High-G stress and orientational stress: physiologic effects of aerial maneuvering.

G stress can readily incapacitate pilots of modern fighter aircraft and result in mishaps due to G-induced loss of consciousness (GLC). The physiologic effects of high-G stress, including decreased head-level blood pressure due to hydrostatic pressure drop and decreased cardiac output due to inadequate venous return, result in the symptoms of visual loss and GLC. The body's primary natural defenses against the effects of G stress in flight, i.e., the neural tissue energy reserve and the cardiovascular baroceptor reflexes, determine the characteristic shape of the G-time tolerance curve, which is presented. Means of raising G tolerance fall into three categories: mechanical, physiological, and educational. Mechanical means include anti-G suits and valves, assisted positive-pressure breathing (APPB) systems, and special seats in which the seatback is reclined and/or the pilot's legs are elevated. Physiological means include frequent exposure to G stress, physical conditioning (weight training and moderate aerobic conditioning), selection of pilots for high natural tolerance, and performance of a vigorous and efficient anti-G straining maneuver. Educational means include briefings on methods of enhancing tolerance, and high-G training in a centrifuge to allow the pilot to perfect his anti-G straining maneuver. An improved anti-G valve, physical conditioning, high-G awareness briefings, and centrifuge training are now being applied in efforts to prevent GLC in current fighter aircraft. Future generations of even more maneuverable aircraft will probably necessitate the use of APPB, pilot selection, and high-G seats for protection of pilots from the effect of sustained high G forces.