Assessment of medial olivocochlear system function in pre-term and full-term newborns using a rapid test of transient otoacoustic emissions.

This study was conducted to investigate maturation of the medial olivocochlear efferent system (MOCS) in pre- and full-term neonates using Quickscreen (Otodynamics Ltd) and to confirm previous findings on transient otoacoustic emission (TEOAE) suppression in neonates. MOCS maturation was investigated in 46 neonates born at the Chaim Sheba Medical Center, Tel Hashomer, Israel, using Quickscreen. All neonates were normal with no family history of general or auditory disease and no risk factors for hearing impairment. MOCS function appears gradually in human pre-term neonates and is considered to reach maturity shortly after term birth. The clinical value of MOCS testing in specific populations of newborns at risk for hearing and/or brainstem function can be legitimately raised as activation of the MOCS clearly alters cochlear output. The present results can be interpreted to support the testing of infants at risk of developing abnormal MOCS function using a commercially available rapid TEOAE measurement system.

[Binaural cochlear implantation: general concept, surgical technique and electrophysiology]. / Implantation cochléaire binaurale.

Cochlear implant have been proven to be safe and cost-effective in deafened adults. Generally, a single cochlear implants is proposed providing monaural audition. Some teams have published interesting results in patients wearing two cochlear implants. The cost of the surgical procedure is greatly increased for bilateral implantation. In an attempt to provide patients with binaural hearing and a better chance to improve their capacity for frequency discrimination without an excessive increase in cost, we developed an new concept and design for binaural cochlear implants. The aim of the present study was to establish the surgical technique for binaural cochlear implantation with a single internal receptor-stimulator. We report descriptive data on surgical procedures performed in two cadavers and in two deafened adults. The special implant is composed of a single receptor-stimulator and two electrode arrays: a short one implanted into the ipsilateral ear and a long one in the contralateral ear. A specially designed tool for endoscopic facial lifting was used to create subcutaneous tunnels from the ipsilateral to the contralateral ear. Insertion into cochleas was unremarkable. Additional time for surgery (compared with mean operative time for routine adult surgery in our unit), and surgical details are discussed. Binaural cochlear implantation is feasible, easy and not very time consuming. Studies are in progress to determine patient benefit. Obtaining auditory brainstem evoked potentials electrically in patients with binaural cochlear implants is possible and provides an interesting mode for in vivo analysis of the long-term effect of profound/total deafness on neural transmission. In our patients, results have demonstrated that neural response properties in auditory pathways are negatively related to duration of deafness.

Peripheral auditory lateralization assessment using TEOAEs.

Previous studies indicate a left-right asymmetry in the function of peripheral auditory system. Contralateral acoustic suppression of TEOAEs (transient evoked otoacoustic emissions) enables assessment of medial olivocochlear efferent system functioning, and has demonstrated that this system is more effective in the right than in the left ear. Moreover, TEOAE amplitudes are lower in the left than in the right ear. The aim of the present experiment was to verify firstly the absence of a relationship between medial efferent system asymmetry and TEOAE amplitude asymmetry, and secondly to study TEOAE input/output function slopes. There was no link between the asymmetries in TEOAE amplitude and in the medial efferent system functioning. Further, as previously shown, the medial olivocochlear system increased the TEOAE input/output function slopes. These TEOAE input/output function slopes seem to be consistent factors in peripheral asymmetry since the slope is lower in the right than in the left ear. Moreover, the lower the TEOAE amplitudes, the greater the TEOAE slopes. The slope asymmetry of the two ears could correspond to earlier saturation or a lower augmentation ability of the TEOAE response in the right ear, where the TEOAE amplitude is higher. This asymmetry in growth slopes reinforces the notion of peripheral auditory lateralization.