Reliability, Validity, and Responsiveness of a 2-Min Walk Test To Assess Exercise Capacity of COPD Patients: Discussion
The significant correlations between the 2MWT and the 6MWT, V02max, and V02max/kg support the validity of the 2MWT as a measure of exercise capacity in COPD patients with moderate-to-severe disease. As anticipated, the strongest correlation was observed between the 2MWT and 6MWT, since they are both walking tests and their results were in agreement with those of previous studies.” The modest but significant correlations observed beWhen comparing the correlations of the 2MWT, 6MWT, and 12MWT with V02max and V02max/kg, the Pearson correlation coefficients for the 2MWT were only slightly lower than those of the 6MWT and 12MWT (Vo2max, 0.454 vs 0.49 to 0.51; Vo2max/kg, 0.555 vs 0.65 to 0.67).’ This demonstrates the fact that a 2MWT can therefore assess exercise capacity as accurately as walking tests of longer duration.
The distances walked in both the 6MWT and 2MWT improve significantly after pulmonary rehabilitation. This finding echoes that of Eiser et al, who reported that the 2MWT is sensitive to change after bronchodilator therapy. However, the 6MWT is more exhausting for patients with severe COPD and more time-consuming in a busy health-care setting. In fact, some patients with severe symptoms may not be able to complete a 6MWT, making the data difficult to interpret. In this study, the less tiring 2MWT was as effective as the 6MWT in demonstrating good responsiveness to change after a 5-week program of pulmonary rehabilitation and may be especially useful for this group of patients. This study has demonstrated that a 2MWT is a reliable, valid, and sensitive tool for the assessment of exercise capacity in COPD patients with moder-ate-to-severe disease. However, several factors need to be considered when using this test. This test may be valid only for persons experiencing moderate-to-severe exercise limitation. The short duration of the timed walk test may not stress the cardiopulmonary function adequately for patients who have mild cardiopulmonary disease, and the ceiling effect may limit the evaluation of the effectiveness of an intervention. Besides, because of its short duration, the magnitude of improvement following an intervention will be small and perhaps difficult to interpret. Further study to investigate the minimal clinically important difference is recommended. itat on
Since the walk test uses a self-pacing protocol, results may be affected by the effects of learning and motivation. Practice walks and standardized procedures should be considered to produce reproducible and comparable results. A walk test provides only a measure of distance covered. However, when walking ability is impaired and is considered a disability in regard to independent ambulation, both qualitative parameters (eg, dynamic balance sufficient for safety to prevent falls) and quantitative parameters (eg, velocity and distance tolerated) need to be described and compared with the realistic functional demands of daily living in the community.
The 6MWT has been shown’ to be an excellent predictor of morbidity and mortality in patients with COPD. A further study to investigate the predictive capability of 2MWT in this regard may therefore be worthy of investigation.
This study has demonstrated that the 2MWT is a reliable, valid, and sensitive test for the assessment of exercise capacity in patients with moderate-to-severe COPD. It is practical, simple, quick, easy to administer, and well-tolerated by patients with severe COPD symptoms. Further studies are recommended to extend and validate the findings presented.