Ontwikkelingen in direct akoestisch cochleaire stimulatie

Developments in direct acoustic cochlear stimulation:Hearing problems have been associated with poor quality of life, cognitive decline and a source of frustration. Over the past years, an essential progress has been made in hearing aids improving the wearing comfort, speech processing in noise and wireless connectivity. In a subgroup of patients with a combination of an important sensorineural hearing loss and a conductive component, defined as severe to profound mixed hearing loss, hearing rehabilitation was lagging behind. Conventional middle ear surgery and/or hearing aids would not suffice to overcome the degree of hearing loss and often local anatomical issues were complicating the hearing aid use. This subgroup is growing in number because of an increased awareness for hearing with two ears and for communicating. Also because of an aging population, the sensorineural hearing loss component is becoming increasingly important.With the recent development of a new hearing system, a direct acoustic cochlear implant (DACI), the inner ear can be stimulated acoustically at the oval window. In this way, the amplified signal is provided directly to the cochlea and pathological external and middle ear structures are bypassed. This dissertation explores, for the first time, the functioning of direct acoustic cochlear stimulation in several domains. First, as guidance for evidence-based research, a systematic review of the literature on the hearing rehabilitation of mixed hearing loss was carried out. Next, the clinical application and thorough evaluation of DACI compared to the best current alternative are described. Finally, objective electrophysiological measures and new coupling strategies for DACI are developed.In the first study, the clinical outcome and safety of a whole range of acoustic hearing implants in adults with mixed hearing loss was assessed through a systematic review of the literature. It was concluded that acoustic hearing implants and the respective various coupling strategies were beneficial in terms of speech perception in quiet, patient-reported outcome measures and safety regarding residual hearing. Overall, the level of evidence and the quality of the included studies was judged to be moderate to low.The second study consisted of a prospective, multicenter evaluation of nineteen subjects with severe to profound mixed hearing loss due to several etiologies. The DACI treatment was compared to the best-aided preoperative treatment. The mean speech reception threshold (SRT), a measure for speech in noise understanding and representative for real-life communication, improved with 7.9 dB compared to the preoperative aided condition for the study cohort. A mean postoperative aided SRT of 2.6 dB SNR was noted. Patient-reported questionnaires indicated a significant global benefit in hearing ability and in quality of life. The DACI surgery was regarded as a safe and efficient treatment.In the third study, we focused on the development of an objective electrophysiological assessment of the device s coupling and stimulation of the entire auditory pathway. By investigating the feasibility of evoked auditory transient (ABR) and steady-state responses (ASSR), we opened the path for future intra-operative applications. Responses were recorded to click trains in the 40 Hz and 90 Hz range in three DACI subjects. A direct stimulation setup for reliable auditory response recording was developed in a first set of experiments. Next, by comparing amplitude growth function and phase delay in the same stimulus range, validity of the recorded responses was confirmed in DACI subjects. Electrophysiological stimulation thresholds could objectively be determined from the ABRs and ASSRs in all subjects and the relation with behavioral thresholds was made. Estimated latencies were in agreement with electrophysiological auditory pathway studies, with apparent latencies of about 40 and 25 ms for 40 and 90 Hz, respectively. For the first time, auditory evoked potentials could reliably be recorded and analyzed in patients with a digital speech processing DACI.The fourth study aimed to explore the coupling of a DACI transducer to an anatomically easy accessible inner ear site, being the lateral semicircular canal (LC). This could simplify and shorten the surgical procedure. Fresh-frozen human cadaver heads were implanted with the DACI device stimulating the LC in different coupling situations. The LC was kept intact, blue-lined (i.e. thinning but keeping the last shell of bone closed) or opened, respectively, and each condition was compared with standard oval window coupling. As a measure of the performance of the device and its coupling efficiency, the round window velocity was determined using a laser Doppler vibrometry setup. Pairwise comparisons in three frequency ranges showed that round window velocity was significantly lower in case of intact LC stimulation than in the standard oval window coupling condition, confirming the added value of direct inner ear stimulation. Equivalent output calculations showed a modest but significant added value of blue-lining over the intact condition. Opening the canal resulted in a significantly higher round window velocity than in the intact or blue-lined conditions for all frequency ranges, similar to the oval window coupling. Experimentally induced stapes footplate fixation did not impede the DACI performance when stimulating the opened LC.In the different studies in this project important steps have been made towards reliable hearing rehabilitation, even in difficult listening situations, objective electrophysiological measures and easier surgery in the challenging treatment of severe to profound mixed hearing loss.nrpages: 176status: publishe