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.

Impact of Home Oxygen Therapy on the Level of Physical Activities in Daily Life in Subjects With COPD.

BACKGROUND: Chronic hypoxemia in patients with COPD is a limiting factor that is associated with disease progression and significantly contributes to decreased physical activity. Although correction of hypoxemia results in physiological improvements, oxygen therapy may be related to social isolation and inactivity. However, few studies have objectively investigated the level of physical activity in daily life (PADL) in these patients. The objective of this study was to compare the level of PADL in subjects with COPD on home oxygen therapy and in subjects with no oxygen therapy, and to investigate whether home oxygen therapy is associated with the level of PADL. METHODS: In this study, 29 subjects with COPD composed the home oxygen therapy group, and 30 subjects with COPD composed the control group. All of them underwent assessment of anthropometric measurements, spirometry, peripheral muscle strength, limitations in activities of dalily living, perception of dyspnea, health status, as well as PADL monitoring. RESULTS: Home oxygen therapy subjects showed less time walking (P = .001), in active physical activities (P = .003), in physical activities ≥ 3 METs (P = .001), and in physical activities < 1.5 METs (P = .042), as well as fewer steps (P = .001). Physical inactivity was present in 24 home oxygen subjects (82.8%) and 18 control subjects (60%). Oxygen therapy was associated with severe physical inactivity (Cramer's V = 0.29, P = .040). The time using oxygen therapy (h/d) was the strongest predictor of the level of PADL (r2 = 0.38-0.43, P < .001). CONCLUSION: Subjects with COPD using oxygen at home showed reduced level of PADL. The results indicate that oxygen therapy is associated with severe physical inactivity and may be a predictor of the level of PADL.