On Tracking the Course of Cerebral Oxygen Saturation and Pilot Performance During Gravity-Induced Loss of Consciousness

Objective: The aim of this study was to track the course of cerebral tissue oxygen saturation (rSO2) and pilot performance during an episode of gravity-induced loss of consciousness (GLOC). Background: GLOC, a major problem facing pilots of high-performance aircraft, is brought about by a sudden reduction in rSO2 as a result of increased +Gz force. It consists of 24 s of complete functional impairment followed by a prolonged period of performance recovery. This study tested the hypothesis that delayed recovery in GLOC is caused by a slow return of rSO2 following removal of the g-force that induced the episode. Method: GLOC was induced in U.S. Air Force personnel via a centrifuge with math and tracking tasks emulating flight performance. A near-infrared spectroscopy unit provided the rSO2 measure. Results: Declines in rSO2 from baseline pinpointed when pilots would cease active flight control and when GLOC would set in. Counter to expectation, rSO2 returned to baseline levels shortly after the centrifuge came to a complete stop following GLOC onset. Nevertheless, performance deficits continued for 49.45 s thereafter. Conclusion: The prolonged performance recovery time in GLOC cannot be attributed to delays in the return of rSO 2. This finding explains why previous ergonomic efforts to shorten the duration of GLOC episodes by increasing the rate of return of rSO 2 have not been fruitful. Evidently, another approach is needed. Application: Such an approach might use the close linkage between loss of rSO2, performance deterioration, and GLOC onset to develop a warning system that would permit pilots to take effective action to avoid GLOC incapacitation.