Isoelectric EEG Research Articles

Oxidative metabolism of the cerebral cortex of the rat in severe insulin-induced hypoglycaemia.

Abstract—Measurements were made of organic phosphates, carbohydrate substrates, amino acids and ammonia in the cerebral cortex, as well as of cerebral blood flow and of cerebral metabolic rate for oxygen and glucose in rats that developed an isoelectric EEG pattern (‘coma’) during insulin‐induced hypoglycaemia. The results were compared to those obtained in control animals, as well as in hypoglycaemic animals with an EEG pattern of slow waves and polyspikes. In animals with slow waves and polyspikes, there was a decrease in all citric acid cycle intermediates except succinate and oxaloacetate, and a decrease in the pool size of intermediates. In animals that had an isoelectric EEG for 5–15 min, there were further decreases in citrate, isocitrate, α‐ketoglutarate, malate and fumarate, but since the concentration of succinate (and oxaloacetate) increased, the pool size remained the same. In isoelectric animals, the results revealed extensive utilization of amino acids by both transamination and deamination reactions. However, since glycogen had disappeared and the amino acid pattern was constant after the first 5 min of isoelectric EEG, further oxidation must have occurred at the expense of non‐carbohydrate, non‐amino acid substrates.There were two‐ to three‐fold increases in cerebral blood flow in animals with slow waves and polyspikes and in animals with isoelectric EEG, and no decrease in the cerebral metabolic rate for oxygen. Since less than half of the oxygen consumption could be accounted for in terms of glucose extraction, the data indicate that severe hypoglycaemia is associated with extensive oxidation of endogenous substrates other than carbohydrates and free acids.

Brain phospholipid metabolism during ischemia.

Molecular mechanisms accounting for the vulnerability of brain to ischemic damage are incompletely understood. To assess the role of membrane integrity, phospholipid metabolism is investigated in subcellular organelles of brain following varying degrees of ischemia. Global brain ischemia is produced in rabbits by combining hypotension and hypoxia (4% oxygen). Restoration of blood pressure and oxygen after a three-minute isoelectric EEG results in full recovery, while a five-minute isoelectric EEG results in either a lack of recovery or neurological deficits. Quantitative analysis of seven phospholipids in subcellular organelles shows no consistent pattern of phospholipid changes following ischemia. Incorporation of radioactive phosphate, on the other hand, discloses moderate alterations following five-minute ischemia. These findings indicate that brain ischemia provokes phospholipid changes, but their role in impairing membrane integrity and in initiating irreversible ischemic brain damage is uncertain.

The effects of hornet venom sac extract on the electrical activity of the cat brain

A method for testing minute quantities of extracts of hornet venom sacs by injection into the vertebral artery of cats is described. Neurotoxic effects of venom sacs manifested by isoelectric EEG and by depression of respiratory centre, appeared prior to cardiovascular manifestations. Injection into the carotid artery necessitated 100 times large amounts of venom and a longer time elapsed before results similar to those after intravertebral injection were obtained. The cardiovascular manifestations preceded the cerebral effect using intracarotid injection. The active fraction seems to be proteinaceous, has antigenic properties and does not cross a dialysis membrane. Incubation of venom with antivenin serum prepared by immunization of a goat caused inactivation of the neurotoxic and hemolytic effects of the venom sac extract.

Acute hexachlorophene encephalopathy: clinico-neuropathological correlation.

This is the first report of neuropathologic findings following oral ingestion of hexachlorophene in the human. The patient was a 7 year old boy who accidentally ingested 45 ml (approx.) of pHisoHex (hexachlorophene).Toxic reactions included nausea, vomiting, anorexia, diarrhea, decrease in visual acuity, blurred vision blindness, somnolence and disorientation. He developed cardiac arrhythmia, fever, isoelectric EEG and finally respiratory and cardiac arrest 61 h after admission.

An experimental model of brain ischemia combining hypotension and hypoxia.

A variety of experimental models for cerebral ischemia are currently available, but none are entirely satisfactory. We are reporting a model which combines hypotension, produced by intravenous Arfonad, with hypoxia, produced by respiring 4% oxygen. Rabbits used are awake but paralyzed with succinylcholine and ventilated mechanically. The electroencephalogram (EEG) is monitored with durally implanted electrodes. Onset of an isoelectric EEG ensues 4.5 ± 0.7 minutes in 17 rabbits studied and is used to measure the degree of ischemic insult. After three minutes of an isoelectric EEG, circulatory restoration is followed by complete functional recovery. After five minutes of an isoelectric EEG, rabbits do not recover or show neurological deficits such as limb weakness. The potential effects of systemic ischemia on these animals are minimized because of the rapid onset of ischemic brain damage. Examination of arterial blood gases, pH, platelets, various organs histologically, and the distribution of carbon-particles in the intracerebral circulation reveals that systemic factors are minimal. Moderately delayed onset of cortical EEG activity and the presence of motor impairment or an inability to respire satisfactorily after extubation indicates that the brunt of ischemic insult is upon brain. Our model has the advantages of simplicity and predictability and offers the opportunity to assess functional impairment after graded degrees of cerebral ischemia. We conclude that our model of cerebral ischemia produced by hypotension and hypoxia is a reasonable alternative to existing methods.

Experimental brain ischemia: protection from irreversible damage with a rapid-acting barbiturate (methohexital).

Experimental brain ischemia was produced in rabbits by coupling systemic hypotension and hypoxia. The animals were paralyzed with succinylcholine and ventilated mechanically. Durally implanted electrodes were used to monitor the severity of ischemia. Five minutes of an isoelectric EEG produced irreversible brain damage in most of the rabbits. Four rabbits receiving the rapid-acting barbiturate, methohexital, in the dosage of 5 mg/kg at the onset of the isoelectric EEG showed complete protection from detectable ischemic damage and recovered dramatically. It is suggested that suppression of brain metabolism with barbiturates during cerebral ischemia is worthy of clinical assessment.

Visual evoked responses during neonatal respiratory disorders in low birth weight infants.

Extract: By using a standard electroencephalograph and a signal averager, the visual evoked response (VER) to paired and single light flashes was recorded from the midline occipital scalp regions in 24 low birth weight infants, 13 of whom were studied during periods of respiratory difficulty. Eleven of the latter died in the neonatal period. In seven infants, at the onset and during marked hypoxemia caused by prolonged apnea or airway obstruction, the following VER abnormalities occurred alone or in combination: marked decrease in amplitude of summed responses, absent summed response to first stimulus of the paired flash, and absent summed responses to both stimuli of the paired flash. In six infants, complete loss of VER's and a marked decrease in electroencephalogram (EEG) amplitude were associated with severe hypoxemia. In four of the six, VER's returned to normal following resuscitation, indicating that severe bioelectric abnormalities may be reversible as the blood gases return toward normal and before permanent brain damage occurs. Following repeated or severe and prolonged hypoxemia in these same six infants, isoelectric EEG's and absent evoked responses recorded terminally persisted for 30 min–8 hr prior to cessation of heart activity; during the terminal period, resuscitative efforts resulted in improved blood gas measurements in four of the six but without return of the VER. Abnormalities in VER's were not found in other infants with respiratory distress in whom recordings were obtained prior to the onset of severe hypoxemia. or prolonged apneic episodes. Of 10 infants who had neuropathologic examination, intracranial hemorrhage was found in 9 and intracerebral hemorrhage was found in 6. Five of the latter infants had abnormal neonatal VER's. The exact range of blood gas values associated with abnormal VER's could not be determined in our study, although normal responses were noted at Po2 values as low as 34, 37, and 38 mm Hg in three infants. Normal VER's obtained in the infants without respiratory disorders were not always associated with normal neurologic examination in later infancy. Speculation: The management of low birth weight infants with respiratory disorders is limited by the lack of methods which reliably and quantitatively evaluate neonatal cerebral function. Evoked responses to light flashes recorded from scalp EEG in premature infants and summed by signal averagers permit objective measurement of brain electrical activity. In low birth weight infants with respiratory difficulties, abnormal

Reflex activity in brain death

O diagnóstico de morte cerebral está baseado em critérios clínicos, eletrencefalográficos e angiográficos. Do ponto de vista clínico deve ser evidenciado o seguinte quadro: coma profundo, midríase paralítica bilateral, ausência de reação a qualquer estímulo externo, apnéia, arreflexia superficial e profunda. Do ponto de vista eletrencefalográfico são necessários dois registros, separados por um intervalo de 24 horas, evidenciando traçados iselétricos. No presente trabalho são estudados 15 pacientes com morte cerebral comprovada do ponto de vista clínico e eletrencefalográfico. Em 8 pacientes havia persistência de atividade reflexa durante a fase de morte cerebral (reflexos profundos e/ou superficiais). Fenômenos de automatismos medulares também foram verificados em 3 pacientes.

The electroretinogram during terminal anoxia in humans

Persistent electroretinograms (ERG) in the presence of truly isoelectric EEGs were noted in five patients who had experienced cerebral anoxia which led to irreversible coma. Following termination of respiratory support of these patients, the summated ERG in response to light flashes was recorded until it was no longer present. The deterioration of the ERG followed a consistent pattern in each patient. After the initial diminution and subsequent obliteration of the b wave, a negative ERG (remnant negativity) persisted. This in turn disappeared. These events occurred over a period lasting up to 33 min. These findings demonstrate that, as in animals, the neural elements of the human retina which give rise to the ERG are less sensitive to anoxia than is the cerebral cortex.

Reversible Iso-electric EEG In Barbiturate Coma

To the Editor.— Iso-electric electroencephalograms have usually been interpreted to constitute cerebral cortical death. However, a case of barbiturate overdose resulted in coma and iso-electric EEG; the EEG reverted to normal with complete recovery of the patient. Report of a Case.— A 69-year-old white woman was admitted to the San Antonio Community Hospital on July 18, 1969, in a comatose state. She had been despondent by the recent death of a son and could not be aroused from sleep on the morning of admission. She had received a prescription for "sleeping pills," but no bottle or suicide note was found. Respirations were labored, and the blood pressure was 90/70 mm Hg. The pupils were in midposition, unresponsive to light, and corneal reflexes were absent. Extremities were flaccid, the deep-tendon reflexes absent, and the patient did not respond to painful stimuli. A spinal tap demonstrated crystalclear fluid under normal pressure, with

The effect of cerebral ischaemia or intracarotid injection of methohexitone on short term memory in goats

Eight goats were surgically prepared with bilateral carotid loops and cranial implants connected to cortical and sub-cortical sites. The goats were trained in 3 delayed response tasks in which they had to choose the correct feeder from 3 situated in a large room. Training continued until the goats were performing successfully in the 3 tasks, usually with delays of up to 10 min. At this stage, the effect of a short period of disruption of brain electrical activity occuring during the delay period was investigated. Unconsciousness and frequently a temporary flattening of the cortical and subcortical EEG was produced either by means of cephalic ischaemia or by intra-carotid injection of methohexitone, a rapidly metabolised barbiturate. It was shown that a period of unconsciousness and temporary flattening of EEG occurring during the delay period did not impair the performance of the goats in the delayed response tasks. Assuming that isoelectric EEG implies absence of unit neuronal activity it is concluded that the type of recent memory involved in delayed response tasks does not require prolonged reverberatory neuronal activity but depends upon some intraneuronal chemical change.

The EEG in acute barbiturate intoxication, with particular reference to isoelectric EEGs : S. Sament and A. D. Huott (Boston, Mass., U.S.A.)

The EEG in acute barbiturate intoxication, with particular reference to isoelectric EEGs : S. Sament and A. D. Huott (Boston, Mass., U.S.A.)

Cerebral blood flow and cerebral death.

At present the diagnosis of cerebral death is based on the absence of manifestations of cerebral function (deep coma, wide pupils, absence of reflexes and spontaneous respiration, isoelectric EEG, etc.) during a variable period of time. However, the absence of vital signs of an organ, even for prolonged periods, is no proof of its death. The death of an organ can only be considered as proved by the demonstration that this organ has remained completely deprived of its blood flow during a period of time that surpasses its ability to survive circulatory arrest. In the case of the brain, the permanent absence of clearance of a radioactive tracer deposed within the brain is considered to demonstrate total absence of flow through it and, thus, to prove cerebral death. As discussed in the text, previous attempts at angiographic “demonstration” of the arrest of cerebral blood flow cannot be accepted uncritically. The value of the present findings in determining the death of a patient with reference to organ transplantation has been discussed.

The Isoelectric Electroencephalogram

Experience with 25 isoelectric electroencephalograms obtained during the past ten years with the 25 "respirator brains" examined during the past three years is presented. Characteristic neuropathological features of the respirator brain consist of severe brain swelling, gray to hemorrhagic discoloration, marked softening, and both anoxic necrosis and autolysis of neurons. An isoelectric EEG, defined as complete loss of cortical electrical activity with maximal amplification, if sustained for an hour or more under appropriate clinical circumstances, is highly suggestive of cerebral death.

The isoelectric electroencephalogram. Significance in establishing death in patients maintained on mechanical respirators.

Experience with 25 isoelectric electroencephalograms obtained during the past ten years with the 25 brains examined during the past three years is presented. Characteristic neuropathological features of the respirator brain consist of severe brain swelling, gray to hemorrhagic discoloration, marked softening, and both anoxic necrosis and autolysis of neurons. An isoelectric EEG, defined as complete loss of cortical electrical activity with maximal amplification, if sustained for an hour or more under appropriate clinical circumstances, is highly suggestive of cerebral death.

Cerebral metabolism during epileptic seizures in man

In order to estimate cerebral metabolic changes during epileptic seizures in man, arterial and cerebral venous PO 2, oxygen saturation, PCO 2, pH, Na + and K +, blood pressure, expiratory CO 2, EEG and cerebral venous flow were recorded during 22 seizures in eleven volunteer epileptic subjects. Generalized seizures with multiple spike and sharp waves in the EEG, “electro-decremental seizures” and petit mal seizures with 3/sec spike and wave complexes were recorded and compared. No changes in the parameters measured of cerebral metabolism or circulation were seen preceding any type of seizure. During seizures some evidence was adduced for an increase of cerebral oxygen consumption and CO 2 production, which was most evident during generalized seizures and minimal during petit mal. The brain tissue was hypoxic during the first phase of all seizures except the “electro-decremental” type. Following generalized seizures there was severe cerebral and systemic acidosis with marked hyperoxia of cerebral venous blood associated with isoelectric EEG and post-ictal paralysis. Evidence was also adduced compatible with a gain of sodium and loss of potassium by the brain during generalized and “electro-decremental seizures”. This was not found during petit mal seizures. It was concluded that post-epileptic paralysis with flattening of the EEG appeared to be initiated by cerebral anoxia but was maintained by cerebral acidosis.

Flat electroencephalograms during 28 days in a case of “encephalitis”

A case diagnosed clinically as encephalitis with completely flat EEG tracings recorded over a period of four weeks, is described; a complete clinical and EEG recovery followed. The rarity of flat records in cases of encephalitis, especially of such a long duration as in this case, followed by a full recovery, is pointed out. This observation indicates that isoelectric EEG's recorded over prolonged periods are not always to be considered as a grave prognostic sign.