title: Estimation of parasympathetic nerve function during sleep in patients with obstructive sleep apnea by instantaneous time-frequency analysis.
abstract: OBJECTIVE
  The pathophysiologic aspects of parasympathetic nerve (PN) function during sleep in patients with obstructive sleep apnea (OSA) studied by classical power spectrum analysis on heart rate variability (HRV) are highly controversial. The controversy is attributed to methodologic concerns, such as poor time resolution involved in power spectrum analysis. We aimed to establish the appropriate method for the investigation of PN function in OSA patients with apneas and hypopneas using instantaneous time-frequency analysis with complex demodulation (CD) and sufficient time resolution.
  
  
  METHODS
  A total of 30 patients with PSG-confirmed mild to severe OSA were recruited for the analysis of frequency spectra contained in R-R intervals (RRI) of overnight electrocardiograph (ECG) tracings. High-frequency (HF) domains ranging between 0.15 and 0.40 Hz were selected for analysis. Among these domains, the HF domain with the maximum instantaneous amplitude was defined as the main HF peak and was used as the surrogate marker of PN discharge. Based on density spectrum array (DSA) map for main HF peak constructed with a time scale of 1s and a frequency resolution of 0.002 Hz (HF-DSA map), the shift in central frequency (CF) of main HF peak over time was continuously monitored. When the main HF peak with the same CF lasted for more than 20 s or 5 min on HF-DSA map, the PN function was considered to be stable or very stable. The measurements were then repeated after continuous positive airway pressure (CPAP) treatment.
  
  
  RESULTS
  The extent of PN-evoked modulation of RRI was enhanced in nonrapid eye movement (NREM) sleep, though the stability was reduced in both NREM and rapid eye movement (REM) sleep. These peculiar behaviors of PN function were reversed by CPAP treatment.
  
  
  CONCLUSIONS
  We found that instantaneous time-frequency analysis allowed estimation of transitional changes in PN function during sleep in OSA patients.
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan. Electronic address: yamaguc@sirius.ocn.ne.jp.
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yamaguchi
authors.affiliation: NoruPro Light Systems Incorporation, 2-11-25 Tokura, Kokubunji-shi, Tokyo 185-0003, Japan.
authors.forename: Noboru
authors.initials: N
authors.lastname: Ohki
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Maiko
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Natsumi
authors.initials: N
authors.lastname: Satoya
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Inoue
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Shigemitsu
authors.initials: S
authors.lastname: Onizawa
authors.affiliation: Department of Urology, Aoyama Hospital, TWMU, 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Maeda
authors.affiliation: Department of Cardiology, Aoyama Hospital, TWMU, 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Haruki
authors.initials: H
authors.lastname: Sekiguchi
authors.affiliation: Comprehensive Medical Center of Sleep Disorders, Aoyama Hospital, Tokyo Women's Medical University (TWMU), 2-7-13 Kita-Aoyama, Minato-ku, Tokyo 107-0061, Japan.
authors.forename: Mayumi
authors.initials: M
authors.lastname: Suzuki
authors.affiliation: Department of Respiratory Medicine, Tokyo Medical University Ibaraki Medical Center, 3-20-1 Chuou, Ami, Inashiki, Ibaraki 300-0395, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Tsuji
authors.affiliation: Department of Respiratory Medicine, Tokyo Medical University Ibaraki Medical Center, 3-20-1 Chuou, Ami, Inashiki, Ibaraki 300-0395, Japan.
authors.forename: Kazutetsu
authors.initials: K
authors.lastname: Aoshiba
authors.affiliation: The First Department of Medicine, TWMU, 8-1 Kawata-cho, Shinjuku-ku, Tokyo 162-8666, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Nagai
mesh_terms: D000368:Aged; D001342:Autonomic Nervous System Diseases / Q000503:physiopathology*; D045422:Continuous Positive Airway Pressure; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010275:Parasympathetic Nervous System / Q000502:physiology*; D017286:Polysomnography / Q000379:methods*; D056152:Respiratory Rate / Q000502:physiology; D012815:Signal Processing, Computer-Assisted; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology* / Q000628:therapy*; D012894:Sleep Stages / Q000502:physiology
keywords: CPAP; Complex demodulation method; Inspiratory gating; Obstructive sleep apnea; Parasympathetic nerve function; Power spectrum analysis; Time–frequency analysis