Effects of electrode deactivation on speech recognition in multichannel cochlear implant recipients

Objectives: The objective of the current study is to evaluate how speech recognition performance is affected by the number of active electrodes that are turned off in multichannel cochlear implants. Several recent studies have demonstrated positive effects of deactivating stimulation sites based on an objective measure in cochlear implant processing strategies. Previous studies using an analysis of variance have shown that, on average, cochlear implant listeners’ performance does not improve beyond eight active electrodes. We hypothesized that using a generalized linear mixed model would allow for better examination of this question.

Methods: Seven peri- and post-lingual adult cochlear implant users (eight ears) were tested on speech recognition tasks using experimental MAPs which contained either 8, 12, 16 or 20 active electrodes. Speech recognition tests included CUNY sentences in speech-shaped noise, TIMIT sentences in quiet as well as vowel (CVC) and consonant (CV) stimuli presented in quiet and in signal-to-noise ratios of 0 and +10?dB.

Results: The speech recognition threshold in noise (dB SNR) significantly worsened by approximately 2?dB on average as the number of active electrodes was decreased from 20 to 8. Likewise, sentence recognition scores in quiet significantly decreased by an average of approximately 12%.

Discussion/conclusion: Cochlear implant recipients can utilize and benefit from using more than eight spectral channels when listening to complex sentences or sentences in background noise. The results of the current study suggest a conservative approach for turning off stimulation sites is best when using site-selection procedures.     

The diagnostic value of measurement of cochlear length and height in temporal bone CT multiplanar reconstruction of inner ear malformation

Conclusion: The cochlear length (CL) and cochlear height (CH) measured through MPR will provide for more accurate quantitative diagnosis of inner ear malformation, and are subsequently convenient for calculating cochlear duct length (CDL) before cochear implant.

Objectives: Qualitative and quantitative diagnosis of inner ear malformation in deaf patients through multiplanar reconstruction (MPR) was performed to provide a reference for cochlear implants.

Methods: One hundred and two cases without sensorineural deafness and 560 patients with sensorineural deafness had MPR of temporal bone computed tomography performed to obtain the standardized cochlear-view and oblique coronal-view images. The inner ear radial lines were measured to formulate normal values for inner ear malformation diagnosing, and the CDL was estimated based on CL.

Results: The normal range values of inner ear radial lines were measured and formulated, of which CL was 8.1–9.59?mm and CH was 3.28–3.90?mm. According to inner ear morphology and the normal values measured above, 61 cases of incomplete partition-type II (IP-II) and a high percentage (27/110, 24.5%) of hypoplasia of cochlea (HC) were diagnosed. The HC group was further divided into 1-turn, 1.5-turn, and 2-turn sub-groups, which had CDL of 15.98?±?1.48?mm, 21.36?±?0.96?mm, and 26.56?±?0.60?mm, respectively.     

NGB基因转染拮抗庆大霉素耳毒性作用的实验研究

目的验证阳离子脂质体介导脑红蛋白(neuroglobin,NGB)基因转染对庆大霉素致豚鼠耳毒性的保护作用。方法将ABR反应阈均不超过40dB SPL的120只健康花色豚鼠随机分为5组,每组24只:Ⅰ组:空白对照组;Ⅱ组:人工外淋巴液对照组(经左耳注入人工外淋巴液);Ⅲ组:人工外淋巴液实验组(经左耳注入人工外淋巴液后肌肉注射庆大霉素);Ⅳ组:空质粒转染组(经左耳注入空质粒pEGFP-C1后肌肉注射庆大霉素);Ⅴ组:NGB基因转染组(经左耳注入pEGFP-NGB后肌肉注射庆大霉素),庆大霉素均经后腿肌肉注射120mg.kg-1.d-1,共给药14天。停止给药后喂养14天,各组均行ABR检测,耳蜗基底膜铺片、免疫组化观察各组豚鼠耳蜗基底膜毛细胞形态学及NGB蛋白表达的变化。结果给药后Ⅰ组ABR反应阈平均为37.22dB SPL(左耳)和36.94dB SPL(右耳),Ⅱ组阈值平均为37.22dB SPL(左耳)和37.50dB SPL(右耳),Ⅲ组阈值平均为119.44dB SPL(左耳)和122.22dB SPL(右耳);Ⅳ组阈值平均为119.72dB SPL(左耳)和120.83dB SPL(右耳);Ⅴ组阈值平均为83.89dB SPL(左耳)和100.56dB SPL(右耳)。Ⅴ组ABR反应阈较Ⅰ组和Ⅱ组显著升高(P<0.05),较Ⅲ组和Ⅳ组显著降低(P<0.05)。Ⅴ组中手术耳ABR反应阈较非手术耳降低(P<0.05)。耳蜗基底膜铺片示Ⅰ组和Ⅱ组内外毛细胞排列整齐,无缺失,Ⅲ组和Ⅳ组内外毛细胞极少量残存,其中ABR阈值大于135dB SPL的豚鼠耳蜗毛细胞几乎消失殆尽,Ⅴ组毛细胞部分缺失,且主要是外毛细胞;免疫组织化学染色示Ⅴ组耳蜗毛细胞NGB蛋白表达量较其余各组均显著增高(P<0.05),其余各组几乎均未见明显阳性表达。结论本研究成功验证了阳离子脂质体介导NGB基因转染对庆大霉素致豚鼠耳毒性具有有效的保护作用。     

Toward a battery of behavioral and objective measures to achieve optimal cochlear implant stimulation levels in children

OBJECTIVES: Children require audible and comfortable stimulation from their cochlear implants immediately after device activation. To accomplish this, a battery of objective measures may be needed that could include the electrically evoked stapedius reflex (ESR), compound action potential from the auditory nerve (ECAP), and/or auditory brain stem response (EABR). In the present study, the following specific research questions were asked: In children using cochlear implants, 1) Can the ECAP, EABR, and ESR be recorded at the time of cochlear implantation? 2) What is the feasibility of measuring the ECAP, EABR, and the ESR repeatedly without the use of sedation over the first year of implant use? 3) Do ECAP, EABR, and ESR thresholds or behavioral measures change over time? 4) What is the relation between ECAP, EABR, and ESR thresholds and behavioral measures of threshold and comfortably loud levels? DESIGN: In 68 children, ECAP, EABR, and ESR responses as well as behavioral measures of stimulation threshold and maximum stimulation were recorded at regular intervals over the first year of implant use. In each child, responses were recorded to electrical pulses provided by three different electrodes along the implanted array. Visual inspections of the stapedius reflex (V-ESR) evoked by activation of the same three electrodes at the time of surgery were performed in an additional 20 children. RESULTS: ECAP and EABR measures were obtained in more than 84% of electrodes tested and 89% of children tested both in the operating room at the time of implant surgery (OR) and after surgery in nonsedated children. ESRs were recorded by using immittance measures in more than 65% of electrodes tested and 67% of children tested by 3 mo of implant use, but this technique was less successful in the OR and during early stages of device use. V-ESRs and ECAP thresholds were higher in the OR than ESRs and ECAPs at postoperative recording times. EABR and ECAP thresholds did not significantly change over the first 6 and 12 mo of implant use, respectively, whereas ESR thresholds increased. Behavioral measures of threshold decreased over time, whereas maximum stimulation levels rose over time. Behavioral measures of threshold and loudness were highly correlated at all test times. ECAP, EABR, and behavioral measures were lower when evoked by an electrode at the apical end of the implanted array than by more basal electrodes. Behavioral thresholds could be predicted mainly by ECAP thresholds, whereas maximum stimulation levels could best be predicted by ESR thresholds; both were significantly affected by the age at implantation. CONCLUSIONS: A combination of nonbehavioral measures can aid in the determination of useful cochlear implant stimulation levels, particularly in young children and infants with limited auditory experience. These measures can be made in the operating room and can be repeated after surgery when needed. Correction factors to predict threshold stimulation levels should be based on ECAP thresholds or EABR thresholds if necessary. Correction factors should be made for at least one apical and mid-array electrode, should take into account the age of the child, and may have to be revised during the first year of implant use. Maximum stimulation levels may be best determined by using the ESR.     

豚鼠耳颞部60Coγ射线照射对耳蜗核影响的实验研究

目的探讨60 Coγ射线照射对豚鼠耳蜗核神经元的影响。方法 48只豚鼠随机分为对照组(8只)和实验组(40只),实验组豚鼠于右耳颞部做一次性40Gy 60 Coγ射线照射后的1、4、7、14、30d行听性脑干反应(audi-tory brainstem response,ABR)测试,然后处死,行耳蜗核石蜡切片HE染色及免疫组织化学染色,观察细胞形态及半胱氨酸天冬氨酸蛋白酶3(Caspase 3)。对照组不予60 Coγ射线照射,行ABR测试后行耳蜗核HE染色,方法同实验组。结果对照组ABR反应阈为29.17±1.95dB SPL,实验组在接受60 Coγ射线照射后1、4、7、14、30dABR阈值升高,分别为31.88±2.59、35.00±3.17、35.83±2.04、39.17±2.05、41.67±2.58dB SPL,照射后4、7、14、30d ABR反应阈与对照组比较差异有统计学意义(P<0.05);实验组各时间点ABR波I、II、III潜伏期及I-II、II-III、I-III波间期延长,与对照组比较差异有统计学意义(P<0.05)。HE染色显示实验组在照射后不同时间点均出现耳蜗核神经细胞肿胀、胞核皱缩或碎裂、尼氏体减少,以14、30天时改变明显。对照组耳蜗核Caspase3免疫组化染色的灰度值为172.33±17.81,实验组60 Coγ射线照射后1、4、7、14、30d耳蜗核Caspase3免疫组化灰度值分别为136.37±24.42、94.67±15.33、91.40±11.71、110.80±4.23、123.56±32.56,两组比较差异有统计学意义(P<0.05)。结论 60 Coγ射线照射可导致耳蜗核损伤;Caspase3表达上调可能与耳蜗核神经元射线损伤有关。     

Estimation of the status of spiral ganglion neurons and Schwann cells in the auditory neural degeneration mouse using the auditory brainstem response

Conclusion: The auditory brainstem response (ABR) wave I threshold, latency and amplitude are insensitive to spiral ganglion neurons (SGNs) degeneration, but are sensitive to the degeneration of Schwann cells and can estimate the status of Schwann cells in a neural degeneration mouse model. The thorough pre-operative ABR assessment would be helpful in predicting cochlear implant performance.

Objectives: This study aimed in finding a non-invasive electrophysiological method to evaluate the status of the auditory nerve and the Schwann cells in sensorineural hearing loss (SNHL) and auditory neuropathy (AN) ears, and providing useful information for candidates screening and outcome prediction in cochlear implantation.

Methods: The frequency-specific acoustic ABR was recorded in mice. The immunohistochemical staining was performed to detect the SGNs and Schwann cells in mice cochlea. The correlations between ABR wave I metrics and SGNs, Schwann cells were investigated.

Results: In SNHL and AN mice cochlea, statistically significant correlations between ABR wave I thresholds, latencies and amplitudes at 8, 16, and 32?kHz and their corresponding SGNs densities were found only in wave I amplitude at 8?kHz. While the ABR wave I metrics at all three frequencies showed strong significant correlations with their corresponding Schwann cells densities.     

Maximal number of pre-synaptic ribbons are formed in cochlear region corresponding to middle frequency in mice

Objective: To investigate whether there are more quantitative pre-synaptic ribbons formed in the cochlear region corresponding to middle-frequency in cochlea of mice.

Methods: Counts of pre-synaptic ribbons were performed using immunostaining and laser confocal microscopy. Hearing thresholds and function of ribbon synapses were estimated by auditory brain response (ABR) and compound action potential (CAP). Cochlear mapping has been achieved to match the frequencies and corresponding regions along the cochlear spiral.

Results: The number of pre-synaptic ribbons in per inner hair cell (IHC) has been found to increase gradually from the base turn, the maximal quantity appeared at the region of 50–70% from the apex. Next, ABR thresholds showed that there was the lowest ABR threshold in the frequency around 8–16?kHz, corresponding to the region of 50–70% from the apex according to the cochlear mapping. Further, CAP amplitudes were estimated, and the maximal value identified at the same frequency (8–16?kHz).

Conclusions: Maximal number of pre-synaptic ribbons is formed in the cochlear region of middle frequency in mice, coupling with the lowest ABR threshold and highest CAP amplitudes. Our study shows that the middle frequency (8–16?kHz) could be the most sensitive region to sound stimuli in mice.     

Sequential bilateral cochlear implant: results in children and adolescents

IntroductionThe use of the bilateral cochlear implants can promote the symmetrical development of the central auditory pathways, thus benefiting the development of auditory abilities and improving sound localization and the ability of auditory speech perception in situations of competitive noise.ObjectiveTo evaluate the ability of speech perception in children and adolescents using sequential bilateral cochlear implants, considering the association of these variables: age at surgery, time of device use and interval between surgeries.MethodsA total of 14 individuals between 10 and 16 years of age, who demonstrated surgical indication for the use of sequential bilateral cochlear implants as intervention in the auditory habilitation process, were assessed. The speech perception ability was assessed through sentence lists constructed in the Portuguese language, presented in two situations: in silence, with fixed intensity of 60 dB SPL, and in competitive noise, with a signal-to-noise ratio of +15 dB. The evaluation was performed under the following conditions: unilateral with the first activated cochlear implant, unilateral with the second activated cochlear implant and bilateral with both devices activated.ResultsThe results of the speech perception tests showed better performance in both silence and in noise for the bilateral cochlear implant condition when compared to the 1st cochlear implant and the 2nd cochlear implant alone. A worse result of speech perception was found using the 2nd cochlear implant alone. No statistically significant correlation was found between age at the surgical procedure, interval between surgeries and the time of use of the 2nd cochlear implant, and the auditory speech perception performance for all assessed conditions. The use of a hearing aid prior to the 2nd cochlear implant resulted in benefits for auditory speech perception with the 2nd cochlear implant, both in silence and in noise.ConclusionThe bilateral cochlear implant provided better speech perception in silence and in noise situations when compared to the unilateral cochlear implant, regardless of the interval between surgeries, age at the surgical procedure and the time of use of the 2nd cochlear implant. Speech perception with the 1st cochlear implant was significantly better than with the 2nd cochlear implant, both in silence and in noise. The use of the hearing aid prior to the 2nd cochlear implant influenced speech perception performance with the 2nd cochlear implant, both in silence and in noise.     

Effects of stimulus level on the speech perception abilities of children using cochlear implants or digital hearing aids

OBJECTIVE: The present investigation was designed to provide information to facilitate the decision of whether a child should continue using digital signal processing (DSP) hearing aids with wide dynamic range compression (WDRC) or be recommended for a cochlear implant, based on the unaided pure-tone average (PTA at 500, 1000, and 2000 Hz). DESIGN: Fifty-two children (ages 5 to 15 yr) with unaided PTAs in the moderately severe to profound range, wearing (DSP) hearing aids with (WDRC) or a Nucleus 24, Clarion 1.2, or CII cochlear implant system, participated: 26 with unaided PTAs from 60 to 98 dB HL using DSP hearing aids and 26 with pre-implant unaided PTAs from 93 to 120 dB HL, using cochlear implants. An open-set speech perception test, the Lexical Neighborhood Test (LNT; ), was administered at intensity levels representative of raised (70 dB SPL) and soft (50 dB SPL) speech at two different times approximately 1 mo apart. Minimum audibility of soft sounds was determined for the children with implants and with DSP hearing aids using warble-tone thresholds at octave intervals between 250 and 4000 Hz. RESULT: Regression analyses and significance testing were used to determine the unaided PTA values at which the performance of the DSP Hearing Aid group (DSP HA group) and Cochlear Implant group on the LNT test were statistically different at the 0.05 significance level. For the 70 dB SPL presentation level, the statistically different PTAs were 113 and 97 dB HL at Time 1 and Time 2, respectively, and 96 and 88 dB HL at 50 dB SPL for Time 1 and Time 2, respectively. CONCLUSIONS: The Unaided PTA at which children in the cochlear implant group would be expected to score significantly better than the children in the DSP HA group was lowest (96 and 88 dB HL) for the lower signal level (50 dB SPL). Assuming that LNT scores at 50 dB SPL are representative of long-term hearing of soft incidental speech that is essential for language learning and fluent communication, the children with PTA values greater than the range from 88 to 96 dB HL would be expected to have significantly better LNT scores with a cochlear implant. These results should be further examined with research efforts focusing on early intervention with optimally fitted DSP hearing aids and cochlear implants.     

Comparison of primary musicality development between children with cochlear implants and children with normal hearing

Abstract

Background: It is beneficial for CI patients listen to music. However it is necessary to take steps to improve the musicality of CI patients.

Objectives: The aims of the study were to evaluate the primary musicality of children with cochlear implants versus those with normal hearing.

Material and methods: Children participating in this study were divided into two groups: the cochlear implant group (CI group) and the normal hearing group (NH group). The ‘Musical Ears Evaluation Form for Professionals’ was used to evaluate the subjects’ primary musicality.

Results: The scores for overall and the three subcategories of primary musicality in children with cochlear implants and in those with normal hearing also improved significantly over time (p?<?.05). The score for overall primary musicality was not significantly different between CI and NH groups in the same hearing age (p?>?.05). There were significant differences between the two groups in the same chronological age (p?<?.05).

Conclusions and significance: The primary musicality in children with cochlear implants was not significantly different from normal hearing ones at the same hearing age. The primary musicality in children with cochlear implants was significantly lower than that of children with normal hearing at the same chronological age.     

Bilateral cochlear implants in children: localization acuity measured with minimum audible angle

OBJECTIVE: To evaluate sound localization acuity in a group of children who received bilateral (BI) cochlear implants in sequential procedures and to determine the extent to which BI auditory experience affects sound localization acuity. In addition, to investigate the extent to which a hearing aid in the nonimplanted ear can also provide benefits on this task. DESIGN: Two groups of children participated, 13 with BI cochlear implants (cochlear implant + cochlear implant), ranging in age from 3 to 16 yrs, and six with a hearing aid in the nonimplanted ear (cochlear implant + hearing aid), ages 4 to 14 yrs. Testing was conducted in large sound-treated booths with loudspeakers positioned on a horizontal arc with a radius of 1.5 m. Stimuli were spondaic words recorded with a male voice. Stimulus levels typically averaged 60 dB SPL and were randomly roved between 56 and 64 dB SPL (+/-4 dB rove); in a few instances, levels were held fixed (60 dB SPL). Testing was conducted by using a "listening game" platform via computerized interactive software, and the ability of each child to discriminate sounds presented to the right or left was measured for loudspeakers subtending various angular separations. Minimum audible angle thresholds were measured in the BI (cochlear implant + cochlear implant or cochlear implant + hearing aid) listening mode and under monaural conditions. RESULTS: Approximately 70% (9/13) of children in the cochlear implant + cochlear implant group discriminated left/right for source separations of 相似文献   

Effect of Stimulation Parameters on Electrically Evoked Auditory Brainstem Responses

It is evident that the conventional technique for cochlear implant adjustment is not suitable for children in their first years of life. In order to find a solution to this problem, the possibility of electrically evoked auditory brainstem response (EABR) recording was investigated. EABRs were recorded in 9 patients with the Nucleus multichannel cochlear implant. The main problems that have to be solved during EABR recording in cochlear implantees are: i) EABR distortion due to the stimulus artefact; and ii) difference in the stimulus presentation rate during EABR registration (low pulse rate) and conventional psychophysical threshold estimation (high pulse rate) in cochlear implant patients. The influence of stimulus artefact on the recording results was minimized by setting the implant to the widest amplifier frequency band and by zeroing the initial segment containing the stimulus artefact with subsequent zero-phase digital filtering. The dependence of the EABR amplitude and latency on the stimulus intensity, width, electrode location and interstimulus interval was investigated. It was concluded that despite the difference revealed between absolute values of EABR thresholds and psychophysical threshold levels, it is possible to calculate implant adjustment parameters based on the EABR data with the proper correction applied.     

Noise induced hearing loss and vestibular dysfunction in the guinea pig

Abstract

This study analysed the acoustic and vestibular functional and morphological modifications in guinea pigs after acoustic trauma. Animals were exposed to noise (6 kHz, at 120 dB SPL for 60 minutes) and then auditory brainstem responses (ABR) and vestibuloocular reflex (VOR) were measured at 6 hours, 1 day, 3, 7, and 21 days after noise. Western blotting and immunostaining for 4-hydroxy-2-noneal (4-HNE) and vascular endothelial growth factor (VEGF) were performed in the cochlear and vestibular regions at 1 and 7 days after noise exposure. A significant decrease of VOR gain was observed on day 1 and the recovery was completed at day 21. ABR threshold values reached a level of 80 dB at day 1 after trauma reaching a value of about 50 dB SPL on day 21. 4-HNE expression, a marker of lipid peroxidation was strongly increased in the cochlea. In the vestibule, 4-HNE immunoreactivity was faint. However, VEGF was up-regulated both in the cochlea and vestibule. In conclusion, the expression of VEGF in both cochlear and vestibular structures suggests a reparative role with potentially therapeutic implications.

Sumario

Este estudio analiza las modificaciones vestibulares funcionales y morfológicas en los cobayos después de un trauma acústico. Los animales fueron expuestos a ruido (6kHz, a 120dB SPL durante 60 minutos) y se midieron las respuestas auditivas de tallo cerebral (ABR) y el reflejo vestíbulo-ocular (VOR); a las 6 horas, al siguiente día y los días 3, 7 y 21 después del ruido. Se realizaron pruebas de Western Blot e inmuno-reacciones para 4-hydroxi-2-noneal (4-HNE) y para factor de crecimiento vascular endotelial (VEGF) en las regiones coclear y vestibu-lar en los días 1 y 7 después de la exposición a ruido. Los resultados mostraron un descenso significativo de la ganancia del VOR en el día 1 y la recuperación fue completa en el día 21. Los umbrales de ABR llegaron a un nivel de 80dB en el día 1 después del trauma, alcanzando un valor de 50dB SPL en el día 21. El marcador 4-HNE, indicativo de peroxidación de los lípidos, estaba bastante aumentado en la cóclea. En la región vestibular, la reacción 4-HNE fue débil. Sin embargo, el VEGF se reguló por incremento tanto en la cóclea como en el vestíbulo. En conclusión, la expresión del VEGF en las estructuras tanto cocleares como vestibulares sugiere un papel reparador con potenciales implicaciones terapéuticas.     

电诱发听性脑干反应和电诱发镫骨肌反射阈值在内耳畸形儿童人工耳蜗植入术后调机中的运用

目的　探讨内耳畸形小儿人工耳蜗植入手术后,植入体电诱发听性脑干反应（electrically evoked auditory brainstem responses,EABR）、电诱发镫骨肌反射阈值（electrically evoked stapedius reflex threshold,ESRT）的变化特点及规律,以指导术后设备调试。方法　将88例澳大利亚Cochlear Nucleus24型人工耳蜗植入手术患儿分为耳蜗形态正常组与内耳畸形组,测试手术后1年内不同时期EABR和ESRT值,术后1年运用行为测试法检测主观阈值（T值）和最大舒适阈（C值）,分析特点及变化规律。结果  内耳畸形组患儿术后不同时期EABR和ESRT阈值较正常组高（P＜0.05）,两组EABR和ESRT阈值变化趋势相同,总的趋势是低频值较低,高频值较高,术后1年EABR和ESRT阈值逐渐增高;两组EABR与T值显著相关,ESRT与C值显著相关。结论　内耳畸形组人工耳蜗植入手术后EABR和ESRT阈值变化规律及特点与正常组患儿相同,阈值可用于指导内耳畸形人工耳蜗植入者手术后设备的调试。     

Estimating the benefit of a second bone anchored hearing implant in unilaterally implanted users with a testband

Conclusion Using a second bone anchored hearing implant (BAHI) mounted on a testband in unilaterally implanted BAHI users to test its potential advantage pre-operatively under-estimates the advantage of two BAHIs placed on two implants.

Objectives To investigate how well speech understanding with a second BAHI mounted on a testband approaches the benefit of bilaterally implanted BAHIs.

Method Prospective study with 16 BAHI users. Eight were implanted unilaterally (group A) and eight were implanted bilaterally (group B). Aided speech understanding was measured. Speech was presented from the front and noise came either from the left, right, or from the front in two conditions for group A (with one BAHI, and with two BAHIs, where the second device was mounted on a testband) and in three conditions for group B (same two conditions as group A, and in addition with both BAHIs mounted on implants).

Results Speech understanding in noise improved with the additional device for noise from the side of the first BAHI (+0.7 to?+2.1?dB) and decreased for noise from the other side (?1.8?dB to??3.9?dB). Improvements were highest (+2.1?dB, p?=?0.016) and disadvantages were smallest (?1.8?dB, p?=?0.047) with both BAHIs mounted on implants. Testbands yielded smaller advantages and higher disadvantages of the additional BAHI (average difference?=??0.9?dB).     

Influence of stimulus presentation rate on intraoperative ECAP thresholds in cochlear implant users

Objective: The objective is to evaluate the influence of the presentation rate on intraoperative ECAP thresholds in cochlear implant users.

Design: The design was data on the ECAP thresholds (t-NRT) as well as the behavioural T- and C-levels have been collected in CI patients of a quaternary otologic referral centre. Measurements of the tNRT thresholds were performed intraoperatively for 250?Hz and 80?Hz presentation rates and correlated to the stabilised T- and C-levels measured at the 5th fitting session, 4-6?months after surgery.

Study sample: There was a study sample of 35 consecutive CI patients. All patients were users of the Nucleus 24RECA (Freedom) or Nucleus CI512 cochlear implants with the Contour Advance-of-Stylet electrode.

Results: The result showed that the t-NRT thresholds were higher for the 250?Hz pulse rate typically used during the intraoperative stimulation under general anaesthesia than for the 80?Hz rate used typically during the postoperative fitting sessions. This difference was more pronounced for the basal electrodes where it exceeded 10 current levels (CL). Pearson’s correlation coefficients between the t-NRT-measurements and the stabilised T- and C-levels r ranged between 0.34 and 0.47.

Conclusion: In conclusion, the magnitude of the ECAP thresholds (t-NRT) recorded intraoperatively depends significantly on the stimulus presentation rate.     

Unitary ototoxic gentamicin exposure may not disrupt the function of cochlear outer hair cells in mice

Background: Previous study showed that mild ototoxic exposure could induce a reversible hearing impairment, and the loss and secondary incomplete recovery of cochlear ribbon synapses could be responsible for the hearing loss. However, it remains unclear whether cochlear outer hair cells’ (OHCs) functions are affected.

Objective: To verify whether the function of OHCs are also affected significantly after the ototoxic exposure.

Methods: Mice were injected intraperitoneally with 100?mg/kg concentration of gentamicin daily for 14 days. Distortion Product of Oto-acoustic Emission (DPOAE) was detected at control (pre-treatment), Day 0, day 4, day 7, day 14 and day 28 after the ototoxic exposure, respectively. In addition, the morphology of OHCs was observed by electron microscopy, OHCs has been counted by light microscopy, and the hearing thresholds were detected by auditory brain response (ABR).

Results: No significant changes have been found in OHC and OHC stereocilia among the experimental groups (p?>?.05). Further, no significant changes or loss was found in the morphology of OHCs either. However, we found ABR threshold elevations occurred after ototoxic exposure.

Conclusions: Unitary ototoxic gentamicin exposure may not disrupt the function of cochlear OHCs in mice, regardless of hearing loss identified in this ototoxic exposure.     

Chronologic changes of nitric oxide concentration in the cochlear lateral wall and its role in noise-induced permanent threshold shift

OBJECTIVE: The objective of this study was to investigate the chronologic changes of nitric oxide (NO) concentration in the cochlear lateral wall and to explore its possible role in permanent threshold shift (PTS) after intense noise exposure. MATERIALS AND METHODS: Seventeen guinea pigs were subjected to a single continuous exposure to broadband white noise at 105 +/- 2 dB sound pressure level (SPL) for 40 hours and were divided into four groups according to various postnoise recovery periods. Another 12 guinea pigs were not exposed to noise and served as controls. The hearing status of all animals was evaluated with auditory brainstem responses (ABR) evoked by condensation "click" sounds. ABR were recorded both prior to noise exposure and immediately before killing the animal. After death, NO concentration in the cochlear lateral wall was directly measured with an NO/ozone chemiluminescence technique. RESULTS: An approximately 1.7-fold increase in NO concentration was observed immediately postnoise exposure, which persisted for up to 28 days. The threshold of ABR elevation (mean, 30 dB SPL) peaked immediately after cessation of noise exposure and gradually resolved to a PTS (mean, 14.5 dB SPL) 56 days after noise exposure when NO concentration had returned to its prenoise exposure level. CONCLUSION: Noise-induced threshold shift, which resolved to a mild PTS, can be partially attributed to NO elevation in the cochlear lateral wall. Our results revealed a nonlinear correlation between ABR recovery and depletion of NO, indicating that the mechanisms of NO changes in the cochlear lateral wall may be more complicated than previously conceived and that other pathophysiologic mechanisms may also play important roles in noise-induced PTS.     

Cochlear implantation in chronic demyelinating inflammatory polyneuropathy†

Objective: To describe a case of chronic inflammatory demyelinating polyneuropathy (CDIP) with bilateral sudden sensorineural hearing loss who subsequently benefited from unilateral cochlear implantation.

Methods: case history review and review of the literature for the terms CDIP, hearing loss, cochleovestibular dysfunction, and cochlear implantation.

Results: A 49-year-old woman presented with bilateral rapidly progressive sensorineural hearing loss (SNHL) 1 month after an upper respiratory tract infection. Hearing loss was not responsive to high-dose steroids and there were no other laboratory abnormalities or physical findings. Within 1 month, she developed ascending motor palsy, requiring long-term ventilator support. This neurologic condition was diagnosed as CDIP and she was successfully treated with plasmapheresis and intravenous immunoglobulin. Her hearing never recovered. At the time of cochlear implant, she had no response at the limits of the audiometer and obtained 0% on AzBio testing. No ABR could be recorded preoperatively. She underwent uneventful cochlear implantation with a perimodilar electrode. One year after activation, she had a PTA of 20?dB and 40% on AzBio sentence testing. Her eABR demonstrated a neuropathy pattern. Only two other cases of CDIP associated with dysfunction of the eighth nerve have been described, and neither had documented profound hearing loss.

Conclusions: Severe SNHL associated with CDIP is rare. Although this patient has good access to sound, speech discrimination is poor at 1-year post implantation. This outcome may be due to incomplete recovery of myelination of the eighth nerve. Other possibilities include loss of peripheral nerve fibers due to the initial viral upper respiratory infection, which may lead to less neural substrate to stimulate.