title: Effects of low ambient temperature on heart rate variability during sleep in humans.
abstract: The effects of cold exposure on heart rate variability (HRV) during sleep were examined. Eight male subjects slept under three different conditions: 3 degrees C, 50-80% relative humidity (RH) [3]; 10 degrees C, 50% RH [10]; and 17 degrees C 50% RH [17]. No significant differences were observed in HRV during rapid eye movement sleep (REM) and wakefulness. The ratio of the low frequency (LF) to high frequency component (HF) of HRV (LF/HF) significantly differed among the conditions during stage 2 and slow wave sleep (SWS) that decreased as the ambient temperature decreased. The normalized LF [LF/(LF + HF)] significantly decreased in 3 and 10 than in 17 during SWS. In low ambient temperature, predominant cardiac parasympathetic activity during stage 2 with no significant difference during REM and wakefulness may cause variations in HRV at transition from stage 2 to REM and wakefulness. These results may partly explain the peak in adverse cardiac events during winter.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 6, 1-1-1, Higashi, Tsukuba, Ibaraki 305-8566, Japan. kazue@tfu-mail.tfu.ac.jp
authors.forename: Kazue
authors.initials: K
authors.lastname: Okamoto-Mizuno
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Tsuzuki
authors.forename: Koh
authors.initials: K
authors.lastname: Mizuno
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ohshiro
mesh_terms: D003080:Cold Temperature; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D017286:Polysomnography; D012894:Sleep Stages / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult