Decline in annual lung function in workers exposed to asbestos with and without pre-existing fibrotic changes on chest radiography

Our plain-English summary of Decline in annual lung function in workers exposed to asbestos with and without pre-existing fibrotic changes on chest radiography, by T. Nakadate (Occupational and Environmental Medicine, 1995).

The study

• Author: T. Nakadate
• Journal: Occupational and Environmental Medicine
• Published: 1995;52(6):368-73
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To examine whether or not workers with pre-existing mild pulmonary fibrosis have accelerated decline in forced expiratory volume in one second (FEV1) or forced vital capacity (FVC), under low level exposure to chrysotile asbestos.

Methods: All male workers in two asbestos manufacturing factories were followed up annually for six years to compare their declines in FEV1 and FVC. The values of FEV1 and FVC were divided by the square of the person's height to adjust for body size differences (FEV1/Ht2 and FVC/Ht2, respectively). Annual change was calculated for each subject as a slope of the simple linear regression with FEV1/Ht2 or FVC/Ht2 regressed according to age. Analysis was conducted on 242 middle aged workers who had normal routine spirometry values, normal chest radiographs or mild pneumoconiosis up to 1/2 grade, without changes either in smoking habit or severity of pneumoconiosis during the study period, and with acceptable spirograms in three or more surveys. The occupational environment, in terms of chrysotile asbestos, had been well controlled below the threshold limit value of Japan at that time--namely, 2 fibres/micromilligrams. RESULTS-There was no significant effect from the interaction between pre-existing mild pulmonary fibrosis and low level of exposure to chrysotile asbestos on the accelerated annual decline of FEV1/Ht2, or FVC/Ht2. Fibrosis significantly contributed to annual changes in FEV1/Ht2, even after adjustment for mean FEV1 and smoking. The point estimate of the contribution was - 4.9 ml/m2/y. No significant independent contribution of exposure was found in decline of either FEV1/Ht2 or FVC/Ht2.

Conclusions: Pre-existing pulmonary fibrosis is an independent risk factor for accelerated annual decline of FEV1, even when mild and stable. Additional decline due to exposure to chrysotile asbestos is less probable if it is well controlled under the current threshold limit value.

In plain English

The author followed male workers at two Japanese asbestos factories, testing their breathing and taking chest X-rays yearly from 1985 to 1991, except 1987. The analysis covered 242 middle-aged workers with normal lung function at the start and chest X-rays that stayed normal or showed stable mild fibrosis (pneumoconiosis grades 1/0 to 1/2). Workplace records showed time-weighted average chrysotile asbestos concentrations below 0.5 fibres/ml; personal exposure levels were not available. Workers with more than one year in asbestos-processing areas were counted as exposed. After adjusting for smoking and average lung function, mild fibrosis was linked to a faster yearly fall in FEV1 (air blown out in one second) divided by height squared: 4.9 ml/m2. The author equated this to 13 ml of FEV1 a year at 165 cm height. Its effect on forced vital capacity was not statistically significant. Neither asbestos exposure alone nor its combination with fibrosis showed a statistically significant effect. The author concluded that pre-existing fibrosis, even mild and stable, is an independent risk factor for faster FEV1 decline. The author noted the few subjects and missing data on past 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: Longitudinal follow-up study of a factory workforce, with spirometry, chest radiography and questionnaire repeated annually
• Who was studied: Male workers at two asbestos manufacturing factories in Japan, followed 1985 to 1991. The original sample was 351 workers who had worked there three years or more in that period. 242 middle-aged workers (aged 30 or over at first examination) were analysed. They had normal routine spirometry, chest X-rays that were normal or showed mild pneumoconiosis up to grade 1/2, and no change in smoking habit or pneumoconiosis grade during follow-up.
• Exposure: Chrysotile asbestos used in making calcium silicate boards, joint and sealing materials and insulating products. Workplace monitoring records showed the time-weighted average concentration controlled below 0.5 fibres/ml, against a Japanese permissible level of two fibres/ml for chrysotile. Personal exposure levels and past cumulative exposure could not be obtained. Workers with more than one year in asbestos-processing work areas during follow-up were classed as exposed. Higher past exposure (before the mid-1970s) was considered probable.
• Main results:
  • In a simple, unadjusted comparison, workers with mild pneumoconiosis tended to show faster annual declines in height-adjusted FEV1 and FVC than workers without it.
  • The combination of pneumoconiosis and asbestos exposure (interaction) was not statistically significant: P = 0.15 for the FEV1/Ht2 slope and P = 0.45 for the FVC/Ht2 slope.
  • After adjustment for smoking and FEV1/Ht2 level, mild pneumoconiosis was associated with an extra annual decline of 4.9 ml/m2/y in FEV1/Ht2 (SEM 1.9, P 0.01 in table 5). The author states this corresponds to an additional annual FEV1 loss of 13 ml for a worker of average height, 165 cm.
  • For FVC/Ht2, pneumoconiosis showed a similar tendency (-3.7 ml/m2/y, SEM 2.3, P 0.10 in table 5), but it was not statistically significant.
  • Asbestos exposure had no statistically significant independent effect on either slope. For FEV1/Ht2 the estimate was -0.8 ml/m2/y (SEM 1.4, P 0.58). For FVC/Ht2 it was -1.6 ml/m2/y (SEM 1.7, P 0.36).
  • Smoking was associated with faster FEV1/Ht2 decline: -2.7 ml/m2/y per pack a day (SEM 1.4, P 0.05). It was not associated with FVC/Ht2 decline: -1.0 ml/m2/y (SEM 1.7, P 0.54).
• The authors' conclusion: The author concluded that pre-existing pulmonary fibrosis, even when mild and stable, is an independent risk factor for accelerated annual decline of FEV1 irrespective of exposure. The author also found no definite evidence of an interaction between mild fibrosis and low chrysotile exposure.
• Limitations the authors state:
  • The study was based on only a few subjects, and exposure before the start of the study was not considered. The author stated that further investigation is needed.
  • Because the exposed group was small, a real interaction could have been missed (type 2 error).
  • Neither a reliable estimate of past cumulative exposure nor each worker's personal exposure level during the study could be obtained. Exposure was therefore classified by work area.
  • Selection bias (the healthy worker effect) was possible: susceptible workers may have been transferred out of asbestos work before the study began. The author judged it unlikely to have seriously biased the results.
  • Fibrosis may simply be a marker of past heavy exposure rather than of susceptibility to faster FEV1 decline.

Topics

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

Medical terms in this study, explained in our Lexicon: Pulmonary Fibrosis, FEV1, Chrysotile, Spirometry, Chest X-Ray, Pneumoconiosis, Habit, Spirogram.

Related studies

• Relationship between chest X-ray findings and pulmonary function tests in dust workers — Y. Tonori, M. Niitsuya, et al. (2005)
• Lung function and radiographic change in chrysotile workers in Swaziland — M. McDermott, M.M. Bevan, et al. (1982)
• Longitudinal decline in lung function in former asbestos exposed workers — E. Algranti, E.M. Mendonça, et al. (2013)
• Agreement between chest radiography and high-resolution computed tomography in diagnosing dust-related interstitial lung fibrosis — R.R. Tiwari (2015)
• Screening of miners and millers at decreasing levels of asbestos exposure: comparison of chest radiography and thin-section computed tomography — M. Terra-Filho, E. Bagatin, et al. (2015)
• High resolution computed tomography and lung function in asbestos-exposed workers with normal chest radiographs — C.A. Staples, G. Gamsu, et al. (1989)

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