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Replacement of the 6-min Walk Test With Maximal Oxygen Consumption in the BODE Index Applied to Patients With COPD^*

An Equivalency Study

^* From the Pulmonary Rehabilitation Center, Universidade Federal de São Paulo/Lar Escola São Francisco, São Paulo, Brazil.

Correspondence to: José R. Jardim, MD, Rua Botucatu, 740 Third Floor, Respiratory Division (Pneumologia/Unifesp), 04023–062, São Paulo SP, Brazil; e-mail: joserjardim{at}yahoo.com.br

Abstract

Introduction: Patients with COPD have decreased exercise capacity and low oxygen consumption (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.

Objectives: To evaluate the degree of association between the values of the BODE index using the 6MWT with the BODE index using maximal O₂ (O₂max) obtained in a maximal incremental test.

Materials and methods: Fifty 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 O₂max obtained during maximal incremental testing on a treadmill.

Results: Correlation between BODE index and O₂ in milliliters per minute per kilogram (r = – 0.41) was weak; the correlation was moderate (r = – 0.64) when O₂ percentage of predicted was used. The BODE index modified by replacing the 6MWT with O₂ showed excellent correlations with O₂ in milliliters per minute per kilogram (r = 0.92) and O₂ percentage of predicted (r = 0.95).

Conclusion: The excellent correlation between the conventional BODE index and the modified BODE index with O₂ replacing the 6MWT enables us to reach the conclusion that the original BODE index is very effective in the evaluation of COPD patients.

Key Words: COPD • exercise test • exercise tolerance • mortality index • mortality prognosis • oxygen consumption