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G-LOC – The Enemy within!

G-LOC is G-induced loss of consciousness, defined as a “state of altered perception wherein one’s awareness of reality is absent as a result of sudden, critical reduction of cerebral circulation caused by increased G force”.

It has been observed during centrifuge training of pilots that the first symptom of G-LOC is a total loss of muscle tone, where one’s head and neck slumps. On regaining consciousness, some may report dreams, though almost half the people do not remember having lapsed into G-LOC. There is a dawning awareness of the situation and stimuli, but an inability to gain motor control, in turn reflecting likely delay in regaining aircraft control, if it occurs in flight! G-LOC may exert a temporary but psychologically crippling effect on the aggressive attitude of a pilot during aerial combat. At times, a sense of embarrassment, fear, confusion, anxiety, euphoria and even give-up attitude may significantly impair combat readiness during the most critical phase of combat. Hence it is valuable to remember that a pilot recovering from G-LOC might be technically conscious, but the lingering psychological factors combined with slow physical recovery certainly puts him at a disadvantage against an alert and conscious enemy pilot.

G-LOC is more than just the loss of consciousness. Loss of vision, consciousness, postural muscular control and memory along with myoclonic convulsions (jerky movements) and dreamlets together constitute a symptom complex defined as the G-LOC Syndrome. Various symptoms of the G-LOC syndrome signify the limits of CNS tolerance to +Gz stress. These symptoms are not the result of abnormal CNS function; they are normal responses of segments of the CNS affected differentially by specific patterns of +Gz induced compromised blood supply or hypoxia.

Characterized by sudden loss of consciousness, the period of incapacitation associated with an episode of G-LOC episode can be divided into two periods: absolute incapacitation, the period during which the pilot is unconscious lasting for an average duration of 15 sec; this is followed by relative incapacitation, during which the pilot is confused and not yet oriented for an average duration of another 15 sec. This may be associated with retrograde amnesia, dream like state and jerky movements during the recovery stage. The pilot may not be in control of aircraft during GLOC for up to 30 sec, with disastrous consequences at times.

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Reference
1. Ernsting’s Aviation Medicine. Rainford DJ, Gradwell DP (Editors). 4th Edition. Hodder Arnold, London 2006.
2. Fundamentals of Aerospace Medicine. DeHart RL, Davis JR (Editors). 3rd Edition. Lippincott, Williams & Wilkins, Philadelphia 2002.

Acknowledgement. Image courtesy Wikimedia Commons

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