Measurement of lung density by x-ray computed tomography. Relation to lung mechanics in workers exposed to asbestos cement

Our plain-English summary of Measurement of lung density by x-ray computed tomography. Relation to lung mechanics in workers exposed to asbestos cement, by P. Wollmer, K. Jakobsson, M. Albin, et al (Chest, 1987).

The study

• Authors: P. Wollmer, K. Jakobsson, M. Albin, U. Albrechtsson, K. Brauer, L. Eriksson, B. Jonson, S. Skerfving, U. Tylén
• Journal: Chest
• Published: 1987;91(6):865-9
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000366).

Abstract

We measured lung density by means of x-ray computed tomography and lung mechanics in 33 workers exposed to asbestos cement and in 39 normal subjects. The exposed group showed evidence of lung fibrosis with reduced static lung volumes and lung compliance, although only three subjects had signs of interstitial fibrosis at standard chest radiography. Lung density was significantly increased in the exposed workers compared to control subjects, with greater differences between nonsmokers than between smokers. Lung density correlated inversely with static lung volumes. There was no appreciable difference in the regional distribution of lung density between exposed workers and control subjects. We conclude that lung density is often increased in workers with mild asbestosis, even in the presence of a normal chest radiograph. Measurement of lung density may be of value in the evaluation of asbestos-exposed workers for assessment of the extent of parenchymal disease.

In plain English

This study, from the University of Lund in Sweden, measured lung density with x-ray computed tomography and tested lung mechanics in 33 male former workers from an asbestos cement factory. They were compared with 39 healthy industrial workers without known asbestos exposure. The exposed workers were chosen for breathlessness, persisting crackles, chest radiograph signs of fibrosis, or abnormal spirometry. Only three showed interstitial fibrosis on a standard chest radiograph. Exposed nonsmokers had significantly lower lung volumes and static lung compliance than reference nonsmokers. Exposed smokers had reduced total lung capacity and compliance. Lung density was significantly higher in exposed nonsmokers at both levels scanned (p less than 0.001). In exposed smokers the difference was significant only at the lung base (p less than 0.05). Among exposed workers, higher density went with lower lung volumes (r = -0.54 with total lung capacity at the base). Density did not correlate significantly with individual asbestos exposure. The authors concluded that lung density is often increased in mild asbestosis even with a normal chest radiograph. They noted the group was small, exposure was low, and smoking effects are hard to separate.

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 comparison of asbestos-exposed workers with a reference group of unexposed workers (CT lung density and lung function measurements)
• Who was studied: 33 male former workers from an asbestos cement factory, Lund, Sweden. They were 6 nonsmokers, 9 exsmokers and 18 smokers, with exsmokers counted as smokers, giving 27 smokers. They were randomly selected from a larger group meeting criteria such as breathlessness, crackles, radiographic fibrosis or abnormal spirometry. The reference group was 39 healthy industrial workers without known exposure to asbestos or other noxious inhalants (20 nonsmokers and 19 current smokers).
• Exposure: Work in an asbestos cement factory; fiber type not stated. Cumulative exposure ranged from 4 to 46 fiber-years per milliliter in nonsmokers and from 0.4 to 50 in smokers. Duration of exposure was 2 to 28 years in nonsmokers and 0.3 to 48 years in smokers. The authors describe the exposure as relatively low.
• Main results:
  • Only three of the 33 exposed workers showed signs of interstitial fibrosis on the standard chest radiograph.
  • Exposed nonsmokers (n=6) had significantly lower lung volumes and static lung compliance than reference nonsmokers. Total lung capacity was a mean 79 versus 99 percent of predicted, and compliance was 54 versus 92 percent of predicted.
  • Exposed smokers (n=27) also showed reduced total lung capacity (mean 87 versus 96 percent of predicted, p less than 0.05) and static compliance (64 versus 79 percent of predicted, p less than 0.01) compared with reference smokers.
  • Lung density was significantly higher in exposed nonsmokers than in control subjects at both the carina and the lung base (p less than 0.001 in both cases).
  • In exposed smokers, a small but statistically significant difference in lung density was found at the base of the lung (p less than 0.05). The difference at the level of the carina was not significant.
  • In the exposed group, lung density at the lung base correlated inversely with total lung capacity (r = -0.54, p less than 0.001), functional residual capacity (r = -0.57, p less than 0.001) and residual volume (r = -0.46, p less than 0.01).
  • There was no appreciable difference in the front-to-back (ventrodorsal) gradient of lung density between exposed workers and the reference group.
  • There was no significant correlation between lung density and individual asbestos exposure in this small group.
  • The authors took the upper limit of normal as the mean plus 2 SD for normal smokers. On that basis, 15 exposed subjects had abnormal lung density. Only four exposed subjects (three nonsmokers and one smoker) had total lung capacity more than 2 SD from the control mean.
  • The basal scan was repeated in eight subjects. In the crest-shaped region, the mean difference between repeat measurements was 11 HU, with a standard deviation of 10 HU.
• The authors' conclusion: The authors concluded that lung density is often increased in workers with mild asbestosis, even with a normal chest radiograph, and appears to be an early indicator of parenchymal damage. They added that further studies are needed before such measurements can be recommended for clinical use.
• Limitations the authors state:
  • Subjects had low asbestos exposure and mild interstitial lung disease, so the findings are not necessarily pertinent to severe asbestosis.
  • The study group was too small to draw conclusions about the relative sensitivity of lung function and lung density measurements.
  • Lung density measurement lacks specificity. Normal smokers have increased lung density, so smoking effects may be hard to separate from asbestos effects.
  • The causes of increased lung density (cells, fluid, blood, or lung deflation) cannot be told apart from density measurements alone.
  • Some exposed smokers probably had early emphysema, which would tend to reduce lung density.
  • Exposure to other inorganic dusts, such as iron oxide in welders, could raise lung density readings and lead to overestimating asbestos-related disease.

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-Cement, Fibrosis, Interstitial Fibrosis, Chest X-Ray.

Related studies

• Pulmonary function, smoking habits, and high resolution computed tomography (HRCT) early abnormalities of lung and pleural fibrosis in shipyard workers exposed to asbestos — S. Neri, P. Boraschi, et al. (1996)
• High resolution computed tomography and lung function in asbestos-exposed workers with normal chest radiographs — C.A. Staples, G. Gamsu, et al. (1989)
• Findings from high resolution computed tomography of the lung and pleura of symptom free workers exposed to amosite who had normal chest radiographs and pulmonary function tests — S. Neri, A. Antonelli, et al. (1994)
• Assessment of therapy responses and prediction of survival in malignant pleural mesothelioma through computer-aided volumetric measurement on computed tomography scans — F. Liu, B. Zhao, et al. (2010)
• Lung function not affected by asbestos exposure in workers with normal Computed Tomography scan — C. Schikowsky, M.K. Felten, et al. (2017)
• Relation between lung function, exercise capacity, and exposure to asbestos cement — P. Wollmer, L. Eriksson, et al. (1987)

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