Effects of spirometry standards in two occupational cohorts

Our plain-English summary of Effects of spirometry standards in two occupational cohorts, by E.A. Eisen, L.C. Oliver, D.C. Christiani, et al (The American Review of Respiratory Disease, 1985).

The study

• Authors: E.A. Eisen, L.C. Oliver, D.C. Christiani, J.M. Robins, D.H. Wegman
• Journal: The American Review of Respiratory Disease
• Published: 1985;132(1):120-4
• Cited by: 61 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. 001148).

Abstract

Characteristics of subjects with nonreproducible lung function tests (test failures) are described in two studies of occupational respiratory disease. According to current guidelines for spirometry, subjects with test failure are excluded from analyses of epidemiologic pulmonary function data. Among 415 Chinese cotton textile workers, the prevalence of byssinosis was 5.8% for subjects with repeatable tests and 13.3% for subjects with test failure. In regression analysis, the estimate of the association between cotton dust exposure and FEV1 decreased when subjects with test failure were excluded. In a second cohort of 378 asbestos-exposed machinists, the prevalence of chronic bronchitis was significantly greater among those with test failure. Considering only subjects with repeatable measurements, FEV1 was lower among textile workers with byssinosis and machinists with chronic bronchitis than among their asymptomatic coworkers. This suggests that, on average, subjects with poor test performance had lower (unobserved) FEV1 values, and therefore that the exclusion of subjects with test failure may cause selection bias.

In plain English

This paper examined workers whose lung function (FEV1) tests were not repeatable, whom guidelines exclude from analyses. The authors reexamined two earlier cross-sectional studies: 415 cotton textile workers in Shanghai, China, and 378 asbestos-exposed railroad machinists in Pennsylvania. Among cotton workers, 18 of 310 (5.8%) with no test failures had byssinosis, versus 14 of 105 (13.3%) with one or two failures. Adjusting for age and smoking, workers with byssinosis had 2.53 times the odds of exclusion for test failure (95% confidence interval 1.21 to 5.32). For machinists with chronic bronchitis, the adjusted odds ratio for test failure was 2.00 (95% confidence interval 1.12 to 3.59). Among those with repeatable tests, symptomatic workers had lower FEV1: 92 versus 100% of predicted for cotton workers with and without byssinosis, and 89 versus 112% for machinists with and without chronic bronchitis. The authors concluded that the repeatability rule excludes people with the poorest lung function and can underestimate exposure effects. They said the cotton-worker findings alone were not conclusive, but called the evidence strong once the lung-function comparisons were added.

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: Methodological analysis of two previously conducted cross-sectional occupational studies, comparing workers with and without nonrepeatable FEV1 tests (test failures)
• Who was studied: 415 cotton textile workers at 2 plants in Shanghai, China, studied in 1981, with a comparison group of 406 unexposed silk workers. 378 active and retired machinists from a central Pennsylvania railroad yard, examined in a 1982 voluntary health survey.
• Exposure: Cotton dust for the textile workers, with an average area concentration of 1.022 mg/m3. Asbestos for the railroad machinists, with no fiber type named: exposure was relatively heavy before steam engines were replaced by diesel locomotives in 1954-1955, and moderate until 1959.
• Main results:
  • Cotton workers, preshift test: byssinosis was reported by 6.6% of workers with a repeatable test, compared with 13.8% of the 65 workers with a test failure.
  • Cotton workers, test failures before or after the shift: byssinosis was found in 18 (5.8%) of 310 workers with no test failures and in 14 (13.3%) of 105 workers with 1 or 2 test failures.
  • If a repeatable test were required at each survey, 14 of the 32 cotton workers with byssinosis would have been excluded from the analysis.
  • Cotton workers: after controlling for age and smoking status, the odds ratio for exclusion was 2.53 (95% confidence interval 1.21, 5.32) for workers with byssinosis compared with those without.
  • Male cotton and silk workers: the estimated dose-response slope for cumulative cotton dust exposure and FEV1 was -1.77 (p = 0.077) in the model with all men. It was -1.56 (p = 0.491) in the model with only men who had repeatable tests. The trends were the same for women, but the associations were smaller.
  • Machinists: those with test failures were 5 years older and had smoked more than coworkers with repeatable tests. The authors reported they also had significantly more chronic bronchitis and pleural plaques (definite or suspect). Table 6 gives chronic bronchitis as 29 (44.4%) among the 67 with test failure versus 82 (26.2%) among the 311 with test success, and plaques as 20 (29.9%) versus 66 (21.2%).
  • Machinists: adjusting for age and pack-years of smoking, the odds ratio for test failure in those with chronic bronchitis was 2.00 (95% confidence interval 1.12, 3.59). Age was also significant, with an odds ratio of 1.03. Smoking was no longer significantly associated with test failure.
  • Among workers with repeatable tests only, mean FEV1 as percent of predicted was significantly lower in the symptomatic group of each cohort. It was 92% versus 100% for cotton workers with and without byssinosis, and 89% versus 112% for machinists with and without chronic bronchitis.
• The authors' conclusion: The authors concluded that the data provide strong evidence that requiring reproducible tests excludes subjects with the poorest lung function. In their view, this causes a loss of statistical power and underestimates dose-response relationships when a true exposure effect exists. They suggested relaxing the reproducibility criterion, using the maximal effort, and comparing excluded subjects with the rest of the cohort.
• Limitations the authors state:
  • The cotton-worker symptom and regression results alone were not conclusive evidence of bias. Higher exposures might be associated with poor test performance rather than with lower FEV1. The authors then used the lung-function comparisons to argue that the excluded workers' unobserved FEV1 values were likely lower.
  • No data were available on machinists who did not perform even one acceptable tracing.
  • In the textile study, associations of age and smoking with test failure could not be examined because the cohort was young and had few pack-years of smoking.
  • A different technician collected the spirometry data in each study. The authors considered it plausible, though not directly addressed, that differences in technician training or skill affected test acceptability rates.
  • The cutoff used to classify a test as reproducible is arbitrary. A 200 ml cutoff would have excluded about half as many subjects.

Topics

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

Medical terms in this study, explained in our Lexicon: Spirometry, FEV1, Selection Bias.

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