Leung ASY, Chan KK, Sykes K, Chan KS

Chest. 2006;130:119-125.

Purpose

To investigate the reliability, validity, and responsiveness of a 2-min walk test (2MWT) in Chinese COPD patients with moderate-to-severe disease.

Methods.

This study consisted of two parts. Forty-seven stable COPD patients with moderate-to-severe disease participated in the first part of study for the investigation of reliability and validity. The demographic and anthropomorphic data collected included age, gender, body weight, height, and body mass index. Each subject performed a pulmonary function test, a cardiopulmonary exercise test, three trials of a 2MWT, and two trials of 6-min-walk test (6MWT) in random order within a 5-day period. Fifteen of these subjects participated in the second part of study for the evaluation of the responsiveness of the 2MWT following pulmonary rehabilitation. The 2MWT and 6MWT were conducted before and after the program for comparison.

Results.

Forty-five subjects (mean [SD] age, 71.8 +/- 8.3 years; mean FEV1, 0.88 +/- 0.27 L) completed the first part of study, and 9 subjects (mean age, 74 +/- 8.7 years; mean FEV1, 0.94 +/- 0.28 L) completed the second part of study. The intraclass correlation coefficient of the repeated 2MWTs was high (R = 0.9994; p < 0.05), mean differences across trials ranged from 0.3 to 0.8 m (95% confidence interval, 3.1 to 4.6 m) demonstrated its high test-retest reliability. Significant correlations were found between the 2MWT and the 6MWT, the maximum oxygen uptake (VO2max) in milliliters per minute, and the VO2max in milliliters per kilogram per minute (r = 0.937, 0.454, and 0.555, respectively; p < 0.0125). Following rehabilitation, there were significant improvements in the mean 2MWT and 6MWT walking distance of 17.2 +/- 13.8 m and 60.6 +/- 35.5 m, respectively, with moderate effect sizes (0.61 and 0.53, respectively) and large standardized mean responses (1.25 and 1.70, respectively). High correlation was found between changes in the 2MWT and the 6MWT (r = 0.70; p < 0.05).

Conclusion.

The 2MWT was shown to be a reliable and valid test for the assessment of exercise capacity and responsive following rehabilitation in patients with moderate-to-severe COPD. It is practical, simple, and well-tolerated by patients with severe COPD symptoms.

Comment.

The 6-minute walk test (6MWT) has become enshrined in current exercise literature for good reason. It replicates a real-life activity and produces results that not only are reproducible and sensitive to intervention but does so in a simple and inexpensive manner. What is often forgotten is the fact that this test is a shortened version of the earlier de facto standard, the 12MWT. As the authors of this article contend, the 6MWT, like the 12MWT before it, may be too long a walk for the patient with severe chronic obstructive pulmonary disease and may also be wasteful of overextended healthcare resources. Literature in support of the 2MWT exists, and this report extends it both by comparing it with the 6MWT and symptom-limited cardiopulmonary exercise testing and by assessing in a small number of subjects the change in response to rehabilitation. The former aspect is more robust, and data are available for 45 patients with moderate to severe chronic obstructive pulmonary disease (mean Forced expiratory volume in 1 second) FEV₁, 41.9% +/- 13% predicted). There is strong correlation with the 6MWT, but this is less striking, although still highly significant, when compared with VO_2max measurements. This is not surprising because the latter would logically correlate better with exercise tests more demanding than a 2MWT, even in the severely impaired patients. The converse, that the short test may be insufficient to adequately assess milder disease, is not addressed in this study. This is an attractive variation on the current standard and certainly merits consideration in the severe chronic obstructive pulmonary disease patient, but it is premature to recommend that this replace the 6MWT because data, especially what constitutes clinically significant change, are largely lacking.

SK