title: Acceleration in other axes affects +Gz tolerance: dynamic centrifuge simulation of agile flight.
abstract: BACKGROUND
  Modern, thrust-vectored jet aircraft have the capability of developing multi-axis accelerations, especially during the performance of "supermaneuvers." These "agile" aircraft are capable of unconventional flight. The human consequences of this agile flight environment are unknown.
  
  
  METHODS
  This multi-axis acceleration environment was studied on the Dynamic Environment Simulator gimbaled centrifuge. There were nine relaxed, unprotected subjects who were exposed to either lateral (+/- 1, +/- 2 Gy), transverse chest-to-back (+1, 2.5, or 4 Gx), or back-to-chest (-1 Gx) sustained acceleration. Positive C (+Gz) acceleration was then added beginning at 1.0 Gz by gradual onset (0.1 Gz x s(-1)) until the subjects lost nearly all of their vision. Baseline +Gz-only relaxed tolerances were measured before and after all combined Gy/Gz and Gx/Gz exposures. Heart rate, percent cerebral oxygen saturation, and cerebral blood volumes were collected during each exposure.
  
  
  RESULTS
  Adding moderate transverse (+Gx) acceleration significantly reduced +Gz tolerance. Relaxed, unprotected +Gz tolerance was reduced approximately 0.25 G when 1.0 or 2.5 Gx was added to the increasing +Gz exposure. Adding moderate lateral Gy significantly increased +Gz tolerance. Relaxed, unprotected +Gz tolerance was increased approximately 0.5 G when +2 Gy or -2 Gy was added to the -Gz exposure. The decrease in cerebral blood volume was significantly less when +Gz was added to -1 Gx compared with the addition of +Gz to +Gx.
  
  
  CONCLUSIONS
  Multi-axis sustained accelerations, such as those experienced during thrust-vectored aircraft maneuvers, can either enhance or reduce the +Gz tolerance of the pilot depending on the direction of the net gravitoinertial force. Gy acceleration in conjunction with Gz acceleration can enhance G tolerance. Gx acceleration in addition to Gz acceleration can reduce G tolerance.
authors.affiliation: Biodynamics and Acceleration Branch, Air Force Research Laboratory, Wright-Patterson AFB, OH 45433, USA. William.albery@wpafb.af.mil
authors.forename: William B
authors.initials: WB
authors.lastname: Albery
mesh_terms: D000054:Acceleration / Q000009:adverse effects*; D000222:Adaptation, Physiological; D000328:Adult; D000337:Aerospace Medicine; D001359:Aviation / Q000379:methods; D001810:Blood Volume / Q000502:physiology; D002498:Centrifugation; D005260:Female; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D018472:Hypogravity / Q000009:adverse effects; D008297:Male; D008991:Monitoring, Physiologic; D018561:Space Simulation; D014785:Vision, Ocular / Q000502:physiology; D000078329:Workforce