A Hrbek

Development of visual and somatosensory evoked responses in pre-term newborn infants

Abstract In 48 newborns born at 24–42 weeks gestational age computer-averaged visual (VERs) and somatosensory (SERs) evoked responses were studied. The following results were obtained: 1. 1. In pre-term newborn infants below 30 weeks gestation the main or only component was a very slow negative wave, most distinct in the corresponding projection area. In the two modalities studied the response patterns were similar but not identical. 2. 2. During further development the slow negative wave gradually decreased and faster components appeared. VER and SER became more and more dissimilar. 3. 3. Constant primary components appeared after 29 weeks gestation in SER and between 32 and 35 weeks in VER. 4. 4. Non-specific SERs at the vertex and in ipsilateral leads increased during development. 5. 5. The latencies of both responses decreased. age was linear after 30 weeks gestation. age was linear after 30 weeks gestation. 6. 6. The amplitude generally decreased during development. Evoked responses are a suitable tool for developmental studies in man because of the close dependence of their variables on cerebral maturation.

Clinical application of evoked electroencephalographic responses in newborn infants. I: Perinatal asphyxia.

Evoked electroencephalographic responses are useful for the study of cerebral maturation in full‐term and pre‐term newborn infants. In an attempt to achieve wider clinical application, 57 newborn infants with differing degrees of perinatal asphyxia were examined. Altogether 154 examinations were performed. In all of them photostimulation was used, and in 72 investigations somatosensory evoked responses were also recorded. The following results were obtained:

Postasphyxial Cerebral Survival in Newborn Sheep after Treatment with Oxygen Free Radical Scavengers and a Calcium Antagonist

ABSTRACT: Acute, severe intrapartum asphyxia was mimicked by tying the umbilical cord in the exteriorized fetal sheep. After a standard time period cardiopulmonary resuscitation was instituted. In the treatment group (n = 14) the lambs were given a composition of scavengers of oxygen-derived free radicals and a calcium channel blocker. The control group of lambs (n = 12) was given placebo. The trial was blind and randomized. Hemodynamic and neurophysiological variables were measured from 30 min before asphyxia to 2 h postresuscitation. Mean arterial blood pressure, sagittal sinus venous pressure, heart rate, and cardiac output did not differ between the two groups although dramatic changes took place during asphyxia and resuscitation. Cerebral blood flow measured by 133-Xe washout method increased in both groups immediately after resuscitation. The treated animals retained an augmented cerebral blood flow during the 2 h postresuscitation while the control animals lost the increase of cerebral blood flow. The treated lambs recovered their somatosensory evoked potentials partially or completely in eight of 14 cases while the same figures for the control lambs were one of 12 cases. Immediately after resuscitation the cerebral reactions recovered to some extent in both groups but during the following 2 h the cerebral cortical function deteriorated in the control group but improved in the treated lambs. It is concluded that part of the brain damage in connection with acute, severe asphyxia may be inflicted by oxygen-derived free radicals released during the reoxygenation phase after resuscitation and that oxygen-derived free radical scavengers and calcium channel blockers may find a place in cardiopulmonary resuscitation.

Changes in the ECG and Somatosensory-Evoked EEG Responses during Intrauterine Asphyxia in the Sheep

Progressive changes in the S-T interval of the fetal ECG were studied in 14 mature lamb fetuses, acutely exteriorized and submitted to a graded hypoxia. The degree of hypoxic stress was measured from

Does Glucose Administration Affect the Cerebral Response to Fetal Asphyxia

Abstract. This study was designed to test whether the fetal brain has an increased resistance towards asphyxia at high levels of blood‐glucose, compared with low levels. 35 fetal sheep were exteriorized and investigated under general anesthesia. Cerebral blood flow (CBF) was estimated with the 133Xenon‐washout method. Cerebral uptake of oxygen, glucose, and lactate was measured. Somatosensory evoked potentials (SEP) were recorded. The fetuses were subjected to controlled asphyxia by ventilating the ewes with gasmixtures low in oxygen. The blood sugar levels of the fetuses were varied over a four‐fold range. During normal oxygenation of the fetus variations in the blood glucose concentration induced considerable changes in the cerebral glucose uptake, whereas CBF and oxygen uptake were unaffected. During asphyxia, hyperglycemia was associated with rapid development of acidosis and reduction in cerebral oxygen consumption together with deterioration of the neurophysiological characteristics of the brain. Far from being beneficial during asphyxia, fetal hyperglycemia appeared to reduce the tolerance of the fetal brain towards asphyxia. This report together with other evidence provides support for the view that extra glucose might be disadvantageous for the asphyxiated fetus.

Clinical Application of Evoked EEG Responses in Infants. III: Congenital Hypothyroidism

Previous studies have shown a close relationship between maturation of the central nervous system and development of evoked EEG responses. In this study, 13 infants with congenital hyperthyroidism were examined between the ages of one week and 17 months in an attempt to evaluate the degree of developmental retardation and the influence of hormonal treatment.

Clinical application of evoked EEG responses in newborn infants. II: idiopathic respiratory distress syndrome.

In an attempt to evaluate the clinical application of evoked electroencephalographic responses in the neonatal period, 16 newborn infants suffering from idiopathic respiratory distress syndrome were examined. Visual evoked responses were recorded in all infants, photic driving in nine and somatosensory evoked responses in all infants, photic driving in nine and somatosensory evoked responses in two. A total of 51 examinations were performed. The following results were obtained:

Cerebral reactions during intrauterine asphyxia in the sheep. II. Evoked electroencephalogram responses.

Extract: Somatosensory evoked electroencephalogram (EEG) responses (SER) were recorded in 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 pH levels were induced by ventilating the ewe with gas mixtures including 8–15% oxygen, either alone or combined with a 10% CO2 mixture, or with an intravenous infusion of bicarbonate to the fetus.The reaction of the SER during hypoxia followed two main patterns, one seen in the immature fetus and one in the more mature fetus. In the immature type of response (seen in all fetuses at or less than 110 days of gestational age) the primary response of the SER is more sensitive to oxygen lack than the secondary components, whereas in the mature type of response (seen at or more than 115 days of gestational age) the reverse is true.At moderate degrees of hypoxia, PaO2 between 15 and 20 mm Hg, the SER were moderately affected provided that the pH of the blood was within normal limits. At lower PaO2, values, and when moderate hypoxia was combined with acidosis, the SER were seriously affected or completely abolished. At PaO2, values above 20 mm Hg an acidosis had no effect on the SER.Speculation: The function of the fetal brain is seriously jeopardized by the combination of hypoxia and acidosis. Therefore, both hypoxia and acidosis should be counteracted during asphyxia to prevent brain damage.

EARLY DIAGNOSIS OF BRAIN DAMAGE AFTER PERINATAL ASPHYXIA BY MEANS OF EVOKED EEG RESPONSES

The early diagnosis of brain damage is stil an important problem and there is a lack of methods which can be used. Recordings of spontaneous electric activity provide no reliable information on the risk of damage after perinatal asphyxia. We try to use evoked EEG responses (ER) for these purposes. Preliminary results were already reported. Material and Method: This paper is based on 198 examinations in 90 neonates and infants with different degree of perinatal asphyxia. Visual evoked responses (VER) and photic driving (PD) were recorded in all of them, Somatosensory responses (SER) in 47 patients. More severe cases were examined several times. EEG was recorded bipolarly from corresponding projection areas and from vertex and averaged on a PDP 12 Digital computer. As stimuli light flashes and electrical pulses applied to n. medianus were used. Results: A number of alterations of ERs was observed. Most important were increased latencies and abnormal patterns of VERs, bad or absent PD and alterations of SERs. In order to express the findings in a quantitative manner a scoring system was devised. The total riskscore correlated well with the degree of asphyxia and with the prognosis. Almost all the infants with a permanent high riskscore developed symptoms of brain damage after a clinically silent period. Conclusion: Recording of ERs is a very usefull objective method for early diagnosis of brain damage after perinatal asphyxia.

108: VISUAL EVOKED RESPONSES IN CONGENITAL HYPOTHYREOIDISM

Visual evoked responses (VER) were studied in 10 children with hypothyreoidism. The age when the disease was discovered varied from 1 week to 1½ years. Five infants were younger than 3 months, three between 3 - 6 months. The diagnosis was in all cases verified by the finding of low levels of T3, T4 or PBJ and markedly increased levels of TSH in blood. Nine ohildrenwere examined repeatedly,.7 younger infants were followed up during several months. In all of them EEG responses to photostimulation were recorded. In 4 infants also somatosensory evoked responses (SER) were examined. Before treatment prolonged latencies and/or less mature patterns of VERs were observed. Most increased latencies were found in infants during the first months of age. During hormonal therapy latencies decreased to the normal level (or below it) and followed then the normal developmental curve. Also the response pattern became normal. Photic driving improved very rapidly, SSRs if recorded, behaved in the same way as VERs. The results show, that VERs are useful for assesment of the degree of the delay in the development of the brain and effectivity of the treatment in congenital hypothyreoidism.