G-induced loss of consciousness (G-LOC) is best defined as what?

• A. Transient fainting from dehydration.
• B. Seizure caused by electrical disturbance.
• C. Loss of consciousness due to brain hypoperfusion.
• D. Vasovagal syncope due to sight of blood.

Answer: (C)

G-LOC happens when high gravity forces reduce blood flow to the brain, so the brain becomes briefly underperfused and you lose consciousness. Under sustained +G, blood pools in the legs and abdomen, venous return to the heart droops, and cerebral perfusion pressure falls below what the brain needs, leading to loss of consciousness. When the G-load decreases, blood flow returns quickly and consciousness is regained. This is why the correct description emphasizes brain hypoperfusion as the cause.

The other scenarios don’t fit the situation specific to high-G flight: dehydration-related fainting is due to low blood volume, not the gravitational redistribution of blood; a seizure is an electrical disturbance; vasovagal syncope is a reflex drop in heart rate and blood pressure often triggered by a stimulus like sight of blood.