Chest
Volume 138, Issue 4, October 2010, Pages 880-887
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Original Research
COPD
Airway Count and Emphysema Assessed by Chest CT Imaging Predicts Clinical Outcome in Smokers

https://doi.org/10.1378/chest.10-0542Get rights and content

Background

Recently, it has been shown that emphysematous destruction of the lung is associated with a decrease in the total number of terminal bronchioles. It is unknown whether a similar decrease is visible in the more proximal airways. We aimed to assess the relationships between proximal airway count, CT imaging measures of emphysema, and clinical prognostic factors in smokers, and to determine whether airway count predicts the BMI, airflow obstruction, dyspnea, and exercise capacity (BODE) index.

Methods

In 50 smokers, emphysema was measured on CT scans and airway branches from the third to eighth generations of the right upper lobe apical bronchus were counted manually. The sum of airway branches from the sixth to eighth generations represented the total airway count (TAC). For each subject, the BODE index was determined. We used logistic regression to assess the ability of TAC to predict a high BODE index (≥ 7 points).

Results

TAC was inversely associated with emphysema (r = −0.54, P < .0001). TAC correlated with the modified Medical Research Council dyspnea score (r = −0.42, P = .004), FEV1% predicted (r = 0.52, P = .0003), 6-min walk distance (r = 0.36, P = .012), and BODE index (r = −0.55, P < .0001). The C-statistics, which correspond to the area under the receiver operating characteristic curve, for the ability of TAC alone and TAC, emphysema, and age to predict a high BODE index were 0.84 and 0.92, respectively.

Conclusions

TAC is lower in subjects with greater emphysematous destruction and is a predictor of a high BODE index. These results suggest that CT imaging-based TAC may be a unique COPD-related phenotype in smokers.

Section snippets

Materials and Methods

The study and manuscript were approved according to the procedures of the LTRC detailed elsewhere.9 This study was also approved by the Institutional Review Board at Brigham and Women's Hospital.

Reliability of Airway Counts

The intra- and interreader reproducibility of airway counts was high, as suggested by the intraclass correlation coefficients. The intraclass correlation coefficients for the TAC and the individual sixth AG, seventh AG, and eight AG were 0.98, 0.85, 0.95, and 0.97 for the intrareader assessments and 0.97, 0.75, 0.90, and 0.86 for the interreader assessments, respectively (Fig 2).

Population Description

Baseline characteristics of the 50 subjects by emphysema groups are shown in Table 1. Subjects with ≥ 25% emphysema

Discussion

In this study of a subset of subjects enrolled in the LTRC, we performed a detailed visual assessment of the third through eighth AG arising from the RB1. There was an inverse association among the TAC, the airway count of the sixth AG to the eighth AG of RB1, and emphysema. Although TAC and airway counts of the sixth AG to the eighth AG were directly related to both spirometric measures of lung function and the distance walked by a subject in 6 min, they were inversely related to both mMRC

Conclusions

In summary, the total CT imaging-based count of airways present in the sixth through eighth AG (TAC) of a subset of smokers enrolled in the LTRC was inversely related to densitometric measures of emphysema and was also a predictor of a high BODE index. This latter observation suggests that CT imaging airway count may be a unique COPD-related clinically relevant phenotype. Additional investigation is needed in a larger sample to further explore the clinical significance of emphysema-associated

Acknowledgments

Author contributions: Dr Diaz: contributed to the writing and final approval of the manuscript.

Dr Valim: contributed to the statistical analysis and the writing and final approval of the manuscript.

Dr Yamashiro: contributed to the reading of CT scans for the reproducibility analysis of visual airway count, and to the writing and final approval of the manuscript.

Dr San José Estépar: contributed to software development, which allowed the CT imaging analysis of emphysema, and to the writing and

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    Funding/Support: This work was supported by the National Institutes of Health [Grants K23HL089353-01A1 and U01089856] and by a grant from the Parker B. Francis Foundation.

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

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