Purpose: To evaluate the relationship between a 6-min walk test (6-MWT) to peak oxygen consumption (V̇O2peak) and ventilatory threshold (VT) in older heart failure (HF) patients, to validate the equation by Cahalin et al., and to develop a new equation to improve the prediction of V̇O2peak from 6-MWT.
Methods: Older patients (> 65 yr) with systolic or diastolic HF (N = 97) performed an exercise test to peak exertion on an upright bicycle ergometer using an incremental protocol. Gas exchange measures were collected along with continuous electrocardiograph monitoring. 6-MWT was performed on an indoor track at a self-selected pace under standardized conditions. The formula of Cahalin et al. was used to predict V̇O2peak from 6-MWT, and a new equation was generated from the measured V̇O2peak-6-MWT relationship from this investigation.
Results: The correlation between 6-MWT and measured V̇O2peak was moderate (r = 0.54) with a standard error of estimate (SEE) of 2.48 mL·kg−1·min−1. The correlation between 6-MWT and VT was weak (r = 0.23), whereas the correlation between V̇O2peak and VT was strong (r = 0.74). Correlations between the measured and predicted V̇O2peak values were moderate (r = 0.54) for both prediction equations, and the SEE was 2.83 versus 1.34 mL·kg−1·min−1 for the Cahalin et al. and the new equation, respectively.
Conclusion: These results indicate that 6-MWT does not accurately predict functional capacity in older HF patients, and questions the validity of using this test to determine functional capacity in older HF patients. Predicting V̇O2peak from equations using 6-MWT also results in substantial variability and, consequently, should not be used in older HF patients where an accurate determination of functional capacity is essential.