GAIN AND MAXIMUM OUTPUT OF IMPLANTABLE HEARING DEVICES IN PATIENTS WITH MODERATE TO SEVERE SENSORINEURAL HEARING LOSS

Abstract

Background: To determine the dynamic range and the maximum output of three current middle ear implants and to discuss optimal candidacy for middle ear implantation. Study Design: Clinical study. Material and Methods: Gain and output measurements were compared for three types of middle ear implants: the Otologics middle ear transducer (MET), the Vibrant Soundbridge (VSB), and the Direct Acoustic Cochlear Stimulator (DACS). The per- formance of these selected implants in users with severe, predominantly sensorineural, hearing loss (50–65 dB HL) was stud- ied. Patients with chronic external otitis and sensorineural hearing loss used either a MET (n=9) or a VSB (n=9) implant. Pa- tients with a predominantly sensorineural hearing loss aſter surgically treated otosclerosis used a DACS (n=4). Patients were selected from two different implant teams but evaluated with the same protocol. The relative gain at threshold level was deter- mined, viz. the bone-conduction threshold minus the aided soundfield threshold, divided by the bone-conduction threshold. Input–output measurements were performed with the devices in linear amplification mode and with unlimited output. In this latter data set, the maximum output and the input dynamic range of the devices were determined. Results: The relative gain for each of the three implants was comparable; however, the values were slightly lower than the gen- erally accepted target values. The input dynamic range of the devices varied, with the widest range for the DACS and Oto- logics devices. Conclusion: The results from this study indicate that the first generation DACS device is a good option for patients with mod- erate/severe sensorineural hearing loss and surgically treated otosclerosis who require a hearing implant.