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How To Measure Lung Volume? FREE TO VIEW

Dan C. Stǎnescu, MD, PhD, FCCP
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From the Cliniques Universitaires Saint Luc, Université Catholique de Louvain.

Correspondence to: Dan C. Stănescu, MD, PhD, FCCP, Cliniques Universitaires Saint Luc, Université Catholique de Louvain, Av Hippocrate 10, Brussels, 1200, Belgium; e-mail: dcstanescu@gmail.com


Financial/nonfinancial disclosures: The author has 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 (http://www.chestpubs.org/site/misc/reprints.xhtml).


© 2010 American College of Chest Physicians


Chest. 2010;138(5):1280-1281. doi:10.1378/chest.10-1369
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To the Editor:

In their recent article in CHEST (May 2010), O’Donnell et al1 report data on total lung capacity (TLC) in 132 patients with airflow obstruction from three hospitals. TLC measured using plethysmography was significantly larger than both TLC of helium (He) and TLC derived from CT scan measurements.

The CT scan is a new method for measuring lung volume. One would expect that the authors, before applying it to patients with airflow obstruction, would compare it with established methods in healthy subjects. Surprisingly, the authors provide practically no information on its validity. General considerations are not a substitute for evidence.

Their findings may be explained by an underestimation of lung volumes using the CT scan method resulting from submaximal inspiration in the supine position. Indeed, vital capacity was not measured in both sitting and supine positions. It is lower in the latter position compared with the former. At one hospital, with patients in the supine position, lung volume was monitored, but not measured, spirometrically during CT scan measurements. At another hospital, “subjects were read instructions from a prepared script.” At a third, “subjects were well practiced in the procedure.”

Measurements of lung volumes were done at three different hospitals–one across the ocean–with three different sets of equipment and with at least three different technicians. No preliminary validation of the accuracy of the measurements with each set of equipment and no comparison of the performances of the different technicians were done, with either regular quality controls and biologic controls. These methodologic problems affect the credibility of the arguments of the authors.

In patients with moderate to severe airflow obstruction, lung spaces are closed. The volume of these spaces is measured using plethysmography. It should be also measured using CT scans, but not using He dilution. Surprisingly, the authors report quite similar results for CT scans and He dilution.

The authors tend to discredit the plethysmographic method, stating, “With the assumption that Pleth[ysmography] was accurate…. Medical texts began to reflect the conclusion that TLC was increased in various obstructive pathologies.” However, they omit mention that this conclusion was reached before 1982. Then and later, it was shown that plethysmography systematically overestimates lung volume in patients with airflow obstruction when they are panting at ≥2 Hz. However, panting at ≤1 Hz corrects the overestimation of lung volume.2-4 Furthermore, O’Donnell et al1 failed to mention data5 showing that interregional pressure differences in patients with airflow obstruction, a hypothesis they favor, are unlikely to explain errors in lung volume using plethysmography.

O’Donnell CR, Bankier AA, Stiebellehner L, Reilly JJ, Brown R, Loring SH. Comparison of plethysmographic and helium dilution lung volumes: which is best for COPD? Chest. 2010;1375:1108-1115. [CrossRef] [PubMed]
 
Rodenstein DO, Stănescu DC, Francis C. Demonstration of failure of body plethysmography in airway obstruction. J Appl Physiol. 1982;524:949-954. [PubMed]
 
Rodenstein DO, Stănescu DC. Frequency dependence of plethysmographic volume in healthy and asthmatic subjects. J Appl Physiol. 1983;541:159-165. [PubMed]
 
Shore SA, Huk O, Mannix S, Martin JG. Effect of panting frequency on the plethysmographic determination of thoracic gas volume in chronic obstructive pulmonary disease. Am Rev Respir Dis. 1983;1281:54-59. [PubMed]
 
Rodenstein DO, Francis C, Stănescu DC. Airway closure in humans does not result in overestimation of plethysmographic lung volume. J Appl Physiol. 1983;556:1784-1789. [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 for COPD? Chest. 2010;1375:1108-1115. [CrossRef] [PubMed]
 
Rodenstein DO, Stănescu DC, Francis C. Demonstration of failure of body plethysmography in airway obstruction. J Appl Physiol. 1982;524:949-954. [PubMed]
 
Rodenstein DO, Stănescu DC. Frequency dependence of plethysmographic volume in healthy and asthmatic subjects. J Appl Physiol. 1983;541:159-165. [PubMed]
 
Shore SA, Huk O, Mannix S, Martin JG. Effect of panting frequency on the plethysmographic determination of thoracic gas volume in chronic obstructive pulmonary disease. Am Rev Respir Dis. 1983;1281:54-59. [PubMed]
 
Rodenstein DO, Francis C, Stănescu DC. Airway closure in humans does not result in overestimation of plethysmographic lung volume. J Appl Physiol. 1983;556:1784-1789. [PubMed]
 
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