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PubMed1979

Development and degeneration of hearing in the C57/b16 mouse: relation of electrophysiologic responses from the round window and cochlear nucleus to cochlear anatomy and behavioral responses.

In disorders of the auditory organ associated with hearing loss, a correlation of the anatomical, behavioral and electrophysiological studies furnishes the investigator several parameters of study to better comprehend the hearing mechanism and the various anatomical structural dysfunctions that relate to the hearing loss. Mice are interesting to study because they carry several types of genes for hereditary deafness. Until recently, it was very difficult to train mice for behavioral hearing threshold testing; however, having developed such a method, the next step was to study the normal mice in these three parameters and extend the studies to mice with hereditary hearing loss. The type of mouse studied in this research was the C57/b16 strain which carries such a gene. The results of the studies indicate that the results of the behavioral and electrophysiological studies relate well to each other, and that light microscopic studies (if taken alone) do not furnish us with the actual functional capability of the structures of the inner ear. It is recommended (and it would be most valuable) that efforts should be made to collect and study human temporal bones with all three parameters of study for a better understanding of the structures of the human inner ear. Reference is made and recommendations given as to the parameters of studies while performing human electrocochleography.

Acoustic Stimulation↗
PubMedDate not supplied

Surgical evaluation of candidates for cochlear implants.

The customary presentation of surgical procedures to patients in the United States consists of discussions on alternative treatment methods, risks of the procedure(s) under consideration, and potential benefits for the patient. Because the contents of the normal speech signal have not been defined in a way that permits a surgeon systematically to provide alternative auditory signals to a deaf patient, the burden is placed on the surgeon to make an arbitrary selection of candidates and available devices for cochlear prosthetic implantation. In an attempt to obtain some information regarding the ability of a deaf patient to use electrical signals to detect and understand speech, the Good Samaritan Hospital and Neurological Sciences Institute cochlear implant team has routinely performed tympanotomies using local anesthesia and has positioned temporary electrodes onto the round windows of implant candidates. The purpose of this paper is to review our experience with this procedure and to provide some observations that may be useful in a comprehensive preoperative evaluation for totally deaf patients who are being considered for cochlear implantation.

Cochlear Implants↗
PubMed1989

Structure of the round window membrane.

In the present study the literature on the round window membrane (RWM) structure was reviewed and the rat used as an animal model to elucidate structural alterations of the RWM occurring during serous (SOM) and purulent (POM) otitis media. In SOM the RWM was about the same thickness as that of the control, whereas in POM it increased about 5-fold. The structural changes in POM were mainly confined to the epithelium facing the middle ear cavity. The normal flat epithelium was transformed into a pseudostratified epithelium with both ciliated and goblet cells. Light microscopy revealed only minor changes in the RWM structure during SOM. However, ultrastructurally, the connective tissue layer exhibited dense accumulations of collagen and elastic fibres which were not observed in either normal or the POM ears. The study showed that different inflammatory conditions of the middle ear cause different structural alterations of the RWM. To what extent these changes also influence differently the permeability of the RWM remains to be elucidated. Obviously ultrastructural studies are needed to be able to characterize the structural changes which appear in the RWM in a diseased ear.

Animals↗
PubMed1991

Cochleotoxicity of otic drops in the chinchilla: comparative study of Bestron and Cortisporin.

Bestron, a new otic preparation containing cefmenoxime, was applied to the round window membrane of the chinchilla and the long-term cochleotoxicity was evaluated by means of electrocochleography. The thresholds of the compound action potential (CAP) in all frequency areas tested ranged within normal values. The input-output and -latency relationships of the CAP resulted in no significant deterioration of hearing. However, identical treatment with Cortisporin resulted in elevated CAP threshold in the high frequency area and deterioration of the input-output and -latency of the CAP. These findings indicate that Bestron is noncochleotoxic as compared with Cortisporin and therefore may be used safely in the treatment of infected ears.

Animals↗
PubMed1995

Electromotile hearing: evidence from basilar membrane motion and otoacoustic emissions.

Electrical stimulation of the cochlea is known to cause auditory sensations in humans and other animals. It also has been shown to produce emissions of sound from the inner ear. In the current study we investigate the relationship between electrically induced motion of the basilar membrane (BM) and the production of otoacoustic emissions. We test the hypothesis that electrical current-induced movements of the outer hair cell (OHC electromotility) result in intracochlear acoustic pressure which causes traveling waves on the BM. Our results demonstrate that the dominant response of the guinea pig inner ear to electric stimulation, at the round window membrane (RW) or across the cochlear duct, is a mechanical response of the organ of Corti. We observed that electrical stimulation of the cochlea produced traveling wave activity on the BM, measured with a laser Doppler velocimeter. The BM motion was accompanied by sound emitted by the cochlea for frequencies up to at least 25 kHz. Furthermore, bipolar rectangular current stimulation produced steady, bipolar displacements of the BM (to 2 nm), indicating functional elongation or contraction of OHCs occurs depending on the polarity of the current pulse. All of the evoked responses were absent after drug treatments eliminated the OHCs. Our data indicate that OHCs undergo electrically evoked displacements capable of producing high-fidelity, high-frequency acoustic energy. The electrically evoked intra-cochlear energy results in conventional traveling waves within the cochlea, as well as emissions of sound from the cochlea. These data provide direct support for a mechanism of cochlear sensitivity and tuning involving high-frequency OHC electromotility. Moreover, the data also indicate that any intra- or extracochlear electric current which affects the electric polarization of OHCs could induce BM traveling waves and cause 'electromotile hearing'. This form of hearing would be one component under the more general definition of the electrophonic effect.

Animals↗
PubMed2005

Intratympanic dexamethasone and hyaluronic acid in patients with low-frequency and Ménière's-associated sudden sensorineural hearing loss.

BACKGROUND: Steroids are widely used for the treatment of cochleovestibular disorders. Direct steroid application in the middle ear cavity, when combined with a round window membrane permeability-modulating substance, increases the level of the steroid reaching the target cells. We measured hearing in patients with idiopathic isolated low-frequency sensorineural hearing loss and in patients with sudden sensorineural hearing loss and a history of Ménière's disease. Contradictory reports about effectiveness of intratympanic steroid therapy on vertigo control and hearing improvement in patients with Ménière's disease exist in the literature. METHODS: Eighteen patients with isolated low-frequency idiopathic sudden sensorineural hearing loss and 21 patients with sudden sensorineural hearing loss and a history of Ménière's disease were prospectively evaluated. The acute effect of the intratympanic application of dexamethasone with hyaluronic acid on hearing outcome after failure of an initial standard treatment with intravenous steroid and vasoactive substances was assessed. Evaluation was based on standard pure-tone audiometry findings. RESULTS: After intratympanic injection of dexamethasone and hyaluronic acid, 14 of the 18 patients with isolated low-frequency sensorineural hearing loss showed a significant improvement in hearing. After intratympanic therapy, 15 patients with a previous history of Ménière's disease and idiopathic isolated low-frequency sensorineural hearing loss showed an improvement in hearing on pure-tone audiometry, four remained unchanged, and two showed a tendency toward a slight deterioration. CONCLUSION: Intratympanic combined dexamethasone/hyaluronic acid application provides a reliable and safe therapeutic option for improvement of hearing in patients with isolated low-frequency idiopathic sudden sensorineural hearing loss or sensorineural hearing loss resulting from Ménière's disease who have failed intravenous steroid and vasoactive treatments.

Adjuvants, Immunologic↗
PubMed1993

[Otorhinolaryngologic aspects of diving sports].

ENT disorders are the most common of all medical problems of diving. This review summarizes the specific conditions and ENT diseases in Scuba diving. During compression failure to equalize the pressure of air-filled cavities surrounded by bone deprives the middle ear or sinuses of aeration. Middle ear barotrauma is the most common barotrauma encountered in divers while sinus barotrauma and especially inner ear barotrauma (with rupture of the round or oval window) are less common. Decompression sickness in primarily the result of inert gas bubbles; deafness and vertigo may result if the inner ear is involved. The ENT examination necessary for assessment of diving fitness focuses on the middle and inner ear as well as the nose, sinuses and larynx. A list of ENT contra-indications is presented that mandate temporary or permanent disqualification from diving.

Barotrauma↗
PubMed1992

Cochlear effects of hyaluronan applied on ruptured round window membrane.

The purpose of the present experimental study was to determine whether hyaluronan (hyaluronic acid, HYA) exerts any functional or morphologic ototoxic effects on the cochlea when in contact with a ruptured round window membrane (RWM). HYA in 1% solution was applied in the round window (RW) niche of rats (n = 6) prior to perforating the RWM. In a control group (n = 6) the RWM was perforated alone. Cochlear functioning and structure were monitored by recording auditory brainstem responses (ABRs) at 2-31.5 kHz and by scanning electron microscopy. Perforation of the RWM alone resulted in immediate loss of ABR thresholds between 6 and 31.5 kHz in 2 of 6 animals. Similar results were obtained after application of HYA into the RW niche and subsequent RWM perforation. In both treatment groups the mean ABR thresholds and mean latencies for wave II at the ABR threshold returned to the pre-surgical (normal) range after 2 months. Also with respect to the cochlear morphology the results in both treatment groups were alike including minor structural changes in hair cell stereociliae but no loss of hair cells. It is concluded that HYA, when instilled into the middle ear with the inner ear opened, is free from cochlear ototoxic effects. Our present findings enhance the potential usefulness of HYA in otosurgery, even in cases when the inner ear has been opened and/or when one wishes to protect the inner ear.

Animals↗
PubMed1992

Tube-perilymph fistula. An experimental study.

Before exploratory tympanotomy, it is difficult to diagnose an idiopathic perilymph fistula (PLF) because of its variable presentations. An animal model tube-PLF on guinea pigs was established to evaluate the change of the sensitivity of the cochlea function and the value of the postural audiometry in PLF. A fine polyethylene tube (O.D. 0.6mm) was inserted into the scala tympani of the basal turn through the incised round window membrane in 10 experimental guinea pigs, and another 5 as controls. The hearing threshold (HT), action potential (AP) latency for stimulus of 105 dB SPL, difference of HT and AP latency from the test ear down to up were measured by electrocochleography (ECoG) immediately after operation and one week later. The HT, AP latency and postural audiometry showed no significant changes immediately but a significant difference one week later in HT (P less than 0.01) and postural audiometry, the AP latency also presented a significant delay (P less than 0.01). The results showed that the tube-PLF model may be a valuable method for studying chronic PLF.

Action Potentials↗
PubMed1989

Rapid changes in cochlear nucleus cell size following blockade of auditory nerve electrical activity in gerbils.

Large spherical cells of the mammalian anteroventral cochlear nucleus (AVCN) receive direct excitatory input from auditory nerve axons. Trans-synaptic regulation of neuronal cell size and cell number after cochlear ablation has been previously demonstrated in neonates of several vertebrate species, including the gerbil. Such changes may be related to loss of spontaneous or evoked auditory nerve electrical activity or to loss of activity-independent factors. We have developed a method to chronically, yet reversibly, block auditory nerve electrical activity without violating the integrity of the inner ear. Tetrodotoxin (TTX) was embedded in an ethylene-vinyl acetate copolymer resin (Elvax). A small piece of Elvax containing TTX was placed next to the round window membrane, which allowed TTX to diffuse into the inner ear. As a measure of the effectiveness of manipulation, the onset, duration, and magnitude of the auditory threshold shift were measured by the auditory brainstem response. The sound-evoked response was abolished within 10 minutes of placement of TTX on the round window membrane. The duration of threshold shift was dose-dependent and lasted 24-46 hours. Implants of Elvax without TTX did not produce a significant threshold shift. TTX, which blocks voltage-gated sodium channels, did not abolish the potassium-based cochlear microphonic response. The consequence of blocking afferent electrical activity on gerbil AVCN large spherical cells was examined by measuring their cross-sectional area after each of four manipulations: unilateral auditory nerve action potential blockade with TTX; unilateral surgical cochlear ablation; ipsilateral TTX exposure/contralateral cochlear ablation; and unilateral sham operation (Elvax without TTX).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1988

[Otologic aspects of diving].

Ear diseases are the most common of all occupational diseases of diving. Otitis externa is the most frequent and troublesome infection in divers especially when the environment is humid. During compression, failure to equalize the pressure of the air-filled cavities surrounded by bone (middle ear, sinus) deprives the middle ear (or sinus) of aeration. Middle ear barotrauma is the most common barotrauma encountered in divers while external ear barotrauma (reversed ear) and inner ear barotrauma (with rupture of the round or oval window) are less common. Decompression sickness (Caisson disease) is primarily the result of inert gas bubbles; deafness and vertigo may result if the inner ear is involved. The most dramatic cause of disorientation under water is that due to vertigo. This vertigo is commonly a transient effect due to unequal caloric stimulation of the two labyrinths. The physical examination of the ear and nose necessary for assessment of diving fitness are discussed. A list of ENT contra-indications is presented which mandate temporary or permanent disqualification from diving.

Barotrauma↗
PubMed2003

The sources of electrically evoked otoacoustic emissions.

It has been hypothesized that electrically evoked otoacoustic emissions (EEOAEs) are generated at a site on the basilar membrane near the stimulating electrode. From this original site, the energy propagates towards the oval window, giving rise to the short time delay component (SDC) of EEOAEs. The energy also propagates towards its characteristic frequency (CF) location, and the emission reflected from the CF location forms a long time delay component (LDC). This hypothesis is directly tested in this study by using an acoustical swept tone to modulate the EEOAEs generated by alternating electric current delivered to the round window niche in gerbils. An acoustical tone with a high sound pressure level or a small frequency separation from the EEOAE frequency induced a strong suppression of the EEOAE LDC, but no obvious suppression of the SDC. When the electrical current frequency was fixed, the swept acoustic tone induced a slight suppression, an enhanced peak, and a strong suppression of EEOAEs as the acoustic frequency was swept from the low to high frequency. These data indicate that the electrical current induced cochlear partition vibration near the stimulating electrode. One part of this energy propagates directly to the ear canal, forming the SDC, and the other part propagates to its CF place and is reflected from there to the ear canal, forming the LDC.

Acoustic Stimulation↗
PubMedDate not supplied

Cochlear electrical activity in the C57BL/6 laboratory mouse: volume-conducted vertex and round window responses.

Remote (vertex-positive, volume-conducted) and local (round window, or RW) responses were simultaneously recorded from the C57BL/6 mouse. Volume-conducted responses were obtained which corresponded to the cochlear microphonic (CM), summating potential (SP), and action potential (AP), as measured at the RW. The vertex PI, corresponding to the AP, had a shorter latency to rarefaction than to condensation clicks. At higher SPL's bimodal PI peaks (a and b) were observed. PIb amplitudes were greater at lower, and PIa amplitudes were greater at higher SPL'S. Responses subsequent to the RW N1 and the volume-conducted P1 were eliminated after the ear was isolated from the brainstem.

Acoustic Stimulation↗
PubMed1993

Bony dehiscence between singular canal and round window niche.

The incidence of bony dehiscence of the human singular canal was studied by examining 409 human temporal bones obtained from 300 individuals. Such a dehiscence was noted in three (0.7%) of the bones from three (1%) of the individuals, all male, aged 2, 6, and 76 years. All of these bony dehiscences were located between the round window niche and the cribrose area of the singular canal. The finding of a microfissure in the vicinity of the bony dehiscence in two of the three cases indicates that such dehiscences occur independently of microfissures. Although the incidence of bony dehiscences of the singular canal is small, these dehiscences appear to have considerable clinical significance in that they form a communication between the middle and inner ears or possibly between the middle ear and the cerebrospinal fluid space.

Adolescent↗
PubMed1997

Induction of free radicals in the cochlea by an aminoglycoside antibiotic.

Free radicals are known to cause damage to biological tissues. We used histochemical methods to examine the emergence of free radicals in kanamycin (KM)-treated guinea pig cochlea. As a preliminary in vitro study, the emergence of free radicals was observed in guinea pig cochlea incubated with KM. In an in vivo study, KM was placed on the guinea pig round window membrane and the emergence of free radicals was observed over time. The emergence of free radicals was observed along the luminal membrane and hair bundles of outer hair cells. The appearance and disappearance of free radicals in the cochlea coincided with the transport of KM into the inner ear. These findings suggest that the emergence of free radicals could be attributed to the administration of KM.

Animals↗
PubMed1981

Development of cochlear potentials in rats.

The development of cochlear function was studied in 81 rat pups by recording the cochlear microphonic (CM) and the compound action potential (AP) from the round window in response to tone bursts and filtered clicks of various frequencies. The first electrophysiological response was the CM which could be obtained from 8- to 9-day-old animals. The AP first appeared at 11-12 days. As development progressed, cochlear potentials showed systematic changes in response parameters: the amplitude and threshold sensitivity of both CM and AP increased progressively with age as N1 latency decreased. All the parameters were within the adult range by the 15th day for the CM and by the 4th week for the AP. The results are discussed in relation to the developmental changes in the middle ear and to the morphological maturation of the organ of Corti.

Animals↗
PubMed1985

Inner ear barotrauma.

Inner ear barotrauma was observed by compressing or decompressing guinea pigs. The barotrauma in compression was greatly influenced by auditory tube function, and, in the animals deprived of this function, we could observe far more severe damage of inner ear hair cells and far more frequent round window rupture than in animals not thus deprived. Barotrauma in decompression was brought about in guinea pigs not deprived of auditory tube function with a decompression speed of 0.1 kg/cm2/sec, which is so severe that even a healthy auditory tube could not endure it. It can be said that the middle and inner ear are more apt to be damaged in decompression than in compression.

Animals↗
PubMed1992

[Experimental defects of the round window membrane].

Previous and current studies of experimentally induced fistulas in the round window membrane (RWM) are reviewed. After puncture (or "micro-perforation") of the RWM leaking perilymph was not been observed and auditory evoked potentials have remained unaltered. In contrast, most publications have reported that gross incisions ("macro-perforations") of the RWM have resulted in the deterioration of auditory evoked potentials, with leaking perilymph and/or cerebrospinal fluid and/or with entrance of air bubbles into the scala tympani depending on the site of the perforation. Spontaneous healing was then observed within 4 to 8 days and was associated with normalization of the auditory evoked potentials. In a very few experimental studies pathophysiological mechanisms were simulated that may be involved clinically in patients with RWM fistulas, i.e. implosive rupture of the RWM due to an acute increase in middle ear pressure or explosive rupture of the RWM that may occur in patients trying to use forced Valsalva maneuvers to equalize decreased middle ear pressures due to blocked Eustachian tubes.

Animals↗