Replacement of the 6-min Walk Test With Maximal Oxygen Consumption in the BODE Index Applied to Patients With COPD : An Equivalency Study

IntroductionPatients with COPD have decreased exercise capacity and low oxygen consumption (V˙o2) during formal cardiopulmonary exercise testing, and lower scores on health-related quality of life questionnaires. When isolated, these three variables show different correlations with COPD mortality. The multidimensional BODE (body mass index[BMI], airflow obstruction, dyspnea, and exercise capacity in COPD) index, which comprises four variables including the 6-min walk test (6MWT), predicts survival in COPD.ObjectivesTo evaluate the degree of association between the values of the BODE index using the 6MWT with the BODE index using maximal V˙o2 ( V˙o2max) obtained in a maximal incremental test.Materials and methodsFifty patients with mild-to-severe COPD (average age, 63.5 ± 9.9 years; FEV1, 65.3 ± 23.6% of predicted) [± SD] had BMI, spirometric function (FVC and FEV1), and dyspnea status (Medical Research Council) evaluated. Two BODE index scores were then completed: one with the 6MWT, and one with the V˙o2max obtained during maximal incremental testing on a treadmill.ResultsCorrelation between BODE index and V˙o2 in milliliters per minute per kilogram (r = − 0.41) was weak; the correlation was moderate (r   = − 0.64) when V˙o2 percentage of predicted was used. The BODE index modified by replacing the 6MWT with V˙o2 showed excellent correlations with V˙o2 in milliliters per minute per kilogram (r   = 0.92) and V˙o2 percentage of predicted (r = 0.95).ConclusionThe excellent correlation between the conventional BODE index and the modified BODE index with V˙o2 replacing the 6MWT enables us to reach the conclusion that the original BODE index is very effective in the evaluation of COPD patients.