Electrophysiological Correlates of +Gz Tolerance Comparison Study.

Abstract : This report describes an evaluation of a helmet mounted system; presently, under development for determination of +Gz induced loss of consciousness (G-LOC). The G-LOC detection system, self-contained and built into a standard flight helmet, consists of a set of dry electrodes, preamplifiers, signal conditioning circuits, and analog-to-digital converter for acquisition of the electroencephalogram (EEG) and electro-oculogram (EOG) signals. The study compares the the EEG activity acquired with the dry electrode system to EEG activity acquired with throw-away, electrocardiogram wet electrodes. Six volunteers were selected from fully qualified centrifuge subjects at Armstrong Laboratory. Each subject experienced the same acceleration profile. In three subjects, the beginning of the M-l straining maneuver could easily be determined from the 3-D dry electrode EEG spectral plots, which may imply that significant motion artifact or low. frequency components of the EMG are in the EEG signal. The rapid rise in EEG low frequencies (less than 4Hz), when the subject began the M-l straining maneuvers are not as obvious from the 3-D wet electrode EEG spectral plot. No G-LOC could be seen, precluding any comments on G-LOC. The results indicate that the dry electrode system is susceptible to motion artifacts that result in large-magnitude; low frequency signals. High-frequencies (24 to 36 Hz) were observed in the 3-D wet electrode EEG of two subjects, which were not as noticeable in the 3-D dry electrode EEG spectral plot. Part of the high-frequencies probably reflect muscle artifact of activity from the reference electrode.