We thank Ganga and Jantz for their interest in our article.1 Assessment of functional capacity in heart failure is complex; available tools are the 6-minute walk test (6MWT), functional class, and cardiopulmonary exercise testing with gas exchange measurements, but each of them evaluates a specific aspect of functional status and their interpretations are complementary.
Any limitations of the interpretation of the 6MWT related to comorbidities are likewise applicable to tests involving oxygen consumption.
A number of the clinical trials carried out to study heart failure have used the 6MWT as the primary endpoint for evaluating the effectiveness of a given treatment and the beneficial effects on the symptoms.2 Likewise, in the study of pulmonary hypertension, comparable to heart failure because of its impact on quality of life, the 6MWT is the only test approved for the assessment of functional class and is the primary endpoint in the assessment of exercise capacity.3
The evaluation of functional capacity using the New York Heart Association (NYHA) functional classification is a subjective assessment from the perspective of the physician that does not correlate perfectly with other patient-centered outcomes, such as quality of life1 and the 6MWT.4 Like other authors,5 we did not include the NYHA class in the model because of the risk of its collinearity with the dependent variable, that is, the 6MWT distance.
Efforts to investigate evaluation methods that provide more information on functional aspects are undoubtedly necessary.
