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At least 469 records · Page 26Linked to original sources
PubMed2003

[Effects of round window membrane rupture on cochlear blood flow and endocochlear potential].

The degree of hearing loss and audiogram shape vary in patients with perilymphatic fistula. The cause of variability is not well known. To determine the effect of perilymphatic fistula on cochlear function, we studied the effect of round window membrane rupture on cochlear blood flow (CBF) by placing a laser-Doppler probe to the basal turn in 20 guinea pigs. In 10, endocochlear potential (EP) was measured by inserting a glass microelectrode through the stria vascularis of the basal turn. During 60 minutes following round window membrane rupture, CBF decrease of more than 15% was observed in 9 of 20 animals, and EP decrease of more than 15% was observed in 5 of 10. A significant correlation was observed between the degree of CBF reduction and EP reduction. In 3 animals in which CBF decreased after round window membrane rupture, temporal bones were studied histologically. One cochlea showed endolymphatic hydrops and another cochlea showed significant hemorrhage in the scala tympani after rupture. These results suggested that CBF impairment is associated with cochlear dysfunction in perilymphatic fistula.

Animals↗
PubMed1995

[Studies on the measurement of the mechanical properties of the round window membrane].

With a microtesting system which can measure the mechanical properties of small tissue membranes, we have measured the mechanical properties of the round window membrane on the guinea pigs and the human. We also found that, as a result of formalin-fixation, round window membranes become weaker and that this effect of formalin-fixation is greater on human round window membranes than on those of guinea pigs. Since the protein in collagen fibers, which are the main constituent of round window membranes, is coagulated and fixed with formalin, we consider that the strength of the membranes decreases and that this is more evident in human membranes, which contain more collagen fiber. Having compared the mechanical properties of the fresh round window membranes of guinea pigs with those of humans, we found that the human membranes are approximately five times stronger than those of guinea pigs. This difference is considered to stem from the species differences. Also, having compared the mechanical properties of the tympanic membranes with those of the round window membranes each species, we found that the round window membranes of guinea pigs are almost the same as their tympanic membranes in terms of strength, whereas human tympanic membranes are stronger and harder than the round window membranes. In view of the minimum pressure causing destruction of human round window membranes, as deduced from the experiment on guinea pigs, it is possible that human round window membranes may be ruptured in the perilymphatic fistula.

Adult↗
PubMed1999

Ototoxicity resulting from combined administration of metronidazole and gentamicin.

HYPOTHESIS: The hypothesis that metronidazole can augment the ototoxicity of gentamicin was tested. BACKGROUND: Metronidazole and gentamicin are antibiotics that are used in combination to provide broad-spectrum antimicrobial coverage. It has been observed clinically that an increased ototoxic effect occurs when these agents are used in combination. METHODS: Groups of guinea pigs were given various doses of gentamicin alone, various doses of gentamicin in combination with metronidazole, or metronidazole alone. Auditory damage was determined electrophysiologically by measurement of the compound action potential. Hair cell damage was quantified by immunofluorescent microscopy. RESULTS: Electrophysiologic data revealed an augmented ototoxic effect when metronidazole was given with both a moderate and a high dose of gentamicin. Thresholds (dB SPLp) for the compound action potential (N1) for animals receiving a medium dose of gentamicin alone (50 mg/kg) were approximately 20-dB SPLp. This threshold increased to approximately 50-dB SPLp when metronidazole (35 mg/kg) was administered along with the medium-dose gentamicin. Additionally, animals receiving high-dose gentamicin (75 mg/kg) alone demonstrated increased N1 thresholds from 85 to 95 when metronidazole (35 mg/kg) was added to the gentamicin regimen. This effect was evident histopathologically by increased cochlear hair cell damage. Outer hair cell loss for animals receiving medium-dose gentamicin alone did not differ from that of controls. When metronidazole (35 mg/kg) was combined, however, outer hair cell loss increased to approximately 50%. CONCLUSIONS: These data support the clinical observation of augmented ototoxicity in patients receiving combined gentamicin and metronidazole. Caution should be used when administering these two agents together. Clinicians should consider other antibiotic strategies whenever possible.

Animals↗
PubMed2000

Abnormal positive potentials in round window electrocochleography.

OBJECTIVE: To describe an atypical waveform, termed an abnormal positive potential (APP), on round window electrocochleograms (RW ECochG) of children and to relate its occurrence to clinical history. STUDY DESIGN: APPs were identified prospectively, and a retrospective analysis was made of these patients' clinical histories, audiograms, and auditory outcomes (hearing aid, cochlear implant, or nonauditory communication) SETTING: Tertiary referral teaching hospital, day surgery and clinics. PATIENTS: All 431 children <110 months of age suspected of a severe to profound hearing loss who underwent RW ECochG from January 1993 to August 1997. INTERVENTION: Diagnostic RW ECochG for auditory threshold estimation. MAIN OUTCOME MEASURE: The presence on the RW ECochG of the APP: an early positive potential in the absence of a compound action potential (CAP). RESULTS: An APP was observed in 34 children. The APP was most marked in response to clicks and 8-kHz tones. The APP click threshold averaged 70 dB hearing loss. The brainstem evoked potential of these children showed an absence of waves, or a broad positive wave with no subsequent waves. Twenty-nine of 30 behavioral audiograms obtained were indicative of severe to profound hearing loss. Auditory outcomes were available from 26 children; 45% of them derived no help from a hearing aid, and 8 children received a cochlear implant. Clinical factors frequently associated with APP were prematurity in combination with kemicterus or hypoxia. CONCLUSIONS: APP thresholds were lower than neural thresholds or behavioral thresholds. Children with APP need close follow-up, because half of those studied needed nonauditory strategies to develop effective communication.

Audiometry, Evoked Response↗
PubMed2002

Effects of furosemide applied chronically to the round window: a model of metabolic presbyacusis.

Hearing thresholds in elderly humans without a history of noise exposure commonly show a profile of a flat loss at low frequencies coupled with a loss that increases with frequency above approximately 2 kHz. This profile and the relatively robust distortion product otoacoustic emissions that are found in elderly subjects challenge the common belief that age-related hearing loss (presbyacusis) is based primarily on sensory-cell disorders. Here, we examine a model of presbyacusis wherein the endocochlear potential (EP) is reduced by means of furosemide applied chronically to one cochlea of a young gerbil. The model results in an EP that is reduced from 90 to approximately 60 mV, a value often seen in quiet-aged gerbils, with no concomitant loss of hair cells. Resulting measures of cochlear and neural function are quantitatively similar to those seen in aging gerbils and humans, e.g., a flat threshold loss at low frequencies with a high-frequency roll-off of approximately -8.4 dB/octave. The effect of the EP on neural thresholds can be parsimoniously explained by the known gain characteristics of the cochlear amplifier as a function of cochlear location: in the apex, amplification is limited to approximately 20 dB, whereas in the base, the gain can be as high as 60 dB. At high frequencies, amplification is directly proportional to the EP on an approximately 1 dB/mV basis. This model suggests that the primary factor in true age-related hearing loss is an energy-starved cochlear amplifier that results in a specific audiogram profile.

Action Potentials↗
PubMed2002

[Attical fixation of the malleus head associated with obstruction of the round window niche by a high jugular bulb].

OBJECTIVE: To report the case of a 52 year-old-woman presenting with a left mixed hearing loss. Surgical exploration revealed an attical fixation of the malleus head associated with obliteration of the round window by a high jugular bulb. METHOD: Surgical exploration revealed this rare association. Attical fixation of the malleus head was treated by a partial prosthesis. The mobility of the chain was normal at the end of the surgical exploration but it was not possible to search for the round window sign because the niche of the round window was obliterated by an high Jugular bulb. RESULTS: Audiogram was unchanged even if CT-scan confirm the good position of the partial prosthesis. CONCLUSION: Surgical treatment of an attical fixation of the malleus head do not seem to be necessary if it is associated with a simultaneous obliteration of the round window. Indeed, obstruction of the round window by a high Jugular bulb can caused a conductive hearing loss.

Female↗
PubMedDate not supplied

[Experimental perilymphatic fistula: the electrocochleographic findings].

The aim of the present study was to evaluate the effect of experimental perilymphatic fistula on cochlear electrophysiological responses. Six albino guinea pigs, in which recording electrodes were implanted in order to record the electrocochleogram, were used. Experimental protocol investigated cochlear responses before the induction of the fistula in the round window membrane perforation and then two month later. Compound action potential thresholds increased immediately after perforation of the round window membrane. The thresholds rapidly recovered. This phenomenon was accompanied by clear-Out reduction in amplitude upon suprathreshold stimulation. This latter observation associated with a decrease in the amplitude of the threshold seems to be a specific audiologic sign of the fistula. The clinical implication are discussed.

Acoustic Stimulation↗