title: Effect of 30-min +3 Gz centrifugation on vestibular and autonomic cardiovascular function.
abstract: BACKGROUND
  Repeated exposure to increased +Gz enhances human baroreflex responsiveness and improves tolerance to cardiovascular stress. However, it is not known whether such enhancements might also result from a single, more prolonged exposure to increased +Gz. Our study was designed to investigate whether baroreflex function and orthostatic tolerance are acutely improved by a single prolonged exposure to +3 Gz, and moreover, whether changes in autonomic cardiovascular function resulting from exposure to increased +Gz are correlated with changes in otolith function.
  
  
  METHODS
  We exposed 15 healthy human subjects to +3 Gz centrifugation for up to 30 min or until symptoms of incipient G-induced loss of consciousness (G-LOC) ensued. Tests of autonomic cardiovascular function both before and after centrifugation included: 1) power spectral determinations of beat-to-beat R-R intervals and arterial pressures; 2) carotid-cardiac baroreflex tests; 3) Valsalva tests; and 4) 30-min head-up tilt tests. Otolith function was assessed during centrifugation by the linear vestibulo-ocular reflex and both before and after centrifugation by measurements of ocular counter-rolling and dynamic posturography.
  
  
  RESULTS
  Of the 15 subjects who underwent prolonged +3 Gz, 4 were intolerant to 30 min of head-up tilt before centrifugation but became tolerant to such tilt after centrifugation. The Valsalva-related baroreflex as well as a measure of the carotid-cardiac baroreflex were also enhanced after centrifugation. No significant vestibular-autonomic relationships were detected beyond a vestibular-cerebrovascular interaction reported earlier in a subset of seven participants.
  
  
  CONCLUSIONS
  A single prolonged exposure to +3 Gz centrifugation acutely improves baroreflex function and orthostatic tolerance.
authors.affiliation: Human Adaptation and Countermeasures Office, National Aeronautics and Space Administration, Lyndon B. Johnson Space Center, Houston, TX 77058, USA. tschlege@ems.jsc.nasa.gov
authors.forename: Todd T
authors.initials: TT
authors.lastname: Schlegel
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Wood
authors.forename: Troy E
authors.initials: TE
authors.lastname: Brown
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Harm
authors.forename: A H
authors.initials: AH
authors.lastname: Rupert
mesh_terms: D000328:Adult; D001341:Autonomic Nervous System / Q000502:physiology*; D017704:Baroreflex / Q000502:physiology*; D002498:Centrifugation; D004244:Dizziness / Q000503:physiopathology; D006801:Humans; D018471:Hypergravity; D008297:Male; D009799:Ocular Physiological Phenomena; D010037:Otolithic Membrane / Q000502:physiology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*