title: The effect of brief headward acceleration on human G tolerance.
abstract: OBJECTIVE
  To generate, on a multi-axial centrifuge, a negative to positive acceleration profile that reproduces the physiological reaction and subjective symptoms experienced by agile aircraft pilots.  Previous research will be summarized and current status of research described.
  
  
  METHODS
  Experiments have been accomplished with the Dynamic Environment Simulator (DES) using different profile generating techniques. The DES was programmed with a set of open-loop profiles that provided five second duration baseline exposures ranging from +1.4 Gz down to -2 Gz followed by rapid transition to positive G levels up 2 to 8 +Gz. Volunteer subjects were instrumented and trained to report visual symptoms.
  
  
  RESULTS
  Both profile generation approaches produce the reduced cardiovascular and subjective tolerance in a subset of subjects tested.  Accumulated stress and motion sickness are factors in quantitative measures.  Use of the anti-G straining maneuver may only temporarily alleviate the symptoms with a second period of visual symptoms even as the G load is removed.  Positive pressure breathing for G (PBG) does not appear to exacerbate the effect, but the advantages gained from PBG may be lost when a sustained G pull is preceded by a negative G push.
  
  
  CONCLUSIONS
  The utility and limitations of using a multi-axial centrifuge for the study of negative to positive G transitions have been described. Greater study is necessary on multiple factors affecting the effect and large numbers of volunteer subjects are needed.
authors.affiliation: Air Force Research Laboratory, Wright Patterson Air Force Base, Dayton, OH 45433-7901, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Chelette
authors.forename: R
authors.initials: R
authors.lastname: Allnutt
authors.forename: W B
authors.initials: WB
authors.lastname: Albery
authors.forename: L D
authors.initials: LD
authors.lastname: Tripp
mesh_terms: D000054:Acceleration; D000222:Adaptation, Physiological; D000337:Aerospace Medicine; D000401:Aircraft / Q000295:instrumentation; D001359:Aviation; D002498:Centrifugation; D006112:Gravitation; D006257:Head; D006801:Humans; D018471:Hypergravity; D008889:Military Personnel; D014474:Unconsciousness / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D014481:United States; D014794:Visual Fields