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R Schoonhoven

Publications and source records attributed to R Schoonhoven.

51 records · Page 3Linked to original sources
PubMed1992

Round-window recorded potential of single-fibre discharge (unit response) in normal and noise-damaged cochleas.

Unit responses (URs) of eighth-nerve fibres have been determined at the round window by spike-triggered averaging in both normal and pathological guinea pig cochleas. The pathology was mainly noise-induced damage. The URs have been analysed with respect to their dependence on the fibre's threshold, characteristic frequency (CF) and spontaneous rate (SR). The results from normal cochleas confirmed earlier data (Prijs, 1986): the UR has a diphasic waveform and the amplitude of its negative first peak is about 0.1 microV. From the six parameters (amplitude, latency, and width of the two peaks) by which the UR was described only the amplitude of the positive peak showed a significant variation with CF: a small decrease with increasing CF (CF-range 0.1 to 20 kHz). This finding may possibly be caused by oscillations in the spike-triggered average for low CFs. URs for most low- and medium-SR fibres were found to be large (greater than 0.3 microV). However, this result is interpreted as an artefact caused by synchrony of fibre spontaneous activity. In damaged cochleas only slight changes of the UR were found: the waveform duration became significantly shorter and on some occasions the positive peak increased in amplitude, but latency and amplitude of the negative component of the UR remained unchanged.

Acoustic Stimulation↗
PubMed1992

Dependence of auditory brainstem response on click polarity and high-frequency sensorineural hearing loss.

An investigation is presented on the effect of click polarity upon the auditory brainstem response (ABR) in cases of simulated high-frequency hearing loss. A high-frequency hearing loss was stimulated in 12 normal subjects by applying a high-pass noise masker, the noise cutoff frequency being varied in half-octave steps through the range of audiometric frequencies. With this paradigm, the effects of click polarity on the ABR are similar to those reported in patients with high-frequency hearing loss, including changes in waveform morphology and substantial peak latency shifts. To evaluate the role of individual cochlear frequency channels in a more direct way, half-octave narrow-band responses were determined by pair-wise subtraction of the high-pass-noise-masked responses. As far as ABR peak latencies are concerned, stimulus polarity effects tend to increase towards the lower frequency bands. Thus, the selective elimination of the contribution to the ABR of cochlear high-frequency channels can be held responsible for the increased dependence of ABR on click polarity observed in high-frequency hearing loss. However, statistical evaluation of peak I, III and V latencies, both in high-pass-noise-masked and in narrow-band ABRs, reveals that the latency effects are not systematic between subjects. Mechanisms producing the observed rarefaction-condensation differences, possible explanations for the large intersubject variability and the consequences for clinical interpretation of ABR are discussed.

Acoustic Stimulation↗
PubMed1991

Models and analysis of compound nerve action potentials.

Upon electrical stimulation of a peripheral nerve, a compound action potential (CAP) can be recorded, a procedure that is widely used to study the functional condition of a nerve. The CAP provides relevant information about such parameters as the number of active myelinated fibers and their propagation velocities. This paper reviews methods of model-based CAP analysis that have emerged during the last decade. First, the basic model formulation for the CAP as resulting from a linear summation of the underlying single fiber action potentials (SFAPs) is discussed. Subsequently, a survey is given of volume conductor model approaches for the prediction of the SFAPs. Attention is then concentrated on the "inverse" problem of extracting relevant nerve parameters from experimentally recorded CAPs. Finally, the applicability of such methods is discussed and a direction for future developments is outlined.

Action Potentials↗
PubMed1990

A longitudinal electrocochleographic study of a case of long-standing bilateral Lermoyez's syndrome.

An 18-year follow-up of a case of bilateral Lermoyez's syndrome is presented. The left ear having reached a stabilized hearing loss about 9 years after the onset of the disease, the right ear, apart from some isolated early periods of hearing loss, started to show the full extent of clinical symptoms after about 16 years. Electrocochleographic observations are presented. Studies were performed twice in the right ear during a period of strongly fluctuating hearing thresholds, once in an impaired and once in a relatively good condition. Electrocochleography of the stabilized left ear was performed as well. The data are compared with electrocochleographical observations in the left ear in its early fluctuating stage. Variation of cochlear physiological data during the fluctuating stage of the disease shows remarkable correspondence between the two ears. The stabilized Lermoyez ear is shown to have developed considerable hair cell loss, but may still have preserved its endolymphatic hydrops. These findings in Lermoyez's syndrome fit well into the observations reported in patients with Menière's disease.

Audiometry, Evoked Response↗
PubMed1990

Latencies of eighth nerve fibre responses with respect to their relative contribution to the compound action potential in the guinea pig.

We present a study of the latencies of click-evoked post-stimulus time histograms (PSTHs) in the guinea pig in the context of the auditory nerve fibre's contribution to the compound action potential (CAP) recorded at the round window. The latencies of the dominant PSTH peak were studied as a function of relevant physiological fibre properties, in particular the characteristic frequency (CF) and the spontaneous discharge rate (SR). We found that high-SR fibres have shorter latencies than low-SR fibres. These findings are discussed in the context of correlation between synaptic morphology and SR as described in the literature. The PSTH latency as a function of CF is described separately for low- and high-CF fibres for each of the two SR subgroups. Finally, we discuss to what extent the various subgroups of fibres contribute to the N1 peak of the CAP, the most commonly studied component.

Action Potentials↗
PubMed1990

Single-fibre responses to clicks in relationship to the compound action potential in the guinea pig.

Poststimulus time histograms (PSTHs) to clicks of standard level were measured in eighth-nerve fibres of normal-hearing guinea pigs. In the context of studying the fibres' contribution to the compound action potential (CAP), the PSTHs are described with the parameters latency (tp), amplitude (Ap) and synchronization (Sp) of the dominant PSTH peak. These parameters are considered in relation to characteristic frequency (CF) and spontaneous rate (SR). An adequate description for tp is one in which tp is constant for non-phase-locking fibres (CF above 3 kHz) and it is an exponential function of CF for phase-following fibres. The low-SR fibres (SR below 5 spikes/s) had smaller amplitudes and longer latencies than the other ones. The variations of Ap with CF can be explained by the varying synchronization of the response.

Acoustic Stimulation↗
PubMed1984

On the optimal choice of a recording electrode in electroneurography.

The influence of the type and size of recording electrodes on compound nerve action potentials was studied in order to establish optimal prerequisites for the application of quantitative analysis methods. A realistic volume conductor model was used to assess the dependence of the recorded signal on the position of the recording electrode with respect to the nerve. The analysis of both compound action potentials (CAPs) and single fibre action potentials (SFAPs) leads to the conclusion that near-nerve recording gives substantially more information. This applies in particular to the fine details in the CAP, such as notches in the main complex and the so-called late components. Subsequently, the influence of needle electrode bare tip length on the recorded signal was investigated by spatially averaging the potentials over the lead-off area. These results were combined with experimentally obtained noise levels for different stainless steel needle electrodes in order to determine the signal-to-noise ratio as a function of bare tip length. It was concluded that for near-nerve recording a needle tip of 1-2 mm gives optimal results in terms of wave shape preservation and signal-to-noise ratio.

Action Potentials↗
PubMedDate not supplied

Sensory potentials and sural nerve biopsy: a model evaluation.

Compound action potentials (CAPs) were recorded from the sural nerve prior to nerve biopsy in patients with various kinds of polyneuropathy. A previously developed volume conductor model for the CAP is applied to analyze the recorded CAPs in close relation with the morphological findings in the biopsy. First, the fiber diameter histograms obtained from the biopsy are used to simulate CAPs, by assuming a linear relation between fiber diameter and propagation velocity. It is concluded that the simulated CAPs deviate systematically from the recorded CAPs. Next, the assumption of a linear diameter-velocity relation is left, and the assumed fiber velocity distribution is adapted to obtain optimal model reconstructions of the recorded CAPs. It is concluded that the model is capable of reconstructing the recorded CAPs, including slow components and small polyphasic potentials in the case of severe fiber loss. It is demonstrated how the diameter histogram and the optimal velocity distribution can be combined to an empirical estimate of the diameter-velocity relation.

Action Potentials↗
PubMedDate not supplied

Lermoyez's syndrome. A follow-up study in 12 patients.

Clinical studies were performed in 12 patients with the Lermoyez syndrome during a close follow-up of 2 to 31 years. The nature and temporal sequences of the symptoms of these patients are described. The incidence of Lermoyez's syndrome, as compared with Meniere's disease, is almost 18%. This is much higher than usually is assumed. In 6 out of 12 patients typical Meniere attacks were found besides their Lermoyez attacks. Almost every one of the 12 patients showed, besides the Lermoyez attacks, also hearing fluctuations without vertigo, and vertigo without hearing fluctuations. The type of vertigo was usually rotating, often with unsteadiness and in 3 patients dropping attacks were sometimes observed. The typical Lermoyez attack lasted several hours. The preceding hearing loss lasted for days to months. The hearing recovered after the attacks and remained stable for days to months. An improved hearing was noticed within some hours after the vertiginous attack in 9 out of 12 cases. Three patients noticed the hearing improvement already during the attack. In 8 out of 12 cases the disease became bilateral.

Deafness↗
PubMedDate not supplied

The prognostic value of electrocochleography in severely hearing-impaired infants.

This paper presents a longitudinal evaluation of electrocochleographic assessment in severely hearing-impaired infants. Electrophysiological data were obtained by transtympanic electrocochleography to tone-burst stimuli at octave frequencies of 500 to 8000 Hz at the age of 0-6 years in a group of 126 subjects. The results are compared with auditory thresholds determined at school age in the same children by means of pure-tone audiometry. Cochlear microphonics could be recorded in virtually all ears, although the majority of subjects had hearing losses of 90 dB and more. Compound action potentials (CAPs) showed waveforms varying from normal to a wide range of abnormalities. Audiometric thresholds correlated generally well with the compound action potential (CAP) thresholds obtained in infancy. The error in the predicted audiometric thresholds is between 15 and 20 dB, as compared with 11 dB reported for more moderate hearing losses. It is shown that, in spite of the high stimulus levels used, substantial frequency-specific threshold information is retained. Occasional large discrepancies in thresholds were often associated with markedly abnormal response waveforms. Among the many cases in which no ABR could be elicited, 68 per cent produced detectable electrocochleographic responses in the 1000-4000 Hz range. It is concluded that electrocochleography is a valuable method for the assessment of residual hearing in infants suspected of having a severe hearing impairment.

Audiometry, Evoked Response↗
PubMedDate not supplied

Long-term audiometric follow-up of click-evoked auditory brainstem response in hearing-impaired infants.

Conventional pure-tone thresholds were collected as determined at ages between 4 and 8 years from a group of 163 infants, tested by auditory brainstem response (ABR) in the age range between 1 and 3 years old for objective hearing assessment. The subjects suffered from a variety of degrees and types of sensorineural hearing impairment. The prognostic value of the ABR peak V thresholds in response to 0.1 ms clicks with respect to the behavioural thresholds at octave frequencies from 125 to 8,000 Hz obtained later is evaluated. Correlation between ABR and behavioural thresholds is largest in the 1,000- to 8,000-Hz frequency range. Predicted pure-tone audiograms (mean and SD) were determined for each 10-dB class of ABR thresholds. SDs are in the order of 15 to 18 dB in the 500- to 4,000-Hz range and slightly higher at adjacent frequencies (i.e., somewhat larger than in comparable adult studies). Mean pure-tone thresholds in the 1,000- to 8,000-Hz frequency range are up to 20 dB worse than ABR thresholds, which is opposite to findings in normally-hearing subjects. Thus, with an increasing degree of sensorineural hearing impairment, pure-tone thresholds increase at a significantly higher rate than ABR thresholds. The observation is explained in terms of reduced temporal integration in cochlear hearing loss. ABR thresholds worse than 80 dB nHL are demonstrated to have very limited predictive value with respect to the amount of residual hearing, not only in the low- but also in the high-frequency range. The presence of otitis media during ABR testing is shown to make estimation errors increase to more than 25 dB (SD).

Acoustic Stimulation↗