Instability of parasympathetic nerve function evaluated by instantaneous time–frequency analysis in patients with obstructive sleep apnea

  • Keisaku Fujimoto
  • Midori Ura
  • Haruna Yamazaki
  • Akikazu Uematsu
Original Article


The purpose was to determine whether the instability of parasympathetic nerve (PN) function is associated with fragmentation of sleep and the instability can be improved by CPAP treatment in obstructive sleep apnea (OSA). Fifty-three OSA and 50 non-OSA subjects were examined by full-PSG and pulse rate variability (PRV) was recorded simultaneously using a photoplethysmograph and evaluated by instantaneous time–frequency analysis using the complex demodulation method. PN and sympathetic nerve (SN) activity were assessed by the mean high-frequency (HF) amplitude and ratio of low-frequency (LF) and HF amplitude (LF/HF ratio), respectively. Furthermore, the shift in central frequency (CF) of the main HF peak over time was monitored continuously. The relative times over which the same main HF peak was sustained for at least 20 s and 5 min in total recording time (%HF20s and %HF5min) were considered as markers of PN stability. Twenty-two of 53 patients with OSA also examined under the treatment with continuous positive airway pressure (CPAP). A significant increase in mean LF/HF ratio and decrease in HF amplitude were observed in severe OSA. Furthermore, both %HF20s and %HF5min were significantly decreased not only in mild-to-moderate OSA but also in severe OSA, and %HF20s was the strongest independent determinant for arousal index. Treatment with

CPAP significantly decreased the LH/HF ratio and increased both %HF20s and %HF5min. These findings suggest that the stability of PN function is impaired by arousal due to repeated apnea and hypopnea in OSA, and that CPAP therapy improves SN activity and PN dysfunction.


Autonomic nerve function Obstructive sleep apnea Heart rate variability Photoplethysmograph Continuous positive airway pressure (CPAP) 



We thank Toshiro Momose and Haruka Suzuki, polysomnography technicians, and students (Aoki M, Kitagawa M, and Harada M) of the Shinshu University School of Health Sciences for their help and support. This research did not receive any specific Grant from funding agencies in the public, commercial, or not-for-profit sectors.

Compliance with ethical standards

Conflict of interest

The authors did not receive any specific grants from funding agencies in the public, commercial, or not-for-profit sectors, and report no conflicts of interest in this work.

Ethical approval

This study was conducted in accordance with the International Conference on Harmonisation-Good Clinical Practice and the Declaration of Helsinki (2008), and was approved by the institutional research ethics committee of Shinshu University School of Medicine (No. 2099).

Informed consent

All subjects were given an adequate explanation of the study and provided written informed consent.


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Copyright information

© Japanese Society of Sleep Research 2018

Authors and Affiliations

  1. 1.Departments of Clinical Laboratory SciencesShinshu University School of Health SciencesMatsumotoJapan
  2. 2.Department of Biomedical Laboratory Sciences, Graduate School of MedicineShinshu UniversityMatsumotoJapan

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