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Results for “Round Window, Ear”

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At least 415 records · Page 23Linked to original sources
PubMed1991

Influence of topically applied adrenergic agents on cochlear blood flow.

This study was designed to assess the role of adrenergic receptors in the control of cochlear blood flow. Laser Doppler flowmetry was used to determine the effects of adrenergic drugs topically applied to the round window membrane of the cochlea. The relative influence of the various receptor types (alpha 1, alpha 2, beta 1, and beta 2) was examined by a selection of agonists and antagonists. The agonists norepinephrine and epinephrine, which have mixed alpha- and beta-receptor effects, and phenylephrine, a strong alpha 1-agonist, all induced a dose-dependent reduction in cochlear blood flow. The agonists isoproterenol (beta-active), salbutamol (alpha 2-active) had no effect on cochlear blood flow. Of the antagonists, when tested alone, only the selective alpha 1-antagonist prazosin had a direct effect on cochlear blood flow, demonstrating an increase in cochlear blood flow. The selective alpha 2-antagonist idazoxan, the beta-antagonist propranolol, and the unselective alpha-antagonist phentolamine had no effect on cochlear blood flow. Interaction studies of agonists and antagonists were performed to specifically define the receptor subclasses responsible for the cochlear blood flow increases with norepinephrine and epinephrine. The results are consistent with the presence of an alpha 1-adrenergic sympathetic control of cochlear blood flow.

Administration, Topical↗
PubMed2002

Quinine affects the response properties of compound action potentials elicited by periodic click trains.

The effects of systemically applied quinine on the compound action potential (CAP) were investigated in 5 guinea pigs. A dose of 200 mg/kg body weight of quinine hydrochloride was administered intramuscularly, and CAPs were recorded at the round window before and after administration. The CAP thresholds of the animals were elevated by 5 to 25 dB approximately 30 minutes after administration, and thresholds recovered in some animals during the experimental session. The CAP waveform elicited by the click train stimulus was abnormal after administration of quinine. The amplitude of the CAPs elicited by the second click was larger than that of those elicited by the first click. These changes may be induced by an abnormally broadened N1 response to the first click in the click train following quinine administration. In contrast, the CAP waveforms elicited by the second click and by the following clicks in the click train appeared normal.

Acoustic Stimulation↗
PubMed2002

Effects of nimodipine on salicylate ototoxicity.

The purpose of this study was to examine the effects of nimodipine on salicylate ototoxicity in guinea pigs. The compound action potential (CAP) was recorded at the round window, and the cochlear blood flow (CBF) was measured simultaneously from the lateral wall of the basal turn of the cochlea by laser Doppler flowmetry. After administration of salicylate (100 mg/kg), the CAP thresholds were significantly elevated, by 5 to 20 dB (p < .05), and the CBF was significantly decreased (p < .05). After administration of nimodipine (2 mg/kg), the CAP thresholds were unchanged, but the CBF had increased significantly (p < .05), while systemic blood pressure had decreased significantly (p < .05). Simultaneous administration of both salicylate (100 mg/kg) and nimodipine (2 mg/kg) resulted in significant elevation of the CAP thresholds (p < .05), while the CBF did not decrease. These results suggest that nimodipine prevents the decrease in CBF induced by salicylate, but that nimodipine does not prevent the deterioration in the CAP.

Action Potentials↗
PubMedDate not supplied

Electrical stimulation of the auditory nerve in cats. Long term electrophysiological and histological results.

Each of five cats (one congenitally deaf) had Pt-Ir electrodes placed in the modiolus. Some electrodes were stimulated with a 100 micronamp, 0.25 msec balanced biphasic 50/sec pulse for 2 hours for a total of 20 to 40 hours each over periods of several months. Pre- and poststimulation measures of click-evoked N1 responses, averaged brain stem potentials, and impedances showed no long-term effects of damage to the nerves. Light microscopy showed very acceptable tissue tolerance and no evidence of damage caused by electrical stimulation. The deaf cat had about 10% residual nerve fibers which responded to stimulation.

Animals↗
PubMedDate not supplied

Surgical treatment of recurrent perilymph fistula with anacusis.

A woman with substantiated well-preserved premorbid cochlear function developed right-sided anacusis due to a perilymph fistula twice at an interval of 20 months. The fistula was presumably a sequel to previous operative damage to the stapes footplate. On both occasions she was treated surgically with a good result.

Audiometry↗
PubMedDate not supplied

Anatomy of the round window niche.

The contributing elements to boundaries of the round window niche are superiorly the tegmen fossula fenestra rotunda (roof support), inferiorly the fustis (depth) and area concamerata, anteriorly the sustentaculum (support) and postis anterior (anterior pillar), and posteriorly the postis posterior (posterior pillar) and the subiculum (underlying supporting structure). Variations in their size and orientation can give rise to significant variability in the overall size and shape of the round window niche.

Cochlea↗
PubMed1989

Dimensions of and vibrations in the round window membrane in cats.

The shape and size of the round window membrane and its vibratory pattern were investigated in cats by use of an optical displacement meter and time-averaged holography. The round window membrane is convex toward the scala tympani and appears to be almost elliptic in shape. The major and minor axes of the membrane are 2,273 and 1,934 microns. The mean degree of convexity is 1,975 microns. Under vibration the area of maximum displacement occurs anteriorly-superiorly at low frequency. As frequency is increased, the maximum displaced area shifts posteriorly-superiorly, then breaks up into several segments.

Animals↗
PubMed1989

Role of perilymphatic fistula in sudden hearing loss: an animal model.

The electrophysiologic response of the guinea pig cochlea was monitored after sequential lesions to Reissner's membrane and the round window (RW). Action potential (AP) responses to click stimuli were recorded from the RW before and after discrete puncture-type lesions were created in the cochlear partition of the second turn. Observed decrements were typically minor, comparable to no greater than 10 dB attenuation of stimulus intensity. The RW membranes then were perforated to create perilymphatic fistulas. Further monitoring demonstrated a rapid (within 5 to 10 minutes), severe decrement in AP amplitude and latency, with complete loss of the AP within 1 hour. Control animals with RW perforations alone did not show these decrements. Correct placement of the second turn lesions was documented by histology. We conclude that discrete lesions in the cochlear duct are not reflected in the AP input-output functions unless there is a fluid leak from the RW, and thus present a possible model for idiopathic sudden hearing loss.

Action Potentials↗
PubMed1989

Cochlear implant revision: effects of reimplantation on the cochlea.

The removal of an indwelling cochlear implant electrode followed by reinsertion of a new device has been a maneuver of uncertain consequences to the cochlea and its surviving neural population. The present study was conducted in an attempt to elucidate the factors that determine whether a reimplantation procedure will be successful. Cochlear implantation followed by explantation and subsequent reimplantation was performed in eight adult cats. Evaluation of cochlear histopathology suggested a significant increase in electrode insertion trauma when there was proliferation of granulation tissue in the round window area and scala tympani. In other cases, atraumatic reinsertion was achieved without apparent injury to the cochlea. The results of a survey of cochlear implant manufacturers and surgeons indicate that electrode replacement can usually be accomplished without adverse effects. Difficulties have been encountered, however, in removing implants with protuberant electrodes and when reimplantation was attempted on a delayed basis following explantation.

Acute Disease↗
PubMed1990

Historical perspectives and concepts in otitis media research at the University of Minnesota.

The University of Minnesota Otitis Media Research Center, formed in 1978, comprises a multidisciplinary research team in the clinical fields of otolaryngology, pediatrics, audiology, and infectious disease as well as the basic science fields of histopathology, epidemiology, microbiology, immunology, biostatistics, pharmacology, physiology, and biochemistry. The team has focused on studies designed to elucidate the pathophysiology of the otitis media continuum, and considerable progress has been made in describing this continuum by using the basic science approaches available in the Center. The collaboration of basic and clinical scientists has created a synergy of goals, ideas, and methods leading to new hypotheses and progress, ultimately resulting in improved patient care methods.

Animals↗
PubMed1991

Electrode insertion trauma in cochlear implantation.

Residual hearing conservation may be important in cochlear implantation of children and of adults with disabling tinnitus responsive to extracochlear stimulation. Damage to the neural elements of the cochlea during electrode insertion may have a negative impact on residual hearing conservation. Histologic analysis of eight temporal bones with cochlear implants reveals trauma at essentially two locations: the round window insertion site and along the basal turn of the cochlea. In four of the bones, insertion at the round window resulted in damage to the osseous spiral lamina and the electrode was inserted through the scala media into the scala vestibuli. Evidence of secondary reactive osseous formation was also noted in these bones. This paper relates the surgical anatomy of the round window to histologic findings and microanatomical dissections. Recommendations for implantation surgery include creation of a cochleostomy by removal of the floor of the round window niche and a superior-to-inferior angle of electrode insertion.

Aged↗
PubMed1997

Summating potential and action potential gradients on and in the vicinity of the round window in guinea pig.

The purpose of this study was to determine the spatial gradients of summating potential (SP) amplitudes, action potential (AP) amplitudes, and SP/AP ratios for recording loci on the round window (RW) membrane and in its vicinity. Sixteen guinea pigs were tested by means of free-field click and tone burst (2.0 kHz) stimuli. Seven recording regions were specified: five equal-area regions on the RW membrane and two basal promontory regions. Statistically significant differences were found between the promontory regions and the RW membrane regions for the SP, AP, and SP/AP obtained with click stimuli, and for the SP and AP obtained with tone burst stimuli. The SP/AP ratio for tone burst stimuli did not differ significantly across the seven regions. The RW membrane was found to be isoelectric, but there were marked spatial gradients on the basal promontory. These results are of consequence for the interpretation of transtympanic electrocochleography recordings.

Animals↗
PubMedDate not supplied

Partial or total eighth nerve section in the treatment of vertigo.

Partial vestibular (singular) neurectomy under general anesthesia through a postauricular approach is an effective method of relieving incapacitating benign positional vertigo, as is the case in 14 of 16 patients (87%) so treated. Middle fossa vestibular neurectomy appears to be a worthwhile procedure to deinnervate the peripheral vestibular system while preserving hearing. The results of 27 middle fossa vestibular neurectomies indicate relief of vertigo in 85% of the patients. The results of treatment on 44 patients undergoing transmeatal-cochleovestibular neurectomy indicated that vertigo was relieved in 19 of 23 (82%) with Meniere's disease and improved in 50% of the patients with post-stapedectomy vertigo and sensorineural hearing loss. Tinnitus was cured or markedly improved in 80% of the patients with Meniere's disease and 70% of the patients with post-stapedectomy sensorineural hearing loss and tinnitus. The transmeatal-transcochlear approach to the internal auditory canal offers advantages over the transmeatal labyrinthectomy or translabyrinthine approach to the internal auditory canal.

Adult↗
PubMedDate not supplied

Singular neurectomy: hypotympanotomy approach.

A modified surgical technique is described for singular neurectomy. The hypotympanotomy approach provides greater ease in exposing the singular canal. Delayed round window overhang removal provides decreased risk of round window trauma. Eight cases done by this technique indicated a lower complication rate than any reported transmeatal series. Selection criteria, results, and complications are discussed. The risk of cochlear damage limits singular neurectomy to patients who are severely incapacitated by benign paroxysmal positional vertigo. Compared with vestibular neurectomy, singular neurectomy avoid risks inherent in intracranial procedures, and the vertigo caused by surgical intervention is less pronounced.

Adult↗
PubMedDate not supplied

Brain stem response evoked by electrical stimulation of the round window of the guinea pig.

The wave that is believed to correspond to wave V in man is an appropriate indicator of auditory nerve excitability because it is not contaminated by nonauditory neurogenic responses to electrical stimulation. The responses to direct electrical stimulation of the auditory nerve could be distinguished from the electrophonic response by the steep input-output function and constant latency of the former. Myogenic responses are prominent unless a muscle relaxant is administered.

Acoustic Stimulation↗
PubMedDate not supplied

Effect of site of stimulation on the guinea pig's electrically evoked brain stem response.

Stimulation by a bipolar modiolus electrode yields a wider dynamic range than does monopolar stimulation at the same site. Stimulation via a single electrode in the scala tympani or scala vestibuli is characterized by a precipitous input-output function, but current passing from one scala to the other generates a discontinuous function with a shallow slope at low intensities and a steep slope at high intensities.

Animals↗