Reduced diffusing capacity as an isolated finding in asbestos- and silica-exposed workers

Our plain-English summary of Reduced diffusing capacity as an isolated finding in asbestos- and silica-exposed workers, by J.G. Garcia, D.E. Griffith, J.S. Williams, et al (Chest, 1990).

The study

• Authors: J.G. Garcia, D.E. Griffith, J.S. Williams, W.J. Blevins, R.S. Kronenberg
• Journal: Chest
• Published: 1990;98(1):105-11
• Cited by: 6 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. 003859).

Abstract

From a cohort of 286 patients referred to an Occupational Medicine Clinic because of exposure to asbestos and/or silica, we identified 53 patients with a reduced diffusing capacity (Dco) (less than 75 percent predicted) as their only abnormality. Specifically, their clinical evaluation, chest roentgenograms, and remaining pulmonary function test results were all normal. These patients were divided into non-smokers (n = 13) and smokers (n = 40). The significance of the isolated reduction in diffusing capacity in these patients (n = 53) was explored with graded exercise testing (n = 19) and bronchoalveolar lavage (BAL) (n = 50). The results obtained from the patients with reduced diffusion were compared with those obtained from comparable smoking (n = 35) and nonsmoking patients (n = 37) in the original cohort who had normal chest roentgenograms and normal results of pulmonary function studies, including normal Dco values (greater than or equal to 75 percent of predicted value). Patients with low diffusion demonstrated a tendency for elevated alveolar to arterial O2 differences both at rest and during exercise, and a significant reduction in exercise capacity (VO2 max) was observed in the smoking patients with reduced diffusion when compared with their smoking counterparts with normal diffusion. All other exercise testing indexes were normal in the study groups and there was no correlation between the percent predicted Dco value and any of the exercise variables. In contrast, BAL revealed significant differences between patient groups. Both the smoking and nonsmoking patient groups with low Dco values had greater numbers of total BAL cells, alveolar macrophages, neutrophils, lymphocytes, and eosinophils in their BAL fluid than did their comparable controls with normal diffusion values. These differences were statistically significant (p less than .05) for total BAL cells and total macrophages in the nonsmoking patients and for total BAL cells, total macrophages, and total lymphocytes in the smoking patients expressed as either the total cell number per BAL or total cells per milliliter of BAL. In contrast to the observed exercise testing results, there was significant and inverse correlation between Dco values and each BAL cell type for all four groups combined as well as nonsmokers alone. The Dco values from smokers were significantly and inversely correlated with total BAL cells and total macrophages. These results suggest that the finding of a reduced Dco may be related to an active inflammatory process in the lung caused by occupational dust exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

In plain English

This study looked at workers exposed to asbestos and/or silica who were referred to an occupational medicine clinic. Most were former employees of a glass bottle manufacturing plant seen for medicolegal evaluation. Of 286 patients, 53 had a reduced diffusing capacity (Dco, a breathing test of how well gas passes into the blood) below 75 percent of predicted, while their chest X-rays and other lung function results were normal. The authors split them into 13 nonsmokers and 40 smokers and compared them with 37 nonsmokers and 35 smokers whose Dco was normal. Exercise test results were generally normal in the 35 patients tested. Smokers with low Dco had significantly lower maximum oxygen uptake than smokers with normal Dco. Lung washing (bronchoalveolar lavage) found significantly more total cells and macrophages in the low-Dco groups, and lower Dco was correlated with higher cell counts. The authors concluded that a low Dco may reflect active inflammation and may identify patients needing closer follow-up, though it may not be enough to diagnose pneumoconiosis. They noted the study was cross-sectional and few patients had exercise tests.

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: Cross-sectional study of patients retrospectively selected from a series of clinic patients, comparing workers with a low Dco to workers with a normal Dco, grouped by smoking history
• Who was studied: 286 patients referred to an occupational medicine clinic because of asbestos and/or silica exposure, most of them former employees of a glass bottle manufacturing plant referred for medicolegal evaluation. 53 had Dco below 75 percent of predicted as their only abnormality: 13 nonsmokers (group 2) and 40 smokers or ex-smokers (group 4). The comparison groups had normal Dco: 37 nonsmokers (group 1) and 35 smokers (group 3).
• Exposure: Occupational exposure to asbestos and silica, with most patients exposed to both. The article does not name the asbestos fiber type. Mean exposure was about 18.7 to 21.4 years for asbestos and 18.3 to 21.6 years for silica across the four groups.
• Main results:
  • Of the 35 patients across the four groups who completed exercise testing (5, 6, 11 and 13 per group), the exercise results were generally normal.
  • Smokers with low Dco (group 4, 13 tested) had a statistically significant reduction in maximum oxygen uptake compared with smokers with normal Dco (group 3, 11 tested): mean 69.8 versus 86.3 percent of predicted.
  • Among the 8 low-Dco patients exercised with arterial blood gas measurements, 4 had an increased alveolar to arterial oxygen difference. Dco values were not correlated with any of the exercise variables.
  • Both low-Dco groups had more total lavage cells, macrophages, neutrophils, lymphocytes and eosinophils than their normal-Dco comparison groups. Total lavage cells were 11.45 in nonsmokers with low Dco versus 6.09 in nonsmokers with normal Dco, and 20.5 in smokers with low Dco versus 13.0 in smokers with normal Dco. The differences were statistically significant for total cells and macrophages in both low-Dco groups.
  • Dco was inversely correlated with every lavage cell type in all groups combined and in nonsmokers. For total cells, r = -.33 (p = .001) combined and r = -.38 (p = .008) in nonsmokers. In smokers, Dco was significantly correlated only with total cells (r = -.24, p = .03) and macrophages (r = -.25, p = .03).
• The authors' conclusion: The authors concluded that the inflammatory cells found by lavage suggest that a low Dco may reflect active inflammation in these patients, independent of smoking. This may not be enough to diagnose pneumoconiosis, but it may indicate patients who need closer follow-up. They also concluded that, on these data, follow-up did not appear to require noninvasive exercise testing.
• Limitations the authors state:
  • The authors stated that the study did not provide enough information to answer its original question about the significance of an isolated low Dco.
  • The study was cross-sectional, with no follow-up information.
  • There were no tissue samples to compare lung structure with lung function.
  • Only a small number of patients had exercise testing.
  • Only graded exercise was performed, with no steady-state measurements, so small changes in gas exchange may have been hard to detect.
  • Cigarette smoking was a major confounding factor.

Topics

Medical terms in this study, explained in our Lexicon: Diffusing Capacity (DLCO), Pulmonary Function Test (PFT), Bronchoalveolar Lavage (BAL), Alveolar Macrophage, BAL Fluid, Macrophage.

Related studies

• Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening — A. Miller, R. Warshaw, et al. (2013)
• Association between neutrophil concentration in bronchoalveolar lavage fluid and recent losses in diffusing capacity in men formerly exposed to asbestos — M.R. Cullen, W.W. Merrill (1992)
• Lung diffusing capacity relates better to short-term progression on HRCT abnormalities than spirometry in mild asbestosis — C.R. Nogueira, L.M. Nápolis, et al. (2011)
• Single breath diffusing capacity in the industrial setting — B. Make, A. Miller, et al. (1982)
• Relationship of mortality, occupation, and pulmonary diffusing capacity to pleural thickening in the First National Health and Nutrition Examination Survey — D.P. Loomis, G.W. Collman, et al. (1989)
• Biphasic lung diffusing capacity: detection of early asbestos induced changes in lung function — Z. Dujić, J. Tocilj, et al. (1992)

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