title: Prediction of electrical impedance parameters for the simulated leg segment of an aircraft pilot under G-stress.
abstract: BACKGROUND
  Blood accumulation in the lower extremities of fighter pilots has been known to induce loss of peripheral vision and consciousness. G suits and anti-G straining maneuvers applied to lower limbs do not work according to the actual status of blood accumulation. Therefore, the problem of blood accumulation in the legs requires further investigation.
  
  
  METHODS
  The leg segment of an aircraft pilot has been modeled as a cylinder containing its anatomical structure of skin-fat layer, muscles, bones, and blood volume in the form of inner cylinders. Finite element analysis (FEA) was applied to the leg model with suitable boundary conditions. Predicted leg-segment electrical impedance (LEI) without blood accumulation has been compared with the measured experimental value using electrical impedance plethysmography (EIP). The effects of 7% blood pooling were analyzed by electrical impedance of the leg segment and its constituents by increasing the diameter of blood volume cylinder.
  
  
  RESULTS
  The LEI has been predicted to be 46.7 omega, which corresponds well with experimental value of 46.0 omega and predicted value, being 1.58% higher. Predicted LEI was reduced to 44.2 omega during simulation of blood accumulation in FE model. The relative contributions of admittance for leg constituents fat, muscle, bones and blood volume are also found to be 2.96, 75.58, 0.33, and 11.13%, respectively.
  
  
  CONCLUSIONS
  A computer simulation technique has been developed to predict electrical impedance parameters of the leg segment and its constituents with and without blood pooling. These results will be useful in further research and clinical applications for aircraft pilots under acceleration (G) stress.
authors.affiliation: Centre for Biomedical Engineering, Indian Institute of Technology Delhi, All India Institute of Medical Sciences, New Delhi.
authors.forename: Munna
authors.initials: M
authors.lastname: Khan
authors.forename: Sujoy K
authors.initials: SK
authors.lastname: Guha
mesh_terms: D000273:Adipose Tissue / Q000502:physiology; D000337:Aerospace Medicine; D001810:Blood Volume; D001823:Body Composition; D001842:Bone and Bones / Q000502:physiology; D003198:Computer Simulation; D020342:Finite Element Analysis; D006112:Gravitation; D006801:Humans; D007866:Leg / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D010992:Plethysmography, Impedance