Aerospace Gravitational Effects

Excerpt

When pilots fly high-performance aircraft, they conduct maneuvers in the air that expose them to high acceleration in the +GZ axis. These +GZ forces acting cephalad-to-foot direction induces cerebral hypotension that may impair cerebral blood flow. G-induced loss of consciousness (G-LOC ) occurs when acceleration forces produce a situation in which the cardiovascular system is unable to supply oxygenated blood to the regions of the nervous system that support consciousness. When aircrew of high-performance aircraft are exposed to +Gz acceleration, symptoms ranging from peripheral visual loss, blackout, and loss of consciousness may occur. A condition known as almost loss of consciousness (A-LOC) first described by the US Navy in the 1980s may occur when a pilot is exposed to +Gz stress at levels that are insufficient to cause G-LOC. It is a syndrome that encompasses a wide variety of cognitive, physical, emotional, and physiological symptoms. The most prevalent symptom is reported to be a disconnection between cognition and ability to act. In centrifuge studies of 500 healthy individuals, individuals who experience G-LOC were observed to have a blank stare and show signs of unconsciousness. The majority of persons who experience G-LOC have myoclonic jerks and which they do not remember after recovery from the episode. The convulsions last for about 4 seconds and occur after the return of cerebral blood flow. Memorable dreams follow the myoclonic jerks.

A study conducted by Green and Steven showed that 20.1% of United Kingdom Royal Air Force (RAF) aircrew had suffered one episode of G-LOC and 82% had suffered two episodes. G-LOC is reported to occur most commonly in training aircrew. Prevalence of G-LOC in front-line aircraft is low at 11.3%, and 6% in fast jet aircraft. It is difficult to predict pilot characteristics that may predispose to G-LOC. The most recent survey done in United Kingdom RAF showed a decrease in the incidence of G-LOC from 20% IN 2005 to about 15% in 2012. Sevilla and Gardner found that time on aircraft type less than 600 hours, pilotage younger than 30 years, and poor anti-G straining maneuver is associated with 72% of G-LOC accidents.