Otoacoustic emissions

Individual similarities and differences in eye-movement-related eardrum oscillations (EMREOs)

We recently discovered a unique type of otoacoustic emission (OAE) time-locked to the onset (and offset) of saccadic eye movements and occurring in the absence of external sound (Gruters et al., 2018). How and why these eye-movement-related eardrum oscillations (EMREOs) are generated is unknown, with a role in visual-auditory integration being the likeliest candidate. Clues to both the drivers of EMREOs and their purpose can be gleaned by examining responses in normal hearing human subjects. Do EMREOs occur in all individuals with normal hearing? If so, what components of the response occur most consistently? Understanding which attributes of EMREOs are similar across participants and which show more variability will provide the groundwork for future comparisons with individuals with hearing abnormalities affecting the ear's various motor components. Here we report that in subjects with normal hearing thresholds and normal middle ear function, all ears show (a) measurable EMREOs (mean: 58.7 dB SPL; range 45-67 dB SPL for large contralateral saccades), (b) a phase reversal for contra- versus ipsilaterally-directed saccades, (c) a large peak in the signal occurring soon after saccade onset, (d) an additional large peak time-locked to saccade offset and (e) evidence that saccade duration is encoded in the signal. We interpret the attributes of EMREOs that are most consistent across subjects as the ones that are most likely to play an essential role in their function. The individual differences likely reflect normal variation in individuals' auditory system anatomy and physiology, much like traditional measures of auditory function such as auditory-evoked OAEs, tympanometry and auditory-evoked potentials. Future work will compare subjects with different types of auditory dysfunction to population data from normal hearing subjects. Overall, these findings provide important context for the widespread observations of visual- and eye-movement related signals found in cortical and subcortical auditory areas of the brain.

Sensory profiles, behavioral problems, and auditory findings in children with autism spectrum disorder

Objective

This study examined the relationship between sensory processing (SP) differences and behavioral problems in children with autism spectrum disorder (ASD). We also investigated whether audiological test results could objectively detect auditory processing differences.

Method

Forty-six children with ASD, ages 3-9 years, were enrolled in the study. Problematic behaviors and sensory processing of children were assessed using scales. The otolaryngologist performed a detailed head and neck examination and a formal audiological examination was performed by an audiologist.

Results

Stereotypy, hyperactivity, and irritability were related to sensation seeking. Stereotypy was also associated with visual processing. Touch processing differences was related to irritability and inappropriate speech. Lethargy was associated with auditory processing. There were no differences in SP and behavior problems in the children whose audiological profiles could be measured between those who passed or failed the test.

Conclusion

There was an association between SP differences and behavioral problems in children with ASD, supporting previous studies. Audiological test results did not reveal the SP differences documented in the parent forms.

Otoacoustic emissions value in patients with idiopathic sudden sensorineural hearing loss

Objectives

This study aimed to determine the prognostic value of otoacoustic emissions (OAEs) in idiopathic sudden sensorineural hearing loss patients.

Methods

The study included 30 subjects with unilateral idiopathic sudden sensorineural hearing loss (ISSNHL). Each patient was evaluated four times: at baseline and after one week, one month, and three months of treatment. During each visit, each patient was subjected to full audiological history, otoscopic examination, basic audiological evaluations, and transiently evoked and distortion product otoacoustic emission (TEOAEs & DEOAEs).

Results

The hearing thresholds (frequency range 250–8000 Hz) and word recognition scores of patients with detectable TEOAEs and DPOAEs improved significantly, whereas no significant improvements were observed in those with no response.

Conclusion

Hearing improvement is better in patients with detectable TEOAEs and DPOAEs. As a result, TEOAEs and DPOAEs are recommended as routine tests in all SSNHL patients to predict outcomes and monitor treatment as TEOAEs and DPOAEs reflect the cochlear OHCs activity.

Derivation of input-output functions from distortion-product otoacoustic emission level maps

Distortion-product otoacoustic emissions (DPOAEs) emerge from the cochlea when elicited with two tones of frequencies f₁ and f₂. DPOAEs mainly consist of two components, a nonlinear-distortion and a coherent-reflection component. Input-output (I/O) functions of DPOAE pressure at the cubic difference frequency, f_DP=2f₁-f₂, enable the computation of estimated distortion-product thresholds (EDPTs), offering a noninvasive approach to estimate auditory thresholds. However, wave interference between the DPOAE components and suboptimal stimulus-level pairs reduces the accuracy of EDPTs. Here, the amplitude P of the nonlinear-distortion component is extracted from short-pulse DPOAE time signals. DPOAE level maps representing the growth behavior of P in L₁,L₂ space are recorded for 21 stimulus-level pairs and 14 frequencies with f₂=1 to 14 kHz (f₂/f₁=1.2) from 20 ears. Reproducing DPOAE growth behavior using a least-squares fit approach enables the derivation of ridge-based I/O functions from model level maps. Objective evaluation criteria assess the fit results and provide EDPTs, which correlate significantly with auditory thresholds (p < 0.001). In conclusion, I/O functions derived from model level maps provide EDPTs with high precision but without the need of predefined optimal stimulus-level pairs.

Two-tone distortion in reticular lamina vibration of the living cochlea

It has been demonstrated that isolated auditory sensory cells, outer hair cells, can generate distortion products at low frequencies. It remains unknown, however, whether or not motile outer hair cells are able to generate two-tone distortion at high frequencies in living cochleae under the mechanical loads caused by surounding tissues and fluids. By measuring sub-nanometer vibration directly from the apical ends of outer hair cells using a custom-built heterodyne low-coherence interferometer, here we show outer hair cell-generated two-tone distortion in reticular lamina motion in the living cochlea. Reticular-lamina distortion is significantly greater and occurs at a broader frequency range than that of the basilar membrane. Contrary to expectations, our results indicate that motile outer hair cells are capable of generating two-tone distortion in vivo not only at the locations tuned to primary tones but also at a broad region basal to these locations.

Ren et al. used an in house heterodyne low-coherence interferometer to measure sub-nanometer vibrations, a proxy for distortion products, in living cochleae of gerbils. They were able to locate the generation source of the outer hair cell in the reticular lamina versus the basilar membrane in vivo.

No otoacoustic evidence for a peripheral basis of absolute pitch

Absolute pitch (AP) is the ability to identify the perceived pitch of a sound without an external reference. Relatively rare, with an incidence of approximately 1/10,000, the mechanisms underlying AP are not well understood. This study examined otoacoustic emissions (OAEs) to determine if there is evidence of a peripheral (i.e., cochlear) basis for AP. Two OAE types were examined: spontaneous emissions (SOAEs) and stimulus-frequency emissions (SFOAEs). Our motivations to explore a peripheral foundation for AP were several-fold. First is the observation that pitch judgment accuracy has been reported to decrease with age due to age-dependent physiological changes cochlear biomechanics. Second is the notion that SOAEs, which are indirectly related to perception, could act as a fixed frequency reference. Third, SFOAE delays, which have been demonstrated to serve as a proxy measure for cochlear frequency selectivity, could indicate tuning differences between groups. These led us to the hypotheses that AP subjects would (relative to controls) exhibit a. greater SOAE activity and b. sharper cochlear tuning. To test these notions, measurements were made in normal-hearing control (N = 33) and AP-possessor (N = 20) populations. In short, no substantial difference in SOAE activity was found between groups, indicating no evidence for one or more strong SOAEs that could act as a fixed cue. SFOAE phase-gradient delays, measured at several different probe levels (20-50 dB SPL), also showed no significant differences between groups. This observation argues against sharper cochlear frequency selectivity in AP subjects. Taken together, these data support the prevailing view that AP mechanisms predominantly arise at a processing level in the central nervous system (CNS) at the brainstem or higher, not within the cochlea.

The Coda of the Transient Response in a Sensitive Cochlea: A Computational Modeling Study

In a sensitive cochlea, the basilar membrane response to transient excitation of any kind–normal acoustic or artificial intracochlear excitation–consists of not only a primary impulse but also a coda of delayed secondary responses with varying amplitudes but similar spectral content around the characteristic frequency of the measurement location. The coda, sometimes referred to as echoes or ringing, has been described as a form of local, short term memory which may influence the ability of the auditory system to detect gaps in an acoustic stimulus such as speech. Depending on the individual cochlea, the temporal gap between the primary impulse and the following coda ranges from once to thrice the group delay of the primary impulse (the group delay of the primary impulse is on the order of a few hundred microseconds). The coda is physiologically vulnerable, disappearing when the cochlea is compromised even slightly. The multicomponent sensitive response is not yet completely understood. We use a physiologically-based, mathematical model to investigate (i) the generation of the primary impulse response and the dependence of the group delay on the various stimulation methods, (ii) the effect of spatial perturbations in the properties of mechanically sensitive ion channels on the generation and separation of delayed secondary responses. The model suggests that the presence of the secondary responses depends on the wavenumber content of a perturbation and the activity level of the cochlea. In addition, the model shows that the varying temporal gaps between adjacent coda seen in experiments depend on the individual profiles of perturbations. Implications for non-invasive cochlear diagnosis are also discussed.

The fluid-structure-electrical interaction in the cochlea enable the basilar membrane, one of the most important structures in the cochlear partition, to display different dynamic patterns depending on the frequency content of the incoming sound. Interestingly, in a healthy cochlea the motion of the basilar membrane shows echoes upon an impulse acoustic stimulation delivered to the ear canal. The delay, duration, and shape of these echoes vary from one cochlea to another. A hypothesis that irregularities of the properties of the cochlear partition coherently scatter acoustic waves and generate echoes is examined. These irregularities are posited to arise, for example, the damage of the sensory cells or the natural randomness in the morphology of the cochlear partition. Here we build a physiologically-based mathematical model to understand the echoes observed in experiments by introducing irregularity to the properties of the sensory cells. We found that the patterns of the echoes depend on the individual profiles of the irregularities. Our work suggest that the ear canal recording, which is correlated to the dynamics of the basilar membrane, can be used as a non-invasive tool not only to diagnose the intracochlear damage but also to interpret these data given its idiosyncratic origin.

Meta-Analysis of Distortion Product Otoacoustic Emission Retest Variability for Serial Monitoring of Cochlear Function in Adults

OBJECTIVE

Distortion product otoacoustic emissions (DPOAEs) have long been heralded as a means to objectively monitor cochlear function and increasingly are becoming a key component in hearing surveillance programs for individuals at risk for ototoxic- and occupational noise-related hearing loss. Yet clinicians are unsure how to define clinically meaningful shifts in DPOAE level. In this study, a meta-analysis approach is used to synthesize the DPOAE level test-retest literature to construct a set of DPOAE level shift reference limits that can be used clinically to define a statistically significant emission change.

DESIGN

The authors reviewed all published articles identified through a Medline search using the terms "Otoacoustic Emission Variability," "Otoacoustic Emission Reliability," "Otoacoustic Emission Repeatability," and "Otoacoustic Emission Test Retest" restricted to DPOAEs, adults, and English language. Articles with DPOAE level data elicited by moderate stimulus levels for f2 frequencies of 1000, 2000, 4000, or 6000 Hz were selected because these stimulus parameters were relatively well represented in the literature. The authors only included articles that reported the standard error of the measurement (SEM) or from which the SEM could be calculated. Meta-analysis was used to estimate the population mean SEM over the included studies. Models were fit separately for each f2 primary and included days since baseline and study-specific random effects.

RESULTS

Ten DPOAE test-retest studies met inclusion criteria for this meta-analysis. The SEM values varied widely across published studies (0.57 to 3.9 dB) and were provided for relatively short time intervals (less than 15 days on average). Time, or days since baseline, was statistically significant at higher f2 frequencies (4000 and 6000 Hz). From the model results, 90% reference limits specific to the f2 and elapsed time between baseline and follow-up measurements were established. Reference limits provided correspond to negative (emission decrement) and positive (emission enhancement) shifts indicative of the amount of measurement variability that, using this approach, must be tolerated as "normal" fluctuations over time. Changes larger than the reference limits are considered significant and warrant follow-up testing.

CONCLUSIONS

The meta-analysis presented provides reference limits that are appropriate for a set of specific f2 frequencies and time intervals. The meta-analysis concerns the SEM statistic directly, so that any preferred reference limit can be computed from the results and should be predicated upon the screening application. The presumed advantage of this meta-analytic approach is increased precision relative to limits suggested by any of the individual studies included in the analysis.

Level dependence of the nonlinear-distortion component of distortion-product otoacoustic emissions in humans

Distortion-product otoacoustic emissions (DPOAEs) emerge when presenting two primary tones with different frequencies f1 and f2 to the cochlea and are commonly used in diagnosis and research to evaluate the functional state of the cochlea. Optimal primary-tone stimulus levels accounting for the different level dependencies of the traveling-wave amplitudes of the two primary tones near the f2-tonotopic place on the basilar membrane are often used to maximize DPOAE amplitudes. However, parameters defining the optimal levels can be affected by wave interference between the nonlinear-distortion and coherent-reflection components of the DPOAE. Here, the components were separated in the time domain using a pulsed stimulus paradigm and optimal levels determined. Based on the amplitude dependence of the nonlinear-distortion components on primary-tone stimulus levels, level parameters yielding maximum DPOAE amplitudes were derived for six normal-hearing adults and compared to data recorded with continuous two-tone stimulation. The level parameters resulting from analysis of the nonlinear-distortion components show dependence on stimulus frequency and small standard deviations. DPOAE input/output functions derived for optimal levels exhibit larger slopes, wider dynamic range and less variability across subjects than those derived for conventional stimulus and analysis conditions, potentially increasing their reliability and sensitivity for assessing cochlea function.

Evaluation of Inner Ear Damage by Using Otoacoustic Emissions in Patients Who Underwent Mastoidectomy and Tympanoplasty Operations in the Early Period

Objective

We aim to demonstrate inner ear damage caused by drilling in the early period. Healthy contralateral ears of patients who underwent mastoidectomy using drill or tympanoplasty without using drill were compared.

Methods

A total of 38 patients (mastoidectomy: 22, tympanoplasty: 16) who were diagnosed as chronic otitis media and were scheduled for surgery were included. Distortion product (dp) otoacoustic emissions measurements were performed on healthy contralateral ears of patients on pre- and post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day.

Results

In mastoidectomy group, dp otoacoustic emission values on post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day at a frequency of 4000 Hz were significantly lower than in tympanoplasty group (p<0.05). In mastoidectomy group, dp values on post-operative 1. hour, 1. day, 2. day, 3. day, and 4. day at 4000 Hz significantly decreased in comparison with pre-operative period (p<0.05). In comparison with pre-operative period, decrease in dp values on post-operative 1. hour, 1. day, and 2. day at 4000 Hz in mastoidectomy group is significantly higher than those in tympanoplasty group (p<0.05). In tympanoplasty group, dp values on post-operative 1. hour at 4000 Hz significantly decreased in comparison with pre-operative period (p<0.05).

Conclusion

Drilling used in mastoidectomy operation damage healthy contralateral ears by causing acoustic trauma. This damage can be determined by otoacoustic emissions in the early period. According to our study, hearing loss is temporary and more distinct at higher frequencies.

Effects of Type 2 Diabetes on Otoacoustic Emissions and the Medial Olivocochlear Reflex

Objective

To demonstrate if cochleopathy in patients with type 2 diabetes with normal audiometric hearing threshold can be detected with otoacoustic emissions or medial olivocochlear (MOC) reflex measurements.

Study Design

Cross-sectional study.

Setting

Tertiary university teaching hospital.

Methods

The study involved 40 type 2 diabetic patients and 24 healthy volunteers. All participants who showed normal otoscopic findings, hearing thresholds, and acoustic admittance were included. Cochlear activity of participants was evaluated by means of distortion product otoacoustic emissions (DPOAEs) and transient otoacoustic emissions (TOAEs). The MOC reflex was evoked with contralateral acoustic stimulation and recorded with DPOAEs and TOAEs.

Result

A comparison of DPOAE and TOAE levels with a t test between patient and control groups revealed no significant difference ( P > .05). A comparison of the MOC reflex response between the 2 groups also revealed no statistically significant difference ( P > .05).

Conclusion

Although decreased OAE amplitude levels were found in diabetic patients, there was no statistically significant difference in OAEs and MOC reflex. Additional studies are needed to evaluate the role of OAEs and MOC reflex in normal-hearing patients with diabetes.

Is noise-induced cochlear neuropathy key to the generation of hyperacusis or tinnitus?

Perceptual abnormalities such as hyperacusis and tinnitus often occur after acoustic overexposure. Although such exposure can also result in permanent threshold elevation, some individuals with noise-induced hyperacusis or tinnitus show clinically normal thresholds. Recent work in animals has shown that a "neuropathic" noise exposure can cause immediate, permanent degeneration of the cochlear nerve despite complete threshold recovery and lack of hair cell damage (Kujawa SG, Liberman MC. J Neurosci 29: 14077-14085, 2009; Lin HW, Furman AC, Kujawa SG, Liberman MC. J Assoc Res Otolaryngol 12: 605-616, 2011). Here we ask whether this noise-induced primary neuronal degeneration results in abnormal auditory behavior, based on the acoustic startle response (ASR) and prepulse inhibition (PPI) of startle. Responses were measured in mice exposed either to a "neuropathic" noise or to a lower-intensity, "nonneuropathic" noise and in unexposed control mice. Mice with cochlear neuropathy displayed hyperresponsivity to sound, evidenced by enhanced ASR and PPI, while exposed mice without neuronal loss showed control-like responses. Gap PPI tests, often used to assess tinnitus, revealed limited gap detection deficits in mice with cochlear neuropathy only for certain gap-startle latencies, inconsistent with the presence of tinnitus "filling in the gap." Despite significantly reduced wave 1 of the auditory brainstem response, representing cochlear nerve activity, later peaks were unchanged or enhanced, suggesting compensatory neural hyperactivity in the auditory brainstem. Considering the rapid postexposure onset of both cochlear neuropathy and exaggerated startle-based behavior, the results suggest a role for cochlear primary neuronal degeneration, per se, in the central neural excitability that could underlie the generation of hyperacusis.

A longitudinal study of changes in distortion-product otoacoustic emissions and pure-tone thresholds in an industrial setting

In a longitudinal study of 76 noise-exposed industrial workers, 34 (68 ears) of them were available for final evaluation after 9 years of observation. Distortion-product otoacoustic emissions (DP) at 65/55 dB SPL and pure-tone audiometry were used to detect noise-induced inner ear changes. Repeated measures analyses of variance were made on the subjects and in a control group, whereas significant threshold shifts (STS) and significant emission shifts (SES) were calculated. Both hearing thresholds and DP showed a high-frequency deterioration, but there was absence of statistical correlation between elevation of hearing thresholds and decrease of DP. There was no clear pattern between individual changes in audiometric thresholds and DP, and all combinations were present: ears with only STS, ears with only SES, ears with both STS and SES and ears with absence of STS and SES. Audiometric changes were maximal at 4 and 6 kHz and DP changes at 2 and 3 kHz. Since significant individual emission changes do not necessarily follow the same pattern as the group-averaged results, the use of DP for monitoring of individual subjects is not advised. However, its use in conjunction with audiometry in hearing conservation programs is highly recommended.

Effects of Stimulus Intensity on Low-Frequency Toneburst Cochlear Microphonic Waveforms

This study investigates changes in amplitude and delays in low-frequency toneburst cochlear microphonic (CM) waveforms recorded at the ear canal in response to different stimulus intensities. Ten volunteers aged 20-30 were recruited. Low-frequency CM waveforms at 500 Hz in response to a 14-ms toneburst were recorded from an ear canal electrode using electrocochleography techniques. The data was statistically analyzed in order to confirm whether the differences were significant in the effects of stimulus intensity on the amplitudes and delays of the low-frequency CM waveforms. Electromagnetic interference artifacts can jeopardize CM measurements but such artifacts can be avoided. The CM waveforms can be recorded at the ear canal in response to a toneburst which is longer than that used in ABR measurements. The CM waveforms thus recorded are robust, and the amplitude of CM waveforms is intensity-dependent. In contrast, the delay of CM waveforms is intensity-independent, which is different from neural responses as their delay or latency is intensity-dependent. These findings may be useful for development of the application of CM measurement as a supplementary approach to otoacoustic emission (OAE) measurement in the clinic which is severely affected by background acoustic noise. The development of the application in the assessment of low-frequency cochlear function may become possible if a further series of studies can verify the feasibility, but it is not meant to be a substitute for audiometry or OAE measurements. The measurement of detection threshold of CM waveform responses using growth function approach may become possible in the clinic. The intensity-independent nature of CMs with regards to delay measurements may also become an impacting factor for differential diagnoses and for designing new research studies.

Transmission of cochlear distortion products as slow waves: a comparison of experimental and model data

There is a long-lasting question of how distortion products (DPs) arising from nonlinear amplification processes in the cochlea are transmitted from their generation sites to the stapes. Two hypotheses have been proposed: (1) the slow-wave hypothesis whereby transmission is via the transverse pressure difference across the cochlear partition and (2) the fast-wave hypothesis proposing transmission via longitudinal compression waves. Ren with co-workers have addressed this topic experimentally by measuring the spatial vibration pattern of the basilar membrane (BM) in response to two tones of frequency f(1) and f(2). They interpreted the observed negative phase slopes of the stationary BM vibrations at the cubic distortion frequency f(DP) = 2f(1) - f(2) as evidence for the fast-wave hypothesis. Here, using a physically based model, it is shown that their phase data is actually in accordance with the slow-wave hypothesis. The analysis is based on a frequency-domain formulation of the two-dimensional motion equation of a nonlinear hydrodynamic cochlea model. Application of the analysis to their experimental data suggests that the measurement sites of negative phase slope were located at or apical to the DP generation sites. Therefore, current experimental and theoretical evidence supports the slow-wave hypothesis. Nevertheless, the analysis does not allow rejection of the fast-wave hypothesis.

Evaluation of cochlear involvement by transient evoked otoacoustic emission test in children with Crimean-Congo hemorrhagic fever

OBJECTIVE

The aim of this study was to investigate cochlear involvement in child patients with Crimean-Congo hemorrhagic fever (CCHF) disease.

METHODS

Twenty-eight CCHF disease patients (56 ears) and 26 sex- and age-matched healthy control subjects (52 ears) were included in the study. Pure-tone audiometry at frequencies 0.25, 0.5, 1, 2, 4, and 6 kHz, immittance measures including tympanometry and acoustic reflex testing, and transient evoked otoacoustic emission (TEOAE) testing were performed in the patients and controls.

RESULTS

The proportion with a result of 'fail' for the TEOAE test in the CCHF patients was not statistically significant from the control group (p>0.05).

CONCLUSIONS

CCHF disease does not impair cochlear function in children. The clinical course of CCHF among children seems to be milder than in adults.

Fast reverse propagation of sound in the living cochlea

The auditory sensory organ, the cochlea, not only detects but also generates sounds. Such sounds, otoacoustic emissions, are widely used for diagnosis of hearing disorders and to estimate cochlear nonlinearity. However, the fundamental question of how the otoacoustic emission exits the cochlea remains unanswered. In this study, emissions were provoked by two tones with a constant frequency ratio, and measured as vibrations at the basilar membrane and at the stapes, and as sound pressure in the ear canal. The propagation direction and delay of the emission were determined by measuring the phase difference between basilar membrane and stapes vibrations. These measurements show that cochlea-generated sound arrives at the stapes earlier than at the measured basilar membrane location. Data also show that basilar membrane vibration at the emission frequency is similar to that evoked by external tones. These results conflict with the backward-traveling-wave theory and suggest that at low and intermediate sound levels, the emission exits the cochlea predominantly through the cochlear fluids.

Comparing the optimal signal conditions for recording cubic and quadratic distortion product otoacoustic emissions

Odd- and even-order distortion products (DPs), evoked by two primary tones (f(1),f(2),f(1)<f(2)), represent different aspects of cochlear nonlinearity. The cubic and quadratic difference tones (CDT 2f(1)-f(2) and QDT f(2)-f(1)) are prominent representatives of the odd and even DPs. Distortion product otoacoustic emissions (DPOAEs) were measured within a primary level (L(1),L(2)) space over a wide range of f(2)f(1) ratios to compare the optimal signal conditions for these DPs. For CDT, the primary level difference decreased as L(1) increased with a rate proportional to the f(2)f(1) ratio. Moreover, the optimal ratio increased with L(1). A set of two formulas is proposed to describe the optimal signal conditions. However, for a given level of a primary, increasing the other tone level could maximize the QDT amplitude. The frequency ratio at the maximal QDT was about 1.3 and quite constant across different primary levels. A notch was found in the QDT amplitude at the f(2)f(1) ratio of about 1.22-1.25. These opposite behaviors suggest that the optimal recording conditions are different for CDT and QDT due to the different aspects in the cochlear nonlinearity. Optimizing the DPOAE recordings could improve the reliability in clinical or research practices.

Clinical investigation of the transient evoked otoacoustic emission test in Crimean–Congo hemorrhagic fever

OBJECTIVE

The aim of this study was to investigate cochlear damage in Crimean-Congo hemorrhagic fever (CCHF) infection.

METHODS

Thirty-two CCHF patients (study group) and 13 healthy people (controls) were included in the study. CCHF patients were also grouped for the presence of fever. CCHF was diagnosed with the presence of CCHF virus-specific IgM antibody or CCHF virus (CCHFV) antigen by ELISA. Cochlear damage was determined by a 'fail' in the transient evoked otoacoustic emission (TEOAE) test.

RESULTS

The proportion of TEOAE test 'fail' results in the CCHF patients was significantly higher than in the control group (p<0.05). We found no increase in the proportion of TEOAE test 'fail' results related to fever in the study group.

CONCLUSIONS

CCHF disease damages cochlear function regardless of fever.

Low-frequency modulation of distortion product otoacoustic emissions in humans

Low-frequency modulation of distortion product otoacoustic emissions (DPOAEs) was measured from the human ears. In the frequency domain, increasing the bias tone level resulted in a suppression of the cubic difference tone (CDT) and an increase in the magnitudes of the modulation sidebands. Higher-frequency bias tones were more efficient in producing the suppression and modulation. Quasi-static modulation patterns were derived from measuring the CDT amplitude at the peaks and troughs of bias tones with various amplitudes. The asymmetric bell-shaped pattern resembled the absolute value of the third derivative of a nonlinear cochlear transducer function. Temporal modulation patterns were obtained from inverse FFT of the spectral contents around the DPOAE. The period modulation pattern, averaged over multiple bias tone cycles, showed two CDT peaks each correlated with the zero-crossings of the bias tone. The typical period modulation pattern varied and the two CDT peaks emerged with the reduction in bias tone level. The present study replicated the previous experimental results in gerbils. This noninvasive technique is capable of revealing the static position and dynamic motion of the cochlear partition. Moreover, the results of the present study suggest that this technique could potentially be applied in the differential diagnosis of cochlear pathologies.

Spectral fine-structures of low-frequency modulated distortion product otoacoustic emissions

Biasing of the cochlear partition with a low-frequency tone can produce an amplitude modulation of distortion product otoacoustic emissions (DPOAEs) in gerbils. In the time domain, odd- versus even-order DPOAEs demonstrated different modulation patterns depending on the bias tone phase. In the frequency domain, multiple sidebands are presented on either side of each DPOAE component. These sidebands were located at harmonic multiples of the biasing frequency from the DPOAE component. For odd-order DPOAEs, sidebands at the even-multiples of the biasing frequency were enhanced, while for even-order DPOAEs, the sidebands at the odd-multiples were elevated. When a modulation in DPOAE magnitude was presented, the magnitudes of the sidebands were enhanced and even greater than the DPOAEs. The amplitudes of these sidebands varied with the levels of the bias tone and two primary tones. The results indicate that the maximal amplitude modulations of DPOAEs occur at a confined bias and primary level space. This can provide a guide for optimal selections of signal conditions for better recordings of low-frequency modulated DPOAEs in future research and applications. Spectral fine-structure and its unique relation to the DPOAE modulation pattern may be useful for direct acquisition of cochlear transducer nonlinearity from a simple spectral analysis.

Initial Audiologic Assessment of Infants Referred From Well Baby, Special Care, and Neonatal Intensive Care Unit Nurseries

Purpose

The purpose of the study was to evaluate the effectiveness of a 2-hr initial audiologic assessment appointment for infants referred from area universal newborn hearing screening (UNHS) programs to a clinical audiology department in an urban hospital.

Method

A prospective auditory brainstem response (ABR)-based protocol, including clicks, frequency-specific tone bursts, and bone-conducted stimuli, was administered by 10 audiologists to 375 infants. Depending on the ABR findings, additional test options included distortion product otoacoustic emissions (DPOAEs), high-frequency tympanometry, and/or otologic examination.

Results

In 88% of the 2-hr test sessions, at least 4 ABR threshold estimates were obtained (i.e., bilateral clicks and either a 500- or 1000-Hz tone burst and a 4000-Hz frequency tone burst for the better ear). The incidence of hearing loss was significantly different across nursery levels: 18% for Level I (well baby), 29% for Level II (special care), and 52% for Level III (neonatal intensive care unit). Hearing loss type was defined at the initial assessment for 35 of the 51 infants with bilateral hearing loss based on bone-conduction ABR, latency measures, DPOAEs, high-frequency tympanometry, and/or otologic examination.

Conclusions

Our findings indicate that a 2-hr test appointment is appropriate for all nursery levels to diagnose severity and type of hearing loss in the majority of infants referred from UNHS. Examination by an otolaryngologist within 24–48 hr further defines the hearing loss and facilitates treatment plans.

Unexceptional sharpness of frequency tuning in the human cochlea

The responses to sound of auditory-nerve fibers are well known in many animals but are topics of conjecture for humans. Some investigators have claimed that the auditory-nerve fibers of humans are more sharply tuned than are those of various experimental animals. Here we invalidate such claims. First, we show that forward-masking psychophysical tuning curves, which were used as the principal support for those claims, greatly overestimate the sharpness of cochlear tuning in experimental animals and, hence, also probably in humans. Second, we calibrate compound action potential tuning curves against the tuning of auditory-nerve fibers in experimental animals and use compound action potential tuning curves recorded in humans to show that the sharpness of tuning in human cochleae is not exceptional and that it is actually similar to tuning in all mammals and birds for which comparisons are possible. Third, we note that the similarity of frequency of tuning across species with widely diverse cochlear lengths and auditory bandwidths implies that for any given stimulus frequency the "cochlear amplifier" is confined to a highly localized region of the cochlea.

Distortion product otoacoustic emissions after intratympanic gentamicin therapy for unilateral Ménière's disease

The treatment of patients with Ménière's disease that do not respond to conventional therapy becomes complicated, particularly when taking into account the issue of hearing damage as well as the control of vertigo. Treatment often involves the intratympanic administration of gentamicin, for which different protocols are used. Hence, it is important that we better understand how this treatment influences hearing, beyond mere audiometric assessments. The aim of this prospective study was to evaluate the effect of intratympanic gentamicin treatment for Ménière's disease on cochlear function, as assessed by otoacoustic emissions. The 41 patients included in the study had been diagnosed with unilateral Ménière's disease as defined by the American Academy of Otolaryngology-Head and Neck Surgery guidelines (1995), and had been refractory to medical treatment for at least 1 year. Intratympanic injections of gentamicin at a concentration of 27 mg/ml were performed at weekly intervals until indications of vestibular hypofunction appeared in the treated ear. Before beginning the treatment and 3 months after ending it, pure tone and speech audiometry tests were performed and the results are expressed in terms of the pure tone average (0.5, 1, 2, and 3 kHz) and the speech discrimination score, respectively. At the same time, a distortion product otoacoustic emission (DPOAE) study was performed and the results are expressed in terms of its presence or absence, and as the amplitude and threshold of the emission. When analyzed 3 months after the treatment had terminated, hearing loss was seen in 13 patients (31.7%). However, no significant change in the threshold and/or amplitude of otoacoustic emissions was observed in any of the patients. Neither were changes in the audiometric stage, number of injections required or the existence of DPOAE before treatment detected. Hence, the treatment method used here for patients with intractable unilateral Ménière's disease can be considered as having a low risk on auditory function, as assessed both audiometrically and with otoacoustic emissions, and can be considered as subablative for hearing function.