THE 6-MIN WALK TEST

Abstract

Dear Editor-in-Chief: While Ingle and Carroll suggest there are "methodological limitations" related to our study of elderly heart failure (HF) patients (4), we appear to arrive at similar conclusions, as they state in their recent manuscript (2) that "when an estimate of peak oxygen consumption (V˙O2peak) is required, incremental exercise testing with metabolic gas exchange measurements cannot be avoided." Specifically, Ingle and Carroll are concerned that we did not provide verbal "encouragement" during the 6-min walk test (6-MWT). We anticipated that over the course of this study, different personnel would administer the 6-MWT, and verbal "interaction" by different personnel would only add variability to our data collection. We did read a standardized script to each subject and controlled the environmental conditions and medication regimen on the day of testing. While verbal encouragement may have increased walking distance of each subject, the effect would have been consistent across all subjects and would not alter the relationships between the variables of interest. Ingle and Carroll also suggest that our "measures of exercise intolerance could be adversely affected by workload selection" and recommend using smaller workload increments (10-15 W·min−1). While there are several advantages to using a more linear "ramping" protocol, we chose a "staged" protocol to collect echocardiographic data during submaximal "steady-state" conditions. Our protocol, which increased the workload by 25 W every 3 min (i.e., 8.3 W·min−1), would likely yield a similar test duration to the protocol recommended. Ingle and Carroll also indicate that we may have excluded "more representative" elderly HF patients. As is the case with any clinical trial, we had specific inclusion and exclusion criteria; yet, "to evaluate the relationship between V˙O2peak and 6-MWT in older HF patients" (4), it was essential that all patients be able to adequately perform both the cardiopulmonary exercise test and the 6-MWT. In the original 6-MWT study in HF patients by Guyatt et al. (1), the exclusion criteria included "limitation of activity because of factors others than fatigue or exertional dyspnea, such as arthritis, claudication in the legs or angina." Furthermore, the mean V˙O2peak (13.5 mL·kg−1·min−1) of our subjects was well below values reported by Ingle et al. (2) and others and does not seem to indicate that we selected a "nonrepresentative" population of older HF patients for this investigation. While Ingle and Carroll indicate "6-MWT as a reproducible test in CHF with no changes in symptoms after 12 months" (3), we have recently presented (5) data on the relationships between changes in V˙O2peak and VT with 6-MWT in a randomized clinical trial of exercise training in older diastolic HF patients. Our results suggest that while the exercise-training group experienced an increase in 6-MWT and V˙O2peak, the control group had no change in V˙O2peak but did demonstrate a significant increase in the 6-MWT. Thus, our preliminary data challenge the validity of using 6-MWT as a serial measure of functional capacity in older HF patients. In closing, we agree with Ingle and Carroll that 6-MWT may be "the choice for assessing submaximal exercise tolerance in elderly CHF patients," but we stand by our conclusion that "direct measurements of V˙O2peak and VT should be preferred outcome measures when an accurate determination of functional capacity is required in elderly HF patients." Sara Maldonado-Martín0, PhD Faculty of Physical Activity and Sport Sciences University of the Basque Country Basque Country, Spain Peter H. Brubaker, PhD Wake Forest University Winston-Salem, NC