The effect of +Gz offset rate on recovery from acceleration-induced loss of consciousness

The incapacitation resulting from +Gz-induced loss of consciousness (G-LOC) depends on the magnitude of the ischemic/hypoxic insult to the central nervous system (CNS). This magnitude is defined by the rate of onset of the +Gz, the +Gz level, the length of time at +Gz, the offset rate, and individual tolerance to +Gz. Offset rates have rarely been emphasized or even reported in +Gz research. This study compared the incapacitation between two groups of asymptomatic men resulting from generally similar rapid onset (greater than 3G/s) +Gz exposures to induce G-LOC but with different +Gz offset rates. For one group (N = 90) of G-LOC exposures the offset rate was 0.97 G/s and for the other group (N = 17) the offset rate was 2.75 G/s. The incapacitation following G-LOC with slower offset resulted in an absolute incapacitation period of 10.47 +/- 3 s, a relative incapacitation of 14.40 +/- 10.05 s, and a total incapacitation period of 25.04 +/- 10.13 s. With the more rapid offset G-LOC exposures the absolute incapacitation was 7.59 (+/- 3.14)s, relative incapacitation 5.40 +/- 3.38 s, and the total incapacitation was 13.20 +/- 4.36 s. The rate of +Gz offset also affects the time following G-LOC before onset of myoclonic convulsions. Rapid offset G-LOC exposures had a shorter period from the onset of unconsciousness to the onset of convulsions as compared to slower offset rates. The convulsion period, however, remained essentially the same. The results strongly favor an ischemic/hypoxic mechanism for G-LOC. The results also document the importance of offset rates in determining the magnitude of the ischemic-hypoxic insult to the CNS.(ABSTRACT TRUNCATED AT 250 WORDS)