Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening

Our plain-English summary of Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening, by A. Miller, R. Warshaw, J. Nezamis (American Journal of Industrial Medicine, 2013).

The study

• Authors: A. Miller, R. Warshaw, J. Nezamis
• Journal: American Journal of Industrial Medicine
• Published: 2013;56(12):1383-93
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Asbestosis is an interstitial lung disease whose radiographic severity has long been graded by the International Labour Office (ILO) profusion score. Its effect on pulmonary function is further impacted by asbestos related pleural thickening.

Objectives: This report aims to describe the relationships between radiographic grading of interstitial and pleural fibrosis and a key test of pulmonary function, the diffusing capacity, which measures gas exchange and has rarely been assessed in large groups, and to confirm the relationship to an independent test of pulmonary function, the vital capacity, which measures a mechanical property of the lungs.

Methods: The data were derived from a survey during the period 1997-2004 of 5,003 workers (all white males) exposed to asbestos in various trades. Tests included chest radiographs read by a certified expert ("B") reader, forced vital capacity (FVC), and carbon monoxide diffusing capacity (DLco). Cigarette smoking was adjusted for in the predictive equation for DLCO . Workers were evaluated at a mobile facility at work sites in four southern states.

Results: Both diffusing capacity and vital capacity were negatively correlated with profusion score over the full spectrum of radiographic severity. ILO profusion scores 0/1 (conventionally classified as normal) and 1/0 (conventionally classified as abnormal) were associated with similar diffusing capacity and vital capacity values. The highest profusion scores were associated with a greater proportionate decrease in diffusing capacity than in FVC. Both tests showed an effect of pleural fibrosis.

Conclusions: Both radiographic severity graded by the profusion score and pleural thickening are correlated with two independent measures of pulmonary function. FVC (which had been reported in smaller work forces) and DLCO (which has not been reported). Both measures show a decrease from normal to intermediate (0/1, 1/0) scores and a further decrease with greater scores, demonstrating the consistency of radiographic and functional assessments.

© 2013 Wiley Periodicals, Inc.

In plain English

This study compared chest X-ray findings with two breathing tests in 5,003 white male workers exposed to asbestos in trades such as plumbing, pipefitting, boilermaking and insulation. They were examined for medicolegal evaluation at mobile sites in Louisiana, Alabama, Mississippi and Tennessee from 1997 to 2004. One certified B reader graded lung scarring (the ILO profusion score) and pleural thickening. Overall, 56.2% had a profusion score of 1/0 or greater and 40.8% had pleural thickening. Forced vital capacity (FVC) and diffusing capacity (DLCO) fell as scores rose. They went from 95.0% and 96.0% of predicted at score 0/0 to 74.7% and 51.8% above 2/1. Scores 0/1 and 1/0 gave similar results, and 0/1 differed from 0/0. Values were lower with pleural thickening except at the highest scores, from 2/1 upward. Diffuse thickening had a greater effect than circumscribed thickening. The authors concluded that all methods available to the physician should be used to separate workers scoring 0/1 or 1/0 who have lung disease from those who do not. They noted that the group was a convenience sample and that medicolegal screening may select more impaired workers.

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 screening survey data (a convenience sample) comparing chest X-ray grading with lung function tests (FVC and DLCO), using one-way analysis of variance
• Who was studied: 6,932 asbestos-exposed male workers were enrolled through their unions and examined at mobile sites from 1997 to 2004 for medicolegal evaluation. They came from Louisiana, Alabama, Mississippi and Tennessee. Female and non-white workers were very few and were excluded. The analysis covered 5,003 white males who had smoking information and satisfactory radiographs, spirometry and diffusing capacity. Their mean age was 62.1 years (range 26 to 94).
• Exposure: Occupational asbestos exposure in various trades: plumbers, pipefitters, boilermakers, machinists, laborers, insulators, carpenters, oil and chemical workers and electricians. Mean years worked with asbestos was 28.0. Fiber types were not specified.
• Main results:
  • Of the 5,003 workers, 2,814 (56.2%) had radiographic asbestosis (profusion score 1/0 or greater). 2,043 (40.8%) had pleural thickening.
  • In all subjects, mean FVC was 4.1 L (91.6% of predicted) and mean DLCO was 26.7 cc/min/mmHg (90.8% of predicted).
  • Mean FVC fell from 95.0% of predicted at score 0/0 to 74.7% at scores above 2/1. Mean DLCO fell from 96.0% to 51.8%. The spread from normal to the highest category was 44.2% of predicted for DLCO and 20.3% for FVC.
  • Scores 0/1 and 1/0 did not differ from each other. Score 0/1 differed significantly from 0/0 (P less than 0.001) for both FVC and DLCO.
  • Mean FVC and DLCO were lower when any pleural thickening was present, except at the highest profusion scores. In Table VII, mean DLCO was higher with pleural thickening than without it at both 2/1 (69.7% versus 67.5% of predicted) and above 2/1 (53.1% versus 47.4%). At score 1/1, the difference between no pleural thickening and pleural thickening was 5.8% of predicted for FVC and 8.0% of predicted for DLCO.
  • Diffuse pleural thickening, alone or with circumscribed thickening, had a greater effect on both FVC and DLCO than circumscribed thickening alone.
  • Diaphragmatic pleural thickening alone had no effect on FVC (0.9% predicted difference at score 1/1, n = 299). It was associated with a large effect on DLCO (8.5% predicted difference at score 1/1).
  • Mean FVC and DLCO by X-ray finding: normal X-ray (n = 1,442) 96.0% and 96.9% of predicted; lung tissue abnormality only (n = 1,518) 92.6% and 92.1%; pleural abnormality only (n = 747) 90.3% and 88.8%; both (n = 1,296) 86.4% and 83.4%.
• The authors' conclusion: The authors concluded that FVC decreased from normal to intermediate scores and decreased further with greater scores, with no difference between the two intermediate scores. They found DLCO behaved similarly at lower scores but decreased more than FVC at higher scores. They stated that findings from all modalities available to the physician should be used to separate workers with scores 0/1 and 1/0 who have lung disease from those without.
• Limitations the authors state:
  • The study population was a convenience sample and may not be representative of the prevalence of asbestos-related findings.
  • Studying workers screened for medico-legal evaluation may select for more impaired participants.
  • Films were read by a single B reader rather than a panel.
  • CT scanning, which is more sensitive and specific for asbestos-related abnormalities, was not used.

Topics

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

Medical terms in this study, explained in our Lexicon: Diffusing Capacity (DLCO), Interstitial Fibrosis, Pleural Thickening, Interstitial Lung Disease, Interstitial, Fibrosis, Chest X-Ray.

Related studies

• Relationship of mortality, occupation, and pulmonary diffusing capacity to pleural thickening in the First National Health and Nutrition Examination Survey — D.P. Loomis, G.W. Collman, et al. (1989)
• 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)
• Vital capacity and one-second forced expiratory volume in Australian male asbestos cement workers — L.N. Balaam, S.F. McCullagh (1975)
• Expiratory and inspiratory forced vital capacity and one-second forced volume in asymptomatic never-smokers in Norway — A. Gulsvik, T. Tosteson, et al. (2001)
• Asbestosis: interstitial pulmonary fibrosis and pleural fibrosis in a cohort of asbestos insulation workers: influence of cigarette smoking — R. Lilis, I.J. Selikoff, et al. (1986)
• Reduced diffusing capacity as an isolated finding in asbestos- and silica-exposed workers — J.G. Garcia, D.E. Griffith, et al. (1990)

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