title: Physiological implications of mechanical effects of +Gz accelerations on brain structures.
abstract: BACKGROUND
  In certain flight configurations, fighter pilots are exposed to high Gz acceleration (G) which may induce inflight loss of consciousness (G-LOC). When acceleration is of high amplitude, and the onset rate very rapid, G-LOC can occur extremely suddenly.
  
  
  OBJECTIVE
  Mechanisms other than brain hypoxia could be involved, enhancing its effects. In order to study the mechanical effects induced by such accelerations on cerebral structures, we estimated the stresses imposed on cerebral tissue when the brain is exposed to +Gz acceleration forces.
  
  
  METHODS
  An "in vitro" experiment was performed to measure brain deformations during centrifugation. A finite element model of the brain was formulated.
  
  
  RESULTS
  Computations indicate that traction and shear stresses are enhanced around the tentorial notch, and that compression stresses increase at the base of the cerebral hemispheres.
  
  
  CONCLUSIONS
  The amplitude of these stresses is not sufficient to directly disturb proper nerve cell functioning. However, they could interfere with brain vessels as external surface forces, thus enhancing vessel collapse and brain ischemia.
authors.affiliation: Institut de Médecine Aérospatiale du Service de Santé des Armées, Brétigny sur Orge, France. aguillaume@imassa.fr
authors.forename: Anne I
authors.initials: AI
authors.lastname: Guillaume
authors.forename: Daniel
authors.initials: D
authors.lastname: Osmont
authors.forename: Daniel
authors.initials: D
authors.lastname: Gaffié
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Sarron
authors.forename: Pierre
authors.initials: P
authors.lastname: Quandieu
mesh_terms: D000337:Aerospace Medicine; D000818:Animals; D001921:Brain / Q000098:blood supply / Q000473:pathology*; D004195:Disease Models, Animal; D006801:Humans; D018471:Hypergravity / Q000009:adverse effects*; D000860:Hypoxia