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Extreme Physiology and Medicine

, 3:9

First Online: 02 May 2014Received: 04 September 2013Accepted: 11 April 2014


BackgroundThe limiting physiological envelope to extreme gravitational stress is defined by neurologic symptoms and signs that result from exceeding neurologic tolerance. The edge of the limiting envelope is defined by the complete incapacitation associated with acceleration +Gz induced loss of consciousness. Should + Gz-induced loss of consciousness occur in-flight, brisk recovery of conscious function is essential for aircraft recovery. If recovery does not occur, accident investigation aimed at preventing such accidents is enhanced by understanding the temporal aspects of the resulting incapacitation. The mechanistic basis of neurological reintegration leading to consciousness recovery is of broad medical and scientific interest.

MethodsRecovery of consciousness episodes from a prospectively developed +Gz-induced loss of consciousness repository of healthy individuals was analyzed to define variables influencing recovery of consciousness. The time from loss to recovery of consciousness as measured by observable signs, is defined as the absolute incapacitation period. The absolute incapacitation period from 760 episodes of loss and recovery of consciousness in healthy humans was analyzed to define +Gz-profile variables that determine the duration of functional neurologic compromise.

ResultsMean time from loss to return of consciousness for 760 episodes of consciousness recovery was 10.4 ± 5.1 s; minimum 1 s; maximum 38 s. Offset rate for the +Gz-exposure deceleration profiles varied from a minimum of 0.17 Gs to a maximum of 7.93 Gs.The curve produced by plotting +Gz-offset rate Gs; y versus absolute incapacitation period s; x described a hyperbolic relationship. The hyperbolic relationship indicates there is a minimum time mean 8.29 ± 3.84 s required for recovery of consciousness when complete loss of consciousness occurs.

ConclusionsMean recovery time from +Gz-induced unconsciousness is dependent on the deceleration profile-s offset rate from the point of loss of consciousness. This relationship is described by a curve plotting offset rate and time for recovery of consciousness. This curve predicts when conscious function should return following exposure to +Gz stress sufficient to cause unconsciousness. The maximum +Gz level of the recovery exposure profile was found to be inadequate for predicting variations in the time for recovery of consciousness.

KeywordsNeurophysiology Ischemia Syncope Acceleration Consciousness Unconsciousness Abbreviations+Gzthe standard terminology used for describing acceleration stress on the human when the direction of the acceleration is headward and the direction of the resultant inertial force is footward

ABSINCAPabsolute incapacitation period unconsciousness period

CPNScephalic nervous system

G-LOC+Gz-induced loss of consciousness

G-ROC+Gz recovery of consciousness

GMAXmaximum +Gz level of the recovery exposure profile

GOFFgradual offset rate-run

LOCloss of consciousness

LOCINDTIloss of consciousness induction time

ROCrecovery of consciousness

ROFFrapid offset rate-run

TOFFtransitional offset rate-run.

Electronic supplementary materialThe online version of this article doi:10.1186-2046-7648-3-9 contains supplementary material, which is available to authorized users.

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Autor: Typ Whinnery - Estrella M Forster - Paul B Rogers


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