Optimizing the Six Minute 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 six-minute-walk test improves test performance. Hence, we attempted to quantify the improvement in six-minute-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 6-10 weeks of pulmonary rehabilitation, performed two six-minute-walks on consecutive days (n=396). Patients also performed two six-minute-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 to change in first-walk distance, change in average-of-two and best-of-two walk distances had better validity and precision. Specifically, six months after randomization to LVRS, changes in average-of-two (r=0.66 vs. 0.58, P=0.01) and best-of-two walk distances (r=0.67, vs. 0.58, P=0.04) better correlated with the change in maximal exercise capacity (i.e. better validity). Also, the variance of change in the average-of-two walk distances was 14-25% less and best-of-two was 14-33% less than the variance of change in the single-walk distance, indicating better precision.
CONCLUSIONS:Adding a second walk to the six-minute-walk test significantly improves its performance in determining response to a therapeutic intervention, improves the validity of COPD clinical trials and would result in a 14-33% reduction in sample size requirements. Hence, it should be strongly considered by clinicians and researchers as an outcome measure for therapeutic interventions in COPD patients.
From the 1Emphysema Research Center, Division of Pulmonary and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA;
SourceChest : 2012 Jun 14 pg
Pub Type(s)JOURNAL ARTICLE