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.

Modified Medical Research Council Dyspnea Scale in GOLD Classification Better Reflects Physical Activities of Daily Living.

BACKGROUND: In multidimensional Global Initiative for Chronic Obstructive Lung Disease (GOLD) classification, the choice of the symptom assessment instrument (modified Medical Research Council dyspnea scale [mMRC] or COPD assessment test [CAT]) can lead to a different distribution of patients in each quadrant. Considering that physical activities of daily living (PADL) is an important functional outcome in COPD, the objective of this study was to determine which symptom assessment instrument is more strongly associated with and differentiates better the PADL of patients with COPD. METHODS: The study included 115 subjects with COPD (GOLD 2-4), who were submitted to spirometry, the mMRC, the CAT, and monitoring of PADL (triaxial accelerometer). Subjects were divided into 2 groups using the cutoffs proposed by the multidimensional GOLD classification: mMRC < 2 and ≥ 2 and CAT < 10 and ≥ 10. RESULTS: Both mMRC and CAT reflected the PADL of COPD subjects. Subjects with mMRC < 2 and CAT < 10 spent less time in physical activities < 1.5 metabolic equivalents of task (METs) (mean of the difference [95% CI] = -62.9 [-94.4 to -31.4], P < .001 vs -71.0 [-116 to -25.9], P = .002) and had a higher number of steps (3,076 [1,999-4,153], P < .001 vs 2,688 [1,042-4,333], P = .002) than subjects with mMRC > 2 and CAT > 10, respectively. Physical activities ≥ 3 METs differed only between mMRC < 2 and mMRC ≥ 2 (39.2 [18.8-59.6], P < .001). Furthermore, only the mMRC was able to predict the PADL alone (time active, r2 = 0.16; time sedentary, r2 = 0.12; time ≥ 3 METs, r2 = 0.12) and associated with lung function (number of steps, r2 = 0.35; walking time, r2 = 0.37; time < 1.5 METs, r2 = 0.25). CONCLUSIONS: The mMRC should be adopted as the classification criterion for symptom assessment in the GOLD ABCD system when focusing on PADL.