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At least 451 records · Page 25Linked to original sources
PubMedDate not supplied

Auditory brainstem potentials in man evoked by electrical stimulation of the round window.

In normal subjects, round-window electrical stimulation provides a sound sensation and supplies brainstem-evoked responses whose form is just the same of those evoked by sound stimulation. This electrical stimulation also provides a sound sensation in more than 90% of cases of total deafness, which means that at least a few auditory nerve fibres are still present. Thus, this test is indispensable when considering surgical rehabilitation with a multichannel cochlear implant. The diagram of this response to an electrical stimulus differs completely in the case of total deafness and in normal subjects. The correlation between the form of these diagrams and the supposed etiology of the deafness is not significant.

Acoustic Stimulation↗
PubMedDate not supplied

Investigations on the critical perilymphatic pressure value causing round window membrane rupture in anesthetized cats.

Increasing perilymphatic fluid pressure was found to be an important factor in the etiology of round window membrane rupture. The critical pressure, causing membrane rupture was determined in anesthetized cats. Its value was found to be in the range 10--30 mmHg (x+/-S.E.M.=23.4+/-17.1). This value was compared with the pressure increases caused by thoracic and abdominal compression, cervical strangulation, forced Trendelenburg position, coughing and sneezing.

Anesthesia↗
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

Vestibular nerve findings in 150 neurectomized patients.

Vestibular nerve specimens obtained at neurectomy were studied by light and electron microscopy in 150 patients with various neuro-otological disorders. The vestibular nerve was considered morphologically normal in only 20% of the cases but the changes observed in most cases were interpreted as artifacts or physiological changes of aging. In nearly half of the cases there was excessive fibrosis of the perineurium or endoneurium of the vestibular nerve, or occurrence of glial tissue within or near Scarpa's ganglion. When these changes are of moderate or severe degree, they may be of pathological significance. Severe nerve cell destruction with subsequent fibrosis, indicating primary neuropathy, was found in four cases.

Adult↗
PubMedDate not supplied

The quivering mutant mouse: hereditary deafness of central origin.

Mice homozygous for the recessive quivering gene are largely unresponsive to sound, although their cochleas appear normal by light microscopy and cochlear hair cells do not degenerate with age. Cochlear potentials and inferior colliculus evoked responses were recorded in quivering mice (qv/qv) and in littermate controls (+/qv or +/+). There were no significant differences between mutants and controls in cochlear microphonic amplitudes or compound action potential thresholds, amplitudes and latencies. However, inferior colliculus evoked responses in mutants were small in amplitude and abnormal in waveform. Latencies were long and thresholds were elevated by at least 50 dB at all frequencies tested. These data suggest that the genetic hearing impairment in quivering mice is retrocochlear.

Action Potentials↗
PubMedDate not supplied

Electrocochleography for different electrode positions in guinea pig.

In 20 guinea pigs the relation between the electrode position on the cochlear surface and the recorded potentials was studied. We found the greatest AP amplitudes at the free lateral part of the cochlea; AP amplitudes decreased when the electrode was moved into the direction of the attachment of the cochlea to the petrous bone. Moving the electrode from the basal turn to the apex the maximal AP amplitude was found at the apex. The most negative SP was always recorded from the apex. This negative SP became smaller when the electrode was moved to the basal turn. Near the round window a small negative SP was recorded for 1 kHz stimuli and a positive SP for most 4 kHz stimuli. Moving the electrode from the free lateral part of the cochlea to the place of attachment to the petrous bone the magnitude of the SP decreased in a fashion similar to the AP amplitude. For 4 kHz stimuli we recorded a range of SP-AP ratios from -0.21 to +0.50 merely by varying the electrode position. Thus the SP-AP ratio highly depends on the electrode position.

Action Potentials↗
PubMedDate not supplied

Histological study of chronic electrode implantation through the round window of the guinea pig.

A platinum-iridium electrode with a Teflon cover tube was chronically implanted through the round window into the scala tympani of the guinea pig. Animals were sacrificed at 30 to 40 weeks after electrode implantation, and the cochleae were observed by scanning electron microscopy or with light microscopy. The results revealed that the electrode was firmly enclosed with fibrous tissue on the inside of the round window and with epithelial tissue on the outside. These tissues were considered to act as a barrier to the entry of infection while preventing leakage of the perilymph.

Animals↗
PubMedDate not supplied

Anatomy of the round window. A histopathological study with a graphic reconstruction method.

The round window was studied in normal adult and infant temporal bones to provide a knowledge base for the study of congenital anomalies of the round window, and to determine whether the round window develops postnatally. Fifty-three temporal bones were studied. Specimens were processed histologically, sectioned horizontally, stained with hematoxylin and eosin, and studied under the light microscope and microprojector. A special method of graphically reconstructing the round window was developed for this study, and was used to define the contour, area, and angle of the round window. We found that the round window is fan shaped. The area of the superoposteriorly located horizontal part (three-sevenths of the round window) and of the inferoanteriorly located vertical part (four-sevenths of the round window) totals approximately 2.29 mm2. In addition the angle between the plane of the tympanic sulcus and the vertical part of the round window was measured, and found to average 73.3 degrees. Lastly, the round window was found not to develop postnatally.

Adult↗
PubMed1988

Experimental study on autograft material for repair of round window rupture.

The healing process following experimentally produced rupture of the round window (RW) and subsequent closure with autograft materials were investigated in guinea pigs. The covering materials studied were fascia and perichondrium, both of which were placed over the RW after extensive rupturing of the RW membrane. The grafts were observed 1, 2, and 3 months after the operation. No substantial difference in the results for the two materials could be discerned. They adhered to the surrounding bone and were incorporated into the RW membrane within 3 months.

Animals↗
PubMed1988

An electrophysiological study on the effect of laser irradiation of round window membrane in the guinea pig.

An argon laser beam was used to irradiate the round window in 17 guinea pigs. Each animal was examined electrophysiologically with an electrode placed on the round window (RW) membrane 3 or 30 days after the irradiation, after which the cochlea was examined morphologically. The RW membrane was found intact in 16 out of 17 animals. All potentials (SP, CM, CAP) were abolished in 8 of the 17 animals. Histologically, perforations of the basilar membrane and Reissner's membrane were observed in 7 of 8 cases. In 4 of the 17 cases, a small effect of irradiation was evident both physiologically and histologically. Significant elevation of thresholds was observed in the remaining 5 animals, where amplitudes of CM, +SP, and CAP decreased at all intensities. Varying degrees of membranous labyrinth destruction can be used without perforating the RW membrane by the present method.

Animals↗
PubMed1995

Mechanical properties of human round window, basilar and Reissner's membranes.

In order to measure the mechanical strength of small and delicate biological specimens, a microtesting system was developed. We measured the mechanical properties of the round window, basilar and Reissner's membranes taken from the autopsied cases. The testing method was a displacement of the specimen by a force sensor needle until rupture. A load-displacement curve was then drawn and the mechanical value of each specimen was calculated. Reissner's membrane was the weakest, though it showed a measurable strength. From the load-displacement curve of the basilar membrane, it could be displaced by a smaller force than the rupture strength of Reissner's membrane. Speculation about the concept of a negative summating potential in Meniere's disease is therefore theoretically possible from a mechanical point of view.

Aged↗
PubMedDate not supplied

Role of the efferent medial olivocochlear system in contralateral masking and binaural interactions: an electrophysiological study in guinea pigs.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas. Particularly, contralateral BBN stimulation suppresses in part ipsilateral peripheral activity. What is the role of such contralaterally induced peripheral suppression in the overall changes in central BAEPs observed during contralateral masking or binaural stimulation? Compound action potentials (CAPs) of the auditory nerve and BAEPs were recorded simultaneously in awake guinea pigs from electrodes chronically implanted on the round window of the cochlea and the surface of the brain. Peripheral and central measures of contralateral masking and binaural interactions were obtained from responses to monaural or binaural clicks, with or without contralateral BBN, recorded before, during, and after the reversible blockade of the MOC function following a single intramuscular injection of gentamicin. Contralateral BBN effectively reduced the amplitudes of CAP and of all BAEP peaks. CAP to ipsilateral click did not, however, change significantly from monaural to binaural click stimulation; still, normal binaural interaction components developed in the BAEPs. When the medial efferent function was blocked by gentamicin, the normal contralateral BBN suppression of CAP and of the earliest BAEP peak was lost; however, the later BAEP peaks were suppressed by contralateral BBN as before gentamicin, and the central binaural interaction components were unchanged. In these experimental conditions, the MOC efferent system seems to play little role in centrally recorded contralateral masking and binaural interactions.

Animals↗
PubMedDate not supplied

Use of frequency modulation combined with amplitude change to elicit frequency-specific whole-nerve response.

The averaged whole-nerve response to frequency modulation combined with amplitude change was recorded from the round window of the guinea pig. A downward shift of 20% in the frequency of a 500-Hz, 1-kHz or 2-kHz pure tone with an amplitude increase elicited the responses. The latency for each frequency was investigated at different intensities. The latency is greater for lower-frequency tones and this latency increase agrees well with the traveling wave delay for the intensity range used in this study. A downward shift with an amplitude decrease failed to yield the response. These findings suggest that the response to a downward shift of frequency with an amplitude increase results from new activation due to an apical extension of the envelope of the traveling wave and thus represents the activity in a restricted area of the basilar membrane. Thus, the frequency-modulated tone in downward direction with increased amplitude can be a frequency-specific stimulus.

Acoustic Stimulation↗
PubMed1990

Perilymphatic fistula in the guinea pig.

Clinical reports on perilymphatic fistulae (PLF) of the round window membrane (RWM) have shown different degrees of hearing loss. However, the hearing can also be entirely unaffected. Experimentally induced PLF of the RWM in animals showed results similar to those of the clinical reports, although some researchers have concluded that perforation of the RWM per se does not necessarily induce significant hearing loss. The purpose of the present study was to clarify if, and how, PLF of RWM in the guinea pig actually affects the auditory action potentials. During 1 h of observation following perforation of the RWM, the immediate and continuous effect of the PLF was evaluated. In more than 50% of the animals, different amounts of threshold shift were obtained. In another group of guinea pigs an attempt was made to clarify the findings by reducing the cerebrospinal fluid pressure before perforating the RWM.

Animals↗
PubMedDate not supplied

Low-frequency biasing of round window responses in guinea pigs and chinchillas.

The acoustic biasing technique using low-frequency sound is of increasing interest to investigators, not only as a means of studying cochlear transduction but also as a promising tool for assessing cochlear pathology such as endolymphatic hydrops. We compared normal modulation patterns of round window responses in guinea pigs and chinchillas, whose low-frequency auditory characteristics are known to be different. A 50-Hz sine wave (90 dB SPL for guinea pigs and 80 dB SPL for chinchillas), which evoked an equivalent magnitude of cochlear microphonics (CM) in both species, was used to modulate the compound action potential (CAP) and the summating potential (SP) elicited by 8-kHz tone bursts. Overall patterns of CAP and SP modulation were almost identical between the two species except for a difference in the phase of 50 Hz CM. The phase of maximum SP enlargement was in accord with that of maximum CAP suppression, which led to inferred basilar membrane (BM) position at maximum scala tympani displacement by between 45 and 90 degrees. More complex or hysteresis effects seemed to be involved in the modulation of CAP and SP magnitude, in addition to the biasing effect owing solely to BM displacement.

Acoustic Stimulation↗
PubMedDate not supplied

Cochlear tuning in the gerbil: a comparison of responses to sinusoidal amplitude modulation and difference tone stimuli.

Vocalizations often have periodic variations of their acoustic waveform envelope. Two simultaneously presented frequencies have an envelope fluctuation with a frequency equal to their difference tone (DT = F2-F1). Sinusoidal amplitude modulation (SAM) of a carrier frequency also produces an envelope fluctuation. Electrical ensemble responses to DT and SAM stimuli were recorded from the gerbil's round window. The predominant frequency of the response to the DT stimuli is F2-F1; to the SAM stimuli, it is the modulation frequency. Both responses are spectrally, temporally, and dynamically non-linear. Forward masking of a low-frequency DT response produced a tuning curve (TC) with a tip at the high-stimulus frequency. Forward masker TCs of a low-frequency SAM ensemble response had tips at the high frequency of the carrier. Tip thresholds and sharpness of tuning of DT and SAM TCs are quite similar, with cochlear neurons having high characteristic frequencies providing sharply tuned information about low frequency acoustic envelope periodicities.

Animals↗
PubMed1982

Ototoxic effects of salicylates on the responses of single cochlear nerve fibres and on cochlear potentials.

Anaesthetized cats were given 400 mg/kg sodium salicylate i.v. producing blood levels in excess of 300-400 mg/kg. Within 10 min of injection, thresholds of fibers had risen by values ranging from 13 to 21 dB. The elevation in thresholds progressed rapidly over the subsequent 5 or so hours, reaching a plateau in about 10 h. The Q10 dB values for tuning of the cochlear fibres decreased by a factor of 3-4 on average over the same period. Likewise, the dynamic range of response was significantly reduced. These effects on the cochlear fibres were reflected in the elevation of the gross cochlear action potential thresholds. In contrast to the findings with other types of cochlear pathology, the mean discharge rate of the subpopulation of cochlear fibres having discharge rates above 20 sp/s was significantly increased by an average of 10-20 sp/s. There was a tendency for this increase to be more marked for fibres with higher characteristic frequencies and to be inversely related to threshold. In addition, 63% of fibres had anomalous temporal patterns of spontaneous activity. In view of the relevance of these data on the ototoxic effects of salicylates for our understanding of tinnitus, the effects of direct electrical current stimulation via the round window have been studied. Positive currents up to at least 600 microA suppressed the spontaneous and evoked activity of all cochlear fibres studied in the normal cochlea. These findings are consistent with the effects of such current stimulation in patients with tinnitus of peripheral origin and support the hypothesis that the neural correlate of such tinnitus is hyperactivity at the cochlear nerve level.

Animals↗
PubMed1999

[Surgical anatomy of the facial nerve and chorda tympani with special reference to cochlear implantation].

The surgical anatomy of the facial nerve (FN), chorda tympani nerve (CT) and round window (RW) in 26 Japanese temporal bone specimens was analyzed. The relationships were classified according to the relative position of these structures and the posterior wall of the external auditory canal (EAC). Most frequently, the widest approach route through the facial recess did not point directly at the RW, but rather at the basal turn. Moreover, the approach route crossed the FN-RW line in a posterior to anterior direction (76.9%) and the CT-RW line frequently crossed the posterior wall of the EAC (92.3%). The latter seemed to provide a critical landmark for avoiding damage to the CT during cochlear implant surgery. Therefore, we recommend inserting the electrode into the basal turn at the promontory. Several other anatomical indices were measured and we extracted the index which was related to the maximum approach amplitude and direction. Preoperative diagnosis may be possible using these indices.

Adolescent↗