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.
Effects of reduced uterine blood flow on electrocortical activity, breathing, and skeletal muscle activity in fetal sheep.
Experiments were conducted in 11 unanesthetized fetal sheep during the last third of gestation to examine the effects of prolonged, reversible reduction in uterine blood flow on fetal electrocortical activity, breathing movements, and skeletal muscle activity. With an adjustable clamp placed around the maternal common internal iliac artery, uterine blood flow was restricted for 2 hours to produce a reduction in fetal arterial oxygen saturation from 56.1% +/- 1.9% to 28.8% +/- 0.7%. When blood flow was reduced, there was a decrease in the percentage of time that fetuses spent in low-voltage electrocortical activity, from 57.5% +/- 3.0% to 37.8% +/- 3.5%, and a decrease in the incidence of both breathing movements and integrated skeletal muscle activity. Younger fetuses (110 to 121 days' gestation) demonstrated a lesser degree of reduction in breathing movements when compared with older fetuses (125 to 140 days) whereas the effects of hypoxemia on electrocortical activity became less apparent with advancing gestational age.
On the prenatal development of function and structure in the somesthetic cortex of the sheep.
Publisher Summary This chapter presents a review of a series of investigations made in cortical systems during recent years on the prenatal development of cortical mechanisms within the parietal cortex. These investigations have been made on sheep which have a relatively long gestation time in comparison with the cat and the rabbit. The chapter mentions that the newborn sheep is behaviorally much more mature than the newborn cat that may indicate that in sheep the cortical functions have reached a higher degree of maturation at birth than in cats. Analogously the sheep fetus shows several cortical mechanisms during the second half of the prenatal period that appear several days after birth in the cat. The investigations to be reviewed cover a prenatal period from ages at which there is cortical “silence” and unresponsiveness up to ages in the fetal sheep corresponding to the postnatal period of the cat. It was therefore possible to catch the relatively early stage at which cortical excitability and cortical synaptic activity first appear. The chapter also discusses the relation between structure and function during this important phase of development.