Association between movement parameters and the gas exchange threshold during the six-minute walk test in patients with heart failure
A K E Freitas, L F L Franca, J P Hoffmann, E P D Senna, H L Vieira, V P Moura, W H Murad, P P D Rocha, A Z UlbrichAbstract
Background
Heart Failure (HF) reduces cardiac output and functional capacity. Combining movement and metabolic response parameters obtained during the Six-Minute Walk Test (6MWT) enables a more comprehensive assessment of this outcome.
Purpose
To associate the dynamics of the movement and the metabolic response during the 6MWT in patients with HF, of different New York Heart Association (NYHA) functional classes.
Methods
Fifty patients (mean age: 58.5 ± 12.2 years) with NYHA class I, II or III HF underwent the 6MWT’s evaluation with a portable metabolic analyser and an accelerometer. Movement was assessed by the steps per minute, velocity and accelerometry’s magnitude vector, whilst metabolic response was assessed by the Gas Exchange Threshold (GET), which was determined by the V-Slope method (Figure 1). GET was the metabolic limit point between mild and moderate walk. Receiver Operating Characteristic (ROC) curves were used to establish movement thresholds, employing GET values as ordinal variables (Table 1). Analysis was conducted in SPSS, Matlab and GraphPad, with a significance level of 5%.
Results
NYHA III patients exhibited worse performances on the 6MWT throughout the parameters evaluated. GET values were 890 mL.min-1, 840 mL.min-1 and 690 ml.min-1, for classes I, II and III respectively. ROC curve results indicate that the relation between metabolic response and movement parameters was statistically significant for steps per minute values, which were 91.6, 88.8 and 68.64 for NYHA classes I, II and III.
Conclusions
Movement parameters are associated with the metabolic response during the 6MWT in patients with HF. Moreover, movement thresholds to achieve moderate walk intensity were progressively reduced as functional capacity clinically determined worsened. Furthermore, the number of steps per minute provides significant information on exercise intensity during walking, in HF patients.For image description, please refer to the figure legend and surrounding text.For image description, please refer to the figure legend and surrounding text.