A common cause of profound deafness is hair cell dysfunction in the cochlea. Cochlear implants (CI) bypass the hair cells via an electrode and stimulate the cochlear nerve directly. Nowadays, it is possible to preserve residual hair cell function and hearing through flexible electrodes and a-traumatic CI surgery techniques; called hearing preservation CI surgery. This may suit partially deaf patients who can use natural low frequency hearing in combination with electric high frequency hearing; so-called hybrid hearing. The aim of this thesis was to elucidate the effectiveness of hearing preservation CI surgery. The thesis demonstrates human cochlear anatomy in relation to CI and evaluates hearing and patient satisfaction after hearing preservation CI surgery. Analyses of human cochlear moulds belonging to the Uppsala collection showed large variations in dimensions and coiling characteristics of the cochlea. Each cochlea was individually shaped. The size and shape of the cochlea influences the position of the electrode. The diameter of the basal cochlear turn could predict insertion depth of the electrode, which is crucial for hearing preservation. The first 21 patients operated with hearing preservation CI surgery in Uppsala, showed preserved hearing. Nine-teen partially deaf patients receiving implants intended for hybrid hearing, were evaluated concerning pure tone audiometry, monosyllables (MS) and hearing in noise test (HINT). They also responded to a questionnaire, consisting of the IOI-HA, EQ-5D VAS and nine questions about residual hearing. The questionnaire results indicated a high degree of patient satisfaction with improved speech perception in silence and noise. This was also reflected by improved results in MS and HINT. Hearing was preserved in all patients, but there was an on-going deterioration of the residual hearing in the operated ear which surpassed the contralateral ear. There were no correlations between the amount of residual hearing and patient satisfaction or speech perception results. Electric stimulation provides a major contribution to speech comprehension in partially deaf patients. All the patients showed a high degree of satisfaction with their CI, regardless of varying hearing preservation.

Le clinicien se trouve parfois confronté à des sujets qui présentent une surdité supérieure à 90 dB HL au-delà de 1 kHz avec une audition résiduelle dans les fréquences graves. Pour réhabiliter les hautes fréquences, il existe aujourd’hui différentes technologies : amplification conventionnelle, compression fréquentielle, implant cochléaire et depuis une dizaine d’année la stimulation électro-acoustique EAS qui consiste à stimuler acoustiquement les sons graves et électriquement les sons aigus via un implant cochléaire. La première partie de cette thèse a consisté à identifier les facteurs qui influencent les capacités des patients sourds partiels à traiter l’information basse fréquence de la parole. Nous avons utilisé un test d’audiométrie vocale filtrée passe-bas. Nos résultats indiquent que les scores d’intelligibilité de la parole sont positivement corrélés avec la durée de la surdité. Ceci signifie qu’avec le temps, ces sujets malentendants apprennent à comprendre avec cette audition type filtre passe-bas, à tel point que certains ont des performances supra-normales pour l’utilisation des basses fréquences. Nos résultats montrent également une corrélation négative entre l’âge d’apparition de la surdité et les scores l’intelligibilité. Ce test pourra aider le clinicien à mieux cibler l’appareillage le plus adapté à chaque profil de patient. La seconde partie de cette thèse, consacrée à l’EAS, a consisté à évaluer par des simulations chez le normo-entendant, diverses stratégies de codage du son par l’implant EAS. Actuellement, la stratégie utilisée pour l’EAS est calquée sur celle de l’implant cochléaire et nos résultats suggèrent que cette stratégie peut être optimisée. / Clinicians may face patients who have a deafness superior to 90 dB HL above 1 kHz with good lowfrequency residual hearing. Today, several technologies are available to provide high frequencies: conventional amplification, frequency compression, cochlear implant since about 10 years Electric-Acoustic Stimulation EAS which consists in stimulating acoustically low frequencies while stimulating electrically high frequency sounds via a cochlear implant. The firt part of this dissertation consisted in identifying the factors which may influence abilities of partially deaf subjects to process low-frequency speech information. We used a low-pass filtered speech test. Our results show that speech intelligibility scores are positively correlated to the duration of deafness. This means that these hearing-impaired subjects learn to understand with this lowpass-like hearing, in such a way that some of them exhibit supranormal abilities for the processing of low-frequency sounds. Our results also show a negative correlation between the age at onset of deafness and speech intelligibility scores. This test may help the clinician to better evaluate which device would be best for every patient’s profile. The second part of this dissertation, about EAS, consisted in evaluating through simulations in normal hearing listeners, several coding strategies by the EAS implant. Now the strategy used for EAS duplicates the strategy used by cochlear implants and our results suggest that this strategy could be optimized.