Key result
Regular walking significantly reduced conditional and distribution entropy (both p≤0.006) and increased permutation entropy (p<0.0001) compared to resting, but changes disappeared after detrending.
Why the study?
Does regular walking alter heart rate variability entropy measures compared to a resting seated position in healthy subjects?
RCT (n=16)
Randomized order
Does regular walking alter heart rate variability entropy measures compared to a resting seated position in healthy subjects?
Effect estimate: Cohen's d = 0.9 for CE, d = 1.7 for DistEn, d = 1.9 for PermEn
p-value: p=≤ 0.006
Multiple entropy analyses and clear reporting of detrending methods are necessary when assessing heart rate variability, as different measures yield inconsistent responses to autonomic changes during walking.
HRV entropy shifts during walking vanish post-detrending; hypothesis-generating and should not yet alter clinical autonomic assessment.
Entropy measures have been extensively used to assess heart rate variability (HRV), a noninvasive marker of cardiovascular autonomic regulation. It is yet to be elucidated whether those entropy measures can sensitively respond to changes of autonomic balance and whether the responses, if there are any, are consistent across different entropy measures. Sixteen healthy subjects were enrolled in this study. Each subject undertook two 5-min ECG measurements, one in a resting seated position and another while walking on a treadmill at a regular speed of 5 km/h. For each subject, the two measurements were conducted in a randomized order and a 30-min rest was required between them. HRV time series were derived and were analyzed by eight entropy measures, i.e., approximate entropy (ApEn), corrected ApEn (cApEn), sample entropy (SampEn), fuzzy entropy without removing local trend (FuzzyEn-g), fuzzy entropy with local trend removal (FuzzyEn-l), permutation entropy (PermEn), conditional entropy (CE), and distribution entropy (DistEn). Compared to resting seated position, regular walking led to significantly reduced CE and DistEn (both p ≤ 0.006; Cohen’s d = 0.9 for CE, d = 1.7 for DistEn), and increased PermEn (p < 0.0001; d = 1.9), while all these changes disappeared after performing a linear detrend or a wavelet detrend (<~0.03 Hz) on HRV. In addition, cApEn, SampEn, FuzzyEn-g, and FuzzyEn-l showed significant decreases during regular walking after linear detrending (all p < 0.006; 0.8 < d < 1), while a significantly increased ApEn (p < 0.0001; d = 1.9) and a significantly reduced cApEn (p = 0.0006; d = 0.8) were observed after wavelet detrending. To conclude, multiple entropy analyses should be performed to assess HRV in order for objective results and caution should be paid when drawing conclusions based on observations from a single measure. Besides, results from different studies will not be comparable unless it is clearly stated whether data have been detrended and the methods used for detrending have been specified.
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Shi et al. (2017) conducted an RCT in Healthy subjects (n=16). Regular walking on a treadmill at 5 km/h vs. Resting seated position was evaluated on Changes in eight entropy measures of heart rate variability (HRV) (Cohen's d = 0.9 for CE, d = 1.7 for DistEn, d = 1.9 for PermEn, p=≤ 0.006). Regular walking significantly reduced conditional and distribution entropy (both p≤0.006) and increased permutation entropy (p<0.0001) compared to resting, but changes disappeared after detrending.
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