Determinants of restrictive lung function in asbestos-induced pleural fibrosis

Our plain-English summary of Determinants of restrictive lung function in asbestos-induced pleural fibrosis, by D.A. Schwartz, J.R. Galvin, C.S. Dayton, et al (Journal of Applied Physiology, 1990).

The study

• Authors: D.A. Schwartz, J.R. Galvin, C.S. Dayton, W. Stanford, J.A. Merchant, G.W. Hunninghake
• Journal: Journal of Applied Physiology
• Published: 1990;68(5):1932-7
• Cited by: 46 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. 003851).

Abstract

We evaluated whether restrictive lung function among asbestos-exposed individuals with pleural fibrosis was caused by radiographically inapparent parenchymal inflammation and/or parenchymal fibrosis. All 24 study participants were sheet metal workers who were nonsmokers with normal parenchyma on posteroanterior chest radiograph. These subjects had either normal pleura (n = 7), circumscribed plaques (n = 9), or diffuse pleural thickening (n = 8). After controlling for age, years in the trade, and pack-years of smoking, we found that sheet metal workers with diffuse pleural thickening had a lower forced vital capacity (P less than 0.001), total lung capacity (P less than 0.01), and CO-diffusing capacity of the lung (P less than 0.05) than those with normal pleura. Similarly, sheet metal workers with circumscribed plaques were found to have a reduced forced vital capacity; however, because of the small number of study subjects, this difference (regression coefficient = -11.0) was only marginally significant (P = 0.06). Although circumscribed plaque and diffuse pleural thickening were both associated with a lymphocytic alveolitis and a higher prevalence of parenchymal fibrosis on high-resolution computerized tomography (HRCT) scan, neither a lymphocytic alveolitis nor the finding of parenchymal fibrosis on HRCT scan influenced the relationship between pleural fibrosis and restrictive lung function. We conclude that pleural fibrosis is associated with restrictive lung function and abnormally low diffusion that appears to be independent of our measures of parenchymal injury (chest X-ray, bronchoalveolar lavage, and HRCT scan).(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This cross-sectional study asked why asbestos-exposed workers with pleural fibrosis (scarring of the lung lining) can have reduced lung volumes. The authors studied 24 sheet metal workers, chosen from 1,211 screened in a union program, all never or former smokers with no lung scarring on chest X-ray: seven with normal pleura, nine with circumscribed plaques and eight with diffuse pleural thickening. Each had breathing tests, lung washing (bronchoalveolar lavage) and high-resolution CT. After adjusting for age, years in the trade and smoking, workers with diffuse pleural thickening scored on average about 27, 25 and 22 percentage points lower than workers with normal pleura on forced vital capacity, total lung capacity and diffusing capacity, each measured as a percentage of the predicted normal value. Workers with plaques scored about 11 points lower on forced vital capacity, only marginally significant (P = 0.06). Pleural fibrosis was linked to more lymphocytes in lavage fluid and more scarring on CT, but these did not explain its link with reduced lung function. The authors concluded this link appeared independent of their lung-injury measures, but suggested such injury likely contributed.

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 comparison of a small group of workers selected from a screening program, using lung function tests, bronchoalveolar lavage and high-resolution CT scans
• Who was studied: 24 sheet metal workers selected from 1,211 screened in a nationwide union-sponsored program. All were never smokers or former smokers (quit at least 5 years earlier) with no interstitial fibrosis on chest X-ray. Seven had normal pleura, 9 had circumscribed plaques and 8 had diffuse pleural thickening. They were recruited by proximity to Iowa City, and all were white. The study dates are not given.
• Exposure: Asbestos exposure as sheet metal workers. The article does not name fiber types or give exposure doses. Groups were compared by type of pleural fibrosis.
• Main results:
  • Compared with workers with normal pleura, and after controlling for age, years in the trade and pack-years of smoking, workers with diffuse pleural thickening had adjusted differences in percent-predicted lung function of about -27 for forced vital capacity (P less than 0.001), -25 for total lung capacity (P less than 0.01) and -22 for diffusing capacity (P less than 0.05). The article's prose calls these a 27%, 25% and 22% reduction.
  • Workers with circumscribed plaques had an adjusted difference of -11.0 in percent-predicted forced vital capacity compared with workers with normal pleura. This was marginally significant (P = 0.06); the article's prose calls it an 11% decrement.
  • Workers with diffuse pleural thickening were more likely than those with normal pleura to have a higher percentage of lymphocytes in lavage fluid. Lymphocyte percentage showed a linear relationship across the three pleural categories (F = 7.50, P = 0.01). The difference between workers with plaques and those with normal pleura was not statistically significant.
  • Parenchymal fibrosis on high-resolution CT was found in 14.3% of workers with normal pleura, 55.6% with circumscribed plaques and 87.5% with diffuse pleural thickening (P less than 0.01, diffuse thickening vs normal). There was a significant trend across the three categories (chi-square for trend = 7.68, P = 0.02).
  • After adjustment, a lymphocytic alveolitis was associated with lower forced vital capacity and total lung capacity, but parenchymal fibrosis on high-resolution CT was not related to reduction in any of the lung function measures
  • When pleural fibrosis, lavage lymphocytes and CT parenchymal fibrosis were analyzed together, pleural fibrosis (or diffuse pleural thickening alone) was the principal determinant of declines in lung volumes and diffusing capacity. Alveolitis and CT fibrosis contributed very little.
• The authors' conclusion: The authors concluded that pleural fibrosis is associated with reduced lung volumes and diffusing capacity, and that this appears independent of its association with lymphocytic alveolitis and CT-detected parenchymal fibrosis. They also suggested that parenchymal injury is likely to be a contributing factor in restrictive lung function in those with asbestos-induced pleural fibrosis.
• Limitations the authors state:
  • Because of financial constraints, the study was limited to 24 subjects. The authors note that small numbers and broad standard deviations meant some differences for workers with plaques were not statistically significant.
  • CT readers could not be blinded to the presence of pleural fibrosis, though they were blinded to its category
  • CT scans were done with subjects lying on their backs, which the authors say may have underestimated parenchymal fibrosis
  • The authors describe lavage and CT as sensitive but not specific measures of parenchymal injury

Topics

Medical terms in this study, explained in our Lexicon: Restrictive Lung Disease, Fibrosis, Inflammation, Parenchymal Fibrosis, Parenchyma, Chest X-Ray, Pleura, Diffuse Pleural Thickening.

Related studies

• Restrictive lung function and asbestos-induced pleural fibrosis. A quantitative approach — D.A. Schwartz, J.R. Galvin, et al. (1993)
• Determinants of restrictive lung function in asbestos-induced pleural fibrosis — C.J. Bergin (1991)
• Pleural determinants of restrictive lung function and respiratory symptoms in an asbestos-exposed population — A. Broderick, L.J. Fuortes, et al. (1992)
• Asbestos-induced pleural fibrosis and impaired lung function — D.A. Schwartz, L.J. Fuortes, et al. (1990)
• Pleural determinants of restrictive lung function and respiratory symptoms in an asbestos-exposed population — P.H. Wright (1993)
• Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? — B. Clin, C. Paris, et al. (2011)

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