title: Effects of gravitational acceleration on cardiovascular autonomic control in resting humans.
abstract: OBJECTIVE
  Previous studies of cardiovascular responses in hypergravity suggest increased sympathetic regulation. The analysis of spontaneous heart rate variability (HRV) parameters and spontaneous baroreflex sensitivity (BRS) informs on the reciprocal balance of parasympathetic and sympathetic regulations at rest. This paper was aimed at determining the effects of gravitational acceleration (a g) on HRV and BRS.
  
  
  METHODS
  Eleven healthy subjects (age 26.6 ± 6.1) were studied in a human centrifuge at four a g levels (1, 1.5, 2 and 2.5 g) during 5-min sessions at rest. We evaluated spontaneous variability of R-R interval (RR), and of systolic and diastolic blood pressure (SAP and DAP, respectively), by power spectral analysis, and BRS by the sequence method, using the BRSanalysis(®) software.
  
  
  RESULTS
  At 2.5 g, compared to 1 g, (1) the total power (P TOT) and the powers of LF and HF components of HRV were lower, while the LF/HF ratio was higher; (2) normalized units for LF and HF did not changed significantly; (3) the P TOT, LF and HF powers of SAP were higher; (4) the P TOT and LF power of DAP were higher; and (5) BRS was decreased.
  
  
  CONCLUSIONS
  These results do not agree with the notion of sympathetic up-regulation supported by the increase in HR and DAP (tonic indices), and of SAP and DAP LF powers (oscillatory indices). The P TOT reduction leads to speculate that only the sympathetic branch of the ANS might have been active during elevated a g exposure. The vascular response occurred in a condition of massive baroreceptive unloading.
authors: Département de Neurosciences Fondamentales, Université de Genève, 1, Rue Michel Servet, 1211, Geneve 4, Switzerland, timothee.fontolliet@unige.ch.
authors: Timothée
authors: T
authors: Fontolliet
authors: Vincent
authors: V
authors: Pichot
authors: Guglielmo
authors: G
authors: Antonutto
authors: Julien
authors: J
authors: Bonjour
authors: Carlo
authors: C
authors: Capelli
authors: Enrico
authors: E
authors: Tam
authors: Jean-Claude
authors: JC
authors: Barthélémy
authors: Guido
authors: G
authors: Ferretti
mesh_terms: D000054:Acceleration; D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology; D001794:Blood Pressure / Q000502:physiology*; D002320:Cardiovascular Physiological Phenomena; D006112:Gravitation; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D012146:Rest / Q000502:physiology*; D055815:Young Adult