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The field of hearing and deafness research is about to enter an era where new cochlear drug delivery methodologies will become more innovative and plentiful. The present report provides a representative review of previous studies where efficacious results have been obtained with animal models, primarily rodents, for protection against acute hearing loss such as acoustic trauma due to noise overexposure, antibiotic use and cancer chemotherapies. These approaches were initiated using systemic injections or oral administrations of otoprotectants. Now, exciting new options for local drug delivery, which opens up the possibilities for utilization of novel otoprotective drugs or compounds that might not be suitable for systemic use, or might interfere with the efficacious actions of chemotherapeutic agents or antibiotics, are being developed. These include interesting use of nanoparticles (with or without magnetic field supplementation), hydrogels, cochlear micropumps, and new transtympanic injectable compounds, sometimes in combination with cochlear implants., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: Epilepsy is a chronic medical disease and is associated with comorbid adverse somatic conditions due to epilepsy itself or its long-term treatment., Objectives: This study evaluated cochlear function in patients with idiopathic epilepsy and treated with carbamazepine (CBZ)., Patients and Methods: Included were 47 patients (mean age = 34.56 ± 7.11 years and duration of illness = 17.84 ± 7.21 years) and 40 healthy subjects. They underwent pure-tone audiometry and transient evoked otoacoustic emission (TEOAE) analyses., Results: Hearing loss (mainly bilateral mild) was reported in one third of patients. Compared to controls, patients had lower TEOAE amplitudes at 1.0-4.0 kHz particularly at high frequencies (3 and 4 kHz). Significant correlations were identified between TEOAE amplitudes with CBZ dose (at 3 kHz: r = -0.554, p = 0.008; at 4 kHz: r = -0.347, p = 0.01), its serum level (at 4 kHz: r = -0.280, p = 0.045) and duration of treatment (at 3 kHz: r = -0.392, p = 0.008; at 4 kHz: r = -0.542, p = 0.001)., Conclusions: Long-term CBZ treatment may result in cochlear dysfunction and auditory deficits., (© 2018 S. Karger AG, Basel.)

This study evaluated the electrocochleographic findings of patients with superior canal dehiscence (SCD) syndrome and determined their diagnostic values and relationships with audiometric parameters. Thirteen symptomatic SCD patients (1 bilateral) confirmed by temporal bone computed tomography (TBCT) and cervical vestibular evoked myogenic potentials (cVEMP) were recruited. SCD sizes were measured on reformatted images in the plane of the superior canal (SC). Results of audiologic tests (audiometry, cVEMP, electrocochleography (ECoG)) for 14 affected and 12 contralateral unaffected ears were evaluated. Relationships between summating potential (SP) to action potential (AP) ratios, as measured by ECoG, and other audiometric parameters were evaluated. Sensitivity analysis of SP/AP ratios was performed by plotting receiver operating characteristic (ROC) curves for SCD syndrome patients and 19 age-matched healthy controls. Mean SP/AP ratio of SCD ears was significantly higher than that of unaffected ears (0.52 versus 0.25, p < 0.001) and SPs were significantly elevated in affected ears (p = 0.011), whereas APs were similar for affected and unaffected ears. SP/AP ratio showed a sensitivity of 92.3% and a specificity of 94.0% for distinguishing SCD syndrome patients given the inclusion criteria applied (symptoms, TBCT, cVEMP threshold) at a cutoff value of 0.34 (p < 0.001). SP/AP ratio was not correlated with SCD size or cVEMP threshold in affected ears. Negative absolute values of bone conduction at low frequency tended to increase with SP/AP ratio. Five out of 13 patients underwent surgical repair experienced symptomatic improvement with normalization of SP/AP ratios. ECoG appears to be a valuable diagnostic adjunct for functional demonstration of the third window in the otic capsule with high sensitivity and specificity, and thus, can support a clinical diagnosis of SCD when used in conjunction with clinical and radiological findings., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Inner ear haemorrhage is a rare disorder with disabling symptoms. Prognosis is generally considered to be poor with essentially no chance of functional recovery. The most common aetiologies are related to blood dyscrasias, anticoagulant therapy or local trauma. The association with autoimmune diseases is exceptional. The authors report a case of sudden deafness with vertigo in a patient with rheumatoid arthritis, caused by labyrinthine haemorrhage. Clinical picture and progress of audiovestibular function are described along with imagiological features from magnetic resonance imaging. Inner ear haemorrhage is a rare disorder with disabling symptoms and poor prognosis. To the best of the authors' knowledge, this is the first case described with documented vestibular function recovery following labyrinthine haemorrhage.

Purpose of the Study: The aim of the present study was to evaluate the ototoxicity of Burow solution., Procedures: Compound action potentials (CAPs) of the eighth nerve were measured before and 30 minutes after the application of the Burow solution in the middle ear cavity., Results: Use of the original Burow solution (pH 3.5) for 30 minutes caused a significant reduction of click sounds. A 2-fold diluted Burow solution (pH 4.4) for 30 minutes caused no reduction in CAP threshold. Burow solution, pH adjusted to 4.5, caused no changes in CAP threshold at 30 minutes. At 24 hours, Burow solution (pH 3.5) caused complete abolition of CAP., Conclusions: Burow solution is ototoxic in the guinea pig when applied in the middle ear cavity for 30 minutes or longer. In the clinical settings, it is advisable to avoid allowing the solution to contact the round window for extended times., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Superior semicircular canal dehiscence syndrome (SCDS) is a clinical disorder that is characterized by vertigo and oscillopsia induced by loud sounds. Transient evoked otoacoustic emissions (TEOAEs) allow to noninvasively check the integrity of the cochlea. The present study aimed at identifying cochlear stress as the result of micro alterations of the cochlear functionality due to anatomic anomaly. 11 SCDS and 10 normal individuals as control group were submitted to history taking, otological examination, basic audiologic evaluation and TEOAEs analysis using the standard wideband protocol and moving time window analysis. Although TEOAEs test results showed no statistically significant difference using the standard protocol, off-line analysis of the waveforms' "effective duration" was statistically significantly shortened (p < 0.0001) when compared to normal ears. In conclusion, dehiscence of bone overlying the superior canal has been shown to have effects on inner ear function in terms of a third mobile window theory, thus altering pressure across cochlear partition with decrease in inner ear impedance.

Objective: To describe a case of pneumolabyrinth secondary to tympanic membrane/ossicular trauma and the subsequent recovery of sensorineural hearing loss managed with conservative measures., Patients: A 15-year-old boy presented to an outside hospital with signs and symptoms of acute hearing loss, vertigo, and tinnitus after penetrating injury to his right tympanic membrane. In addition, computed tomography demonstrated air density within the vestibule., Interventions: The patient was managed conservatively with bed rest, avoidance of straining, corticosteroids, and antibiotics., Main Outcome Measures: Computed tomography, audiologic testing., Results: Patient recovered near-normal hearing subjectively. There was closure of the air-bone gap (

Objective: To observe the changes of auditory steady-state response (ASSR) threshold in guinea pigs with posterior semicircular canal fistula., Methods: In 10 guinea pigs, a window was opened in the posterior semicircular canal of the left ear with the right ear serving as the control for testing the ASSR under anesthesia with pentobarbital sodium., Results: The mean and standard deviation of ASSR threshold (dB SPL) at 0.5, 1, 2, and 4 kHz in the left ear was 35.00+/-14.33, 25.50+/-12.37, 20.00+/-9.37 and 20.00+/-9.18, respectively, and was 31.00+/-16.19, 25.50+/-12.34, 18.00+/-6.96 and 18.50+/-6.71 in the right ear, respectively. Paired-sample t test showed no significant difference in the ASSR at the same frequency between the two ears., Conclusion: Small fistula by surgery causes no significant hearing loss in guinea pigs.

In a previous communication, we demonstrated that the introduction of air into the scala tympani of the cochlea causes a decrease of cochlear potentials; however, the change in endocochlear dc potential (EP) was mild and the decreased cochlear microphonics (CM) and compound action potentials (CAP) were, at least partially, reversible. In contrast, we have now found that air perfusion (3-60 microliters/min) in the scala vestibuli decreased cochlear potentials more drastically than that in the scala tympani. The change in the EP after air perfusion in the scala vestibuli was characterized by a decrease of the negative EP in response to anoxia. The CM drastically decreased upon the initiation of air perfusion and no recovery was observed after refilling of the perilymph. Histological examination showed collapse of Reissner's membrane in 12 out of 17 cochleas examined. The extent and frequency of the collapse increased with an increase in the amount of air perfused in the scala vestibuli. As the minimal amount of air needed to cause inner ear damage by air perfusion in the scala vestibuli is as small as 3 microliters, it is possible that the prognosis is worse in cases with fistula of the oval window compared to that of the round window area, if the pneumolabyrinth is involved in the pathophysiology of perilymphatic fistula. It is also indicated that air inflation of the middle ear is dangerous in cases with fistula in the oval window.

Changes of endocochlear potential (EP), cochlear microphonic potential (CM) and summating potential (SP) were studied in guinea pig cochlea after four weeks blockade of the endolymphatic sac and duct. The EP, CM and SP were measured with a microelectrode through the spiral ligament of the first turn. EP was decreased by 15%. The minimum CM output produced by tone burst of six frequencies (0.5, 1, 2, 4, 5 and 8 KHz) had reduced by 83.1%, 82.4%, 84.5%, 84.2%, 47.2% and 54.2% respectively, and the maximum CM output had declined by 54.3%, 41%, 43.2%, 21.1%, 26% and 24% separately. The minimum SP output caused by 4, 5 KHz tone burst had declined by 62.4% and 70.5%, and the maximum SP output had decreased by 41.5%, 45.2% in the early experiments. These results indicate that EP, CM and SP all underwent decreases. The extent of CM declination at low frequencies was larger than that at the high frequencies in the early experiments. The mechanisms of influence on EP, CM and SP in early experimental endolymphatic hydrops are discussed.

The inner ear pathology of experimental perilymphatic fistula (EPLF) is described. EPLF was produced by injecting artificial perilymph into the subarachnoid space, or by suctioning 4 microL of perilymph through one of the round window membranes of the guinea pig. The animals were either killed immediately, or were kept alive for 3 weeks to 3 months. The conventional celloidin embedding method was employed for morphologic study. Vestibular function of the animals was tested by observing spontaneous nystagmus and positional nystagmus after the experiment. The caloric test was also performed. Various pathologic changes of the membranous labyrinth were observed. In the cochlea these included rupture or collapse of Reissner's membrane, bulging of Reissner's membrane, loss of hair cells, and compression of the organ of Corti. Pathology of the otolithic organs and semicircular canals mainly consisted of collapse of the membranous labyrinth. Clinical symptoms in patients with perilymphatic fistula (PLF) are explained, based on our experimental findings. Electronystagmography (ENG) of EPLF animals showed either no caloric response or, with a longer duration, caloric irregularity. Prolonged unsteadiness in patients may be due to "floating" labyrinth.

The case is described of a patient with rheumatoid disease and evidence of vasculitis who developed acute vestibuloauditory dysfunction resulting in total deafness, which was assumed to be secondary to a vasculitic process affecting the vestibulocochlear nerve. Treatment of the underlying vasculitic process, despite effecting a general improvement of the patient's rheumatoid disease, did not significantly improve the auditory dysfunction.

Perilymphatic fistula is now widely recognized to cause acute profound hearing loss. It is still controversial, however, which mechanism it is that causes the reversible hearing loss. Recently, it has been suggested by two groups of researchers that the intrusion of air bubbles into the perilymphatic space (a condition called pneumolabyrinth or aerolabyrinth) through the ruptured labyrinthine window(s) may be one of the causes. In order to examine the mechanism underlying the hearing loss associated with pneumolabyrinth, the perilymphatic space of the guinea pig cochlea was perfused with air and cochlear potentials were recorded. Although perfusion of the scala tympani with air at a rate as high as 200 microliter/min caused an immediate and drastic decrease of the cochlear microphonics (CM) and the compound action potential (AP), it had little effect on the endocochlear dc potential (EP) during perfusion for 20 min. A decline in EP was seen in half the ears, but only when the duration of perfusion exceeded 30 min. These results show that the EP has an amazing resistance to air trapped in the scala tympani of the cochlea and that the initial decrease of hearing acuity after the elimination of perilymph from the scala tympani (or introduction of air into the scala tympani) is probably due to interference in CM and AP generation mechanisms rather than to strial dysfunction.

The effect of viral infection in the cochlea was investigated by inoculation of live cytomegalovirus or inactivated virus. Auditory thresholds were measured on the day of inoculation and on the terminal day. Two to 8 days following inoculation, the animals were killed and the cochleas were evaluated histologically. The compound nerve potential showed an increase in threshold prior to the cochlear microphonic, indicating the nerve was affected prior to the outer hair cells. All experimental cochleas contained inflammatory and cytomegalic inclusion cells and showed degenerative changes. The number of infected cells was small relative to the histopathology. Control cochleas had normal structure and function. The degeneration, therefore, might be mediated by inflammation as well as by the cytopathic effect of the virus. Viral infections, therefore, might be better managed with anti-inflammatory therapy in addition to antiviral agents.

Intensity difference limens were measured for various frequencies and intensities of sinusoidal and pulsatile electrical stimulation in monkeys with electrodes implanted in the scala tympani, scala vestibuli, modiolus, or middle ear. Difference limens decreased, as a function of initial stimulus intensity, from values of 1.5-3 dB near threshold to as low as 0.5 dB near the upper limit of the dynamic range. If sensation level was held constant, difference limens decreased as a function of frequency up to about 500 Hz, and then remained constant. They were similar across a variety of electrode placements and separations if differences in threshold and dynamic range were taken into account. However, difference limens measured in severely damaged ears were slightly smaller than those in moderately damaged ears. The near miss to Weber's law, characteristic of acoustic difference limens, was not seen with electrical stimuli. Differences limens for electrical stimuli were roughly one-half those for acoustic stimuli; thus, part of the deficit in dynamic range for electrical stimulation compared with acoustic stimulation is countered by the smaller intensity differences limens for electrical stimuli.

The vessels emerging from one side of the basilar artery are supplied exclusively by the homolateral vertebral artery. Since blood flow is laminar through the vertebrobasilar system, mixing between two sides does not normally occur. Based on this fact, an experimental model for research on cochlear hypoxia is proposed and described. The animal's own blood flow in the vertebral artery is completely replaced by a stream of poorly oxygenated blood injected retrogradely through the ipsilateral axillary artery. In this way, the territory supplied by the vessels emerging from this side of the basilar artery, including the ear, is rendered hypoxic. The changes in the cochlear action potentials induced by the reduced oxygen supply are recorded by a chronically implanted electrode and analyzed.

Animal models of vascular disorders are identified or developed for the evaluation of functional deficits and morphologic alterations. This information will serve a useful purpose for a better understanding of sudden deafness, Meniere's disease, and presbycusis. The study of microcirculation of the inner ear vessels reveals that their responses to various stimuli, such as anoxia, sympathetic nerve stimulation, hypothermia, and drugs, are different from those of the middle ear vessels. In sudden occlusion of the major vascular supply to the inner ear, the cochlea is found to be more vulnerable than the vestibular labyrinth; outer and inner hair cells and stria vascularis are most often affected. Animal models for Meniere's disease are also described, and the importance of vascularity at the endolymphatic duct and sac is discussed from an etiologic viewpoint. In presbycusis, animal models show sensory cell and spiral ganglion cell atrophies in different locations than in human cochleas, and the relationship between these atrophies and vascular impairments is not clear at the present time.

Thirty five patients of either sex suffering from tuberculosis were administered streptomycin 0.75 g (im daily, upto 14 yr and above 45 yr of age) and 1 g (im daily for age 15-45 yr) with other antitubercular drugs and followed for audiological status. Five patients were dropped as they developed vestibular dysfunction. Varying degree of hearing loss was detected in 4 of 10 patients in group I (below 15 yr), in 2 of 9 patients in group II (15-45 yr) and in 6 of 11 patients in group III (above 45 yr). Cochlear toxicity of streptomycin was not found to be related to does or duration of therapy. Supportive therapy restored hearing in 2 patients of group I and 1 of group II. None of the patients in group III showed recovery. It is recommended that patients on long-term streptomycin therapy should be periodically subjected to audiometric examination to detect any hearing loss.

The purpose of this study was to determine whether patterns of phoneme identification error differ among listeners with cochlear and retrocochlear auditory disorder. Speech intelligibility performance was analyzed in 15 patients with confirmed eighth-nerve disorder and in 15 patients with cochlear disorders, matched to the retrocochlear group for age and audiometric configuration, using confusion matrices derived from responses to a monosyllabic word list. Results indicated that: (1) vowel errors were more prevalent in the retrocochlear group and varied directly with increasing stimulus presentation level; and (2) consonant errors did not differ in type or relative frequency between the two groups, nor was there a level-dependent effect for consonant errors. These results are supported by the results of closed-set vowel identification tests and thus do not appear to be an artifact of open-set testing. Vowel errors may account for a major part of the speech 'rollover' phenomenon typical of retrocochlear auditory dysfunction.

A study was carried out on vestibular and cochlear measures of 20 patients with internal ear disorders. It was shown that the vestibular findings do not always match the cochlear ones. A comparison of the various quantitative measures of the post-caloric responses with the clinical picture indicated that the average slow-phase velocity provides a good measure of the vestibular function. The correlation coefficients between the average slow-phase velocity of the post-caloric responses and those of the per- and post-rotatory responses were higher than those based on the maximum slow-phase velocity value. The diagnostic significance of the rotatory test is assessed against the clinical findings.

Saccular and cochlear endolymphatic potentials (SEP and CEP) were recorded in 33 normal animals. We confirmed that SEP is not produced in the saccule per se, but is a potential leak from the cochlea. CEP was reduced to one-tenth of the original value when it reached the saccule. Endolymphatic hydrops was provoked in 32 animals, and CEP and SEP were successfully recorded in 29 and 20 cases, respectively. The measurements were performed in the 2nd, 4th and 12th postoperative week. Both CEP and SEP decreased in magnitude as time elapsed after the surgery. This reduction is attributed to the strial dysfunction. In advanced hydrops, CEP transmission to the saccule is greatly inhibited. It is concluded that the saccular dysfunction can occur in the hydropic ear.

Guinea pigs (GP) were exposed to 10 impulses of 164 dB (SPL). Measuring of cochlear microphonics (CM) at frequencies between 0.5 and 10 kHz and morphological examination of the cochlea by the surface preparation technique followed 2 hours, 2 and 6 weeks after exposure to impulse noise. During the 2 hours following noise exposure the amplitudes of CM decreased in all tested frequencies, while recovery of CM never could be observed at this time. Subsequent morphological changes in the structure of the organ of Corti could be found. They varied considerably between the tested animals. 2 and 6 weeks after exposure to 10 impulses all GP had irreversible defects in the cochlea in an extent from an incomplete pattern of outer hair cells up to a total lack of areas of the organ of Corti. Only in GP with morphological damages in a small extent CM were recordable again. A good agreement of functional and morphological results was established. It can be concluded that exposure to few single impulses with peaks of sound pressure of sufficient intensity will produce irreversible morphological defects in the cochlea, resulting in marked functional injury, if the damaged area is large enough.

Measures of cochlear selectivity can be obtained from compound responses using tone-on-tone masking procedures [Dallos and Cheatham, J. Acoust. Soc. Am. 59, 591--597 (1976)]. For the normal guinea pig, cochlear fiber tuning is sharper by a factor of 1.8 than AP tuning curves using simultaneous masking (threshold criterion = 25% N1 amplitude reduction). Anesthesia does not appear to affect AP tuning. In pathological cochleas, AP tuning is broadened by a factor of 2--3, and differences between forward and simultaneous masking curves are reduced. Tuning changes can sometimes occur without threshold elevation. AP tuning curves were obtained from humans during transtympanic electrocochleography. For subjects with near normal thresholds, Q10dB values (simultaneous masking) are approximately 2.3 at 2 kHz, 3.6 at 4 kHz, and 4.7 at 8 kHz. Using the relationship between cochlear fiber tuning and AP tuning in the guinea pig, estimates of human cochlear fiber tuning are 4.2 at 2 kHz, 6.5 at 4 kHz, and 8.5 at 8 kHz. Patients with threshold elevations of more than 30 dB resulting from cochlear deafness have AP tuning curves less sharply tuned by a factor of 2--3.

Apical lesions of the cochlea may be caused by direct trauma, impairment of blood supply, contamination of perilymphatic fluid and endolymphatic hydrops. It is proposed that endolymphatic hydrops causes apical lesions when endolymph or its components leak into the perilymphatic fluid and pass through the helicotrema to degrade the tissue fluid environment of the sensory and neural structures in this area.

Comparisons were made for two species (chinchilla and mongolian gerbil) among mean behavioral audiogram, mean just detectable action potential (AP) responses to tone bursts, and single-fiber response thresholds at the characteristic frequency, averaged in one-octave bands. In normal animals and in a group of Kayamycin-treated chinchillas, these mean measures appear to have a well-ordered relationship. Unit and AP thresholds are within 10 dB from one another throughout the frequency range. Behavioral thresholds are usually 15--20 dB more sensitive, but the three curves are roughly parallel except at the highest frequencies, where the behavioral threshold begins to increase approximately one-half octave above the physiological ones. Individual examples for four gerbils and four chinchillas having hair cell losses due to Kanamycin intoxication reinforce the notion based on mean data that in most cases AP thresholds can serve to predict the behavioral threshold configuration.

One of the basic functions of the cochlea is to separate out the frequency components which are present in complex sounds. This frequency selectivity can be measured objectively in the clinic from the compound action potential (AP) during transtympanic electrocochleography, using a two-tone masking paradigm. An AP is evoked by a test tone near to threshold, and a measure is made of the frequency bandwidth over which this AP can be suppressed by a continuous pure tone masker. In normal-hearing subjects, this frequency range is 0.17-0.39 octaves (test tone pip at 4 or 8 kHz). In patients with cochlear deafness, this bandwidth is greatly enlarged, ranging from 0.42-2.2 octaves. Some observations suggest that a deterioration in frequency selectivity can occur before any important threshold elevation. The early detection of this could be a warning sign of potential cochlear susceptibility. In the clinic the measure is already of use: a deterioration is a positive indication of cochlear involvement in a hearing loss.

The cause of perilymph fistula, a subgroup of sudden deafness, has not been clearly understood. To study its etiology quantitatively, the inner ear pressure monitoring system with a computer controlled pressurizing device and three types of low-pressure monitoring sensors was constructed and utilized in ex vivo experiments using white guinea pigs. Hypothesizing that cerebrospinal pressure increases cause rupture of the round window membrane, direct and indirect pressurization to cerebrospinal region and simultaneous measurement of inner ear and cerebrospinal pressures were carried out. Ruptures of the round window membranes were seen in the experiments with direct saline infusion into the cochlea when the increment of inner ear pressure exceeded 500 mmH2O. There was no sign of rupture when squeezing abdomen was employed as an indirect pressurization, although cerebrospinal pressure increased.

There is convincing evidence that the cochlear aqueduct is normally patent in humans and is of relatively constant size. It probably plays an important role in the balance between the perilymphatic, endolymphatic, and cerebrospinal fluid pressures. The flow rate of liquids through tubes is a linear function of pressure, viscosity, and length of the tube but is a fourth degree power function of the radius of the lumen. For this reason, the radius is the most critical factor determining the flow rate. Small variations in size of the cochlear aqueduct can cause very large variations in flow rate through it.

A patient with a large congenital cholesteatoma of the left temporal bone is presented. The case is unique in that, although the cholestetoma invaded all three semicircular as well as the basal coil of the cochlea, the patient retained normal hearing. She had an almost complete left-sided facial paralysis, yet she retained sensori-neural hearing postoperatively, in spite of removal of the superior part of the labyrinth (semicircular canals and utricle). The possible mechanisms behind such an unusual event are discussed together with the possible function of the utriculo-endolymphatic valve.

The dysfunction of the stria vascularis in the viable dominant spotting mutant mouse results in the reduction or the absence of the endocochlear potential. However, these mutants respond to an intense acoustic stimulus with a Preyer reflex (pinna twitch). This study used 14C autoradiography and electromyography to investigate central auditory responses in this mutant. There were three main findings: autoradiography demonstrated an increase in the metabolic rate within each of the central auditory nuclei during noise exposure compared with silence; electromyographic recordings indicated that there was no tensor tympani muscle reflex; the mutants were found to be susceptible to audiogenic seizures. It was concluded that the central auditory pathway of the viable dominant spotting mutant could be activated despite the abnormal strial function. Absence of the tensor tympani muscle reflex, together with auditory deprivation, might contribute to the susceptibility to audiogenic seizures.

During etacrynic acid intoxication in the guinea pig, patterns of click-evoked compound electrocochleographic responses are similar to those observed in Menière and retro-cochlear human pathologies. Using high frequency tone bursts, SP, CM and AP were studied after intracardiac injection of etacrynic acid. The evolution of SP precedes that of CM and AP. Its change in polarity could be related to that reported for EP by Bosher et al. (1973). While during the recovery period SP overshoots (after 90 min), CM and AP increase more slowly (up to about 7 days) and in most cases AP amplitudes do not exceed 70-80% of their original value (25 days). N1, when present, keeps its classical pattern durint the entire evolution, whatever its amplitude and latency variations are. The early positive peak or negative shift observed in click-evoked human pathological electrocochleography can therefore be identified as SP. Thus this response is the indication of the presence of hair cells and of the impairment of the nerve fibre stimulation or response.

All subjects with implanted cochlear stimulators demonstrated evidence of abnormal postural stability without their stimulators activated. Instability increased when they were tested with cochlear stimulation units turned on, and additional instability was demonstrated in four of these subjects when tested in noise. These findings suggest that the electrical stimulation delivered by the cochlear prosthesis is not limited to the auditory system. The precise characteristics of electrical stimulation devices designed for stimulations limited to the cochlea and their spurious effects upon motor performance should be investigated. The design of future intralabyrinthine auditory electrical prostheses must include hardware designs and stimulus paradigms that avoid undesirable vestibular system stimulation.

Evaluation of clinical application of evoked oto-acoustic emission (OAE) as an objective cochlear function test was studied in normal hearing subjects, retrocochlear and cochlear deafness cases. In normal hearing subjects, OAE responses showed good reproducibility while the minimum detectable level of OAE varied between subjects. We found that the interaural difference of minimum detectable level of OAE is the best indicator of cochlear damage. As both OAE and ECochG originate from the hair cells, we compared the behavior of OAE and ECochG in cases with retrocochlear deafness. We found that OAE exhibited the same behaviour as CM in ECochG in these cases. In cases of cochlear deafness, in spite of the recovery of the hearing thresholds to within normal levels, the minimum detectable level of OAE remained at an average of about 4. 4dB higher as compared to normal hearing subjects. This demonstrates that a minimal cochlear damage likely to go undetected by pure tone audiometry is detected by OAE measurement. We conclude that OAE must be added to the growing list of tests in the objective assessment of cochlear function.

The procedures for conducting and interpreting Stapedial Reflex Decay (SRD) are discussed. A modification of currently used procedures and interpretations in which testing is conducted at 750 and 1500 Hz as well as 500, 1000 and 2000 Hz is also discussed. Abnormal decay is defined as fatigue to half-life in less than 6.2 seconds. The SRD test patterns of 464 ears with cochlear lesions and 68 ears with retrocochlear lesions are presented and discussed. The findings are strongly supportive of SRD testing using the proposed procedures and interpretations.

Loss of auditory function was correlated with different pathological findings in the inner ear of the rabbit after 15 or 30 min exposure to high level broad band (2-7 kHz) noise. The ears from animals with post-exposure times ranging from 1 to 23 months were analysed by scanning electron microscopy (SEM). Complete cochleograms with quantification of loss of hair cells and damage to stereocilia were produced. Loss of function was defined by determining behavioural threshold, threshold of auditory brainstem response (ABR) to narrow-band stimuli and threshold of the middle ear muscle reflex (MER). A small scattered loss of OHCs and slight disarray of stereocilia were found in non-exposed ears of young animals, but fusion of IHC cilia was not observed. Normal auditory function was not found in any noise exposed animal with abnormal morphology. A loss of threshold sensitivity of up to about 30-40 dB was noted without loss of hair cells in the corresponding region of the cochlea. The mildest structural damage that correlated to a functional alteration consisted of damage to stereocilia of IHC. This correlated well to the MER threshold shift. In two animals a shift of MER threshold of about 20 dB was the only functional abnormality. In ears with more extensive IHC damage loss of OHCs was also found and these animals had primarily an increase in auditory threshold shift with only a small additional change in MER threshold. It is concluded that in the rabbit and with the methods used the IHC stereocilia are the structures most susceptible to damage by the noise used and that the degree of injury can be fairly well assessed by functional tests of a type that is used also routinely in the audiological clinic.

Masking level differences (MLD) for 500 Hz pure tones and for spondees were obtained from 48 subjects. Twelve were without otologic or neurologic complaints (normal), 12 had high frequency, noise-induced hearing losses, 12 were diagnosed otologically as having Ménière's disorder, and 12 had neurologically diagnosed central nervous system (CNS) disorders. Results indicated that high frequency, noise-induced hearing losses do not affect MLD for 500 Hz stimuli, but do diminish the size of MLD for speech. Masking level differences for both 500 Hz and spondees were decreased for the Ménière's disorder group. The group of patients having CNS disorders attributed to multiple sclerosis, to inflammatory lesion of the pons, to degenerative processes of the cerebellum and adjacent nervous tissue, or to brain stem cerebrovascular accident had normal hearing according to conventional pure tone and speech testing, but attained smaller than normal MLD for 500 Hz and spondees. These findings agree closely with results obtained in an earlier study and continue to suggest that, given normal peripheral auditory function, MLD tests may have unique value in detection of subtle lesions of the central auditory nervous system.

The causes of cochlear labyrinthisation after stapedotomy are discussed. The evolution is favorable after early diagnosis and treatment. Three cases are reported.

A series of 13 patients where surgery confirmed retrocochlear lesions in the cerebellopontine angle was tested preoperatively by electro-cochleography. The following conclusions can be drawn: 1. Compound action potentials (CAP) of the acoustic nerve could be registered by electro-cochleography in all patients regardless of the fact whether hearing on the side of the lesion could be demonstrated in pure tone audiometry or not. 2. The threshold latency for the 2 kHz sinustone-burst elicited compound action potential was within the normal range if hearing on the side of the lesion could be shown in pure tone audiometry. Threshold latency for 2 kHz CAP was shortened pathologically when hearing on the side of the lesion was absent in pure tone audiometry.

Deposition of bone within the fluid spaces of the cochlea is encountered commonly in cochlear implant candidates and previously has been considered a relative contraindication to the use of multichannel intracochlear electrodes. This contraindication has been based on possible mechanical difficulty with electrode insertion as well as uncertainty about the potential benefit of the multichannel device in the patient. Fifteen profoundly deaf patients with partial ossification of the basal turn of the cochlea received implants with long intracochlear electrodes (11, Nucleus; 1, University of California at San Francisco/Storz; and 3, Symbion/Inneraid). In 11 cases, ossification had been predicted preoperatively by computed tomographic scan. Electrodes were completely inserted in 14 patients, and partial insertion was accomplished in one patient. All patients currently are using their devices and nine of 12 postlingually deaf patients have achieved some degree of open-set speech discrimination. This series demonstrates that in experienced hands, insertion of long multichannel electrodes into partially ossified cochleas is possible and that results are similar to those achieved in patients who have nonossified cochleas.

Common potentials used to evaluate cochlear function are the ac cochlear potential (ACCP), N1 and the positive dc endocochlear potential (EP). The ACCP is an electrical analogue of the sound stimulus; its source is the electrical activity of the cochlear hair cells. N1 is a volume conductor recorded action potential of the auditory nerve. The EP is the positive polarization of the middle compartment of the cochlea (scala media) with respect to the other compartments (the scalae tympani and vestibuli); the stria vascularis is apparently responsible for the EP. Generally, ototoxic drugs and very intense broad-band noise affect the basal portion of the cochlea first and, because of tonotopic organization, the ACCP responses to high frequency pure tones are affected before those to the low frequencies. However, the correlation between the effect of an ototraumatic agent on the ACCP and its effect on cochlear morphology is not always reliable. The correlations between changes in N1 and EP and in cochlear morphology are even less precise. Also discussed will be the cochlear effects of noise and the ototoxic interactions between drug/drug, noise/drug, and noise/drug/otitis media.