Performance difference on the six-minute walk test on tracks of 20 and 30 meters for patients with chronic obstructive pulmonary disease: validity and reliability

Abstract

Background: Functional capacity assessment is important in patients with chronic obstructive pulmonary disease (COPD). It can be performed by the six-minute walk test (6MWT) on a 30-meter track. However, such space is not always available in clinical settings.

Objectives: To compare the performance between the 6MWT on a 30- (6MWT₃₀) and 20-meter (6MWT₂₀) track; to evaluate the validity and reliability of the 6MWT₃₀ and the 6MWT₂₀; and to determine for which patients track length has the greatest impact on performance.

Methods: Patients with COPD randomly performed two 6MWT₃₀ and two 6MWT₂₀ on two different days and were also assessed using the COPD Assessment Test (CAT) and modified Medical Research Council (mMRC) scale.

Results: Thirty patients (23 men; mean ± standard deviation FEV₁%pred: 45.6 ± 12.1) participated in the study. They walked a greater distance on the 6MWT₃₀ than on the 6MWT₂₀ [mean difference: 22.1 m (95% CI: 12, 32 m)]. The longer the 6MWT₃₀ distance, the greater the difference between the 2 tests (r = 0.51; p = 0.004). The 6MWT₂₀ showed high reliability [ICC: 0.96 (95% CI: 0.77, 0.99)] and the results were associated with the distance walked on the 6MWT₃₀ (r = 0.86), CAT (r = -0.53), and mMRC (r = -0.62). Patients who walked ≥430 m in the 6MWT₃₀ presented a difference between the tests greater than those who walked <430 m (34.5 ± 23.3 m vs. 12.6 ± 24.1 m; respectively; p = 0.01).

Conclusions: Performance was higher on the 6MWT₃₀, with the difference increasing as performance improved. Therefore, the 6MWT₂₀ is valid and reliable to evaluate functional capacity but should not be considered interchangeable with the 6MWT₃₀, especially for the less disabled patients with COPD.

Keywords: Activities of daily living; Exercise test.; Outcome assessment (health care); Pulmonary disease, chronic obstructive.