Symptoms and pulmonary functions as measures of morbidity

Our plain-English summary of Symptoms and pulmonary functions as measures of morbidity, by M.R. Becklake (The Annals of Occupational Hygiene, 1994).

The study

• Author: M.R. Becklake
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):569-80, 418
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

A contemporary list of non-malignant respiratory conditions associated with exposure to environments contaminated by chrysotile asbestos dust includes pulmonary parenchymal and pleural fibrosis, small airway abnormality and conditions affecting the large airways such as chronic bronchitis and chronic airflow limitation. The first two are attributed to the specific biological effects of asbestos dust, the latter two to nonspecific effects of exposure to mineral dusts and/or other airborne pollutants in workplaces contaminated by asbestos dust. Prevalence rates for all the clinical markers of morbidity (radiographic change, lung function deficit and symptoms) have been shown to increase with increasing exposure to chrysotile but more steeply when exposure is in textile and other manufacturing plants than in mining and milling. The presence of amphiboles such as tremolite in the airborne dust may also result in steeper exposure-response relationships, while exposure in crocidolite mining results in very much steeper exposure-response relationships. Clinical asbestosis, though less frequent and less severe than previously, is still associated with increased moribidity, while localized pleural fibrosis in the form of plaques with minimal or no parenchymal fibrosis, currently the most frequently encountered non-malignant asbestos related condition encountered in clinical practice, may also be associated with morbidity, including lung function deficit. Determinants of progression of chrysotile-related parenchymal and pleural radiographic abnormality include duration and time since first exposure and, possibly, continued exposure after first appearance of radiographic changes. Progression of asbestos-related airway disease, documented as lung function loss over time, may, under the influence of continued exposure, be comparable to the progression observed under the influence of continued smoking.

In plain English

This paper was a review, read at a 1993 workshop on chrysotile asbestos. It looked at published human evidence on how symptoms, lung function and chest X-ray changes relate to asbestos exposure, mostly but seldom only to chrysotile. In the Quebec studies it reviewed, X-ray changes were more common and rose more steeply with exposure in two asbestos factories than among chrysotile miners and millers. Exposure-response slopes were steeper in the Thetford mining region than in the Asbestos area, possibly because of tremolite, and much steeper for crocidolite miners. Across reviewed studies, pleural abnormality was linked to average lung volume losses of 5 to 15%. Pleural plaques were tied to smaller lung function losses than diffuse pleural thickening. In reviewed cross-sectional studies of workers with little or no X-ray asbestosis, lung function loss linked to asbestos exposure was comparable to that linked to smoking, as in three of four longitudinal studies. The author wrote that asbestosis cannot yet be considered benign. The author noted many reviewed workforces had also been exposed to other fibres.

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: Narrative review of published human studies (workshop paper)
• Who was studied: Asbestos-exposed workforces in previously published studies. These included Quebec chrysotile miners and millers (1015 workers), a Quebec textile factory (118 workers) and a Quebec construction and insulation products factory (272 workers). Other studies covered railroad workers, plumbers and pipe fitters, sheet metal workers, insulators, asbestos cement workers and shipyard workers.
• Exposure: Mainly chrysotile, often with other fibres. These included tremolite contamination of ore, and amosite and crocidolite in some manufacturing plants. The review covered mining and milling, textile, construction and insulation products, and use or removal of asbestos-containing materials.
• Main results:
  • In the Quebec studies reviewed, X-ray abnormality was more common and rose more steeply with exposure in the textile factory and the construction and insulation products factory than among chrysotile miners and millers. Small irregular opacities (1/0 or more) were found in 20.9% of textile workers, 19.7% of construction and insulation products workers, and 7.8% of miners and millers. Pleural change was found in 15.7%, 28.0% and 4.7% respectively. Breathlessness and lung function deficits were also more frequent in the two factories.
  • Among Quebec chrysotile miners and millers, exposure-response slopes were steeper in the Thetford region than in the Asbestos area. The author suggested tremolite contamination of the ore as one possible explanation.
  • Reviewed studies reported much steeper exposure-response slopes for South African and Australian crocidolite miners than for Quebec chrysotile miners and millers.
  • In the reviewed studies, average lung volume deficits attributable to pleural abnormality ranged from 5 to 15%.
  • In three reviewed studies, circumscribed pleural plaques were associated with lung function deficit independently of diffuse pleural thickening. That deficit was less severe than the one associated with diffuse pleural thickening.
  • Reviewed studies showed that asbestosis was still accompanied by a lung function deficit.
  • Parenchymal X-ray disease progressed in 7% of 86 Quebec chrysotile production workers who left the industry in the 1950s. It progressed in 25% of 217 current and ex-workers. The author called this some evidence that continued exposure after diagnosis affected progression unfavourably.
  • In reviewed cross-sectional studies of workers with little or no X-ray asbestosis, the lung function deficit associated with asbestos exposure was comparable to that associated with smoking in the same workforces.
  • Of four reviewed longitudinal studies of asbestos-exposed workforces, three found effects of exposure comparable to those of smoking.
  • In one reviewed study of shipyard workers, the risk of dying from ischemic heart disease was increased in several groups. Risk ratios were 3.3 for impaired lung function and 3.1 for asbestosis, but plaques were not linked to increased risk. For shortness of breath, risk ratios were 3.0, 4.0 and 11.4 for grades 1 to 3.
• The authors' conclusion: The author concluded that the comparability of asbestos-related and smoking-related lung function loss added weight to the evidence that the association between lung function deficit and asbestos exposure is causal and clinically important. The author also stated that asbestosis cannot yet be considered a benign condition.
• Limitations the authors state:
  • Few of the reviewed workforces were exposed to chrysotile only.
  • In the Quebec three-workforce comparison, no analysis excluded subjects with X-ray asbestosis or pleural change. The separate roles of parenchymal and airway disease therefore could not be estimated.
  • The cross-sectional studies of airway disease could not examine time relationships or the exposure-response sequence directly.
  • In one reviewed study, the link between X-ray abnormality and higher mortality may have been confounded by cumulative exposure. More evidence is needed on whether plaques add to cancer risk.
  • Cigarette smoking confounds findings on chronic bronchitis, chronic airflow limitation and small airway abnormality.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibrosis, Amphibole Group, Tremolite, Crocidolite, Parenchymal Fibrosis.

Related studies

• The relation among pulmonary function, chest roentgenographic abnormalities, and smoking status in an asbestos-exposed cohort — L. Rosenstock, S. Barnhart, et al. (1988)
• Pulmonary functional impairment and symptoms in women in the Los Angeles Harbor area — K.H. Kilburn, R. Warshaw, et al. (1985)
• 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)
• Correlation between respiratory symptoms and pulmonary function in asbestos-exposed workers — C.A. Brodkin, S. Barnhart, et al. (1993)
• Navy Asbestos Medical Surveillance Program (1984-1990): linear regression analysis for effect of asbestos exposure on pulmonary function testing — B.K. Bohnker, L.S. Betts, et al. (2004)
• Navy Asbestos Medical Surveillance Program (1991-1999): linear regression analysis for the effect of asbestos exposure on pulmonary function testing — B.K. Bohnker, L.S. Betts, et al. (2004)

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