Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities

Our plain-English summary of Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities, by R. Lilis, A. Miller, J. Godbold, et al (American Journal of Industrial Medicine, 1991).

The study

• Authors: R. Lilis, A. Miller, J. Godbold, E. Chan, I.J. Selikoff
• Journal: American Journal of Industrial Medicine
• Published: 1991;20(2):145-61
• Cited by: 45 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Pleural fibrosis due to asbestos exposure was fully appreciated considerably later than pulmonary interstitial fibrosis due to similar exposure. This is well exemplified by the fact that pleura face on was included in the International Labour Office's International Classification of Radiographs of Pneumoconioses only in the last revision of the Classification. The functional relevance of pleural fibrosis, in particular circumscribed pleural fibrosis, has remained controversial. Since pleural fibrosis can occur at various sites (diaphragmatic plaques, chest wall in profile and face on, mediastinal) and can be of different thickness and extent, a comprehensive integrative assessment of pleural fibrosis was undertaken in order to permit a quantitative study of relationships between pleural fibrosis and pulmonary function. This approach was used for chest X-ray films of 1,584 asbestos insulation workers examined (1981-1983); 1,185 (75%) had pleural fibrosis. The distribution pattern of the integrative pleural index was found to be different in the subgroup with circumscribed (n = 975) from that with diffuse (n = 197) pleural fibrosis, with a higher profusion of high INDEX values in the latter. Stepwise regression analysis indicated that there was a significant inverse relationship between forced vital capacity (FVC) and the integrative index of pleural fibrosis in the subgroup with circumscribed pleural fibrosis. In the subgroup with diffuse pleural fibrosis, the obliteration of costophrenic angle(s), even with pleural fibrosis of limited extent, resulted in marked decrement in FVC% predicted; higher values of INDEX did not result in additional significant reductions of FVC. In those with both parenchymal and pleural abnormalities (n = 862) the pleural index was found to make a significant contribution, independent of that of parenchymal abnormalities, to decrements of FVC. Since pleural fibrosis has gradually become the predominant radiologically detectable abnormality in asbestos exposed workers, establishing its quantifiable functional relevance is useful.

In plain English

The authors analysed chest X-rays from 1,584 asbestos insulation workers, most with over 30 years of exposure, examined in 1981-1983, and breathing-test results from 1,536 of them. They built a combined score (the pleural INDEX) from the width, extent, location and calcification of pleural thickening recorded under the 1980 ILO X-ray classification. Pleural fibrosis appeared on 1,185 films (75%). Average forced vital capacity (FVC, a measure of lung volume) fell as the INDEX rose: 89% of predicted with no pleural fibrosis, 83% for INDEX 1-3 and 4-6, and 71% for INDEX 22 or more. In workers with circumscribed pleural fibrosis, a higher INDEX was significantly linked to lower FVC after allowing for time since first exposure, lung-tissue abnormalities on X-ray and smoking. In those with diffuse pleural fibrosis, even the lowest INDEX went with a mean FVC of 69% predicted, and the INDEX itself was not statistically significant. The authors concluded that both types reduced FVC, diffuse more markedly. They noted that lung scarring not yet visible on X-ray could not be completely excluded.

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 analysis of chest X-rays and spirometry from a medical survey of members of a prospectively followed cohort
• Who was studied: 1,584 asbestos insulation workers whose chest films were read under the 1980 ILO classification. The overall analysis of FVC against the pleural INDEX included 1,536 of them. All were members of a cohort of 17,800 men, asbestos insulation workers in the United States and Canada, established in 1967. They were examined between July 1981 and November 1983 in field studies in 19 US cities.
• Exposure: Long-term occupational asbestos exposure as insulation workers, for the majority over 30 years. Fiber types are not specified.
• Main results:
  • Of the 1,584 chest X-ray films, 1,185 (75%) showed pleural fibrosis.
  • The overall analysis relating FVC to the pleural INDEX included 1,536 workers.
  • Years since first asbestos exposure was the only variable significantly correlated with the pleural INDEX. Age, years exposed and smoking were also tested.
  • The geometric mean INDEX was 5.81 among all 1,185 workers with pleural fibrosis. It was 5.06 in the circumscribed pleural fibrosis subgroup (n = 975) and 10.97 in the diffuse pleural fibrosis subgroup (n = 210). Over 50% of the diffuse subgroup had an INDEX above 12.
  • Mean FVC % predicted decreased as the INDEX increased: 89% in those without pleural fibrosis (INDEX 0), 83% for INDEX 1-3 and 4-6, and 71% for the highest INDEX group (22 or more).
  • In the circumscribed pleural fibrosis subgroup (n = 950 in the regression), the INDEX had a significant (p less than .0001) inverse relationship with FVC. This held after adjustment for duration from onset of exposure, profusion of small opacities and cigarette smoking.
  • In the diffuse pleural fibrosis subgroup, even the lowest INDEX was associated with a mean FVC of 69% predicted. In regression (n = 197), the pleural index did not reach statistical significance (p = .0750). Years since first exposure and profusion of small opacities were significant.
  • In the subgroup with both pleural and parenchymal abnormalities, the pleural index was a significant contributor to lower FVC, independent of parenchymal abnormalities. Years since first exposure and smoking were also significant.
  • In simple models, an INDEX of 5 predicted an FVC of 85% of predicted in the absence of parenchymal abnormalities. A small-opacity profusion score of 1/1 predicted the same 85% in the absence of pleural abnormalities.
• The authors' conclusion: The authors concluded that both diffuse and circumscribed pleural fibrosis had a negative effect on FVC % predicted, with more marked decrements in diffuse pleural fibrosis. In circumscribed pleural fibrosis, they concluded, the higher the INDEX, the lower the FVC. In diffuse pleural fibrosis, they attributed the reduction mainly to the presence of a blunted costophrenic angle rather than to the size of the INDEX.
• Limitations the authors state:
  • Parenchymal (lung tissue) fibrosis that was not yet visible on X-ray could not be completely excluded in some cases.
  • The weighting of the components of the pleural INDEX was arbitrary, although guided by plausibility.
  • Detection of pleural fibrosis on the standard chest X-ray, which the study relied on, is incomplete compared with autopsy or CT findings.

Topics

Medical terms in this study, explained in our Lexicon: Fibrosis, Asbestos Exposure, Interstitial Fibrosis, Pleura, Chest X-Ray, Insulator, Costophrenic angle.

Related studies

• Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups--insulators and sheet metal workers — R. Lilis, A. Miller, et al. (1992)
• 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)
• The effect of asbestos-induced pleural fibrosis on pulmonary function: quantitative evaluation — 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)
• Spirometric impairments in long-term insulators. Relationships to duration of exposure, smoking, and radiographic abnormalities — A. Miller, R. Lilis, et al. (1994)
• Relationship between chest X-ray findings and pulmonary function tests in dust workers — Y. Tonori, M. Niitsuya, et al. (2005)

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