title: Circadian profile of cardiac autonomic nervous modulation in healthy subjects: differing effects of aging and gender on heart rate variability.
abstract: Circadian Profile of Heart Rate Variability.
  
  
  BACKGROUND
  Although heart rate variability (HRV) has been established as a tool to study cardiac autonomic activity, almost no data are available on the circadian patterns of HRV in healthy subjects aged 20 to 70 years.
  
  
  RESULTS
  We investigated 166 healthy volunteers (81 women and 85 men; age 42 +/- 15 years, range 20-70) without evidence of cardiac disease. Time-domain HRV parameters were determined from 24-hour Holter monitoring and calculated as hourly mean values and mean 24-hour values. All volunteers were fully mobile, awoke around 7 A.M., and had 6 to 8 hours of sleep. Circadian profiles of vagus-associated HRV parameters revealed a marked day-night pattern, with a peak at nighttime and a plateau at daytime. The characteristic nocturnal peak and the day-night amplitude diminished with aging by decade. Estimates of overall HRV (geometric triangular index [TI], SD of NN intervals [SDNN]) and long-term components of HRV (SD of the averages of NN intervals for all 5-min segments [SDANN]) were low at nighttime and increased in the morning hours. There was a significant decline of 24-hour values of all HRV parameters (P < 0.001) and a strong negative correlation (P < 0.001) with increasing age. Mean 24-hour RR interval (P < 0.001), SDNN, mean SD of NN intervals for all 5-minute intervals (SDNNi), and SDANN (all P < 0.01) were significantly higher in men. Younger men also exhibited significantly higher values for vagus-associated parameters (root mean square successive difference [rMSSD], P < 0.05; SDNNi, P < 0.01); however, gender differences diminished with increasing age.
  
  
  CONCLUSIONS
  Normal aging is associated with a constant decline of cardiac vagal modulation due to a significant decrease of nocturnal parasympathetic activity. The significant gender-related difference of HRV decreases with aging. These findings emphasize the need to determine age-, gender-, and nycthemeral-dependent normal ranges for HRV assessment.
authors.affiliation: Medizinische Kinik II, Medizinische Universität zu Lübeck, Lübeck, Germany. Bonnemeier@medinf.mul-uebeck.de
authors.forename: Hendrik
authors.initials: H
authors.lastname: Bonnemeier
authors.forename: Gert
authors.initials: G
authors.lastname: Richardt
authors.forename: Jürgen
authors.initials: J
authors.lastname: Potratz
authors.forename: Uwe K H
authors.initials: UK
authors.lastname: Wiegand
authors.forename: Axel
authors.initials: A
authors.lastname: Brandes
authors.forename: Nina
authors.initials: N
authors.lastname: Kluge
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D001341:Autonomic Nervous System / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D006321:Heart / Q000294:innervation* / Q000502:physiology*; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012737:Sex Factors; D013223:Statistics as Topic; D014630:Vagus Nerve / Q000502:physiology