K. Burian

PERCEPTS FROM THE VIENNA COCHLEAR PROSTHESISa

This report includes psychophysical data on some of the 13 patients who have been equipped with intracochlear electrodes and the 6 patients who have received an extracochlear electrode. Thresholds and uncomfortable listening levels versus frequency, amplitude difference limens, and gap detection in noise and frequency difference limens have been determined and represent some essential characteristics of prosthetic hearing.

Reimplantation of a Molded Scala Tympani Electrode: Impact on Psychophysical and Speech Discrimination Abilities

Revision surgery was successfully performed on two Vienna cochlear implant patients. Twenty months and 40 months, respectively, after initial insertion into the cochleas of two bilaterally deaf patients, electrodes were removed from the scala tympanis and replaced by electrodes of the same design. Psychophysical and speech data gathered before and after the revision surgery were compared. These were thresholds, loudness scalings, amplitude difference limens, pitch scalings, frequency difference limens, and speech tests in the “stimulation only” modality. No negative changes were found. The data available demonstrate a continuous improvement in performance over many months of practice with the sound processor. This development was not impeded by the revision surgery. Thus, it was demonstrated that the removal and replacement of a molded scala tympani electrode is feasible.

Designing of and experience with multichannel cochlear implants.

The technology of two different multichannel cochlear prosthetic devices is described. The clinical results after electrical stimulation in five implanted patients are discussed.

DESIGN AND FABRICATION OF MULTIWIRE SCALA TYMPANI ELECTRODESa

A suitable stimulation electrode is a crucial part of an auditory prosthesis for the deaf. A number of different sites for the placement of such electrodes have been suggested and are being investigated. At present, the optimum site for electrode placement is still being discussd. As yet no results have been found that could scientifically demonstrate an advantage of multichannel stimulation versus single-channel stimulation. It will take some time and more experience with both types of systems before this question can be answered. This report deals with multichannel electrodes that are designed to be inserted into the scala tympani via the round window. Other sites for multichannel electrodes that have been tried or are being used, as well as other approaches into the cochlea, will not be discussed. The majority of researchers working on multichannel implants prefer the access into the scala tympani via the round window. The main reason for this is the short duration and comparatively small risk of the implant surgery required as compared to methods in which wires are put into the cochlea or close to it from outside its outer wall. The requirements that a suitable scala tympani electrode must fulfill are similar to the requirements for electrodes of other neuroprostheses. They have to achieve an unknown degree of neuronal selectivity. This task involves adequate geometry of the electrode body and the stimulating areas and the possibility of sufficiently atraumatic placement in close-enough proximity to the excitable structures. If the number of channels exceeds ten and the spacing between electrode contacts has to be less than 1 mm, then thinor thick-film techniques seem to offer an especially adequate tool for the realization of multichannel stimulation electrodes. Investigators at a number of centers have worked or are working on the design of thin-film electrodes for cochlear prostheses. Several problems have to be overcome before it will be possible to use modern thin-film techniques for the realization of scala tympani electrodes and to be able to eventually benefit from their lower production costs.

Hören über ein Cochlea-Implantat

SummaryThe actual type of cochlear implant used by the Viennese team is described. The indication for implantation is discussed. In two patients the praeoperative electrostimulation of the promontory is demonstrated. The surgical procedure of the implantation as well as the postoperative course is shown and reported in two cases. In a very extensive testprogramm on words and open speech the rehabilitation of understanding in two patients with heriditary and luetic deafness is demonstrated.

Das Cochlearimplantat und seine psychosozialen Auswirkungen bei 36 Patienten

In a study on 36 cochlear implant patients questionnaires answered pre- and postsurgically were analyzed. One year after implantation patients demonstrated significant changes on some of the test items. Although results show that the patients accept their device, some of their wishes and hopes remain unsatisfied.

Selection of Patients

The Vienna Group uses two types of cochlear prosthesis, a unichannel extracochlear and a four-channel endocochlear device with unichannel stimulation. The limitations in patient selection are the same for both, except for the auditory status. My answer to the first two questions therefore involves a definition of what we call deafness and residual hearing. The endocochlear four-channel prosthesis is limited to patients who have bilateral deafness with pure-tone thresholds above 95 dB, with or without hearing of words, absence of noise discrimination, and no visual unaided word or sentence comprehension even with the use of bilateral hearing aids. The extracochlear unichannel prosthesis is limited to patients who have pure-tone thresholds of 85 dB and above, hearing of words but no visual unaided word or sentence comprehension even with the use of hearing aids. The main difference here is that the patients of this group are able to understand some numbers and to discriminate environmental sounds. This very important function must be preserved. This is only possible with an extracochlear device. Regarding the question of pre- or post-lingual deafness, I should like to state that the majority of our 35 patients were post-lingually deaf. Only recently we accepted a small number of pre-lingual deaf patients, though one should realize that the rehabilitation of speech comprehension in these patients takes much longer than in the post-lingual deaf and that the results achieved after a reasonable rehabilitation period can only be compared within the same group of pre-lingual deaf patients, because it will probably never be as good as in the post-lingual deaf group. To questions number 4 and 5, concerning age limitation, I should like to comment that it seems very reasonable to me to decrease the age below 13-15 years which is now our present age limitation. There are nevertheless also a few valid arguments against this. In most patients below 10 years it is very difficult to obtain reliable data with preoperative electrical stimulation-a subjective test which has to be performed under local anaesthesia. The second argument concerns the post-operative rehabilitation. From my experience it seems to be very difficult to effect a consistent rehabilitation procedure because of various psychological and environmental circumstances. These objections are probably not justified with the age group of 24 years because their rehabilitation coincides with the physiological development of speech and hearing. I believe that this age group should be our future goal when it becomes possible to test the electrical sensitivity of nerve fibres objectively, for example, with the registration of electrical evoked BSP under general anaesthesia; only extracochlear stimulation would be warranted in small children. Besides the audiometric criteria mentioned, we have the following restrictions to cochlear implants.

Preliminary Speech Perception Results through a Cochlear Prosthesis

Psychophysical as well as speech comprehension tests have been used in bilaterally deaf patients implanted with a four-channel cochlear prosthesis. The best open speech comprehension without lip-reading was obtained in a 24-year-old patient C. K. with progressive total hereditary deafness. This speech perception was achieved using a small portable stimulator activating only one of the four channels of the implant in a bipolar scala tympani electrode configuration.