Optimizing the 6-min walk test as a measure of exercise capacity in COPD.
BACKGROUND
It is uncertain whether the effort and expense of performing a second walk for the 6-min walk test improves test performance. Hence, we attempted to quantify the improvement in 6-min walk distance if an additional walk were to be performed.


METHODS
We studied patients consecutively enrolled into the National Emphysema Treatment Trial who prior to randomization and after 6 to 10 weeks of pulmonary rehabilitation performed two 6-min walks on consecutive days (N = 396). Patients also performed two 6-min walks at 6-month follow-up after randomization to lung volume reduction surgery (n = 74) or optimal medical therapy (n = 64). We compared change in the first walk distance to change in the second, average-of-two, and best-of-two walk distances.


RESULTS
Compared with the change in the first walk distance, change in the average-of-two and best-of-two walk distances had better validity and precision. Specifically, 6 months after randomization to lung volume reduction surgery, changes in the average-of-two (r = 0.66 vs r = 0.58, P = .01) and best-of-two walk distances (r = 0.67 vs r = 0.58, P = .04) better correlated with the change in maximal exercise capacity (ie, better validity). Additionally, the variance of change was 14% to 25% less for the average-of-two walk distances and 14% to 33% less for the best-of-two walk distances than the variance of change in the single walk distance, indicating better precision.


CONCLUSIONS
Adding a second walk to the 6-min walk test significantly improves its performance in measuring response to a therapeutic intervention, improves the validity of COPD clinical trials, and would result in a 14% to 33% reduction in sample size requirements. Hence, it should be strongly considered by clinicians and researchers as an outcome measure for therapeutic interventions in patients with COPD.
Emphysema Research Center, Division of Pulmonary and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA.
Divay
D
Chandra
Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD.
Robert A
RA
Wise
Department of Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
Hrishikesh S
HS
Kulkarni
Division of Pulmonary and Critical Care Medicine, Mayo Clinic, Rochester, MN.
Roberto P
RP
Benzo
Division of Pulmonary and Critical Care Medicine, Temple University School of Medicine, Philadelphia, PA.
Gerard
G
Criner
Division of Pulmonary Sciences and Critical Care Medicine, National Jewish Medical and Research Center, Denver, CO.
Barry
B
Make
Emphysema Research Center, Division of Pulmonary and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA.
William A
WA
Slivka
Department of Medicine and Family and Preventive Medicine, University of California, San Diego, CA.
Andrew L
AL
Ries
Department of Medicine, University of Pittsburgh Medical Center, Pittsburgh, PA.
John J
JJ
Reilly
Division of Pulmonary and Critical Care Medicine, University of Michigan Medical Center, Ann Arbor, MI.
Fernando J
FJ
Martinez
Emphysema Research Center, Division of Pulmonary and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA. Electronic address: sciurbafc@upmc.edu.
Frank C
FC
Sciurba
D000368:Aged; D001993:Bronchodilator Agents / Q000627:therapeutic use; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D017063:Outcome Assessment, Health Care; D011013:Pneumonectomy; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology* / Q000534:rehabilitation / Q000628:therapy; D015203:Reproducibility of Results; D012129:Respiratory Function Tests; D016138:Walking / Q000502:physiology*
D001993:Bronchodilator Agents