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Power Spectral Analysis of the Neonatal Primate Electroencephalogram during Acute Hypoxemia

The effect of acute graded hypoxemia on the electroencephalogram (EEG) of five prematures and five full term Macaca nemestrina in the neonatal period was determined using power spectral analysis–a technique that obviates the limitations of visual inspection. The EEG of selected epochs was analyzed by a Fast Fourier Transform program (POWER) during the 20 min of each trial of hypoxemia and compared with simultaneous arterial oxygen tensions. Levels of hypoxemia were graded as profound (PaO2 = 15–25 Torr); severe (PaO2 = 26–35 Torr), moderate (PaO2 = 36–50 Torr), or mild (PaO2 = 51–75 Torr). The EEG during normoxemia had a band width of 0.5 to 10 Hz and a peak power at 1–3 Hz. During mild hypoxemia, an increase in power in the delta range (0–3.5 Hz) occurred in the oldest animals. At moderate hypoxemia, the youngest animals showed a depression of absolute power in the delta band. A slowing of the EEG and decrease in power in the theta frequency range (4–8 Hz) followed when severe hypoxemic levels were reached. During profound hypoxemia, all animals at each postnatal age exhibited a significant decrease in EEG power at the delta and theta frequencies (P < 0.025) except 3-wk-old full term animals in which there was no significant change in the delta band. These results clarify and extend previously reported effects of hypoxemia on the neonatal EEG.Speculation: The hypoxic-induced sequence of changes in the frequency and amplitude of the neonatal primate electroencelphalogram occur as a consequence of "neurotransmitter failure." At the isoelectric threshold, hyperpolarization from hyperkalemia results in electrical silence.