Non-REM sleep marker for wearable monitoring: Power concentration of respiratory heart rate fluctuation

Junichiro Hayano, Norihiro Ueda, Masaya Kisohara, Yutaka Yoshida, Haruhito Tanaka, Emi Yuda

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


A variety of heart rate variability (HRV) indices have been reported to estimate sleep stages, but the associations are modest and lacking solid physiological basis. Non-REM (NREM) sleep is associated with increased regularity of respiratory frequency, which results in the concentration of high frequency (HF) HRV power into a narrow frequency range. Using this physiological feature, we developed a new HRV sleep index named Hsi to quantify the degree of HF power concentration. We analyzed 11,636 consecutive 5-min segments of electrocardiographic (ECG) signal of polysomnographic data in 141 subjects and calculated Hsi and conventional HRV indices for each segment. Hsi was greater during NREM (mean [SD], 75.1 [8.3]%) than wake (61.0 [10.3]%) and REM (62.0 [8.4]%) stages. Receiver-operating characteristic curve analysis revealed that Hsi discriminated NREM from wake and REM segments with an area under the curve of 0.86, which was greater than those of heart rate (0.642), peak HF power (0.75), low-to-high frequency ratio (0.77), and scaling exponent a (0.77). With a cutoff >70%, Hsi detected NREM segments with 77% sensitivity, 80% specificity, and a Cohen's kappa coefficient of 0.57. Hsi may provide an accurate NREM sleep maker for ECG and pulse wave signals obtained from wearable sensors.

Original languageEnglish
Article number3336
JournalApplied Sciences (Switzerland)
Issue number9
Publication statusPublished - 2020 May 1


  • Detrended fluctuation analysis
  • Electrocardiography
  • Heart rate variability
  • Power spectrum
  • REM sleep
  • Respiration
  • Sleep stage

ASJC Scopus subject areas

  • Materials Science(all)
  • Instrumentation
  • Engineering(all)
  • Process Chemistry and Technology
  • Computer Science Applications
  • Fluid Flow and Transfer Processes


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