Cerebral Reactions during Intrauterine Asphyxia in the Sheep. II. Evoked Electroencephalogram Responses

Abstract

Somatosensory evoked electroencephalogram (EEG) responses (SER) were recordedin 19 fetal lambs with gestational ages varying from 66 to 140 days. The ewes were anesthetized with chloralose and the fetuses were exteriorized with intact umbilical circulation. Periods of hypoxia at different p H levels were induced by ventilating the ewe with gas mixtures including 8-15yG oxygen, either alone or combined with a 10yo COr mixture, or with an intravenous infusion of bicarbonate to the fetus.

Cerebral reactions to intrauterine asphyxia in the sheep. III. Effects of alterations of hematocrit and viscosity

“…Moreover in the hypoxic group, multiple regression analysis demonstrated a significant reduction of the residual variance when oxygen extraction was correlated to arterial pH and oxygen Saturation in combination compared to when correlated to Saturation alone. Thus, the same impairment of oxygen extraction by the brain during the combination of hypoxia and acidosis is demonstrated äs in the previous studies [2,6], and this impairment was not relieved by decreasing the blood viscosity.…”

“…The present study was prompted by findings in the exteriorized fetal lamb that the combination of hypoxia and acidosis impaired the cerebral functions in terms of electrical activity and oxygen consumption more seriously than hypoxia alone [2,6]. Since these findings could be explained by a reduction of the oxygen extraction from the blood it was considered relevant to evaluate the possibility that microcirculatory and rheological factors contributed to the deleterious eftect of combined hypoxia and acidosis.…”

“…Only one type of plasma substitute was used in each experiment. A more detailed account of the experimental procedures is given in [2,6].…”

“…Likewise, the fact that an individual can withstand a period of asphyxia but survive with a permanent brain damage is thoroughly documented. In an attempt to evaluate the role of a few specified factors in the causation of the insult to the brain a series of experiments were conducted on the fetal lamb [2,6]. In these experiments it was demonstrated that hypoxia altered the electrical activity of the .brain, äs measured by the somato-sensory evoked EEG responses (SER).…”

Brainstem Auditory Evoked Responses in the Newborn Lamb

“…Previous investigators have established the anatomical location of the various short latency potentials as originating from specific nuclei or ascending tracts within the auditory pathway from the coch lear nucleus to the midbrain [9], These poten tials have been shown to be elicitable in many species including humans, dogs, mon keys, kittens, and rats [2], Several investiga-tors have studied the developmental changes of the evoked potential in newborn kittens and have observed a lower stimulus decibel threshold required to elicit a stimulus, an increased resistance to fast click rates, better definition of wave forms, and a decrease in the latency of the response [10,25]. Similar findings have been noted in human neonates [4,24,31] and this technique has been used for detection of auditory and brainstem dis ease associated with neonatal asphyxia, pre maturity, drug toxicity, as well as structural and demyelinating disorders [18,26,30,32], BAER have not yet been studied in the newborn or fetal lamb, although this model has been used extensively in perinatal and developmental physiology.…”