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.