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The inspiratory capacity/total lung capacity ratio as a predictor of survival in an emphysematous phenotype of chronic obstructive pulmonary disease

Authors French A, Balfe D, Mirocha J, Falk J, Mosenifar Z

Received 31 October 2014

Accepted for publication 10 January 2015

Published 13 July 2015 Volume 2015:10(1) Pages 1305—1312

DOI https://doi.org/10.2147/COPD.S76739

Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 3

Editor who approved publication: Dr Richard Russell

Aimee French, David Balfe, James M Mirocha, Jeremy A Falk, Zab Mosenifar

Cedars-Sinai Medical Center, Division of Pulmonary and Critical Care Medicine, Los Angeles, CA, USA

Background: Forced expiratory volume in 1 second (FEV1) grades severity of COPD and predicts survival. We hypothesize that the inspiratory capacity/total lung capacity (IC/TLC) ratio, a sensitive measure of static lung hyperinflation, may have a significant association with survival in an emphysematous phenotype of COPD.
Objectives: To access the association between IC/TLC and survival in an emphysematous phenotype of COPD.
Methods: We performed a retrospective analysis of a large pulmonary function (PF) database with 39,050 entries, from April 1978 to October 2009. Emphysematous COPD was defined as reduced FEV1/forced vital capacity (FVC), increased TLC, and reduced diffusing capacity of the lungs for carbon monoxide (DLCO; beyond 95% confidence intervals [CIs]). We evaluated the association between survival in emphysematous COPD patients and the IC/TLC ratio evaluated both as dichotomous (≤25% vs >25%) and continuous predictors. Five hundred and ninety-six patients had reported death dates.
Results: Univariate analysis revealed that IC/TLC ≤25% was a significant predictor of death (hazard ratio [HR]: 2.39, P<0.0001). Median survivals were respectively 4.3 (95% CI: 3.8–4.9) and 11.9 years (95% CI: 10.3–13.2). Multivariable analysis revealed age (HR: 1.19, 95% CI: 1.14–1.24), female sex (HR: 0.69, 95% CI: 0.60–0.83), and IC/TLC ≤25% (HR: 1.69, 95% CI: 1.34–2.13) were related to the risk of death. Univariate analysis showed that continuous IC/TLC was associated with death, with an HR of 1.66 (95% CI: 1.52–1.81) for a 10% decrease in IC/TLC.
Conclusion: Adjusting for age and sex, IC/TLC ≤25% is related to increased risk of death, and IC/TLC as a continuum, is a significant predictor of mortality in emphysematous COPD patients. 

Keywords: emphysema, pulmonary function testing, mortality

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