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At least 775 records · Page 43Linked to original sources
PubMed1993

Endolymphatic sac morphology after instillation of hyperosmolar hyaluronan in the round window niche.

One hundred and sixty-eight mice were injected with hyaluronan (HA) of varying tonicity in the middle ear and compared with 81 control animals to study the effects of hypertonic solutions in the middle ear on inner ear fluid homeostasis and endolymphatic sac (ES) response. Six hours after 1.9% HA and 4, 6 and 8 h after 4% HA deposition there was a significant increase in the proportion of granule-containing light epithelial cells in the ES as compared with controls indicating an enhanced secretory activity from the epithelial lining. Six, 8 and 10 h after deposition of 4% HA, the ES volume was significantly reduced. The secretory activity and the ability of the ES to vary its volume could be specific responses to dehydration of the inner ear resulting from the high colloid osmotic pressure exerted by concentrated HA. The secretion of high-molecular substances into the ES may serve to keep the ES lumen patent and thus ensure a proper ES function and/or to regulate the intralabyrinthine volume and fluid pressure. Whether the findings may have clinical relevance for Ménière's patients remains to be elucidated.

Animals↗
PubMed1999

On a novel type of neuron with proposed mechanoreceptor function in the human round window membrane--an immunohistochemical study.

An immunohistochemical study was performed on surgically obtained human fresh cochlear tissue, using synaptophysin antibodies. After immediate aldehyde fixation and decalcification in Na-EDTA serial cryosections were made of the cochlea including the round window membrane (RWM). Apart from highly specific immunostaining of spiral ganglion cells and unmyelinated nerve fibers an immunoreactive neuroreceptor could be demonstrated at the postero-medial insertion of the RWM. The perikaryon showed intense synaptophysin immunoreativity with a distal process projecting into the fibrous stroma of the RWM displaying structural specializations suggestive of a mechanoreceptor function. It is speculated whether the neuroreceptor may be involved in the proprioception and/or mechanoreception of tensile forces generated within the lamina propria during displacement of the yielding RWM in the bony labyrinth. Such a function could be important for the regulation of perilymph pressure.

Basilar Membrane↗
PubMed1981

Passage of albumin from the middle ear to the inner ear in otitis media in the chinchilla.

A study of the permeability of the middle ear-inner ear interface for macromolecules was carried out in chinchillas with open and obstructed eustachian tubes utilizing tritiated human serum albumin and immunoelectrophoresis. Tritiated albumin was placed in the round window niche area or normal animals and animals in which the eustachian tubes had been obstructed for 24 hours or 14 days. The tritiated albumin was allowed to remain in the middle ear cavity for 24 hours, Samples of middle ear effusion, perilymph, blood and cerebrospinal fluid were collected and measured for radioactivity. Radioactivity was demonstrated in the perilymph. Samples of middle ear effusions and perilymph were also studied by immunoelectrophoresis with goat antihuman albumin. Albumin placed in the round window niche of an experimental animal could be recovered unchanged in the perilymph. The results suggest a pathophysiologic explanation for the association of otitis media and sensorineural hearing loss or endolymphatic hydrops.

Animals↗
PubMed1998

How body size affects middle-ear structure and function and auditory sensitivity in gekkonoid lizards.

Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered to the tympanic membrane than when it was delivered to the columella footplate. The findings show clearly that increased body size (or age) is accompanied by functional changes in the auditory periphery.

Action Potentials↗
PubMed1995

Effects of electrical current configuration on potential fields in the electrically stimulated cochlea: field models and measurements.

Potential distributions measured within the scala tympani of the anesthetized guinea pig support the assertion that focusing is possible when currents are appropriately delivered to the electrodes in the scala tympani. Results obtained with a lumped-element model agree with measurements made in the inner ears of monkeys during monopolar and bipolar stimulation. The predictions are closer for potential distributions apical to the stimulating electrode than they are for basal distributions. In one monkey, in which electrodes were implanted in the middle ear as well as in the inner ear, we obtained measurements of the impedance from inside the scala tympani to points within the middle ear. These impedances are smaller that those initially used in the model, in which the round window membrane was assumed to have a relatively high impedance. A model of the common ground configuration was developed using finite electrode impedances. Finite impedances broaden the potential distributions in this model. Potential distributions from the lumped element model are compared with those obtained with an analytical model, to suggest ways in which focused and unfocused stimuli can affect the excitation of neurons in the implanted ear.

Animals↗
PubMed2000

Reoperations after cochlear implantation.

During the 14-year history of cochlear implantation at Semmelweis University, 95 implantations were performed. There were 15 reoperations, and 2 patients had been operated 3 times. All of the reoperated patients received round window or intracochlear MedE1 devices. Successful reinsertion of the electrode was performed without significant difficulty, though in some cases osteoneogenesis was found in the round window or in the scala tympani. None of the patients suffered any inner ear abnormalities due to the first implant, and even the patient with a third implant in the same ear had excellent results and obtained better discrimination scores with the new device. In the authors' opinion, on the basis of the accumulated experience of nearly 100 implantations and 15 reoperations, replacement of the early generation extracochlear implants is most advisable and can be accomplished without adverse effects.

Cochlear Implantation↗
PubMed1995

Sound pressure gain produced by the human middle ear.

The acoustic function of the middle ear is to match sound passing from the low impedance of air to the high impedance of cochlear fluid. Little information is available on the actual middle ear pressure gain in human beings. This article describes experiments on middle ear pressure gain in six fresh human temporal bones. Stapes footplate displacement and phase were measured with a laser Doppler vibrometer before and after removal of the tympanic membrane, malleus, and incus. Acoustic insulation of the round window with clay was performed. Umbo displacement was also measured before tympanic membrane removal to assess baseline tympanic membrane function. The middle ear has its major gain in the lower frequencies, with a peak near 0.9 kHz. The mean gain was 23.0 dB below 1.0 kHz, the resonant frequency of the middle ear; the mean peak gain was 26.6 dB. Above 1.0 kHz, the second pressure gain decreased at a rate of -8.6 dB/octave, with a mean gain of 6.5 dB at 4.0 kHz. Only a small amount of gain was present above 7.0 kHz. Significant individual differences in pressure gain were found between ears that appeared related to variations in tympanic membrane function and not to variations in cochlear impedance.

Acoustic Stimulation↗
PubMedDate not supplied

The pathway enabling external sounds to reach and excite the fetal inner ear.

The human fetus in utero is able to respond to sounds in the amniotic fluid enveloping the fetus after about 20 weeks gestation. The pathway by which sound reaches and activates the fetal inner ear is not entirely known. It has been suggested that in this total fluid environment, the tympanic membrane and the round window membrane become 'transparent' to the sound field, enabling the sounds to reach the inner ear directly through the tympanic membrane and the round window membrane. It is also possible that sounds reach the inner ear by means of tympanic membrane--ossicular chain--stapes footplate conduction (as in normal air conduction). There is also evidence that sounds reach the fetal inner ear by bone conduction. Several animal and human models of the fetus in utero were studied here in order to investigate the pathway enabling sounds to reach and activate the fetal inner ear. This included studying the auditory responses to sound stimuli of animals and humans under water. It was clearly shown in all the models that the dominant mechanism was bone conduction, with little if any contribution from the external and middle ears. Based on earlier experiments on the mechanism and pathway of bone conduction, the results of this study lead to the suggestion that the skull bone vibrations induced by the sound field in the amniotic fluid enveloping the fetus probably give rise to a sound field within the fetal cranial cavity (brain and CSF) which reaches the fetal inner ear through fluid communication channels connecting the cranial cavity and the inner ear.

Animals↗
PubMed2005

The relationship of the round window membrane to the cochlear aqueduct shown in three-dimensional imaging.

The round window membrane and cochlear aqueduct complex in the guinea pig are reconstructed with 3D-imaging, using orthogonal plane fluorescence optical sectioning (OPFOS). The 3D-images show that the periotic duct and the aqueduct are connected to a pouch-like extension of the round window. The function of this may be regulation of aqueduct flow resistance under the influence of a pressure difference between inner ear fluid and middle ear.

Animals↗
PubMed2001

Quantitative anatomy of the round window and cochlear aqueduct in guinea pigs.

In order to analyze the entry of solutes through the round window membrane, a quantitative description of round window anatomy in relationship to scala tympani is required. High-resolution magnetic resonance microscopy was used to visualize the fluid spaces and tissues of the inner ear in three dimensions in isolated, fixed specimens from guinea pigs. Each specimen was represented as consecutive serial slices, with a voxel size of approximately 25 microm(3). The round window membrane, and its relationship to the terminal portion of scala tympani in the basal turn, was quantified in six specimens. In each image slice, the round window membrane and scala tympani were identified and segmented. The total surface area of the round window membrane averaged 1.18 mm(2) (S.D. 0.08, n=6). The length and variation of cross-sectional area as a function of distance for the cochlear aqueduct was determined in five specimens. The cochlear aqueduct was shown to enter scala tympani at the medial limit of the round window membrane, which corresponded to a distance of approximately 1 mm from the end of the scala when measured along its mid-point. These data are of value in simulating drug and other solute movements in the cochlear fluids and have been incorporated into a public-domain simulation program available at http://oto.wustl.edu/cochlea/.

Animals↗
PubMed1995

Middle ear mechanics of type IV and type V tympanoplasty: I. Model analysis and predictions.

An analysis of type IV and type V tympanoplasty procedures was performed using a quantitative model of the acoustic and mechanical properties of the stapes, cochlea, round window shield, and cavum minor air space. Realistic values for the impedance of these structures were determined from anatomic and functional measurements in normal ears. These model values lead to predicted type IV hearing results that match well with the best surgical results over a broad frequency range (125-4000 Hz). A parametric study of alterations in the model impedances reveals that a good hearing result depends on a mobile stapes, proper aeration of the cavum minor air space, and a sufficiently stiff graft shield. Intersubject variations in the cochlear impedance also can have a significant effect on the postsurgical hearing response.

Acoustic Impedance Tests↗
PubMed1980

Sound pressures in the basal turn of the cat cochlea.

Techniques were developed for measuring sound pressure in the cochlea with calibrated, liquid-filled, piezoelectric probe microphones. Sound pressures were measured in scala vestibuli and scala tympani in the basal turn in 25 cats for tones from 20--10 000 Hz. Control experiments indicated that intracochlear pressures were essentially uninfluenced by the measuring technique, and were conducted to the cochlea via the ossicular chain. Intracochlear pressures are linearly related to pressure at the tympanic membrane for tone levels at least as high as 105 dB SPL, and are relatively independent of depth of probe insertion in the scalae. The transfer ratio of sound pressure in scala vestibuli to that at the tympanic membrane increases in magnitude over the frequency range 50--1000 Hz to reach a maximum value of 15--30 dB, and decreases at higher frequencies, thus demonstrating that the middle ear provides a frequency-dependent pressure gain. At frequencies below 40 Hz, the pressures in scala vestibuli and scala tympani are approximately equal and are both determined by the round-window membrane compliance. At frequencies above 100 Hz, the round-window membrane impedance is small compared to the acoustic input impedance of the cochlea, and the pressure in scala vestibuli considerably exceeds that in scala tympani; consequently, the pressure difference across the cochlear partition is approximately equal to the pressure in scala vestibuli.

Animals↗
PubMed1998

Toynbee Memorial Lecture 1997. Middle ear mechanics in normal, diseased and reconstructed ears.

A review of the structure-function relationships in normal, diseased and reconstructed middle ears is presented. Variables used to describe the system are sound pressure, volume velocity and acoustic impedance. We discuss the following: (1) Sound can be transmitted from the ear canal to the cochlea via two mechanisms: the tympanoossicular system (ossicular coupling) and direct acoustic stimulation of the oval and round windows (acoustic coupling). In the normal ear, middle-ear pressure gain, which is the result of ossicular coupling, is frequency-dependent and smaller than generally believed. Acoustic coupling is negligibly small in normal ears, but can play a significant role in some diseased and reconstructed ears. (2) The severity of conductive hearing loss due to middle-ear disease or after tympanoplasty surgery can be predicted by the degree to which ossicular coupling, acoustic coupling, and stapes-cochlear input impedance are compromised. Such analyses are used to explain the air-bone gaps associated with lesions such as ossicular interruption, ossicular fixation and tympanic membrane perforation. (3) With type IV and V tympanoplasty, hearing is determined solely by acoustic coupling. A quantitative analysis of structure-function relationships can both explain the wide range of observed post-operative hearing results and suggest surgical guidelines in order to optimize the post-operative results. (4) In tympanoplasty types I, II and III, the hearing result depends on the efficacy of the reconstructed tympanic membrane, the efficacy of the reconstructed ossicular chain and adequacy of middle-ear aeration. Currently, our knowledge of the mechanics of these three factors is incomplete. The mechanics of mastoidectomy and stapedectomy are also discussed.

Biomechanical Phenomena↗
PubMed1984

Comparison of electrode sites in electrical stimulation of the cochlea.

There is considerable controversy about the "best" location for single channel cochlear implant electrodes. We measured the electrically induced auditory brain stem response (EABR) in a series of normal to totally denervated cat ears in response to promontory (P), round window (RW) and scala tympani (ST) stimulation. The status of the ganglion cell population was then assessed by light microscopy. In ears with light to medium ganglion cell loss the ST EABR yielded the most definitive input-output functions. RW responses were present at increased thresholds and smaller peak amplitudes. P responses were worse or even missing completely. In severely damaged ears, including some with no detectable ganglion cells, ST and RW EABRs were both markedly reduced with considerable overlap between the two sites. P responses, when present, were almost buried in the electrical noise near threshold. Extrapolating these results to humans suggests that when ganglion cell loss is very severe the RW or ST is an acceptable stimulation site. When ganglion cell loss is moderate or better, ST electrodes are superior.

Animals↗
PubMed1986

Basilar membrane mechanics at the base of the chinchilla cochlea. II. Responses to low-frequency tones and relationship to microphonics and spike initiation in the VIII nerve.

Low-frequency stimuli (40- to 1000-Hz tones) have been used to correlate the motion of the 8-to 9-kHz place of the chinchilla basilar membrane with the cochlear microphonics recorded at the round window and with the responses of auditory nerve fibers with appropriate characteristic frequency. At the lowest stimulus frequencies, maximum displacement of the basilar membrane toward scala tympani occurs in near synchrony with maximum rarefaction at the eardrum and maximum negativity at the round window; at higher frequencies, the mechanical and microphonic response phases progressively lag rarefaction, reaching - 240 deg at 1000 Hz. At most frequencies (40-1000 Hz) near-threshold neural responses, once corrected for neural travel-time and synaptic delays, somewhat lead (by some 40 deg) maximal scala tympani displacement and maximal negativity of the round window microphonics. The variation of sensitivity with frequency is similar for basilar membrane displacement and microphonic responses: Under open-bulla conditions, sensitivity is constant for frequencies between 100 and 1000 Hz; below 100 Hz, sensitivity decreases at rates close to 12 dB/oct toward lower frequencies. Neural response sensitivity matches BM displacement more closely than BM velocity.

Action Potentials↗
PubMed2000

Frequency characteristics of sound transmission in middle ears from Norwegian cattle, and the effect of static pressure differences across the tympanic membrane and the footplate.

For 23 cadaver ears from Norwegian cattle, frequency characteristics for the round-window volume displacement relative to the sound pressure at the eardrum have been measured, and are compared to earlier results for human ears [M. Kringlebotn and T. Gundersen, J. Acoust. Soc. Am. 77(1), 159-164 (1985)]. For human as well as for cattle ears, mean amplitude curves have peaks at about 0.7 kHz. At lower frequencies, the mean amplitude for cattle ears is about 5 dB smaller than for human ears. The amplitude curves cross at about 2 kHz, and toward higher frequencies the amplitude for cattle ears becomes increasingly larger. If amplitude curves are roughly approximated by straight lines above 1 kHz, the slope for cattle ears is about -5 dB/octave as compared to about -15 dB/octave for human ears. The phase of the round-window volume displacement lags behind the phase of the sound pressure at the tympanic membrane. The phase lag is close to zero below 0.2 kHz, but increases to about 3.5 pi at 20 kHz for cattle ears, as compared to less than 2 pi for human ears. Further investigations are needed in order to explain the observed differences. Sound transmission in the ear decreases with an increasing static pressure difference across the tympanic membrane, especially at frequencies below 1 kHz, where pressure differences of 10 and 60 cm water cause mean transmission losses of about 10 and 26 dB, respectively, the losses being somewhat larger for overpressures than for underpressures in the ear canal. At higher frequencies, the transmission losses are smaller. For small overpressures, and in a limited frequency range near 3 kHz, even some transmission enhancement may occur. Static pressure variations in the inner ear have only a minor influence on sound transmission. Static pressures relative to the middle ear in the range 0-60 cm water cause mean sound transmission losses less than 5 dB below 1 kHz, and negligible losses at higher frequencies.

Animals↗