Exercise tolerance in COPD is only moderately well predicted by airflow obstruction assessed by forced expiratory volume in 1 second (FEV(1)). We determined whether other phenotypic characteristics, including computerized tomography (CT) measures, are independent predictors of 6 minute walk distance (6MWD) in the COPDGene(®) cohort.

METHODS:COPDGene(®) recruits non-Hispanic Caucasian and African-American current and ex-smokers. Phenotyping measures include post-bronchodilator FEV(1)%predicted, inspiratory and expiratory CT lung scans. We defined %emphysema as percent lung voxels below -950 Hounsfield Units (HU) on the inspiratory scan and %gas trapping as percent lung voxels below -856 HU on the expiratory scan.

RESULTS:Data of the first 2,500 participants of the COPDGene(®) cohort were analyzed. Participant age was 61±9 y; 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 stages I-IV respectively. Higher %emphysema and %gas trapping predicted lower 6MWD (p<0.001). However, in a given spirometric group, after adjustment for age, gender, race, and BMI, neither %emphysema nor %gas trapping, nor their interactions with FEV(1)%predicted, remained a significant 6MWD predictor. In a given spirometric group, only 16-27% of variance in 6MWD could be explained by age, male gender, 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 measures of emphysema and gas trapping were not predictive of 6MWD after adjustment for other phenotypic characteristics.