Consciousness monitoring using near-infrared spectroscopy (NIRS) during high +Gz exposures.

The relationship between human consciousness and oxygen saturation (rSO(2)) in cerebral tissue under high +Gz stress was non-invasively monitored by near-infrared multiple wavelength spectroscopy (NIRS). We studied the drop in rSO(2) levels in human subjects during exposure to various head-to-foot acceleration (+Gz) profiles. These profiles included sustained +Gz plateaus and repeated short duration +Gz pulses of varying duration. The end point in this study was +Gz-induced loss of consciousness (G-LOC). The rSO(2) levels under normal (asymptomatic), almost loss of consciousness (A-LOC) and G-LOC conditions were recorded. Correlations among decrease in rSO(2), +Gz pulse duration, +Gz stress level and incapacitation time (ICAP) after G-LOC were also investigated. It was found that once rSO(2) fell to a certain level, G-LOC occurred. This threshold was repeatable and independent of the +Gz level or duration. It was also observed that the total ICAP after G-LOC was dependent on the length of time that rSO(2) remained below the G-LOC threshold level, i.e. the longer the rSO(2) level remained below the G-LOC induction level, the longer the subject remained unconscious. These results may prove to be useful in designing closed loop control systems for personal protective gear for pilots of high performance aircraft.

Noninvasive monitoring of human consciousness by near-infrared spectroscopy (NIRS) during high +Gz stress.

Noninvasive monitoring of the relative change in oxygen saturation (rSO2) in cerebral tissue by near-infrared multi-wavelength spectroscopy (NIRS) was investigated in humans under high acceleration (+Gz) stress. These profiles included sustained 15-second +Gz plateaus and repeated short duration +Gz pulses of varying duration. The end points in this study were loss of consciousness due to high +Gz exposure (GLOC). In many cases subjects demonstrated cognitive and physical symptoms related to reduced cerebral blood flow without frank unconscious, which has been called Almost Loss of Consciousness (ALOC). Both the rSO2 levels during and after the +Gz exposures and the total time subjects were incapacitated after GLOC were recorded. It was found that while the drop in rSO2 at the onset of GLOC was lower during pulse exposures as compared to sustained exposures, the total time to recovery from GLOC was longer during the sustained runs. By applying a better understanding of the nature and timing of +Gz-induced changes in cerebral tissue oxygenation, more efficient control systems for personal protective gear for pilots of high performance aircraft can be implemented.