Optimization of a Non-invasive Electrophysiological Method for Studying the Functionality of Auditory Nerve Fibers

Overview

Acoustic overexposure can induced temporary or hearing loss. Usually hearing loss is associated with cochlear cell damages. Recently, a new pathological entity was described and called "hidden hearing loss". In animal model, the histopathology revealed a selective reduction in the number of auditory fibers, resulting in a decrease in the amplitude of wave I of the auditory brainstem response. Electrocochleography (Ecog) is a method for recording the electrical potentials of the cochlea (e.g. wave I). In clinical routine, Ecog is performed invasively with sedation or local anesthesia. Actually, a non invasive approach could be perform but it seems necessary to optimize this method and to define reference values in healthy volunteers.

The sound overexposure is a major cause of hearing disorders. The installation of hearing disorders can be temporary or permanent. Most of the time the investigators see a rise in hearing thresholds that can be accompanied by tinnitus. However, sometimes-hearing disorders aren't characterized by higher auditory threshold but by a complaint of understanding in noise. Two explanation are the either possible with a lesion at the peripheral level (sensory organ) or central lesion (auditory pathways). Peripheral damage is easily analysed by conventional tests such as the audiogram. Concerning the central lesions, through to the Electrocochleography, one sees a diminution of the wave I which corresponds to the nerve fiber injury. The wave I can more easily be analysed by the Electrocochleography method. This technique previously used an electrode deposited trans-tympanically in contact with the sensory organ. But, the evolution of a non-invasive technique is now available. However, several assemblies of the electrode are then possible without knowing the impact of these on the morphology of the wave I. Moreover, no normative values are also referenced in the literature on the population without hearing problems. It's in this context that clinical study is carried out in order to optimize the technique on the assembly of the electrode and the acoustic stimulation delivered. After this analyses and obtaining an optimal technique it's envisaged to study the morphology of the wave I in healthy volunteers aged 18-25 years. A pre-inclusion visit will verify the volunteers doesn't have a hearing disorders through a questionnaire, otoscopy, tympanometry and audiometry. Then two steps will be realized. The first is to evaluate the morphology of wave I according to assembly of electrode and acoustic stimulation delivered (machine calibration or calibration in the external auditory canal). The second step will provide normative values for people 18-25 years old who aren't hearing-impaired. Volunteers will have the choice to participate in one or both stages. The aim is to obtain wave I reference values for Electrocochleography technique. The secondary objectives are to analyse the impact of the assembly of the electrode and the adaptation of the acoustic stimulation presented.