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Correspondence |

FVC, Total Lung Capacity, and the Differential Association to MortalityFVC, Total Lung Capacity, and Mortality FREE TO VIEW

Jon Andrew Hardie, MD, PhD
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From the Institute of Medicine, University of Bergen.

Correspondence to: Jon Andrew Hardie, MD, PhD, Institute of Medicine, University of Bergen, Laboratory Bldg, N-5021 Bergen, Norway; e-mail: Jon.hardie@med.uib.no


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. See online for more details.


Chest. 2012;142(5):1354. doi:10.1378/chest.12-1642
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To the Editor:

I would like to thank Pedone et al1 for their recent article in CHEST (April 2012). The article presented data on the association between pulmonary restriction, properly defined as having a total lung capacity (TLC) below the fifth percentile of the reference population (lower limit of normal [LLN]), and all-cause mortality. As the authors correctly pointed out, defining restriction as FVC<80% predicted (or even lower than the LLN) is neither specific nor sensitive as an indicator of true restriction.2 They presented a hazard ratio for death of 2.73 when FVC<LLN and of 6.87 when TLC<LLN. Assumably, much of the increased risk due to FVC<LLN is due to true restriction (the subset of FVC<LLN that also has TLC<LLN), although this was not specifically presented in the article. I believe that it would be a very helpful (and probably fairly easy) addition to their analysis to present the hazard ratio for death separately for those with FVC<LLN and TLC<LLN compared with FVC<LLN but TLC>LLN. The hypothesis behind this requested analysis would be that FVC<LLN but without true restriction (TLC>LLN) does not show increased risk of death (or shows a lower risk of death). I realize that with only 17 deaths total, this may not give results that achieve statistical significance, but lacking other similar data, the results may help us to interpret studies of FVC where TLC is not available.

An additional comment: In Figure 2, the survival lines for the reference categories, respectively for FVC>LLN and TLC>LLN, are identical. This seems a bit strange because even though the deaths represented in these two lines could be identical, the numerator of the percentage must be different.

Pedone C, Scarlata S, Chiurco D, Conte ME, Forastiere F, Antonelli-Incalzi R. Association of reduced total lung capacity with mortality and use of health services. Chest. 2012;141(4):1025-1030. [CrossRef] [PubMed]
 
Vandevoorde J, Verbanck S, Schuermans D, et al. Forced vital capacity and forced expiratory volume in six seconds as predictors of reduced total lung capacity. Eur Respir J. 2008;31(2):391-395. [CrossRef] [PubMed]
 

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References

Pedone C, Scarlata S, Chiurco D, Conte ME, Forastiere F, Antonelli-Incalzi R. Association of reduced total lung capacity with mortality and use of health services. Chest. 2012;141(4):1025-1030. [CrossRef] [PubMed]
 
Vandevoorde J, Verbanck S, Schuermans D, et al. Forced vital capacity and forced expiratory volume in six seconds as predictors of reduced total lung capacity. Eur Respir J. 2008;31(2):391-395. [CrossRef] [PubMed]
 
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