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Paired inspiratory-expiratory chest CT scans to assess for small airways disease in COPD

Craig P Hersh12*, George R Washko2, Raúl San José Estépar2, Sharon Lutz3, Paul J Friedman5, MeiLan K Han6, John E Hokanson4, Philip F Judy7, David A Lynch8, Barry J Make9, Nathaniel Marchetti10, John D Newell11, Frank C Sciurba12, James D Crapo9, Edwin K Silverman12 and The COPDGene Investigators

Author Affiliations

1 Channing Division of Network Medicine, Brigham and Women’s Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA, 02115, USA

2 Division of Pulmonary and Critical Care Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA

3 Department of Biostatistics, Colorado School of Public Health, Aurora, CO, USA

4 Department of Epidemiology, Colorado School of Public Health, Aurora, CO, USA

5 Department of Radiology, University of California, San Diego, CA, USA

6 Division of Pulmonary and Critical Care Medicine, University of Michigan Health System, Ann Arbor, MI, USA

7 Department of Radiology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA, USA

8 Department of Radiology, National Jewish Health, Denver, CO, USA

9 Division of Pulmonary and Critical Care Medicine, National Jewish Health, Denver, CO, USA

10 Section of Pulmonary and Critical Care Medicine, Temple University, Philadelphia, PA, USA

11 Department of Radiology, University of Iowa, Iowa City, IA, USA

12 Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, USA

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Respiratory Research 2013, 14:42  doi:10.1186/1465-9921-14-42

Published: 8 April 2013

Abstract

Background

Gas trapping quantified on chest CT scans has been proposed as a surrogate for small airway disease in COPD. We sought to determine if measurements using paired inspiratory and expiratory CT scans may be better able to separate gas trapping due to emphysema from gas trapping due to small airway disease.

Methods

Smokers with and without COPD from the COPDGene Study underwent inspiratory and expiratory chest CT scans. Emphysema was quantified by the percent of lung with attenuation < −950HU on inspiratory CT. Four gas trapping measures were defined: (1) Exp−856, the percent of lung < −856HU on expiratory imaging; (2) E/I MLA, the ratio of expiratory to inspiratory mean lung attenuation; (3) RVC856-950, the difference between expiratory and inspiratory lung volumes with attenuation between −856 and −950 HU; and (4) Residuals from the regression of Exp−856 on percent emphysema.

Results

In 8517 subjects with complete data, Exp−856 was highly correlated with emphysema. The measures based on paired inspiratory and expiratory CT scans were less strongly correlated with emphysema. Exp−856, E/I MLA and RVC856-950 were predictive of spirometry, exercise capacity and quality of life in all subjects and in subjects without emphysema. In subjects with severe emphysema, E/I MLA and RVC856-950 showed the highest correlations with clinical variables.

Conclusions

Quantitative measures based on paired inspiratory and expiratory chest CT scans can be used as markers of small airway disease in smokers with and without COPD, but this will require that future studies acquire both inspiratory and expiratory CT scans.

Keywords:
Emphysema; Chest CT scan; Small airways; Lung function tests; Smoking