Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups--insulators and sheet metal workers

Our plain-English summary of Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups--insulators and sheet metal workers, by R. Lilis, A. Miller, J. Godbold, et al (Environmental Research, 1992).

The study

• Authors: R. Lilis, A. Miller, J. Godbold, S. Benkert, X. Wu, I.J. Selikoff
• Journal: Environmental Research
• Published: 1992;59(1):49-66
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Two large (N = 1584 and N = 1330) population groups of workers exposed to asbestos as insulators (I) or sheet metal workers (SM) were compared. Prevalence rates of radiographic changes including pleural fibrosis (circumscribed and diffuse) were found to be much higher in I than SM. An integrative index of pleural fibrosis (INDEX) showed similar distribution patterns in the two groups; the effect of INDEX on FVC% predicted was more marked in insulators. Factors that could contribute to this difference are thought to be the higher prevalence of interstitial pulmonary fibrosis (probably including that which is not yet radiologically detectable) in I than in SM, the possibility of more extensive pleural fibrosis in areas not accessible to the standard chest X ray (and thus not affecting INDEX) and a higher proportion of diffuse pleural fibrosis in the I group.

In plain English

This study compared chest X-rays and breathing tests in two groups of asbestos-exposed workers: 1,584 insulation workers and 1,330 sheet metal workers. The authors describe the sheet metal workers' exposure as intermittent and lower. Every type of X-ray change was more common in insulators. Abnormalities of the lung tissue itself (parenchymal) were seen in 54.4% of insulators versus 17.4% of sheet metal workers. Pleural abnormalities were seen in 74.8% versus 36.0%, and diffuse pleural fibrosis in 13.3% versus 3.2%. The authors scored pleural scarring with a combined index. The spread of index scores looked similar in both groups. However, forced vital capacity (how much air the lungs can blow out, as a percent of the expected value) fell more steeply with rising index in insulators. Among sheet metal workers with pleural changes only, the index's independent effect on this measure approached statistical significance (P = 0.06). The authors concluded that these lung-function decrements were less marked in sheet metal workers than in insulators. They noted that their index relied on standard chest X-rays only.

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 study of two asbestos-exposed occupational groups, using chest X-rays read by one certified B reader under the ILO classification, pulmonary function tests, questionnaires, and multiple regression analysis
• Who was studied: 1,584 insulation workers and 1,330 sheet metal workers. The article text does not state the location or the dates of examination.
• Exposure: Occupational asbestos exposure; fiber types are not named. The sheet metal workers' exposure came mainly from asbestos insulation used in construction, largely from other trades' work, and was intermittent and generally considered lower than the insulators'. No airborne measurements were available.
• Main results:
  • Total parenchymal abnormalities were found in 54.4% of insulators versus 17.4% of sheet metal workers. Total pleural abnormalities were found in 75% (Table 1: 74.8%) of insulators versus 36% (36.0%) of sheet metal workers.
  • Profusion of small opacities of category 2 or higher was found in 155 insulators (9.8%). Higher profusion was found in only 15 sheet metal workers (1.2%).
  • Diffuse pleural fibrosis was present in 3.2% of sheet metal workers (8.8% of all their pleural fibrosis) and in 13.3% of insulators (17.7% of all their pleural fibrosis).
  • The distribution pattern of the pleural index was very similar in the two groups. 64% of sheet metal workers had no radiographically detectable pleural fibrosis, compared with 25% of insulators.
  • In both groups, forced vital capacity (FVC% predicted) fell sizably once the pleural index reached about 12. The decrements were consistently larger in insulators, by about 200 to 300 ml.
  • In sheet metal workers, the independent contribution of the pleural index to FVC approached statistical significance in those with pleural abnormalities only (P = 0.06). It did so less in those with pleural and parenchymal abnormalities (P = 0.09).
  • Among workers with pleural abnormalities only, the difference between sheet metal workers and insulators appeared only in nonsmokers. The curves for smokers in the two groups were almost identical.
  • The authors reanalyzed a restricted group of insulators (at least 35 years since onset of exposure and profusion score below 2). In this group, the relationship of FVC to duration since onset of exposure and to profusion of small opacities was eliminated.
• The authors' conclusion: The authors concluded that decrements in FVC% predicted with increasing pleural index were less marked in sheet metal workers, who had intermittent and lesser asbestos exposure, than in insulators. They found the difference smallest in the subgroup with pleural abnormalities only.
• Limitations the authors state:
  • No quantitative measurements of the airborne asbestos concentrations to which sheet metal workers were exposed were available.
  • The pleural index was based on standard chest X-ray films only. More extensive pleural fibrosis in areas the standard X-ray cannot show could not be excluded in the more heavily exposed group.
  • Interstitial lung fibrosis not detectable on X-ray could not be excluded, and may have been more frequent in insulators.
  • The two groups differed in time since onset of exposure: 6.5% of sheet metal workers and 15.0% of insulators had less than 30 years. This difference could affect the comparison.

Topics

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

Related studies

• Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities — R. Lilis, A. Miller, et al. (1991)
• Relation of spirometric function to radiographic interstitial fibrosis in two large workforces exposed to asbestos: an evaluation of the ILO profusion score — A. Miller, R. Lilis, et al. (1996)
• The effect of asbestos-induced pleural fibrosis on pulmonary function: quantitative evaluation — 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 National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group — L.S. Welch, D. Michaels, et al. (1994)
• Pulmonary fibrosis in asbestos insulation workers with lung cancer: a radiological and histopathological evaluation — H.M. Kipen, R. Lilis, et al. (1987)

Browse more research in Environmental Research, or return to medical research.