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At least 1,045 records · Page 58Linked to original sources
PubMed1994

[A new electrode (HN-5) for CM measurement in extra-tympanic electrocochleography].

A new electrode (HN-5) for CM measurement in extra-tympanic electrocochleography (ECochG) has been developed. The electrode consists of a silver wire 2.0 mm in diameter and 5 cm in length connected to a low noise cable. The electrode impedance values were low and the frequency characteristics were excellent. In order to explore various artifacts, the electrode was inserted into a glass cup containing 100 ml of tap water, which served as a dummy ear. A sound stimulus with an intensity of 90 dBnHL was delivered by a shielded loudspeaker located 50 cm from the dummy ear (glass cup). In this dummy test, contamination with measurable artifacts, such as electromagnetic inductions generated by a sound transducer and the CM-like mechanical vibrations which activated the dummy ear acoustically, was kept within the noise levels inherent in the recording system. The CMs were recorded from subjects with normal hearing by placing an electrode adjacent to the postero-inferior rim of the tympanic membrane (annulus tympanicus). Short tone bursts were employed as acousti stimuli and delivered by the shielded loudspeaker. CM detection thresholds were very low and CM-like responses with delayed onset time (delayed CM) were clearly observed at lower stimulus levels. The input-output curves of the CMs and delayed CMs were non-linear. These findings from the CMs did not differ from those obtained by the transtympanic needle electrode technique. Responses obtained had satisfactory S/N ratios and resulted in almost the same average calculations as those with transtympanic ECochG.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

[Effects of acoustic overstimulation of 2F1-F2 distortion product in cochlear microphonics].

The cochlear microphonics (CM) response to two-tone stimuli was measured before and after exposure to 4 kHz pure tone at 100 dB SPL or 125 dB SPL. The 2f1-f2 distortion products in the CM (CM-DPs) were markedly suppressed by the sound exposure at either intensity, although the loss of CM output at the primary frequencies was limited to 4 dB or less. The suppression of CM-DPs was greater as the intensity of primary tones decreased, especially at primary intensities below 55 dB. These results show that the active transduction process in the cochlea was affected by acoustic overstimulation. This impairment of active transduction was postulated to be an initial process in developing noise induced temporary and/or permanent threshold shift.

Acoustic Stimulation↗
PubMed1996

[Assessment of cochlear functions of patients with acoustic neuromas].

Electrocochleographic cochlear microphonics (ECochG-CM) and Evoked Otoacoustic Emissions (EOAE) were recorded for 17 patients with acoustic neuromas to assess their cochlear functions. ECochG-CM was recorded by a transtympanic needle electrode technique. The acoustic stimuli of EOAE were short tone bursts and thresholds of detection of the slow components were determined. In 13 of the 17 patients, elevated detection thresholds of ECochG-CM and/or abnormal interaural differences in detection thresholds of the slow components of EOAE were observed. The patients with hearing loss and an elevated thresholds of CM were believed to have cochlear impairments. Those with hearing loss and a relatively low detection threshold of CM were thought to have cochlear nerve damage and a smaller degree of cochlear impairment. The correlation of ECochG-CM and EAOE was 0.799. Both ECochG-CM and EOAE were useful in evaluating the cochlear functions of patients with acoustic neuromas. Although EOAE was easier to apply clinically, ECochG was indispensable when detailed examinations of cochlear functions were necessary.

Adult↗
PubMed1996

[Experimental research on delayed responses in cochlear microphonics records in guinea pigs].

Clinical application of evoked otoacoustic emissions (EOAEs) is expected to serve as an objective indicator of inner ear function. Delayed extra waves (delayed responses) from human cochlear microphonics (CMs) have been observed and they appear to be electrical correlates of EOAEs. Delayed responses must be examined for their relation to EOAEs in animal experiments before clinical application. The present experiment was performed to elucidate the relationship between delayed responses and the EOAEs in guinea pigs. Delayed responses to weak sound stimuli were recorded from the round window and from the scala media. The second waves, which corresponded to CMs, were compared with the fourth or fifth waves. The input-output curves of the fifth waves saturated earlier and crossed the curves of the second waves. Both the second wave and the fifth wave decreased in anoxia, but their time course of amplitude changes in anoxia were different. EOAEs peaked between 2.5 kHz and 3.5 kHz in the frequency distribution. The EOAEs also were anoxia-sensitive, corresponding to changes in the CMs and the delayed responses in the time course of anoxia. The results of the present experiment demonstrate that the delayed responses were electrical correlates of the EOAEs. EOAEs are believed to represent energy leaks to the external and middle ear from intracochlear micromechanics linked to retrograde transduction mechanism of the outer hair cells. This was supported by the relationship between the delayed responses from the CMs and the EOAEs. The EOAEs and delayed responses may serve as tools for application in clinical testing as acoustical and electrical indicators of intracochlear micromechanical function.

Animals↗
PubMed1997

[Effects of short-term tone exposure on DPOAEs].

Test parameter combinations are known to affect DPOAE measurement. The present study was attempted to find out if different test parameter combinations affect DPOAEs' utility in reflecting the change of cochlear function. Pure tones of moderate intensity (82 dB SPL) and short duration (3 min) were introduced into rabbit's ear canal to cause temporary change of cochlear mechanics, and the change of amplitude of 2f1-f2 DPOAE representing 10 kHz over 10 minutes after the exposure was monitored using equal- and different primary level combinations. It was found that, under the same exposure condition, 2f1-f2 DPOAEs induced by primaries of different levels (L2 = L1 - 12 dB) had showed more initial reduction in amplitude and slower recovery than that induced by primaries of equal levels (L1 = L2). The difference may indicate that there are multiple physiological processes that contribute to the generation of 2f1-f2 DPOAE and that change of DPOAE test parameters may selectively reveal different DPOAE generating processes.

Acoustic Stimulation↗
PubMed1997

[Effect of perilymphatic fistula on distortion product otoacoustic emissions in guinea pigs].

Perilymphatic fistula was induced in 11 healthy guinea pigs to study its effects on distortion product otoacoustic emissions (DPOAEs). DPOAE amplitudes decreased significantly right after formation of the fistula (P < 0.01), and recurred to near pretreatment level in animals whose fistula healed. The amplitude remained below pretreatment level 18 days after fistulization in those animals whose fistula failed to heal. Under light microscope, the organ of Corti was seen normal. The authors feel that DPOAEs may be helpful in detecting perilymphatic fistula.

Acoustic Stimulation↗
PubMed2001

[Response property of tone burst transmission of partially implantable middle ear implant in vivo].

OBJECTIVE: To investigate the characteristics of tone burst transmission of the middle ear implant(MEI). METHODS: Ten adult rabbits with normal hearing were used. A silver ball electrode was placed at the round window membrane to measure cochlear microphonics (CM) when sounds were presented before and after the implantation of the MEI. The tone burst was the acoustic stimulus. RESULTS: Frequency response functions without and with the MEI in rabbit model were calculated, and their amplitude-frequency curves ranging from 0.5 to 6 kHz resembled each other in shape with gain factors about 15 dB at the frequencies above 1 kHz. CONCLUSION: The results of this study indicated that the frequency response of the device fitted the speech transmission and it had high fidelity with little noise.

Animals↗
PubMed1992

[Speech perception and otoacoustic emissions by pre-processing sound in the inner ear].

Direct observations of the basilar membrane movements show that sound perception can no longer be regarded as a passive process: vulnerable, energy-consuming amplification processes are required in the cochlea. The outer hair cells (OHC) fulfil this demand morphologically and functionally. These sensory cells have a double role: they perceive sound and thus modulate the cochlear biomechanics through their motile activity. The key event of sound transduction is performed by the inner hair cells (IHC) after active sound amplification in the OHC. The control of the OHC is assured by the efferent olivocochlear fibres which release acetylcholine (ACh) and gamma-aminobutyric acid (GABA) into the synaptic cleft at the basal pole of the OHC. Nicotinergic acetylcholine and GABA receptors within the outer cell membrane of OHC were identified and characterised. The application of the neurotransmitter GABA to the basal pole of vital OHC leads to a reversible elongation of the cylindrical cell body while ACh induces a reversible, slow contraction of the sensory cells. These two neurotransmitters are supposed to counteract in the control of the cochlear amplifier. The reciprocal distribution of ACh and GABA receptors and their counteracting function (contraction vs elongation) has an additional impact on the modulation of OHC function. The result is an even more diversified control of the cochlear amplifier. The energy-consuming cochlear amplifications are reflected by an epiphenomenon, i.e. the otoacoustic emissions (OAE). These are emitted by the cochlea and can be divided into "spontaneous OAE", "transitory evoked OAE" (TEOAE), "stimulus frequency OAE" and "distortion product OAE". The TEOAE are now an integrated part of audiological diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Basilar Membrane↗
PubMed1992

[Improvement of clinical results by digitalization of a single channel cochlear implant].

For 1973 we have been among the first to claim the multichannel cochlear implant superiority regarding single channel efficacy. However we actually thing that single channel cochlear implant is indispensable in case of total ossified cochlea, and very useful when efficacy/coast ratio must be considered. In order to narrow the gap between multi and single channel device efficacy, we used the new microprocessors possibilities to digitalize the analogic emietter of the single channel system, which we designed in 1987. Owing to a PC keyboard the new emietter allows the speech therapist to select the frequency band width of the input signal, and to determine the threshold level and the dynamic value as a function of six steps values of the stimulus wave frequency. These improvements supply the patient with a better speech intelligibility excepted for vowels discrimination. Comparison of clinical results obtained through the two analogic and digital systems are reported on 4 post lingually and 4 pre lingually deaf patients.

Adolescent↗
PubMed2005

Sensitivity and specificity of portable transient otoacoustic emission (TEOAE) in newborn hearing screening.

Early identification and management of hearing impairment is very valuable. The goal standard measurement of hearing loss is by brainstem evoked response (BSER). This prospective study was conducted in Hospital University Kebangsaan Malaysia (HUKM) to determine the sensitivity and specificity of transient evoked otoacoustic emission (TEOAE) as a screening tool for hearing impairment from February 1999 to February 2000. One hundred and thirty-three newborns from postnatal ward and seventy-eight newborns from neonatal intensive care unit (NICU) were screened for possible hearing loss using portable TEOAE. This study showed that TEOAE is a very sensitive but moderately specific screening tool.

Cochlear Microphonic Potentials↗
PubMed2005

[Study of unilateral auditory neuropathy in infants].

OBJECTIVE: To study neurophysiological characteristics in infants with unilateral auditory neuropathy (UAN). METHOD: Audiological measurements (acoustic immittance, stapedial reflex, EOAE, ABR, CM, MLR and ERP) and peripheral neurological tests were conducted and evaluated in 3 infants with UAN. All patients received CT scan and/or MRI examination. RESULT: Three patients had type "A" tympanogram. The ipsilateral and crossed stapedial reflexes were elicited in healthy ears, while those were absent in affected ears. Affected ears in 3 cases showed no ABR but normal CM and EOAE. All of them had normal MLR and ERP (P300 and MMN) recording. Peripheral neurological tests and CT and/or MRI showed no abnormality. CONCLUSION: Neurophysiological characteristics in infants with UAN were similar with bilateral AN. The diagnosis of UAN in infants should focus on analyzing their neurophysiological characteristics and imaging examinations. Combining use of EOAEs, ABR and CM was recommended. It was necessary to follow up the infants with AN.

Cochlear Microphonic Potentials↗
PubMed2005

Universal newborn hearing screening.

Hearing loss is one of the most common congenital anomalies, occurring in approximately 1-2 infants per 1000. Left undetected, hearing impairments in infants can negatively impact speech and language acquisition, academic achievement, social and emotional development. These negative impacts can be diminished and even eliminated through early intervention at or before 6 months of age. Reliable screening tests that minimize referral rates and maximize sensitivity and specificity are available. The goal of universal neonatal hearing screening is to maximize linguistic and communicative competence and literacy development for children who are hard of hearing or deaf. Audiologic and medical evaluations should be in progress before 3 months of age. Infants with confirmed hearing loss should receive intervention before 6 months of age from health care and education professionals with expertise in hearing loss and deafness in infants and young children.

Achievement↗
PubMed1991

[Measuring evoked otoacoustic emissions at various times during intubation anesthesia].

Evoked otoacoustic emissions (EOAE) remain intraindividually similar in repeated measurements. After application of medication for general anesthesia no significant changes of EOAE could be seen. Damping of amplitude and energy, mostly seen in the late phase of general anesthesia, might be caused by possible middle ear pressure changes from nitrous oxide. The recording of EOAE under general anesthesia provides an additional method in objective infant hearing evaluation and expands our diagnostic tools in those cases when children do not cooperate.

Anesthesia, General↗
PubMed1991

Effects of L-glutamine, glutaminase and glutamine synthetase on CAP threshold of cochlear nerve of guinea pig.

Negative direct current (-DC 300 microA) stimulation was applied to the round window of the guinea pig cochlea to exhaust the pre-synaptic intracellular reserves of the transmitter in hair cells, and then the scala tympani was perfused respectively with L-glutamine, glutamine synthetase and glutaminase. Experimental results showed that the negative DC electrical stimulation applied to the round window elevated the CAP threshold of the cochlear nerve in the basal turn of the cochlea, which recovered over a period of approximately 17-39 min. The perfusion of L-glutamine apparently elevated the CAP threshold. The recovery of the CAP threshold following electrical stimulation, however, was accelerated by the perfusion of 10 mmol/L L-glutamine. The time for recovery only took about 5-6 min. The perfusion of enzyme glutamine synthetase elevated the CAP threshold by 50 dB, while glutaminase had little effect. These results suggest that the effect of L-glutamine on the CAP threshold in the cochlea of the guinea pig appears to be that of a potent depolarizing agent which accelerates the recovery of the CAP threshold during the depletion of the transmitter, and L-glutamine may be the candidate for the afferent excitatory transmitter.

Animals↗