The physiological limitations of performance during acceleration.

A PILOT'S TOLERANCE to eyeballs-down acceleration can be readily assessed from the g stress levels at which he loses vision and then consciousness. With g stress applied at right angles to the spinal axis (eyeballs in or eyeballs out), however, the cardiovascular impairment is so much less severe that there is no comparably dramatic end point to mark tolerance. A crude evaluation of tolerance to transverse acceleration is possible from the period for which a pilot will endure the g stress in a centrifuge before he voluntarily terminates the run but ,this is subject to a large number of unmeasurable variables, such as motivation, competitiveness, and experience. The acceleration stresses encountered by the crew of a space vehicle on reentry will vary ~ddely with the lift-drag ratio of the vehicle and with the pilot's orientation relative to the dh'ection of motion of the vehicle. Numerous centrifuge studies have shown that healthy men can remain conscious under sustained EBI and EBO accelerations of high magnitude 1, 9 but the adequate performance of control tasks during reentry clearly requires more ,than mere maintenance of consciousness. Therefore, the development and implementation of refined criteria of pilot tolexance to EBO and EBI accelerations are essential not only for the further basic investigation of the physiological effects of acceleration but also for the objective evaluation of personnel, restraint systems, and the level of control performance that can be reasonably expected of men under reentry conditions. A contimfing study conducted by the Ames Research Center is directed to this end. Experienced test pilots have performed sophisticated tracking tasks under acceleration and their performances were evaluated by the techniqnes described, t, 2, s Concurrent physiologi, cal experiments have been conducted in an effort to correlate psychomotor ~performance with changes in p,hysiological functions. The experiments have been chiefly concerned with three organ systems most acutely ,affected by acceleration stress, namely visual, circulatory, and respirato W. A particularly important aspect of this program is that the development of a suitable restraint system ~0, t~. 12 has permitted us to study pilots under acceleration