title: Physiologic +Gz tolerance responses over successive +Gz exposures in simulated air combat maneuvers.
abstract: BACKGROUND
  Fighter aircraft pilots are exposed to repetitive headward acceleration (+Gz) during air combat maneuvering. The objective of this study was to compare physiologic responses and the calculated +Gz tolerances of multiple successive +Gz exposures with the responses of the first +Gz exposure.
  
  
  METHODS
  There were 13 subjects who performed simulated air combat maneuvering (SACM) profiles composed of 10 rapid-onset rate +Gz cycles with different combinations of short- or long-duration +Gz plateaus (8 or 20 s) and +Gz pauses (1 or 15 s). +Gz, plateaus were individually set at levels inducing strong physiologic responses while the +Gz pause was set at 1.4 Gz. Head-level systolic pressure, ear opacity, and vision quality were measured.
  
  
  RESULTS
  The nadirs of head-level systolic pressure, ear opacity, and visual quality during each +Gz plateau were higher in subsequent cycles compared to the first +Gz cycle. There was an average increase in calculated +Gz tolerance of 0.35 +/- 0.21 Gz following the first +Gz cycle. SACMs with short +Gz pauses produced greater increases in +Gz tolerance than SACMs with long +Gz pauses.
  
  
  CONCLUSIONS
  Cardiovascular and visual responses were improved over the course of successive +Gz cycles, indicating that the risk of +Gz-induced loss of consciousness was not increased beyond the first +Gz cycle. The increase in +Gz tolerance beginning with the second cycle is attributed to a carryover of compensatory responses, primarily vasoconstriction, with possible contribution from greater venous return and baroreflex enhancement.
authors.affiliation: Individual Readiness Section, Defence Research and Development Canada - Toronto, Toronto, Ontario, Canada. lalande.sophie@mayo.edu
authors.forename: Sophie
authors.initials: S
authors.lastname: Lalande
authors.forename: Fred
authors.initials: F
authors.lastname: Buick
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D000337:Aerospace Medicine; D017704:Baroreflex / Q000502:physiology*; D018660:Blood Pressure Monitoring, Ambulatory; D006801:Humans; D018471:Hypergravity; D008889:Military Personnel; D014794:Visual Fields