Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities

Our plain-English summary of Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities, by A. Miller, R. Lilis, J. Godbold, et al (Chest, 1994).

The study

• Authors: A. Miller, R. Lilis, J. Godbold, E. Chan, X. Wu, I.J. Selikoff
• Journal: Chest
• Published: 1994;105(1):175-82
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A study of 2,611 long-term asbestos insulators was well suited to provide information on (1) the prevalence of spirometric impairments in a large, well-defined population and (2) the effects of cigarette smoking, radiographic abnormalities, and duration from onset of exposure on pulmonary function. Prevalences are reported by a mutually exclusive classification of impairments (normal, restrictive, obstructive, small airways, and combined) as well as by abnormality of specific spirometric tests (FVC, FEV1/FVC, and midexpiratory time). Only 3 percent of nonsmokers (NS) had obstruction and 6 percent a decreased FEV1/FVC. Frequency of restriction did not vary by smoking history; it was 31 percent in NS and current smokers (CS) and 34 percent in ex-smokers (XS). Obstruction (present in 17 percent) and combined impairment (in 18 percent) were most common in CS. The FEV1/FVC was decreased in 35 percent of CS and 18 percent of XS. The FVC was decreased in 49 percent of CS, 44 percent of XS, and 33 percent of NS. Normal spirometry was most common when the radiograph was normal (almost half the workers with normal radiographs had normal spirometry). Nevertheless, FVC was reduced in 27 percent of those with normal radiographs and a normal radiograph was seen in 11 percent of workers with restriction. Restrictive and combined impairments were most frequent when both parenchyma and pleura were abnormal. Restriction was more frequent in isolated pleural disease (seen in 34 percent such subjects) than in isolated parenchymal disease (22 percent). The contribution of pleural fibrosis to reduced FVC and of asbestos exposure and smoking both to reduced FVC and to reduced FEV1/FVC was confirmed by regression analysis. That reduced FVC and reduced FEV1/FVC are both more frequent in insulators who have smoked (compared with NS insulators or smokers in the general population) suggests an interaction between asbestos and smoking in producing both these physiologic abnormalities.

In plain English

This study examined breathing tests (spirometry) and chest X-rays in 2,611 men from the asbestos insulators' union. They were examined in 19 US and Canadian cities in 1981 to 1983; 87 percent were at least 30 years past first exposure. Normal spirometry was found in 44 percent of nonsmokers, 31 percent of ex-smokers and 17 percent of current smokers. Restrictive impairment did not vary by smoking history. Combined impairment occurred in 18 percent of current smokers and 3 percent of nonsmokers. Among workers with normal X-rays, 27 percent had a reduced forced vital capacity (FVC). Restriction was more frequent with pleural disease alone (34 percent) than with parenchymal disease alone (22 percent). In regression analysis, each year since first exposure was associated with an FVC lower by 0.44 percent of predicted, and smoking was the major influence on the FEV1/FVC ratio. The authors concluded that the findings suggest an interaction between asbestos and smoking. They noted the group was partly a survivor population, and that the relative effects of pleural versus parenchymal fibrosis may not apply to other asbestos-exposed groups.

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 field survey of spirometry and chest radiographs in a union cohort of asbestos insulators, with regression analysis
• Who was studied: Active and retired members of the International Brotherhood of Heat, Frost and Asbestos Insulation Workers who had been in the union on January 1, 1967. Of 2,907 men examined in 1981 to 1983, complete data were available on 2,611. Of these, 2,270 (87 percent) were at least 30 years from first exposure. The group included 515 nonsmokers, 875 current smokers and 1,221 ex-smokers.
• Exposure: Occupational asbestos exposure as insulators using end products, mostly before regulation (before the early to mid-1970s). Exposure was measured as years from onset of exposure (mean 35.1 years). Cigarette smoking was measured in pack years. Fiber types are not named in the article.
• Main results:
  • Normal spirometry was found in 44 percent of nonsmokers and 17 percent of current smokers. Obstruction was found in 17 percent of current smokers and 3 percent of nonsmokers. Ex-smokers had normal spirometry in 31 percent.
  • Restrictive impairment did not vary by smoking history: 158 of 515 nonsmokers (30.7 percent), 275 of 875 current smokers (31.4 percent) and 417 of 1,221 ex-smokers (34.2 percent).
  • Combined impairment was found in 18 percent of current smokers and 3 percent of nonsmokers, with ex-smokers intermediate.
  • Decreased FVC was found in 33 percent of nonsmokers, 44 percent of ex-smokers and 49 percent of current smokers.
  • Decreased FEV1/FVC was found in 6 percent of nonsmokers, 18 percent of ex-smokers and 35 percent of current smokers.
  • Among the 421 workers with normal chest radiographs, 21.1 percent had restriction and 5.9 percent had combined impairment, so 27 percent had a reduced FVC.
  • Restriction was more frequent in workers with isolated pleural disease (34 percent) than in those with isolated parenchymal disease (22 percent), p less than 0.001.
  • Normal spirometry became less frequent, and restriction and combined impairment more frequent, with longer time since first exposure. Reduced FVC was found in 54.3 percent of workers more than 40 years from onset. Reduced FEV1/FVC did not change with duration from onset.
  • In regression analysis of all 2,611 subjects, each year from onset of exposure was associated with a decrease in FVC of 0.44 percent of predicted, or 15.3 percent of predicted for 35 years. Pleural involvement was associated with a decrease of 4.8 percent of predicted, and parenchymal plus pleural involvement with a decrease of 7.5 percent of predicted.
  • In the regression analysis, cigarette smoking was the major influence on the FEV1/FVC ratio. Pleural involvement did not significantly affect it.
  • Among nonsmoking insulators, 31 of 515 (6 percent) had reduced FEV1/FVC. The authors said this did not provide strong evidence that asbestos inhalation by itself causes obstruction.
  • Compared with the authors' earlier random sample of the general population of Michigan, diminished FVC was more frequent in the insulators: 5.9 percent of Michigan nonsmokers versus 33.4 percent of insulator nonsmokers.
• The authors' conclusion: The authors concluded that the greater frequency of both reduced FVC and reduced FEV1/FVC in insulators who smoked suggests an interaction between asbestos and smoking. They also stated that pleural fibrosis has an important effect on lung function.
• Limitations the authors state:
  • Spirometry alone could not show whether combined impairment was mainly restriction or air trapping. Full lung volumes, which would be needed to tell, could not be measured in this field survey.
  • The group was partly a survivor population, in which those with the most severe fibrosis were more likely to have died.
  • The relative effects of pleural versus parenchymal fibrosis found in this study may not apply to other asbestos-exposed populations, because this group was selected for long duration and heavy exposure.
  • Part of the effect attributed to time since first exposure on the airway measures may reflect age or smoking, because these variables move together.

Topics

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

Medical terms in this study, explained in our Lexicon: Insulator, FEV1/FVC Ratio, Spirometry, Parenchyma, Pleura, Fibrosis, Asbestos Exposure.

Related studies

• Radiographic abnormalities in asbestos insulators: effects of duration from onset of exposure and smoking. Relationships of dyspnea with parenchymal and pleural fibrosis — R. Lilis, A. Miller, et al. (1991)
• 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)
• Railroad workers with pleural plaques: I. Spirometric and nitrogen washout investigation on smoking and nonsmoking asbestos-exposed workers — U. Hjortsberg, P. Orbaek, et al. (1988)
• Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities — R. Lilis, A. Miller, et al. (1991)
• Long term radiological effects of short term exposure to amosite asbestos among factory workers — R. Ehrlich, R. Lilis, et al. (1992)
• Asbestos exposure, cigarette smoking, and airflow limitation in long-term Canadian chrysotile miners and millers — R. Bégin, R. Boileau, et al. (1987)

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