LetterCorrespondence

Promoting the Inclusion of Lung Volumes in the Reversibility Evaluation

Helmi Ben Saad
Respiratory Care February 2017, 62 (2) 255-256; DOI: https://doi.org/10.4187/respcare.05277

To the Editor:

I read with great interest the recent paper of McCartney et al1 highlighting the importance of lung volumes in the investigation of reversibility of air-flow obstruction. Because lung hyperinflation has become a major concern in the management of COPD, such papers should be encouraged. However, 2 points should be highlighted.

First, in the above retrospective study,1 change in residual volume (RV) was expressed as a percentage from the initial value ([post-bronchodilator minus pre-bronchodilator]/pre-bronchodilator), and 5 thresholds (8, 10, 12, 15, and 20%) were tested. However, in the literature, other interesting ways to express reversibility with different thresholds have been evaluated. Among them, an absolute value decrease of −300 mL (post-bronchodilator minus pre-bronchodilator)2,3 or a −10% decrease from predicted value ([post-bronchodilator minus pre-bronchodilator]/predicted value)2,4 were considered as clinically important2–4. In a Tunisian study2 including 366 heavy smokers divided into 2 groups (hyperinflated [n = 314] and free from lung hyperinflation [n = 52]), it was found that in the hyperinflated group, and compared with changes in FEV1 and FVC (a 12% and 0.2-L increase), the above RV changes detected more respondents (54% for FEV1 and FVC vs 65% for RV). This was not the case for the group free from lung hyperinflation (23% for FEV1 and FVC vs 35% for RV). Moreover, in the hyperinflated group free from air flow obstruction (n = 58) and compared with changes in FEV1 and FVC, the above changes in RV detected more respondents (24% for FEV1 and FVC vs 71% for RV). According to the authors, it seems essential to include RV as a criterion of reversibility evaluation.2

Second, I agree with McCartney et al1 that “there is no clear consensus on what constitutes reversibility in subjects with air flow obstruction.”5,6 This could be a source of confusion and/or misdiagnosis for clinicians and respiratory researchers. However, to better understand how subjects with COPD respond to bronchodilators, it will be more helpful to derive post-bronchodilator spirometric norms from healthy subjects.5 However, to date, only 2 post-bronchodilator spirometric reference values in adults have been published.7,8

In conclusion, in daily practice, reversibility should be identified in all subjects with COPD using the changes not only in FEV1 and FVC as primary outcomes, but also RV. Sufficient evidence is now available to justify promoting this message, particularly through the consensus statements of highly influential organizations like the Global Initiative for Chronic Obstructive Lung Disease9 and the American Thoracic and European Respiratory Societies.10 It is time for professional societies to standardize the spirometric criteria of airway reversibility in COPD.

Footnotes

  • Dr Ben Saad has disclosed no conflicts of interest.

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