Airways obstruction from asbestos exposure. Effects of asbestosis and smoking

Our plain-English summary of Airways obstruction from asbestos exposure. Effects of asbestosis and smoking, by K.H. Kilburn, R.H. Warshaw (Chest, 1994).

The study

• Authors: K.H. Kilburn, R.H. Warshaw
• Journal: Chest
• Published: 1994;106(4):1061-70
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: To define the apparent steps in developing airways obstruction vs restrictive lung disease in men exposed to asbestos for more than 20 years who had never smoked vs cigarette smokers.

Design: Physiologic signs of asbestosis were studied in cross-sectional age-matched groups of never, current, and ex-cigarette smoking workers.

Setting And Participants: The study included 8,720 asbestos-exposed construction and shipyard workers in the United States.

Measurements: FVC, FEV1, FEF25-75, and FEF75-85 were measured by spirometry and total lung capacity (TLC) by planimetry of standard chest radiographs and adjusted for height, age, and duration of cigarette smoking and expressed as percentage of predicted. TLC minus FVC yielded RV. We compared means and mean residuals (measurement minus group mean) expiratory flows and lung volumes in 1,146 men with pulmonary asbestosis age matched to 1,146 without asbestosis who had similar durations of asbestos exposure and to 370 men without asbestos exposure. Next, flows and volumes were regressed against the International Labour Office (ILO) profusion scale of irregular opacities on chest radiographs (PIO) and the duration of asbestos exposure for 1,777 never smokers (NS), 4,550 current smokers, and 2,393 ex-smokers.

Results: Asbestos exposure in NS men decreased expiratory flows and increased TLCs compared with unexposed NS men. Further reductions in flows and FVC and increases RV/TLC with radiographic asbestosis were not statistically significant. As the PIO increased from 1/1 to 3/3, obstruction and air trapping increased significantly but TLC did not.

Conclusions: Asbestos exposure reduced flows and produced air trapping after 20 years in workers who never smoked. Smoking increased these abnormalities.

In plain English

This cross-sectional study measured lung function in 8,720 men screened at 47 United States sites who had been exposed to asbestos-containing insulating materials. Their exposure had begun at least 15 years earlier and lasted at least 5 years. The article does not say which asbestos fiber types these workers were exposed to. The authors compared 1,146 men with asbestosis on chest X-ray with 1,146 age-matched exposed men without it, and with 370 unexposed men from a Michigan population sample. Among never smokers, exposed men without asbestosis had significantly lower late-exhalation airflow and more air trapping than unexposed men. Men with asbestosis had still lower flows and forced vital capacity than the exposed men, but these extra differences were not statistically significant. Among current smokers, the step from exposure to asbestosis brought significant added impairment. As X-ray severity rose, airflow fell and air trapping rose, while total lung capacity did not change. The authors concluded that asbestos exposure reduced flows and produced air trapping in never smokers, and that smoking increased these abnormalities.

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 study comparing age-matched groups within never, current and ex-smoker categories, plus regression of lung function against chest X-ray severity (ILO profusion of irregular opacities) and duration of asbestos exposure
• Who was studied: 8,720 asbestos-exposed men (construction and shipyard workers, many of them union boilermakers, pipefitters and metal and chemical trades workers) examined at 47 sites across the United States. The study date range is not given. 1,146 white men with asbestosis (ILO 1/0 or greater) were each age-matched to an exposed man without asbestosis (ILO 0/0 or 0/1). Each group contained 119 never smokers, 722 current smokers and 305 ex-smokers. They were also compared with 370 men without asbestos exposure from a Michigan population sample (119 never, 166 current, 85 ex-smokers). The regressions used 1,777 never smokers, 4,550 current smokers and 2,393 ex-smokers.
• Exposure: Occupational exposure to asbestos-containing insulating materials, beginning 15 or more years earlier and lasting at least 5 years. The article does not state the fiber types these workers were exposed to. It mentions chrysotile and amosite only when discussing earlier animal studies. Table 1 gives mean exposure durations in the matched groups ranging from 28.4 to 32.2 years. Cigarette smoking was analyzed as a second factor.
• Main results:
  • Never smokers, asbestos-exposed without asbestosis versus unexposed: significantly lower FEF75-85 (80.6 vs 99.0 percent predicted, p 0.0001) and lower FEV1/FVC (75.6 vs 80.0). They also had higher total lung capacity (106.5 vs 99.6 percent predicted) and higher RV/TLC (42.5 vs 30.3).
  • Never smokers with asbestosis versus unexposed: flows and FVC were lower, and TLC and RV/TLC were higher, with all differences significant. For example, FVC was 94.3 vs 99.7 percent predicted (p 0.004).
  • Never smokers with asbestosis versus age-matched exposed never smokers without asbestosis: flows and FVC were lower, but the differences were not statistically significant.
  • Current smokers: unlike never smokers, men with asbestosis showed significant additional impairment compared with exposed men without asbestosis. The exceptions were midflow (FEF25-75) and RV/TLC.
  • Current and ex-smokers with asbestos exposure or asbestosis showed greater reductions in flows, FEV1 and FVC, and larger TLCs, than never smokers in the same groups. The authors described this as a synergistic effect of smoking and asbestos.
  • In never smokers, as ILO profusion increased, FVC, FEV1, FEV1/FVC, FEF25-75 and FEF75-85 decreased, total lung capacity did not change, and RV/TLC (air trapping) increased.
  • In never smokers, ILO profusion explained 6.6 percent of the variance in RV/TLC and below 3.1 percent for other measures. Duration of asbestos exposure explained more of the variance in RV/TLC and FEV1/FVC (adjusted r2 of 11 percent and 4 percent).
• The authors' conclusion: The authors concluded that asbestos exposure reduced airflow and produced air trapping in workers who never smoked, and that smoking increased these abnormalities. In their discussion, they argued that the apparent 'restrictive' pattern in asbestosis reflects air trapping from airway obstruction reducing FVC while total lung capacity is maintained.
• Limitations the authors state:
  • The unexposed comparison group was smaller and was not age-matched. Its values were age-adjusted instead, because matching would have lost many subjects and statistical power.
  • The lung function decline in smokers has not been studied prospectively.
  • Variability in reading chest X-rays, especially at the borderline between ILO 0/1 and 1/0, could enhance or reduce differences in lung function. A single reader read all films.
  • Total lung capacity measured from chest X-rays may underestimate volume.
  • Using cross-sectional data to infer the course of disease over time rests on the assumption that average behavior in each age group mirrors population trends.

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, Restrictive Lung Disease, FEV1, Spirometry, Total Lung Capacity (TLC), Chest X-Ray, Asbestosis.

Related studies

• Association between increased small airway obstruction and asbestos exposure in patients with asbestosis — X. Yang, Y. Yan, et al. (2018)
• Review of the Kilburn and Warshaw Chest article--airways obstruction from asbestos exposure — R.N. Jones, H.W. Glindmeyer, et al. (1995)
• Airway obstruction in asbestos-exposed shipyard workers: with and without irregular opacities — K.H. Kilburn, R.H. Warshaw (1990)
• Airways obstruction among older construction and trade workers at Department of Energy nuclear sites — J.M. Dement, L. Welch, et al. (2010)
• Does asbestos exposure cause airway obstruction, in the absence of confirmed asbestosis? — J. Ameille, M. Letourneux, et al. (2010)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)

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