title: Circadian and ultradian rhythms in heart rate variability.
abstract: OBJECTIVE
  Heart rate variability (HRV) patterns reflect the changing effect of sympathetic and parasympathetic modulation of the autonomic nervous system. While overall and circadian heart rate (HR) and HRV are well characterized by traditional measures, there is currently no method to measure ultradian cycles of HR and HRV.
  
  
  METHODS
  HR/HRV for each 2-min interval was calculated using normal-to-normal interbeat intervals from overnight polysomnographic ECGs in 113 subjects, aged 58+/-10 years (65 male, 48 female). HR, SDNN2, high-frequency power (HF) and the LF (low-frequency power)/HF ratio were plotted. A curve-fitting algorithm, developed in MatLab, identified cyclic patterns of HR/HRV and extracted parameters to characterize them. Results were compared for older vs. younger patients, males vs. females, with vs. without severe sleep apnea, and for the upper and lower half of sleep efficiency.
  
  
  RESULTS
  Ultradian patterns for different HR/HRV indices had variable correspondences with each other and none could be considered surrogates. Differences were seen for all comparison groups, but no one marker was consistently different across comparisons.
  
  
  CONCLUSIONS
  Each HR/HRV parameter has its own rhythm, and the correspondence between these rhythms varies greatly across subjects. Quantification of ultradian patterns of HRV is feasible and could provide new insights into autonomic physiology.
authors.affiliation: 1. Division of Cardiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Phyllis K
authors.initials: PK
authors.lastname: Stein
authors.forename: Peter P
authors.initials: PP
authors.lastname: Domitrovich
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Lundequam
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Duntley
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Freedland
authors.forename: Robert M
authors.initials: RM
authors.lastname: Carney
mesh_terms: D000367:Age Factors; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D001683:Biological Clocks; D002940:Circadian Rhythm; D003198:Computer Simulation; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D009991:Oscillometry / Q000379:methods; D012737:Sex Factors; D012891:Sleep Apnea Syndromes / Q000503:physiopathology*