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Original Research |

Six-Minute Walk Distance Predictors, Including CT Scan Measures, in the COPDGene CohortPredictors of 6-Min Walk Distance in Smokers

Mehdi Rambod, MD; Janos Porszasz, MD, PhD; Barry J. Make, MD, FCCP; James D. Crapo, MD, FCCP; Richard Casaburi, PhD, MD, FCCP; the COPDGene Investigators
Author and Funding Information

From the Rehabilitation Clinical Trials Center (Drs Rambod, Porszasz, and Casaburi), Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA; and National Jewish Health (Drs Make and Crapo), Denver, CO.

Correspondence to: Richard Casaburi, PhD, MD, FCCP, Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, 1124 W Carson St, Torrance, CA 90502; e-mail: casaburi@ucla.edu


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

Funding/Support: The project described was supported by the National Heart, Lung, and Blood Institute [U01HL089897 and U01HL089856].


© 2012 American College of Chest Physicians


Chest. 2012;141(4):867-875. doi:10.1378/chest.11-0870
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Background:  Exercise tolerance in COPD is only moderately well predicted by airflow obstruction assessed by FEV1. We determined whether other phenotypic characteristics, including CT scan measures, are independent predictors of 6-min walk distance (6MWD) in the COPDGene cohort.

Methods:  COPDGene recruits non-Hispanic Caucasian and African American current and ex-smokers. Phenotyping measures include postbronchodilator FEV1 % predicted and inspiratory and expiratory CT lung scans. We defined % emphysema as the percentage of lung voxels < −950 Hounsfield units on the inspiratory scan and % gas trapping as the percentage of lung voxels < −856 Hounsfield units on the expiratory scan.

Results:  Data of the first 2,500 participants of the COPDGene cohort were analyzed. Participant age was 61 ± 9 years; 51% were men; 76% were non-Hispanic Caucasians, and 24% were African Americans. Fifty-six percent had spirometrically defined COPD, with 9.3%, 23.4%, 15.0%, and 8.3% in GOLD (Global Initiative for Chronic Obstructive Lung Disease) stages I to IV, respectively. Higher % emphysema and % gas trapping predicted lower 6MWD (P < .001). However, in a given spirometric group, after adjustment for age, sex, race, and BMI, neither % emphysema nor % gas trapping, or their interactions with FEV1 % predicted, remained a significant 6MWD predictor. In a given spirometric group, only 16% to 27% of the variance in 6MWD could be explained by age, male sex, Caucasian race, and lower BMI as significant predictors of higher 6MWD.

Conclusions:  In this large cohort of smokers in a given spirometric stage, phenotypic characteristics were only modestly predictive of 6MWD. CT scan measures of emphysema and gas trapping were not predictive of 6MWD after adjustment for other phenotypic characteristics.

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