Minimally Important Difference of the 20-m 6-Minute Walk Test in Individuals With COPD.

BACKGROUND: The 20-m 6-min-walk test (6MWT20) is a valid, reliable alternative for functional capacity assessment; however, its responsiveness and minimally important difference (MID) have yet to be investigated. The aim of this study was to assess the responsiveness and MID of the 6MWT20 in individuals with COPD. METHODS: Fifty-three subjects completed the study from August 2011-March 2020. The following were assessed: lung function, activities of daily living (ADLs), functional capacity 6MWT20, dyspnea, health status, quality of life, and limitations in ADLs. The primary outcome was the 6MWT20 distance. RESULTS: The study demonstrated that the 6MWT20 is responsive to pulmonary rehabilitation (PR), with an average improvement of 39 ± 36.3 m (P < .001) and an effect size of 1.07. The learning effect declined to 1.45% after PR, with an intraclass correlation coefficient of 0.99 (95% CI 0.98-0.99). The receiver operating characteristic curve indicated a cutoff point of 20 m for the MID of the 6MWT20 based on the MIDs for the modified St George Respiratory Questionnaire (sensitivity 87%, specificity 69%, area under the curve 0.80 [95% CI 0.66-0.90], P < .001, Youden index 0.56) and the number of steps (sensitivity 92%, specificity 73%, area under the curve 0.83 [95% CI 0.70-0.92], P < .01, Youden index 0.56). CONCLUSIONS: The 6MWT20 is responsive to PR, and the MID for the test is 20 m (17-47 m).

Physiological Responses to the 6-min Step Test in Patients With Chronic Obstructive Pulmonary Disease.

PURPOSE: To describe physiological responses during the 6-min step test (6MST) in patients with chronic obstructive pulmonary disease (COPD), to investigate whether COPD severity and test interruptions could determine different physiological responses, and to test the reproducibility of 6MST performance. METHODS: Cross-sectional study. Patients with moderate to very severe COPD underwent lung function assessment and 2 6MSTs, with physiological responses measurement by a gas analyzer and a near-infrared spectroscopy device. RESULTS: Thirty-six patients (29 men; forced expiratory volume in the first second of expiration [FEV1] = 51.1 ± 13.6%pred) participated in the study. Most of the physiological variables stabilized between the second and fourth minutes of the 6MST, except the respiratory rate and heart rate (HR), which stabilized after the fifth minute. The patients who interrupted the 6MST showed higher minute ventilation to maximal voluntary ventilation ratio ((Equation is included in full-text article.)E/MVV; all test minutes) and HR (first and second minutes) (P < .05) and worse pulmonary function (FEV1 = 1.37 ± 0.37 L vs 1.82 ± 0.41 L, P = .002, and 47.2 ± 13.2%pred vs 56.6 ± 12.4%pred, P = .04, respectively) than those who did not interrupt the 6MST. However, their performance was similar (P = .11). 6MST performance and physiological variables were reproducible, and there was a learning effect of 6.28%. CONCLUSIONS: The 6MST showed a stabilization of the most physiological variables. In addition, interruptions were usually made by patients with a greater impairment of lung function and they presented greater increased ventilatory demand during the 6MST. However, these interruptions do not interfere with 6MST physiological responses. Moreover, the 6MST is a reliable test to evaluate the functional capacity of patients with COPD.