Relation of spirometric function to radiographic interstitial fibrosis in two large workforces exposed to asbestos: an evaluation of the ILO profusion score

Our plain-English summary of Relation of spirometric function to radiographic interstitial fibrosis in two large workforces exposed to asbestos: an evaluation of the ILO profusion score, by A. Miller, R. Lilis, J. Godbold, et al (Occupational and Environmental Medicine, 1996).

The study

• Authors: A. Miller, R. Lilis, J. Godbold, X. Wu
• Journal: Occupational and Environmental Medicine
• Published: 1996;53(12):808-12
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To analyse quantitatively the relations of spirometric lung function (forced vital capacity (FVC)) to radiographic interstitial pulmonary fibrosis (assessed by the International Labour Organisation (ILO) profusion score of small irregular opacities) in two large workforces exposed to different intensities of asbestos. These analyses consider the question whether a similar profusion score n differently exposed workers is associated with a similar effect on lung function.

Methods: Surveys of two workforces, insulators (n = 2611) and sheet metal workers (n = 1245), by the same investigators allowed comparison of the effects of the two levels of exposure to asbestos. The two groups were of similar age and had similar percentages of non-smokers and smokers. All radiographs were read by the same expert reader.

Results: Consistent with their less continuous and less intense exposure to asbestos, metal workers had: (a) far less frequent radiographic asbestosis (profusion score > or = 1/0, 17.5% v 59.6% for insulators): (b) less severe radiographic asbestosis (only 1.1% had scores > or = 2/1 v 13.3% of insulators); (c) a similar slope to that seen in insulators for the relation between FVC and profusion score when pleural thickening was absent; (d) less frequent pleural fibrosis (36% v 75%); and (e) less frequent restrictive impairment (23% v 33%). In both insulators and metal workers, lung function was below normal even when lung fields were normal, FVG fell with increasing profusion, it was lower in smokers and in those with pleural thickening at comparable profusion scores, and these was no difference in FVC between scores 0/1 and 1/0.

Conclusion: The decrease in FVC with increasing profusion score in both workforces as well as the similar slopes for the relation between FVG and profusion score and the similar FVG at similar scores in the absence of pleural thickening confirm the ILO profusion score as an acceptable assessment of pulmonary fibrosis.

In plain English

This study compared breathing tests with chest X-rays in 2,611 North American insulators surveyed in 1983-4 and 1,295 sheet metal workers surveyed in 1986-7. Another 35 metal workers lacking complete breathing tests were excluded. Surveys targeted workers with at least 20 years in the trade. One expert reader scored lung scarring on the International Labour Organisation (ILO) profusion scale. Lung capacity was measured as forced vital capacity (FVC). Metal workers had far less scarring: 71.4% scored normal versus 15.9% of insulators. In metal workers, FVC fell as scores rose, but less steeply than in insulators. Without pleural thickening, slopes were similar. Even normal lung-field scores (0/- or 0/0) came with below-normal FVC: 88.0% of predicted in metal workers. It did not differ between scores 0/1 and 1/0. It was lower in smokers and with pleural thickening. Restrictive impairment affected 23% of metal workers and 33% of insulators. The authors concluded that this confirms the ILO profusion score as an acceptable assessment of lung fibrosis. They noted that too few metal workers without pleural thickening had higher scores for a full comparison.

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: Comparative cross-sectional surveys of two workforces using the same methods, with linear and multiple regression relating FVC to ILO profusion score
• Who was studied: 2,611 insulators (surveyed 1983-4) and sheet metal workers in North America (surveyed 1986-7). Of 1,330 metal workers, 35 lacked complete spirometry and were excluded, leaving 1,295.
• Exposure: Occupational asbestos exposure as insulators or sheet metal workers, mostly at least 20 years in the trade; the authors describe metal workers' exposure as less continuous and less intense. Fiber types are not specified.
• Main results:
  • Profusion score 0/- or 0/0 (normal) in 71.4% of metal workers vs 15.9% of insulators
  • In metal workers, FVC fell with increasing profusion score (P = 0.0003)
  • The slope of the FVC decrease was significantly less in metal workers than in insulators
  • In the absence of pleural thickening, the slope of FVC decline was similar in the two workforces
  • Metal workers with normal lung fields (profusion scores 0/- or 0/0) had a mean FVC of 88.0% of predicted, below the expected 100%
  • In metal workers, FVC was no lower for a score of 1/0 than for 0/1
  • FVC values in smokers were consistently lower than in non-smokers
  • Among metal workers who did not smoke, FVC showed no relation to profusion score within the narrow range of scores they had
  • In metal workers, FVC was lower at each profusion score except 0/1 when pleural thickening was present
  • Restrictive impairment in 23% of metal workers vs 33% of insulators; decreased FVC in 33% vs 44%
  • About 80% of metal workers with decreased FVC had normal lung fields on X-ray (scores 0/-, 0/0 or 0/1)
  • In the multiple regression of all workers, each step on the seven-point profusion scale was associated with an FVC decrease of 0.55% of predicted in metal workers and 1.68% in insulators
• The authors' conclusion: The authors concluded that the fall in FVC with increasing profusion score in both workforces, the similar slopes, and the similar FVC at similar scores without pleural thickening confirm the ILO profusion score as an acceptable assessment of pulmonary fibrosis.
• Limitations the authors state:
  • Too few metal workers without pleural thickening had higher profusion scores to compare with insulators across the insulators' range of scores
  • Only seven metal workers without pleural thickening had profusion scores of 1/0 or higher, all smokers, which made the planned regression model for workers without pleural thickening unproductive
  • Only four non-smoking metal workers had scores above 1/1

Topics

Medical terms in this study, explained in our Lexicon: Interstitial Fibrosis, Interstitial, Pulmonary Fibrosis, Insulator, Pleural Thickening, Fibrosis.

Related studies

• Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups--insulators and sheet metal workers — R. Lilis, A. Miller, et al. (1992)
• Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening — A. Miller, R. Warshaw, et al. (2013)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)
• Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities — R. Lilis, A. Miller, et al. (1991)
• Radiographic abnormalities in asbestos insulators: effects of duration from onset of exposure and smoking. Relationships of dyspnea with parenchymal and pleural fibrosis — R. Lilis, A. Miller, et al. (1991)
• The effect of asbestos-induced pleural fibrosis on pulmonary function: quantitative evaluation — R. Lilis, A. Miller, et al. (1991)

Browse more research in Occupational and Environmental Medicine, or return to medical research.