Insulation workers in Belfast. 1. Comparison of a random sample with a control population

Our plain-English summary of Insulation workers in Belfast. 1. Comparison of a random sample with a control population, by W.F. Wallace, J.H. Langlands (British Journal of Industrial Medicine, 1971).

The study

• Authors: W.F. Wallace, J.H. Langlands
• Journal: British Journal of Industrial Medicine
• Published: 1971;28(3):211-6
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001380).

Abstract

Wallace, W. F. M., and Langlands, J. H. M. (1971).Brit. J. industr. Med.,28, 211-216. Insulation workers in Belfast. 1. Comparison of a random sample with a control population. A sample of 50 men was chosen at random from the population of asbestos insulators in Belfast and matched with a control series of men of similar occupational group with respect to age, height, and smoking habit. Significantly more of the insulators complained of cough and sputum and had basal rales on examination. Clubbing was assessed by means of measurements of the hyponychial angle of both index fingers. These angles were significantly greater in the group of insulators. Twenty-one insulators had ϰ-rays which showed pleural calcification with or without pulmonary fibrosis; one control ϰ-ray showed pulmonary fibrosis. The insulators had no evidence of airways obstruction but static lung volume was reduced and their arterial oxygen tension was lower than that of the controls and their alveolar-arterial oxygen gradient was greater.

In plain English

This study compared 50 randomly chosen Belfast-area asbestos insulators with 50 Belfast Corporation employees matched for age, height and smoking habit who had minimal asbestos exposure. Insulators had 4 to 48 years of asbestos exposure (mean 16.1 years). The article does not name fiber types. More insulators than controls reported cough (33 against 18) and sputum (37 against 23), and more had rales (9 against 1). Breathlessness was commoner in insulators, but the difference was not quite statistically significant. Finger measurements showed a shift toward clubbing in insulators. Twenty-one of the 50 insulators had definitely abnormal chest x-rays, against one control. Insulators had smaller static lung volumes and lower arterial oxygen tension, but unaffected airflow. The authors noted that the average lung function disturbance was relatively mild. Because 31 of the 50 control x-rays were smaller 100mm films, the comparison could have been biased, but the authors judged this could explain only a very small part of the difference. The authors concluded that these features are useful in diagnosing asbestosis in a population and that a control series is important.

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 a random sample of insulation workers with a matched control group (clinical examination, finger casts, sputum, chest x-ray and lung function tests)
• Who was studied: 53 insulators were randomly selected from the union list of all insulators in Northern Ireland, excluding men living beyond about 20 miles of Belfast. 50 were examined (94% of those selected). The 50 controls were Belfast Corporation employees: 41 in transport maintenance, 6 in the gas department, 1 plumber and 2 student laboratory technicians.
• Exposure: Work as asbestos insulators, with 4 to 48 years of exposure (mean 16.1, standard deviation 7.5 years). Fiber types are not stated. Among the controls, 12 said they occasionally cut asbestos sheeting and one had worked as an insulator for three years.
• Main results:
  • Cough (33 insulators against 18 controls) and sputum (37 against 23) were significantly more common in insulators (P less than 0.01). Dyspnoea (23 against 16) was only almost significant (P between 0.10 and 0.05).
  • Rales were found in 9 insulators and 1 control (P less than 0.02).
  • The hyponychial angle, a measure of finger clubbing, was significantly greater in insulators (right and left index fingers 184.6 and 186.0 degrees) than in controls (180.4 and 181.1 degrees).
  • Asbestos bodies were seen in the sputum of 9 of 42 insulators examined and in none of 27 control sputa.
  • 21 of the 50 insulators had definitely abnormal chest x-rays. Of these, 14 showed definite fibrosis and 1 showed pleural calcification only. One control had a definite abnormality: diffuse fibrosis not typical of asbestosis. For x-ray grades 3 to 6 combined, P was less than 0.001.
  • Insulators had significantly smaller residual volume (1.55 against 1.78 litres, P less than 0.05) and total lung capacity (5.71 against 6.16 litres, P less than 0.01). These differences were greater than predicted from age and height.
  • Insulators had lower arterial oxygen tension (85.6 against 93.4 mm, P less than 0.001) and a greater alveolar-arterial oxygen difference (24.0 against 15.5 mm, P less than 0.01). Dynamic lung volumes (airflow) showed no significant differences.
  • The authors noted that the average lung function disturbance was relatively mild despite the large excess of abnormal x-rays. They suggested that much of the dyspnoea was due to factors other than asbestos.
• The authors' conclusion: The authors concluded that an abnormal chest x-ray, cough, sputum, clubbing, rales, reduced static lung volume, reduced arterial oxygen tension and increased alveolar-arterial oxygen difference, without airways obstruction, are useful in diagnosing asbestosis in a population. Because such abnormalities occur fairly commonly in any industrial population, they considered a control series important.
• Limitations the authors state:
  • 31 of the 50 control x-rays were 100mm mass-radiography films, which could have biased the comparison. The authors judged that any such bias could account for only a very small part of the difference in definite abnormality.
  • Because not all control x-rays were full-size films, the standard ILO classification could not be used.
  • Some controls had contact with asbestos.

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, Habit, Sputum, Clubbing, Pleural Calcification, Pulmonary Fibrosis.

Related studies

• Insulation workers in Belfast. 3. Mortality 1940-66 — P.C. Elmes, M.J. Simpson (1971)
• Insulation workers in Belfast. A further study of mortality due to asbestos exposure (1940-75) — P.C. Elmes, M.J. Simpson (1977)
• Correlation between respiratory symptoms and pulmonary function in asbestos-exposed workers — C.A. Brodkin, S. Barnhart, et al. (1993)
• 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)
• The relative importance of clinical, radiological and pulmonary function variables in evaluating asbestosis and chronic obstructive airway disease in asbestos workers — G.M. Regan, B. Tagg, et al. (1971)
• Asbestosis following brief exposure in cigarette filter manufacture — A.M. Goff, E.A. Gaensler (1972)

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