Different COPD disease characteristics are related to different outcomes in the 6-minute walk test.

BACKGROUND: Chronic obstructive pulmonary disease (COPD) can lead to severe disability as the disease advances. The 6-minute walk test (6MWT) is commonly used to measure functional capacity in COPD patients and has three potential outcomes; walking distance, oxygen desaturation, and self-perceived dyspnea assessed by the Borg scale, all reflecting different aspects of COPD. The aim of this study was to identify predictors of all 3 outcomes of 6MWT in patients with COPD.

METHODS: 370 COPD patients, aged 40-75 yrs, were included from the first phase of the Bergen COPD cohort study. They were examined with spirometry, bioelectrical impedance measurements, 6MWT, Center for Epidemiologic Studies of Depression (CES-D) Scale, Medical Research Council (MRC) dyspnea scale, Charlson index for co-morbidities, self-reported physical activity questionnaire, plasma levels of C-reactive protein (CRP) and arterial blood gases.

RESULTS: Significant predictors in the multivariate analyses were sex, age, FEV(1) in % predicted, symptoms of dyspnea (MRC), co-morbidities (Charlson Index) and self-reported physical activity for walking distance, FEV(1) in % predicted and PaO(2) for oxygen desaturation, and body composition, smoking and co-morbidities for self-perceived dyspnea assessed by the Borg scale.

CONCLUSION: Several COPD characteristics have predictive value for the 6MWT, and some COPD characteristics are more strongly related to specific 6MWT outcomes than others.