Does asbestos exposure cause airway obstruction, in the absence of confirmed asbestosis?

Our plain-English summary of Does asbestos exposure cause airway obstruction, in the absence of confirmed asbestosis?, by J. Ameille, M. Letourneux, C. Paris, et al (American Journal of Respiratory and Critical Care Medicine, 2010).

The study

• Authors: J. Ameille, M. Letourneux, C. Paris, P. Brochard, A. Stoufflet, E. Schorle, A. Gislard, F. Laurent, F. Conso, J.C. Pairon
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 2010;182(4):526-30
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Rationale: Whether occupational exposure to asbestos causes airway obstruction remains controversial.

Objectives: This study evaluated lung function in relation to cumulative exposure to asbestos in a large cohort of retired or unemployed workers exposed to asbestos.

Methods: The study population consisted of 3,660 volunteer subjects. An individual cumulative exposure index to asbestos was calculated for each subject, and information was obtained on smoking status. Pulmonary function tests were performed in all subjects; high-resolution chest computed tomography was also performed in 3,335 subjects.

Measurements And Main Results: Values of FEV(1)/FVC and FEF(25-75%) did not differ between five classes (quintiles) of cumulative exposure to asbestos, and no significant correlation was observed between cumulative exposure to asbestos and pulmonary function parameters, after adjustment for sex, tobacco consumption, emphysema, and body mass index. Furthermore, the proportion of abnormal pulmonary function tests did not differ between the five classes of cumulative exposure to asbestos.

Conclusions: The results do not support a causal relationship between asbestos exposure alone and airway obstruction. However, the study sample may not be representative of all people occupationally exposed to asbestos, because a fraction of subjects with previously diagnosed asbestosis probably did not participate in this screening program.

In plain English

This cross-sectional study asked whether past work exposure to asbestos was linked to airway obstruction. It was part of a French screening program for asbestos-related disease, run from October 2003 to December 2005 in four regions. It included 3,660 retired or unemployed volunteers exposed to asbestos at work, and 96.1% were men. Industrial hygienists estimated each person's cumulative exposure from their job history. The article does not say which asbestos fiber types the participants were exposed to. Everyone had lung function tests. After accounting for sex, smoking and body mass index, the authors found no significant correlation between cumulative exposure and the airflow measures used to detect obstruction. The share of abnormal results on those measures also did not differ across five exposure groups. Residual volume and total lung capacity were significantly negatively associated with each person's exposure index, which the authors read as suggesting restriction, not obstruction. The authors concluded that their results do not support a causal relationship between asbestos exposure and airway obstruction. They cautioned that the volunteers may not represent all exposed workers, partly because some people already diagnosed with asbestosis probably did not take part.

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 within a pilot screening program for asbestos-related diseases
• Who was studied: 3,660 volunteer retired or unemployed workers previously exposed to asbestos at work, in four regions of France (Aquitaine, Rhone-Alpes, Haute-Normandie, Basse-Normandie), screened October 2003 to December 2005. 3,519 (96.1%) were male, mean age 63.2 years. High-resolution chest CT was done in 3,335 of them (91.1%).
• Exposure: Occupational asbestos exposure; the article does not say which fiber types the participants encountered. Industrial hygienists calculated a cumulative exposure index from work-history questionnaires. Each exposed job's duration in years was multiplied by an intensity weight (0.01 low/passive, 0.1 low-intermediate, 1 high-intermediate, 10 high), and the results were added up. The index is expressed in exposure units times years, not fiber-years. Mean exposure duration was 27.7 years.
• Main results:
  • Across five exposure groups (quintiles), adjusted for sex, smoking status and body mass index, FEV1/FVC did not differ (p = 0.18) and FEF25–75% showed borderline differences (p = 0.06). FVC and FEV1 differed (p = 0.01), but the differences were small and showed no dose–response pattern.
  • When each person's exposure index was analyzed against their lung function, there was no significant correlation with FVC, FEV1, FEV1/FVC or FEF25–75%.
  • In the same individual-level analysis, residual volume (slope -0.013, p = 0.03) and total lung capacity (slope -0.008, p = 0.01) were significantly negatively associated with cumulative exposure. The authors described this as suggestive of increasing restriction, not obstruction. Across the five exposure groups, neither measure fell steadily.
  • The proportion of abnormal results did not differ across exposure quintiles for FVC, FEV1, FEV1/FVC or FEF25–75%. For example, abnormal FEV1/FVC was 39 (6%) in the lowest and 43 (5.6%) in the highest quintile. Abnormal residual volume rose from 52 (9.8%) to 91 (13.1%) (trend p = 0.02), and abnormal total lung capacity rose from 55 (10.2%) to 96 (13.8%) (trend p = 0.03).
  • Smokers and ex-smokers had significantly lower FVC, FEV1, FEV1/FVC and FEF25–75% than nonsmokers.
  • In a quality-control re-analysis limited to 589 lung function tests judged 'perfect' or 'satisfactory', the authors again found no correlation between cumulative exposure and airway obstruction.
• The authors' conclusion: The authors concluded that the results did not show a dose–response relationship and do not support a causal relationship between asbestos exposure and airway obstruction.
• Limitations the authors state:
  • Participants were volunteers recruited for screening, and most had reached retirement age without severe respiratory disease, so they may not represent all occupationally exposed people.
  • Some people with previously diagnosed asbestosis probably did not take part.
  • People in the higher exposure groups could be a survivor population of more resistant individuals.
  • Lung function tests were done in many locations by many different physicians or technicians.
  • Exposure assessment may be inaccurate, since there were no airborne fiber measurements or detailed data on how often exposure occurred.
  • Lung function could not be compared with interstitial abnormalities on CT because readings of those abnormalities varied too much.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Occupational Exposure, Cumulative Exposure, Pulmonary Function Test (PFT), Emphysema.

Related studies

• Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? — B. Clin, C. Paris, et al. (2011)
• Does asbestos exposure (asbestosis) cause (clinical) airway obstruction (small airway disease)? — A. Miller, W.N. Rom (2010)
• Association between increased small airway obstruction and asbestos exposure in patients with asbestosis — X. Yang, Y. Yan, et al. (2018)
• High prevalence of reversible airway obstruction in asbestos-exposed workers — S. Delpierre, M.J. Delvolgo-Gori, et al. (2002)
• Airway obstruction in asbestos-exposed shipyard workers: with and without irregular opacities — K.H. Kilburn, R.H. Warshaw (1990)
• Airways obstruction from asbestos exposure. Effects of asbestosis and smoking — K.H. Kilburn, R.H. Warshaw (1994)

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