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PubMed2002

A model for perilymphatic fistula induced hearing loss in the guinea pig cochlea.

In cases of sudden, reversible hearing loss where perilymphatic fistulas are thought to be the cause, a multitude of causes have been postulated. These include perilymphatic pressure changes, Simmons' double-break theory, perilymphatic hemorrhage, pneumolabyrinth, and others. This study was proposed to explore the role pneumolabyrinth may have in this pathology. Guinea pigs were fitted with cochlear perfusion pumps pumping artificial perilymph into the left scala tympani. One group of animals received a bubble ( approximately 1.5-2 microl) introduced into the scala tympani while the other group of animals received continuous infusion of artificial perilymph. The animals' cochlear function was monitored using distortion product otoacoustic emissions (DPOAEs) while the animals' behavior was assessed to evaluate for vestibular dysfunction. While unaffected by pump surgery, animals that received air into the scala tympani had their DPOAEs eliminated by day 2 after pump placement. On day 6, positional changes in the DPOAEs were observed where the left lateral decubitus position showed a sharp demarcation at 4 kHz, where lower DPOAE frequencies were abolished and higher ones minimally affected, with DPOAEs normal in the prone position. By days 8 and 20, DPOAEs recovered to normal amplitudes. Vestibular dysfunction was never detected in any animal that received a pneumolabyrinth. All control animals receiving a continuous perilymph infusion exhibited no loss of cochlear function throughout the testing period. The reversible nature of pneumolabyrinth induced hearing loss and the pneumolabyrinth's sole presence (without other possible causes of hearing loss, such as pressure differentials or round window membrane perforations) are powerful indicators of the role of air in the pathology of perilymphatic fistulas. In addition, the fluctuation of the hearing loss with positional changes supports the use of positional audiometry when evaluating perilymphatic fistulas.

Air↗
PubMed1992

Low-frequency modulation of compound action potential in experimental perilymphatic fistula and endolymphatic hydrops.

We have tested the hypothesis that the cause of cochlear dysfunction associated with perilymphatic fistula (PLF) is closely related to endolymphatic hydrops (ELH). Using guinea pigs, we studied the tone-burst elicited compound action potential (CAP) and its modulation as caused by a 50 Hz biasing tone in experimental PLF. We compared these results with those of experimental ELH. Following perilymph aspiration through the perforated round window membrane, mild but significant elevations of CAP thresholds at tested frequencies were found. A reduction in the amplitude of cochlear microphonics (CM) for a 50 Hz sine wave appeared to correlate with these CAP threshold changes. However, there were no significant changes in the modulation effect of the 50 Hz biasing tone on the CAP elicited by an 8 kHz tone burst. This finding differed from that in ears with experimental ELH, in which significant reductions of both 50 Hz CM and the degree of CAP modulation were consistently observed. We concluded that it is unlikely that the underlying mechanisms of a modification to the low frequency response of the base of the cochlea following perilymph aspiration is linked to that of experimental ELH.

Acoustic Stimulation↗
PubMed2006

Fate of embryonic stem cells transplanted into the deafened mammalian cochlea.

Spiral ganglion neurons (SGNs), the primary afferent neurons of the cochlea, degenerate following a sensorineural hearing loss (SNHL) due to lack of trophic support normally received from hair cells. Cell transplantation is emerging as a potential strategy for inner ear rehabilitation, as injected cells may be able to replace damaged SGNs in the deafened cochlea. An increase in the number of surviving SGNs may result in improved efficacy of cochlear implants (CIs). We examined the survival of partially differentiated mouse embryonic stem cells (MESCs), following xenograft transplantation into the deafened guinea pig cochlea (n=15). Cells were delivered directly into the left scala tympani via microinjection through the round window. Small numbers of MESCs were detected in the scala tympani for up to 4 weeks following transplantation and a proportion of these cells retained expression of neurofilament protein 68 kDa in vivo. While this delivery method requires refinement for effective long-term replacement of damaged SGNs, small numbers of MESCs were capable of survival in the deafened mammalian cochlea for up to 4 weeks, without causing an inflammatory tissue response.

Animals↗
PubMed1985

Technique and indications for the French multichannel cochlear implant "Chorimac-12" for total deafness rehabilitation.

To obtain some speech discrimination without lip reading it is necessary to elicit different frequency sound sensations in the totally deaf cochlea. Thus, electrically proofs compartments must be created all along the cochlear keyboard. The placement of twelve intracochlear electrodes is greatly facilitated by using our electrode-bearer, which is introduced through the round window by a posterior tympanotomy approach. However, partial or complete ossification of the cochlea may sometimes necessitate the use of our first technique of placement of electrodes one by one with Silastic pieces through twelve cochlear fenestrations. The indications for implanting depend on certain immutable criteria (total deafness, auditory response to electrical stimulation of the round window, patient's motivation), but other criteria are also described and discussed (socialization level, cochlear ossification, and preoperative electrophysiologic data). Associated handicaps (autism, blindness, tetraplegia) are not contraindications and often represent supplementary reasons for implantation.

Adolescent↗
PubMed2006

Surgical aspects of cochlear implantation: mechanisms of insertional trauma.

The development of hybrid electroacoustic devices has made conservation of residual hearing an important goal in cochlear implant surgery. Our laboratory has recently conducted anatomical studies directed toward better understanding mechanisms underlying loss of residual hearing associated with electrode insertion. This paper provides an overview of observations based on microdissection, scanning electron microscopy and temporal bone histology relating to inner ear injury that may occur during implant surgery. Trauma to cochlear structures including lateral wall tissues, the basilar membrane, the osseous spiral lamina and the modiolus is considered in relation to the implications of specific types of injury for hearing preservation. These findings are relevant to the design of future implant devices and to various important issues regarding the surgical technique used for implantation, including the possible use of the round window as a portal of entry for electrode insertion.

Cochlea↗
PubMed1988

The shape of the ear's temporal window.

This article examines the idea that the temporal resolution of the auditory system can be modeled using a temporal window (an intensity weighting function) analogous to the auditory filter measured in the frequency domain. To estimate the shape of the hypothetical temporal window, threshold was measured for a brief sinusoidal signal presented in a temporal gap between two bursts of noise. The duration of the gap was systematically varied and the signal was placed both symmetrically and asymmetrically within the gap. The data were analyzed by assuming that the temporal window had the form of a simple mathematical expression with a small number of free parameters. The values of the parameters were adjusted to give the best fit to the data. The analysis assumed that, for each condition, the temporal window was centered at the time giving the highest signal-to-masker ratio, and that threshold corresponded to a fixed ratio of signal energy to masker energy at the output of the window. The data were fitted well by modeling each side of the window as the sum of two rounded-exponential functions. The window was highly asymmetric, having a shallower slope for times before the center than for times after. The equivalent rectangular duration (ERD) of the window was typically about 8 ms. The ERD increased slightly when the masker level was decreased, but did not differ significantly for signal frequencies of 500 and 2000 Hz. The temporal-window model successfully accounts for the data from a variety of experiments measuring temporal resolution. However, it fails to predict certain aspects of forward masking and of the detection of amplitude modulation at high rates.

Adult↗
PubMed2006

Demonstration of a longitudinal concentration gradient along scala tympani by sequential sampling of perilymph from the cochlear apex.

Local applications of drugs to the inner ear are increasingly being used to treat patients' inner ear disorders. Knowledge of the pharmacokinetics of drugs in the inner ear fluids is essential for a scientific basis for such treatments. When auditory function is of primary interest, the drug's kinetics in scala tympani (ST) must be established. Measurement of drug levels in ST is technically difficult because of the known contamination of perilymph samples taken from the basal cochlear turn with cerebrospinal fluid (CSF). Recently, we reported a technique in which perilymph was sampled from the cochlear apex to minimize the influence of CSF contamination (J. Neurosci. Methods, doi: 10.1016/j.jneumeth.2005.10.008 ). This technique has now been extended by taking smaller fluid samples sequentially from the cochlear apex, which can be used to quantify drug gradients along ST. The sampling and analysis methods were evaluated using an ionic marker, trimethylphenylammonium (TMPA), that was applied to the round window membrane. After loading perilymph with TMPA, 10 1-muL samples were taken from the cochlear apex. The TMPA content of the samples was consistent with the first sample containing perilymph from apical regions and the fourth or fifth sample containing perilymph from the basal turn. TMPA concentration decreased in subsequent samples, as they increasingly contained CSF that had passed through ST. Sample concentration curves were interpreted quantitatively by simulation of the experiment with a finite element model and by an automated curve-fitting method by which the apical-basal gradient was estimated. The study demonstrates that sequential apical sampling provides drug gradient data for ST perilymph while avoiding the major distortions of sample composition associated with basal turn sampling. The method can be used for any substance for which a sensitive assay is available and is therefore of high relevance for the development of preclinical and clinical strategies for local drug delivery to the inner ear.

Animals↗
PubMed1977

Perilymph fistulas secondary to gunshot wound. Localization with a radioactive pharmaceutical.

The symptoms, clinical evaluation, routes of formation, and repair of perilymph fistulas are reviewed. We report a case with oval and round window perilymph fistulas secondary to a gunshot wound. A radioactive pharmaceutical was injected into the subarachnoid space in the lumbar area. Subsequent radioactivity was detected at the sites of the fistulas. We discuss the implications and a suggested technique for fistula detection.

Adult↗
PubMed1992

Repeated measurements of compound action potential: evaluation of the ototoxicity of otic drops.

Consecutive CAP threshold shifts were studied in chinchillas following round window application of Cortisporin Otic Suspension for 10 minutes. A marked deterioration in CAP threshold was observed at 24 hours following otic application but these threshold shifts were reversible at lower frequencies. The shifts were progressive at higher frequencies at the 4 week measurement. The progressive high frequency loss with recruitment and with normal EP levels implies some hair cell dysfunction due directly to Cortisporin Otic Suspension ototoxicity and/or secondarily to middle ear inflammatory reactions to the otic. Short-term studies of ototopical drugs may result in misleading assessments as to the pattern and degree of ototoxicity. Long-term (i.e., one month or longer) studies are recommended for accurate ototoxicity assessment.

Action Potentials↗
PubMed2006

Cochlear function after selective spiral ganglion cells degeneration induced by ouabain.

BACKGROUND: Ouabain, a cardiac glycoside that specifically binds to Na/K-ATPase and inhibits its activity, was applied to gerbils to develop a method for studying auditory neuropathy. METHODS: Ouabain was applied to the round window of the cochlea in each gerbil by using a piece of gelfoam with 3 microl or 24 microl (1 mmol/L) ouabain solution. The changes of the threshold of auditory brainstem response, cochlear function round window electrocochleography, as well as the morphological changes of the spiral ganglion cells of the cochlea were observed after application of ouabain for 24 hours or 96 hours. RESULTS: In ouabain treated gerbils, auditory brainstem response and compound action potential thresholds showed either elevation or no response at all. However, the thresholds of cochlear microphonic and distortion product otoacoustic emissions were not affected. Degeneration and necrosis of some spiral ganglion cells in ears with applications of ouabain (24 hours, 3 microl, 1 mmol/L; 96 hours, 24 microl, 1 mmol/L ouabain). The number of spiral ganglion cells was decreased (24 hours, 3 microl, 1 mmol/L ouabain) or near to a total loss (96 hours, 24 microl, 1 mmol/L ouabain). CONCLUSIONS: These results indicate a high degree of independence between the spiral ganglion cells and the outer hair cell systems in the cochlear transduction mechanism. The method used in this study would provide a valuable tool for studying auditory neuropathy.

Action Potentials↗
PubMed1989

Kinetic experiments with radionuclides concerning the perilymph-blood barrier in a guinea pig model.

Since 1950 many animal radiotracer experiments have been performed to study inner ear kinetics. For the most part in these studies, radionuclides were applied systemically, following which a discontinuous probing of inner ear fluids or of inner ear tissues was done. Two techniques have been developed in the Section for Experimental Otorhinolaryngology of the University of Würzburg. These have been adapted to the direct and continuous measurements of inner ear efflux kinetics for several hour periods. For this purpose, only a tiny amount of radiotracer need be applied directly to the inner ear. Experiments were done on the anesthetized guinea pig as an animal model. In the first technique, a collimator-detector system is focused precisely on the cochlea, which had been quickly resealed after application of the radionuclide bolus via two small holes in the basal turn of the cochlea. The second technique makes use of a perilymph cycling system, whereby a small outer volume includes a microcuvette with a so-called artificial round window. By this latter cycling technique, perilymph clearance kinetics of all kinds of radiotracers--with the exception of tritium labelled ones--can be measured. Calculations from clearance kinetics show that quite small particles with particle weights up to 100, such as the chlorine anion and the potassium cation, as well as urea, glycerol, pyruvate, and lactate, exhibit perilymphatic half-lives varying from 45 to 60 min. These half-live data are plausible in regard to cochlear blood flow measured previously via an independent technique developed by Angelborg et al.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Surgical procedure and implanted material description.

The 12 intracochlear electrode placement is greatly facilitated by using our electrode-bearer which is introduced through the round window via a posterior tympanotomy approach. However, partial or complete ossification of the cochlea may oblige us to use again our first technique of one-by-one electrode placement, using Silastic pieces through 12 cochlear fenestrations. The microconnectors and the receptor are also described.

Cochlea↗
PubMed1988

[Variations of the position of the stapes in the fossula of the round window and their surgical value].

The authors studied variations of the position of stapes in the fossula of ovale window on 300 preparations of temporal bones, under operating microscope. They noted three possible positions of the stapes: most commonly downwards to the promontorium (76%), much less frequently (15%) towards the bottom of the fossula, and rarely upwards to the facial canal (9%). Knowledge of these anatomic variations is of great importance in surgical procedures performed in this region.

Adult↗
PubMed2006

Tissue resistivities determine the current flow in the cochlea.

PURPOSE OF REVIEW: In individuals with severe to profound hearing loss, cochlear implants bypass normal inner ear function by applying electrical current directly into the cochlea, thereby stimulating cochlear nerve fibers. Stimulating discrete populations of spiral ganglion cells in cochlear implant users' ears is similar to the encoding of small acoustic frequency bands in a normal-hearing person's ear. Thus, spiral ganglion cells stimulated by an electrode convey the information contained by a small acoustic frequency band. Problems that refer to the current spread and subsequent nonselective stimulation of spiral ganglion cells in the cochlea are reviewed. RECENT FINDINGS: Cochlear anatomy and tissue properties determine the current path in the cochlea. Current spreads largely via scala tympani and across turns. While most of the current leaves the cochlea via the modiolus, the facial canal and the round window constitute additional natural escape paths for the current from the cochlea. Moreover, degenerative processes change tissue resistivities and thus may affect current spread in the cochlea. SUMMARY: Electrode design and coding strategies may result in more spatial stimulation of spiral ganglion cells, resulting in a better performance of the electrode-tissue interface.

Cochlea↗
PubMed1978

Genesis of the round window rupture syndrome; some experimental observations.

Clinical and experimental evidence has revealed that rupture of the round window membrane, by itself, is not a major cause of sensorineural hearing loss. Eighteen guinea pigs underwent removal of the round window. The status of cochlear function was determined by recording the cochlear microphonic. An average loss of only about 6 db was observed after surgery. It is felt that there must commonly be more cochlear damage concurrent with window rupture to explain the significant and often relatively immediate hearing losses seen in clinical practice. The site(s) of this primary trauma has not yet been discovered, but it would seen reasonable in the light of recent reports that the perilymphatic vessels, the vas spirale, the stria vascularis and/or the intergrity of the cochlear duct might be involved in the genesis of this hearing loss. We propose that the term "round window rupture syndrome" be used as a more accurate description of this entity. The round window damage provides evidence of more devastating trauma within the cochlea. Thus, the clinician, being alerted, should not stop his therapeutic efforts with surgical closure of the RW. Better prognosis for the patient, as well as leading into new avenues for the investigation of cochlear function, would be the result.

Animals↗
PubMedDate not supplied

Surgical treatment of long-term sensorineural hearing loss due to labyrinthine fistula.

Perilymphatic fistula, usually in the round or oval window, causes a variety of symptoms, including sensorineural hearing loss. Surgical repair of these fistulas has resulted in restoration of hearing in some cases. It has been suggested that surgery must be performed within 2 months of the trauma if improvement in hearing is to occur. This paper presents the case of a patient whose fistula and resulting hearing loss had persisted ten years before surgical repair. Restoration of normal hearing and discrimination of speech occurred in the ear which had previously presented a severe sensorineural hearing loss with no useful discrimination for speech. The authors usge audiologists and otolaryngologists to consider the possibility of fistula in cases of sudden hearing loss, even when years have elapsed since the trauma. Their experience suggests that surgery may be successful in restoring hearing after many years.

Adult↗
PubMed2006

Combined electroacoustic stimulation in conventional candidates for cochlear implantation.

OBJECTIVE: To report on combined ipsilateral electrical and acoustic stimulation in a subset of conventional candidates for cochlear implantation where preoperative pure tone thresholds were </=60 dB HL for 250 and 500 Hz. METHODS: Subjects were 10 adults implanted with the Nucleus 24 Contour Advance perimodiolar electrode array. Soft surgical procedures were strictly observed: </=1.5-mm cochleostomy hole placed anterior and inferior to the round window, a Healon bubble placed over the opening to prevent entry of foreign bodies, and no suction applied. The electrode array was inserted 17 mm to the first marker rib using the recommended 'advance-off-stylet' technique. Pure tone hearing threshold levels were recorded pre-, and postoperatively at 1-2 and 6-12 months. Speech recognition was tested for cochlear implant (CI) alone and combined with ipsilateral hearing aid for 7 subjects who retained significant residual hearing in the implanted ear at 1-2 months after operation. RESULTS: There were 3/10 cases where 1-2 months after operation low-frequency responses were considered vibrotactile only (>85-110 dB HL, 250-500 Hz). In the remaining 7 cases, residual hearing was maintained up to at least 6 months after operation with minor changes. Insertion depth angles in these cases ranged from 285 to 420 degrees . For these subjects, the mean preoperative score for words presented at 65 dB SPL was 22%. Mean postoperative scores were 56% for CI alone, and 68% for CI plus ipsilateral hearing aid (p < 0.05, paired t). For sentences presented in multitalker babble noise at 5 dB SNR, mean scores were 61% CI alone, and 75% CI+IpsiHA (p < 0.01, paired t). CONCLUSIONS: Hearing was conserved during surgery and over time in 70% of conventional candidates implanted with the Nucleus 24 Contour Advance CI who had significant levels of preoperative low-frequency residual hearing (</=60 dB HL). These conventional candidates for CI also benefited from improved speech recognition in noise when using combined ipsilateral electrical and acoustic stimulation.

Acoustic Stimulation↗
PubMedDate not supplied

Acoustic reflex decay in chinchillas during a long-term exposure to noise.

Reflex decay to 0.5 kHz octave-band noise at 95 dB SPL was measured in chinchillas during four 2-hr exposure periods separated by 11-min quiet intervals. Round window electrodes were implanted in six animals. Measures of acoustic reflex decay were inferred from amplitude changes in the cochlear microphonic generated by the octave-band noise. Reflex decay followed essentially the same time course during each exposure period. Vigorous muscular contraction to the signal onset was followed by gradual decay that asymptoted between 30 and 50% of its initial value. The process of decay seemed to be complete sometime between 8 and 30 min. The results suggest that the middle ear muscles in chinchillas provide some protective function during exposures of fairly long duration.

Animals↗