g-force induced loss of consciousness (abbreviated as G-LOC, pronounced "JEE-lock") is a term generally used in
aerospace physiology to describe a
loss of consciousness occurring from excessive and sustained
g-force
The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...
s draining blood away from the brain causing cerebral
hypoxia. The condition is most likely to affect
pilots of high performance
fighter and
aerobatic aircraft or
astronaut
An astronaut (from the Ancient Greek (), meaning 'star', and (), meaning 'sailor') is a person trained, equipped, and deployed by a List of human spaceflight programs, human spaceflight program to serve as a commander or crew member of a spa ...
s, but is possible on some
extreme amusement park rides. G-LOC incidents have caused fatal accidents in high performance aircraft capable of sustaining high ''g'' for extended periods.
High-g training for pilots of high performance aircraft or spacecraft often includes ground training for G-LOC in special
centrifuges, with some profiles exposing pilots to 9 ''g''s for a sustained length of time.
Effects of ''g''-forces
Under increasing positive ''g''-force, blood in the body will tend to move from the head toward the feet. For higher intensity or longer duration, this can manifest progressively as:
*
Tunnel vision – loss of peripheral vision, retaining only the center vision;
*
Greyout
A greyout is a transient loss of vision characterized by a perceived dimming of light and color, sometimes accompanied by a loss of peripheral vision. It is a precursor to fainting or a blackout and is caused by hypoxia (low brain oxygen level ...
– a loss of color vision;
* Blackout – a complete loss of vision, but retaining consciousness; and
* G-LOC – where consciousness is lost.
Under negative ''g'', blood pressure will increase in the head, which could result in the dangerous condition known as
redout
A redout occurs when the body experiences a negative g-force sufficient to cause a blood flow from the lower parts of the body to the head. It is the inverse effect of a greyout, where blood flows away from the head to the lower parts of the bo ...
.
Due to the high level of sensitivity that the eye’s retina has to hypoxia, symptoms are usually first experienced visually. As the retinal blood pressure decreases below
Intraocular pressure (usually 10–21 mm Hg), blood flow begins to cease to the retina, first affecting perfusion furthest from the optic disc and central retinal artery with progression towards central vision. Skilled pilots can use this loss of vision as their indicator that they are at maximum turn performance without losing consciousness. Recovery is usually prompt following removal of ''g''-force, but a period of several seconds of disorientation may occur. Absolute incapacitation is the period of time when the aircrew member is physically unconscious and averages about 12 seconds. Relative incapacitation is the period in which the consciousness has been regained, but the person is confused and remains unable to perform simple tasks. This period averages about 15 seconds. Upon regaining cerebral blood flow, the G-LOC victim usually experiences myoclonic convulsions (sometimes called the ‘funky chicken’) and full amnesia of the event is often experienced. Brief but vivid dreams have been reported to follow G-LOC. If G-LOC occurs at low altitude, this momentary lapse can
prove fatal, and even highly experienced pilots can pull straight to a G-LOC condition without first perceiving the visual onset warnings that would normally be used as the sign to back off from pulling any more ''g''s.
The human body is much more tolerant of ''g''-force when it is applied
anteriorly to posteriorly (front to back or Gx) than when applied
longitudinally (along the length of the body). However, most sustained ''g''-forces incurred by pilots are applied longitudinally. This has led to experimentation with
prone pilot aircraft designs which lies the pilot face down or (more successfully) reclined positions for astronauts. A similar concept, the
supine cockpit exists.
Thresholds
The ''g'' thresholds at which these effects occur depend on the training, age and fitness of the individual. An untrained individual not used to the ''G''-straining manoeuvre can black out between 4 and 6 ''g'', particularly if this is pulled suddenly. A trained, fit individual wearing a ''g'' suit and practicing the straining manoeuvre can, with some difficulty, sustain up to 12-14''g'' without loss of consciousness. The
Blue Angels
The Blue Angels, formally named the U.S. Navy Flight Demonstration Squadron, are a Aerobatics, flight demonstration squadron of the United States Navy.. Blue Angels official site. Formed in 1946, the unit is the second oldest formal aerobatics ...
regularly sustain 3–5 second bursts of 7.5 ''g'' thresholds.
See also
*
Index of aviation articles
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Articles related to aviation include:
A
Aviation accidents and incidents
– Above Mean Sea Level (AMSL)
– ADF
– Acces ...
*
2015 Shoreham Airshow crash, an accident claimed by the pilot to be caused by G-LOC.
*
g-force
The g-force or gravitational force equivalent is a Specific force, mass-specific force (force per unit mass), expressed in Unit of measurement, units of standard gravity (symbol ''g'' or ''g''0, not to be confused with "g", the symbol for ...
s
*
G-suit
A g-suit, or anti-''g'' suit, is a flight suit worn by aviators and astronauts who are subject to high levels of acceleration force ( g). It is designed to prevent a black-out and g-LOC (g-induced loss of consciousness) caused by the blood poo ...
*
Junkers Ju 87 WWII investigations in to G-LOC
*
Redout
A redout occurs when the body experiences a negative g-force sufficient to cause a blood flow from the lower parts of the body to the head. It is the inverse effect of a greyout, where blood flows away from the head to the lower parts of the bo ...
*
Firestone Firehawk 600, a
Champ Car
Champ Car World Series (CCWS) was the series sanctioned by Open-Wheel Racing Series Inc., a Governing body, sanctioning body for American open-wheel car racing that operated from 2004 to 2008. It was the successor to Championship Auto Racing T ...
race that was cancelled due to the g-loads the drivers were experiencing being high enough to cause g-LOC.
*
Euthanasia Coaster, a hypothetical roller-coaster designed to cause all passengers to suffer a fatally prolonged g-LOC.
References
{{Reflist
External links
G-LOC, Could It Happen to You?G-Force, Jerk, and Passing Out in a Centrifuge
Articles containing video clips
Physiology
Acceleration