Defining risk in aerospace medical unconsciousness research

The maneuverability envelopes of current and future fighter/attack aircraft exceed unprotected human tolerance to environmental stress. Human exposure to unconsciousness therefore can result not only inflight, but in research and training laboratories which endeavor to provide methods of enhanced protection for aircrew. Solving the problem of unconsciousness requires a thorough understanding of the phenomenon itself. This can only be accomplished by defining the psychophysiologic aspects of unconsciousness and techniques to prevent its occurrence or enhance recovery, should it occur. The safety of experimental human exposure to G-LOC however, remains of some concern. A framework for discussing the relative insult to the central nervous system may be constructed from what is currently known about G-LOC. The results of animal experimentation allow an estimation of the central nervous system tolerance to hypoxia without permanent alteration of tissue integrity. Clinical medicine documentation of syncope and fainting episodes, coupled with a long history of uncomplicated G-LOC episodes suggests that a certain window of safe exposure exists. Utilization of G-LOC as an endpoint included exposure of very large numbers of humans to unconsciousness without significant complication. Animal experimentation suggests that 180 s of central nervous system hypoxia is associated with uncomplicated recovery. Human exposure as long as 100 s has also been safely accomplished. Centrifuge G-LOC exposure typically results in only 15-20 s of central nervous system hypoxia. As long as G-LOC experimentation using humans is performed within well defined limits, it may be accomplished within an acceptable risk envelope.(ABSTRACT TRUNCATED AT 250 WORDS)