Showing papers in "Neurophysiologie Clinique-clinical Neurophysiology in 1998"

Hierarchy of micro-arousals and the microstructure of sleep

Abstract: This review is aimed at providing an overview concerning the hierarchy of different kinds of micro-arousals (without awakening) during slow wave sleep (SWS), and to summarize available data on the dynamic interplay of phasic events constituting the microstructural web of sleep EEG. K-complexes are considered elementary forms of arousal during SWS. They carry characteristics of evoked potentials, which provide subattentive information processing and have at the same time level-setting sleep maintenance functions. Micro-arousals are more complex arousal-dependent phasic events in the hierarchy. One class of recurring micro-arousals are preceded by K-complexes, while others, such as phases of spontaneous transitory activation--type micro-arousals-- represent higher levels of arousal, and are associated with EEG desyncronization, increased muscle activity and signs of autonomous arousal. All types of micro-arousals function in a complex interrelationship with another phasic event--sleep spindles--interpreted as microstates inhibiting sensory inflow through the thalamic relay system. Lastly the CAP (cyclic alternating pattern) phenomenon offers a global framework for characterizing and measuring arousal instability. Appearance of CAP sequences reflects arousal instability in a higher duration range than individual micro-arousals. They represent an arousal control mechanism reflecting that all arousing influences set into motion an oscillatory level setting system around the referential state providing a flexible adaptation for the system to defend it against perturbations. The whole arousal (without awakening) hierarchy thus seems to play an essential role in sleep regulation, serving both cyclicity and maintenance of sleep and providing at the same time flexible contact between sleeper and environment--preserving the possibility to wake up in case of any biological danger, and tailoring sleep program according to actual environmental or inner demands. Although at present there are no accepted rules for microstructural evaluation of sleep, microstructural aspects provide a more dynamic picture both about the preprogrammed and reactive changes in sleep. This approach gives us some clues to better understand sleep disorders as well. Several studies concerning microstructural analysis of certain sleep disorders are also reviewed.

Evaluation of acute ischemic stroke using quantitative EEG: a comparison with conventional EEG and CT scan.

Abstract: The sensitivity of quantitative electroencephalogram (EEG) was compared with that of conventional EEG in patients with acute ischaemic stroke In addition, a correlation between quantitative EEG data and computerized tomography (CT) scan findings was carried out for all the areas of lesion in order to reassess the actual role of EEG in the evaluation of stroke Sixty-five patients were tested with conventional and quantitative EEG within 24 h from the onset of neurological symptoms, whereas CT scan was performed within 4 days from the onset of stroke EEG was recorded from 19 electrodes placed upon the scalp according to the International 10-20 System Spectral analysis was carried out on 30 artefact-free 4-sec epochs For each channel absolute and relative power were calculated for the delta, theta, alpha and beta frequency bands and such data were successively represented in colour-coded maps Ten patients with extensive lesions documented by CT scan were excluded The results indicated that conventional EEG revealed abnormalities in 40 of 55 cases, while EEG mapping showed abnormalities in 46 of 55 cases: it showed focal abnormalities in five cases and nonfocal abnormalities in one of six cases which had appeared to be normal according to visual inspection of EEG In a further 11 cases, where the conventional EEG revealed abnormalities in one hemisphere, the quantitative EEG and maps allowed to further localize abnormal activity in a more localized way The sensitivity of both methods was higher for frontocentral, temporal and parieto-occipital cortical-subcortical infarctions than for basal ganglia and internal capsule lesions; however, quantitative EEG was more efficient for all areas of lesion in detecting cases that had appeared normal by visual inspection and was clearly superior in revealing focal abnormalities When we considered the electrode related to which the maximum power of the delta frequency band is recorded, a fairly close correlation was found between the localization of the maximum delta power and the position of lesions documented by CT scan for all areas of lesion excepting those located in the striatocapsular area

EEG power spectra of normal preadolescent twins. Gender differences of quantitative EEG maturation

Abstract: Summary To determine developmental changes of quantitative EEG maturation, we investigated the electroencephalogram (EEG) power spectra in a sample of 72 pairs of healthy twins (144 subjects, 75 girls and 69 boys) ranging in age from 7–15 years. Main spectral parameters were measured in 16 EEG channels. The statistical significance of differences in the EEG power spectra was compared in relation to age and gender. Gender differences were tested by comparing the EEG parameters of boys and girls in the whole sample and separately in the subgroup of dizygotic twins of the opposite sex (DZO twin pairs). A statistically significant decrease of absolute power occurred with increasing age. A significant redistribution of relative power also appeared in higher age, mainly consisting of a progressive increase of alpha 2 power inversely related to relative alpha 1 and theta power. Polynomial regression models of the relation between alpha 2 and theta relative power with age were best described by a 5-order function. The mean frequency of activity across all spectra also increased with age and was maximal in the eldest subjects (13–15 years), with a significantly higher mean frequency of alpha 2 power in females. Similar age and gender differences were less marked in the subgroup of DZO twin pairs. The topographic distribution of spectral bands in normal subjects suggested an earlier maturation of midparietal or occipital than frontocentral regions, and indicated that the growth spurt does not occur simultaneously over homologous right and left hemisphere regions at the same age.

Ageing effects on flash visual evoked potentials (FVEP) recorded from parietal and occipital electrodes.

Abstract: The effects of ageing on flash visual evoked potentials (FVEP) recorded from 6 posterior parietal and occipital sites were studied in a sample of 73 healthy subjects of between 20 and 86 years of age. Latencies of components P1, N1 and P2, and amplitudes of components P1 and P3 increased linearly with age at all emplacements. The results obtained from occipital electrodes are in line with previous reports and additionally show that i) the effects of age constantly increase over time, and ii) age affects not only the early but also the later components (> 150 ms) of the FVEP. The overall pattern of results suggests that elderly subjects show slower transmission of visual information and deficiencies in the inhibitory regulation of activity generated during the arrival of repetitive non-attended visual stimulation. The findings with parietal electrodes show that ageing effects are more marked at these emplacements than at occipital electrodes. Furthermore, this raises the question of a possible differential involvement of primary and nonprimary visual cortex by age, but this hypothesis can only be explored with high-intensity multichannel recordings and dipolar modelling.

Maturation du sommeil pendant les deux premières années de vie : aspects quantitatif, structurel et circadien

Abstract: Resume Ce travail presente la maturation du sommeil pendant les deux premieres annees de vie, sur la base d'une etude longitudinale de 15 enfants normaux enregistres a domicile pendant 24 heures, aux âges de 3, 6, 9, 12, 18 et 24 mois. Le developpement des differents stades et parametres du sommeil est etudie d'un point de vue quantitatif, structurel et circadien. Pour ce faire, differentes analyses ont ete faites sur les donnees issues des enregistrements polygraphiques interpretes selon les criteres «adulte proposes par Rechtschaffen et Kales en 1968 [54]. Les resultats mettent en evidence la presence, tres tot, de certains parametres du sommeil de l'adulte, comme la duree moyenne stable des episodes de sommeil paradoxal (SP), la diminution rapide des quantites de ce stade de sommeil qui sont egales a celles de l'adulte des 9 mois, la grande quantite de sommeil lent profond dans le premier cycle de sommeil des 3 mois, et la stabilite de l'acrophase du rythme circadien du SP. Ce positionnement de l'acrophase correspond a la periode de grande densite du SP en fin de nuit chez l'adulte. D'autres parametres, comme l'augmentation des stades 1 et 2 du sommeil lent, l'augmentation de la latence du SP avec disparition a 9 mois des endormissements en SP, l'augmentation de la stabilite du sommeil par diminution des eveils nocturnes et des mouvements corporels, pourraient etre en relation avec la maturation des structures du systeme nerveux central impliquees dans les mecanismes du sommeil (maturation des voies thalamocorticales, des connections rostrocaudales entre le pont et le thalamus). Ces processus maturatifs pourraient etre fortement influences par l'environnement. Enfin, l'augmentation avec l'âge de l'amplitude du rythme circadien de sommeil pourrait jouer un role, d'une part, dans l'allongement du cycle de sommeil a 12 mois, et, d'autre part, dans l'installation du processus homeostasique de sommeil analysee sur l'evolution temporelle du sommeil lent profond

Mesure de l'effort respiratoire (pression œsophagienne) et estimation des résistances des voies aériennes supérieures au cours de l'enregistrement de sommeil : indications, limites, résultats

Abstract: During polysomnography, measurement of airflow and respiratory effort are essential for classifying the type of respiratory event and for evaluating the efficacy of treatment. There are various ways to measure respiratory effort, the reference technique being oesophageal manometry. This measures fluctuations in intrathoracic pressure which correspond to variations in upper airway resistance and therefore allows differentiation between central and obstructive respiratory events. Thus the simple snorer can be distinguished from an individual with the upper airway resistance syndrome (UARS). In the UARS abnormally high resistance develops in the upper airway in the absence of identifiable apnoeas and hypopnoeas. The characteristic cresendo-decresendo pattern of the oesophageal pressure signal, when associated with the micro-arousals which are responsible for the hypersomnolence, is pathognomonic of this condition. The clinical application of oesophageal manometry is limited by its poor tolerance in certain individuals and by the potential deleterious effect the catheter itself has on sleep quality and on the dynamics of the upper airway. Other less invasive techniques, such as nasal pressure and pulse transit time, are currently under evaluation.

Electrophysiological evidence of a relationship between idiopathic carpal and tarsal tunnel syndromes.

Abstract: Electrophysiological findings are reported suggesting a relationship between idiopathic tarsal (TTS) and carpal tunnel syndromes (CTS) to explain that the coexistence of both entrapment syndromes in the same patients is not coincidental. Sixty-five patients with idiopathic CTS and 15 with idiopathic TTS were selected. None of the patients with CTS reported any symptoms, nor did they have any signs of TTS, and vice versa. Distal sensory conduction velocity (SCV) of the tibial nerve was reduced in ten of 65 patients with CTS; in five of these ten patients, tibial distal motor latency (DML) was also delayed. Reduced SCV and increased DML were evident in the median nerve of two patients with TTS. The mean of DML and SCV of the tibial nerve in the CTS group and of the median nerve in the TTS group were significantly reduced with respect to the control group without differences in the conduction of the ulnar, deep peroneal and sural nerves. This indicates that there was subclinical involvement of the median and tibial nerves in these patients. Besides having a narrow carpal tunnel, patients with CTS presumably also have a narrow tarsal tunnel and vice versa, and are therefore prone to develop both nerve entrapment syndromes. The different incidence of the two syndromes is explained on the basis of anatomical and functional differences between the two nerves.

Increased cortical inhibition induced by apomorphine in patients with Parkinson's disease

Abstract: Summary The electromyographic silent period following the motor potential evoked hy cortical magnetic stimulation is decreased in parkinsonian patients. In this study we investigated whether the decrease in the silent period is connected only with parkinsonian symptoms. We evaluated the effect of apomorphine (a potent and rapid dopamine agonist) on the changes in the peripheral and central silent period in 29 patients with Parkinson's disease and in two patients affected by multisystem atrophy (MSA). Apomorphine injection was found to induce a significant improvement in the central silent period in parkinsonian patients but not in the MSA patients, suggesting a relation between the clinical parkinsonian symptoms (akinesia and rigidity) and the silent period duration. The central silent period changes after apomorphine injection could be used as an adjunctive, safe and effective diagnostic tool to assess dopamine responsiveness of parkinsonian syndromes.

Apport des potentiels évoqués cognitifs à la connaissance des mécanismes du test de Stroop

Abstract: Resume Le test de Stroop est fonde sur l'interference entre la lecture et la denomination de noms de couleurs non concordantes. Pour savoir si ce conflit etait perceptif ou moteur, les potentiels evoques de longue latence ont ete enregistres simultanement. Dans la mesure ou la latence et l'amplitude de ces potentiels rendent compte de la progression du traitement de l'information, leurs modifications en fonction du type de stimulation doivent renseigner sur les mecanismes qui sous-tendent ce conflit. Chez 18 sujets sains, trois derivations medianes ont ete utilisees pour enregistrer les potentiels evoques au cours d'une tâche de lecture et de denomination. Dans chaque serie, il y avait 216 stimulations comportant soit les mots ≪ rouge, vert ou bleu ≫ colores de facon congruente ou non, soit des stimulations neutres, chaque categorie etant equiprobable. L'effet Stroop comportemental ne se manifeste pas sur la latence de la P300, ce qui laisse penser que le conflit se situe a un niveau moteur. Cette donnee est confirmee par l'existence d'une negativite pre-motrice aux stimulations non-congruentes apparaissant entre 400 et 205 ms avant la reponse, et qui n'existe pas lors de la lecture. Par ailleurs, dans les deux consignes, lecture et denomination, les stimulations congruentes font apparaitre une positivite entre 260 et 310 ms apres la stimulation, qui se manifeste en occipital pour la lecture et en frontal pour la denomination. Il reste donc possible qu'une interaction des voies d'analyse specialisees de la stimulation (lecture et couleur) se produise aussi a un niveau precoce.

Low intensity galvanic vestibulo-ocular reflex in normal subjects.

Abstract: Summary An electrical stimulation in man applied between the two mastoids could facilitate the distinction between labyrinthine and retrolabyrinthine lesions by stimulating directly the primary vestibular afferences. However, for this test to be really effective in current medical practice, the results obtained in normal subjects must be symmetrical and reproducible one day to another. The ocular responses induced by a constant electrical stimulation of 2.5 mA, applied between the two mastoids for 30 s (electrically evoked vestibulo-ocular reflex [EVOR]), in one direction and the other, were quantified in ten healthy subjects. Each subject was studied in two different sessions separated by 1 week. Horizontal eye movements were recorded in darkness by an infrared light reflection eye-tracking system. Slow-phase velocity and nystagmus frequency were about 20% higher when the cathode was on the right mastoid than when it was on the left mastoid. This directional preponderance (DP) displayed large individual differences between the two sessions. The reproducibility of the reflectivity (mean of right and left EVOR) was high ( r about 0.8). The weak reproducibility of the DP makes the EVOR at weak intensity inadequate to evaluate unilateral vestibular hypofunction. On the other hand, because of the high reproducibility of reflectivity, the EVOR should be effective in detecting bilateral vestibular hypofunction. Moreover, because of the weak intensity of stimulation, no local anaesthesia is needed so the manoeuvre is easy to repeat in case of chronic diseases.

Evaluation of early motor and sensory evoked potentials in cervical spinal cord injury

Abstract: Summary To determine the efficacy of motor evoked potentials (MEP) and sensory evoked potentials (SEP) in the assessment of severe cervical injury, 17 subjects with severe cervical injury were studied. During the 1st week post-injury and post-surgical treatment, all subjects were submitted to electromyogram (EMG) recordings, dermatomal somatosensory evoked potentials (D.SEP), posterior tibial nerve somatosensory evoked potentials (PTN.SEP), MEP and bilateral cervical electrical stimulations with recording of the diaphragm. For the D.SEP, the latencies of the N9 and N20 responses and the conduction time (N9–N20) were measured in the upper limbs: the latencies of the P40 and P60 responses were measured in the lower limbs. MEP were recorded from distal upper and lower limb muscles following transcianial electrical stimulation of the cortex. (Magnetic stimulation was not indicated because of implanted metallic material in the cervical skull of many patients.) A SEP und MHP grading system was used to improve the assessment of different root neurological levels. In patients with incomplete lesions PTN.SEP, D.SEP and MEP responses could be recorded in territories that were clinically deficient Patients with complete lesions and absent SEP and MEP responses had a poor outcome. A good correlation was found between the severity of the spinal cord injury und SEP grading. For MEP, the presence or absence of intercostal responses (C4) to cervical and cortical stimulation was the best prognostic indicator. The combined electrophysiological exploration of MEP and SEP proved to be a useful tool for monitoring patients with severe spinal cord injury.

Applications de la stimulation magnétique corticale

Abstract: In the last decade, a new electrophysiological tool has become available since the development of painless magnetic stimulators able to activate the primary motor cortex and the motor roots in conscious man. Therefore, it became possible to measure the conduction time within fast-conducting central motor pathways by substracting from the total latency of muscle responses elicited by cortical stimuli the conduction time in peripheral nerves. This technique proved sensitive enough to illustrate early abnormalities of central motor conduction in various neurological diseases such as multiple sclerosis, amyotrophic lateral sclerosis, cervical spondylotic myelopathy, degenerative ataxias or hereditary spastic paraplegias. When recorded early after stroke, motor evoked potentials are also a valuable tool to predict functional outcome. They can also illustrate subtle pathophysiological disturbances in diseases where there is no direct involvement of central motor pathways such as Parkinson's disease, dystonia or epilepsy. Magnetic cortical stimulation also offers unique opportunities to explore intracerebral inhibitory and excitatory circuits and mechanisms of brain plasticity. The recent development of rapid rate stimulators also enables functional studies of non-motor cerebral regions such as visual or frontal cortices. Moreover, rapid rate stimulation seems useful in the treatment of drug-resistant depression but the safety of this procedure, particularly with regard to the production of seizures or kindling, remains to be fully documented.

Quantitative EEG in subcortical neglect

Abstract: Right-sided capsulo-lenticular strokes may cause left visuo-spatial neglect. The neural mechanism most frequently evoked to account for the occurrence of related cognitive disorders is remote cortical dysfunction in the posterior part of the right hemisphere. We studied 33 patients with capsulo-lenticular stroke, with (n = 16) or without (n = 17) associated subcortical neglect. A 20-channel EEG cartography system was used. Four regions of interest were delineated on the topographic map. Absolute delta and theta amplitude peaks were obtained, as well as left-to-right ratios between activities in homologous regions of interest. The population was subdivided into two groups according to the presence or absence of neglect. Delta activity was higher in neglect patients than in patients without neglect, but the magnitude of delta activity differences between the two groups of patients did not depend on the site. The left-to-right ratio of delta activity between posterior homologous regions was lower in neglect patients, suggesting that right posterior dysfunction producing an imbalance between these regions might contribute to the emergence of the attention disorder.

Indications de l'EEG dans les confusions mentales et les troubles du comportement

Abstract: Even in 1998 at the time of brain imaging, EEG recording is undoubtedly useful in clinical psychiatry when a true cerebral disease takes the form of an acute psychiatric disorder. Though the real place of EEG recording cannot be yet accurately quantified, it may help guide the diagnosis, as it is of either positive (ie, confirming the diagnosis via additional information) or negative (ie, rejecting various etiologies) value. Most of the time, only the former is considered in published studies. The clinical value of EEG recording in psychiatry emergency unit is therefore still not clearly established. The study of patients admitted during two years in the emergency unit at Sainte-Anne hospital (Paris, France) does not bring new conclusions, mainly because of bias in the modalities of admission and follow-up. As well, the role of EEG recording for the diagnosis of non-psychiatric diseases in psychiatry emergency units cannot be defined today. The authors review clinical situations where EEG recording is still highly advisable.

Indications urgentes de l'EEG dans la situation d'un traumatisme crânien, chez l'enfant et chez l'adulte

Abstract: Resume L'EEG apres une perte de connaissance initiale a la suite d'un traumatisme crânien peut montrer un ralentissement et des ondes lentes posterieures, traduisant une commotion cerebrale, particulierement chez les enfants, mais il peut exister une discordance entre l'electrogenese cerebrale et la clinique pendant plusieurs semaines. L'EEG est bien correle avec la profondeur du coma post-traumatique, sa reactivite aux stimulations a une valeur particuliere. Chez l'enfant, d'importantes alterations EEG sont frequentes, des graphoelements paroxystiques sont possibles, l'evolution est pauvrement correlee avec le trace initial. En reanimation, l'utilisation des techniques d'EEG numerise continu offre de nouvelles possibilites. Devant un deficit suggerant une lesion cerebrale focalisee, le scanner realise dans les 24 heures est prioritaire. Apres un traumatisme crânien, l'EEG et la surveillance clinique peuvent suffire en cas de risques moderes mais, en cas de risques eleves, un EEG sera enregistre apres un scanner normal. En dehors de problemes toxiques ou metaboliques, le scanner sera fait en urgence a la recherche d'un hematome intracrânien en cas d'alteration de la conscience non expliquee par l'importance du traumatisme crânien; s'il est normal, l'EEG sera fait en urgence a la recherche d'une focalisation. L'EEG peut mettre en evidence un etat de mal non convulsif, surtout chez les personnes âgees. En cas de crises precoces, il est preferable d'enregistrer l'EEG dans les 24 heures. En periode postcritique, l'EEG sera fait en urgence en cas de syndrome confusionnel persistant plus de 30 minutes, a la recherche d'un etat de mal non convulsif. L'EEG a peu de valeur predictive dans l'apparition d'une epilepsie post-traumatique, mais des anomalies paroxystiques, surtout focales, constituent un facteur de risque. En cas de probleme medico-legal, l'existence de signes sur un document realise precocement constitue un element utile a l'expert.

Corrélations entre déficits cliniques, potentiels évoqués moteurs et sensitifs, et aspects radiologiques à l'IRM dans la syringomyélie malformative. A propos de 27 cas

Abstract: Twenty-seven patients (15 males, 12 females, age range: 16-66 years) were admitted for malformative syringomyelia diagnosed on MRI with measures of syrinx extending and transverse diameter. Posterior tibial somatosensory evoked potentials (PT SEP), median (M SEP), trigeminal (V3 SEP), brain stem auditory evoked potentials (BEAP), cortical and cervical motor evoked potentials (MEP) were correlated with clinical and radiological findings. SEP abnormalities were not correlated with the duration of symptoms. PT SEP proved to be more sensitive than M SEP. MEP abnormalities were very frequent (87% of the cases), even without clinical motor deficits. Trigeminal SEP were more sensitive than BEAP which were not related to the presence of associated cranio-vertebral abnormalities. We found no significative relationship between clinical and radiological results. Moreover, there was a positive relationship between electrophysiological and radiological results: abnormal trigeminal SEP were detected in 85% of the patients with high cervical syringomyelia. In all cases, trigeminal SEP and MEP should be done in association with M and PT SEP as both of them detect subclinical evidence of spinal cord dysfunction in syringomyelia.

Selective abnormality of the N13 spinal SEP to dermatomal stimulation in patients with cervical monoradiculopathy

Abstract: Scalp somatosensory evoked potentials (SEP) to dermatomal stimulation have so far proved to be only partially useful in the diagnosis of monoradiculopathy, mostly in cases without motor impairment. The aim of our study was to test the sensitivity of the spinal N13 potential in uncovering lesions of single cervical roots. We studied five patients suffering from cervical monoradiculopathy, using a recording technique allowing specific recording of the genuine N13 potential which is probably generated by dorsal horn cells. No patient showed signs of muscle impairment and needle EMG was always normal. In four patients, the N13 SEP was absent following stimulation of the dermatome corresponding to the damaged root, while both the lemniscal P14 and the cortical N20 components were normal. SEP recorded after stimulation of upper limb troncular nerves showed no abnormality in all patients. Our findings suggest that the N13 potential, the loss of which after dermatomal stimulation could be due to deafferentation of dorsal horn neurones, is particularly sensitive to initial root compression. Therefore, our montage allowing analysis of the genuine N13 SEP can improve the sensitivity of dermatomal SEP recording in patients with cervical monoradiculopathies.

Effets de la clomipramine sur la somnolence diurne et sur les paramètres respiratoires dans un cas de syndrome de Prader-Willi

Abstract: The association of Prader-Willi-syndrome with breathing disturbances such as sleep apnea syndrome and/or hypoxemia during REM sleep, REM sleep abnormalities and excessive daytime sleepiness is well known. We report the case of an 11-year-old boy who presented with Prader-Willi syndrome, obesity (body mass index [BMI] = 45.6), severe obstructive sleep apnea syndrome and significant daytime sleepiness on multiple sleep latency test. Behavioral disorders did not allowed the use of continuous positive pressure in this patient. Therefore, clomipramine (20 mg per day) was administered. Sleep examination over 8 months showed: slight weight loss (BMI = 44.4), persistence of severe obstructive sleep apnea syndrome, slight improvement in nocturnal hypoxemia, and disappearance of excessive daytime drowsiness with mean sleep latency of 15 min 37 s (less than 2 min before treatment) and no diurnal REM sleep periods. However, clomipramine had no effect on hyperphagia.

Neuromonitorage et anesthésie dans la chirurgie du rachis

Abstract: The authors report the main effects of anaesthetic drugs that are used alone or in association with anaesthetic protocols on somatosensory evoked potentials (SEP) and on motor evoked potentials (MEP). In the first part of the article, the effects are analysed on SEPs and MEPs that are obtained from non-invasive methods; in the second part, the effects of anaesthesia are analysed with respect to invasive methods of EP recordings. The current increase of invasive techniques of neuromonitoring by SEPs and MEPs is in relation with the weak effect of anaesthetics on evoked responses. Total intravenous anaesthesia (TIVA) provides stable anaesthesia for non-invasive SEP neuromonitoring only if bolus is avoided. With TIVA and other anaesthetic techniques, the introduction of repetitive stimulation provides new possibilities for non-invasive MEP neuromonitoring.

Électroencéphalogramme en urgence au cours de la souffrance cérébrale périnatale : indications et résultats

Abstract: The main contribution of EEG during intensive care in infants with hypoxic-ischemic encephalopathy is i) to help determine whether infants with subtle clinical manifestations present with epileptic seizures, ii) to determine whether paralyzed or heavily sedated infants present with convulsive phenomena, iii) to assess the therapeutical response to anticonvulsants, 4) to contribute, in combination with ultrasound scanning, to diagnostic evaluation of the severity of lesions, and to provide valuable prognostic informations via the analysis of the background activity, as normal EEG is highly predictive of normal outcome, whereas various abnormal EEG features are constantly associated with subsequent major neurological abnormalities or death. These EEG features are readily available from a very early stage and may both precede and be prognostically more sensitive than information obtained from ultrasound. Recording of neonatal electroencephalogram requires awareness of the normal development of electroencephalographic features in the newborn, skilled technicians, and experienced readers of EEG tracings.

Le monitorage des potentiels évoqués mixtes neurogènes au cours de la chirurgie du rachis: une bonne solution?

Abstract: Resume La chirurgie du rachis, en particulier celle comportant une modification des courbures, expose a des complications neurologiques rares mais gravissimes par leur retentissement fonctionnel. Le monitorage peroperatoire de la moelle epiniere au cours de ces interventions a ete initialement realise a l’aide des potentiels evoques somesthesiques. La survenue de faux negatifs a conduit les neurophysiologistes a y associer une surveillance des voies motrices par differentes techniques d’enregistrement des potentiels evoques moteurs. Les potentiels evoques mixtes neurogenes enregistres a partir d’un nerf peripherique en reponse a la stimulation de la moelle en amont du site chirurgical representent une alternative permettant une surveillance combinee des voies motrices et sensitives de la moelle. Cette technique, dont la sensibilite a detecter une lesion medullaire a ete demontree experimentalement et cliniquement, presente de nombreux avantages. Elle est simple a mettre en œuvre, permet une acquisition rapide des potentiels et est realisable en permanence tout au long des temps a risque de la chirurgie.

L'EEG d'urgence en pédiatrie dans les troubles de la vigilance, la confusion mentale et les troubles du comportement: étude rétrospective

Abstract: Resume L'electroencephalogramme (EEG) d'urgence aide a apprecier l'etat de la vigilance aussi bien chez l'enfant que chez l'adulte. Afin de determiner la valeur diagnostique et pronostique de l'EEG d'urgence en cas de confusion mentale, de troubles du comportement ou de troubles de la vigilance chez l'enfant, nous avons fait une etude retrospective chez 397 enfants âges de 2 mois a 16 ans. Les EEG ont ete pratiques moins de 24 heures apres une consultation d'urgence pour confusion ou trouble aigu du comportement (n = 106) ou apres admission pour coma en unite de soins intensifs (n = 291). L'EEG a apporte des indications diagnostiques principalement en cas de pathologie convulsivante ou d'encephalopathie hepatique. Chez les enfants comateux, nous avons etabli une classification en 4 stades EEG de severite croissante. Cette classification a ete comparee aux echelles EEG deja publiees dans la litterature, elle est apparue tres proche de celle de Pampiglione et Harden [18] etablie dans une population de 150 enfants apres arret cardiaque. La valeur pronostique pejorative de l'EEG apparait surtout en cas de trace postanoxique dit ≪burst-suppression≫ ou dans les traces isoelectriques de mort cerebrale. Nous concluons que, en dehors de ces situations, la valeur diagnostique et pronostique d'une classification de l'EEG d'urgence en pediatrie est modulee par une surveillance clinique et EEG repetees.

The infernal machine

Abstract: Rarely is reading a book as disappointing as when you begin in vague agreement with the author only to finish by pulling your hair out in frustration. No history of terrorism is ever going to be without controversy: even the decision what to include in that book can be questioned. No selfrespecting reader would expect an account that would offer comfortable moral certitude and unambiguous delineation of the world in the Manichean “us” and “them.” Everyone familiar with history would know that reality is a lot murkier and more sordid than the triumphalist accounts of the victors or the tragically heroic epics of the losers would suggest. And yet... the difficulty of writing an objective exposition should not be an excuse for not trying hard enough.

Résisteur de starling et stabilité du couple sommeil-ventilation

Abstract: Resume Les voies aeriennes superieures se caracterisent par une structure en trois segments composes d'un segment collabable (le pharynx), interpose entre deux segments rigides (les fosses nasales en amont, l'arbre tracheobronchique en aval). Cette structure conditionne un comportement particulier du segment collabable, qui peut etre le siege d'une modalite d'ecoulement de l'air dans laquelle le debit ne depend pas de la pression en aval, mais est limite a une valeur maximale qui depend exclusivement de la pression en amont et de la pression tissulaire autour du segment collabable; ce comportement de resisteur de Starling peut se modeliser sous le nom d'effet chute d'eau. Les voies aeriennes superieures peuvent ainsi se trouver dans trois etats : un etat d'occlusion complete (debit nul) ; un etat d'occlusion partielle avec limitation de debit, et un etat de permeabilite normale ou le debit depend du gradient de pression entre amont et aval. La structure anatomique du pharynx determine pour une part la situation qui prevaut, mais des facteurs fonctionnels jouent un role majeur ; parmi eux, le niveau de vigilance est a la fois determinant de l'etat fonctionnel de la paroi pharyngee et determine par les stimulations issues des mecanorecepteurs sous la dependance de l'activation des muscles respiratoires. Il s'etablit ainsi un jeu de relations reciproques entre niveau de commande ventilatoire, collapsibilite pharyngee et seuil d'eveil qui permet de rendre compte de la majorite des situations ventilatoires, stables ou instables, rencontrees au cours du sommeil. Le niveau du seuil d'eveil est crucial pour la stabilite de la ventilation ; en effet, c'est lui qui determine si une combinaison de valeurs de debit, d'effort respiratoire et de gaz du sang peut se maintenir ou est interrompue par un eveil.

Prédiction au moyen des potentiels évoqués endogènes et exogènes de l'évolution favorable d'un coma prolongé.

Abstract: A neurophysiological follow-up (EEG, exogenous and endogenous evoked potentials--EP) was performed over a 4-month period in a patient who presented a long-lasting coma following a cardiac arrest and an amniotic embolism. A pure anoxic aetiology was ruled out starting from the second day on the basis of a dissociation between mildly altered flash visual EP and markedly altered somatosensory EP, indicating focal brain-stem pathology. Endogenous EP reappeared after 12 days. This patient recovered consciousness after 51 days. Despite the absence of MRI abnormalities, we put forward the hypothesis that a brain-stem embolism had, in fact, worsened the clinical picture of an actually moderate anoxia. This case exemplifies the interest of an integrated neurophysiological approach (EEG, exogenous three-modality EP and endogenous EP) in the early evaluation of coma. It also illustrates the complement between structural imaging and functional assessment of the nervous system.

EEG en urgence et traumatisme crânien

Abstract: The aim of this study is to review indications for emergency EEG in case of brain trauma. The authors emphasize the indication of emergency EEG for the diagnosis of either cerebral death or early post traumatic seizures, and for the monitoring of intensive neurological treatments. Emergency EEG and diagnosis of cerebral death has been reviewed in another issue of this journal. Diagnosis of early post-traumatic seizures may be difficult in case of cranial trauma in either the presence or the absence of coma. Emergency EEG help guide the diagnosis of electrical signs of seizures, thus indicating that treatment with antiepileptic drugs is advisable. Severe post-traumatic coma requires barbiturate impregnation and moderate hypothermia. In this last case, emergency EEG is essential for the monitoring of pharmacological treatments. The authors conclude that continuous EEG monitoring could in the future substitute for standard EEG recorded in emergency.

Revue de la littérature internationale consacrée aux potentiels évoqués en 1997

Abstract: En novembre 1997, l’introduction. dans le Medline de I’annCe &~~ul&. des seuls mats cl& rvokrti p~te&~/ et (‘\\VTHI relafetl yotrntiul permettait d’identif‘ier environ 750 a1mracl.s. C’est dire l’ampleur d’un travail de revue de la IittCraturc consac& aux potentiels Cvoqi16a en 1997. C”est dire dgalement que cette revue rcll’vera d’un choix guide, non seulement par I’importance des papiers publiks ou I’impression yue ceux-ci susciteront des di;bats intksaantc dans un futur prochc, mais Cgalement pal les affinitks de I’auteur... C’es~ dire ent’in que les diffkents sujets abordks ne pourrant Etre qu’esyuisks, au risque dc dormer au locteur l’imprcssion d’crl avoir a la fois trop dit et pas asset dit. Trois types dc travaux seront successivement enGsagks : les t?tudcs consackes B la genitse dt:s potentiels &oyu& chez le stl.jet normal. Its applications cliniques ct I’inttH croissant des potentlels ~voyuCs en psychologic et en neuropsychiatrie cogniti\\c.