A simplified explanation for the occurrence of G-force induced Loss of Consciousness (G-LOC) are rapidly increasing and sustained +Gz loads, acting on the human body, hindering the heart to maintain the blood circulation to the head. The result is an insufficient oxygen supply of the brain, maintenance of venous return to the heart and the maintenance of blood pressure and blood flow to the brain.
Consequences of G-LOC are that many aircrew who experience G-LOC fail to report it and the G-LOC accident statistics rely on pilot reporting and may under-represent the problem. G-LOC causes severe damages and loss of lives and leads to annual Air Force material losses of several hundred million Euros.
As +Gz level increases from +1 to +5 Gz the eye-level blood pressure is significantly lower than the heart blood pressure. Due to the eye-to-heart distance, the eye-level blood pressure decreases to a value resulting in G-LOC, if no intervention is made.
Such interventions are wearing an anti-G-suit and performing Anti-G Straining Manoeuvres