Clinical results of AutoNRT, a completely automatic ECAP recording system for cochlear implants.

OBJECTIVE: AutoNRT is the completely automatic electrically evoked compound action potential (ECAP) measuring algorithm in the recently released Nucleus Freedom cochlear implant system. AutoNRT allows clinicians to automatically record T-NRT profiles that in turn can be used as a guide for initial fitting. The algorithm consists of a pattern recognition part that judges if the traces contain an ECAP and an intelligent flow that optimizes the measurement parameters and finds the ECAP threshold (T-NRT). The objective of this study was to determine how accurate, reliable, and fast the automatic measurements are. DESIGN: Data on more than 400 electrodes were collected as part of the multicenter clinical trial of the Nucleus Freedom cochlear implant system. T-NRT values determined by the algorithm were compared with T-NRT determinations on the same data by different human observers. Also, the time the measurements took was analyzed. RESULTS: In 90% of the cases, the absolute difference between the AutoNRT and the human observer determined T-NRT was less than 9 CL; the median absolute difference was 3 CL. A second experiment, in which a group of human observers were asked to analyze NRT data, showed high variability in T-NRT; in some cases, two experienced clinicians disagreed by more than 30 current levels. Compared with the group, AutoNRT performed as well as the "average" clinician, with the advantage that the AutoNRT threshold determinations are objective. Analysis of the timing data showed an average intraoperative measurement time of less than 20 sec per electrode with a standard deviation of 5 sec, suggesting that the total array of 22 electrodes can be measured intraoperatively in about 7 minutes on average. CONCLUSIONS: AutoNRT provides comparable accuracy to an average clinician but with the added benefit of significant time savings over manual recordings. This makes it a valuable tool for clinical measurement of ECAP threshold in cochlear implant recipients.

Preservation of residual hearing with cochlear implantation: how and why.

CONCLUSIONS: Hearing may be conserved in adults after implantation with the Nucleus Contour Advance perimodiolar electrode array. The degree of hearing preservation and the maximum insertion depth of the electrode array can vary considerably despite a defined surgical protocol. Residual hearing combined with electrical stimulation in the same ear can provide additional benefits even for conventional candidates for cochlear implantation. OBJECTIVES: We present preliminary results from a prospective multicentre study investigating the conservation of residual hearing after implantation with a standard-length Nucleus Contour Advance perimodiolar electrode array and the benefits of combined electrical and acoustic stimulation. MATERIAL AND METHODS: The subjects were 12 adult candidates for cochlear implantation recruited according to national selection criteria. A "soft" surgery protocol was defined, as follows: 1-1.2-mm cochleostomy hole anterior and inferior to the round window; Nucleus Contour Advance electrode array inserted using the "Advance-off-stylet" technique; and insertion depth controlled by means of three square marker ribs left outside the cochleostomy hole. These procedures had been shown to reduce insertion forces in temporal bone preparations. Variations in surgical techniques were monitored using a questionnaire. Pure-tone thresholds were measured pre- and postoperatively. Patients who still retained thresholds <90 dB HL for frequencies up to 500 Hz were re-fitted with an in-the-ear (ITE) hearing aid. Word recognition was tested in quiet and sentence perception in noise for the cochlear implant alone and in combination with an ipsilateral hearing aid. RESULTS: Hearing threshold level data were available for 12 patients recruited from 6 of the centres. Median increases in hearing threshold levels were 23, 27 and 33 dB for the frequencies 125, 250 and 500 Hz, respectively. These median increases include the data for two patients who had total loss of residual hearing due to difficulties encountered during surgery. "Cochlear view" X-ray images indicated that the depth of insertion varied between 300 and 430 degrees, despite modest variations in the length of the electrode inserted (17-19 mm). The insertion angle had some influence on the preservation of residual hearing at frequencies of 250-500 Hz. Six of the 12 patients retained sufficient hearing for effective use of an ipsilateral ITE hearing aid (< or = 80 dB HL at 125 and 250 Hz; < or = 90 dB HL at 500 Hz). Word recognition scores in quiet were improved from 10% to 30% with the cochlear implant plus ipsilateral hearing aid in 3 patients who had at least 3 months postoperative experience. Signal:noise ratio thresholds for sentence recognition were improved by up to 3 dB. Patients reported that they experienced greatly improved sound quality and preferred to use the two devices together.

Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6-month postoperative results.

OBJECTIVE: To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. DESIGN: : Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45 degrees N45 degrees and at S-45 degrees N+45 degrees . Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. SETTING: Tertiary referral centers with a cochlear implant program. PATIENTS: Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. RESULTS: For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between -10 dB and -11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source. In addition, as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences, a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal, which is referred to as a binaural squelch effect. On average, for the group, this resulted in a statistically significant improvement in speech comprehension scores of 8% in the bilateral listening condition compared with the scores for the better ear alone. Through assessment of comprehension of coincidental speech in noise and speech in quiet, a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores. Binaural stimulation also led to a significant improvement in localization ability over either monaural condition, with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation. CONCLUSION: Similar to what has been observed for bilateral acoustic stimulation in the past, bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect, providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects, all of which combine to lead to improved speech comprehension over unilateral listening conditions. The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet.

Evaluation of the neural response telemetry (NRT) capabilities of the nucleus research platform 8: initial results from the NRT trial.

The purpose of this study was to evaluate the performance of the new features of the Nucleus Research Platform 8 (RP8), a system developed specifically for research purposes The RP8 consists of a research implant, a speech processor and a new NRT software (NRT v4), and includes comparisons of the different artefact-cancellation methods, NRT threshold, and recovery function measurements. The system has new artefact-suppression techniques and new diagnostic capabilities; their performance has been verified in animal experiments. In this study, NRT data were collected from 15 postlingually deafened adult cochlear implant patients intraoperatively and up to 6 months postoperatively after switch-on. The initial investigation in two clinics in Europe focused primarily on the enhanced NRT capabilities Results from the trial in two European clinics indicate that NRT measurements can be obtained with lower noise levels. A comparison of the different artefact-cancellation techniques showed that the forward-masking paradigm implemented in the Nucleus 3 system is still the method of choice. The focus of this report is on recovery function characteristics, which may give insight into auditory nerve fiber properties with regard to higher stimulation rates.

Clinical relevance of the distance between the cochlea and the facial nerve in cochlear implantation.

HYPOTHESIS: To elucidate possible mechanisms of facial nerve costimulation after cochlear implantation that are supposed to result from the close cochlea to facial nerve contact. BACKGROUND: One of the postoperative complications of cochlear implantation is facial muscle twitching, which has preferentially been found in otosclerotic patients. It impairs hearing benefits because of deactivation of electrodes and can still not be adequately prevented. METHODS: A total of 13 temporal bones were dissected to quantify where the labyrinthine portion of the facial nerve is closest to the scala tympani, the placement site of the cochlear implantation electrode array. After the typical operative procedures to find out the number of electrodes lying closest to the facial nerve were performed, a cochlear implantation array was inserted into four specimens. The clinical records of 14 otosclerotic patients were investigated to correlate these results with the position of in vivo deactivated electrodes. RESULTS: The closest distance between the scala tympani and the nerve was only 0.33 mm (+/-0.14). On average, after insertion of 23 electrode resp. marking rings, the facial nerve was reached. This is clinically the position of most frequently deactivated electrodes to prevent postoperative facial nerve costimulation. CONCLUSIONS: These investigations support the hypothesis that a direct current spread at the site of the facial nerve crossing the cochlear basal turn is most likely the reason for postoperative facial muscle twitching facilitated in otospongiotic bone. Prevention could therefore be achieved by cochlear implantation designs and surgical techniques that take into consideration the site of closest contact.

Functional MR imaging of the auditory cortex with electrical stimulation of the promontory in 35 deaf patients before cochlea implantation.

BACKGROUND AND PURPOSE: Promontory testing is used for preoperative assessment of the auditory pathway before cochlear implantation. This method depends on patient cooperation and cannot be used in children or disabled persons. Promontory stimulation during functional MR imaging (fMRI) provides a new and objective method to test the integrity of the auditory pathway. To evaluate the method, we performed this prospective study in deaf adult patients. METHODS: fMRI of the auditory pathway with electrical stimulation of the promontory was performed in 35 profoundly deaf patients, bilaterally in seven. For safe stimulation inside the MR environment, a specially designed nerve stimulator was used. We acquired nine sections parallel to the sylvian fissure by using an echo-planar pulse sequence (1.5 T). To evaluate the number of pixels in the auditory cortex, areas were counted and the minimum confidence level (p(st) value) was determined. The auditory pathway was called intact when the minimal p(st) value was 10(-5) or when the minimal p(st) value was 10(-4) in at least five activated pixels. RESULTS: Images in 85% of patients reporting an auditory sensation showed activation of the contralateral auditory cortex. In the group of patients reporting no hearing sensation, images in 75% did not show activation. CONCLUSION: This method can prove the intactness of the auditory pathway and help the surgeon in decision making before cochlear implantation. However, a negative finding should not be interpreted as indicating a nonfunctioning auditory pathway. Additional technical refinements and experience are needed to further improve this method.

Intraoperative electrically elicited stapedius reflex threshold is related to the dosage of hypnotic drugs in general anesthesia.

Today cochlear implantation is a widely used means of treatment in deafness and severe hearing disorders in adults, children, and infants. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. However, especially in infants and young children, this fitting process can be difficult because of limited communication capabilities. The use of intraoperatively obtained stapedius reflex thresholds has been proposed for postoperative speech processor fitting, but the influence of anesthetics on threshold values needs to be taken into account. In a retrospective study with 20 patients between 3 and 43 years of age, a highly significant correlation between the dosage of methohexital and the mean stapedius reflex threshold value could be shown (r = 0.65, p = .002). We conclude that more reliable threshold values can be obtained by reducing the dosage of hypnotics to achieve a lighter level of hypnosis during stapedius reflex measurement. To achieve a light, but still sufficient level of hypnosis, electroencephalographic monitoring including automatic interpretation of the complex raw signal should be used.

Virtual endoscopy of the middle ear: experimental and clinical results of a standardised approach using multi-slice helical computed tomography.

Virtual endoscopy (VE) enables non-invasive 3D endoluminal imaging of the middle ear by post-processing of CT data. To optimise the clinical application a standardised approach was evaluated in normal and pathologic cases. Data acquisition was performed using multi-slice helical CT in 20 normal patients and 15 patients with malformation or trauma. Virtual endoscopy of the tympanic cavity and 3D images of the ossicles were generated using surface and volume rendering. Qualitative assessment of the representation of anatomical structures was performed in normal patients. In 15 pathological cases the diagnostic benefit was evaluated by comparing the 3D images to the 2D images and intra-operative findings. In all 35 cases 3D imaging was possible using the standardised approach. The ossicular chain as well as the bony and soft tissue structures of the tympanic cavity were visualised in 20 normal patients. In 7 of 8 patients with malformation and 1 of 7 patients with trauma the original diagnosis was changed by 3D imaging. Standardisation and evaluation of the method in normal patients is essential as it enhances the diagnostic reliability. Virtual endoscopy facilitates understanding of the complex anatomy of the middle ear. In cases of suspected malformation and confirmed trauma it is helpful for diagnosis and surgical planning.