Manifestations of Brief Instantaneous Anoxia in Man

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Abstract
Cerebral manifestations of anoxia induced by rapid (0.2 second) decompression to a barometric pressure of 68-70 mm Hg while breathing O2 were studied in a series of tests varying in duration from 6 to 18 seconds in 2 subjects. Changes in blood O2 saturation, in respiration and in the response to an acoustic signal were recorded and serial photographs taken in addition to the eeg. Three distinct phases of functional deterioration could be distinguished: (a) A state of automatism 13-15 seconds after decompression of 6 or more seconds duration with confusion, lack of discrimination and judgement associated with amnesia and activation of normal rhythms in the eeg. (b) A phase of arrest with sudden loss of consciousness at 17-19 seconds after decompression of 8 or more seconds duration. All spontaneous movements cease and face and eyes assume a mask-like expression while posture is still maintained. (C) Gradual loss of postural tone counteracted by brisk muscular contractions beginning at 19-20 seconds after exposure for at least 12 seconds. The eeg deteriorates progressively in this phase with predominance of slow frequencies and temporary absence of all activity. Certain analogies between these phenomena and the changes in consciousness during epileptic seizures were established. When circulation time is taken into account, the net anoxic survival time of the most sensitive cerebral functions appears to be 4-5 seconds, while loss of comprehension ensues at 7-8 seconds.

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