Performance and physiological effects of acceleration-induced (+ Gz) loss of consciousness

Loss of consciousness (LOC) was intentionally induced by exposing eight volunteers to individually-titrated levels of head-to-foot acceleration (+ Gz) using 2- and 4-s onset rates (mean = 6.1 + Gz required to induce LOC) and a gradual, .067 G X s-1 onset rate (mean = 7.2 Gz required). Subjects were trained over a prior 2-week period on a multitask battery comprising three simultaneously executed tasks representative of those required in piloting, and then centrifuged to LOC at each of the three onset rates on alternate days. Performance was assessed for 5 min prior and 7 min after each LOC. Primary results indicated: a) significant and substantial impairment in the two discrete response secondary tasks (choice reaction time and arithmetic computation), with mean recovery to pre-LOC levels within 3 min on each task, b) no group mean impairment for the primary, compensatory tracking task, c) substantial individual variation in physiologically and behaviorally defined recovery from LOC, d) a negative influence of aerobic fitness on G tolerance and LOC recoverability, and e) that recovery effects were not generally dependent upon onset rate. Mean absolute incapacitation (head dropped) for the rapid onset rates was 12.1 s. For the gradual onset rate, mean absolute incapacitation was 16.6 s. Mean relative incapacitation (head erect, no voluntary task engagement) for the rapid onset rates was 11.6 s; for the gradual onset rates, mean relative incapacitation was 15.7 s. Evidence for retrograde amnesia effects was equivocal.