title: Mathematical modeling of the push-pull effect for various acceleration profiles and countermeasures.
abstract: BACKGROUND
  The push-pull maneuver (PPM) can lead to loss of consciousness in pilots of high-performance aircraft. Modeling of the physical and physiological aspects of this phenomenon should allow improved countermeasures.
  
  
  METHODS
  A structurally based mechanistic computer model was developed to incorporate dynamic carotid baroreflex responses and detailed modeling of vessel segments for different anatomic regions. The model was used to predict the effect of the PPM on cardiovascular responses and the protection afforded by extended coverage anti-G suits (ECGS) and neck pressure.
  
  
  RESULTS
  The model was validated by comparing the simulation results with previously published experimental data obtained during centrifuge and tilt-table studies. Simulations of various PPM acceleration profiles indicated that +Gz tolerance was reduced in the presence of higher +Gz levels prior to the push phase, more -Gz levels during the push phase, and prolongation of the push phase. On the other hand, the onset rate for the two phases had only minor effects on +Gz tolerance. Model output suggested that improved protection could be provided by an ECGS with minimal inflation delay and a multilevel pressure schedule in which the leg bladders inflated to a higher pressure than the abdominal bladder. Modeling application of a 100-mmHg neck pressure during the push phase partly inactivated the carotid baroreflex, but induced only a small increase in tolerance.
  
  
  CONCLUSIONS
  Mathematical modeling and simulation showed that +Gz tolerance for the PPM might be increased by improving the design and inflation schedule of the ECGS.
authors.affiliation: Department of Computer Application, Fourth Military Medical University, Xi'an, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Li-Fan
authors.initials: LF
authors.lastname: Zhang
authors.forename: Hong-Bing
authors.initials: HB
authors.lastname: Lu
authors.forename: Guo-Peng
authors.initials: GP
authors.lastname: Zhang
authors.forename: Huang-Sheng
authors.initials: HS
authors.lastname: Pu
mesh_terms: D000054:Acceleration; D000222:Adaptation, Physiological; D017704:Baroreflex; D002320:Cardiovascular Physiological Phenomena; D002339:Carotid Arteries / Q000502:physiology; D002498:Centrifugation; D003198:Computer Simulation; D005676:Gravity Suits; D006801:Humans; D008955:Models, Cardiovascular; D018667:Tilt-Table Test