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At least 1,063 records · Page 59Linked to original sources
PubMed1991

Hearing loss and pneumococcal meningitis: an animal model.

Clinical studies of predisposing factors in the development of hearing loss secondary to bacterial meningitis have produced conflicting results. An animal model of meningogenic labyrinthitis was developed for more precise study of these parameters. Rabbits were inoculated intrathecally with 10(5) pneumococci to induce meningitis. Hearing thresholds were measured using auditory-evoked responses to 1 kHz, 10 kHz, and click stimuli before infection and every 12 hours thereafter. Profound deafness occurred in all subjects at an average of 48 hours following infection. The incidence and severity of hearing loss was strongly correlated with the duration of meningitis. Temporal bone histology revealed acute inflammation of all perilymphatic spaces including the cochlear aqueduct. This model demonstrated that the risk and severity of hearing loss increase with the duration of meningitis and suggested that the cochlear aqueduct is an anatomic pathway for the extension of infection from the cerebrospinal fluid to the cochlea. The implications for therapy in humans is discussed.

Acoustic Stimulation↗
PubMed2005

Quantitative experimental assessment of the factors contributing to hearing loss in serous otitis media.

OBJECTIVE: This study was designed to quantitatively assess the contribution of various factors to the conductive hearing loss in otitis media. BACKGROUND: In the conductive hearing loss seen in cases of serous otitis media, various volumes of fluid of different viscosities along with subatmospheric (negative) pressure are found in the middle ear. METHODS: To evaluate the contribution of each of these factors to hearing loss, various volumes of saline, whole blood, or glycerol were applied to the open middle ear cavity of guinea pigs for short periods of time and auditory function was evaluated by recording the threshold of auditory nerve-brainstem evoked responses. In some of the saline experiments, the bulla cavity was also sealed, allowing a subatmospheric (negative) pressure to develop in the cavity as water was osmotically absorbed because of the gradient in colloid osmotic pressure between saline and blood in the vessels lining the middle ear cavity. In other experiments, a thoracic drainage system was connected to the middle ear cavity to induce desired negative middle ear pressures. RESULTS: The degree of hearing loss increased as larger volumes of fluid were introduced into the middle ear, reaching a maximum of 15 to 16 dB. There was no difference in the degree of hearing loss induced by saline or by fluids with viscosities up to 1,000 times greater than that of water (glycerol). A subatmospheric pressure in the middle ear contributed only a small additional (1-2 dB) threshold elevation. CONCLUSION: The major factor contributing to hearing loss in serous otitis media is the volume of fluid in the middle ear, irrespective of its viscosity. The contribution of negative middle ear pressure is much smaller.

Analysis of Variance↗
PubMed1996

Hearing thresholds.

Explore the source record for details and available documents.

Auditory Threshold↗
PubMedDate not supplied

Effect of high perilymphatic potassium on brainstem evoked response audiometric thresholds.

The perilymphatic space of the cat cochlea was perfused with a solution containing a high potassium ion concentration. The auditory response threshold was monitored with brainstem evoked response audiometry. In the majority of animals the initial perfusion produced a reversible decline in response threshold. With repeat perfusions, there was a variable degree of non-reversible response decline leading ultimately to a total loss of the auditory response.

Animals↗
PubMed1975

[Audiological observations of a patient with auditory agnosia].

A case is reported in which a patient was become unable to identify all kinds of auditory material, including speech, despite only subnormal audiometric thresholds (i.e. "auditory agnosia"). The following audiological disorders were shown: some fragility in the perception of brief sound stimuli, difficulties to apprehending prolonged series of stimuli (rhythms), defective sound localization, an increase in the homolateral and in the contralateral effects of masking sounds. On the other hand, differential thresholds for frequency and for intensity, as well as fusion thresholds, were little affected, or unaffected. A complete dissociation appeared between the auditory evoked potentials and the audiometric thresholds; a year after the first examination, and the following years, the auditory potentials were largely reduced, or even have elapsed for one ear, while the audiometric thresholds seem to remain nearly the same.

Agnosia↗
PubMed1968

Auditory detection and perception in normal man and in patients with adrenal cortical insufficiency: effect of adrenal cortical steroids.

Auditory detection thresholds for sinusoidal tones and various tests of auditory perception were determined in 12 patients with adrenal cortical insufficiency (seven with Addison's disease and five with panhypopituitarism) and compared to those in normal volunteers. In adrenal cortical insufficiency auditory detection sensitivity was significantly more acute than normal, and judgments of loudness and of the contralateral threshold shift were made at levels more than 20 db below those of normal subjects. Thus both the lower and the upper limits of the dynamic auditory range are significantly decreased in these patients. Speech discrimination ability of the patients was significantly impaired as was their difference limens, their alternate binaural loudness balances, and their ability to localize tones in space. Treatment of the patients with deoxycorticosterone acetate decreased serum potassium concentration, raised serum sodium concentration, and produced gains in body weight but did not alter auditory detection or perception. Treatment with prednisolone or with maintenance doses of carbohydrate-active steroids returned auditory detection and perception to normal in every patient tested. The inability of the untreated patients to perform the various auditory perception tasks indicates that they have a defect in their ability to integrate incoming sensory stimuli. This defect may be related to the alteration in the timing of transmission of neural impulses along axons and across synapses which occurs in these patients when their carbohydrate-active steroid is removed. This decreased integrative capacity occurs at the same time that they are able to detect many types of sensory stimuli significantly better than normal subjects. This interrelationship between increased detection sensitivity and decreased perceptual ability is dependent upon the absence of carbohydrate-active steroids, for when these steroids are replaced both detection sensitivity and perceptual ability revert to normal.

Addison Disease↗
PubMed1982

Interaural crosstalk in the cat.

The physiologically effective interaural acoustic crosstalk in cat was measured by means of binaural threshold differences for single auditory-nerve fibers and for cochlear microphonics. There were generally two maxima, at about 800 Hz and 3 kHz, attaining values as high as -25 dB (transmission to cochlea via contralateral ear re transmission via ipsilateral ear) in some cats. This figure could be reduced to -50 dB by mechanically isolating the acoustic drivers from each other and from the stereotaxic head frame.

Animals↗
PubMed1963

Size and reliability of frequency-difference thresholds determined with operant tracking procedure.

Auditory frequency discrimination thresholds have been determined by a "tracking procedure" at five frequencies and two intensity levels for a group of four cats. Intra-animal thresholds were found to be quite stable, and there was good inter-animal agreement among three of the four cats. Although quite stable, the tracking thresholds were larger than those which had been obtained using an avoidance procedure. However, because of the several differences between the tracking procedure and avoidance conditioning procedure, no conclusions can be drawn concerning the efficacy of the different types of reinforcement in determining the ultimate limit of the animals' discrimination ability.

Animals↗
PubMed1988

Hearing in the ferret (Mustela putorius): effects of primary auditory cortical lesions on thresholds for pure tone detection.

1. Pure tone thresholds were determined for five adult male ferrets before and after bilateral ablation of primary auditory cortex. Complete audiograms ranging from 0.016 to 48 kHz were obtained for two animals. The remaining three animals were tested at five frequencies selected to assess hearing throughout the audible range (0.125, 0.5, 2.0, 8.0, and 32.0 kHz). 2. Shortly after surgery one animal had elevated thresholds across the entire frequency range with the most pronounced hearing loss above 12.0 kHz. Four other animals had no elevation of thresholds at low and midrange frequencies but suffered a hearing loss at very high frequencies (32 kHz). 3. Repeated testing over a period of several months revealed substantial recovery of sensitivity. There was complete recovery of sensitivity in the low- and middle-frequency range of the audiogram. Some hearing loss persisted at the extreme upper end of the audiogram (32 kHz), but in two cases there was evidence of recovery at this frequency as well. 4. Following determination of absolute thresholds all animals were assessed for their ability to localize sound in space. Minimum audible angles were obtained on midline as well as within both left and right hemifields, i.e., around 0, -60 and +60 degrees azimuth. All animals had severe and persistent deficits in their ability to localize brief sounds within the lateral fields, but were still capable of midline localization.

Animals↗
PubMed1991

Changes in cochlear sensitivity do not alter relative thresholds of different spontaneous rate categories of primary auditory nerve fibres.

The CF thresholds of three different spontaneous firing rate categories of single auditory nerve fibres were measured in guinea pigs with widely differing cochlear sensitivities. The CF thresholds for all fibres were compared to the CAP thresholds at the same frequencies. The relationship between single fibre CF threshold and CAP thresholds for the three different fibre categories remained unchanged despite the very wide range of absolute CAP thresholds. The widely ranging CAP thresholds in these animals were probably due to varying degrees of outer hair cell pathology and these data therefore support the notion that in normal animals, the origin of differences in threshold between fibres with different spontaneous rates, lies in the properties of the inner hair cells and/or their synapses with afferent dendrites.

Action Potentials↗
PubMed1997

Auditory and tactile bone-conduction thresholds using three different oscillators.

Determination of tactile bone-conduction (BC) thresholds is essential to provide proper diagnosis of individuals with profound hearing loss. In this study, auditory and tactile BC thresholds were compared using three oscillators: the Radioear B-70-A, B-71, and B-72 with mastoid and forehead placement. Subjects included 12 adults with normal hearing (to establish auditory thresholds) and 12 adults with profound sensorineural hearing loss (to establish tactile thresholds). All 24 subjects were tested at octave intervals from 250 through 4000 Hz. As demonstrated in previous studies, tactile thresholds were lower for the low frequencies. Some differences in tactile thresholds were evinced as a function of different oscillators. One fact that emerged from this study is the lower tactile threshold with forehead placement as compared to the mastoid. While ostensibly a disadvantage to forehead BC testing, there are some clinical advantages to be gleaned from this discovery.

Acoustic Stimulation↗
PubMedDate not supplied

Neonatal auditory brain-stem response threshold and latency: 1 hour to 5 months.

Auditory brain-stem evoked responses were recorded in normal neonates and infants ranging in age from less than 1 h to 5.5 months. The average threshold in neonates 0-5 h old was 29 dB greater than that in adults, reaching the adult threshold range within 2 weeks. The latency of wave I in 0-5 h neonates was 1.81 msec and reached the adult range within 2 weeks. The V-I interpeak latency in 0-5 h neonates was 5.3 msec and did not reach adult values within the period of this study.

Brain Stem↗
PubMed1996

Auditory enhancement at the absolute threshold of hearing and its relationship to the Zwicker tone.

Auditory enhancement describes an improvement in the detection of a tonal signal in a broad-band masker with a spectral gap at the signal frequency if the signal is delayed in its onset relative to the masker. This auditory enhancement may be based on an increase of the effective signal level instead of a decline in the effective masker level. In order to evaluate whether this signal enhancement also exists at the threshold of hearing, we measured the absolute threshold for pure-tone pulses of different frequencies with and without preceding band-rejected noise. Such noise also causes the sensation of the Zwicker tone-a faint pure tone lasting for a few seconds immediately after the noise presentation. The pitch of this sensation is a complex function of the noise parameters but always lies at a frequency within the rejected band. During the Zwicker tone sensation, auditory sensitivity for tone pulses at frequencies adjacent to the Zwicker tone was improved by up to 13 dB instead of being reduced which might be expected due to the presence of the simultaneously audible Zwicker tone. The failure to influence this threshold shift with low-frequency tones and measurements of the ear's acoustical response indicate that this threshold improvement may be produced through neuronal disinhibition rather than through a release from mechanical suppression in the cochlea.

Acoustic Stimulation↗
PubMed1981

Glutamate and aspartate: alteration of thresholds and response patterns of auditory neurons.

Iontophoretic application of the excitant amino acids glutamate and aspartate onto neurons in the chinchilla cochlear nucleus results in a lowering of the threshold of response to auditory stimuli. Neurons that display 'on'-type phasic responses to toneburst stimuli may become tonic, sustained responders with iontophoretic application of glutamate or aspartate. The ability of either glutamate or aspartate to effect changes in thresholds and response patterns of cochlear nucleus neurons is further evidence that one of these amino acids may be the afferent transmitter of the auditory nerve. The effects seen with these excitant amino acids may also provide insight into the underlying synaptic events involved in the generation of a particular response pattern.

Animals↗