Acoustical modulation of electrically evoked otoacoustic emission in intact gerbil cochlea

In order to study the interaction between mechanical-electrical and electrical-mechanical transductions of outer hair cells (OHCs) in vivo, we observed the acoustically induced changes in the electrically evoked otoacoustic emission (EEOAE). One pole of a bipolar electrode was placed in the round window niche and the other pole on the surface of the first cochlear turn in the gerbil. A microphone and a speaker were used to monitor the EEOAE and to deliver an acoustical tone, respectively. It was found that a high sound level acoustical tone enhanced the EEOAE fine structure at frequencies below the acoustical frequency, and suppressed the overall level of the EEOAE at frequencies above the acoustical frequency. In addition, the EEOAE at frequencies approximately one half octave lower than the acoustical frequencies were relatively more enhanced or showed relatively less suppression than at other frequencies. The amplitudes of these changes had a positive relationship with acoustical tone levels. Furosemide eliminated the acoustically caused EEOAE change indicating that the acoustically caused change in the EEOAE is a phenomenon of the normal cochlea. One possible mechanism for the results is that the electrically and acoustically evoked basilar membrane (BM) vibrations interact at the EEOAE generation site and change the local mechanical and electrical properties. The second possible mechanism is that the acoustical stimulus creates an impedance discontinuity at its characteristic frequency location leading to a change in the reflected electrically evoked traveling wave, which may enhance or suppress the EEOAE by the vector summation of two waves.     

Fine structure and multicomponents of the electrically evoked otoacoustic emission in gerbil

Like the acoustically evoked distortion product otoacoustic emissions (DPOAE), the amplitude spectrum of the extracochlear electrically evoked otoacoustic emission (EEOAE) also shows peaks and valleys, which are termed the fine structure (FS) of the EEOAE. The hypothesis that the FS of the EEOAE is generated by multiple wave interactions in the cochlea is investigated by examining the relationship between the FS and the multiple-delay components of the EEOAE. The bulla of the gerbil was exposed using a ventral surgical approach. One pole of a bipolar electrode was placed in the round window niche, and the other pole on the surface of the first cochlear turn. A microphone was used to measure electrically evoked sound pressure change in the ear canal. A recently developed multicomponent analysis method was used to detect the EEOAE multiple delays. It was found that the FS is the spectral representation of the multiple-delay components. The relative power of a prominent long delay component (LDC) shows a negative relationship to the electrical stimulus level. Both the FS and the LDC were abolished by intravenous furosemide. Reconstructed signals showed that mathematical removal of the EEOAE LDC also completely eliminated the FS. These data demonstrate that the FS and the EEOAE multicomponents are properties of normal cochlear mechanics in a healthy ear and that the FS is a manifestation of the multicomponents. The findings in this study strongly indicate that the FS of the EEOAE evoked by extracochlear electrical stimulation is generated by wave interaction in the cochlea. The similarity between the EEOAE FS and the DPOAE FS suggests that they may share the same mechanism.     

The effects of efferent activation on the acoustically and electrically evoked otoacoustic emission

The effects of efferent activation on the otoacoustic emission were measured in anesthetized guinea pigs. The otoacoustic emission (2F(1)-F(2)) was evoked by the conventional method of presenting either two continuous tones or a sinusoidal current to the round window (RW) of the cochlea. The efferent effects on the acoustically evoked emission are greatest at low stimulus levels and least for high levels. The efferent effects on the electrically evoked emission (EEOAE) are relatively constant across current levels. In each case, efferent activation resulted in an initial large reduction in the emission amplitude followed by a smaller and more constant reduction. Strychnine eliminated the efferent effects independent of the method of emission activation. Strychnine had no effect on the EEOAE, suggesting that the RW current did not evoke a local efferent effect. Slow versus fast efferent effects were observed in the recovery of the emission amplitude at the termination of efferent activation. Only a fast recovery in the emission amplitude was observed for stimuli below 10 kHz while the amplitude recovery had fast and slow components for stimuli presented above 10 kHz.     

The sources of electrically evoked otoacoustic emissions

It has been hypothesized that electrically evoked otoacoustic emissions (EEOAEs) are generated at a site on the basilar membrane near the stimulating electrode. From this original site, the energy propagates towards the oval window, giving rise to the short time delay component (SDC) of EEOAEs. The energy also propagates towards its characteristic frequency (CF) location, and the emission reflected from the CF location forms a long time delay component (LDC). This hypothesis is directly tested in this study by using an acoustical swept tone to modulate the EEOAEs generated by alternating electric current delivered to the round window niche in gerbils. An acoustical tone with a high sound pressure level or a small frequency separation from the EEOAE frequency induced a strong suppression of the EEOAE LDC, but no obvious suppression of the SDC. When the electrical current frequency was fixed, the swept acoustic tone induced a slight suppression, an enhanced peak, and a strong suppression of EEOAEs as the acoustic frequency was swept from the low to high frequency. These data indicate that the electrical current induced cochlear partition vibration near the stimulating electrode. One part of this energy propagates directly to the ear canal, forming the SDC, and the other part propagates to its CF place and is reflected from there to the ear canal, forming the LDC.     

Clinical application of evoked otoacoustic emission

Evaluations were made concerning the efficiency and location of the optimal index values of the e-OAE recording method of ILO88 on 10 normal hearing subjects and 10 subjects having inner ear hearing loss. Furthermore, noise from the surrounding environment, noise made during the time of measurement, and the depth of probe insertion into the external auditory meatus as well as the type of probe tip used, were also studied in relation to its effect on the e-OAE recording method in 5 other normal hearing subjects. The results were as follows; 1) Total echo power (TEP) and the highest peak between the 1-2kHz frequency range (HPP1-2) were considered to be the optimal index values for ILO88. 2) The surrounding noise did not cause any significant change in the TEP and HPP1-2 values. 3) Noise during the actual measurement by the patient did not cause any significant change in the TEP and HPP1-2 values. 4) The depth of probe insertion into the external auditory meatus had no significant effect upon the TEP and HPP1-2 values. 5) Data reproducibility was difficult and e-OAE power was less for the pinch pump type ear cuff compared to the rubber and silicon probe tips. In conclusion, TEP and HPP1-2 were considered to be the optimal index values for ILO88, and with the use of an appropriate probe tip, it is possible to obtain accurate data with the application of the e-OAE recording method regardless of external noise from the surrounding environment or by patients such as infants.     

Transient evoked otoacoustic emission measurement in infants

Transient evoked otoacoustic emissions (TEOAEs) were measured and evaluated in 194 ears of 101 subjects under 4 years old who were suspected of hearing loss, using a ILO88 Otoacoustic Emission Analyzer, to study the basic characteristics of this measure and its utility for hearing screening. The mean time necessary to record TEOAEs in both ears was short, about 3 minutes. In 58 ears judged as normal hearing within 30 dB in ABR, TEOAE levels in infants aged less than 2 months were significantly higher than in those aged more than 1 year, especially in the high frequency bands (4-kHz and 5-kHz bands). One case which had been judged as bilateral moderate-to-profound hearing impairment in initial ABR testing showed good responses in TEOAEs, indicating normal cochlear function, and obvious wave Vs in follow-up ABRs recorded at 30 dB nHL confirmed normal auditory function. Therefore, in a case like this one, suspected of retardation in brain stem maturation, TEOAE is more useful than ABR as a hearing screening technique. Since external and middle-ear factors caused poor TEOAE responses in some cases which had been judged as normal hearing by ABR. TEOAE seems to be more sensitive in detecting external and middle ear problems than ABR. Moreover, TEOAE measurement of infants was easy and noninvasive. We conclude that TEOAE is an excellent tool for screening auditory function in infants.     

Effects of salicylate on electrically evoked otoacoustic emissions in the guinea pig

Clinically, salicylates have been known to have a ototoxic side effect of reversible hearing loss and to reduce the voltage-dependent length change (electromotility) in experiments on isolated outer hair cells (OHC). In order to clarify how the reduction of OHC electromotility due to salicylates contributes to cochlear dysfunction in vivo, we observed compound action potentials (CAP) threshold as well as the outputs of the electrically evoked otoacoustic emissions (EEOAE) before and after intravenous administration of 500 mg/kg sodium salicylate in a guinea pig model. A silver ball electrode placed on the round window membrane of the animal was used for both recording of the CAP and stimulation to elicit the EEOAE. The CAP threshold to tone bursts with frequencies from 2 to 10 kHz elevated by 13 to 22 dB, and outputs of the EEOAE decreased approximately 4 dB for 5 kHz stimulation, and 12 dB for 8 kHz after salicylate administration. These results suggested that systemically administered salicylate also reduced the electromotility of the OHC, and caused the hearing impairment in vivo.     

用瞬态诱发性耳声发射对新生儿进行听力筛选

目的：用瞬态诱发性耳声发射（ｔｒａｎｓｉｅｎｔ　ｅｖｏｋｅｄ　ｏｔｏａｃｏｕｓｔｉｃ　ｅｍｉｓｓｉｏｎｓ, ＴＥＯＡＥ）对新生儿进行听力筛选。方法：用英国Ｏｔｏｄｙｎａｍｉｃ公司生产的ＩＬＯ－９２耳声发射仪进行测试,刺激声为疏波短声,声强度为 ７３～８６ｄＢ ＳＰＬ,脉冲宽度为 ８０μｓ,刺激方式为“３＋１”（三个正相波后接一个 ３倍振幅的负相波）非线性模式。结果;共对７７３例新生儿进行ＴＥＯＡＥ听力筛选,３例诊断为双耳轻一中度感音神经性耳聋,２例为单耳感音性听力下降;另有１２例被诊断为传导性听力下降,系中耳渗液所致。结论：ＴＥＯＡＥ用于新生儿听力筛选具有快速、简单、客观、无创的优点,不仅可查出感音神经性聋,还可查出传导性听力下降。     

Influence of spontaneous otoacoustic emission (SOAE) on transiently evoked otoacoustic emission (TEOAE)

The literature has reports on the influence of spontaneous otoacoustic emission (SOAE) on transiently evoked otoacoustic emission (TEOAE), but most do not take factors such as age, gender, and hearing level into consideration. We focused on these conditions. Subjects were 78 women with normal hearing aged 19 to 24 years (mean = 21.4). All had pure tone thresholds of 15 dB HL or better at 1 kHz, 2 kHz, and 4 kHz. ILO88 was used to record TEOAE and SOAE. Echo power (EP) and reproducibility (Repro) were compared between groups with and without SOAE. No significant audiometric difference was seen between groups. Total echo power (TEP) and whole reproducibility (WR) were significantly greater in the group having SOAE, consistent with previous reports (p < 0.01). EP and Repro classified by frequency bands were also significantly greater in the group having SOAE at 1 kHz to 4 kHz. Subjects were divided based on the number of SOAE and the above parameters compared. We found that as the SOAE number increased, EP and Repro increased. In conclusion, the existence of SOAE influences TEOAE parameters and must be taken into account during clinical testing.     

Clinical investigation of individual differences in evoked otoacoustic emission]

Factors causing individual differences in evoked otoacoustic emission (e-OAE) were investigated in 223 ears of 159 persons with normal hearing. After recording e-OAE to click by using ILO88, the relation between the intensity of e-OAE and factors such as age, sex, small differences in hearing, volume of the external auditory canal, static compliance, developmental extent of the mastoid cavity and presence or absence of spontaneous otoacoustic emission (s-OAE) were studied. The volume of the external auditory canal and static compliance were estimated from a tympanogram measured by Teledyne TA-2C and the developmental extent of the mastoid cavity was measured with a Schüller X-ray film. A correlation was found between the intensity of e-OAE and two factors, the age and the s-OAE, but not between the intensity of e-OAE and other factors. From the fact that the percentage of s-OAE present declines with aging, the presence or absence and the characteristics of s-OAE were considered to be a factor causing individual differences in e-OAE.     

Age-specific changes of evoked otoacoustic emission of different classes]

In different age groups of healthy subjects we registered two classes of evoked otoacoustic emission (OAE): delayed evoked OAE and OAE at the frequency of fault product. The findings show progressive decline of the amplitude of the otoacoustic response in subjects aged over 30-40 years. It is evident that sensor cells of Corti's organ may alter as early as over 30 years of age.     

Quinine-induced alterations of electrically evoked otoacoustic emissions and cochlear potentials in guinea pigs.

Quinine is a well-known ototoxic drug which may affect portions of the auditory system with different biochemical effects, causing reversible hearing loss and tinnitus. Recent investigations indicate that quinine at high concentrations can act directly on cochlear outer hair cells to affect their motility and the mechanical response of the basilar membrane. This study aimed to investigate the effect of quinine on the electromotility of outer hair cells in vivo by means of measuring the electrically evoked otoacoustic emissions (EEOAEs), and the relationship between EEOAE and hearing sensitivity alterations in guinea pigs. Quinine was infused into the scala tympani with concentrations between 0.05 and 5 mM. An alternating current (35 microA RMS) swept from 400 Hz to 40 kHz was applied to the round window to evoke the EEOAE. The compound action potential (CAP), cochlear microphonic (CM) and summating potential (SP) were also measured. Results show that quinine affects the EEOAE in a dose-dependent manner and that its effects are reversible. Two aspects of the EEOAE were affected by quinine, depending on concentration: (1) the 'fine structure' only for concentrations below 0.1 mM and (2) the overall amplitude and the 'fine structure' for concentrations above 0.1 mM. At 5 mM the fine structure was completely absent and the mean amplitude of the EEOAE greatly decreased. Multiple component analysis shows the short delay component of the EEOAE is related to the mean value of the amplitude spectrum while the long delay component is related to the fine structure. The alterations of the EEOAE are roughly comparable to that of the cochlear potentials. A 'threshold concentration' for quinine's effects was found at 25 microM. CAP was significantly affected at 25 microM while EEOAE, CM and SP were not. Enhancement of the EEOAE amplitude was noticed in five out of 20 animals in the current study. The enhancement appears only related to the EEOAE mean level or short delay component. The results suggest that quinine can affect in vivo electromotility of outer hair cells at low concentration and therefore change the cochlear amplifier performance via an effect on electro-mechanical transduction. Its effects on the cochlear spiral ganglion neurons and/or their presynaptic process are also suggested, and these are speculated to be the primary sites for quinine's effects on the auditory system.     

Effects of impulse noise on transiently evoked otoacoustic emission in soldiers

The aim of the study was to assess the effects of exposure to impulse noise on TEOAE, as compared to PTA. The study comprised 92 soldiers, subjected to impulse noise during military service. The control group consisted of secondary school students, not exposed to noise. Extended high frequency PTA, and TEOAE were recorded before and after one year of military service. The total level of noise and spectrum analysis were performed for all kinds of weapons, separately. The highest levels of noise for weapons were related to frequencies from 1.6-16 kHz. After military service significant deterioration of hearing was observed on average by 6 dB exclusively at the frequencies of 10 and 12 kHz. TEOAE reduction was registered predominantly at frequencies of 2, 3 and 4 kHz, with the greatest decrease at 2 kHz (p <0.02). The control group did not show any significant audiometric changes as well as TEOAE during the time of experiment.     

Effect of inner and outer hair cell lesions on electrically evoked otoacoustic emissions

When the cochlea is stimulated by a sinusoidal current, the inner ear emits an acoustic signal at the stimulus frequency, termed the electrically evoked otoacoustic emission (EEOAE). Recent studies have found EEOAEs in birds lacking outer hair cells (OHCs), raising the possibility that other types of hair cells, including inner hair cells (IHCs), may generate EEOAEs. To determine the relative contribution of IHCs and OHCs to the generation of the EEOAE, we measured the amplitude of EEOAEs, distortion product otoacoustic emissions (DPOAEs), the cochlear microphonic (CM) and the compound action potential (CAP) in normal chinchillas and chinchillas with IHC lesions or IHC plus OHC lesions induced by carboplatin. Selective IHC loss had little or no effect on CM amplitude and caused a slight reduction in mean DPOAE amplitude. However, IHC loss resulted in a massive reduction in CAP amplitude. Importantly, selective IHC lesions did not reduce EEOAE amplitude, but instead, EEOAE amplitude increased at high frequencies. When both IHCs and OHCs were destroyed, the amplitude of the CM, DPOAE and EEOAE all decreased. The increase in EEOAE amplitude seen with IHC loss may be due to (1) loss of tonic efferent activity to the OHCs, (2) change in the mechanical properties of the cochlea or (3) elimination of EEOAEs produced by IHCs in phase opposition to those from OHCs.     

Correlation of transiently evoked to distortion-product otoacoustic emission measures in healthy children

OBJECTIVE: Transiently evoked (TEOAEs) and distortion-product otoacoustic emissions at the 2f1-f2 frequency (DPOAEs) are being used as a clinical tool for diagnosis of peripheral auditory pathology. Because both tests are fast and non-invasive, they may be an excellent method for hearing screening in infants and children. The purpose of this study was to compare the TEOAE and DPOAE measures obtained in a group of healthy children. METHODS: Sixty-six school-aged children with normal hearing were included in the study. Subjects with recent otologic disease or abnormal tympanograms were excluded. TEOAEs and DPOAEs were performed using a DP Echoport ILO 292 Otodynamics analyzer connected to a portable personal computer. Correlation between TEOAE amplitudes and DPOAE levels was estimated. RESULTS: Correlation between TEOAE amplitudes and DPOAE levels was highly significant across all measured frequencies. Correlation was more significant at the middle frequencies than at the low and high frequencies. CONCLUSIONS: Although frequency specific information may be obtained by both tests, most reliable results were obtained at the middle frequencies. TEOAE values were more prominent at low frequencies, whereas DPOAEs were more effective at high frequencies. Both methods are reliable, objective, fast and useful tests of the cochlear status and should be included in the standard audiological diagnostic work-up of children.     

A correlative study of evoked otoacoustic emission properties and audiometric thresholds

Summary Correlations were made between the detection thresholds of evoked otoacoustic emissions (EOAEs), subjective click thresholds, and mean audiometric thresholds in 240 normal and hearing-impaired ears. EOAEs have never been observed when subjective click thresholds or mean audiometric thresholds were equal to or greater than 35 dB HL. EOAEs were always found when click thresholds were equal to or lower than 15dB HL and when mean audiometric thresholds were equal to or lower than 22dB HL. The incidence of EOAEs decreased and EOAE thresholds increased with increasing click or mean audiometric thresholds.     

Behaviour of delayed evoked otoacoustic emission under forward masking paradigm.

The behaviour of delayed evoked otoacoustic emission (DEOAE) has been studied in normally hearing adults under a conventional forward-masking paradigm, and subjective measurements were carried out additionally for comparison. The clicks served as signals and the noise bursts were used as masker. In different experimental sets, signal and masker intensity, masker duration, and the interval between masker and maskee were altered. At masker levels corresponding to the subjective post-masking threshold of the clicks, the DEOAE was unaffected, i.e. had no noticeable alteration, compared with click stimulation without masking. Even at higher masker levels the inaudible clicks elicited clearly discernible DEOAEs. The forward-masking detection threshold of DEOAE ('DEOAE post-masking threshold') was reached at masker levels approximately 35 dB above the subjective post-masking threshold. The gap between subjective and DEOAE post-masking threshold vis-à-vis the masker level was also evident at different masker durations and different time intervals between masker and maskee. Central neural and peripheral receptor mechanisms are suggested to be the constituents of the masking phenomenon. The neural mechanism is involved at low masker levels. The receptor mechanism effectively joins the neural one at masker levels exceeding the threshold of psychoacoustic masking. The progressive increase in the number of auditory units from the periphery to the centre in the hearing system, linked with an increase in inhibition, can help to explain these effects.     

A correlative study of evoked otoacoustic emission properties and audiometric thresholds

Correlations were made between the detection thresholds of evoked otoacoustic emissions (EOAEs), subjective click thresholds, and mean audiometric thresholds in 240 normal and hearing-impaired ears. EOAEs have never been observed when subjective click thresholds or mean audiometric thresholds were equal to or greater than 35 dB HL. EOAEs were always found when click thresholds were equal to or lower than 15 dB HL and when mean audiometric thresholds were equal to or lower than 22 dB HL. The incidence of EOAEs decreased and EOAE thresholds increased with increasing click or mean audiometric thresholds.     

Distortion evoked otoacoustic emission using GSI 70 analyzer for neonatal screening

OBJECTIVE: Following the recommendation of the United State National Institute of Health Consensus Conference in 1993, otoacoustic emissions (OAE) are now used internationally for hearing screening. The GSI 70 OAE screener provides the means for carrying out OAE recordings within a short period of time and includes an automatic evaluation of results. The aim of this study was to determine the reliability of recordings in comparison with available standards in brainstem audiometry. METHOD: OAE recorded in 29 hearing-impaired suspected infants and young children (aged 1 months-7 years old) in order to compare the result of the GSI 70 screener with the result of ABR. This study was conducted in the outpatient clinic of the Tokyo University Hospital. RESULT: Our study showed that the GSI 70 screener has higher false negative rate compared with ABR results (P<0.01). Consequently, an OAE measuring method, is also provides high sensitivity and easy to use. However, there was no trend toward increased refer rates with increased age. CONCLUSION: Our findings show that the GSI 70 screener can meet the demands of systematic hearing screening in infants and young children, although there is a tendency to miss cochlear impaired cases.     

Spontaneous and impulsively evoked otoacoustic emission: indicators of cochlear pathology?

The first author's right ear produces a spontaneous otoacoustic emission (SOAE) at 7529 Hz and 16 dB SPL. An external continuous tone is able to suppress the SOAE. The 3 dB iso-suppression curve is broadly tuned and displaced, relative to the SOAE, toward higher frequencies. An audiogram notch exists at frequencies just below that of the SOAE.

We explain the occurrence of both spontaneous and impulsively evoked OAEs in terms of disruption of active feedback mechanisms of the OHCs upon basilar membrane vibration. According to this hypothesis, each segment of the organ of Corti feeds back positively upon its segment of basilar membrane and negatively upon adjacent segments. If a patch of OHC loss exists, adjacent segments of the basilar membrane are released from the negative feedback and respond to an impulsive stimulus with exaggerated oscillations at their resonance frequencies, thus producing OAEs. At particularly sharp transitions between normal and abnormal regions of the organ of Corti SOAEs may be generated.