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 FEV 1% 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.
Bibliographical noteFunding Information:
Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Porszasz is a consultant with Forest Laboratories, Inc; Novartis Pharmaceuticals Corporation; and Boehringer Ingelheim GmbH. Dr Make has received grant funds (controlled by National Jewish Health) from and participated in advisory boards or has been a speaker for the National Heart, Lung, and Blood Institute; Abbott Laboratories; AstraZeneca; Dey Pharma, LP; Forest Laboratories, Inc; MedImmune, LLC; Merck and Company; Novartis Pharmaceuticals Corporation; NycoMed International Management GmbH; Respironics-Philips Healthcare; GlaxoSmithKline plc; Nabi Biopharmaceuticals; Boehringer Ingelheim GmbH; Pfizer Inc; and Synovian Inc. Dr Casaburi has received grant funds (controlled by Los Angeles Biomedical Research Institute) from and participated in advisory boards or has been a speaker for the National Heart, Lung, and Blood Institute; AstraZeneca; Forest Laboratories, Inc; Novartis Pharmaceuticals Corporation; Respironics-Philips Healthcare; Boehringer Ingelheim GmbH; Pfizer Inc; Breath Technologies, Inc; Theratechnologies Inc; F. Hoffman-La Roche Ltd; Osiris Therapeutics Inc; Actelion Pharmaceuticals Ltd; and Bayer Healthcare Pharmaceuticals. Drs Rambod and Crapo have reported that no potential conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.
Funding/Support: The project described was supported by the National Heart, Lung, and Blood Institute [U01HL089897 and U01HL089856] .