Mathematical models for predicting straining G-level tolerances in reclined subjects.
Mathematical models that predict straining G-level tolerances of subjects reclined > 55 degrees are described. Straining G-level tolerances are defined as those G-levels of exposures that require the use of the anti-G straining maneuver (AGSM). A subject reclined > 55 degrees has a reduced inspiratory volume that limits the maximum intrathoracic pressure that can be developed that is the basis for the AGSM. Therefore the inability to perform a maximum AGSM reduces the maximum G-level that can be tolerated. G-level tolerances of subjects at seat-back angles between 75 degrees and 55 degrees are modeled. The use of positive pressure breathing (PBG) to increase G-level tolerance is considered. Maximum G-level tolerances are dependent upon anti-G suit pressures (psi) used and are predicted as follows: 55 degrees = 11.7 and 12.7 G with 7 and 10 psi; 65 dergrees = 12.1 and 12.8 G with 6 and 9 psi; and 75 degrees = 13.4 and 14.2 G with 5 and 8 psi anti-G suit pressure.
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Human Effectiveness Directorate Det 5, Air Force Research Laboratory, Brooks AFB, TX 78235-5118, USA.
D000054:Acceleration; D000222:Adaptation, Physiological; D000337:Aerospace Medicine; D001794:Blood Pressure; D005676:Gravity Suits; D006801:Humans; D018471:Hypergravity; D007320:Inspiratory Capacity; D008954:Models, Biological; D011175:Positive-Pressure Respiration; D011187:Posture / Q000502:physiology*; D011312:Pressure; D014797:Vital Capacity