NIRS Monitoring of Pilots Subjected to +Gz Acceleration and G-Induced Loss of Consciousness (G-LOC)
As far back as 1918, incidences of pilots losing control of their aircraft due to fainting after a high +Gz maneuver were reported, with recovery about 20 seconds later without any apparent side effects. With increasing improvements in the performance of aircraft technology, particularly maneuverability and speed, the incidence of pilots losing consciousness in flight increased, as well as a rise in fatalities due to aircraft crashes. The definition of this phenomenon is "G-induced loss of consciousness" (G-LOC) which is further described as "a state of altered perception wherein (one's) awareness of reality is absent as a result of sudden, critical reduction of cerebral blood circulation caused by increased G force". The duration of G-LOC has been observed to average about 12 seconds (range 2 to 38 sec.) of unconsciousness, called the absolute incapacitation period, followed by a conscious, but confused / disoriented state for another 12 seconds (range 2 to 97 sec.) called the relative incapacitation period, in which the pilot still does not have full control of the aircraft. Losing control of an aircraft for 12 seconds or more is often fatal to the pilot at the high rate of speed an aircraft travels. The danger of losing consciousness is especially high in today's fighter jet aircraft, with the maneuverability that can cause high +Gz stress, which can overwhelm all of the pilot's anti G countermeasures to remain conscious. The return of purposeful movement (full pilot control of aircraft) follows the relative incapacitation period. To study this phenomenon, we used a non-invasive NIRS system of our design to monitor cerebral oxygenation changes of pilots subjected to high +Gz acceleration and G-LOC. Changes in oxyhemoglobin, deoxyhemoglobin, and total hemoglobin were recorded from pilots experiencing high +Gz acceleration, loss of consciousness, and recovery. In my presentation, I will discuss the general background of G-LOC, and then discuss observations and results of our study.