Spectral analysis of fetal sheep EEG during hypoxia.
Abstract Power spectra and coherence functions were obtained on samples of EEG recorded from fetal sheep in utero . Hypoxia was produced by respiring the ewe on gas mixtures containing reduced oxygen pressure. With both halothane and local anesthesia, the EEG changes associated with hypoxia consisted of an early power reduction in higher frequencies followed by a reduction of over-all amplitude leading to the isoelectric stage. The times at which statistically significant changes occurred were not earlier during the progressive fall of fetal arterial pO 2 than visual estiamtes of abnormality made on line from the paper record and were in all cases later than significant cardiovascular changes.
EEG, ECG, and acid-base observations during acute fetal hypoxia.
Abstract The effects of hypoxia on the EEG, heart rate, and acid-base status of fetal sheep were studied in 28 experiments which permitted simultaneous blood determinations on both sides of an intact placenta. Alterations in heart rate and rhythm preceded significant elevations of lactate concentrations and occurred prior to unambiguous changes in the EEG. A bradycardia preceded the onset of the isoelectric stage of the fetal EEG. The consistency of this finding suggested an etiologic relation. The time to recovery of normal EEG rhythms was a function of the length of the isoelectric stage but not of the total period of hypoxia or time to the onset of the isoelectric stage.
Fetal and maternal electroencephalography in the guinea pig.
Abstract This study describes the technique and demonstrates the usefulness of simultaneous maternal and fetal electroencephalography in guinea pigs. The earliest brain waves noted were in a 24-g fetus (47 days). Frequency of waveforms and voltage increased as fetal maturity increased. The addition of pentobarbital changed the fetal electrical patterns and correlated closely with similar maternal changes. Anoxia in the maternal guinea pig, by clamping the trachea, produced parallel and almost synchronous changes in the maternal and fetal recordings.