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Correspondence |

Lung Volumes in COPD: Not Only the Total Lung Capacity FREE TO VIEW

Simone Scarlata, MD; Luciana Paladini, MD; Matteo Cesari, MD, PhD; Raffaele Antonelli Incalzi, MD
Author and Funding Information

From the Unit of Respiratory Pathophysiology (Drs Scarlata, Paladini, Cesari, and Incalzi), Health Centre for Elderly People (CeSA), Università Campus Biomedico; the “Alberto Sordi” Foundation (Drs Scarlata, Paladini, Cesari, and Incalzi); and the “Cittadella della Carità Foundation (Dr Incalzi).

Correspondence to: Simone Scarlata, MD, Unit of Respiratory Pathophysiology, Health Centre for Elderly People (CeSA), Università Campus Biomedico, Via Alvaro del Portillo, 5, 00128 Rome, Italy; e-mail: s.scarlata@unicampus.it


Financial/nonfinancial disclosures: The authors have reported to CHEST that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;138(1):233. doi:10.1378/chest.10-0045
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To the Editor:

We read with extreme interest the recently published work by O’Donnell and colleagues (May 2010).1 Comparing lung volumes obtained using different techniques in a sample of patients with severe airflow limitation, the authors conclude that plethysmography systematically overestimates lung volumes with regard to gas dilution and thoracic imaging techniques. We believe it is meritorious to assess how the available diagnostic methods differ in determining lung volumes in the context of severe bronchial obstruction. However, we think the authors might have derived more from their data and results.

We are afraid the implementation of the present study results in the clinical setting might be limited. In fact, the main reason for measuring lung volumes in subjects with COPD is to determine the presence and degree of lung hyperinflation. To the radiologist, hyperinflation of the lungs implies an increase in total lung capacity (TLC) because this is the lung volume at which chest radiographs are normally obtained. In a clinical context, however, hyperinflation implies an abnormal increase in the volume of gas in the lungs at the end of tidal (functional residual capacity [FRC]) or maximal (residual volume [RV]) expiration.2 Moreover, hyperinflation is sometime inferred from an increase in the RV/TLC (Motley index) and the FRC/TLC ratios, commonly used as a surrogate of air trapping. Unfortunately, the authors do not mention any of these other parameters in their study. This is, in our opinion, a major concern because TLC in COPD patients varies as a function of the prevalent phenotype (increased in emphysema, often normal in chronic bronchitis); therefore, it cannot be used routinely to address pulmonary hyperinflation in COPD. Conversely, RV and FRC are strongly related to the severity of airflow obstruction.

On the one hand, Dykstra and colleagues3 did not find a significant association between TLC and the degree of airway obstruction. On the other hand, such a relationship is well established between RV/TLC or FRC/TLC, proper indexes of hyperinflation, and the severity of bronchial obstruction.4,5 Moreover, to further complicate the clinical interpretation of lung volume changes in COPD, it can be observed that RV increase usually antedates that of FRC and then TLC.6

In conclusion, the article by O’Donnell and colleagues1 has merit in documenting substantial differences in lung volumes assessed by different methods in patients with severe COPD. Future studies are needed to expand these results by evaluating how hyperinflation and air trapping contribute to explaining the observed differences.

O’Donnell CR, Bankier AA, Stiebellehner L, Reilly JJ, Brown R, Loring SH. Comparison of plethysmographic and helium dilution lung volumes: which is best in COPD? Chest. 2010;1375:1108-1115. [CrossRef] [PubMed]
 
Gibson GJ. Pulmonary hyperinflation a clinical overview. Eur Respir J. 1996;912:2640-2649. [CrossRef] [PubMed]
 
Dykstra BJ, Scanlon PD, Kester MM, Beck KC, Enright PL. Lung volumes in 4,774 patients with obstructive lung disease. Chest. 1999;1151:68-74. [CrossRef] [PubMed]
 
Burrows B, Strauss RH, Niden AH. Chronic obstructive lung disease. 3. Interrelationships of pulmonary function data. Am Rev Respir Dis. 1965;91:861-868. [PubMed]
 
Bégin P, Grassino A. Inspiratory muscle dysfunction and chronic hypercapnia in chronic obstructive pulmonary disease. Am Rev Respir Dis. 1991;1435 Pt 1:905-912. [PubMed]
 
Pellegrino R, Brusasco V. On the causes of lung hyperinflation during bronchoconstriction. Eur Respir J. 1997;102:468-475. [CrossRef] [PubMed]
 

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References

O’Donnell CR, Bankier AA, Stiebellehner L, Reilly JJ, Brown R, Loring SH. Comparison of plethysmographic and helium dilution lung volumes: which is best in COPD? Chest. 2010;1375:1108-1115. [CrossRef] [PubMed]
 
Gibson GJ. Pulmonary hyperinflation a clinical overview. Eur Respir J. 1996;912:2640-2649. [CrossRef] [PubMed]
 
Dykstra BJ, Scanlon PD, Kester MM, Beck KC, Enright PL. Lung volumes in 4,774 patients with obstructive lung disease. Chest. 1999;1151:68-74. [CrossRef] [PubMed]
 
Burrows B, Strauss RH, Niden AH. Chronic obstructive lung disease. 3. Interrelationships of pulmonary function data. Am Rev Respir Dis. 1965;91:861-868. [PubMed]
 
Bégin P, Grassino A. Inspiratory muscle dysfunction and chronic hypercapnia in chronic obstructive pulmonary disease. Am Rev Respir Dis. 1991;1435 Pt 1:905-912. [PubMed]
 
Pellegrino R, Brusasco V. On the causes of lung hyperinflation during bronchoconstriction. Eur Respir J. 1997;102:468-475. [CrossRef] [PubMed]
 
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