Auditieve hersenstampotentialen bij de mens : een studie van enkele fundamentele eigenschappen en hun klinische toepassing

The aim of the author's research described in this thesis was to obtain abetter understanding of a number of the fundamental characteristics of brainstem potentials and to establish normal values. This aim is described in chapter I, following a discussion of the possibilities and limitations of objective and subjective audiometry, an outline of the development of electroaudiometry and a description of the regions of origin of brain stem potentials and their nomenclature. The experimental set-up is discussed in chapter II, where the signal-tonoise ratio receives special attention. The description of the clinical application of brain stem audiometry in chapter VIII is based on both the literature and personal research. Chapter IX gives some practical suggestions for the application of brainstem audiometry. The author's own research, which is described in chapter III-VII, deals with the following subjects: 1. The aceurenee of and normal values for brain stem potentials. The occurrence of brain stem potentials and their normal values were investigated in 20 healthy subjects, 19 men and 1 woman, with normal hearing and ages varying from 20-53 years. The stimulus used had a wide frequency spectrum, with an intensity of 70 dB HL and a repetition rate of 10 Hz. The responses were filtered with a high-pass filter, cut-off frequency 300 Hz, 24 dB/oct., and a !ow-pass filter, cut-offfrequency 3000Hz, 24 dB/oct. After averaging 16,000 responses to binaural stimulation it was possible to identify the peaks P2 to P5 inclusive, for 75, 70, 85 and 100°/o of the test subjects respectively, while after averaging 4,000 responses to manaural stimulation the proportions were 65, 63, 78 and 98% respectively. The amplitudes of the responses were highly variable. The latendes were constant within narrow limits (table 3.1). The average latency for peak P5 was 7.0 ms with a standard deviation of0.35 ms. The interaurallatency difference averaged 0.02 ms and had a standard deviation of0.27 ms. 2. The distribution of brainstem potentials over the scalp. The distribution of brainstem potentials over the scalp was investigated to establish whether there are any electrode positions where the response originates primarily from the left or the right half of the brain stem. In order to do this the responses were recorded at 5 points on the nasion-vertex-inion line and the vertex-mastoid process line. The responses on the latter were obtained after ipsi- and contralateral stimulation with respect to the active electrode

Semilongitudinal and axial CT planes in assessing cochlear patency in cochlear implant candidates.

Item does not contain fulltextOBJECTIVE: To investigate how cochlear patency as seen on computed tomography (CT), using axial plus semilongitudinal planes, is correlated with findings at surgery in cochlear implant patients. METHODS: Pre-operative CT scans of 45 patients were reviewed by three, independent observers. They classified the cochlear patency and recorded the location of any suspected decreased patency. The results were compared with the findings noted during surgery. RESULTS: In nine patients a decreased cochlear patency was found at surgery. The sensitivity and specificity of CT assessment were, respectively, 56-33-11% and 100-86-94%. The interobserver reproducibility is reflected in a mean kappa of 0.46. The sensitivity increased when only patients suffering from post-meningitic deafness were considered. CONCLUSION: Our study suggests that CT scans can be useful in assessing cochlear patency, especially in patients with post-meningitic deafness. This good performance might be explained by the combined use of scans in semilongitudinal and axial planes

Cochlear implantation in 53 patients with otosclerosis: demographics, computed tomographic scanning, surgery, and complications.

OBJECTIVES: To collect data from a large number of cochlear implant recipients with otosclerosis and to make an assessment of these patients' clinical characteristics, computed tomographic scans, surgical findings, and complications, and to quantify the occurrence of postoperative facial nerve stimulation. STUDY DESIGN: Retrospective multicenter study. PATIENTS: Fifty-three patients with otosclerosis from four cochlear implant centers in the United Kingdom and The Netherlands were reviewed. Sixty surgical procedures were performed in these patients: 57 devices were placed in 56 ears. RESULTS: The computed tomographic imaging demonstrated retrofenestral (cochlear) otosclerotic lesions in the majority of patients. Although not statistically significant, the extent of otosclerotic lesions on the computed tomographic scan as categorized in three types tends to be greater in patients with rapidly progressive hearing loss, in patients in whom there is surgically problematic insertion of the electrode array, and in patients with facial nerve stimulation. In four patients, revision surgery had to be performed. Twenty of 53 (38%) patients experienced facial nerve stimulation at various periods postoperatively. CONCLUSION: Cochlear implant surgery in patients with otosclerosis can be challenging, with a relatively high number of partial insertions and misplacements of the electrode array demanding revision surgery. A very high proportion of patients experienced facial nerve stimulation mainly caused by the distal electrodes. This must be discussed with patients preoperatively

Speech perception after cochlear implantation in 53 patients with otosclerosis: multicentre results.

Item does not contain fulltextOBJECTIVES: To analyse the speech perception performance of 53 cochlear implant recipients with otosclerosis and to evaluate which factors influenced patient performance in this group. The factors included disease-related data such as demographics, pre-operative audiological characteristics, the results of CT scanning and device-related factors. METHODS: Data were reviewed on 53 patients with otosclerosis from 4 cochlear implant centres in the United Kingdom and the Netherlands. Comparison of demographics, pre-operative CT scans and audiological data revealed that the patients from the 4 different centres could be considered as one group. Speech perception scores had been obtained with the English AB monosyllable tests and Dutch NVA monosyllable tests. Based on the speech perception scores, the patients were classified as poor or good performers. The characteristics of these subgroups were compared. RESULTS: There was wide variability in the speech perception results. Similar patterns were seen in the phoneme scores and BKB sentence scores between the poor and good performers. The two groups did not differ in age at onset of hearing loss, duration of hearing loss, progression, age at onset of deafness, or duration of deafness. CONCLUSIONS: The clinical presentation of the otosclerosis (rapid or slow progression) did not influence speech perception. Better performance was related to less severe signs of otosclerosis on CT scan, full insertion of the electrode array, little or no facial nerve stimulation and little or no need to switch off electrodes

Predictive factors for success with a cochlear implant

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Predictive factors for success with a cochlear implant

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