Association between increased small airway obstruction and asbestos exposure in patients with asbestosis

Our plain-English summary of Association between increased small airway obstruction and asbestos exposure in patients with asbestosis, by X. Yang, Y. Yan, C. Xue, et al (The Clinical Respiratory Journal, 2018).

The study

• Authors: X. Yang, Y. Yan, C. Xue, X. Du, Q. Ye
• Journal: The Clinical Respiratory Journal
• Published: 2018;12(4):1676-1684
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Asbestos exposure may cause asbestos-related lung diseases including asbestosis, pleural abnormalities and malignancies. The role of asbestos exposure in the development of small airway obstruction remains controversial. Anatomic and physiologic small airway abnormalities may develop as part of the pathophysiologic process of asbestosis. We hypothesized that inhalation of asbestos may induce small airway defects in addition to asbestosis and pleural abnormalities.

Methods: In total, 281 patients with newly diagnosed asbestosis were evaluated. Clinical data were collected from the patients' medical charts. The patients were classified into various stages according to their chest X-ray findings using the International Labour Organization classification. Pulmonary function was evaluated by plethysmography and the forced oscillation technique.

Results: Expiratory flow, including the predicted values of the maximum expiratory flow between 25% and 50% of the forced vital capacity (MEF25-50 ), was significantly lower in the different stages of asbestosis. Accordingly, the predicted percentage of R5 -R20 was significantly higher with increasing stages of asbestosis. Furthermore, the duration of exposure to asbestos was significantly associated with the forced expiratory volume in the first second (FEV1 )/forced vital capacity (FVC) ratio and the predicted percentage of MEF25 or MEF50 according to the regression analysis in non-smoking patients with asbestosis. The predicted percentage of FEV1 or the FEV1 /FVC ratio was significantly lower and the predicted percentage of R5 -R20 was significantly higher in smokers than non-smokers.

Conclusions: The patients with asbestosis have small airway obstructive defects that are significantly associated with asbestos exposure.

© 2017 The Authors. The Clinical Respiratory Journal Published by John Wiley & Sons Ltd.

In plain English

This single-hospital study examined lung function in 281 patients newly diagnosed with asbestosis in Beijing, China, from 2007 to 2015. Of 341 patients recruited, 60 were excluded, 50 of them for lung cancer or mesothelioma. All had been exposed to chrysotile, mostly while making asbestos textiles or asbestos-based products. Small airway flow measures (MEF25 and MEF50) differed significantly among chest X-ray stages of asbestosis, lowest in stage II rather than stage III. Peripheral airway resistance (R5–R20) was higher at more advanced stages. The authors reported that, among 185 patients classed as non-smokers (apparently including ex-smokers), longer exposure was significantly associated with FEV1/FVC, MEF25 and MEF50 after accounting for age, but the coefficients and standard errors in their table do not appear to support significance. Smokers had lower FEV1 and FEV1/FVC and higher R5–R20 than non-smokers. The authors concluded that patients with asbestosis had small airway obstructive defects, although the obstruction was relatively small on spirometry. They noted that asbestosis was diagnosed without examining lung tissue. Other figures in the article also conflict.

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: Single-centre study of lung function in a cohort of patients with asbestosis, comparing chest X-ray stages and comparing smokers with non-smokers, with regression analysis of exposure duration
• Who was studied: 341 outpatients newly diagnosed with asbestosis were recruited at Beijing Chao-Yang Hospital, China, January 2007 to December 2015. 60 were excluded (50 for lung cancer or mesothelioma, 10 for incomplete lung function testing), leaving 281. Of these, 169 (60.1%) were women and 96 (34.2%) were smokers. By ILO X-ray stage, 196 were stage I, 67 stage II and 18 stage III.
• Exposure: Chrysotile dust or fibers. 235 patients (83.6%) worked in the manufacture of asbestos textiles or asbestos-based products. 46 (16.4%) were exposed to asbestos products at work (for example, heat insulation and boiler maintenance workers). Exposure was measured only as duration in years; the mean was 16.3 years (standard deviation 12.2).
• Main results:
  • Small airway flow measures differed significantly among asbestosis stages, but did not fall steadily with stage. Values were lowest in stage II. MEF25 was 51.0, 37.8 and 46.3 % predicted in stages I, II and III (P=0.004). MEF50 was 60.1, 44.2 and 55.2 % predicted (P=0.001).
  • Peripheral airway resistance (R5–R20) rose with stage: 222.2 % predicted in stage I, 368.2 in stage II and 383.1 in stage III (P=0.013). Total (R5) and central (R20) resistance were described as within the normal range.
  • FVC, FEV1, TLC and DLCO decreased significantly with increasing stage. The FEV1/FVC ratio did not differ among stages: 77.5% in stage I, 76.9% in stage II and 78.1% in stage III (P=0.879).
  • Spirometry patterns among the patients with asbestosis: 34.5% normal, 28.8% restrictive, 19.6% obstructive and 17.1% mixed.
  • Smokers (n=96) compared with non-smokers (n=185): FEV1 was 69.3 versus 75.3 % predicted (P=0.043), and FEV1/FVC was 75.5% versus 78.6% (P=0.018).
  • R5–R20 was 260.8 % predicted in smokers versus 213.0 in non-smokers (reported P=0.000). MEF25 and MEF50 were low in both groups and did not differ significantly between them.
  • In the 185 non-smokers, after accounting for age, the authors reported that exposure duration was significantly associated with FEV1/FVC (coefficient -0.14, SE 0.09), MEF25 (-0.24, SE 0.25) and MEF50 (-0.40, SE 0.28). However, each standard error is as large as or not much smaller than its coefficient, which does not appear consistent with the table's P less than 0.05 markers. This group appears to include the 38 ex-smokers. Exposure was not marked as significant for R5 or R5–R20.
  • R5–R20 was negatively correlated with MEF25 (r = -0.341), MEF50 (r = -0.443) and MEF75 (r = -0.383) across the patients.
• The authors' conclusion: The authors concluded that patients with asbestosis had small airway obstructive defects, although the obstruction was relatively small according to spirometry.
• Limitations the authors state:
  • Asbestosis was diagnosed from exposure history, clinical features and imaging, without examining lung tissue.
  • Citing another study, the authors noted that a radiologic diagnosis of mild asbestosis can overlap with smoking-associated fibrosis in heavy smokers.
  • Relying on spirometry may underestimate problems in patients with both fibrosis and emphysema.
  • There were no air measurements and no detailed information on how often each job involved exposure, so exposure was measured only as years of exposure.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Chest X-Ray, FEV1.

Related studies

• Does asbestos exposure cause airway obstruction, in the absence of confirmed asbestosis? — J. Ameille, M. Letourneux, et al. (2010)
• Does asbestos exposure (asbestosis) cause (clinical) airway obstruction (small airway disease)? — A. Miller, W.N. Rom (2010)
• 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)
• Auscultated forced expiratory time as a clinical and epidemiologic test of airway obstruction — D.G. Kern, S.R. Patel (1991)

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