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Steven D. Nathan, MD, FCCP; A. Whitney Brown, MD; Nargues A. Weir, MD, FCCP
Author and Funding Information

From the Advanced Lung Disease and Transplant Program, Department of Medicine, Inova Fairfax Hospital.

Correspondence to: Steven D. Nathan, MD, FCCP, Advanced Lung Disease and Transplant Program, Department of Medicine, Inova Fairfax Hospital, 3300 Gallows Rd, Falls Church, VA 22042; e-mail: steven.nathan@inova.org


Financial/nonfinancial disclosures: The authors have reported to CHEST the following conflicts of interest: Dr Nathan has served as a consultant for Intermune; Gilead Sciences, Inc; Actelion Pharmaceuticals Ltd; GeNO LLC; Boehringer-Ingelheim GmbH; Bayer; Genentech; and United Therapeutics Corporation. He has received grant funding from Intermune; Gilead Sciences, Inc; Actelion Pharmaceuticals Ltd; Boehringer-Ingelheim GmbH; and FibroGen, Inc. He has also served on speakers’ bureaus for Gilead Sciences, Inc; Actelion Pharmaceuticals Ltd; and United Therapeutics Corporation. Dr Brown has served on an advisory board for Gilead Pharmaceuticals. Dr Weir is the recipient of grant funding from Gilead Pharmaceuticals.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.


Chest. 2014;145(6):1440-1441. doi:10.1378/chest.14-0720
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Published online
To the Editor:

In our recent article in CHEST,1 we showed that replacing “far” with “fast” in the instruction provided to patients resulted in an average improvement of about 50 m in the distance attained. It is intriguing that a one-letter substitution (“st” for “r”) can stimulate such an improvement, as well as an ongoing debate. Dr Vanjare and colleagues question the value of optimizing the 6-min walk test (6MWT) distance as a reflection of a patient’s ability to do daily activities. However, the 6MWT is a submaximal exercise test designed to determine the patient’s capacity to perform activities of daily living.2 The American Thoracic Society guidelines on the 6MWT state that “the self-paced 6MWT assesses the submaximal level of functional capacity.”2 Although some patients achieve their submaximal functional capacity in activities of daily living, many do not. It is the capacity that needs to be assessed and not the true activity level at home. Several studies that are investigating sedentary lifestyles and means to improve upon them address this very topic.3,4

Our findings are pertinent to the very salient issue of the use of the 6MWT in clinical trials. Although the baseline 6MWT predicts outcomes, the change in the 6MWT distance does not.5 Therefore, the 6MWT has fallen into disfavor as a study end point. We hypothesized in our article that improving the 6MWT precision and reproducibility may be facilitated by maximizing the distance attained. Indeed, this concept is the foundation for our follow-up study (termed “the fast and the furious”), which is currently in the recruitment phase. Patients perform three 6MWTs on 2 separate days: (1) a standard 6MWT with the “far” instruction, (2) a 6MWT with the “fast” instruction, and (3) a 6MWT test with the fast instruction but a stronger (“furious”) menu of scripted instructions each minute to encourage more effort. The hypothesis being tested is that the greater the effort and distance, the less variability in subsequent 6MWTs. We can report that there is a trend supporting this hypothesis among the 12 patients studied thus far, as depicted in Table 1.

Table Graphic Jump Location
Table 1 —Variation and Reproducibility in Walk Distance With Differing Instructions (n = 12)

Data are presented as median (interquartile range). 6MWT = 6-min walk test.

Dr Vanjare and colleagues also raise the issue of whether sufficient time (15 min) was allowed between walks. To our knowledge, the American Thoracic Society recommendation for 1 h of rest between walks has never been tested or validated, and it is likely based on intuition and expert opinion. Unfortunately, adhering to this recommendation would increase the duration of four random walk tests in a day to 5 h or longer, thereby reducing the feasibility of our study. If patients were increasingly tired from prior walks, then one would expect less of a difference between the fast and far walks when the far test was performed first. To further test this hypothesis, we revisited the order sequence of the far and the fast walks and identified those who performed the fast test first (n = 8) or the far test first (n = 6) and then evaluated the difference between the fast and the far walks for the individual subjects (Table 2).

Table Graphic Jump Location
Table 2 —Difference in Distance by Sequence of Walk Type

Data are presented as median (interquartile range).

Although the numbers are small, outperformance with the fast instruction appears to be consistent regardless of the order of the tests. Therefore, based on this subgroup analysis, we feel that 15 min of rest is sufficient.

We thank Dr Vanjare and colleagues for their interest in our article and for fostering this discussion, which has enabled us to provide further insight into the performance of this conceptually simple, yet remarkably controversial, test.

References

Weir NA, Brown AW, Shlobin OA, et al. The influence of alternative instruction on 6-min walk test distance. Chest. 2013;144(6):1900-1905.
 
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med. 2002;166(1):111-117.
 
Moy ML, Weston NA, Wilson EJ, Hess ML, Richardson CR. A pilot study of an Internet walking program and pedometer in COPD. Respir Med. 2012;106(9):1342-1350.
 
Quon BS, Patrick DL, Edwards TC, et al. Feasibility of using pedometers to measure daily step counts in cystic fibrosis and an assessment of its responsiveness to changes in health state. J Cyst Fibros. 2012;11(3):216-222.
 
Gabler NB, French B, Strom BL, et al. Validation of 6-minute walk distance as a surrogate end point in pulmonary arterial hypertension trials. Circulation. 2012;126(3):349-356.
 

Figures

Tables

Table Graphic Jump Location
Table 1 —Variation and Reproducibility in Walk Distance With Differing Instructions (n = 12)

Data are presented as median (interquartile range). 6MWT = 6-min walk test.

Table Graphic Jump Location
Table 2 —Difference in Distance by Sequence of Walk Type

Data are presented as median (interquartile range).

References

Weir NA, Brown AW, Shlobin OA, et al. The influence of alternative instruction on 6-min walk test distance. Chest. 2013;144(6):1900-1905.
 
ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: guidelines for the six-minute walk test. Am J Respir Crit Care Med. 2002;166(1):111-117.
 
Moy ML, Weston NA, Wilson EJ, Hess ML, Richardson CR. A pilot study of an Internet walking program and pedometer in COPD. Respir Med. 2012;106(9):1342-1350.
 
Quon BS, Patrick DL, Edwards TC, et al. Feasibility of using pedometers to measure daily step counts in cystic fibrosis and an assessment of its responsiveness to changes in health state. J Cyst Fibros. 2012;11(3):216-222.
 
Gabler NB, French B, Strom BL, et al. Validation of 6-minute walk distance as a surrogate end point in pulmonary arterial hypertension trials. Circulation. 2012;126(3):349-356.
 
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