The 6-Min Walk Distance, Peak Oxygen Uptake, and Mortality in COPD

In patients with COPD, the maximal oxygen uptake ( V˙o2) measured at peak exercise and the 6-min walk distance (6MWD) have been associated with survival; however, no study has compared the strength of the association in the same patients. In this study, we compared the association between the 6MWD and peak V˙o2 and mortality in 365 patients with COPD. Patients' cardiopulmonary cycle ergometry test results and 6MWD were determined at entry, and patients were followed up for a mean period of 67 months. There were 171 deaths. Compared with survivors, nonsurvivors were older (mean [± SD] age, 67.9 ± 8 vs 65.9 ± 8 years, respectively; p = 0.008), had worse mean FEV1 (36.5 ± 12 vs 42.6 ± 14 L, respectively; p = 0.02), had lower mean peak V˙o2 (9.8 ± 3 vs 11.8 ± 3.6 mL/Kg/min, respectively; p < 0.0001), lower mean 6MWD (312 ± 104 vs 377 ± 95 m, respectively; p < 0.0001), and lower mean exercise minute ventilation (37.4 ± 12 vs 42.3 ± 13 L/min, respectively; p = 0.004). Univariate analysis showed that peak V˙o2 and 6MWD as well as comorbidity, FEV1, and body mass index were associated with death. Logistic regression analysis with mortality as the dependent variable revealed that 6MWD (hazard ratio [HR], 0.996; 95% confidence interval [CI], 0.993 to 0.999; p < 0.01) had a stronger association than the peak V˙o2 (HR, 0.971; 95% CI, 0.959 to 1.000; p = 0.050) with mortality. This study shows the 6MWD is as good predictor of mortality as the peak V˙o2 in patients with COPD.