Early Diagnosis of Respiratory Abnormalities in Asbestos-Exposed Workers by the Forced Oscillation Technique

Our plain-English summary of Early Diagnosis of Respiratory Abnormalities in Asbestos-Exposed Workers by the Forced Oscillation Technique, by P.M. de Sá, H.A. Castro, A.J. Lopes, et al (PloS One, 2016).

The study

• Authors: P.M. de Sá, H.A. Castro, A.J. Lopes, P.L. Melo
• Journal: PloS One
• Published: 2016;11(9):e0161981
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The current reference test for the detection of respiratory abnormalities in asbestos-exposed workers is spirometry. However, spirometry has several shortcomings that greatly affect the efficacy of current asbestos control programs. The forced oscillation technique (FOT) represents the current state-of-the-art technique in the assessment of lung function. This method provides a detailed analysis of respiratory resistance and reactance at different oscillatory frequencies during tidal breathing. Here, we evaluate the FOT as an alternative method to standard spirometry for the early detection and quantification of respiratory abnormalities in asbestos-exposed workers.

Methodology/principal Findings: Seventy-two subjects were analyzed. The control group was composed of 33 subjects with a normal spirometric exam who had no history of smoking or pulmonary disease. Thirty-nine subjects exposed to asbestos were also studied, including 32 volunteers in radiological category 0/0 and 7 volunteers with radiological categories of 0/1 or 1/1. FOT data were interpreted using classical parameters as well as integer (InOr) and fractional-order (FrOr) modeling. The diagnostic accuracy was evaluated by investigating the area under the receiver operating characteristic curve (AUC). Exposed workers presented increased obstruction (resistance p<0.001) and a reduced compliance (p<0.001), with a predominance of obstructive changes. The FOT parameter changes were correlated with the standard pulmonary function analysis methods (R = -0.52, p<0.001). Early respiratory abnormalities were identified with a high diagnostic accuracy (AUC = 0.987) using parameters obtained from the FrOr modeling. This accuracy was significantly better than those obtained with classical (p<0.001) and InOr (p<0.001) model parameters.

Conclusions: The FOT improved our knowledge about the biomechanical abnormalities in workers exposed to asbestos. Additionally, a high diagnostic accuracy in the diagnosis of early respiratory abnormalities in asbestos-exposed workers was obtained. This makes the FOT particularly useful as a screening tool in the context of asbestos control and elimination. Moreover, it can facilitate epidemiological research and the longitudinal follow-up of asbestos exposure and asbestos-related diseases.

In plain English

This Brazilian study tested whether the forced oscillation technique (FOT), a breathing test done during normal breathing, could detect early lung-function changes in asbestos-exposed workers. The authors compared 39 exposed workers with 33 controls who had normal spirometry and no smoking or lung-disease history. Of the exposed workers, 32 had chest X-rays graded 0/0 and 7 were graded 0/1 or 1/1. The article does not state the asbestos fiber type. The exposed workers had lower spirometry values and higher resistance on FOT. Among the exposed, smokers and non-smokers did not differ significantly on spirometry or FOT results. Under a stricter cross-check called leave-one-out cross-validation, none of the standard FOT measures or simpler-model measures kept adequate accuracy. One measure from a 'fractional-order' model, inertance (L), kept an area under the curve of 0.987. In the authors' comparisons, L was significantly more accurate than the best standard FOT measure and than spirometry. The authors concluded that the FOT could serve as a screening tool. They noted limits: only 39 exposed workers, a single Brazilian site, and no gold-standard test for early damage.

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: Observational diagnostic-accuracy study of prevalent cases, comparing exposed workers with controls
• Who was studied: 72 subjects tested at the State University of Rio de Janeiro, Brazil (study dates not given). There were 33 controls with normal spirometry and no smoking or lung-disease history. There were 39 asbestos-exposed workers: 32 with chest X-rays graded 0/0 and 7 graded 0/1 or 1/1. Smoking did not exclude exposed workers. The exposed workers were older on average (62 vs 53.3 years).
• Exposure: Occupational asbestos exposure; the fiber type and jobs are not stated. Mean exposure period was 13.5 ± 10 years in the 0/0 group and 11.6 ± 6.77 years in the 0/1 to 1/1 group.
• Main results:
  • Exposed workers had significantly lower spirometry values than controls (for example, FVC 2.90 vs 3.93 L).
  • Plethysmography showed no significant decrease in mean lung volumes among exposed workers, though mean values were near the lower normal limit.
  • FOT resistance measures were higher in exposed workers than in controls (p less than 0.001), and dynamic compliance was lower.
  • Among exposed workers, 20 of 32 in category 0/0 and 3 of 7 in category 0/1 to 1/1 were current or former smokers.
  • Within the exposed group, smokers and non-smokers did not differ significantly on spirometry or FOT.
  • FOT measures correlated with spirometry at levels the authors called reasonable to moderate. Inertance (L) was most strongly associated with FEV1 in litres (R = -0.52).
  • Under leave-one-out cross-validation, no classical FOT or integer-order (eRIC) model measure reached adequate accuracy (AUC of 0.80 or more).
  • The fractional-order inertance (L) had an AUC of 0.998 in the initial ROC analysis and 0.987 under cross-validation.
  • The accuracy of L was significantly higher than that of the best classical FOT measure, Z4 (p = 0.0008), and the best eRIC measure, Rp (p = 0.0006).
  • The most accurate FOT measures always had a higher AUC than the spirometry measures. The difference was significant for L (p less than 0.005).
• The authors' conclusion: The authors concluded that fractional-order FOT measures outperformed standard and integer-order analysis. In their view, the high accuracy makes the FOT useful for early diagnosis and as a screening tool in asbestos control.
• Limitations the authors state:
  • Only 39 exposed workers were studied, so the exact sensitivity and specificity remain unknown; the authors call for larger studies.
  • The study used a single site in Brazil, and its generalizability to other populations is unknown.
  • No gold-standard test defined early respiratory changes; a clinical criterion of exposure was used to separate controls from exposed workers.
  • FOT devices are less portable than spirometers.

Topics

Medical terms in this study, explained in our Lexicon: Spirometry, Asbestos Exposure.

Related studies

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• Pulmonary function, smoking habits, and high resolution computed tomography (HRCT) early abnormalities of lung and pleural fibrosis in shipyard workers exposed to asbestos — S. Neri, P. Boraschi, et al. (1996)
• Inter-reader variability in chest radiography and HRCT for the early detection of asbestos-related lung and pleural abnormalities in a cohort of 636 asbestos-exposed subjects — E. Ochsmann, T. Carl, et al. (2010)
• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques. 1. UICC crocidolite asbestos — J.C. Evans, R.J. Evans, et al. (1973)
• Studies on the deposition of inhaled fibrous material in the respiratory tract of the rat and its subsequent clearance using radioactive tracer techniques — A. Morgan, J.C. Evans, et al. (1975)

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