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The two-minute walk test (2MWT) is less well validated than the well-known six-minute walk test (6MWT) as a field walking test in patients with chronic obstructive pulmonary disease (COPD). The primary objective of this study was to compare the accuracy of the 2MWT to the 6MWT in detecting exercise-induced oxygen desaturation in patients with severe COPD. Twenty-six patients with COPD (age: 61 ± 10 years, forced expired volume in one second: 37 ± 10%) that were normoxemic at rest performed a 2MWT and a 6MWT under normal ambient conditions on two consecutive days in random order. Oxygen saturation, total walking distance, heart rate, breathing frequency, dyspnea, and leg fatigue were evaluated. Average walking distances were 150 m (95% confidence interval (95% CI): 134–165 m) and 397 m (95% CI: 347–447 m) for the 2MWT and 6MWT, respectively ( r = 0.80, p < 0.0001). The difference in minimum oxygen saturation during the 2MWT (83%, 95% CI: 81–86%) and 6MWT (mean 82%, 95% CI: 80–84%) was not statistically different and the data strongly correlated between the groups ( r = 0.81, p < 0.0001). Other measurements from the 6MWT, including heart rate, breathing rate, and levels of perceived exertion were also comparable in 2MWT. The 2MWT showed comparable validity in detecting exercise-induced oxygen desaturation in patients with severe COPD compared to the 6MWT.

Background: Conventional pulmonary rehabilitation programs improve exercise tolerance but have no effect on pulmonary function in patients with chronic obstructive pulmonary disease (COPD). The role of controlled breathing using respiratory biofeedback during rehabilitation of patients with COPD remains unclear. Objectives: To compare the effects of a conventional 4-week pulmonary rehabilitation program with those of rehabilitation plus controlled breathing interventions. Methods: A randomized controlled trial was performed. Pulmonary function (FEV1), exercise capacity (6-min walking distance, 6MWD), health-related quality of life (chronic respiratory questionnaire, CRQ) and cardiac autonomic function (rMSSD) were evaluated. Results: Forty COPD patients (mean ± SD age 66.1 ± 6.4, FEV1 45.9 ± 17.4% predicted) were randomized to rehabilitation (n = 20) or rehabilitation plus controlled breathing (n = 20). There were no statistically significant differences between the two groups regarding the change in FEV1 (mean difference –0.8% predicted, 95% CI –4.4 to 2.9% predicted, p = 0.33), 6MWD (mean difference 12.2 m, 95% CI –37.4 to 12.2 m, p = 0.16), CRQ (mean difference in total score 0.2, 95% CI –0.1 to 0.4, p = 0.11) and rMSSD (mean difference 2.2 ms, 95% CI –20.8 to 25.1 ms, p = 0.51). Conclusions: In patients with COPD undergoing a pulmonary rehabilitation program, controlled breathing using respiratory biofeedback has no effect on exercise capacity, pulmonary function, quality of life or cardiac autonomic function.

Chronic obstructive pulmonary disease (COPD) is associated with impaired exercise tolerance, but it has not been established to what extent cardiac autonomic function impacts on exercise capacity.To evaluate whether there is an association between airflow limitation and cardiac autonomic function and whether cardiac autonomic function plays a role in exercise intolerance and daily physical activity (PA) in patients with COPD.Univariate and multivariate analyses were performed to evaluate the association between both 6-minute walking test (6MWT) and PA (steps per day) and pulmonary function, cardiac autonomic function (HR at rest, HRR and heart rate variability, HRV) in patients with COPD.In 154 COPD patients (87 females, mean [SD]: age 62.5 [10.7] years, FEV(1) %predicted (43.0 [19.2]%), mean HR at rest was elevated (86.4 [16.4] beats/min) and HRV was reduced (33.69 [28.96] ms) compared to published control data. There was a significant correlation between FEV(1) and HR at rest (r = -0.32, p0.001), between HR at rest and 6MWD (r = -0.26, p = 0.001) and between HR at rest and PA (r = -0.29, p = 0.010). No correlation was found between HRV and 6MWD (r = 0.089, p = 0.262) and PA (r = 0.075, p = 0.322). In multivariate analysis both HR and FEV(1) were independent predictors of exercise capacity in patients with COPD.In patients with COPD the degree of airflow limitation is associated with HR at rest. The degree of airflow limitation and cardiac autonomic function, as quantified by HR at rest, are independently associated with exercise capacity in patients with COPD.