Unconsciousness in flight and its prevention.

The physiological mechanism underlying two of the most potent causes of loss of consciousness in flight, viz. hypoxic hypoxia and exposure to rapid onset of high +GZ accelerations have been explored in this paper, using principally experimental work conducted at the Royal Air Force Institute of Aviation Medicine. The influence of the composition of the gas breathed before and after sudden decompression of the pressure cabin of an aircraft at high altitude has been described together with the physiological basis of the present standards for preventing disturbances of performance due to hypoxia following rapid decompression. The value and limitations of pressure breathing with oxygen at high pressures in preventing hypoxia on exposure to altitudes above 40,000 feet have been discussed together with the series of partial pressure suits used in the Royal Air Force. The mechanisms and occurrence of G-induced loss of consciousness in pilots of combat aircraft have been reviewed. The increasing likelihood of loss of consciousness due to G in new very agile combat aircraft is considered together with the limitations of the standard methods of enhancing G tolerance. The adoption and development of pressure breathing together with chest counterpressure and extended-cover G trousers which provide excellent protection against high levels of acceleration is described.