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At least 253 records · Page 14Linked to original sources
PubMed1988

Changes of the permeability of round window membrane in otitis media.

The effects of endotoxin, exotoxin, and otitis media on the permeability of the round window membrane (RWM) in chinchillas was investigated by detecting tetraethylammonium chloride, applied to the RWM, using a potassium-selective microelectrode in the scala tympani. The RWM, 48 hours following the application of endotoxin or exotoxin, became significantly more permeable to tetraethylammonium chloride than the normal RWM. Two weeks after the obstruction of the eustachian tube, the permeability of the RWM was decreased. These results suggest that bacterial toxins and the consequential migration of chemical inflammatory mediators act as promotive factors of RWM permeability, and that a pathologic thickness of the RWM and the presence of effusion induced by the obstruction of the eustachian tube acts as an inhibitory factor. In the clinical role of RWM permeability in human otitis media, these two factors must be taken into consideration.

Animals↗
PubMed1988

Permeability of the human round-window membrane to cationic ferritin.

An ultrastructural study was done in three sequential steps to determine if the human round-window membrane was permeable to macromolecules. Cationic ferritin was first placed for one hour in the round-window niche of two live rhesus monkeys. The same tracer was then placed in the same manner in two rhesus monkeys that had been dead for one hour. In both groups, cationic ferritin was observed to traverse the round-window membrane through pinocytotic vesicles into the scala tympani. After establishing that the transport capabilities of the round-window membrane of the monkey remained present one hour after death, cationic ferritin was placed for one hour in the round-window niche of two humans who had been dead for 30 minutes and one hour. The tracer was observed to traverse the round-window membrane through pinocytotic vesicles into the scala tympani in both humans. This report may be the first to document morphologically the permeability of human round-window membranes to macromolecules.

Animals↗
PubMed1989

Middle-latency responses. II. Variation among stimulation sites.

We investigated the relationship between thresholds of the electrically evoked auditory brain-stem response (EABR) and the electrically evoked middle-latency response (EMLR), and the variation in EMLR thresholds and dynamic ranges with site of stimulation. The EABRs and EMLRs were recorded in albino guinea pigs in response to electrical stimulation at the round window, promontory, scala tympani, and modiolus. The EABR and EMLR thresholds were similar. There was no significant difference between thresholds for round-window and scala tympani stimulation. Amplitude/intensity functions for the EMLR differed with site of stimulation. The EMLR seems to be comparable with the EABR for assessing the electrical excitability of the auditory pathway with less electrical artifact contamination. In this respect, round-window and scala tympani stimulation sites are equally efficacious.

Animals↗
PubMed1992

Electrocochleographic recordings in acute and healed perilymphatic fistula.

In this study, the summating potential (SP) and action potential (AP) amplitude ratio was measured in 15 guinea pigs before and after surgical induction of a round window fistula. The round window fistula was then allowed to heal, and recordings were obtained after 1 month. Stimuli included 8000-Hz and 2000-Hz tone bursts and click stimuli at levels ranging from 100-dB peak equivalent sound pressure level to AP threshold. Immediately after fistula induction, a statistically significant enlargement in the SP/AP amplitude ratio occurred in response to the click and the 8000-Hz tone-burst stimuli. No change in the SP/AP amplitude ratio was observed for the 2000-Hz stimuli. After healing, the SP/AP amplitude ratio generally returned to prelesion values. No unhealed perilymphatic fistulas were observed in any of the 15 guinea pigs at 1 month after fistula induction. Considering the difficulty of diagnosing perilymphatic fistula in humans, it is encouraging to note that, at least in animals, noninvasive electrophysiologic recordings may perhaps be sensitive to the presence of patent perilymphatic fistula.

Action Potentials↗
PubMed2000

Topographical relationships among the facial nerve, chorda tympani nerve and round window with special reference to the approach route for cochlear implant surgery.

The topographical relationships among the facial nerve (FN), chorda tympani nerve (CT), and round window (RW) in 22 temporal bone specimens were analyzed morphometrically in order to examine which route is widest through the facial recess between the FN and CT during cochlear implant surgery and in order to establish some criteria to assist in the evaluation of the best surgical approach. Two lines, i.e., the FN-RW line and CT-RW line, were speculated as limitations of a visual field for this surgery. According to the relative position of these structures, including the posterior wall of the external auditory canal (EAC) and an inserted pin-gage that indicates the hypothetical widest approach route, the relationships were classified into five types. Most frequently, the widest approach route through the facial recess did not point directly at the RW, but at the basal turn at the promontory. Moreover, this approach route crossed the FN-RW line in a posterior to anterior direction and the CT-RW line frequently crossed the posterior wall of the EAC. 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.

Adolescent↗
PubMed1999

Ototoxicity of sodium nitroprusside is not due to nitric oxide.

Sodium nitroprusside (SNP) has been used as a donor for nitric oxide (NO) to study the effects of NO on the mammalian cochlea. In the present study, we set out to determine whether NO was the chemical responsible for the ototoxic effects seen after the application of SNP at the round window membrane of the adult guinea pig cochlea. In the first instance, NO released from S-nitrosocysteine, a compound not related to cyanide, has no toxic effect on the hair cells of the cochlea. Light-exposed SNP that could no longer produce NO, light-exposed SNP to which acetylcysteine (ATC) or hydroxycobalamin (HCL) was added to eliminate cyanide, and freshly prepared SNP to which ATC or HCL was added were also tested. Six groups of animals consisting of three animals in each group were used. The single chemical or combination of chemicals stated above was soaked in a piece of gelfoam that was then applied to the round window membrane of the animal under ketamine-xylasine anesthesia. The animals were reanesthetized 3 days later and perfused for scanning electron microscopy and hair cell quantitative analysis. The results showed that, in animals given S-nitrosocysteine, no hair cell loss was noted, while light-exposed SNP led to severe hair cell damage similar to that seen after the administration of fresh SNP. In animals treated with the mixture of light-exposed SNP and ATC or HCL, or fresh SNP with ATC or HCL, ototoxicity was significantly attenuated. These results have convincingly demonstrated that NO at a certain level is not destructive to auditory hair cells and the hair cell loss observed after SNP application is most likely due to the cyanide released from the SNP instead of NO.

Acetylcysteine↗
PubMed1995

Orientation for cochlear implant surgery in cases with round window obstruction: a computer reconstruction study.

In order to improve cochlear implant surgery in patients with obstructed round windows, surgical orientations of the round window and scala tympani relative to the stapes footplate were examined in ten normal temporal bones using a computer-aided, three-dimensional reconstruction and measurement technique. The round window was found to be exactly inferior to the midpoint of the inferior margin of the stapes footplate in most cases. An optimal point on the promontory wall for drilling to reach the bottom of the scala tympani of the basal turn was found to lie approximately 1.5 mm anterolateral or anterolateral inferior to a point 3 mm inferior to the midpoint of the inferior margin of the stapes footplate. A combination of the transmeatal and facial recess approaches made it possible to consistently reach the scala tympani, and demonstrated that this approach was also applicable to patients with obstructed round windows.

Adolescent↗
PubMed1995

Modulation of cochlear responses in the guinea pig by low-frequency, phase-shifted maskers following noise trauma.

Low-frequency acoustic biasing using an intensive phase-shifted, low-frequency masker was studied according to its ability to determine disorders of cochlear micromechanics following noise trauma in the guinea pig as animal model. Statistical analyses proved that this technique allowed electrophysiological differentiation of controls versus groups with different degrees of experimentally induced threshold shifts. To substantiate group differences an intensity of at least 70 dB SPL was required for the 52 Hz masker and the difference in relation to the test-tone intensity had to be +/- 10 or +/- 20 dB SPL. The noise-traumatized cochlea could be identified by means of a threshold shift for the 5 microV pseudothreshold, a low modulation span of the compound action potential amplitude (< 25-50 microV frequency dependent), and reduced positive summating potential amplitude with negative non-modulating values within the different measurement phases for 1 and 2 kHz stimulation.

Acoustic Stimulation↗
PubMed1992

Effects of anoxia on the cochlear summating potential in the guinea pig.

The cochlear summating potential (SP) was recorded extracochlearly from the apex and the round window in 25 guinea pigs, applying anoxia during periods of 1-2 min. For 2 and 8 kHz tone pips at 80 and 60 dB SPL, respectively, the initially negative SP at the apex diminished and even became positive during oxygen cut-off. After restoration of oxygenation, the change in SP reversed direction and was followed by a large negative undershoot. At the round window, the initially positive SP evoked by 8 kHz, 60 dB SPL tone pips followed exactly the same time course, but with inverted polarity, while the majority of the recordings of the initially negative SP evoked by 2 kHz, 80 dB SPL tone pips followed a course similar to the apical negative SP. However, the negative round window SP showed only slight polarity reversal and no undershoot. A small number of the recordings at the round window for 2 kHz showed an increase of the negative SP during anoxia followed by a decline of the SP and recovery after anoxia. The similar time course of the initially negative SP at the apex and the initially positive SP at the round window failed to support the hypothesis of a multi-component SP. However, the polarity reversal during anoxia and the different reactions to anoxia of the 2 kHz round-window SP suggest that the SP may consist of several different components.

Animals↗
PubMed1994

Holmium: YAG laser surgery in obliterated cochleas: an experimental study in human cadaver temporal bones.

A pulsed holmium:YAG laser (lambda = 2120 nm) was used to reopen the basal turn of artificially obliterated human cochleas in freshly dissected cadavers. This allowed intracochlear insertion of the stimulation electrode of a cochlear implant under simulated surgical conditions. Laser energy was transmitted through a 400-microns nylon fiber via the opened facial recess directly to the round window niche. At an energy level of 500 mJ per 2.5 microseconds pulse, a repetition rate of 2 Hz, and an exposure time of 20-30 s, the photo-ablative mechanism of laser-bone interaction led to a 8-10 mm recanalization of the basal turn of the cochlea without damaging surrounding structures. The artificial bony occlusion and the recanalized basal turn of the cochlea were visualized by means of computed tomography and studied under light microscopy, using a histologic thin-section technique.

Aluminum Silicates↗
PubMed1982

Cochlear mechanisms at low frequencies in the guinea pig.

The study of the cochlear microphonic and of the intracochlear sound pressure in guinea pigs shows that the behavior of the cochlea at very low frequencies is controlled by three discrete elements: (a) the compliance of the whole basilar membrane; (b) the acoustic resistance of the helicotrema; (c) the compliance of the round window. The part of each of these elements has been established. The compliance of the whole basilar membrane produces constant amplitudes at frequencies lower than the minimum frequency at which a travelling wave is present (130 Hz). In fact, this constant amplitude range is limited by connection of the two cochlear scalae through the helicotrema resistance. This protecting mechanism produces an attenuation slope for frequencies lower than 80 Hz. The compliance of the round window does not modify the slope of the cochlear microphonic, but it induces a constant sound pressure in scala tympani up to 200 Hz. Decreasing of the sound pressure in the scala vestibuli is, therefore, limited for frequencies less than 30 Hz by this constant value of the sound pressure in scala tympani.

Acoustic Stimulation↗
PubMed1989

Scanning electron microscopic studies of the capillaries crossing the scala tympani.

Scanning electron microscopic examinations were carried out on the perilymphatic space bordering the round window in guinea pigs. A number of small vessels were found crossing free through the lumen of the scala tympani in this area. The larger number (5-10) of these capillaries are suspended between the bony cochlear wall and the terminal net of fibrocytes which covers the cochlear opening of the cochlear aqueduct and spreads onto the basal third of the round window membrane. Other capillaries (3-5) cross the lumen of the scala tympani from the outer cochlear wall to the modiolus. All of these capillaries have a thin endothelium and a very thin pericytic covering. These findings suggest that the capillaries crossing the perilymphatic space may give rise to a different chemical composition of the perilymph bordering the round window in comparison with the more upper parts of the scala tympani.

Animals↗
PubMed1979

"Neural" responses to acoustic stimulation after destruction of cochlear hair cells.

Electrophysiological and histological observations in guinea pig's cochleas after amikacin treatment (14 X 450 mg/kg) confirm the results obtained in a former experiment: clear, short-latency, click-evoked responses were recorded in cochleas with only very few hair cells remaining at the extreme apex. Detailed analysis of these responses strongly indicates a neural origin and confirms their low-frequency sensitivity. Careful histological observations confirm the extensive hair cell loss and the preservation of nerve fibers in the remnants of the organ of Corti and of the vestibular sense organs. These results suggest that the acoustical vibrations either stimulate the vestibular receptors or act directly or through some kind of mechano-electrical transduction on the remaining cochlear nerve fibers.

Amikacin↗
PubMed1987

The effect of round window membrane rupture on endolymphatic and perilymphatic pressures.

We used a guinea pig model to investigate the effect of round window membrane rupture on endolymphatic and perilymphatic pressures under conditions known to increase these pressures: anoxia, hypercapnia, increased intracranial pressure, and occlusion of the vein of the cochlear aqueduct. When the round window membrane was not ruptured, increases in endolymphatic pressure paralleled the perilymphatic pressure following exposure to each of the experimental conditions. After the round window membrane had been ruptured, however, no increases in perilymphatic pressure or endolymphatic pressure were seen. These results suggest that endolymphatic pressure is dependent on perilymphatic pressure, even when the round window membrane is ruptured.

Animals↗
PubMed1978

[The structure of the round window membrane studied by thin section.- freeze-fracture- and scanning electron microscopic technique (author's transl)].

In thin sections of the round window membrane of chinchilla there were found tight junctions between the cells of the outer and of the inner cell layer as well. Their structure was demonstrated in freeze-fracture replica, and in the scanning electron microscope both faces of the membrane appeared uninterrupted. The tight junctions between the mucosal cells constantly became visible and are considered impermeable; however, the junctions connecting the mesothelial cells, which face the perilymph, demonstrated high susceptibility against differences in preparation and were structurally different.

Animals↗
PubMed1982

Frequency-dependence of early auditory evoked responses in the guinea pig.

Neural auditory responses in the guinea pig, monitored by surface electrodes (brain stem potentials and frequency-following responses) and by electrodes at the round window, were analyzed for evidence of frequency dependence in the range from 500 Hz to 15 kHz. The characteristics of the brain stem potentials and frequency-following responses with stimuli near threshold intensity for frequencies below 2 kHz indicate that this activity derives from the excitation of apical regions of the basilar membrane. The same interpretation applies to the potentials recorded at the round window. Comparison of the responses seen with surface electrodes and those appearing at the round window reveals that the broad potential PI of the brain stem response to low-frequency stimuli corresponds to the compound action potential, while the frequency-following responses correspond to phase-locked responses in the acoustic nerve.

Animals↗
PubMed1984

First results of chronic electrical stimulation with a round-window electrode in totally deaf patients.

A few patients who had become totally deaf in adulthood were chronically implanted with an electrode on the round window. Elicitable auditory sensations were limited but proved beneficial enough for a small portable stimulator to be suggested for everyday use. Over a period of several months subjects were monitored several times for a few days at the laboratory and trained to make better use of their prosthesis. Such a device appears safe and patients have become attached to its use. One subject suffering from tinnitus was also given another stimulator delivering positive direct current which suppresses the tinnitus.

Adult↗