The relative importance of clinical, radiological and pulmonary function variables in evaluating asbestosis and chronic obstructive airway disease in asbestos workers

Our plain-English summary of The relative importance of clinical, radiological and pulmonary function variables in evaluating asbestosis and chronic obstructive airway disease in asbestos workers, by G.M. Regan, B. Tagg, J. Walford, et al (Clinical Science, 1971).

The study

• Authors: G.M. Regan, B. Tagg, J. Walford, M.L. Thomson
• Journal: Clinical Science
• Published: 1971;41(6):569-82
• Cited by: 23 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. 001373).

Abstract

1. The relative power of sixteen clinical, radiological and pulmonary function variables for evaluating asbestosis and chronic obstructive airway disease has been assessed by principal component analysis of the data from a survey of 201 asbestos workers. 2. A decrease in the transfer factor (diffusing capacity) for carbon monoxide followed by a decrease in the vital capacity had the greatest power to measure the severity of both types of disease but had little ability to distinguish between the two. 3. In decreasing order of potency, the best indicators for distinguishing between asbestosis and obstructive airway disease were forced expiratory volume as a proportion of vital capacity, phlegm, radiological pleural thickening, cough and finger clubbing. Low values in FEV/VC and high values in phlegm and cough indicated obstructive airway disease: high values of pleural thickening and finger clubbing indicated asbestosis in the present context. 4. The analysis also provided numerical scores for each individual that could be plotted on a two-dimensional diagram. Orientation along one axis showed the degree of involvement of individuals by lung disease, whereas separation along the other axis depended on the nature of the disease process, asbestosis and obstructive airway disease in this instance.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This was a survey of 201 male asbestos workers from three factories that made brake linings and insulating materials. All had worked with raw asbestos for at least 3 years. The article does not name the asbestos fiber type. The authors used a statistical method called principal component analysis on sixteen clinical, X-ray and lung function measurements. They wanted to see which measurements best showed lung disease and which best told asbestosis apart from chronic obstructive airway disease. A fall in the transfer factor (how well the lungs pass carbon monoxide into the blood), followed by a fall in vital capacity, best measured how severe either disease was, but did little to tell the two apart. The best separators, in order, were FEV/VC (forced expiratory volume as a proportion of vital capacity), phlegm, pleural thickening on X-ray, cough and finger clubbing. Twenty-four workers were certified with asbestosis, either at the survey or 1 to 3 years later. All but two of them fell in the area of the plot that the authors linked to asbestosis. The authors concluded the method offered objective help, at least in the population studied. They noted it probably could not separate the effects of age from those of exposure.

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 analysed by principal component analysis of sixteen clinical, radiological and pulmonary function variables
• Who was studied: 201 Caucasian male workers who had worked with raw asbestos in three factories for at least 3 years. They were drawn from 291 eligible workers, of whom 256 volunteered; 55 were excluded for missing observations (50) or other inhalation exposures (5). Fourteen of the 201 were already certified as having asbestosis at the survey.
• Exposure: Work with raw asbestos in manufacture of brake linings and insulating materials; exposure expressed as number of years from first exposure; fiber type not stated
• Main results:
  • In all 201 workers, a decrease in transfer factor followed by a decrease in vital capacity had the greatest power to measure severity of both asbestosis and obstructive airway disease, but little ability to distinguish between them
  • The most important variables for discriminating asbestosis from obstructive airway disease were, in order, FEV/VC, phlegm, X-ray pleural thickening, cough and finger clubbing
  • Low FEV/VC and high phlegm and cough pointed to obstructive airway disease; high pleural thickening and finger clubbing pointed to asbestosis in this context
  • Of the 24 workers certified with asbestosis (14 at the survey, 10 within 1 to 3 years afterwards), all but two lay in the upper left quadrant of the plot. Of the 13 with presumptive obstructive airway disease, all but two lay in the lower left quadrant.
  • The analysis placed in the asbestosis quadrant nine subjects who were certified 1 to 3 years after the survey
  • Crepitations, clubbing and X-ray abnormalities had high and almost equal weightings as indicators of asbestosis
  • Holding other variables constant, older workers were more likely to have lung disease
  • Of 156 sputum specimens, 46 (30%) had asbestos bodies and 98 (63%) had asbestos fibres. The counts showed little correlation with the main indicators of asbestosis or with exposure, so they were left out of the analysis.
• The authors' conclusion: The authors concluded that the analysis agreed well with official certification of asbestosis. They said principal component analysis offers objective help in assessing these workers, at least in the population their study group represents.
• Limitations the authors state:
  • The first two components (26% and 13%) accounted for only 39% of the total variance
  • The analysis was probably unable to separate the effects of age and exposure, because few young workers had long exposure and few old workers had short exposure
  • Twenty-eight subjects were left out because the membrane component (Dm) could not be measured for technical reasons; the authors concluded this introduced no bias
  • Total lung capacity was excluded because field conditions likely caused it to be underestimated in some cases of airway obstruction
  • The transfer factor's measurement error is almost certainly greater than that of vital capacity
  • The simplified X-ray coding might be improved in larger populations

Topics

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

Medical terms in this study, explained in our Lexicon: Diffusing Capacity (DLCO), Pleural Thickening, Clubbing.

Related studies

• Total lung capacity. An insensitive measure of impairment in patients with asbestosis and chronic obstructive pulmonary disease? — S. Barnhart, L.D. Hudson, et al. (1988)
• Pulmonary function of nonsmoking female asbestos workers without radiographic signs of asbestosis — X.R. Wang, E. Yano, et al. (1998)
• Auscultated forced expiratory time as a clinical and epidemiologic test of airway obstruction — D.G. Kern, S.R. Patel (1991)
• Prevalence of obstructive lung disease in a general population: relation to occupational title and exposure to some airborne agents — P.S. Bakke, V. Baste, et al. (1991)
• Correlation between respiratory symptoms and pulmonary function in asbestos-exposed workers — C.A. Brodkin, S. Barnhart, et al. (1993)
• Prevalence of chronic respiratory disease. Asbestosis in ship repair workers — B.G. Ferris, M.V. Panadive, et al. (1971)

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