title: Sex differences in cardiac sympathovagal balance and vagal tone during nocturnal sleep.
abstract: OBJECTIVE
  To analyze sex differences in nocturnal vagal tone and cardiac sympathovagal balance during sleep in healthy men and women.
  
  
  METHODS
  In two groups of healthy, non-obese adults (15 men and 14 women), sleep was polygraphically recorded and heart rate variability was assessed during an awake period prior to sleep and during sleep. Vagal tone was estimated by the high-frequency (HF) power component of heart rate variability, and sympathovagal balance was indexed by the ratio of low-frequency (LF) power to HF power.
  
  
  RESULTS
  As compared to women, men showed decreases in vagal tone and increases in sympathovagal balance. During rapid eye movement (REM) sleep, a withdrawal of vagal tone occurred with an increase in sympathetic dominance. Men showed a greater increase of sympathovagal balance during REM sleep than women. Secondary analyses covarying for differences in reproductive hormone levels, physical activity, and sleep measures did not alter the results.
  
  
  CONCLUSIONS
  The marked increase in cardiac sympathetic drive during REM sleep in men has implications for understanding sex differences in the risk of cardiovascular events. Additionally, these data offer a pathway to explain the peak in cardiac arrhythmias and sudden cardiac death seen more often in the morning hours.
authors.affiliation: Cousins Center for Psychoneuroimmunology, UCLA Semel Institute for Neuroscience, 300 Medical Plaza, Suite 3-109, Los Angeles, CA 90095-7057, USA.
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Valladares
authors.forename: Sam M
authors.initials: SM
authors.lastname: Eljammal
authors.forename: Sarosh
authors.initials: S
authors.lastname: Motivala
authors.forename: Cindy L
authors.initials: CL
authors.lastname: Ehlers
authors.forename: Michael R
authors.initials: MR
authors.lastname: Irwin
mesh_terms: D000328:Adult; D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D017286:Polysomnography; D012016:Reference Values; D012737:Sex Factors; D012890:Sleep / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D014630:Vagus Nerve / Q000502:physiology*