title: Circadian rhythm of autonomic cardiovascular control during Mars500 simulated mission to Mars.
abstract: BACKGROUND
  The Mars500 project was conceived to gather knowledge about the psychological and physiological effects of living in an enclosed environment during 520 d as would be required for a real mission to Mars. Our objective was to investigate the circadian profile of heart rate variability (HRV) in the context of the Mars500 study.
  
  
  METHODS
  Before, during, and after confinement, 24-h EKG records were obtained from the six crewmembers who participated in the mission. Autonomic activity was evaluated through time and frequency domain indexes of HRV analysis. Circadian rhythmicity was assessed both by averaging hourly HRV along wake and sleep scheduled periods and by fitting a 24-h harmonic to the hourly means.
  
  
  RESULTS
  During confinement, wake HRV showed (mean +/- SE) a progressive increase in mean RR interval (from 778 +/- 24 ms to 916 +/- 42 ms), and in the amplitude (values are wavelet power coefficients) of very low (from 13.3 +/- 0.3 to 14.1 +/- 0.2) and high (from 7.8 +/- 0.4 to 8.3 +/- 0.3) frequency components. During sleep, the relative amplitude of the high frequency component of HRV decreased (from 11.8 +/- 1.6 to 9.4 +/- 1.8 normalized units). Overall, sleep-wake differences of HRV showed a progressive decrease of the relative amplitude of the high frequency component. Also, circadian HRV rhythms were dampened during confinement.
  
  
  CONCLUSIONS
  Data revealed diminished amplitude of the rest-activity pattern of the autonomic nervous system parasympathetic function. Reduced daylight exposure and mood changes could account for this observation.
authors.affiliation: Departamento de Docencia e Investigación, Facultad de Ciencias Médicas, Universidad Católica Argentina and Consejo Nacional de lnvestigaciones Científicas y Técnicas (CONICET), Buenos Aires, Argentina.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Vigo
authors.forename: Francis
authors.initials: F
authors.lastname: Tuerlinckx
authors.forename: Barbara
authors.initials: B
authors.lastname: Ogrinz
authors.forename: Li
authors.initials: L
authors.lastname: Wan
authors.forename: Guido
authors.initials: G
authors.lastname: Simonelli
authors.forename: Evgeny
authors.initials: E
authors.lastname: Bersenev
authors.forename: Omer
authors.initials: O
authors.lastname: Van Den Bergh
authors.forename: André E
authors.initials: AE
authors.lastname: Aubert
mesh_terms: D000328:Adult; D000339:Affect; D018480:Astronauts; D001341:Autonomic Nervous System / Q000502:physiology*; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D012890:Sleep / Q000502:physiology; D013026:Space Flight; D014851:Wakefulness / Q000502:physiology