Improvement of cochlear implant performance: changes in dynamic range

Effect of modified programming parameters on sound field thresholds, speech perception and CAEP among children using CP802 processor

Optimizing and validating programming parameters of Thresholds(T) and most comfortable levels(C) is very important in young children using a cochlear implant who may not be able provide behavioral responses. The present study attempts to describe the changes in T/C level with behavioral and Cortical Auditory Evoked Potentials (CAEP) responses. Twenty participants using CI24RE (ST) implant with CP802 speech processor participated in the study. Three experimentally 'sham' programs were created by a) decreasing T levels, b) raising T levels or c) decreasing C levels in the 'everyday' program. Sound field thresholds and speech perception at 50dBHL were measured for all experimental and everyday programs. Acoustically evoked CAEP measures, namely thresholds for three different stimuli of/ba/,/da/and/ga/, along with amplitude and latency at 80dBnHL were recorded for all programs. The results indicated that modification of T levels did not have significant effect on CAEP threshold, latency, amplitude as also on behavioral measures of sound field thresholds and speech perception. However, reduction of C levels resulted in significantly poor sound field thresholds, speech perception as well as CAEP thresholds. Furthermore, it was found that there was a significant correlation between behavioral measures of sound field threshold and speech perception with CAEP measures. Thus, from the present study it may be concluded that behavioral and CAEP responses can be used as indicator to reflect changes in C levels resulting changes in behavioral measures in users of CP802 speech processors.

Apical Reference Stimulation: A Possible Solution to Facial Nerve Stimulation

OBJECTIVES

Postimplantation facial nerve stimulation is a common side-effect of intracochlear electrical stimulation. Facial nerve stimulation occurs when electric current intended to stimulate the auditory nerve, spread beyond the cochlea to excite the nearby facial nerve, causing involuntarily facial muscle contractions. Facial nerve stimulation can often be resolved through adjustments in speech processor fitting but, in some instances, these measures exhibit limited benefit or may have a detrimental effect on speech perception. In this study, apical reference stimulation mode was investigated as a potential intervention to facial nerve stimulation. Apical reference stimulation is a bipolar stimulation strategy in which the most apical electrode is used as the reference electrode for stimulation on all the other intracochlear electrodes.

DESIGN

A person-specific model of the human cochlea, facial nerve and electrode array, coupled with a neural model, was used to predict excitation of auditory and facial nerve fibers. These predictions were used to evaluate the effectiveness in reducing facial nerve stimulation using apical reference stimulation. Predictions were confirmed in psychoacoustic tests by determining auditory comfort and threshold levels for the apical reference stimulation mode while capturing electromyography data in two participants.

RESULTS

Models predicted a favorable outcome for apical reference stimulation, as facial nerve fiber thresholds were higher and auditory thresholds were lower, in direct comparison to conventional monopolar stimulation. Psychophysical tests also illustrated decreased auditory thresholds and increased dynamic range during apical reference stimulation. Furthermore, apical reference stimulation resulted in lower electromyography energy levels, compared to conventional monopolar stimulation, which suggests a reduction in facial nerve stimulation. Subjective feedback corroborated that apical reference stimulation alleviated facial nerve stimulation.

CONCLUSION

Apical reference stimulation may be a viable strategy to alleviate facial nerve stimulation considering the improvements in dynamic range and auditory thresholds, complemented with a reduction in facial nerve stimulation symptoms.

Do the minimum and maximum comfortable stimulation levels influence the cortical potential latencies or the speech recognition in adult cochlear implant users?

INTRODUCTION

Cochlear implants (CI) programming is based on both the measurement of the minimum levels required to stimulate the auditory nerve and the maximum levels to generate loud, yet comfortable loudness. Seeking for guidance in the adequacy of this programming, the cortical auditory evoked potentials (CAEP) have been gaining space as an important tool in the evaluation of CI users, providing information on the central auditory system.

OBJECTIVE

To evaluate the influence of mishandling of electrical stimulation levels on speech processor programming on hearing thresholds, speech recognition and cortical auditory evoked potential in adult CI users.

MATERIAL AND METHODS

This is a prospective cross-sectional study, with a sample of adult unilateral CI users of both sexes, aged at least 18 years, post-lingual deafness, with minimum experience of 12 months of device use. Selected subjects should have average free field hearing thresholds with cochlear implant equal to or better than 34 dBHL and monosyllable recognition different from 0%. Individuals who could not collaborate with the procedures or who had no CAEP recordings were excluded. Participants were routinely programmed, and the map was named MO (optimized original map). Then three experimentally wrong maps were made: optimized original map with 10 current units below the maximum comfort level (C), named MC- (map minus C); optimized original map with minus 10 current units at minimum threshold level (T), named MT- (map minus T) and optimized original map with 10 current units above minimum level (T), named MT + (map plus T). In all programs, participants underwent free-field auditory thresholds from 250Hz to 6000Hz, recorded sentences and monosyllabic recognition tests presented at 65dB SPL in quiet and in noise, and free field CAEP evaluation. All tests were performed in an acoustically treated booth, in a randomized order of map presentation. Data were compared by Wilcoxon test.

RESULTS

Thirty individuals were selected and signed an informed consent form. The MC- map provided worsening of all free field thresholds, quiet and noise speech recognition, and P1 wave latency delay with significant difference from the results with the MO map. The MT- map worsened the hearing thresholds and statistically significantly reduced the P2 wave latency; MT+ map improved free field thresholds except 6000Hz, worsening speech recognition, without statistical significance.

CONCLUSIONS

The results suggest that maximum levels below the optimal thresholds lead to worse cochlear implant performance in both hearing thresholds and speech recognition tests in quiet and noise, increasing CAEP component P1 latency. On the other hand, the manipulation of minimum threshold levels showed alteration in audibility without significant impact on speech recognition.

The influence of stimulation levels on auditory thresholds and speech recognition in adult cochlear implant users

Objective: This study aims to evaluate the influence of minimum and maximum stimulation levels on auditory thresholds and speech recognition abilities in adult cochlear implant users. Method: Fifteen adults implanted with a Cochlear® device with over 12 months listening experience. Participants underwent routine programming for optimization of minimum (T) and maximum comfort (C) stimulation levels, which was saved in Program 1 (MO). Three further maps were constructed artificially adjusting the measured levels: Program 2 - MO with 10 fewer electrical current units at C level (MC-); Program 3 - MO with 10 fewer electric current units at T level (MT-); and Program 4 - MO with 10 more electric current units at T level (MT+). Sound field thresholds, recorded sentence recognition and monosyllable tests were presented in quiet and in noise. Results: There were significantly better thresholds at 1, 3, 4, and 6 kHz frequencies in MT+ and worse in MC-. A statistically significant difference was observed for sentences in quiet and monosyllables in quiet and noise with changing C levels, with worsening of the results for MC- program. Conclusion: The results suggest that T levels above the behavioural threshold provided an improvement in sound field thresholds but did not influence performance on speech recognition tests in quiet and in noise. In contrast, C levels below the behavioural comfort level worsened sound field thresholds and led to poorer performance in tests of sentence recognition in quiet and monosyllable recognition in quiet and in noise.