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Biomedical subjects

M Toupet

Publications and source records attributed to M Toupet.

At least 19 recordsLinked to original sources
PubMed1997

Unilateral vestibular neuritis with otolithic signs and off-vertical axis rotation.

Off-vertical axis rotation (OVAR) at constant velocity is a dynamic otolith stimulus that induces horizontal and vertical eye movement responses. To determine the value of this examination as a test for unilateral otolithic hypofunction, we compared the OVAR responses of patients suffering from acute vestibular neuritis (VN) without any sign of otolith affection, with those of patients suffering from acute VN with otolithic signs. The horizontal eye movement bias component shows directional preponderance (DP) significantly higher in patients with otolithic signs than in patients not presenting them. However, as bias DP also reflects the imbalance between right and left horizontal canals activity, this greater bias DP could be explained by the more severe canals impairment-evaluated by caloric test-found in patients with otolithic signs. No significant difference can be shown on horizontal modulation. The DP of vertical modulation is significantly higher in patients presenting otolithic signs than in patients not presenting them: in the case of otolithic signs, the responses are smaller during rotations toward the affected side. Therefore, this variable could be used as an indication of unilateral otolithic hypofunction.

Adult↗
PubMed1997

[Rotatory impulse test does not replace caloric tests].

We sought to determine whether the rotatory impulsional test was capable of exploring the canalar function with sufficient precision to replace the caloric test, as it has been recently affirmed. We first compared the observed preponderance from this test with that measured during a sinusoidal (20 and 4 s) test. We observed that, in the case of a significant preponderance for a given test, there was complete redondance with the preponderance observed with any other test. The rotatory impulsional test does not present any specific advantage compared to other kinetic test as far as the observation of the preponderance phenomenon. We then compared the preponderance with the results of the caloric tests and came to the following conclusions i) the absence of preponderance does not allow us to predict the absence of vestibular deficit, due to the fact that 37% of the deficits were compensated for including acoustic neuroma; ii) the presence of a preponderance does not allow a priori to say whether it is of vestibular, cervical, or central origin and systematic caloric tests shows that almost one fourth of preponderance observed is not associated with unilateral weakness iii) supposing that a clinical argument allow us to conclude as to the probable vestibular origin of a vestibular preponderance, the direction of this preponderance does not allow us to determine which side is involved. In fact, if the undercompensated deficits are 3 times more frequent than overcompensated deficits, the proportion of preponderance not linked to a significant deficit indicates that the probability of encountering a preponderance related to a specific undercompensated deficit is approximately 50%. We thus did not find in the rotatory impulsional test any specific advantage allowing us to predict the laterality of a vestibular lesion.

Caloric Tests↗
PubMed1996

Unilateral peripheral semicircular canal lesion and off-vertical axis rotation.

Off vertical axis rotation (OVAR) is a stimulus that can be used to assess the otolith-ocular reflex. However, experimental data suggest that isolated unilateral lesion of the lateral semicircular canal (SCC) nerve could modify responses to OVAR. Thus, to determine what nystagmus variables are not affected by SCC dysfunction and might be used as indices of otolithic disease, responses to OVAR were compared in 39 healthy controls and in 19 patients suffering from acute unilateral vestibular neuritis (VN), without any sign of otolith dysfunction. Horizontal and vertical slow phase velocities (SPV) were measured during earth vertical axis rotation (EVAR), and during OVAR at a tilt angle of 9 degrees and rotation velocity of 60 degrees/s. During OVAR, horizontal SPV consists of a sinusoidal modulation superimposed on a sustained bias opposite to the rotation. Vertical SPV consists of a sinusoidal modulation without bias. In patients, the bias shows directional preponderance (DP) toward the healthy side, strongly correlated to EVAR nystagmus DP. It would therefore simply reflect an imbalance, produced by the unilateral peripheral vestibular lesion, between right and left vestibular nuclei activity. On the other hand, vertical and horizontal modulations are not significantly different in patients and controls. Since the cause and the site of VN are not known, we cannot be sure that patients had pure SCC deafferentation. However, as all of them had SCC paresis it is concluded that OVAR modulations are not affected by a strong dysfunction of the pathways issued from the SCCs.

Adolescent↗
PubMed1994

[Vertigo in children].

Oto-neurologic investigation in the child with vertigo is fundamentally important. In 3% of cases, it reveals the presence of a cerebral tumour. Technical difficulties in examining a child under 5 years of age stem from their fear of the dark, insecurity in a medical setting and a labile attention span. Major causes are migraine (in 28% of cases) and childhood idiopathic paroxysmal vertigo, and recurring vestibular disorders (13% of cases). Classic disorders such as Ménière's disease are rare in the child (3% of cases), as are benign paroxysmal positional vertigo and cupulolithiasis (only 5% of children with vertigo).

Adolescent↗
PubMed1991

Orthostatic postural control in vestibular neuritis: a stabilometric analysis.

Posturographic data for 182 vestibular neuritis patients were recorded on a static posturographic platform (stabilometry) with the patients' eyes both open and closed. Three of the parameters studied are presented here: mean position of the center of pressure, area of the statokinesigram, and Romberg's quotient. Vestibular neuritis modifies the performance of the fine-postural system in unpredictable ways, varying with the subject. It may disturb either the mean position of the center of pressure or the integration of visual input. Sixty of the patients in this study did not use visual input to stabilize their position in relation to their surroundings. The value of stabilometry as a method for observing the integration of visual input in the control of orthostatic posture is discussed.

Adult↗
PubMed1987

[Posturography should be included in the vertigo test].

After a brief review of different systems involved in postural control, we describe a method of posturography for exploring vestibulospinal pathways, in which postural oscillations of subject standing on a platform are recorded with eyes open then with eyes closed, and in different head and gaze positions. In normals, only closing of eyes interferes significantly with balance. Posturography is important in vertigo examinations, because it can show: vestibuloocular and vestibulospinal pathway lesions, associated or not; whether there is compensation for imbalance by visual input; cervical origin of vertigo, if any; and, in acute vestibular deficit, that good test results suggest a favorable prognosis.

Adult↗
PubMed1986

[Neurinomas with normal brain stem auditory evoked potentials].

Of 145 neurinomas operated upon, 2% had normal brain stem auditory evoked potentials (BERA). Potentials were obtained by means of a special technique allowing extraction every 600 ms and its follow up with time (brain stem temporal dynamic). This score of 2% was also that reported by some American authors who associate electrocochleography with BERA. The latter provide an accurate diagnosis in 96% of cases of all types of tumors taken together and in 91% of cases of small tumors. Furthermore, the performance of conventional scan imaging is accurate in only 25% of small tumors whereas gas meatocysternography detects more than 95% of cases. The latter method is therefore the most sensitive one but it possesses the disadvantage of being invasive and of costing much more than BERA, which remains therefore the least invasive examination providing the best and earliest diagnosis.

Brain Stem↗
PubMed1985

[Does proprioception of the extrinsic eye muscles participate in equilibrium, vision and oculomotor action?].

Extrinsic eye muscles respond to both proprioceptive and visual impulses. Histology of ocular proprioceptive receptors shows them to be qualitatively and original, neuromuscular bundles are found in primates, and so called "palisade sensory nerve endings" in felines. Golgi's osteotendinous receptors are apparently absent. The number of muscle receptors is high and their proportion in relation to muscle weight even more so. The afferent pathway for this sensory system initially accompanies the motor fibers of oculomotor III, IV, ans VI nerves. Some fibers continue with these nerves to the brain stem while others join the ophthalmic branch of the trigeminal nerve (probably in the cavernous sinus). Cell bodies of proprioceptive fibers are located either in the mesencephalic root of the trigeminal nerve and in the Gasserian ganglion. The superior colliculus, center of eye-head coordination integration, also receives proprioceptive data. Proprioceptive afferent signals also project on two cerebellar cortex regions, one in the VI th and VII th lobules of the posterior lobe vermis, the other in the flocculus, all major centers for control and interaction of visuocervicovestibular activity. Extraocular proprioceptive impulses play an important role as do visual influx, in the maturation of the visual cortex in mammalia. Moreover, maintenance of binocular integration appears to require both coherent binocular vision and balanced bilateral, extraocular afferent impulses. Clinical consequences are multiple. Proprioceptive imbalance due to oculomotor dysfunction could explain the attendant visual deficit, which is reversible after correction of they motor disorder. Forced excentration of gaze provokes equilibrium disturbances in normal subjects. In cases of oculomotor palsy, the accompanying vertigo often observed could thus be due à lack of coordination between the intention of movement and its execution. Many oculomotor signs are dependent on the position of gaze alone, in the absence of any visual guide: end-position nystagmus gaze nystagmus, rebound nystagmus, gaze drift, periodic alternating and vertical superior nystagmus, ocular flutter and opsoclonus, nystagmus retractorius, etc. Proprioceptive impulses from extrinsic eye muscles are probably necessary for assessment of orbital coordinates of the ocular globe position during target fixation: this emphasizes the importance of this proprioceptive factor in the origin of ocular jerks. Proprioceptive impulses may play a crucial role in the triggering of the rapid phase of nystagmus, thus conditioning the variations in amplitude seen in provoked nystagmus tests.

Afferent Pathways↗
PubMed1982

Optokinetic, vestibular, and optokinetic-vestibular responses in albino and pigmented rats.

Horizontal eye movements and neuronal activity in the vestibular nuclei and pretectum were recorded in albino and pigmented rats in response to optokinetic, vestibular (VS), combined visual-vestibular (VVS) sinusoidal stimulations. 1. VOR slow phase velocity in VS condition leads head velocity. This phase lead is smaller in albino than in pigmented rats. 2. Presence of vision (VVS) improves the phase angle of the VOR in both strains, especially at low frequencies. In pigmented rats the VOR is perfectly compensatory with respect to phase at all frequencies whereas in albinos the eye velocity still leads the head velocity. 3. There is no difference in the response characteristics of vestibular nuclear neurons (VN) to VS between albino and pigmented rats which could explain the difference in their VORs. 4. In the pigmented rat, there is a strong optokinetic input to VN which provokes a shift of the response peak towards peak head velocity. These visual-vestibular interactions at VN level are in agreement with the changes in the phase angle of the VOR. 5. In albino rat, there are no differences in the response characteristics of VN between VS and VVS, thus the decrease of the VOR phase lead observed in VVS compared to VS is due either to visual-vestibular interactions outside of the vestibular nuclei or to some general arousing effect of light. 6. Recording of responses of pretectal neurons to visual stimulation in albino rats has shown that they are activated in a phasic or tonic way by light on ("On cells") or off ("Off cells"). Contrary to the pigmented rat, pretreated neurons in albino exhibited no detectable direction specific optokinetic responses.

Animals↗
PubMed1982

[Flutter-opsoclonus: report on three cases (author's transl)].

Three cases of spontaneous saccadic ocular movements are reported, each with one or several electrooculographic recordings. Case 1 is a typical ocular flutter during a myoclonic encephalitis with cerebellar signs. Case 2 is an ocular flutter occurring in the course of an acute inflammatory polyneuropathy with cerebellar signs after cytomegalovirus infection. Case 3 began with permanent dissociated opsoclonus, then conjugated opsoclonus and ended with vertical flutter in a patient suffering from bronchial carcinoma. While some definitions are unclear, clinical, electrooculographic and etiological data support a unicist point of view on flutter-opsoclonus.

Adult↗
PubMed1982

[Convergence of visual and neck proprioceptives on the vestibulo-ocular reflex arc and the "vestibulo-cerebellum" (author's transl)].

Linked to the vestibular reflex, ontologically the most primitive, nuchal and visual proprioceptive afferent impulses heighten perception of movement and the position of the head and body in space. The final goal of these reflexes appears to be maintenance of the visual axis and of posture. They are under cerebellar control which adapts responses according to sensory interactions, and probably increases reactions when a deficiency exists. Functional exploratory tests in patients with positional or postural vertigo should include the study of responses to separate or combined stimulation of these three types of receptor according to the three planes of the semicircular canals.

Animals↗
PubMed1982

[Nystagmus and benign paroxysmal vertigo (author's transl)].

Audio-impedence, vestibular, caloric, and electronystagmograph tests were conducted in 22 patients with benign paroxysmal vertigo. The disorder is provoked by certain sudden head movements, a latency period of several seconds occurring between the end of the movement and the onset of vertigo. This markedly differentiates it from other types of vertigo. It is of brief duration and associated with autonomic nervous system signs. Nystagmus, usually rotatory, is provoked by the particular head movement involved or by Hallpike's manoeuver. Results of the majority of tests were normal, occasional slight anomalies being observed after calibrated caloric vetibular test. This benign affection appears to be due to a bilateral, or more frequently unilateral mechanical lesion of the posterior semicircular canal cupula. It runs a extremely variable course, usually not exceeding four months, and is an indication of choice for vestibular reeducation, for which new techniques have been developed.

Electronystagmography↗
PubMed1982

[How spontaneous nystagmus modifies nystagmus induced by caloric vestibular stimulation, studied in 34 patients with vestibular neuritis].

Spontaneous nystagmus modifies the degree of rotatory pendular and caloric vestibular nystagmic responses, provoking directional preponderance towards the same side. Until now, no true correlation has been able to be established between directional preponderance intensity and that of spontaneous nystagmus, correlation between these two parameters depending, in fact, on a third factor; vestibular reflectivity. Spontaneous nystagmus can apparently be defined as a directional preponderance inversely proportional in degree to vestibular reflectivity (the reflectivity of a vestibule being the sum of the hot and cold stimulation response indices). This phenomenon produces a thermal preponderance during the caloric test, and "vestibular recrutment" during the rotatory pendulum test. These findings are the result of 56 measurements conducted in 34 patients with vestibular neuritis. There was also a significant increase in vestibular reflectivity on the healthy side in these patients, suggesting both central and peripheral lesions. Because of the difficulty sometimes encountered when attempting to relaste the different concepts of overall vestibular responses, a new clinical unit of measure is proposed: the number of nystagmic jerks in 30 s. Hinchcliffe has previously employed this unit for the vestibular response, but it is now proposed for more general application to measurement of reflectivity, mean directional preponderance, unilateral directional preponderance, and mean thermal preponderance.

Caloric Tests↗
PubMed1982

[The functional investigation of vestibular balance and oculomotor function in 17 children with apparently congenital unilateral deafness and normal contralateral hearing].

Thorough study of vestibular and oculomotor function as well as radiological investigations were undertaken in 17 subjects with an apparently congenital unilateral cophosis. In 5 cases there was vetsibular hypovalence on the same side as the cophosis and bilateral impairment in 2 cases. No central abnormality was found. In one case tomograms showed atresia of the internal auditory meatus. The aetiopathogenesis of this labyrinthine involvement remains mysterious.

Adolescent↗
PubMed1981

[The diagnostic value of vertical nystagmus in the simultaneous bilateral calibrated caloric vestibular test (author's transl)].

Vertical nystagmus provoked by simultaneous bilateral caloric stimulation has been known since 1907 (Bàràny). However, if a controlled and calibrated injection os water at 44 degrees C or 30 degrees C for 30 seconds at a flow rate of 250 ml/minute is given in normal subjects, this stimulus is insufficient to provoke a response, whilst in subjects with a central vestibular disorder there appear upward vertical movements with hot stimulation and downward movements with cold stimulation. The degree of this response is proportional to the degree of horizontal nystagmic responses to classical unilateral caloric tests. The authors feel that vertical nystagmic responses to simultaneous bilateral caloric stimulation reflect a loss of control of the vestibular reflex activity of the superior semicircular canals.

Adult↗