Total lung capacity. An insensitive measure of impairment in patients with asbestosis and chronic obstructive pulmonary disease?

Our plain-English summary of Total lung capacity. An insensitive measure of impairment in patients with asbestosis and chronic obstructive pulmonary disease?, by S. Barnhart, L.D. Hudson, S.E. Mason, et al (Chest, 1988).

The study

• Authors: S. Barnhart, L.D. Hudson, S.E. Mason, D.J. Pierson, L. Rosenstock
• Journal: Chest
• Published: 1988;93(2):299-302
• Cited by: 17 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. 000187).

Abstract

The total lung capacity (TLC) is frequently used as a measure of respiratory impairment in patients with asbestosis. Because asbestosis and chronic obstructive pulmonary disease (COPD) exert opposite effects on the TLC, it may be an insensitive measure of impairment in patients with both abnormalities. To assess this, we compared asbestos-exposed patients with functional evidence of COPD and radiographic evidence of interstitial fibrosis (group 1) to those with interstitial fibrosis alone (group 2). Despite the two groups being comparable in degree of radiographic "fibrosis," no case of restrictive impairment (reduced TLC) was identified among those with both interstitial fibrosis and COPD (group 1), compared to 33 percent of those with interstitial fibrosis alone (group 2). In addition, those patients with both interstitial fibrosis and COPD, compared to those with interstitial fibrosis alone, were found to have greater impairment as measured by alveolar-arterial oxygen difference and diffusing capacity. We conclude that the TLC is an insensitive measure of impairment due to asbestosis in patients with the common setting of coexistent asbestosis and COPD.

In plain English

In a retrospective chart review at the University of Washington's Occupational Medicine Program clinic in Seattle, the authors studied asbestos-exposed patients whose chest X-rays showed interstitial fibrosis (ILO profusion 1/0 or higher). They compared 17 patients who also had airflow obstruction indicating chronic obstructive pulmonary disease (COPD) (group 1) with 24 who had fibrosis alone (group 2). The groups did not differ significantly in age, smoking pack-years, years since first asbestos exposure, X-ray profusion grade or pleural abnormalities. Mean total lung capacity (TLC) was 104 percent of predicted in group 1 and 87 percent in group 2. No group 1 patient had restrictive impairment (reduced TLC), compared with eight (33 percent) in group 2. Yet group 1 had lower diffusing capacity (55 versus 66 percent of predicted) and a wider alveolar-arterial oxygen difference. The authors concluded that TLC is an insensitive test of the effect of asbestos-induced fibrosis in patients who also have COPD. They noted limitations including possible smoking-related X-ray misclassification, clinic selection bias, X-ray readers not always blinded, and a small sample.

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: Retrospective chart review comparing two groups of clinic patients (cross-sectional comparison)
• Who was studied: Patients seen in the Occupational Medicine Program's diagnostic clinic (University of Washington, Seattle) with a history of asbestos exposure. The article reports an eligible population of 141 subjects. Of these, 64 had radiographic fibrosis (ILO profusion 1/0 or higher) and 5 were excluded for incomplete data. A further 18 with intermediate FEV1/FVC ratios were not analysed. Analysis compared 17 patients with interstitial fibrosis and COPD (group 1) with 24 patients with interstitial fibrosis alone (group 2). Dates of the study period are not given.
• Exposure: History of asbestos exposure, with fiber types and jobs not specified. Smoking was also recorded. Mean pack-years were 49 (group 1) and 39 (group 2). Mean time from first asbestos exposure was 34 years (group 1) and 33 years (group 2).
• Main results:
  • Mean TLC was 104 percent of predicted in group 1 (fibrosis and COPD) versus 87 percent of predicted in group 2 (fibrosis alone), p less than 0.001.
  • Restrictive impairment was defined as TLC at least 1.65 standard deviations below predicted. It was found in no patient in group 1, compared with eight (33 percent) in group 2, p less than 0.05.
  • Within each ILO profusion category, group 1 had a greater mean TLC than group 2 (p less than 0.05).
  • Mean single-breath diffusing capacity was lower in group 1 than in group 2: 55 percent versus 66 percent of predicted, p less than 0.05.
  • Mean alveolar-arterial oxygen difference was wider in group 1 than in group 2: 212 percent versus 158 percent of predicted in the text, p less than 0.05. Table 4 prints 213 and 157.
  • There were no significant differences between the groups in age, race, height, smoking pack-years or years from first asbestos exposure.
  • Profusion grade 1/1 or higher was found in 53 percent (9/17) of group 1 and 63 percent (15/24) of group 2. Pleural abnormalities were found in 71 percent of group 1 and 92 percent of group 2. Neither difference was statistically significant.
• The authors' conclusion: The authors concluded that in patients with asbestos exposure, radiographic fibrosis and COPD, TLC is an insensitive test for the functional effect of asbestos-induced fibrosis. They said caution should be used in excluding adverse respiratory effect of asbestos exposure on the basis of TLC when airflow obstruction is present.
• Limitations the authors state:
  • Smoking could bias results and cause radiographic misclassification, possibly placing patients with only COPD into group 1.
  • COPD-related lung hyperexpansion in group 1 may have led to underestimation of small opacity profusion.
  • Because of selection into the clinic population, the results may not apply to other asbestos-exposed groups.
  • X-ray readers were not always blinded to pulmonary function results.
  • Latency (time since first exposure) may not accurately reflect differences in asbestos exposure between the groups.
  • The small sample may limit power to detect differences between groups.
  • The authors could not apportion how much COPD and asbestosis each contributed to impairment.

Topics

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

Medical terms in this study, explained in our Lexicon: Total Lung Capacity (TLC), COPD, Interstitial Fibrosis, Fibrosis, Diffusing Capacity (DLCO).

Related studies

• The relative importance of clinical, radiological and pulmonary function variables in evaluating asbestosis and chronic obstructive airway disease in asbestos workers — G.M. Regan, B. Tagg, et al. (1971)
• The validity of radiographic estimation of total lung capacity in patients with respiratory disease — G.P. Pappas, C.A. Brodkin, et al. (1998)
• 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)
• Incident chronic obstructive pulmonary disease associated with occupation, industry, and workplace exposures in the Health and Retirement Study — S.R. Silver, W.A. Alarcon, et al. (2021)
• Relationships between chronic obstructive pulmonary disease and lung cancer: biological insights — E. Barreiro, V. Bustamante, et al. (2016)
• A somatic TSHR mutation in a patient with lung adenocarcinoma with bronchioloalveolar carcinoma, coronary artery disease and severe chronic obstructive pulmonary disease — J.W. Kim, S. Lee, et al. (2012)

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