How the threshold "r" influences approximate entropy analysis of heart-rate variability

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Calculation of approximate entropy (ApEn) requires to select the correct threshold "r". Previous studies recommended r to be between 0.1 and 0.25 times the signal standard deviation, and now r=0.2 is used in almost all HRV studies. Recently it has been claimed that for fast signal dynamics, r=0.2 may lead to erroneous conclusions, while r maximizing ApEn, rMAX, correctly assesses entropy. We verified 1) if rMAX differs from r=0.2 also for HR; and 2) if all r values in the 0.1-0.25 range provide similar ApEn measures. For this aim, we recorded R-R intervals in 10 young subjects for 10', in supine and sitting positions, and calculated ApEn(r) for r between 0.02 and 1.20, identifying rMAX and ApEn(rMAX). rMAX felt into the recommended range, but it significantly differed from 0.2. At the extremes of the range, the effects of posture change on ApEn were even opposite: ApEn(0.25) decreased while ApEn(0.1) increased. Therefore the choice of r is critical even in HRV studies.

Original languageEnglish
Title of host publicationComputers in Cardiology
Number of pages4
Publication statusPublished - 2008
EventComputers in Cardiology 2008, CAR - Bologna, Italy
Duration: Sep 14 2008Sep 17 2008


OtherComputers in Cardiology 2008, CAR

ASJC Scopus subject areas

  • Computer Science Applications
  • Cardiology and Cardiovascular Medicine


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