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Results for “Cochlear Microphonic Potentials”

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At least 991 records · Page 55Linked to original sources
PubMed1991

Otoacoustic emissions in normal and hearing-impaired children and normal adults.

Although distortion-product otoacoustic emissions (DPOEs) have been studied in adults recently, there is little information regarding them in young children. DPOEs and click-evoked otoacoustic emissions (CEOEs) were measured from a same group of normal and hearing-impaired children (age 4 through 10 years) and normal adults (age 22 through 29 years). Measurements of DPOEs in 13 children's ears with normal hearing showed higher levels of emissions in the 700- to 1400-Hz and 5.7-kHz regions relative to the data obtained in 10 normal adult ears. The 22 ears of children with sensorineural hearing loss demonstrated agreement between pure-tone audiograms and "DPOE audiograms." Measurements of CEOEs revealed that the average level of emission in 15 normal-hearing children's ears was slightly lower than that previously obtained in newborns, but slightly higher than that of adults. In children, the CEOE spectral components in the 4- to 6-kHz region were lower than in newborns, but higher than in adults. These results support the view that the DPOEs and CEOEs comprise a valuable tool in assessment of cochlear function in subjects of all ages.

Acoustic Stimulation↗
PubMed1980

The influence of ultrasound and temperature on the cochlear microphonic response following a round window irradiation.

Impairment of cochlear function was investigated following ultrasonic irradiation of the vestibule and the cochlea through the round window in cats and guinea pigs. Selective destruction of the vestibular balance mechanism with negligible impairment of cochlear microphonic response was achieved, provided that the ultrasound beam was directed away from the cochlea and towards the ampulla of the superior semicircular canal. Directing ultrasound into the cochlea produced a depression in C.M. which was greatest in the higher frequency responsive area corresponding to the region of the first two cochlear turns. The degree of cochlear microphonic depression increased as the duration of irradiation was extended. The occurrence of a significant temperature increase accompanying the application of ultrasound implicated the involvement of a thermal mechanism in addition to the mechanical disruptive effect of ultrasound.

Animals↗
PubMedDate not supplied

Immediate alterations in the impulse noise exposed organ of Corti of the guinea pig.

Cochlear microphonics and morphological changes in the organ of Corti were examined in guinea pigs exposed to 1 or 10 impulses of 164 dB SPL. Immediately after noise exposure the CM amplitudes of frequencies between 500 and 10000 Hz delcined severly with an accelerating tendency during the next 2 hours. The decrease in CM in two groups differed insignificantly. 10 minutes after impulse exposure, whole-mount specimens showed mainly swollen and translocated nuclei of outer hair cells. After 2 hours we found large quantities of pyknotic nuclei, karyorrhexis, and gaps in the normal OHC pattern. Despite minor numerical differences in injured cells of either group, exposure to 10 impulses caused a greater degree of irreversible alteration. Altogether, altered hair cells were only localized in the basal and lower second turn, and their numbers were relatively small. This stands in contrast to severe decrease of CM from low to high frequencies. Hair cell injury and additional mechanical lesion of the reticular membrane caused many sites of leakage, allowing interchange of endo-and peri-lymph. This effect is considered to be the main cause of functional damage indicated by rapid CM decline.

Animals↗
PubMedDate not supplied

Cochlear vascular and electrophysiological effects in the guinea pig to 4 kHz pure tones of different durations and intensities.

Round window cochlear microphonic recordings from 33 guinea pigs were obtained prior to and following exposure to a 4 kHz pure tone at levels ranging from 124 dB to 140 dB for 5 to 80 minutes. When electro-physiological evaluation was complete, the animals were killed and tje cochlear tissues prepared using a soft-surface preparation technique. Experimental and control animals were mixed and randomly assessed without prior knowledge of the groups to which the specimens belonged. Histopathological observations were quantified and computer analysed. Statistical analyses suggest that noise exposure results in an overall decrease in blood flow to the cochlea with slight intracochlear increases in flow, perhaps compensatory in nature, to locations corresponding to the 4 kHz exposed region. Results implied that the initial localized hair cell damage known to occur as a result of overexposure to a discrete pure tone is not caused by a decreased blood flow. Relationships between electro-physiological and vascular changes and noise 'dose' are discussed.

Acoustic Stimulation↗
PubMedDate not supplied

Neurotransmitters in the cochlea and the cochlear nucleus.

The inhibitory efferent transmitter in the cochlear is most likely acetylcholine. The afferent transmitter (between hair cells and primary afferent fibres) is not known. There is some evidence for glutamate (or aspartate) but the high concentrations necessary to activate the afferents when these amino-acids are applied intracochlearly may indicate that their effects is unspecific. A number of other transmitter candidates can be safely ruled out at these synapses. In the cochlear nucleus of transmitter between primary afferents and secondary cells is probably glutamate (or aspartate).

Acetylcholine↗
PubMed1982

The ototoxic interaction of viomycin, capreomycin and polymyxin B with ethacrynic acid.

The ototoxic interaction between the aminoglycoside antibiotics (streptomycin, kanamycin, etc.) and the loop-inhibiting diuretics (ethacrynic acid, furosemide and bumetanide) has been well documented. This interaction causes extensive destruction of the hair cells of the cochlea. Brummett et al. (1974) demonstrated that this interaction did not occur with the non-loop-inhibiting diuretics and kanamycin. The present study was undertaken to determine if antibiotics other than the aminoglycosides could produce the ototoxic interaction when combined with a loop-inhibiting diuretic. Three antibiotics-viomycin, capreomycin, and polymyxin B- when given with ethacrynic acid were found to produce cochlear hair cell damage that was similar to that produced by aminoglycoside antibiotics administered with ethacrynic acid. Therefore, the interaction appears to be specific to the loop-inhibiting diuretics but not specific for the aminoglycoside antibiotics.

Aminoglycosides↗
PubMedDate not supplied

Correlation of audiometric data with changes in cochlear hair cell stereocilia resulting from impulse noise trauma.

In a previous experiment, after chinchillas had been exposed to impulse noise trauma, plastic-embedded surface preparations of the organ of Corti were examined with the light microscope. A consistent relationship between cochlear hair cell loss and hearing loss was not found (Hamernik et al., 1980). In the present study, four cochleas from that experiment were sectioned and examined with the transmission electron microscope to determine if their were consistent patterns of damage to the sensory cells at the ultrastructural level that would more closely correlate with the audiometric data. Alterations of the outer hair cell stereocilia were found when threshold was elevated 15 to 30 dB. The membranes of the stereocilia appeared loose and wrinkled and the stereocilia were no longer erect. In some cases, predominantly in the first row of outer hair cells, stereocilia were missing and in other cases, stereocilia were fused. Within these giant stereocilia, the rootlets of the individual stereocilia had disintegrated. Other alterations in sensory cell ultrastructure, though present, had no consistent pattern and could not be related to changes in hearing thresholds. Only the changes in the outer hair cell stereocilia appeared to correlate with hearing loss and the degree of damage was reflected in the amount of threshold elevation.

Animals↗
PubMed1983

Cochlear morphology in relation to loss of behavioural, electrophysiological, and middle ear reflex thresholds after exposure to noise.

Loss of auditory function was correlated with different pathological findings in the inner ear of the rabbit after 15 or 30 min exposure to high level broad band (2-7 kHz) noise. The ears from animals with post-exposure times ranging from 1 to 23 months were analysed by scanning electron microscopy (SEM). Complete cochleograms with quantification of loss of hair cells and damage to stereocilia were produced. Loss of function was defined by determining behavioural threshold, threshold of auditory brainstem response (ABR) to narrow-band stimuli and threshold of the middle ear muscle reflex (MER). A small scattered loss of OHCs and slight disarray of stereocilia were found in non-exposed ears of young animals, but fusion of IHC cilia was not observed. Normal auditory function was not found in any noise exposed animal with abnormal morphology. A loss of threshold sensitivity of up to about 30-40 dB was noted without loss of hair cells in the corresponding region of the cochlea. The mildest structural damage that correlated to a functional alteration consisted of damage to stereocilia of IHC. This correlated well to the MER threshold shift. In two animals a shift of MER threshold of about 20 dB was the only functional abnormality. In ears with more extensive IHC damage loss of OHCs was also found and these animals had primarily an increase in auditory threshold shift with only a small additional change in MER threshold. It is concluded that in the rabbit and with the methods used the IHC stereocilia are the structures most susceptible to damage by the noise used and that the degree of injury can be fairly well assessed by functional tests of a type that is used also routinely in the audiological clinic.

Animals↗
PubMedDate not supplied

Prolongation of the cochlear microphonic in man. Cochlear microphonic ringing.

During routine extra-tympanic electrocochleographic (ECochG) recording we have observed that in many cases more cycles are seen in the cochlear microphonic (CM) recording than are present in the acoustic stimulus. We have termed this phenomenon CM 'ringing'. Ringing is present in 69% of our normal subjects and in 43% of patients with deafness of different aetiologies. In the cochlear and Ménière subgroups those cases showing ringing have a significantly larger CM amplitude (p less than 0.001 and p less than 0.01 respectively). The possible origin of this phenomenon is discussed.

Audiometry↗
PubMedDate not supplied

Influence of altered middle ear pressure on cochlear microphonics.

Patients with otitis media with effusion often have impaired hearing loss caused by bone conduction. Among several possible causes for this hearing loss, the influence of middle ear pressure upon hearing was examined. Cochlear microphonics (CM) of guinea pigs were recorded under positive or negative pressure created simultaneously in the middle ear and in the external ear canal. CM was recorded from each turn (basal, second, third and apical). Whereas under negative pressure CM decreased suddenly but soon became stable, under positive pressure CM normalized gradually after the initial drop. Thus, in the stable state, CM amplitude was low under negative pressure but was slightly subnormal under positive pressure. One possible explanation is that perilymphatic efflux appears to cause such recovery of CM under positive pressure. it is postulated that perilymphatic inflow does not seem to occur under negative pressure, since CM and perilymphatic pressure were stable.

Animals↗
PubMedDate not supplied

Effects of aging on normal hearing loss and noise-induced threshold shift in albino and pigmented guinea pigs.

In a previous investigation into noise-induced hearing loss by comparing 2-month-old albino with pigmented guinea pigs, albinos displayed significantly greater shifts in cochlear microphonic (CM) threshold and less recovery than the pigmented animals 7 days after noise exposure. The present study compared the responses of 14-month-old albino and pigmented guinea pigs to the same noise parameters used previously. Thresholds for the first detectable elicitation of CM for three pure tones were recorded prior to, at 90 min and at 7 days after a 45-min exposure to 126 dB broadband noise. Before exposure to noise, thresholds for pigmented guinea pigs were 24 dB higher than those in the albinos. Following noise exposure, the pigmented animals showed less than half the amount of threshold shift displayed by the albinos. This change ws attributed to the higher pre-exposure thresholds in the pigmented guinea pigs. Converging lines of evidence suggest that cochlear pigmentation may have both protective and toxic influences on the inner ear.

Aging↗
PubMed1988

Audiological aspects of idiopathic perilymphatic fistula.

Audiological findings in 40 patients with surgically confirmed idiopathic perilymphatic fistula were investigated. Most patients complained of roaring tinnitus, hearing impairment, ear fullness, and hyperacusis. However, a popping sound and a streaming water-like sound were noticed only in 8. Pure-tone sensitivity included every kind of hearing impairment, from sudden profound, to normal sensitivity. Development of hearing impairment was sudden, and deteriorated further, fluctuating in order of frequency. In the early stage of perilymphatic fistula patients had low-frequency hearing impairment and evidenced dominant-negative SP in the electrocochleogram. These findings suggest that a fistula of the inner ear window is not solely responsible for the wide variety of signs and symptoms, and that there must be simultaneous lesions in the membranous labyrinth.

Adolescent↗