Relation of airway responsiveness to duration of work in a dusty environment

Our plain-English summary of Relation of airway responsiveness to duration of work in a dusty environment, by P. Ernst, R.E. Dales, F. Nunes, et al (Thorax, 1989).

The study

• Authors: P. Ernst, R.E. Dales, F. Nunes, M.R. Becklake
• Journal: Thorax
• Published: 1989;44(2):116-20
• 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. 000075).

Abstract

Health selection within a workforce has been found in several industries and appears to be more pronounced in dustier occupations. In this study of airway disease among workers exposed to asbestos and man made mineral fibres, 215 of 246 construction insulators 50 years old or less and currently working in the Montreal area were examined. Spirometry was completed successfully in 214 workers without known asbestosis and 207 underwent methacholine bronchoprovocation testing. Airway responsiveness was expressed as PC15, the concentration of methacholine causing a 15% fall in the forced expiratory volume in one second (FEV1). Exposure to asbestos and synthetic mineral fibre dust was estimated from the total hours of work in the trade since first employment. After the effect of age, height, and pack years of smoking had been taken into account, no relation was found between hours of work and any indices obtained from the forced expiratory manoeuvre (FEV1/FVC, MMF). After the effect of airway calibre (FEV1/FVC), age, and pack years of cigarette consumption had been taken into account, airway responsiveness decreased as the total hours of work in the trade increased. These findings suggest that workers with greater levels of airway responsiveness are more sensitive to exposure in a dusty workplace and in consequence are less likely to continue. In studies of workforces a survivor effect of this nature will tend to weaken the relation between lung function abnormality and occupational exposure.

In plain English

This study examined 215 of 246 invited male construction insulators aged 20-50 in the Montreal area, exposed to asbestos and synthetic mineral fibres and without known asbestosis, in 1984. 214 completed breathing tests, and 207 had a methacholine challenge of airway reactivity. Exposure was estimated only from total hours worked, because dust measurements were mostly unavailable. Breathing-test results were linked to smoking but not to hours of work. Airway responsiveness was lower in men who had worked more hours (standardised coefficient 0.227, p 0.02, adjusted for airway calibre, age and smoking). It was measured as the methacholine concentration that cut the air breathed out in one second by 15%. 126 of the 207 tested men never reached that fall and were assigned 64 mg/ml. Adjusted averages were 19.2, 25.4 and 34.3 mg/ml in the thirds with the fewest, middle and most hours. Higher values mean less reactive airways. The finding held after excluding 11 men with small irregular opacities on chest X-ray. The authors concluded that workers with more reactive airways may reduce exposure or leave dusty work, making effects of fibre exposure on airflow harder to detect.

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: Cross-sectional study of a currently working group of insulators, with breathing tests, methacholine challenge testing and linear regression analysis
• Who was studied: Male construction insulators aged 20-50 living in the Montreal area without known asbestosis. 246 were invited and 215 (87%) were examined, with a mean age of 37 (SD 8). 214 completed spirometry and 207 had methacholine testing. Health measures were done in 1984.
• Exposure: Asbestos and synthetic (man made) mineral fibre dust in insulation work. Exposure was estimated only as total hours worked in the trade, from pension records (1974-84), union records (1964-74) and an extrapolation for years before 1964. The study population was split into short (under 13,592 hours), medium (13,592-29,212 hours) and long (over 29,212 hours) groups.
• Main results:
  • Lung function declined significantly with pack years of smoking, but no spirometric index (FEV1, FVC, MMF, Vmax25) was associated with hours of employment. For hours of work, the standardised coefficients ranged from -0.012 to -0.062, with p values from 0.34 to 0.86.
  • In regression adjusted for FEV1/FVC, age and pack years, hours of work was directly related to log PC15 (standardised coefficient 0.227, p 0.02). This means that bronchial responsiveness decreased as hours of work increased.
  • Mean PC15, adjusted for FEV1/FVC, was 19.2 mg/ml in the short exposure group (n=72), 25.4 mg/ml in the medium group (n=71) and 34.3 mg/ml in the long group (n=72). These means include the subjects who did not reach PC15 and were assigned 64 mg/ml.
  • FEV1/FVC% strongly determined airway responsiveness. Neither age nor pack years of smoking significantly influenced PC15.
  • When age and pack years were removed from the model, the association between hours of work and PC15 was stronger (p = 0.009).
  • After excluding 11 men whose chest radiographs showed 1/0 or greater profusion of small irregular opacities, the decrease in responsiveness with hours of work was similar and still statistically significant.
  • Of the 207 subjects who had methacholine testing, 126 did not reach PC15 and were arbitrarily assigned a value of 64 mg/ml.
• The authors' conclusion: The authors concluded that developing airway hyperresponsiveness may lead workers to a self-sought, probably self-protective decrease in exposure to dusty work. They wrote that this may favour selection out of the workforce, which would reduce the likelihood of detecting an effect of asbestos and synthetic mineral fibre exposure on bronchial airflow measurements.
• Limitations the authors state:
  • Workplace hygiene surveys and dust measures were mostly unavailable, so exposure was based on duration of work only.

Topics

Medical terms in this study, explained in our Lexicon: Insulator, Spirometry, FEV1, FEV1/FVC Ratio, Occupational Exposure.

Related studies

• Occupations and exposures in the work environment as determinants for rheumatoid arthritis — A.R. Olsson, T. Skogh, et al. (2004)
• The acute effects of chrysotile asbestos exposure on lung function — K.W. Harless, S. Watanabe, et al. (1978)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)
• Airways obstruction from asbestos exposure. Effects of asbestosis and smoking — K.H. Kilburn, R.H. Warshaw (1994)
• Work environment of plants manufacturing asbestos-containing products in Japan — T. Higashi, H. Hori, et al. (1994)
• Airway function in lifetime-nonsmoking older asbestos workers — R. Bégin, A. Cantin, et al. (1983)

Browse more research in Thorax, or return to medical research.