Lung function in asbestos-exposed workers, a systematic review and meta-analysis

Our plain-English summary of Lung function in asbestos-exposed workers, a systematic review and meta-analysis, by D. Wilken, M. Velasco Garrido, U. Manuwald, et al (Journal of Occupational Medicine and Toxicology, 2011).

The study

• Authors: D. Wilken, M. Velasco Garrido, U. Manuwald, X. Baur
• Journal: Journal of Occupational Medicine and Toxicology
• Published: 2011;6:21
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: A continuing controversy exists about whether, asbestos exposure is associated with significant lung function impairments when major radiological abnormalities are lacking. We conducted a systematic review and meta-analysis in order to assess whether asbestos exposure is related to impairment of lung function parameters independently of the radiological findings.

Methods: MEDLINE was searched from its inception up to April 2010. We included studies that assessed lung function parameters in asbestos exposed workers and stratified subjects according to radiological findings. Estimates of VC, FEV1 and FEV1/VC with their dispersion measures were extracted and pooled.

Results: Our meta-analysis with data from 9,921 workers exposed to asbestos demonstrates a statistically significant reduction in VC, FEV1 and FEV1/VC, even in those workers without radiological changes. Less severe lung function impairments are detected if the diagnoses are based on (high resolution) computed tomography rather than the less sensitive X-ray images. The degree of lung function impairment was partly related to the proportion of smokers included in the studies.

Conclusions: Asbestos exposure is related to restrictive and obstructive lung function impairment. Even in the absence of radiological evidence of parenchymal or pleural diseases there is a trend for functional impairment.

In plain English

This was a systematic review and meta-analysis of earlier studies. The authors searched MEDLINE to April 2010 and other sources. They included 30 studies (27 cross-sectional, one case-control, two follow-up) of workers exposed to asbestos on the job, and pooled data for 9,921 of 15,097 subjects. Lung function, measured as percent of predicted, was grouped by imaging findings. Pooled vital capacity was 95.7% of predicted (95% CI 93.9 to 97.3) in workers with normal imaging, 89.0% (95% CI 86.5 to 91.5) with pleural fibrosis and 86.5% (95% CI 83.7 to 89.4) with asbestosis. FEV1 (air blown out in one second) followed a similar pattern, and FEV1/VC was slightly reduced in all groups. Studies using chest X-ray generally showed lower values than CT studies, though for FEV1/VC the authors described only a tendency, and results varied greatly between studies. The authors concluded that asbestos exposure causes restrictive and obstructive lung function impairment, even without radiological findings. They noted that the pooled values were within normal limits used for individuals, that smoking effects could not be clearly separated, and that bias may have caused underestimation.

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: Systematic review and meta-analysis of published studies (random effects model), with subgroup analyses and meta-regression
• Who was studied: 30 studies (27 cross-sectional, one case-control, two follow-up) found through MEDLINE (from its start to April 2010), congress proceedings, reference lists and the authors' archive. Together they covered 15,097 subjects, and data for 9,921 were usable in the meta-analysis. Study sizes ranged from 19 to 3,383.
• Exposure: Occupational asbestos exposure in various jobs, for example asbestos manufacturing, insulation work, shipyards, asbestos cement, railway, sheet metal work and construction. The article does not analyse fiber types. Mean exposure duration, where reported, ranged from 8.4 plus or minus 6.1 to 32.7 plus or minus 6.7 years. Fibre-year estimates were rarely reported.
• Main results:
  • Vital capacity in workers with no radiological evidence of asbestos-related pleural or parenchymal disease: 95.7% of predicted (95% CI 93.9, 97.3).
  • Vital capacity in workers with pleural fibrosis (pleural plaques and/or diffuse pleural thickening): 89.0% of predicted (95% CI 86.5 to 91.5; 14 studies).
  • Vital capacity in workers with radiological findings of asbestosis: 86.5% of predicted (95% CI 83.7, 89.4). This was the largest loss.
  • FEV1 was already reduced in workers with no radiological evidence of asbestos-related disease, and more so in those with pleural or parenchymal disease. Table 2 gives 93.6% of predicted for normal imaging, 89.2% for pleural fibrosis and 85.7% for asbestosis.
  • For vital capacity, studies using conventional chest X-ray gave lower estimates than studies using CT in all three imaging groups.
  • In workers with pleural disease, FEV1 was 83.9% of predicted (95% CI 77.2, 90.5) in studies using chest X-ray, compared with 93.7% (95% CI 87.6, 99.9) in studies using CT.
  • FEV1/VC was slightly reduced even in workers without radiological signs of disease, to a similar degree as in those with pleural disease or asbestosis. For this measure, the authors described only a tendency to lower values in X-ray studies.
  • Differences between studies (heterogeneity) were very high for vital capacity in all three imaging groups.
  • In the regression analysis, studies with a higher proportion of never-smokers tended to show less FEV1 impairment. This was not statistically significant.
  • The regression analysis indicated lower FVC and FEV1 with increasing mean exposure duration. However, the subgroup results by exposure duration were inconsistent.
• The authors' conclusion: In the article's conclusions, the authors wrote that asbestos exposure causes restrictive as well as obstructive lung function impairment. They added that asbestos-exposed workers may show impairment even without radiological evidence of pleural fibrosis or asbestosis. The abstract phrases this as 'is related to'.
• Limitations the authors state:
  • Bias in the included studies may have led to underestimation of lung function impairment. The authors name the dilution effect, healthy worker effects, mostly cross-sectional designs and the general exclusion of former workers.
  • Heterogeneity between studies was high, partly because test quality varied and 12 different sets of reference values were used.
  • Exposure intensity differed widely between studies but was rarely reported, so it could not be analysed.
  • Few studies accounted for smoking appropriately, so smoking effects could not be clearly separated from asbestos effects.
  • The study cannot say whether the group-level impairments are clinically relevant for individuals. The pooled estimates were within the normal limits applied to individuals.

Topics

Medical terms in this study, explained in our Lexicon: Systematic Review, Meta-Analysis, Asbestos Exposure, FEV1.

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