Transient and maintained changes of the spontaneous occipital EEG during acute systemic hypoxia

It has been reported that during systemic hypoxia the spectral power of spontaneous EEG (closed eyes) increases, except for the power in the alpha band, which decreases. It is surmised that after a sudden decrease in inspired oxygen, the EEG parameters and SaO2 show similar temporal characteristics. Normobaric acute hypoxia in 14 healthy subjects was evoked by breathing a hypoxic gas. Frequency spectra were calculated from occipital recordings and quantified together with the parameters of the spectral alpha peak. During the first 20 min of exposure, SaO2 decreases exponentially. With eyes open, the frequency bands show a transient increase in power (110-160%). The peak-time of the transient is shorter for the alpha and beta1 bands (4.5 min) than for the delta2 and theta bands (7 min). After the transient, the bands reach sustained power levels ca. 65% higher than the control value. The frequency of the alpha peak decreases with 0.61 +/- 0.16 Hz (mean +/- SE). In contrast to the eyes-closed condition, the peak amplitude increases (41 +/- 12%). During systemic hypoxia many characteristics of the spontaneous EEG with open eyes differ from those under normoxia, and alpha activity deviates strongly from that during hypoxia with closed eyes. During the first 20 min of exposure changes in power are most prominent and do not follow the change of SaO2. Monitoring total EEG power with open eyes, SaO2 and respiration gives a good impression of the hypoxia-related neurophysiological state of the subject