Cochlear function in ears with immunomediated inner ear disorder

The aim of the present study was to evaluate the performance of ears with inner ear disorder, responsive to immunosuppressive drugs, in advanced tests designed to assess primary cochlear functions (temporal integration, frequency selectivity, cochlear mechanics). The results of this study suggest that immunomediated inner ear disease results, in the acute clinical stage, in the development of endolymphatic hydrops, which increases the stiffness of the vibrating structures within the inner ear and causes dysfunctions of the outer hair cells. Our patients presented with upsloping or flat sensorineural hearing loss, absence of evoked otoacoustic emissions and distortion-product otoacoustic evoked emissions and abnormal temporal integration, frequency selectivity and cochlear mechanics. Following immunosuppressive treatment, hydrops recovered, hearing subsequently returned to normal, the audiometric curve became flat at low-to-middle frequencies and primary cochlear function tended to normalize. This study seems to support the usefulness of testing primary cochlear functions in order to monitor the clinical course of immunomediated inner ear disorders.     

Cochlear function and speech recognition in the elderly.

The aim of the current study was to evaluate the performance of elderly subjects in advanced tests that assess primary cochlear functions (temporal summation, frequency selectivity, cochlear mechanics) and relate them to speech recognition scores. The results show that measures of primary cochlear function in elderly subjects are worse than in young adults, suggesting that receptor failure primarily involved presbyacusis'. Moreover, the data suggest that significant changes in the conductive structures within the inner ear could be involved in age-related hearing loss. Peripheral function deterioration seems to be highly relevant for speech recognition; in fact, it was found that the elderly with the poorest speech recognition scores also had the worst frequency selectivity.     

Cochlear Function and Speech Recognition in the Elderly: Funcián coclear y discriminación del lenguaje en los adultos mayores

The aim of the current study was to evaluate the performance of elderly subjects in advanced tests that assess primary cochlear functions (temporal summation, frequency selectivity, cochlear mechanics) and relate them to speech recognition scores. The results show that measures of primary cochlear function in elderly subjects are worse than in young adults, suggesting that receptor failure is primarily involved in ‘presbyacusis’. Moreover, the data suggest that significant changes in the conductive structures within the inner ear could be involved in age-related hearing loss. Peripheral function deterioration seems to be highly relevant for speech recognition; in fact, it was found that the elderly with the poorest speech recognition scores also had the worst frequency selectivity.     

Evoked otoacoustic emissions in sensorineural hearing impairment: its clinical implications

This study was performed for the purpose of determining whether or not evoked otoacoustic emissions are useful as a clinical test. Two hundred and twenty-six sequences of the emission in response to stimulus tone bursts were averaged. The detection threshold of the emission was elevated in ears of inner ear impairment with profound sensorineural hearing loss, such as inner ear anomaly, mumps deafness, or sudden deafness, but it was not observed in ears of functional deafness. The mean interaural differences of emission threshold were near 35 dB in unilateral inner ear impairments with profound hearing loss. There was a positive correlation between the interaural difference of audiometric threshold and that of emission threshold in sudden deafness ears with various degrees of hearing loss. The incidence of continuous emission, whose duration was longer than 6 msec, was 30% in normal hearing ears and it was close to 90% in ears with bilateral or unilateral dip type hearing loss. The result was verified in a survey of a junior high school brass band. The conclusion is that there is clinical usefulness for the evoked otoacoustic emissions in evaluating cochlear function and in predicting noise susceptibility.     

Intra- and intersubject variability of acoustically evoked otoacoustic emissions. I. Transiently evoked otoacoustic emissions]

BACKGROUND: Acoustically evoked otoacoustic emissions are becoming increasingly significant in the clinical monitoring of cochlear function in adults. Any interpretation of these measurements in a clinical setting must consider their intra- and intersubject variability. METHODS: Transiently evoked otoacoustic emission (TEOAE) measurements were performed in 32 normally hearing adults in three weekly test sessions. Each ear was tested twice per session, and the results were statistically analyzed. RESULTS: All test candidates had measurable TEOAEs. Statistically significant differences in TEOAE amplitudes were neither found between two measurements at the same day, nor at weekly intervals. No statistically significant amplitude differences were found between right and left ear of the same candidate. TEOAE amplitudes in women were always higher than in men with statistically significant differences in the 2, 3, and 4 kHz frequency band. CONCLUSIONS: These results indicate that monitoring of the inner ear status can be reliably performed using TEOAE measurements. Changes in TEOAE amplitudes effectively indicate changes in the cochlear function.     

Otoacoustic emissions]

Spontaneous sound signals emitted from the inner ear were first recorded by Kumpf and Hoke in 1970. Kemp reported phenomena of sounds which were emitted by the ear responding to acoustic stimulation. These "otoacoustic emissions" are supposed to be generated in the outer hair cells. Active contractions of the actin and myosin in these cells produce a frequency specific cochlear amplifier mechanism. Although the clinical value of spontaneous otoacoustic emissions is yet unclear, as well as role in tinnitus, the recording of click-evoked otoacoustic emissions has now become diagnostic routine. Click-evoked otoacoustic emissions cannot be recorded in ears with cochlear mid-frequency hearing losses > or = 25 dB. However, the use of sinus tones or distortion products as stimuli promises more frequency-specific results. Most important for the quality of measurement is complete closure of the external ear canal, correct positioning of the recording probe, maximal suppression of background noise and sufficient compliance of the patient, especially when testing children. Middle ear effusions also prevent recording. Responses to a standard of 260 stimulations are averaged and identified as "true" emissions by their sufficient reproducibility and characteristic pattern in frequency analysis. Currently, the recording of click-evoked otoacoustic emissions can be used to detect early discrete lesions of the outer hair cells. Their use as a screening tool concerning cochlear hearing disorders is already possible in newborn children. Isolated central hearing disorders still cannot be detected by this diagnostic procedure.     

Patterns of evoked otoacoustic emissions associated with acoustic neuromas

Evoked otoacoustic emissions (OAEs) are assumed to reflect healthy outer hair cell function. Over the past few years, evoked OAEs have been shown to be useful as indicators of cochlear hearing loss. Because basic studies have shown that OAEs are extremely sensitive to cochlear anoxia and hypoxia, as well as to the adverse effects of many inner ear diseases, it is possible that these objective tests can provide some insight into the fundamental basis of the hearing loss exhibited by patients with acoustic neuromas. The primary aim of the present study was to examine the effects of acoustic neuromas on the amplitudes of evoked OAEs and to compare these findings with tumor-induced hearing levels. To this end, tests of behavioral audiometry, distortion-product otoacoustic emissions and transiently evoked otoacoustic emissions were performed on 44 patients with verified acoustic neuromas. The results demonstrated that the majority of ears with acoustic neuromas displayed one of two distinct patterns of evoked OAEs: a cochlear pattern or a noncochlear pattern. Although behavioral hearing thresholds were higher with larger tumors, OAE levels exhibited no clear relationship to tumor size. The present findings support the notion that acoustic neuromas may cause hearing impairment according to two types of influence that act at different levels of the peripheral auditory system. The tumor's cochlear effect on evoked OAE activity is most likely caused by an indirectly mediated compromise of the organ of Corti's vascular supply. It is probable that the direct pressure of the tumor on the eighth cranial nerve is responsible for the observed noncochlear effects.     

Preserved otoacoustic emissions in postparotitis profound unilateral hearing loss: a case report

We report a case of a profound unilateral sensorineural hearing loss following epidemic parotitis, with good response of otoacoustic emissions. The patient was a 12-year-old girl who had developed a unilateral hearing impairment 2 weeks after the onset of mumps. Pure tone audiometry confirmed a profound left sensorineural hearing loss. The affected ear showed an absence of auditory brain stem responses, whereas transient evoked otoacoustic emissions and distortion product otoacoustic emissions were preserved. Epidemic parotitis virus is likely responsible for an impairment of inner hair cells, primary afferent fibers or their synapses, or a combination of these areas, and it does not seem to have a specific tropism for cochlear outer hair cells. Further follow-up will be necessary to differentiate the present case from auditory neuropathy.     

Clinical applications of otoacoustic emissions.

On the basis of recent advances in auditory physiology, new tests of cochlear function have been developed using measures of otoacoustic emissions. In the present report, the clinical potential for each of the four basic emission types is examined. In addition, the practical advantages of examining the ear with two specific types of evoked emissions, transiently evoked and distortion-product otoacoustic emissions, are reviewed in detail. Finally, the future role of tests of otoacoustic emissions in the diagnosis of hearing impairment is discussed. The current view is the evoked emissions hold promise as an essential part of the clinical examination of the auditory system.     

Cochlear function in young and adult Fischer 344 rats

Fischer 344 (F344) rats are often used as an animal model for investigation of the mechanisms underlying age-related hearing loss. The aim of this study was to assess cochlear function in young (1-month-old) and adult (6-month-old) F344 rats using recording of otoacoustic emissions and auditory brainstem responses (ABRs). The results were compared with control groups of Long Evans (LE) rats of the same ages. The results demonstrate a significant increase in the hearing threshold in F344 rats in comparison with LE rats, expressed mainly at low frequencies (1-2 kHz). In F344 rats, transient evoked otoacoustic emissions were not measurable and distortion product otoacoustic emissions could be detected within a frequency range of 2.4-6.3 kHz. Tympanometric measurements did not reveal any differences in middle ear parameters between F344 and LE rats. The amplitudes of click-evoked ABRs were significantly lower in 6-month-old F344 rats than in LE rats, but other parameters of the ABRs were almost identical in both rat strains. The results demonstrate a significant deficit in low-frequency hearing and altered otoacoustic emissions in both young and adult F344 rats, suggesting a defect of the inner ear sensory epithelium at the apical part of the cochlea.     

Early detection of cisplatin-induced ototoxicity using evoked otoacoustic emissions

In a prospective study we examined the effects of cisplatinum on the amplitude of evoked otoacoustic emissions and thus on cochlear micromechanics. 29 patients were examined. Amplitude changes of click-evoked otoacoustic emissions were compared with the threshold of pure-tone audiometry. We observed that an amplitude loss of otoacoustic emissions is a sensitive tool for the early detection of cochlear dysfunction. "Minimal lesions" of the inner ear were observed at an earlier stage during the current therapy than when using conventional audiometry. Measuring and recording otoacoustic emissions enables to diagnose beginning cochlear lesions caused by ototoxic drugs before they become clinically manifest.     

Otoacoustic emissions and extended high-frequency hearing sensitivity in young adults Emisiones otoacústicas y sensibilidad extendida a frecuencias altas en adultos jóvenes

The relationship between hearing sensitivity in the extended high-frequency region (8–16 kHz) and (1) the presence of synchronized spontaneous otoacoustic emissions (SSOAEs) and (2) the strength of click-evoked and distortion product otoacoustic emissions (CEOAEs and DPOAEs) was investigated in 104 ears of 57 young adults. The age range was confined to 16 to 19 years. All subjects had normal hearing in the conventional audiometric frequency range (0.5–8 kHz). Ears with detected SSOAEs had better hearing sensitivity in the extended high-frequency region and also higher levels of CEOAEs and DPOAEs than ears with undetected SSOAEs. The results support the hypothesis that the presence of SSOAEs is indicative of an ear with highly normal cochlear function over a broad frequency range.     

Distortion-product otoacoustic emissions. Values for clinical use.

Distortion-product otoacoustic emissions are otoacoustic emissions evoked by two pure tones. They are proposed as a frequency-specific test of the mechanical properties of the cochlea. The aim of this study was to measure distortion-product otoacoustic emissions in a clinical setting to establish the most interesting values suitable for clinical use and the clinical interest of the method. The statistical analysis of the data points out some clinically interesting values: (1) a screening limit value of 30 dB hearing level and when measuring distortion-product otoacoustic emissions in response to 52 dB sound pressure level for studying active frequency selective mechanisms; (2) a screening limit value of 50 dB hearing level and when measuring distortion-product otoacoustic emissions in response to 72 dB sound pressure level for studying passive cochlear mechanisms; and (3) the slope of the input-output function. All physiologic properties of the cochlea fit with these basic distortion-product otoacoustic emission properties. These criteria can be used whatever the population studied and the material used for distortion-product otoacoustic emissions recordings. Distortion-product otoacoustic emissions can be used as a screening test to separate (1) subjects with normal hearing and subjects with a hearing threshold above 30 dB hearing level (distortion-product otoacoustic emissions in response to a 52 dB sound pressure level "primaries" [ie, pure tones] stimulation intensity), and (2) patients with a hearing threshold above or below 50 dB hearing level (distortion-product otoacoustic emissions in response to a 72 dB sound pressure level primary stimulation intensity). Distortion-product otoacoustic emissions cannot be used as a more precise audiometric test.     

A Dominantly Inherited Progressive Deafness Affecting Distal Auditory Nerve and Hair Cells

We have studied 72 members belonging to a large kindred with a hearing disorder inherited in an autosomal dominant pattern. We used audiological, physiological, and psychoacoustic measures to characterize the hearing disorders. The initial phenotypic features of the hearing loss are of an auditory neuropathy (AN) with abnormal auditory nerve and brainstem responses (ABRs) and normal outer hair cell functions [otoacoustic emissions (OAEs) and cochlear microphonics (CMs)]. Psychoacoustic studies revealed profound abnormalities of auditory temporal processes (gap detection, amplitude modulation detection, speech discrimination) and frequency processes (difference limens) beyond that seen in hearing impairment accompanying cochlear sensory disorders. The hearing loss progresses over 10–20 years to also involve outer hair cells, producing a profound sensorineural hearing loss with absent ABRs and OAEs. Affected family members do not have evidence of other cranial or peripheral neuropathies. There was a marked improvement of auditory functions in three affected family members studied after cochlear implantation with return of electrically evoked auditory brainstem responses (EABRs), auditory temporal processes, and speech recognition. These findings are compatible with a distal auditory nerve disorder affecting one or all of the components in the auditory periphery including terminal auditory nerve dendrites, inner hair cells, and the synapses between inner hair cells and auditory nerve. There is relative sparing of auditory ganglion cells and their axons.     

Auditory neuropathy in childhood

Objectives: Auditory neuropathy is a recently described disorder in which patients demonstrate hearing loss for pure tones, impaired word discrimination out of proportion to pure tone loss, absent or abnormal auditory brainstem responses, and normal outer hair cell function as measured by otoacoustic emissions and cochlear microphonics. We have identified eight pediatric patients having hearing deficits that are most likely due to a neuropathy of the eighth nerve. In this study, the results of audiologic testing performed with these eight children are described. Study Design: Retrospective review of audiologic findings in eight children with auditory neuropathy. Methods. Each subject was tested with pure tone and speech audiologic testing, auditory brainstem response, and click-evoked otoacoustic emissions. Results of these tests were tabulated and summarized. Results: Pure tone audiologic testing revealed five children with upsloping sensorineural hearing loss, two with high frequency loss, and one with a mild, flat configuration. Six children demonstrated poor word discrimination scores, and the other two had fair to good word discrimination. All eight subjects had normal distortion product and transient otoacoustic emissions. All eight children demonstrated absent or marked abnormalities of brainstem auditory evoked potentials. These findings suggest that while cochlear outer hair cell function is normal, the lesion is located at the eighth nerve. Conclusions: Recent advances in otoacoustic emissions testing permit differentiation of neural deafness from sensory deafness. This paper describes the clinical presentation and audiologic findings in pediatric auditory neuropathy, as well as the recommended management of these patients. Otolaryngologists should be aware of this disorder and implications for its management, which differs from treatment of sensorineural hearing loss. Key Words: Auditory neuropathy, childhood, hearing loss, auditory brainstem response, evoked otoacoustic emissions.     

Study of auditory function in children with chronic lung diseases

Objective

Chronic hypoxia has an evident effect on cochlear function and hearing sensitivity. Otoacoustic emissions’ testing is efficient in detecting subtle cochlear dysfunction. This cross sectional study was designed to assess the cochlear function in children with chronic lung diseases who were exposed to prolonged hypoxia and prolonged use of ototoxic drugs (as aminoglycosides) using basic audiological evaluation and transient evoked otoacoustic emissions testing.

Methods

The study was carried out on 30 Egyptian children with chronic lung disease recruited from the Pediatric Chest Clinic, Children's hospital, Ain Shams University. Twenty normal children were included as control.

Results

Six patients (20%) showed abnormal otoacoustic emissions. A significant effect of hypoxia on otoacoustic emissions findings was found (P < 0.05). However, there was no significant effect of inhaled aminoglycosides on auditory functions whether pure tone audiometry, speech audiometry and transient evoked otoacoustic emissions testing.

Conclusions

Children with chronic lung diseases are liable to cochlear dysfunction due to prolonged hypoxia. Inhaled aminoglycosides in chronic lung diseases is relatively safe on auditory functions.     

Otoacoustic Emissions from Residual Oscillations of the Cochlear Basilar Membrane in a Human Ear Model

Sounds originating from within the inner ear, known as otoacoustic emissions (OAEs), are widely exploited in clinical practice but the mechanisms underlying their generation are not entirely clear. Here we present simulation results and theoretical considerations based on a hydrodynamic model of the human inner ear. Simulations show that, if the cochlear amplifier (CA) gain is a smooth function of position within the active cochlea, filtering performed by a middle ear with an irregular, i.e., nonsmooth, forward transfer function suffices to produce irregular and long-lasting residual oscillations of cochlear basilar membrane (BM) at selected frequencies. Feeding back to the middle ear through hydrodynamic coupling afforded by the cochlear fluid, these oscillations are detected as transient evoked OAEs in the ear canal. If, in addition, the CA gain profile is affected by irregularities, residual BM oscillations are even more irregular and tend to evolve towards self-sustaining oscillations at the loci of gain irregularities. Correspondingly, the spectrum of transient evoked OAEs exhibits sharp peaks. If both the CA gain and the middle-ear forward transfer function are smooth, residual BM oscillations have regular waveforms and extinguish rapidly. In this case no emissions are produced. Finally, and paradoxically albeit consistent with observations, simulating localized damage to the CA results in self-sustaining BM oscillations at the characteristic frequencies (CFs) of the sites adjacent to the damage region, accompanied by generation of spontaneous OAEs. Under these conditions, stimulus-frequency OAEs, with typical modulation patterns, are also observed for inputs near hearing threshold. This approach can be exploited to provide novel diagnostic tools and a better understanding of key phenomena relevant for hearing science.     

Evolution of recruitment at different frequencies during the development of endolymphatic hydrops in the guinea pig

Summary The study of human temporal bones has identified endolymphatic hydrops as a common feature of several diseases. In particular it is systematically found in those bones removed from patients with premortem Menière's disease. Menière's disease is known to induce sensorineural pathology with recruitment, which changes with the evolution of the hearing loss, and is suspected to induce a cochlear conductive loss by a possible increase in static pressure of endolymph. Amplitude/intensity functions of sensorineural responses can reflect recruitment and/ or conduction loss. Experimentally induced hydrops in animals provokes cochlear physiological alterations, some of which closely resemble certain features of Menière's disease. In the present study using a guinea-pig animal model, we have examined amplitude/intensity functions at the round window for cochlear microphonics (RWCM), summating potentials (RWSP) and action potentials (CAP) at different stages of hearing loss in experimentally induced hydrops. During the period of fluctuating thresholds there was reduction of maximal RWCM amplitude, no change in RWSP and recruitment on the CAP. At a later stage when the audiogram was flat and fluctuations were no longer seen, RWCM remained unchanged. At this time RWSP could show recruitment while CAP amplitudes at all intensities were reduced, indicating either a cochlear conductive loss and/or a general depression of neural activity.