Recognizing +Gz-induced loss of consciousness and subject recovery from unconsciousness on a human centrifuge.

Human exposure to +Gz-induced loss of consciousness (G-LOC) remains of some concern relative to the well-being of the individuals experiencing the unconscious episodes. Detailed kinetic analysis of over 500 G-LOC episodes on a human centrifuge allowed an evaluation of the time for subjective recognition by observers of the onset of G-LOC and subsequent recovery to normal baseline conditions. The characteristics of early, coincident, and late recognition of the onset of G-LOC were evaluated. Earlier recognition of G-LOC was observed to occur when the rate of onset of the +Gz-stress was gradual (less than 0.6 G/s). Rapid onset rate (greater than 0.6 G/s) exposures were more likely to result in late recognition of G-LOC. The duration of the resulting period of unconsciousness (absolute incapacitation) was very sensitive to the time for recognition of G-LOC and most rapid return to a normal (+1 Gz) environment. The absolute incapacitation increased significantly from early (10.7 s) to coincident (11.4 s) to late (13.2 s) recognition of G-LOC which differed by a total of only 4.6 s. The results allow development of an initial standard of care envelope for apparently safe exposure of human subjects to centrifuge G-LOC since no adverse effects were observed with any of the exposures. The results also demonstrate the extreme sensitivity of the central nervous system to small changes in exposure to +Gz-stress which can be accurately measured.