Over the last five years the Symphonix Vibrant soundbridge (VSB), an implantable hearing device, has proven an effective alternative treatment modality for patients suffering from moderate to severe sensorineural hearing loss. The results from the majority of our 40 patients are very encouraging but reveal clinical variations in benefit influenced by the coupling of the transducer to the ossicular chain. This study describes a set-up for measuring the sound pressure level in the external auditory canal when the middle ear implant is activated. The reverse transfer function allows the transducer performance to be determined both intra- and postoperatively. The sound pressure level shows a strong correlation with the stapes footplate displacement and free-field audiometry.

The preliminary results show a promising new approach to the use of hearing prostheses for patients suffering from moderate to severe sensorineural hearing loss.

The Symphonix Vibrant Soundbridge is a new and promising treatment modality for patients suffering from moderate to severe sensorineural hearing loss. Further improvement of the good results can be expected with improved coupling of the transducer to the ossicular chain and further development of signal processing.

Group II ( p > 0.001), whereas only wave V latency and amplitude were improved in Group 1 ( p < 0.01). These results (see Figure 2) show that the changes due to auditory deprivation are greatly reversible under electrical stimulation. DiscussionEABRs have been obtained in several multichannel CI devices (Pelizzone et al., 1989; Shallop et al., 1990; Brown et al., 1994; Gallego et al., 1996; Brown et al., 1999; Gordon et al., 2002), mainly in adult patients and/or after several months of electrical stimulation. All patients of our study were children and most of them were implanted before the age of 5 years. This could explain the differences that we observed such as longer latencies in the intraoperative EABR recorded in congenitally deafened children (Group II, near 4.5 ms instead of 3.8-4 ms as in most studies). These findings could be due to a reduced number of neurons and/or an impaired myelination in the central auditory pathways as recently suggested by animal studies of immature auditory pathways (Hardie and Shepherd, 1999). Electrical stimulation induced different changes in early congenitally deafened children (Group II) and in progressively deafened children (Group I). This could indicate that more profound changes were induced by cochlear implantation in congenitally deafened children (maturation or plastic modifications of the neural circuits) than in progressively deafened children. These data are consistent with those found by others in cortical potentials and support the concept of early implantation in congenitally deafened children (Ponton et al., 1999).