Is the 6-min walking test a sub-maximal exercise test in heart failure patients?

Abstract

The study by Jehn et al. (2009) is interesting and adds important information to the discussion about the 6-min walking test as a sub-maximal exercise test in heart failure patients. The current study compared the cardiorespiratory responses during a 6-min walking test performed in a corridor with those during a maximal cycle ergometer exercise test in patients with three different stages of heart failure based on the peak oxygen uptake (VO2peak): group 1: [25.2 ml/kg per minute; group 2: between 17.5 and 25.2 ml/kg per minute and group 3: \17.5 ml/kg per minute. The authors concluded that heart failure patients with a VO2peak \17.5 ml/kg per minute reached higher levels of respiratory response during the 6-min walking test compared with patients with a VO2peak [25.2 ml/kg per minute. These data would benefit from being expressed relative to the responses to incremental exercise on the treadmill, rather than the cycle ergometer; i.e., treadmill walking being more closely related to walking test performance. In addition, the authors could have used the prognostic cutoff point for VO2peak in heart failure patients to divide the groups: 14 ml/kg per minute (Mehra et al. 2006), or more recently 12.5 ml/kg per minute (Guimaraes et al. 2009) instead of the 17.5 ml/kg per minute criterion. The discussion on the nature of the sub-maximal 6-min walking test is not new. Guimaraes et al. 2002 evaluated the cardiorespiratory response of 12 male heart failure patients (New York Heart Association functional class III and 15.4 ml/kg per minute) in a treadmill cardiopulmonary exercise test and in a 6-min walking test. The tests showed that the respiratory exchange ratio at end exercise was of the order of 1.0 (mean of 1.06). The respiratory exchange ratio during the 6-min walking test represented 94% of the peak respiratory exchange ratio reached in the cardiopulmonary exercise test. It is known that peak respiratory exchange ratio above 1.05 represents an effort near to the maximum in heart failure patients (Carvalho et al. 2009a, b). The study by Guimaraes contests, for the first time, the sub-maximal status of the classical 6-min walking test and proposes a new method to perform this test using the Borg Scale between ‘‘relatively easy’’ and ‘‘slightly tiring’’. This new method assures the 6-min walking test as sub-maximal. The Borg Scale is recognised as an important tool of self-monitoring and self-regulation of the exercise (Carvalho et al. 2009a, b). A second study (Guimaraes et al. 2008) showed that the 6-min walking test using the Borg Scale in heart failure patients is reproducible and once more that this methodology assures the 6-min walking test as sub-maximal. Thus, the study by Jehn et al. provided new perspectives for the evaluation of the 6-min walking test by taking into account the different cardiorespiratory responses on the different functional status of the heart failure patients.