Geneva experience with the Ineraid multichannel cochlear implant

Evaluación del implante coclear como técnica de tratamiento de la hipoacusia profunda en pacientes pre y post locutivos

INTRODUCTION

These are the objectives planned for this study: 1. Evaluate the results from the communication point of view. 2. Evaluate the cochlear implant (CI) impact on the quality of life. 3. Evaluate medical complications and technical failures. 4. Assess direct and indirect costs generated during the phases of a cochlear implantation programme. 5. Determine which factors have a high impact on the clinical evolution and the financial cost.

MATERIALS AND METHOD

A population of 877 patients, postlingual and prelingual, adults and children, have been studied. They were treated in 5 Spanish centres with cochlear implant programmes. Audiometric tests and global questionnaires on life quality have been carried out. Medical and CI technology complications have also been computed. Direct and indirect economic costs of a cochlear implant have been calculated.

RESULTS

Postlocutive-implanted patients reached the 40 dB SPL threshold in the Pure Tone Audiometry, and this result was maintained during the 12-year evolution. In Vowels test, it evolved from a 30% on pre-stimulation to 80-90%, in Disyllables words test it evolved from a 10% to a 50-60%, and in CID Sentences test it evolved from an 18% to a 60-70%. In the prelocutive population, results were influenced by the child's age at implantation. The best results were obtained by the children who had been implanted earlier. Those implanted between 0 and 3 years old evolved in the Vowels test from 0% during pre-stimulation to 95%, from a 0% to a 90% in Disyllables words test and from a 0% to a 90-95% in CID Sentences test. Also, the speech acquisition and development of the pre-locutive population was also influenced by the implantation age. An 80% of postlocutive adult patients stated a mood and sociability improvement after the cochlear implantation. They did not show health changes in general nor relevant modifications in the attention they usually received from relatives and friends. Severe medical-surgical complications were registered for a 3.42% of the cases, a 7.06% of mild medical-surgical complications and a 3.07% of technical breakdowns in the internal components of the CI. Financial cost of implantation for a post-locutive adult oscillated between 36,912 Euro and 37,048 Euro, and between 37,689 Euro and 44,273 Euro for a pre-locutive child.

CONCLUSIONS

Cochlear implants clearly enhance communication skills of the implantees. Results obtained for the prelocutive implanted population justify the creation of hearing screening programmes in new-borns. Postlocutive implanted adults have expressed satisfaction for the results obtained. However, they did perceive some limitations in situations of unfavourable acoustic conditions. An analysis of direct and indirect costs related to a CI programme has been made. It may be useful to carry out reports on the cost-benefit ratio in this field. The low index of complications observed shows which cochlear implant treatment technique complies with the adequate safety margins. The factors influencing the most in the evolution are: duration of hearing deprivation, age at implantation, cochlear anatomy and functionality of the auditory pathway, patient's and relative's motivation, and the coexistence of other handicaps associated to hearing losses.

Effects of the acoustical dynamic range on speech recognition with cochlear implants

The amplitude compression function in a speech processor for cochlear implants maps the wide acoustical dynamic range of sounds into the smaller electrical dynamic range available on the implanted electrodes. In this study, we examined the effects of systematic variations of the acoustical dynamic range of the compression function on speech recognition with cochlear implants. Statistical measures of the amplitude distribution of speech sounds were made in each channel of a research speech processor providing more than 50 dB of input signal-to-noise ratio. Several systematic variations of the dynamic range of the compression function were implemented on this basis, and speech recognition was determined using vowel and consonant identification tests in three experienced cochlear implant users. Results demonstrated that the acoustical dynamic range of the compression function does have a significant effect on speech recognition with cochlear implants. They suggest that a dynamic range of about 45 dB is necessary for optimal speech recognition.

Within-patient longitudinal speech reception measures with continuous interleaved sampling processors for ineraid implanted subjects

OBJECTIVE

To assess within-subject changes in speech reception over time in a group of Ineraid subjects fitted with continuous interleaved sampling (CIS) wearable processors fabricated in Geneva. To compare asymptotic performance between CIS and Ineraid processors for the same subjects.

DESIGN

Twelve patients, all users of the 4-channel Ineraid cochlear implant system for several years and with no previous experience of CIS processors in daily life, were equipped with Geneva Wearable Processors programmed to implement a high-rate CIS sound processing strategy using four to six channels. Their speech reception performance with CIS processors was monitored over a period of 1 yr with consonant and vowel identification tests. For comparison, speech reception performance also was measured with Ineraid processors before switching to CIS and after 6 mo of non-use of Ineraid processors.

RESULTS

At fitting, CIS processors produced significantly better consonant identification but no better vowel identification. Subsequently, consonant and vowel scores with CIS processors improved progressively to asymptote after 6 mo of daily use. At 6 mo and beyond, performance with CIS processors was significantly superior to that obtained with Ineraid processors on both consonant and vowel identification tests. Control tests made with Ineraid processors after 6 mo of non-use of the device yielded results that were indistinguishable from those obtained before the study.

CONCLUSIONS

The full potential of the CIS strategy is not revealed at fitting. Accumulation of daily experience provides significant improvements, asymptotic performance being reached after about 4 to 6 mo of use. All Ineraid users might greatly benefit from CIS processors.

First field trials with a portable CIS processor for the Ineraid multichannel cochlear implant

The continuous interleaved sampling (CIS) strategy is a promising sound processing strategy for multichannel cochlear implants which provides immediate improvements in speech recognition when tested on Ineraid users: patients with only a few hours of experience (in laboratory testing) with the CIS strategy score better than with the Ineraid prosthesis they used since they, were implanted. The goal of this study was to evaluate the benefits that can be gained by the use of the new strategy in every day life. Two patients, implanted with the Ineraid multichannel cochlear implant, were equipped with a portable numerical processor programmed to implement a high rate CIS strategy. Their speech recognition was evaluated periodically with consonant and vowel identification tests for more than 6 months of use. Tests were also made with the Ineraid processor during the same experimental sessions and patients were regularly interviewed about their experience. Performance with the portable CIS processor was superior or equal to that obtained previously in the laboratory with the same strategy. Both patients achieved the best scores in 6 years of cochlear implant use. Qualitative reports from the patients suggest that the CIS strategy can improve "hearing" performance of cochlear implant users in many important situations of every day life. Altogether, these results hold great promises for all users of the Ineraid multichannel cochlear implant.

Channel interactions in patients using the Ineraid multichannel cochlear implant

Electrode interactions were investigated on two totally deaf patients fitted with the Ineraid multichannel cochlear implant. Currents were applied to the most apical electrode (the 'perturbation' electrode) and their effects on psychophysical thresholds on the other electrodes (the 'test' electrodes) of the intracochlear array were studied. Two experimental protocols were used. In experiment I, we used a detection protocol to study how the perception of signals presented on each test electrode was affected by subthreshold, simultaneous or non-simultaneous stimulation of the perturbation electrode. Strong electrode interactions were observed with simultaneous stimulation and monotonically decreased as a function of electrode separation. Electrode interactions were weak with non-simultaneous stimulation. In experiment II, we used a discrimination protocol to study how the perception of signals presented on the test electrode was affected by suprathreshold, non-simultaneous stimulation of the perturbation electrode. Subjects could discriminate stimulation of 'perturbation+test' versus 'perturbation alone' when the level of stimulation on the test electrode was near threshold. These results demonstrate that strong electrode interactions in the Ineraid multichannel cochlear implant system are generated by electrical field summation due to simultaneous stimulation of different electrodes, and that one can reduce electrode interactions by sequential activation of the electrodes. These observations might help to understand basic phenomena underlying recent significant improvements in speech recognition scores when switching from simultaneous to interleaved pulsatile stimulation in patients wearing the same cochlear implant system (Wilson et al., 1991).