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Biomedical subjects

A Gentine

Publications and source records attributed to A Gentine.

18 recordsLinked to original sources
PubMed1992

[Neuroendocrine giant-cell epithelioma. Description of a clinical case and review of the literature].

Neuroendocrine tumors are rare neoplasms of the larynx and hypopharynx. This tumors are divided in paragangliomas (usually benign, although malignant case have been reported), large cell neuroendocrine carcinoma, described in this case as a primary pharyngo-laryngeal locate, and small cell neuroendocrine carcinoma (characterized by early and diffuse metastatic disease, and best treated by radiotherapy and chemotherapy). Through the international literature, the authors reviewed the characteristics of the large cell neuroendocrine tumors and their management.

Aged↗
PubMed1992

[Laryngeal sarcoidosis: apropos of a case].

The authors report an unusual case of laryngeal sarcoidosis. After having explained it, they describe the elements of diagnosis about this rarely isolated pathology, its complications and treatment as well.

Adrenal Cortex Hormones↗
PubMed1992

[Sudden deafness. Analysis of a series of 117 cases].

A retrospective study have been conducted in 117 cases of sudden sensori-neural hearing loss, between 1988 and 1991, int he department of Head and Neck Surgery (Strasbourg). After a brief review of actually treatments, they show, in a statistic and comparative analysis, that efficacy of therapeutics are never significant. This results are compared with international bibliography, and show that treatments of sudden loss remains doubtful.

Audiometry↗
PubMed1992

[Post-traumatic aneurysm of the internal carotid artery].

The authors present a typical case of a traumatic internal carotid aneurysm rupture appearing 40 years after a blunt head trauma and surgically treated with success. The etiopathogenic and clinical aspects are reviewed and the important place of the angiography in diagnostic and therapeutical strategy is discussed.

Aged↗
PubMed1991

Modelling the action of caloric stimulation of the vestibule. II. The mechanical model of the semi-circular canal considered as an inflatable structure.

In order to explain the mechanical effects that arise when a semi-circular canal is thermally stimulated in the horizontal position (i.e. in the absence of gravity effects) a physical model was used. The duct (corresponding to the canal) is deformable, the pressure transducer (corresponding to the ampulla) is not deformable. There is no thermal similarity but a dynamical similarity has been respected, so the mechanical phenomena occurring in the semi-circular canal and in the model are identical. The time scale is close to one. The physical model showed that the relative volume variations (fluid/duct) due to caloric stimulation lead to a pressure variation measured by the pressure transducer at the place of the ampulla and the cupula. The time history and the value of this pressure depend on the mechanical and thermal properties of the duct and the fluid. The qualitative responses of the physical model and of the vestibulo-ocular reflex after caloric stimulation were coherent. A numerical model simulating the same mechanisms yielded a quantitative estimation of the transcupular pressure arising in a horizontal semi-circular canal (i.e. without gravity dependent effects) during caloric stimulation. The physical model and the numerical simulation take no account of the inflating pressure variation.

Caloric Tests↗
PubMed1991

Modelling the action of caloric stimulation of vestibule. III. Caloric nystagmus induced by osmotic pressure variation.

The properties of the membranous wall of the semi-circular canal and of the labyrinthine fluids give as a result the inflating pressure of this inflatable structure. The difference of osmotic pressure between perilymph and endolymph, which is involved in this problem, depends on temperature. Therefore, a caloric stimulation leads to a change in the inflating pressure. A numerical model, similar to the model used to study the effects of relative volume variations, gives a quantitative estimation of the transcupular pressure arising in a horizontal semi-circular canal (i.e. without gravity dependent effects) during a caloric stimulation, according to the inflating pressure change. As a consequence, it appears that rotational and caloric stimulations are not quite similar. The caloric stimulation leads not only to a transcupular pressure difference but also to a change in inflating pressure. As a result of the change in inflating pressure, the stiffness of the cupula varies. This modifies the gain and the dynamics of the vestibulo-ocular reflex, and may explain the asymmetry between hot and cold stimulations.

Caloric Tests↗
PubMed1991

Modelling the action of caloric stimulation of the vestibule. IV. The global mechanical model.

Caloric stimulation acts on the bio-accelerometer (the semi-circular canal), as on engineered ones, through second order type multiple pathways. Three temperature induced peripheral actions have been described in our previous reports. The hydrostatic mechanism induces in the endolymph a gravity dependent transcupular stationary pressure difference. The differential expansion of the membranous duct and its content creates a local volume variation, while the modification of the transmembranous exchanges causes a local pressure variation. These two last mechanisms are gravity independent. They depend on parameters of the membrane, and induce a transcupular transient pressure difference and a stationary variation of the inflating pressure. It seems reasonable to assume the independency of these three mechanisms. If this assumption is true, than the global effect of caloric stimulation should be the sum of the effects of the three partial mechanisms. It is shown here that, for the physical model, this assumption holds. For humans, in the more general frame of the caloric vestibulo-ocular reflex experiments reported in the first paper, qualitatively and quantitatively this assumption holds, too. The model predicts a percentage of gravidity dependent effects of about 75%. It is shown that the reported human experiments lead to compatible estimates of this percentage. For humans in the earth gravity field, enduring the caloric stimulation it is not necessary to include neither otolithic interactions, nor significant modifications of the mecano-neural transduction, in the limits of precision of today's experimentation.

Caloric Tests↗
PubMed1991

[Vestibular test in Menière's disease].

When it is well known that the electronystagmographic examination cannot diagnose the Meniere's disease, it is very useful to ensure that no other pathology is involved and for the follow up of the patients. The vestibulo-oculogram, on the other hand, suggests the presence of hydrops, according to the mechanical model.

Electronystagmography↗
PubMed1991

[Modeling of the semi-circular canal, application to labyrinthine hydrops].

The angular accelerometer of vertebrates, the semi circular canal, is a pressure gage. The transformation, acceleration to pressure, is due to the inertia of the endolymph. In the 0 to 1 Hz frequency interval, the endolymph-cupula system can be described by a second order, localised parameter model with two real time constants. This mechanical model explains the occurr]nces of the vestibular-ocular reflex during rotatory stimulations. However, some features of the response to caloric stimulations cannot be explained from this unique point of view. To correspond to these features, the SCC has to be considered as an inflatable structure, sensitive to weak pressure variations between the endolymph and perilymph. Different parameters of the mechanical model, the internal radius of the membranous canal, the dimension of the cupula and its elasticity coefficient depend on the inflating pressure. Ménière's disease is caracterised by hydrops, i.e. an increase of the pressure in the membranous SCC. The different mechanisms related to this hydrops, in particular introducing the inflating pressure as a second input to the ampular system, associated to a new concept of the mechanoneural transduction can explain the classical vestibular symptoms of Ménière's disease. Therefore, this overall mechanical model of the SCC indicates that hydrops is the mechanical cause of Ménière's disease and the primary cause is more likely to be a defect in the regulation loop of the inflating pressure.

Biophysical Phenomena↗
PubMed1988

[Computer-assisted vestibular tests].

The labyrinth is a sensor of vibration. Therefore, multifrequency vestibular stimulation proves indispensable in obtaining a more accurate study of the VOR. We chose to use a pseudo-random binary sequence, generated on a mini computer. The angular velocity instructions are made up of eight repetitive sequences, the spectrum of energy in which is adapted to the frequency range of VOR. A process eliminating the quick phases, the blinking and other artefacts is applied to the nystagmic response, in order to observe only the slow phase velocity. The velocity of eye and chair are compared and the transfer function of VOR is performed. Gain, phase, coherence function and predominance of the mean slow phase velocity between left and right responses are the four indices which define VOR function. The multifrequency rotatory test is interesting for topographic diagnosis, and makes out three diagnostic ranges: a mechanical peripheral, a neurosensory peripheral and a central one. Two practical measures could help the propagation of this method: a simpler vestibular stimulation in order to suppress the rotatory chair, a simplified method of data processing using a personal computer.

Diagnosis, Computer-Assisted↗
PubMedDate not supplied

Modelling the action of caloric stimulation of the vestibule. I. The hydrostatic model.

In this first article of four the problem is displayed using experiments on humans for two kinds of gravity related positions. In each case the nystagmus depends sinusoidally on a particular orientation of the canal to the vertical. In each case, too, a dissymmetry of the response occurs. This kind of behavior confirms that the caloric stimulation induces both a gravity dependent and a gravity independent effect. A simple mechanical model gives account of the gravity dependent effect. It does not imply the otolithic system. Since the cupula adheres to the ampullar wall and to the crista, this is a hydrostatic model in contrast to Bárány's model, which is of hydrodynamic type.

Adult↗