking had comparatively minor effects. Exposure was linked only to worsening breathlessness and, for one X-ray reader only, to worsening lung tissue (parenchymal) changes. The authors called these essentially negative findings, similar to an earlier X-ray study of the same workforce. They noted that the follow-up of under 8 years may have been too short, that exposure during follow-up was not counted, and that the exposure measure may be too crude.

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: Longitudinal follow-up (repeat survey) of a previously studied group of workers, comparing measurements from 1967–1968 with measurements in 1974
• Who was studied: 1,015 male Quebec chrysotile asbestos miners and millers. They were selected by stratified random sampling, weighted toward older ages, from a register of about 6,000 current workers as of 31 October 1966, and were first surveyed in 1967–1968. At restudy in 1974, 91 had died and 105 were not reexamined. A further 97 were reexamined by questionnaire only, were mostly retired, and were excluded. Of the 722 men analysed, 445 had questionnaire and lung function tests only, and 277 also had usable pairs of chest radiographs.
• Exposure: Chrysotile asbestos dust in mining and milling. A cumulative exposure index in million particles per cubic foot-years was calculated from each man's work history up to 31 October 1966 and was not updated. Men were divided into four exposure groups: under 10, 10 to 99, 100 to 199, and 200 or more mpcf-years.
• Main results:
  • Among all 722 men, age was significantly related to new abnormalities (attack) and to progression/regression of breathlessness, forced vital capacity (FVC) and maximum midexpiratory flow (MMEF).
  • Age also significantly influenced the rate of new pleural abnormality on chest radiographs.
  • Smoking had comparatively minor effects. It was significant for new MMEF abnormality and for progression/regression of FVC abnormality.
  • After adjustment for age and smoking, the only associations with exposure were for progression of breathlessness (dyspnea) and for progression of parenchymal radiographic change, the latter by one of the three readers only. Crude (unadjusted) rates of new parenchymal and pleural abnormality and of parenchymal progression in the 277 men with radiographs had increased with exposure.
  • When change was related to average values, men in poorer average condition showed greater deterioration. When change was related to initial values instead, each positive relationship became significantly negative, which the authors said was predicted by regression to the mean.
• The authors' conclusion: The authors concluded that these essentially negative findings were similar to those of an earlier longitudinal radiograph survey of the same workforce. They suggested that, in the modern era, exposure as measured in this study may have become less important to outcome.
• Limitations the authors state:
  • The follow-up period of less than 8 years may have been too short to detect effects beyond those attributable to ageing.
  • Exposure during the follow-up period was not taken into account, although the authors did not believe this alone explained the weak exposure-response findings.
  • The exposure measure may be too crude a reflection of how much dust is retained in the lung.
  • The analysis of how first-examination findings predicted later change was complicated by regression to the mean.
  • Effects attributed to age might instead reflect how long dust has resided in the lung.

Topics

Medical terms in this study, explained in our Lexicon: Quebec Chrysotile, Dyspnea, Parenchyma, Pleura.

Related studies

• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Clinical measurement in Quebec chrysotile miners: use for future protection of workers — M.R. Becklake (1979)
• Magnetic lung measurements of relation to occupational exposure in asbestos miners and millers of Quebec — D. Cohen, T.S. Crowther, et al. (1981)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• The combination of effects on lung cancer of cigarette smoking and exposure in quebec chrysotile miners and millers — F.D. Liddell, B.G. Armstrong (2002)

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