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Query: UMLS:C0494475 (tonic-clonic seizure)
 1,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The intrinsic processes involved in the initiation and arrest of seizures are not completely understood. Cortical and cerebellar inhibitory mechanisms, accumulation of metabolic products, and glial uptake of extracellular potassium (K+o), anions, and released neurotransmitters are all important processes that limit focal firing and terminate a seizure once it has been initiated. Of these, the intrinsic cortical inhibitory mechanisms--i.e., recurrent and surround inhibition--appear to be the most important. Active cation and anion transport processes are two metabolic events that have yet to be elucidated but clearly could be involved in terminating a seizure discharge. For example, without an active mechanism to transport chloride, opening of the chloride channel by the inhibitory transmitter GABA would not result in increased chloride permeability. The transient hypoxia and hypercapnia and lactic acidosis that follows a severe tonic-clonic seizure produces a mixed systemic metabolic and respiratory acidosis. In experimental animals, the hypercapnia that results is sufficient to block seizure discharges. Increasing the CO2 concentration significantly reduces the extension to flexion (E/F) ratio of mice given maximal electroshock seizures (MES) and increases the time required for 50% of the animals to recover sufficiently from a first MES to be able to have another MES. The decreased E/F ratio and the increased recovery time (RT50) are both indicative of a decrease in seizure activity. Since the extent to which CO2 is allowed to accumulate in the brain is regulated by the glial specific enzyme carbonic anhydrase (CA), it follows that the glial cell has an integral role in the mechanisms involved in arresting seizure activity. In contrast, hypoxia increased the E/F ratio and decreased the RT50, evidence that seizure activity was enhanced. Another metabolic factor affecting duration of seizure activity, susceptibility to seizures, and recovery from seizures is glucose. Recovery from seizures depends in part on an adequate supply of this energy source. An inverse correlation (R = 0.95) between RT50 and blood sugar was found when the blood sugar was altered experimentally by treatments that altered the endocrine status (pancreatectomy, treatment with alloxan, cortisol, insulin, glucagon, and dextrose). Since glial cells contain (as glycogen) the small amount of glucose present in the brain, they probably hasten the ability of the brain to recover normal function following a seizure.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Role of glial cation and anion transport mechanisms in etiology and arrest of seizures. 370 23

In the present study, experimental exposures to hyperbaric oxygen (HBO2) were performed (30-min exposure to 2.8 bar (280 kPa) pure oxygen). During all phases of the experiment, blood flow velocity in the right middle cerebral artery was monitored with transcranial Doppler (TCD) sonography. Time courses of heart rate, blood pressure, respiratory rate, end-tidal CO2, and TCD mean velocity (Vmean) are described for a group of 23 subjects during uncomplicated exposure to HBO2 and for three subjects who showed signs of central nervous system (CNS) O2 toxicity, including one subject with a HBO2-induced generalized tonic-clonic seizure. Hyperbaric oxygen decreased Vmean an effect that could not completely be explained by changes in end-tidal CO2. The findings of the present study are in agreement with the concept that an increase in partial oxygen pressure is the primary factor underlying CNS O2 toxicity. Of the variables analyzed, the TCD Vmean is the most valuable variable for monitoring a HBO2 exposure. The Vmean showed the most pronounced change during HBO2 application, and in one subject a sudden increase in Vmean during HBO2 exposure heralded toxicity before clinical signs. It should be realized, however, that the small series of subjects with toxicity in this study does not allow us to draw definite conclusions.
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PMID:Transcranial Doppler sonographic measurements of middle cerebral artery flow velocity during hyperbaric oxygen exposures. 893 Dec 83

A 60-year-old man without comorbidity underwent a totally extraperitoneal repair of bilateral inguinal hernias under general anesthesia. Forty minutes after the procedure he developed a slow, shallow respiratory pattern with a respiratory rate of 5/min and a self-limiting grand mal seizure lasting 30 seconds. Arterial blood gas analysis indicated significant hypercarbia and acidosis. The total dose of morphine administered was 20 mg intravenously. Naloxone was administered and the respiratory rate improved. The patient was discharged after 24 hours after making a good recovery and has had no further seizures a year after surgery. Although hypercarbia is a well-known complication of laparoscopic surgery when CO2 is used for insufflation, this, to the best of our knowledge, is the first reported case of a patient sustaining a grand mal seizure resulting from CO2 narcosis after laparoscopic surgery. The possible mechanisms are discussed.
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PMID:Carbon dioxide narcosis and grand mal seizure complicating laparoscopic herniorrhaphy. 1731 57