Biomedical subjects

D Gegu

Publications and source records attributed to D Gegu.

4 recordsLinked to original sources

PubMed1984

Prognostic evaluation of the multichannel cochlear implant.

Preoperative appreciation of the future clinical results of the multichannel cochlear implant is important to assess in the case of pre- or post-lingual total deafness, in order to improve the patients selection. The psychological status of the future implanted is one of the main concerns because the post-operative reeducation efficacity depends on the patient's motivation. The Round Window electrical stimulation test supplies us with important and measurable data (electrical threshold level, tone decay test). The age of the patient, the age and the etiology of the deafness, the vestibular status and the cochlear tomodensitometry only offer non-decisive informations. The patient's socialisation level is a considerable factor. But per-operative observations are sometimes and surprisingly determinant (electrode impedances, ossified cochlea). Moreover immediate post-operative electrical and psychophysic data must also be considered.

Auditory Perception↗

PubMed1984

Results of the round window electrical stimulation in 460 cases of total deafness.

In order to avoid false and quantitatively unprecise responses the stimulating electrode must be directly placed on the round window membrane. That necessitates a transmeatal approach removing the eardrum, which is commonly achieved under local anesthesia. The positive response is subjectively easy to identify; it may be objectively registered by means of brain stem evoked responses; this registration is indispensable in case of children who need general anesthesia. This positive response signifies that some cochlear nerve fibers are still present, and therefore that the rehabilitation of the cochlear implant is possible. Among the 460 totally deaf, stimulated patients, more than 93% of them presented a positive response. The threshold level voltage value represents a statistically significant representation of the functional value of the electrode nerve interface. The features of the tone decay tests, which may be also subjectively or objectively performed, present important data which may be used to predict the clinical results that can be obtained by the cochlear implant.

Adolescent↗

PubMed1984

Implant material tolerance.

After surgical and antibiotic destruction of guinea pig cochleas non specific lesions appear which seem more due to this destruction than to the electrode implantation or chronic stimulation. Moreover, despite these lesions, the electrical threshold level value necessary to elicit brain stem evoked responses in these implanted animals does not vary in time. The electrical chronic stimulation of the newborn deafened guinea pigs cochlea prevents the cochlear nucleus atrophy observed in the non stimulated animals. In man the implanted material tolerance is perfect provided this material is covered by a Silastic or teflon sheet and is located far from the skin incision. Degradation of isolating material occurred only in case of chronic movements. For this reason device and electrodes must be placed above and behind the ear. The waterproofness of the implanted receptor is indispensable to avoid physiological liquid penetration inside the electronic device. High level voltage stimulation may involve bubble formation responsible for temporary system failure; this drawback is suppressed by enlarging the electrode tip surface allowing low level stimulation. The threshold level and the frequency discrimination of the implanted electrodes did not change for more than 6 years. Post-operative infection occurred especially in case of pre-operative chronic otitis; it may be due also to the large use of "Histoacryl". However, these infections, which never affected the threshold level voltage of the implanted electrodes, are no longer encountered since we use "Tissucol", exclude the middle ear closing the Eustachian tube, and employ our electrode bearer.

Animals↗

PubMed1984

Sound signal processing.

In the CHORIMAC-12, the French device, the whole speech information despite its redundancy is transmitted to the few cochlear nerve fibers that are still present. Only loud speech intensities between 40 db and 100 db are introduced in a filter battery which gives out the frequency information in 12 channels including the 100-6000 Hz. This 60 db intensity scale is transmitted in a compression rate of about 6 db. The time sampling is 3 msec. A 12 electrode bearer or 12 separate electrodes (in case of ossified cochlea) transmit the electrical information. The electrical stimulus is a square wave: its frequency is equal or inferior to 300 Hz; its voltage may vary between 2.5 and 6.5 volts; its duration may vary between 0 and 200 mu sec. The performances of the system is demonstrated by means of a system of computerized psychophysic tests and speech intelligibility tests.

Cochlear Implants↗