Evoked Otoacoustic Emissions Amplitude Research Articles

Early Maturation of Evoked Otoacoustic Emissions and Medial Olivocochlear Reflex in Preterm Neonates

The present study was designed to investigate the early maturation of the brainstem regulation of the cochlear function in preterm neonates. Evoked otoacoustic emissions (EOAE) and their regulation via the medial olivocochlear efferent (MOC) reflex were investigated in a large population of preterm neonates and compared with full-term neonates and young babies from birth to 4 y and school-aged children. In 28-wk preterm neonates, EOAE were seen in the mid-frequency range. These responses extended both to the low (down to 1025 Hz) and high (up to 6152 Hz) frequency ranges at 38 wk of gestational age and remained stable up to 4 mo. At this stage, the amplitude of EOAE overlapped adult values. EOAE amplitudes then decreased to reach adult values at 3 y of age. Maturation of MOC efferents innervating the outer hair cells was investigated by studying the suppressive effect of contralateral sound on the EOAE amplitudes (MOC reflex). The first MOC responses were recorded in preterm neonates of 32-33 wk of gestational age, reaching adult-like values at 37 wk of gestational age. The maximum effect of MOC efferent activation occurred between 2000 and 4000 Hz. These results suggest that, in humans, MOC efferents mature in utero. Thus, testing the MOC reflex may have a clinical relevance to detect an abnormal development of the auditory pathways, particularly of a brainstem circuitry not explored through conventional testing.

EOAE I/O curves in inner ear impairments

Input/output (I/O) curves of evoked otoacoustic emissions (EOAEs) reveal a saturation at 30 dB or thereabout above their detection threshold. It has been suggested that such I/O relation corresponds to that of the basilar membrane vibration related with an active electro-mechanical process of outer hair cells. EOAEs in response to 1–2 kHz short tone bursts were measured. EOAEs were examined in ears with idiopathic sudden hearing loss (HL), low tone type acute sensorineural HL, Ménière's disease and noise-induced HL. Three types of shift that were downward, horizontal and combined were observed in their I/O curves. The downward shift was seen mainly in the ears with high tone HL and the horizontal shift was in the ears with low tone HL. Three types of shift were observed in the ears of Ménière's disease, in which glycerol administration augmented EOAE amplitude beyond the normal saturation level of its cotralateral side. Measurements of EOAE I/O curves are useful for diagnosis of inner ear impairments related to outer hair cell dysfunction in ears with sensorineural HL.

The interaction between ear and sex differences and stimulus rate

Evoked otoacoustic emissions (EOAEs) are produced by the cochlea in response to acoustic stimuli and provide an objective and non-invasive measure of cochlear function. A new technique, based on maximum length sequences (MLSs), enables stimulus rates of up to 5000 clicks/s to be used. Conventional EOAE amplitude differs between ears and sexes, female subjects having responses of greater amplitude than male subjects and right ears larger responses than left ears. As a prerequisite to clinical use it is necessary to establish if these differences occur with the MLS OAE technique and whether they change with stimulus rate. Eighty ears of normally hearing adults between the ages of 18 and 40 years were tested. MLS OAEs were recorded at eight stimulus rates ranging from 40/s to 5000/s. Two stimulus levels and two recordings were made at each stimulus rate. Female subjects were found to have statistically significantly larger MLS OAEs than male subjects and gave larger amplitude responses in the right ears. The difference was not significant between male right and left ears. A rate effect was also demonstrated with the amplitude of the MLS OAEs decreasing with an increase in rate. The study provides normative data for MLS OAE testing and shows that females have MLS OAEs of larger amplitude than males and that as the click stimulus rate increases the significance of this difference decreases. Female right ears also have MLS OAEs of greater amplitude than female left ears.

Paradoxical Effects of Contralateral White Noise on Evoked Otoacoustic Emissions in Ears with Acoustic Neuroma

A contralateral suppression effect on evoked otoacoustic emissions (EOAEs) is usually present in normally hearing subjects and in patients with sensorineural hearing loss, while it is absent or reduced in ears to which the vestibular nerve has been cut and in ears with acoustic neuroma (AN). To date, a paradoxical effect, that is an increase in EOAE amplitude during contralateral stimulation, has been described in one ear with sensorineural hearing loss of unknown aetiology and in three ears with AN (two in the present paper). Evidence has been provided that the contralateral suppression effect on EOAEs is accomplished largely, if not entirely, via the medial olivocochlear bundle (OCB). According to clinical data the absence or the reduced amount of contralateral suppression effect on EAOEs may be attributed to a totally, or partially, damaged or malfunctioning medial OCB. The way in which a contralateral noise may increase EOAE amplitude is more difficult to explain. One attractive hypothesis is that this paradoxical effect is a result of some pathological adaptive process in the medial OCB.

Medial olivocochlear system stabilizes active cochlear micromechanical properties in humans

To investigate the involvement of the medial olivocochlear system (MOCS) in outer hair cell (OHC) motility stabilization, evoked otoacoustic emissions (EOAEs) were recorded in 20 normal-hearing subjects and in eight vestibular-neurotomized subjects, successively in the presence and absence of low-intensity contralateral acoustic stimulation. Intrasubject EOAE amplitude variability was assessed as the standard deviation computed over several successive recordings. In normal-hearing subjects, a significantly lower EOAE amplitude variability with contralateral acoustic stimulation (CAS) was observed in subjects in whom the CAS induced the greatest EOAE amplitude reduction. This result could not be attributed to the EOAE amplitude reduction itself, since variability was otherwise found to increase when EOAE amplitude decreased. Moreover, statistically significant correlations between EOAE amplitude attenuation and EOAE amplitude variability under CAS were observed. In the eight subjects operated for vestibular neurotomy, no such effect was found. Being sectioned in vestibular-neurotomized subjects, the MOCS can no longer exert its effects. These results strongly support the notion that MOCS activity, as induced by CAS, elicits a reduction in EOAE amplitude variability in normal-hearing subjects. This finding and some of its possible implications for understanding the role of the MOCS in hearing in humans are discussed.

Contralateral suppression and stimulus rate effects on evoked otoacoustic emissions

Transiently evoked otoacoustic emissions (EOAE) were recorded in normal-hearing humans using pseudorandom pulse trains. This allowed the effect of increasing stimulus rate to be studied on EOAE amplitudes, input–output (I/O) functions and suppression by contralateral stimulation. EOAEs are very probably due to micromechanical properties of cochlear outer hair cells, and contralateral suppression is considered to result from olivo-cochlear efferent activation. EOAEs at various stimulus rates showed excellent reproducibility. Total EOAE amplitude diminished as interstimulus interval (ISI) decreased from 20 to 3 ms, but not for ISIs under 3 ms. The amplitude reduction was significant only on EOAE spectrum bands below 3.4 kHz. I/O functions, which kept a linear pattern, were steeper, and contralateral suppression was lower, with the highest stimulus rate (1111 c/s) relative to other rates. The EOAE decline with increasing stimulus rate might be due to incomplete recovery after adaptation of outer hair cells. The lower contralateral suppression at high stimulus rates suggests that crossed olivo-cochlear bundle action is lessened when outer hair cells are responding to a high-rate stimulus. An explanation may be that contralateral stimulation and a high-rate ipsilateral stimulus act via the same mechanisms, i.e., that high-rate stimulation activates an ipsilateral efferent loop.

Cochlear dysfunction in IDDM patients with subclinical peripheral neuropathy.

To investigate the function of the auditory pathway from the cochlea to the auditory cortex in subjects with IDDM. Brain stem, middle-, and long-latency auditory-evoked responses and evoked otoacoustic emissions were measured in 48 normally hearing IDDM patients and in age- and sex-matched nondiabetic subjects. Peripheral neuropathy was diagnosed by nerve conduction velocity (NCV) at the peroneal and sural nerves. Auditory brain stem responses (ABRs) reflect auditory pathway function within the brain stem; middle-latency responses (MLRs) and long-latency responses (LLRs) originate from the auditory cortex; and evoked otoacoustic emissions (EOAEs) give objective information about preneural, mechanical elements of the cochlear function. A subclinical peripheral neuropathy was found in 12 diabetic patients. We found higher latencies of waves I (t = 4.4, P < 0.0001), III (t = 3.7, P = 0.0004), and V (t = 2.7, P = 0.008) of ABRs in diabetic patients (I: 1.7 +/- 0.13 ms; III: 3.9 +/- 0.17 ms; V: 5.7 +/- 0.24 ms), compared with those of the control group (I: 1.6 +/- 0.13 ms; III: 3.7 +/- 0.18 ms; V: 5.6 +/- 0.17 ms). However, neither central transmission time (i.e., the wave interpeak I-V) nor MLRs and LLRs were found to be significantly different in diabetic and control subjects. Mean EOAE amplitude was found to be significantly reduced (F = 4.2, P = 0.02) in diabetic patients with a reduced NCV (7.6 +/- 3.9 dB; Scheffé test: P = 0.03), but not in those without neuropathy (9.1 +/- 4.2 dB), compared with the control group (10.8 +/- 3.1 dB). No correlations were found between duration of diabetes and EOAEs or between sural NCV and peroneal NCV and metabolic control. EOAEs were not correlated with peroneal and sural NCVs. Our results indicate that the early preneural dysfunction of cochlear receptors causes a prolonged activation of the peripheral portion of the auditory pathway, while signal conduction along the central auditory pathway was shown to be normal in diabetes.

Medial Olivocochlear Efferent System in Humans Studied With Amplitude-Modulated Tones

Evoked otoacoustic emissions (EOAEs) are assumed to be generated by outer hair cells (OHCs). It is now generally accepted that EOAEs represent a means of functional exploration of the active micromechanical properties of OHCs. Efferent fibers of the medial olivocochlear system (MOCS) are connected along the sides and the bases of OHCs. Some studies have shown that a suppression effect on EOAE amplitude is induced by the MOCS neurons during contralateral stimulation, presumably by modification of OHC motility. The contralateral acoustic stimuli used in experiments on the EOAE suppression effect have consisted mainly of sounds without a slow temporal fluctuation in their envelopes (broad-band noise, narrow-band noise, pure tones, or clicks). To elucidate further the parameters of MOCS activation, in the present study we looked at the contralateral suppression effect of amplitude-modulated (AM) tones. The results showed that EOAE amplitude was reduced with AM tones compared with no contralateral acoustic stimulation. The suppression effect mainly depended on three parameters. 1) Contralateral stimulation intensity: EOAE suppression occurred only with intensities > or = 40 dB SL. 2) The greater the modulation depth, the greater the suppression effect: statistical analysis showed a significant effect for 75 and 100% modulation depth. 3) The 100- and 140-Hz modulation frequencies gave the greatest suppression effect for 100 and 75% modulation depths. The suppression effect was frequency specific. The greatest decreases were observed when the carrier frequency of the contralateral AM tone was close to the frequency of the EOAE under study, i.e., 1 and 2 kHz. Acoustic cross talk and middle ear effects, which cannot be completely excluded, are discussed. However, the demonstrated frequency specificity of the EOAE suppression effect, together with observed presence of contralateral EOAE suppression in patients without stapedial reflex and the very weak intensities used (i.e., below acoustic reflex threshold), suggested that it was unlikely that the observed effects were due merely to middle ear reflexes. Our results confirm further the contralateral suppression effect on human cochlea mechanisms and show that the suppression effect can be influenced by amplitude modulations of the suppressor, characteristic of sounds in the environment.

Effect of intravenous injection of lidocaine HCl on evoked otoacoustic emissions in tinnitus case

This study was performed to examine the influence of lidocaine HCl on evoked otoacoustic emissions (EOAE) in tinnitus case. EOAE were recorded before and after intravenous injection of lidocaine HCl in 19 patients with unilateral tinnitus. EOAE amplitudes were significantly increased after injection of lidocaine HCl for 10 minutes. Between the effective group and the non-effective group of lidocaine HCl for tinnitus, significant differences were recognized after injection of lidocaine HCl for 10 minutes. These results suggested that lidocaine HCl stimulated cochlear mechanics. Significant differences were not recognized at any time between the group of hearing loss with unknown origin, the group of Meniere's disease and the group of tinnitus without hearing loss.

Evidence of Peripheral Hearing Asymmetry in Humans: Clinical Implications

Auditory system hemispheric asymmetry in language processing is well-established, and there are many indications of lateralization as of the peripheral auditory system i.e., as of the cochlea. The left ear is more susceptible to noise damage; tinnitus is more predominant there, while spontaneous otoacoustic emissions (SOAEs) are more often found in the right ear. The present study addressed the following two questions: Does this right-ear SOAE prevalence exist as early as preterm birth? Is there any functional asymmetry in the medial olivo-cochlear (MOC) efferent system, known to modulate outer hair cell contractions? The study involved 483 preterm neonates (gestional age: 24-37 weeks) and 70 right-handed adults (age: 18-31 years). In each ear, SOAEs and evoked otoacoustic emissions (EOAEs) were recorded and analysed, and, for the adults, functional MOC system assessment was made. Results showed SOAEs and EOAE amplitude to be right-predominant and in adults a right MOC functional predominance. These results indicate peripheral auditory system lateralisation, and an early origin thereof. The MOC system being thought to play a protective role, its physiological lateralisation may be relevant to the left prevalence of tinnitus and of auditory fatigue.

Forward masking of transiently evoked otoacoustic emissions

To explore the mechanisms of cochlear regulation systems, two tone phenomena of transiently evoked otoacoustic emissions (EOAEs) were measured using a forward masking paradigm in normal human ears. EOAEs were elicited by probe tone (1 kHz, 25 dBnHL, 3 ms duration), with or without a preceding masker tone (841 Hz, 35-85 dBnHL, 10-300 ms duration, 5-160 ms interval). In the intensity study, EOAEs showed decrements in amplitude according to the masker intensity. To evaluate the effects of the stapedial reflex (SR), the forward masking in facial palsy cases without SR was also measured. For the higher intensity masker, SR effects were observed in normal cases. The duration study showed a little but almost constant decrement with lower intensities, below the SR threshold, and a 20 ms or more duration masker. The interval study showed the decrement even with low and middle (35/55 dBnHL) intensity masker when the intervals were short. As the intervals were shortened, the decrement in EOAEs amplitude became greater. These results suggest that not only the olivocochlear bundle but also other mechanisms, e.g. short-term adaptation and/or lateral inhibition, may affect the forward masking of EOAEs.

Evoked otoacoustic emissions in preterm infants

Since Kemp's discovery of the otoacoustic emissions phenomenon [7], much study has been given to understanding the nature of it and its ontogeny. Development of the evoked otoacoustic emissions (EOAE) has spurred much interest because they may used as a valid and relatively quick test to assess cochlear integrity in the very youngest patients. One thing that has been learned is that EOAE amplitudes are much larger in normal ears of infants than in normal ears of adults. We asked about the form of this development in a longitudinal, rather than cross-sectional, study in an investigation on children born before 40 weeks post-conceptional age. We were able to examine reliably five ears of four preterm babies while they remained in the neonatal intensive care unit. The EOAEs of these ears were then studied to determine whether and how they changed over time. To do this, we examined both their amplitudes and their spectral properties. It turned out that there are properties of the EOAE spectrum that may be related to post-conceptional age. These are described herein. These findings are expected to have considerable clinical utility as more and more researchers are able to confirm their validity.

Evoked Otoacoustic Emissions in Children in Relation to Middle Ear Impedance

The influence of changes in middle ear impedance with and without serotympanon on the measurement of evoked otoacoustic emissions (EOAE) was investigated in 108 children between 3 and 12 years of age. Children with proven serotympanon never showed good EOAE. In those who only had changes in middle ear impedance without a serotympanon, the decrease in EOAE amplitude was more related to the magnitude of conductive hearing loss than to the change in impedance itself. These results are compared with those of a neonatal screening project in which some of the 532 healthy fullterm newborns showed poor emissions in the first days of life. It seems reasonable to assume that this is due to incomplete pneumatization of the middle ears of these children, especially as a control audiogram later in their lives showed normal hearing thresholds.

Differential effects of ear-canal pressure and contralateral acoustic stimulation on evoked otoacoustic emissions in humans

The effect of ear canal pressure variation (ECPV) on click evoked otoacoustic emissions (EOAEs) was compared to the suppressive effect observed with contralateral acoustic stimulation (CAS) in 11 healthy subjects. Both total EOAE amplitude and amplitude of 200 Hz frequency bands (22) were analyzed. Our results revealed that the ECPV as the CAS induced a decrease of the total EOAE amplitude; these two factors showed an additive effect when they are conjoint. The study of the EOAE frequency bands showed that the majority of them decreased under CAS and ECPV; however, a few bands are not affected. Moreover, it appeared that amplitude of the EOAE frequency bands were not modified in a similar way between the two factors: indeed some bands around 4.1 kHz did not decrease either by CAS or ECPV. These results suggest that these applied factors exert different actions on EOAEs. Moreover, the lack of a decrease effect for the same bands, both with CAS and ECPV, may explain the vulnerability of some cochlear locations.

Evozierte otoakustische Emissionen und ihre Beeinflussung durch kontralaterale akustische Stimulation

The active vibration of the basilar membrane as well as evoked otoacoustic emissions (EOAE) are probably based on the motile properties of cochlear outer hair cells (OHC). In the present study we examined the effects of contralateral acoustic stimulation on ipsilateral EOAE and thereby the active cochlear micromechanics. Contralateral white noise with intensities below 30 dB HL enhanced the EOAE amplitude, whereas higher sound levels reduced the evoked acoustic emissions. Similar effects of contralateral acoustic stimuli on ipsilateral EOAE were observed in patients with a conductive hearing loss. However, the required sound levels were higher compared to probands with normal hearing. In controls with unilateral deaf patients white noise up to 60 dB HL did not alter the EOAE amplitude. We concluded, that in patients with normal hearing or unilateral conductive hearing loss, effects of contralateral acoustic stimulation on evoked ipsilateral sound emissions may be due to the activation of crossed olivo-cochlear efferents reaching the OHCs.

Effect of contralateral acoustic stimulation on active cochlear micromechanical properties in human subjects: dependence on stimulus variables

1. Outer hair cells (OHCs) have active micromechanical properties that are thought to be the origin of evoked otoacoustic emissions (EOAEs). In the present study, click-evoked otoacoustic emissions were recorded in humans with or without various contralateral acoustic stimulations. A previous study, concentrating on contralateral stimulation with broadband noise, had shown a decrease of the EOAE amplitude in humans. Results support a role for the efferent system in cochlear mechanics; indeed, medial efferent neurons of the olivocochlear bundle terminate on the OHCs. To obtain a better understanding of the medial efferent system functioning in humans, the present study looked at the contralateral suppressive effect as a function of stimulus parameters. 2. The study of the input-output function of the EOAE amplitude with and without a 50-dB SPL contralateral broadband noise showed that the suppressive effect was equivalent to a mean reduction of 3.77 dB. 3. For the EOAEs to tone pips, the contralateral suppressive effect was strongest when the contralateral ear stimuli were narrow bands that were centered around the central EOAE frequency. This frequency specificity disappeared for contralateral narrow band noise levels greater than 50 dB SPL. 4. The contralateral suppressive effect was also observed with transient contralateral sounds (nonfiltered clicks). Significant reductions of the EOAE amplitude were seen with contralateral click levels as low as 17.5 dB SL. Above this level, the EOAE amplitude decreased as the contralateral stimulus level increased. This effect was still present in subjects without any stapedial reflex, but absent in total unilateral hearing-loss subjects. Therefore this suppressive effect is unlikely to be due to alteration of the middle ear function or to transcranially conducted sound. 5. When the contralateral interclick interval exceeded 14.2 ms. the suppressive effect was smaller. With contralateral stimulus level maintained subjectively constant, the effect was found to disappear when the interclick interval was greater than 49.9 ms. A saturation of the contralateral suppressive effect was observed for click rates greater than 70/s (interclick interval less than 14.2 ms). 6. Our study confirms and specifies the contralateral sound suppression effect on cochlear mechanisms in humans, assessing the equivalent reduction, showing a frequency specificity and extending these findings to contralateral transient sounds. Any influence of the acoustic crosstalk was eliminated. A role played by middle ear muscles cannot be absolutely ruled out but is not necessary to produce such a contralateral suppressive effect (the effect being found in subjects after surgical removal of the stapedius muscle) and could not explain the frequency specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative assessment of human cochlear function by evoked otoacoustic emissions

The amplitudes of evoked otoacoustic emissions (EOE) and their detection threshold were measured in 44 normal young adults and 118 patients with two categories of cochlear dysfunction, acoustic trauma and presbycusis. A different method was used for each category: detection of click EOE or of stimulus frequency emissions. A partial correlation and multivariate analysis was performed for both groups of results to investigate the relations between EOE threshold and pure tone audiometric thresholds (250 to 8000 Hz). Only one significant correlation was found, linearly relating EOE threshold and hearing threshold at 2 kHz ( P < 0.001), independently of the origin of cochlear dysfunction. It suggests that EOE threshold is not frequency-specific since the frequency of EOE at threshold was nearly always close to 1 kHz. A simple model is proposed, based on the assumption that EOE amplitudes and threshold are proportional to the total number of residual active sites in the organ of Corti, i.e. to the total length of active basilar membrane. It is shown that this model accounts for the results disclosed by the statistical analysis and fits the experimental data. It can be used for quantitatively predicting the residual cochlear activity of a patient. However, the EOE threshold is only sensitive to already important cochlear alterations and this parameter does not seem to allow a follow-up of early stages of cochlear dysfunction.

Evoked Ofoacoustic Emissions in Normal Hearing Infants and Children

Evoked otoacoustic emissions (EOAEs) are a promising tool for evaluating cochlear status in children. Preliminary data from normal-hearing subjects ranging from birth to 29.9 years old are discussed. EOAEs are present and robust in infant ears. However, there is a statistically significant decrease in EOAE amplitude for a fixed stimulus level with increasing age even in a carefully screened sample. At the present time it is unclear if these age-associated changes are due to normal developmental changes in the external and/or middle ear acoustics, normal developmental changes in cochlear mechanics and/or everyday cochlear wear and tear. Issues related to further application of evoked emissions to pediatric populations are discussed.

聴力正常者における誘発耳音響放射の検討

Evoked otoacoustic emissions (EOE) were investigated bilaterally in 25 normal-hearing subjects. Three acoustic click stimuli, produced by one sinusoid of 1kHz, 2kHz or 4kHz were used.EOE were recorded from all ears, and their input-output functions were nonlinear. Among three click stimuli, EOE amplitudes were the highest in most ears by 1kHz click stimulus, but EOE thresholds did not differ significantly. EOE thresholds by 1kHz click stimulus existed between -25dBSL and 15dBSL, and their distribution had one peak at 0dBSL. The mean value of them was -2.2dBSL. Therefore, it was considered that the EOE thresholds of 1kHz click stimulus approximated the psychoacoustic thresholds of this stimulus. The interaural difference of EOE thresholds was small, and it was less than 10dB in 80.0% of total subjects. EOE thresholds had good reproducibility.From these results, it can be concluded that EOE can be useful for examining cochlear function and that the EOE threshold can be a significant parameter for EOE measurement.