Utility of the total step count during the 6-minute walk test in COPD

Abstract

Introduction: The 6-minute walk distance (6MWD) in the 6-minute walk test (6MWT) has been used to examine subjective dyspnea and clinical outcomes and predict mortality in patients with COPD. Aims and objectives: We hypothesized that the total step count (TSC) during the 6MWT would be a more useful index than the 6MWD. In this prospective observational study, we assessed the utility of the TSC in patients with mild to moderate COPD. Methods: Subjects included 59 outpatients with COPD (56 males and 3 females; median age: 72 (49-82) years; %FEV1, 64.4%). Spirometry and the 6MWT were performed while the subjects were in a stable condition. A 3-axis accelerometer (Anypal Walk, FUKUDA DENSHI Co. Ltd., Tokyo, Japan) was used to measure the 6MWD, TSC, and the number of steps per second (NSPS). Results: The mean values of the examined parameters were as follows: 6MWD, 407.8 m; TSC, 618.3 steps; and NSPS, 1.78 steps/sec. Significant correlations were detected between the TSC and the lowest oxygen saturation value obtained by pulse oximetry (SpO 2 ), max Borg scale, modified Medical Research Council (MRC) scale, and %FEV1(Table1). NSPS was also correlated with the lowest SpO 2 value, max Borg scale, modified MRC scale, and the %FEV1. The 6MWD was correlated with the max Borg scale, modified MRC scale, and %FEV1, but not with the lowest SpO 2 value. Conclusions: TSC is more useful than the 6MWD for evaluating dyspnea and oxygen desaturation during the 6MWT.