Longitudinal decline in lung function in former asbestos exposed workers

Our plain-English summary of Longitudinal decline in lung function in former asbestos exposed workers, by E. Algranti, E.M. Mendonça, E. Hnizdo, et al (Occupational and Environmental Medicine, 2013).

The study

• Authors: E. Algranti, E.M. Mendonça, E. Hnizdo, E.M. De Capitani, J.B. Freitas, V. Raile, M.A. Bussacos
• Journal: Occupational and Environmental Medicine
• Published: 2013;70(1):15-21
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: This study was designed to assess the effect of asbestos exposure on longitudinal lung function decline.

Methods: A group of 502 former asbestos-cement workers with at least two spirometry tests 4 years apart. Repeated evaluations included respiratory symptoms questionnaire, spirometry and chest imaging. Asbestos exposure was ascertained as years of exposure, an index of cumulative exposure and latency time. The mixed effects model was used to evaluate the effect of exposure on the level and rate of change in forced expiratory volume in 1 s (FEV(1)) and forced vital capacity (FVC).

Results: Mean age at entry was 51 (SD 9.9) years, mean latency time 25.6 (SD 10.0) years, mean follow-up time 9.1 (SD 2.8) years and mean number of spirometry tests 3.5. The FEV(1) level was significantly related to pack-years of smoking at entry and during the follow-up, the index of cumulative asbestos exposure at entry, and the presence of asbestosis at follow-up. The FVC level was significantly related to pack-years of smoking during the follow-up, cumulative asbestos exposure at entry, asbestosis and pleural thickening at follow-up, and body mass index at entry. Asbestos exposure was not associated with increasing rates of FEV(1) and FVC decline. However, FEV(1) regression slopes with age, estimated by terciles of cumulative exposure, showed significant differences. Combined effects of smoking and exposure conferred further acceleration in lung function decline.

Conclusions: Occupational exposure in asbestos-cement industry was a risk factor for increased lung function decline. The effect seems to be mostly concentrated during the working period. Smoking and exposure had synergic effects.

In plain English

The authors followed 502 former workers from one asbestos-cement plant in Brazil. The workers were first examined between 1995 and 2005 and had at least two breathing tests (spirometry) 4 or more years apart. Average follow-up was 9.1 years. The plant used chrysotile from 1941 to 1992 and smaller amounts of crocidolite in pipe production until 1979. Lacking fibre measurements, the authors estimated exposure with a job dustiness index. Higher cumulative exposure was associated with lower lung function. At the group's average index, the estimated loss was 125 ml in FEV1 (air blown out in one second) and 136 ml in FVC (total air blown out), compared with 121 ml of FEV1 from 20 pack-years of smoking. Asbestosis was associated with a loss of about 200 ml in FEV1 and FVC. In the main models, exposure was not significantly associated with a faster yearly decline. Heavier smokers in the highest exposure third declined more steeply than non-smokers in the lowest. The authors concluded the exposure effect was mostly concentrated during the working period.

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: Longitudinal (repeated-measurement) study of a cohort of former workers, analysed with linear mixed effects models
• Who was studied: 502 former asbestos-cement workers from one plant in Brazil, drawn from 947 first examined between 1995 and 2005, with at least two spirometry tests 4 or more years apart (data ending May 2010); mean age at entry 51.2 years, mean follow-up 9.1 years
• Exposure: Dust at an asbestos-cement plant: chrysotile (Brazilian or imported) from 1941 until 1992, crocidolite in smaller amounts in pipe production until 1979. Exposure was measured as years of exposure (mean 13.5), latency, and a semiquantitative cumulative exposure index (years in each job times a 1 to 10 dustiness score; mean 87.6)
• Main results:
  • The 502 subjects had 1778 spirometry tests in total, a mean of 3.5 per subject; the mean group FEV1 slope was −38 ml/year
  • At the cohort's mean cumulative exposure index (87.6), the estimated loss was 125 ml in FEV1 and 136 ml in FVC levels, compared with a 121 ml FEV1 loss from smoking 20 pack-years at entry
  • Asbestosis was associated with a loss of about 200 ml in FEV1 and FVC levels
  • Pleural thickening (score 1) was associated with a mean FVC loss of 82.5 ml, and each kg/m2 unit of BMI with 23 ml
  • In the main models, neither cumulative exposure nor asbestosis was significantly associated with the rate of decline over follow-up; only pack-years between evaluations was
  • By thirds (terciles) of cumulative exposure, annual FEV1 decline was 37.2, 39.8 and 38.3 ml/year; the slopes differed significantly by analysis of variance, and the highest-exposure third started at a lower FEV1 level
  • Heavier smokers in the highest exposure third, compared with non-smokers in the lowest exposure third, started 396 ml lower in FEV1 at age 40 and declined more steeply
  • When stratified by smoking, the cumulative exposure index was a significant term only for non-smokers
• The authors' conclusion: The authors concluded that cumulative exposure was related to lower FEV1 in a dose-response manner. No significant association with the FEV1 slope over follow-up was shown, which they took to mean the effect of exposure was mostly concentrated during the working period. They also concluded that smoking and exposure combined increased the rate of FEV1 decline.
• Limitations the authors state:
  • Exposure was assessed with a semiquantitative index because there were no objective fibre measurements
  • Changes in production methods and plant environment over time were not taken into account in the cumulative exposure
  • Possible non-participation bias: compared with non-participants, participants were older, more exposed and had more pleural thickening and asbestosis
  • Subjects may have had further harmful exposures after leaving the asbestos-cement industry
  • Concomitant exposure to cement dust may have played a role in lung function decline
  • Diffusing capacity (DLCO) could not be evaluated because only a subset had routine DLCO testing

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 Exposure, Asbestos-Cement, Spirometry, Cumulative Exposure, Latency, Pleural Thickening, Occupational Exposure.

Related studies

• Decline in annual lung function in workers exposed to asbestos with and without pre-existing fibrotic changes on chest radiography — T. Nakadate (1995)
• Risk and significance of chest radiograph and pulmonary function abnormalities in an elderly cohort of former nuclear weapons workers — M.A. Mikulski, P.G. Hartley, et al. (2011)
• 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)
• Lung function not affected by asbestos exposure in workers with normal Computed Tomography scan — C. Schikowsky, M.K. Felten, et al. (2017)
• Lung function among asbestos cement factory workers: cross-sectional and longitudinal study — A. Siracusa, C. Cicioni, et al. (1984)
• Ventilatory function after exposure to various respirable hazards in a population of former coal miners — G.M. Calvert, M. Moore, et al. (1991)

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