[Reproducibility of somatosensory evoked potentials and EEG in normal humans under hyperbaric oxygenation]

Hyperbaric oxygenation (HBO) was reported to have a favorable influence on ischemic brain dysfunction, and also appeared to be useful in improving brain edema. Somatosensory evoked potentials (SEP) and EEG would be available as indicators of brain function. The purpose of this paper is to study reproducibility of the N1-amplitude of SEP and EEG under HBO. Materials were 10 normal volunteers, from 21 to 31 (mean age: 26) years old. Two stimulating needle electrodes were inserted into the skin at the wrist and somatosensory stimulations were applied to the median nerve with 1 msec duration square pulses. Stimulation pulses were generated regularly every 1 sec., and stimulus intensity was adjusted just above the thumb twitch threshold. Monopolar EEGs were recorded from 16 silver-cup electrodes on the scalp, and SEPs were recorded by averaging 250 responses in those EEGs using computer technique. N1-amplitude was determined by the vertical distance between peaks of the P1 and N1 components. EEGs were analyzed by Fast Fourier Transform and the square root of the averaged power of each frequency band (delta, theta, alpha 1, alpha 2, beta) was obtained and evaluated as the equivalent potential. EEGs under the influence of sleeping or artifacts, such as electromyograms, eye lid movements and wandering of the base line, were excluded in evaluating the EEGs. SEPs and EEGs recorded consecutively. The first record was taken before HBO under air breathing at 1ATA, the second during HBO under pure oxygen breathing at 2ATA, and the third after HBO under air breathing at 1ATA once again.(ABSTRACT TRUNCATED AT 250 WORDS)