Asbestos-induced pleural fibrosis and impaired lung function

Our plain-English summary of Asbestos-induced pleural fibrosis and impaired lung function, by D.A. Schwartz, L.J. Fuortes, J.R. Galvin, et al (The American Review of Respiratory Disease, 1990).

The study

• Authors: D.A. Schwartz, L.J. Fuortes, J.R. Galvin, L.F. Burmeister, L.E. Schmidt, B.N. Leistikow, F.P. LaMarte, J.A. Merchant
• Journal: The American Review of Respiratory Disease
• Published: 1990;141(2):321-6
• Cited by: 97 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000039).

Abstract

To assess the clinical significance of asbestos-induced pleural fibrosis, we evaluated the relationship between radiographic evidence of pleural fibrosis and spirometric values in 1,211 sheet metal workers. Of those with pleural fibrosis (n = 334), 78% had circumscribed plaques and 22% had diffuse pleural thickening involving the costophrenic angle. Factors that were found to be associated with the presence and type of pleural fibrosis included increased age (p less than 0.001), more years in the trade (p less than 0.0001), more years since first exposure to asbestos (p less than 0.0001), more pack-years of cigarette smoking (p less than 0.01), and the presence and degree of interstitial fibrosis (p less than 0.0001). After controlling for these potential confounders (age, years in the trade, latency, pack-years of smoking, and ILO profusion category), linear multivariate regression models demonstrated that both circumscribed plaques (p = 0.007) and diffuse pleural thickening (p = 0.008) were independently associated with decrements in FVC but not with decrements in the FEV1/FVC ratio. Furthermore, our data indicate that the effect of diffuse pleural thickening on decrements in FVC is approximately twice as great as that seen with circumscribed pleural plaques. We conclude that the presence and type of pleural fibrosis among asbestos-exposed workers is independently associated with a pattern of spirometry that is suggestive of an underlying restrictive defect in lung function.

In plain English

This study asked whether scarring of the lung lining (pleural fibrosis) on chest X-rays was linked to lower breathing-test results in asbestos-exposed sheet metal workers. In 1986 the sheet metal workers' union offered medical examinations to members with at least 25 years in the trade. The authors analysed 1,211 male workers from the Midwest who had both a chest X-ray and spirometry. Of the 334 with pleural fibrosis, 78% had circumscribed plaques and 22% had diffuse pleural thickening. The authors accounted for age, height, time since first exposure, smoking and lung scarring visible on X-ray (interstitial fibrosis). After this, both plaques and diffuse thickening were associated with lower forced vital capacity (FVC) but not with a lower FEV1/FVC ratio. The adjusted analysis estimated FVC as 270 ml lower with diffuse thickening and 140 ml lower with plaques, compared with normal pleura. The authors concluded that pleural fibrosis independently predicted a breathing pattern consistent with restrictive lung function. They noted that workers with pleural fibrosis might have more lung scarring than their X-ray grade showed. They speculated that scarring or inflammation not seen on routine X-rays could explain the findings.

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: Analysis of data from a union-sponsored medical screening programme (chest X-rays and spirometry examined together at one point in time)
• Who was studied: 1,211 male sheet metal workers from 12 union locals in the midwestern United States, active and retired, with at least 25 years in the trade, examined from 1986. These were the participants (1,223 of about 2,643 offered) who had both a chest film and spirometry.
• Exposure: Asbestos exposure in the sheet metal trade. No fiber type or measured doses are reported. Exposure was represented by years in the trade (mean 32.7 plus or minus 6.7 years) and years since first employment (latency).
• Main results:
  • Of the 334 workers with pleural fibrosis, 78% had circumscribed plaques and 22% had diffuse pleural thickening involving the costophrenic angle
  • In multivariate models, both circumscribed plaques (p = 0.007) and diffuse pleural thickening (p = 0.008) were independently associated with lower FVC, but not with a lower FEV1/FVC ratio
  • In the adjusted multivariate regression (Table 7), the estimated difference in FVC compared with workers with normal pleura was 270 ml lower for workers with diffuse pleural thickening and 140 ml lower for workers with circumscribed plaques, about twice as large for diffuse thickening. These are adjusted estimates from a single examination, not observed group averages or measured falls over time.
  • Diffuse pleural thickening was associated with significant decrements in FEV1. Workers with circumscribed plaques had modest but significant increases in the FEV1/FVC ratio.
  • Within groups with and without interstitial fibrosis on X-ray, percent-predicted FVC declined with type of pleural fibrosis. Without interstitial fibrosis: 94.7 (normal pleura, n=797), 90.3 (plaques, n=178), 85.7 (diffuse, n=28), p = 0.0002. With interstitial fibrosis: 83.3 (n=80), 80.1 (n=80), 73.6 (n=46), p = 0.009.
  • After controlling for age, smoking behavior and pack-years were not significantly related to the presence or type of pleural fibrosis
• The authors' conclusion: The authors concluded that pleural fibrosis among asbestos-exposed persons is an independent predictor of spirometry patterns consistent with restrictive lung function, with diffuse thickening having about twice the effect of plaques. They speculated that subclinical alveolitis or interstitial fibrosis not seen on routine chest X-rays may be responsible.
• Limitations the authors state:
  • Within each X-ray grade of lung scarring, workers with pleural fibrosis may have more parenchymal fibrosis than those with normal pleura. More detailed measures such as high-resolution CT or tissue samples would be needed to test this.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Fibrosis, Diffuse Pleural Thickening, Costophrenic angle, Interstitial Fibrosis, Latency, FEV1/FVC Ratio, Pleural Plaques, Spirometry.

Related studies

• Determinants of restrictive lung function in asbestos-induced pleural fibrosis — D.A. Schwartz, J.R. Galvin, et al. (1990)
• Asbestos-induced pleural fibrosis and impaired exercise physiology — J.F. Shih, J.S. Wilson, et al. (1994)
• Restrictive lung function and asbestos-induced pleural fibrosis. A quantitative approach — D.A. Schwartz, J.R. Galvin, et al. (1993)
• 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)
• A systematic review of the association between pleural plaques and changes in lung function — L. Kopylev, K.Y. Christensen, et al. (2015)
• Risk and significance of chest radiograph and pulmonary function abnormalities in an elderly cohort of former nuclear weapons workers — M.A. Mikulski, P.G. Hartley, et al. (2011)

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