title: Six-minute walk distance predictors, including CT scan measures, in the COPDGene cohort.
abstract: BACKGROUND
  Exercise tolerance in COPD is only moderately well predicted by airflow obstruction assessed by FEV(1). 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 FEV(1) % 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.
authors.affiliation: Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Rambod
authors.affiliation: Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA.
authors.forename: Janos
authors.initials: J
authors.lastname: Porszasz
authors.affiliation: National Jewish Health, Denver, CO.
authors.forename: Barry J
authors.initials: BJ
authors.lastname: Make
authors.affiliation: National Jewish Health, Denver, CO.
authors.forename: James D
authors.initials: JD
authors.lastname: Crapo
authors.affiliation: Rehabilitation Clinical Trials Center, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA. Electronic address: casaburi@ucla.edu.
authors.forename: Richard
authors.initials: R
authors.lastname: Casaburi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004646:Emphysema / Q000503:physiopathology; D017079:Exercise Tolerance; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D029424:Pulmonary Disease, Chronic Obstructive / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D012907:Smoking / Q000503:physiopathology; D013147:Spirometry; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D016138:Walking