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PubMedDate not supplied

Channel interaction in cochlear implant users evaluated using the electrically evoked compound action potential.

One likely determinant of performance with a cochlear implant is the degree of interaction that occurs when overlapping subsets of nerve fibers are stimulated by various electrodes of a multielectrode array. The electrically evoked compound action potential (ECAP) can be used to assess physiological channel interaction. This paper describes results from two different methods of analysis of ECAP channel interaction measures made by the Nucleus neural response telemetry system. Using a forward-masking stimulus paradigm, masker and probe pulses are delivered through different electrodes. The response to the probe is then dependent on the extent of overlap in the stimulated neural populations. The amplitude of response to the probe as a function of masker electrode position then reflects the degree of overlap between the population of neurons responding to the masker and those stimulated by the probe. Results demonstrate large variations across individual implant users as well as across electrodes within an individual. In general, the degree of interaction is shown to be dependent on stimulus level.

Action Potentials↗
PubMed2005

Superior semicircular canal dehiscence: a series of 13 cases.

Increasingly more detailed imaging techniques have recently highlighted the frequent occurrence of bony labyrinthine dehiscence. Among them, superior canal dehiscence (SCD) has been described in a number of cases presenting different features. Here, we report a series of 13 cases, in which the detection of vestibular evoked myogenic potentials (VEMPs) in response to stimuli of abnormally low intensity as compared to normal responses led us to suspect the presence of a 'third window effect'. An accurate HRCT investigation allowed the diagnosis of SCD. Anamnestic and symptomatologic differences seem difficult to explain, although in our opinion a dural rupture could be at the basis of the onset of pathologic manifestations after many years of silence of a probably malformative condition.

Acoustic Stimulation↗
PubMedDate not supplied

Sudden deafness: a retrospective evaluation of dextran therapy.

A retrospective evaluation was performed in 112 patients treated during a 10-year period as inpatients with the diagnosis idiopathic sudden hearing loss. Excluding all patients in whom later other diagnosis were established, like Ménière's disease, collagenoses, mumps etc., 101 patients remained. 80 of them had been treated consistently according to a protocol as having idiopathic sudden hearing loss. These patients had all 5-day treatment with low molecular weight dextran and nicotinic acid and vitamin B during 1 month. 68% did completely recover or were markedly improved (> 30 dB), another 19% were fairly improved (10-30 dB). Statistical analysis showed that all retrocochlear signs or nystagmus made the prognosis less favorable. To wake up with the hearing loss was more favorable than a daytime debut. A mid-frequency loss had always a good prognosis. Because no untreated controls were included in the study, it was not possible to evaluate the specific effect of the treatment. The results obtained from this study have changed the treatment policy in our clinic.

Adult↗
PubMedDate not supplied

Degeneration patterns in human ears exposed to noise.

Various forms of sensorineural degeneration patterns related to noise exposure are illustrated in six pairs of temporal bones selected from a group of 33 male patients with histories of noise exposure. For the entire group the commonest form of lesion, associated with a 4-kHz dip in the audiogram, was a relatively diffuse degeneration in the second quadrant of the basal turn, in the 9-13 mm area. An advanced form of this lesion had a wide gap of more or less complete sensorineural degeneration affecting the entire second quadrant and displaying various degrees of extension toward the apex and base. The pattern associated with an "abrupt high-tone loss," with more or less complete hair cell and nerve degeneration in both the second and first quadrants and extending to the basal end of the cochlea, was rare. In one case this pattern appeared to have evolved from the first type of lesion as the remaining nerve fibers in the first quadrant had degenerated. The protective effect of the acoustic shadow of the head for the right ear, in shooting from the right shoulder, is demonstrated for the higher frequencies. Two almost identical cases of sharply-circumscribed single areas of degeneration in the first quadrant and one case with two such areas represent the third type of lesion. In one of these cases there was a history of firearm usage. It is postulated that this type of lesion is caused by impulse noise. In most of the material the degeneration pattern differed markedly from the diffuse degeneration seen with presbycusis. Degeneration patterns with knife-sharp transitions between completely degenerated and apparently undamaged areas appear to be characteristic of noise-induced injuries.

Adult↗
PubMedDate not supplied

Effect of conductive hearing loss and middle ear surgery on binaural hearing.

This study investigated whether conductive hearing loss reduces normal binaural hearing advantages and whether binaural hearing advantages are normal in patients who have had hearing thresholds improved by middle ear surgery. Binaural hearing was assessed at a test frequency of 500 Hz using the masking level difference and interaural time discrimination thresholds. Results indicated that binaural hearing is often poor in conductive lesion patients and that the reduction in binaural hearing is not always consistent with a simple attenuation of the acoustic signal. Poor binaural hearing sometimes occurs even when middle ear surgery has resulted in bilaterally normal hearing thresholds. Our preliminary results are consistent with the interpretation that auditory deprivation due to conductive hearing loss may result in poor binaural auditory processing.

Adolescent↗
PubMedDate not supplied

Auditory brain stem responses in rhesus monkey with otitis media with effusion.

Auditory brain stem response (ABR) tests were conducted on 17 anesthetized juvenile rhesus monkeys. Recordings were obtained for 13 control ears without otitis media with effusion (OME) and seven experimental ears with OME. The results demonstrated an increase in response latencies for the experimental ears with OME at each of four stimulus presentation levels (80, 60, 40, and 20 dB hearing level). Interwave latencies were the same for both groups of ears. The results suggest an average 25-dB peripheral loss of predominantly middle ear origin associated with OME. The ABR appeared to be a viable technique for documenting auditory impairment associated with OME in this nonhuman primate model.

Acoustic Stimulation↗
PubMed2006

The neural representation of consonant-vowel transitions in adults who wear hearing AIDS.

Hearing aids help compensate for disorders of the ear by amplifying sound; however, their effectiveness also depends on the central auditory system's ability to represent and integrate spectral and temporal information delivered by the hearing aid. The authors report that the neural detection of time-varying acoustic cues contained in speech can be recorded in adult hearing aid users using the acoustic change complex (ACC). Seven adults (50-76 years) with mild to severe sensorineural hearing participated in the study. When presented with 2 identifiable consonant-vowel (CV) syllables ("shee" and "see"), the neural detection of CV transitions (as indicated by the presence of a P1-N1-P2 response) was different for each speech sound. More specifically, the latency of the evoked neural response coincided in time with the onset of the vowel, similar to the latency patterns the authors previously reported in normal-hearing listeners.

Aged↗
PubMed1984

The current status of auditory brainstem response testing in neonatal populations.

The use of auditory brainstem response (ABR) for assessment of hearing in the neonate has not been without challenge. Although numerous articles have appeared, agreement regarding the utility of neonatal ABR testing does not exist. In review of the current studies and commentaries, a clear majority are favorable to neonatal ABR testing. These studies along with current test procedures are discussed.

Audiometry↗
PubMed1994

Frequency selectivity in patients with acoustic neuroma.

Frequency selectivity was compared in subjects with hearing loss due to acoustic neuroma and cochlear pathology, and normal listeners. A particular interest was the role of probe tone parameters on the shape of the tuning curve. Psychophysical tuning curves (PTCs) were measured for each of two equal energy 2000-Hz probe tones (10 dB SL/300 msec and 17 dB SL/60 msec), using simultaneous 1/3-octave narrow-band noise maskers centered at 1, 1.25, 1.6, 2.5, 3.15, and 4 kHz. The results showed that the critical masker levels obtained for impaired listeners were significantly greater than those from normal subjects. The slope of the low-frequency limb of the PTC was steeper for normal compared to hearing-impaired listeners but there was no difference due to site of lesion. In all three groups, the critical masker levels obtained with the short probe were significantly greater than those for the long probe, negating the hypothesis that equal energy probes would yield the same outcomes. Tuning in listeners with hearing loss was highly correlated with audiometric threshold but not with tumor size, width of the internal auditory canal, or tumor location within the cerebellopontine angle. The main conclusion was that cochlear and retrocochlear hearing loss are similar with respect to their effect on frequency selectivity.

Acoustic Stimulation↗
PubMed1995

Lateralization and discrimination of dichotic clicks: evidence from patients with brainstem lesions and normal cohorts.

The ability to lateralize and discriminate dichotic clicks was tested in multiple sclerosis patients with normal audiograms and in normal cohorts. Lateral position spread over a greater range with interaural level differences than with interaural time differences, and was related to the two asymmetries by different functions. Measures of binaural acuity were inversely related to the slopes of the two functions. One group of patients performed normally with both types of interaural asymmetry, another group performed normally only with level differences; a third group of patients could not perform normally with either.

Adult↗
PubMed2004

Use of auditory brainstem responses for the early detection of ototoxicity from aminoglycosides or chemotherapeutic drugs.

Effective objective HF (high-frequency) testing methodology provides for the early detection of ototoxic hearing loss because it typically progresses from high to low frequencies. Such early detection is considered necessary to prevent hearing loss from progressing into the frequency range important for understanding speech. Objective tests must be reliable, sensitive to hearing change, and time efficient. Auditory brainstem responses (ABRs) appear well suited to this task; however, current ABR techniques have limitations. Conventional clicks stimulate middle (1-4 kHz) rather than high frequencies (>8 kHz). Responses to HF tone bursts require considerable recording time. We hypothesized that using HF band-limited clicks (HF clicks) could overcome these limitations. Two different HF clicks, with bandwidths of 8-14 kHz were used to elicit ABRs. The current study compared responses among these stimuli. The results demonstrate the reliability of HF-click responses and of tone bursts presented in trains.

Adult↗
PubMedDate not supplied

Electrophysiological monitoring of the cochlea during and after total destruction of the organ of corti.

A series of acoustically evoked potentials can be recorded from the cochlea up to the auditory cortex in guinea pigs where the organ of Corti has been totally destroyed after extensive treatment with amikacin, but where some of the spiral ganglion neurons always remain and where the vestibular receptors are only slightly affected. The cochlear responses have been monitored in guinea pigs permanently implanted with a round window electrode and receiving such treatment. The normal auditory nerve compound action potential disappears within a few days, while the very typical response (diphasic, short latency (0.3 ms) small amplitude) appears. This response then remains remarkably constant in time as far as we could observe (up to almost one year). This response might be a component of the normal response, undiscernible under normal conditions but revealed by the selective impairment of the labyrinth by amikacin, in contrast to the global effect of every other known otodestructive agent. Some basic questions still remain: which fibres are effectively stimulated (cochlear or vestibular), what are their central projections, and what kind of sensation is conceivably associated with these responses?

Amikacin↗
PubMed1997

Blood flow-independent accumulation of cisplatin in the guinea pig cochlea.

Considerable interindividual variability in the ototoxic effect of cisplatin has become the unpredictable dose-limiting factor in its use as curative as well as palliative therapy. The drug accumulates in highly vascular areas in the cochlea, causing dose-related hair cell loss. The purpose of this study was to assess blood flow-dependent aspects of cisplatin absorption in the cochlea in order to better understand factors that may influence cisplatin-induced ototoxicity. The effect of reduced cochlear blood flow on the ototoxic action of cisplatin was studied in guinea pigs. Before cisplatin administration the cochlear vasculature in each animal was unilaterally pre-constricted, by the application of 2% epinephrine to the round window. A 20-30% reduction in cochlear blood flow, assessed by laser Doppler flowmetry, was maintained before and after intravenous infusion of 0.1% cisplatin. Cisplatin infusion affected cochlear blood flow but not vessel conductivity. The cochlear blood flow decrease, maintained by local epinephrine application to the round window during cisplatin infusion, did not alter the cisplatin-induced hearing loss. In addition, the concentration of free cisplatin in scala tympani perilymph did not differ between epinephrine-treated and non-treated ears. Our results indicate that cisplatin transport into the cochlea is not an energy-dependent process in the lateral wall vasculature.

Animals↗
PubMed1989

Electrically evoked responses in Cochlear implant patients.

Highly reproducible recordings of evoked responses elicited by electrical stimulation of the auditory nerve were obtained in a group of 4 totally deaf patients implanted with a multichannel intracochlear prosthesis. They were compared to auditory evoked responses obtained in a normal-hearing subject tested with the same equipment. The most striking observation drawn from these data is certainly the close resemblance, at all latencies, between evoked responses elicited by electrical stimulation and those elicited by acoustic stimulation. The remarkable correspondence of waveform morphology, waveform amplitude and interpeak latencies provides indirect evidence that the same sequence of events is triggered in the central auditory system in both cases. Those aspects of the responses which differ significantly are easily interpreted by the physical and physiological properties of the different types of stimulation.

Auditory Perception↗
PubMed1990

Filter effects and low stimulation rate on the middle-latency response in newborns.

Auditory middle-latency responses (MLR) have been recorded in 25 newborns at 60 dB nHL using two wide band-pass filter conditions and a slow stimulation rate of 2/s. With both types of filter, the MLR consisted in an initial positive wave followed by a negative component (Na) and a positive component (Pa). In newborns, this positive component appears in the vicinity of 45 ms and is more prolonged than the Pa of the MLR in adults. The probability of obtaining MLR after averaging only 500 signals was higher with a high-pass filter setting of 10 Hz (12 dB/octave), as compared with 5 Hz (12 dB/octave). No significant differences were found in the detectability rate of MLR between the two-filter band-pass settings. It is important to note that some MLR were unstable and not easily replicable. Therefore, the clinical application of these components is still doubtful.

Auditory Pathways↗