From laboratory to clinic: a large scale study of distortion product otoacoustic emissions in ears with normal hearing and ears with hearing loss

The influence of distributed source regions in the formation of the nonlinear distortion component of cubic distortion-product otoacoustic emissions

Distortion product otoacoustic emissions (DPOAEs) are evoked by two stimulus tones with frequency f₁ and f₂ of ratio f₂/f₁  in the range between approximately 1.05 and 1.4. This study theoretically and experimentally analyzes the cubic 2f₁-f₂ DPOAE for different stimulus levels of one of the tones while the other is constant. Simulations for f₂/f₁ of 1.2 and moderate stimulus levels (30-70 dB sound pressure level) indicate that cubic distortion products are generated along a relatively large length of the basilar membrane, the extent of which increases with stimulus level. However, apical from the place of maximum nonlinear force, the wavelets generated by these distributed sources mutually cancel. Therefore, although the spatial extent of the primary DPOAE sources broadens with increasing stimulus level (up to 1.5 oct), the basilar-membrane region contributing to the DPOAE signal is relatively narrow (0.6 oct) and level independent. The observed dependence of DPOAE amplitude on stimulus level can be well-approximated by a point source at the basilar-membrane place where the largest distortion product (maximum of the nonlinear force) is generated. Onset and offset of the DPOAE signal may contain amplitude overshoots (complexities), which are in most cases asymmetrical. Two-tone suppression was identified as the main cause of these onset and offset complexities. DPOAE measurements in two normal-hearing subjects support the level dependence of the steady-state DPOAE amplitude and the asymmetry in the onset and offset responses predicted by the theoretical analysis.

Monitoring Protocols for Cochlear Toxicity

The need for monitoring hearing and auditory function during drug therapy and other treatments that have the potential to cause hearing loss is well documented. Besides the main purpose of ototoxic monitoring, which is to provide feedback to the attending physician about the effects the treatment is having on the auditory system, it is also helpful in setting expectations for the patient and his/her family about the communication issues that may result from the drug therapy. This article will review tests available to an audiologist, both subjective and objective, that can be used to effectively monitor hearing levels and auditory function during treatment. Published guidelines and various ototoxic monitoring protocols are reviewed regarding tests administered, what constitutes a significant change in test results and how these findings are reported, and the impact significant changes may have on the course of treatment. Test protocols from different institutions are compared for both similarities and contrasts. Effective scheduling and test location are key to a successful monitoring program. Finally, the need to streamline ototoxic monitoring of hearing and auditory function to reduce test time and make it less stressful and tiresome on the patient will be considered.

An evaluation of the Sennheiser HDA 280-CL circumaural headphone for use in audiometric testing

Objective: Evaluation of the Sennheiser HDA 280-CL circumaural headphone for the determination of (1) equivalent threshold sound pressure levels (ETSPL) for 125-18,000 Hz.; (2) real ear attenuation (250-8000 Hz); (3) insertion loss (63-18,000 Hz); (4) frequency response (125-18,000 Hz); (5) total harmonic distortion (THD) (125-10,000 Hz); and, (6) linearity (11,200-18,000 Hz).Study Sample: Twenty-five normal hearing adults aged 18-25 participated in (1) and (2).Design: (1) Hearing thresholds were measured using the Sennheiser HDA 280-CL. Frequency specific ETSPL values were calculated in an artificial ear. (2) Sound field thresholds were measured with the ears open and covered with the headphone to obtain the real ear attenuation thresholds (REAT). These values were used to determine the maximum permissible ambient noise levels (MPANL). (3) A B&K HATS mannequin recorded the output levels of a broadband pink noise with the ears open and covered with the headphones. (4, 5) The frequency response, THD and linearity were measured in an artificial ear.Results: Values for ETSPL, REAT, MPANL, insertion loss, as well as measures of frequency response, THD and linearity are presented.Conclusions: The Sennheiser HDA 280-CL meets the requirements for audiometric testing and the values presented can be used for calibration.

Optimizing Clinical Interpretation of Distortion Product Otoacoustic Emissions in Infants

OBJECTIVES

The purpose of this study was to analyze distortion product otoacoustic emission (DPOAE) level and signal to noise ratio in a group of infants from birth to 4 months of age to optimize prediction of hearing status. DPOAEs from infants with normal hearing (NH) and hearing loss (HL) were used to predict the presence of conductive HL (CHL), sensorineural HL (SNHL), and mixed HL (MHL). Wideband ambient absorbance was also measured and compared among the HL types.

DESIGN

This is a prospective, longitudinal study of 279 infants with verified NH and HL, including conductive, sensorineural, and mixed types that were enrolled from a well-baby nursery and two neonatal intensive care units in Cincinnati, Ohio. At approximately 1 month of age, DPOAEs (1-8 kHz), wideband absorbance (0.25-8 kHz), and air and bone conduction diagnostic tone burst auditory brainstem response (0.5-4 kHz) thresholds were measured. Hearing status was verified at approximately 9 months of age with visual reinforcement audiometry (0.5-4 kHz). Auditory brainstem response air conduction thresholds were used to assign infants to an NH or HL group, and the efficacy of DPOAE data to classify ears as NH or HL was analyzed using receiver operating characteristic (ROC) curves. Two summary statistics of the ROC curve were calculated: the area under the ROC curve and the point of symmetry on the curve at which the sensitivity and specificity were equal. DPOAE level and signal to noise ratio cutoff values were defined at each frequency as the symmetry point on their respective ROC curve, and DPOAE results were combined across frequency in a multifrequency analysis to predict the presence of HL.

RESULTS

Single-frequency test performance of DPOAEs was best at mid to high frequencies (3-8 kHz) with intermediate performance at 1.5 and 2 kHz and chance performance at 1 kHz. Infants with a conductive component to their HL (CHL and MHL combined) displayed significantly lower ambient absorbance values than the NH group. No differences in ambient absorbance were found between the NH and SNHL groups. Multifrequency analysis resulted in the best prediction of HL for the SNHL/MHL group with poorer sensitivity values when infants with CHL were included.

CONCLUSIONS

Clinical interpretation of DPOAEs in infants can be improved by using age-appropriate normative ranges and optimized cutoff values. DPOAE interpretation is most predictive at higher F2 test frequencies in young infants (2-8 kHz) due to poor test performance at 1 to 1.5 kHz. Multifrequency rules can be used to improve sensitivity while balancing specificity. Last, a sensitive middle ear measure such as wideband absorbance should be included in the test battery to assess possibility of a conductive component to the HL.

Using Thresholds in Noise to Identify Hidden Hearing Loss in Humans

OBJECTIVES

Recent animal studies suggest that noise-induced synaptopathy may underlie a phenomenon that has been labeled hidden hearing loss (HHL). Noise exposure preferentially damages low spontaneous-rate auditory nerve fibers, which are involved in the processing of moderate- to high-level sounds and are more resistant to masking by background noise. Therefore, the effect of synaptopathy may be more evident in suprathreshold measures of auditory function, especially in the presence of background noise. The purpose of this study was to develop a statistical model for estimating HHL in humans using thresholds in noise as the outcome variable and measures that reflect the integrity of sites along the auditory pathway as explanatory variables. Our working hypothesis is that HHL is evident in the portion of the variance observed in thresholds in noise that is not dependent on thresholds in quiet, because this residual variance retains statistical dependence on other measures of suprathreshold function.

DESIGN

Study participants included 13 adults with normal hearing (≤15 dB HL) and 20 adults with normal hearing at 1 kHz and sensorineural hearing loss at 4 kHz (>15 dB HL). Thresholds in noise were measured, and the residual of the correlation between thresholds in noise and thresholds in quiet, which we refer to as thresholds-in-noise residual, was used as the outcome measure for the model. Explanatory measures were as follows: (1) auditory brainstem response (ABR) waves I and V amplitudes; (2) electrocochleographic action potential and summating potential amplitudes; (3) distortion product otoacoustic emissions level; and (4) categorical loudness scaling. All measurements were made at two frequencies (1 and 4 kHz). ABR and electrocochleographic measurements were made at 80 and 100 dB peak equivalent sound pressure level, while wider ranges of levels were tested during distortion product otoacoustic emission and categorical loudness scaling measurements. A model relating the thresholds-in-noise residual and the explanatory measures was created using multiple linear regression analysis.

RESULTS

Predictions of thresholds-in-noise residual using the model accounted for 61% (p < 0.01) and 48% (p < 0.01) of the variance in the measured thresholds-in-noise residual at 1 and 4 kHz, respectively.

CONCLUSIONS

Measures of thresholds in noise, the summating potential to action potential ratio, and ABR waves I and V amplitudes may be useful for the prediction of HHL in humans. With further development, our approach of quantifying HHL by the variance that remains in suprathreshold measures of auditory function after removing the variance due to thresholds in quiet, together with our statistical modeling, may provide a quantifiable and verifiable estimate of HHL in humans with normal hearing and with hearing loss. The current results are consistent with the view that inner hair cell and auditory nerve pathology may underlie suprathreshold auditory performance.

Longitudinal Development of Distortion Product Otoacoustic Emissions in Infants With Normal Hearing

OBJECTIVES

The purpose of this study was to describe normal characteristics of distortion product otoacoustic emission (DPOAE) signal and noise level in a group of newborns and infants with normal hearing followed longitudinally from birth to 15 months of age.

DESIGN

This is a prospective, longitudinal study of 231 infants who passed newborn hearing screening and were verified to have normal hearing. Infants were enrolled from a well-baby nursery and two neonatal intensive care units (NICUs) in Cincinnati, OH. Normal hearing was confirmed with threshold auditory brainstem response and visual reinforcement audiometry. DPOAEs were measured in up to four study visits over the first year after birth. Stimulus frequencies f1 and f2 were used with f2/f1 = 1.22, and the DPOAE was recorded at frequency 2f1-f2. A longitudinal repeated-measure linear mixed model design was used to study changes in DPOAE level and noise level as related to age, middle ear transfer, race, and NICU history.

RESULTS

Significant changes in the DPOAE and noise levels occurred from birth to 12 months of age. DPOAE levels were the highest at 1 month of age. The largest decrease in DPOAE level occurred between 1 and 5 months of age in the mid to high frequencies (2 to 8 kHz) with minimal changes occurring between 6, 9, and 12 months of age. The decrease in DPOAE level was significantly related to a decrease in wideband absorbance at the same f2 frequencies. DPOAE noise level increased only slightly with age over the first year with the highest noise levels in the 12-month-old age range. Minor, nonsystematic effects for NICU history, race, and gestational age at birth were found, thus these results were generalizable to commonly seen clinical populations.

CONCLUSIONS

DPOAE levels were related to wideband middle ear absorbance changes in this large sample of infants confirmed to have normal hearing at auditory brainstem response and visual reinforcement audiometry testing. This normative database can be used to evaluate clinical results from birth to 1 year of age. The distributions of DPOAE level and signal to noise ratio data reported herein across frequency and age in normal-hearing infants who were healthy or had NICU histories may be helpful to detect the presence of hearing loss in infants.

Tinnitus and Auditory Perception After a History of Noise Exposure: Relationship to Auditory Brainstem Response Measures

OBJECTIVES

To determine whether auditory brainstem response (ABR) wave I amplitude is associated with measures of auditory perception in young people with normal distortion product otoacoustic emissions (DPOAEs) and varying levels of noise exposure history.

DESIGN

Tinnitus, loudness tolerance, and speech perception ability were measured in 31 young military Veterans and 43 non-Veterans (19 to 35 years of age) with normal pure-tone thresholds and DPOAEs. Speech perception was evaluated in quiet using Northwestern University Auditory Test (NU-6) word lists and in background noise using the words in noise (WIN) test. Loudness discomfort levels were measured using 1-, 3-, 4-, and 6-kHz pulsed pure tones. DPOAEs and ABRs were collected in each participant to assess outer hair cell and auditory nerve function.

RESULTS

The probability of reporting tinnitus in this sample increased by a factor of 2.0 per 0.1 µV decrease in ABR wave I amplitude (95% Bayesian confidence interval, 1.1 to 5.0) for males and by a factor of 2.2 (95% confidence interval, 1.0 to 6.4) for females after adjusting for sex and DPOAE levels. Similar results were obtained in an alternate model adjusted for pure-tone thresholds in addition to sex and DPOAE levels. No apparent relationship was found between wave I amplitude and either loudness tolerance or speech perception in quiet or noise.

CONCLUSIONS

Reduced ABR wave I amplitude was associated with an increased risk of tinnitus, even after adjusting for DPOAEs and sex. In contrast, wave III and V amplitudes had little effect on tinnitus risk. This suggests that changes in peripheral input at the level of the inner hair cell or auditory nerve may lead to increases in central gain that give rise to the perception of tinnitus. Although the extent of synaptopathy in the study participants cannot be measured directly, these findings are consistent with the prediction that tinnitus may be a perceptual consequence of cochlear synaptopathy.

A Longitudinal Analysis of Pressurized Wideband Absorbance Measures in Healthy Young Infants

OBJECTIVES

Wideband absorbance (WBA) is an emerging technology to evaluate the conductive pathway (outer and middle ear) in young infants. While a wealth of research has been devoted to measuring WBA at ambient pressure, few studies have investigated the use of pressurized WBA with this population. The purpose of this study was to investigate the effect of age on WBA measured under pressurized conditions in healthy infants from 0 to 6 months of age.

DESIGN

Forty-four full-term healthy neonates (17 males and 27 females) participated in a longitudinal study. The neonates were assessed at 1-month intervals from 0 to 6 months of age using high-frequency tympanometry, acoustic stapedial reflex, distortion product otoacoustic emissions, and pressurized WBA. The values of WBA at tympanometric peak pressure (TPP) and 0 daPa across the frequencies from 0.25 to 8 kHz were analyzed as a function of age.

RESULTS

A linear mixed model analysis, applied to the data, revealed significantly different WBA patterns among the age groups. In general, WBA measured at TPP and 0 daPa decreased at low frequencies (<0.4 kHz) and increased at high frequencies (2 to 5and 8 kHz) with age. Specifically, WBA measured at TPP and 0 daPa in 3- to 6-month-olds was significantly different from that of 0- to 2-month-olds at low (0.25 to 0.31 kHz) and high (2 to 5 and 8 kHz) frequencies. However, there were no significant differences between WBA measured at TPP and 0 daPa for infants from 3 to 6 months of age.

CONCLUSIONS

The present study provided clear evidence of maturation of the outer and middle ear system in healthy infants from birth to 6 months. Therefore, age-specific normative data of pressurized WBA are warranted.

Chirp-Evoked Otoacoustic Emissions and Middle Ear Absorbance for Monitoring Ototoxicity in Cystic Fibrosis Patients

OBJECTIVES

The goal of this study was to investigate the use of transient-evoked otoacoustic emissions (TEOAEs) and middle ear absorbance measurements to monitor auditory function in patients with cystic fibrosis (CF) receiving ototoxic medications. TEOAEs were elicited with a chirp stimulus using an extended bandwidth (0.71 to 8 kHz) to measure cochlear function at higher frequencies than traditional TEOAEs. Absorbance over a wide bandwidth (0.25 to 8 kHz) provides information on middle ear function. The combination of these time-efficient measurements has the potential to identify early signs of ototoxic hearing loss.

DESIGN

A longitudinal study design was used to monitor the hearing of 91 patients with CF (median age = 25 years; age range = 15 to 63 years) who received known ototoxic medications (e.g., tobramycin) to prevent or treat bacterial lung infections. Results were compared to 37 normally hearing young adults (median age = 32.5 years; age range = 18 to 65 years) without a history of CF or similar treatments. Clinical testing included 226-Hz tympanometry, pure-tone air-conduction threshold testing from 0.25 to 16 kHz and bone conduction from 0.25 to 4 kHz. Experimental testing included wideband absorbance at ambient and tympanometric peak pressure and TEOAEs in three stimulus conditions: at ambient pressure and at tympanometric peak pressure using a chirp stimulus with constant incident pressure level across frequency and at ambient pressure using a chirp stimulus with constant absorbed sound power across frequency.

RESULTS

At the initial visit, behavioral audiometric results indicated that 76 of the 157 ears (48%) from patients with CF had normal hearing, whereas 81 of these ears (52%) had sensorineural hearing loss for at least one frequency. Seven ears from four patients had a confirmed behavioral change in hearing threshold for ≥3 visits during study participation. Receiver operating characteristic curve analyses demonstrated that all three TEOAE conditions were useful for distinguishing CF ears with normal hearing from ears with sensorineural hearing loss, with an area under the receiver operating characteristic curve values ranging from 0.78 to 0.92 across methods for frequency bands from 2.8 to 8 kHz. Case studies are presented to illustrate the relationship between changes in audiometric thresholds, TEOAEs, and absorbance across study visits. Absorbance measures permitted identification of potential middle ear dysfunction at 5.7 kHz in an ear that exhibited a temporary hearing loss.

CONCLUSIONS

The joint use of TEOAEs and absorbance has the potential to explain fluctuations in audiometric thresholds due to changes in cochlear function, middle ear function, or both. These findings are encouraging for the joint use of TEOAE and wideband absorbance objective tests for monitoring ototoxicity, particularly, in patients who may be too ill for behavioral hearing tests. Additional longitudinal studies are needed in a larger number of CF patients receiving ototoxic drugs to further evaluate the clinical utility of these measures in an ototoxic monitoring program.

Objective audiometry with DPOAEs : New findings for generation mechanisms and clinical applications

Background

Distortion product otoacoustic emissions (DPOAEs) and transient-evoked otoacoustic emissions (TEOAEs) are sound waves generated as byproducts of the cochlear amplifier. These are measurable in the auditory canal and represent an objective method for diagnosing functional disorders of the inner ear. Conventional DPOAE and TEOAE methods permit detection of hearing impairment, but with less than desirable accuracy.

Objective

By accounting for DPOAE generation mechanisms, the aim is to improve the accuracy of inner-ear diagnosis.

Methods

DPOAEs consist of two components, which emerge at different positions along the cochlea and which may cause artifacts due to mutual interference. Here, the two components are separated in the time domain using short stimulus pulses. Optimized stimulus levels facilitate the acquisition of DPOAEs with maximum amplitudes. DPOAE and Békésy audiograms were recorded from 41 subjects in a clinically relevant frequency range of 1.5–6 kHz.

Results

The short stimulus pulses allowed artifact-free measurement of DPOAEs. Semilogarithmic input–output functions yielded estimated distortion product thresholds, which were significantly correlated with the subjectively acquired Békésy thresholds. In addition, they allowed detection of hearing impairment from 20 dB HL, with 95% sensitivity and only a 5% false-positive rate. This accuracy was achieved with a measurement time of about 1–2 min per frequency.

Conclusion

Compared to conventional DPOAE and TEOAE methods, separation of DPOAE components using short-pulse DPOAEs in combination with optimized stimulus parameters considerably enhances the accuracy of DPOAEs for diagnosing impairment of the cochlear amplifier.

Hearing Norton Sound: a community randomised trial protocol to address childhood hearing loss in rural Alaska

INTRODUCTION

The population in rural Alaska experiences a disproprionately high burden of infection-mediated hearing loss. While the state mandates school hearing screening, many children with hearing loss are not identified or are lost to follow-up before ever receiving treatment. A robust, tribally owned healthcare system exists in Alaska, but children with hearing loss must first be identified and referred for existing infrastructure to be used. This trial will evaluate a new school hearing screening and referral process in rural Alaska, with the goal of improving timely identification and treatment of childhood hearing loss.

METHODS AND ANALYSIS

Comparative effectiveness community randomised trial testing digital innovations to improve school hearing screening and referral in 15 communities in the Norton Sound region of northwest Alaska, with data collection from October 2017 to February 2020. All children (K-12) attending school in Bering Strait School District with parental informed consent and child assent will be eligible (target recruitment n=1500). Participating children will undergo both the current school hearing screen and new mobile health (mHealth) screen, with screening test validity evaluated against an audiometric assessment. Communities will be cluster randomised to continue the current primary care referral process or receive telemedicine referral for follow-up diagnosis and treatment. The primary outcome will be time to International Statistical Classification of Diseases, 10th Revision, ear/hearing diagnosis from screening date, measured in days. Secondary outcomes will include: sensitivity and specificity of current school and mHealth screening protocols measured against a benchmark audiometric assessment (air and bone conduction audiometry, tympanometry and digital otoscopy); hearing loss prevalence; hearing-related quality of life; and school performance (AIMSweb). Intention-to-treat analysis will be used.

ETHICS AND DISSEMINATION

This study has been approved by the Institutional Review Boards of Alaska Area, Norton Sound and Duke University and is registered on clinicaltrials.gov. Results will be distributed with equal emphasis on scientific and community dissemination.

TRIAL REGISTRATION NUMBER

NCT03309553; Pre-results.

Predictors of Hearing-Aid Outcomes

Over 360 million people worldwide suffer from disabling hearing loss. Most of them can be treated with hearing aids. Unfortunately, performance with hearing aids and the benefit obtained from using them vary widely across users. Here, we investigate the reasons for such variability. Sixty-eight hearing-aid users or candidates were fitted bilaterally with nonlinear hearing aids using standard procedures. Treatment outcome was assessed by measuring aided speech intelligibility in a time-reversed two-talker background and self-reported improvement in hearing ability. Statistical predictive models of these outcomes were obtained using linear combinations of 19 predictors, including demographic and audiological data, indicators of cochlear mechanical dysfunction and auditory temporal processing skills, hearing-aid settings, working memory capacity, and pretreatment self-perceived hearing ability. Aided intelligibility tended to be better for younger hearing-aid users with good unaided intelligibility in quiet and with good temporal processing abilities. Intelligibility tended to improve by increasing amplification for low-intensity sounds and by using more linear amplification for high-intensity sounds. Self-reported improvement in hearing ability was hard to predict but tended to be smaller for users with better working memory capacity. Indicators of cochlear mechanical dysfunction, alone or in combination with hearing settings, did not affect outcome predictions. The results may be useful for improving hearing aids and setting patients’ expectations.

Short Term Test-Retest Reliability of Contralateral Inhibition of Distortion Product Otoacoustic Emissions

BACKGROUND AND OBJECTIVES

Strength of medial olivocochlear reflex can be measured reliably using contralateral inhibition of distortion product otoacoustic emissions (DPOAEs) when its fine structure is considered. However, measurement of fine structure of DPOAE is difficult with clinical equipment. Thus, this study investigated the clinically relevant test-retest reliability of contralateral inhibition of DPOAEs. Subjects and.

METHODS

Twenty-six young adults with normal hearing sensitivity participated. DPOAEs were recorded at 27 discrete f2 frequencies between 800 Hz and 8,000 Hz at frequency resolution of 8 points per octave with and without contralateral white noise presented at 50 dB SPL. To check for short term inter-session reliability, contralateral inhibition of DPOAEs were recorded in three sessions, two recording sessions on first day separated by 30 minutes and third time after one week of the first session. Within each session, DPOAEs were recorded twice in single probe-fit condition to test for intra-session reliability.

RESULTS

Cronbach's alpha was calculated having poor reliability (α≤ 0.7) of contralateral inhibition of DPOAEs in both intra-session and inter-session conditions for most of the tested frequencies. 95% confidence intervals of contralateral inhibition magnitude also showed large variability.

CONCLUSIONS

The current results showed that though DPOAE amplitudes were highly reliable across sessions, amount of inhibition of DPOAEs was not reliable when DPOAEs were measured at discrete frequencies. These findings are concurrent with the literature.

Screening Methods for Age-Related Hearing Loss in Older Patients with Cancer: A Review of the Literature

As people grow older, they may experience loss in hearing sensitivity. Age-related hearing loss may negatively affect the patient’s quality of life as it may lead to social isolation. In older patients with cancer, hearing loss can seriously interfere with the patient’s ability to deal properly with all aspects of their disease, and may have a cumulative effect on their already decreased quality of life. Therefore, the proper screening of those conditions is essential in order to optimise the patient’s comfort during and after treatment. This review article aims at providing a concise image of the nature of age-related hearing loss, and provides an overview of the screening methods that could be used in older patients with cancer.

Reflection- and Distortion-Source Otoacoustic Emissions: Evidence for Increased Irregularity in the Human Cochlea During Aging

Previous research on distortion product otoacoustic emission (DPOAE) components has hinted at possible differences in the effect of aging on the two basic types of OAEs: those generated by a reflection mechanism in the cochlea and those created by nonlinear distortion (Abdala and Dhar in J Assoc Res Otolaryngol 13:403-421, 2012). This initial work led to the hypothesis that micromechanical irregularity ("roughness") increases in the aging cochlea, perhaps as the result of natural tissue degradation. Increased roughness would boost the backscattering of traveling waves (i.e., reflection emissions) while minimally impacting DPOAEs. To study the relational effect of aging on both types of emissions and address our hypothesis of its origin, we measured reflection- and distortion-type OAEs in 77 human subjects aged 18-76 years. The stimulus-frequency OAE (SFOAE), a reflection emission, and the distortion component of the DPOAE, a nonlinear distortion emission, were recorded at multiple stimulus levels across a four-octave range in all ears. Although the levels of both OAE types decreased with age, the rate of decline in OAE level was consistently greater for DPOAEs than for SFOAEs; that is, SFOAEs are relatively preserved with advancing age. Multiple regression analyses and other controls indicate that aging per se, and not hearing loss, drives this effect. Furthermore, SFOAE generation was simulated using computational modeling to explore the origin of this result. Increasing the amount of mechanical irregularity with age produced an enhancement of SFOAE levels, providing support for the hypothesis that increased intra-cochlear roughness during aging may preserve SFOAE levels. The characteristic aging effect-relatively preserved reflection-emission levels combined with more markedly reduced distortion-emission levels-indicates that SFOAE magnitudes in elderly individuals depend on more than simply the gain of the cochlear amplifier. This relative pattern of OAE decline with age may provide a diagnostic marker for aging-related changes in the cochlea.

Assessing Sensorineural Hearing Loss Using Various Transient-Evoked Otoacoustic Emission Stimulus Conditions

OBJECTIVES

An important clinical application of transient-evoked otoacoustic emissions (TEOAEs) is to evaluate cochlear outer hair cell function for the purpose of detecting sensorineural hearing loss (SNHL). Double-evoked TEOAEs were measured using a chirp stimulus, in which the stimuli had an extended frequency range compared to clinical tests. The present study compared TEOAEs recorded using an unweighted stimulus presented at either ambient pressure or tympanometric peak pressure (TPP) in the ear canal and TEOAEs recorded using a power-weighted stimulus at ambient pressure. The unweighted stimulus had approximately constant incident pressure magnitude across frequency, and the power-weighted stimulus had approximately constant absorbed sound power across frequency. The objective of this study was to compare TEOAEs from 0.79 to 8 kHz using these three stimulus conditions in adults to assess test performance in classifying ears as having either normal hearing or SNHL.

DESIGN

Measurements were completed on 87 adult participants. Eligible participants had either normal hearing (N = 40; M F = 16 24; mean age = 30 years) or SNHL (N = 47; M F = 20 27; mean age = 58 years), and normal middle ear function as defined by standard clinical criteria for 226-Hz tympanometry. Clinical audiometry, immittance, and an experimental wideband test battery, which included reflectance and TEOAE tests presented for 1-min durations, were completed for each ear on all participants. All tests were then repeated 1 to 2 months later. TEOAEs were measured by presenting the stimulus in the three stimulus conditions. TEOAE data were analyzed in each hearing group in terms of the half-octave-averaged signal to noise ratio (SNR) and the coherence synchrony measure (CSM) at frequencies between 1 and 8 kHz. The test-retest reliability of these measures was calculated. The area under the receiver operating characteristic curve (AUC) was measured at audiometric frequencies between 1 and 8 kHz to determine TEOAE test performance in distinguishing SNHL from normal hearing.

RESULTS

Mean TEOAE SNR was ≥8.7 dB for normal-hearing ears and ≤6 dB for SNHL ears for all three stimulus conditions across all frequencies. Mean test-retest reliability of TEOAE SNR was ≤4.3 dB for both hearing groups across all frequencies, although it was generally less (≤3.5 dB) for lower frequencies (1 to 4 kHz). AUCs were between 0.85 and 0.94 for all three TEOAE conditions at all frequencies, except for the ambient TEOAE condition at 2 kHz (0.82) and for all TEOAE conditions at 5.7 kHz with AUCs between 0.78 and 0.81. Power-weighted TEOAE AUCs were significantly higher (p < 0.05) than ambient TEOAE AUCs at 2 and 2.8 kHz, as was the TPP TEOAE AUC at 2.8 kHz when using CSM as the classifier variable.

CONCLUSIONS

TEOAEs evaluated in an ambient condition, at TPP and in a power-weighted stimulus condition, had good test performance in identifying ears with SNHL based on SNR and CSM in the frequency range from 1 to 8 kHz and showed good test-retest reliability. Power-weighted TEOAEs showed the best test performance at 2 and 2.8 kHz. These findings are encouraging as a potential objective clinical tool to identify patients with cochlear hearing loss.

Distortion-product otoacoustic emissions in workers exposed to urban stressors

The study aimed to compare the distortion-product otoacoustic emissions (DPOAEs) with the pure-tone audiometry and to analyze the changes in participants exposed to noise. The results show a prevalence of participants with impaired DPOAEs higher than the prevalence of participants with impaired audiometries in the total sample, in men, and in outdoor workers and a prevalence of impaired DPOAEs and of impaired audiometries in men higher than in women and in outdoor workers higher than in indoor workers. The comparison of mean values between outdoor and indoor workers shows a significant difference only on some frequencies, in the DP-gram. The results suggest a higher effectiveness of DPOAEs compared with the pure-tone audiometry in identifying the presence of any damage in individuals exposed to noise at an early stage.

Supra-threshold auditory brainstem response amplitudes in humans: Test-retest reliability, electrode montage and noise exposure

The auditory brainstem response (ABR) is a sub-cortical evoked potential in which a series of well-defined waves occur in the first 10 ms after the onset of an auditory stimulus. Wave V of the ABR, particularly wave V latency, has been shown to be remarkably stable over time in individual listeners. However, little attention has been paid to the reliability of wave I, which reflects auditory nerve activity. This ABR component has attracted interest recently, as wave I amplitude has been identified as a possible non-invasive measure of noise-induced cochlear synaptopathy. The current study aimed to determine whether ABR wave I amplitude has sufficient test-retest reliability to detect impaired auditory nerve function in an otherwise normal-hearing listener. Thirty normal-hearing females were tested, divided equally into low- and high-noise exposure groups. The stimulus was an 80 dB nHL click. ABR recordings were made from the ipsilateral mastoid and from the ear canal (using a tiptrode). Although there was some variability between listeners, wave I amplitude had high test-retest reliability, with an intraclass correlation coefficient (ICC) comparable to that for wave V amplitude. There were slight gains in reliability for wave I amplitude when recording from the ear canal (ICC of 0.88) compared to the mastoid (ICC of 0.85). The summating potential (SP) and ratio of SP to wave I were also quantified and found to be much less reliable than measures of wave I and V amplitude. Finally, we found no significant differences in the amplitude of any wave components between low- and high-noise exposure groups. We conclude that, if the other sources of between-subject variability can be controlled, wave I amplitude is sufficiently reliable to accurately characterize individual differences in auditory nerve function.

Sequential analysis as a tool for detection of amikacin ototoxicity in the treatment of multidrug-resistant tuberculosis

OBJECTIVE

To investigate early detection of amikacin-induced ototoxicity in a population treated for multidrug-resistant tuberculosis (MDR-TB), by means of three different tests: pure-tone audiometry (PTA); high-frequency audiometry (HFA); and distortion-product otoacoustic emission (DPOAE) testing.

METHODS

This was a longitudinal prospective cohort study involving patients aged 18-69 years with a diagnosis of MDR-TB who had to receive amikacin for six months as part of their antituberculosis drug regimen for the first time. Hearing was assessed before treatment initiation and at two and six months after treatment initiation. Sequential statistics were used to analyze the results.

RESULTS

We included 61 patients, but the final population consisted of 10 patients (7 men and 3 women) because of sequential analysis. Comparison of the test results obtained at two and six months after treatment initiation with those obtained at baseline revealed that HFA at two months and PTA at six months detected hearing threshold shifts consistent with ototoxicity. However, DPOAE testing did not detect such shifts.

CONCLUSIONS

The statistical method used in this study makes it possible to conclude that, over the six-month period, amikacin-associated hearing threshold shifts were detected by HFA and PTA, and that DPOAE testing was not efficient in detecting such shifts.

Auditory Brainstem Response Altered in Humans With Noise Exposure Despite Normal Outer Hair Cell Function

OBJECTIVES

Recent animal studies demonstrated that cochlear synaptopathy, a partial loss of inner hair cell-auditory nerve fiber synapses, can occur in response to noise exposure without any permanent auditory threshold shift. In animal models, this synaptopathy is associated with a reduction in the amplitude of wave I of the auditory brainstem response (ABR). The goal of this study was to determine whether higher lifetime noise exposure histories in young people with clinically normal pure-tone thresholds are associated with lower ABR wave I amplitudes.

DESIGN

Twenty-nine young military Veterans and 35 non Veterans (19 to 35 years of age) with normal pure-tone thresholds were assigned to 1 of 4 groups based on their self-reported lifetime noise exposure history and Veteran status. Suprathreshold ABR measurements in response to alternating polarity tone bursts were obtained at 1, 3, 4, and 6 kHz with gold foil tiptrode electrodes placed in the ear canal. Wave I amplitude was calculated from the difference in voltage at the positive peak and the voltage at the following negative trough. Distortion product otoacoustic emission input/output functions were collected in each participant at the same four frequencies to assess outer hair cell function.

RESULTS

After controlling for individual differences in sex and distortion product otoacoustic emission amplitude, the groups containing participants with higher reported histories of noise exposure had smaller ABR wave I amplitudes at suprathreshold levels across all four frequencies compared with the groups with less history of noise exposure.

CONCLUSIONS

Suprathreshold ABR wave I amplitudes were reduced in Veterans reporting high levels of military noise exposure and in non Veterans reporting any history of firearm use as compared with Veterans and non Veterans with lower levels of reported noise exposure history. The reduction in ABR wave I amplitude in the groups with higher levels of noise exposure cannot be accounted for by sex or variability in outer hair cell function. This change is similar to the decreased ABR wave I amplitudes observed in animal models of noise-induced cochlear synaptopathy. However, without post mortem examination of the temporal bone, no direct conclusions can be drawn concerning the presence of synaptopathy in the study groups with higher noise exposure histories.

Cochlear dysfunction and microvascular complications in patients with type 1 diabetes mellitus

Sensorineural hearing impairment has been associated with DM, and it is probably linked to the same pathophysiological mechanisms as well-established in microvascular diabetes complications. The study of otoacoustic emissions (OAEs) is useful to identify subclinical cochlear dysfunction. Therefore, the aim of this study was to evaluate the association between abnormal OAEs responses, diabetic kidney disease (DKD) and diabetic cardiac autonomic neuropathy (CAN). We performed a cross-sectional study with 37 type 1 DM patients without auditory symptoms, submitted to the study of Distortion Product Otoacoustic Emissions (DPOAEs) and screened for DKD and CAN. The otoacoustic emissions responses were considered abnormal in 27/37 (73%) patients. A correlation was found between abnormal OAEs responses and presence of DKD (r = 0.36, p < 0.05), and 14/16 (88%) patients with a lower amplitude of OAEs in 8 kHz frequency band presented DKD. Abnormal OAEs responses in the 6 kHz frequency band were correlated with the presence (r = 0.41, p = 0.01) and severity of CAN (r = 0.44, p < 0.001). Additionally, 7/9 (78%) patients with abnormal OAE responses in this frequency also presented abnormal CAN scores. Our results suggest that abnormal otoacoustic emissions responses in high frequency bands are associated with diabetes microvascular complications and could be a risk marker for DKD and CAN, presenting low sensitivity and high specificity. Therefore, assuming that hearing impairment is a pre-clinical stage of hearing loss, performing distortion product otoacoustic emissions in T1DM patients with microvascular complications could be useful to identify those who would be benefit with regular audiologic follow up and tighter diabetes control.

Efferent modulation of pre-neural and neural distortion products

Distortion product otoacoustic emissions (DPOAEs) and distortion product frequency following responses (DPFFRs) are respectively pre-neural and neural measurements associated with cochlear nonlinearity. Because cochlear nonlinearity is putatively linked to outer hair cell electromotility, DPOAEs and DPFFRs may provide complementary measurements of the human medial olivocochlear (MOC) reflex, which directly modulates outer hair cell function. In this study, we first quantified MOC reflex-induced DPOAE inhibition at spectral fine structure peaks in 22 young human adults with normal hearing. The f1 and f2 tone pairs producing the largest DPOAE fine structure peak for each subject were then used to evoke DPFFRs with and without MOC reflex activation to provide a related neural measure of efferent inhibition. We observed significant positive relationships between DPOAE fine structure peak inhibition and inhibition of DPFFR components representing neural phase locking to f2 and 2f1-f2, but not f1. These findings may support previous observations that the MOC reflex inhibits DPOAE sources differentially. That these effects are maintained and represented in the auditory brainstem suggests that the MOC reflex may exert a potent influence on subsequent subcortical neural representation of sound.

The Effect of Ethnicity on Wideband Absorbance of Neonates with Healthy Middle Ear Functions in Malaysia: A Preliminary Study

BACKGROUND AND OBJECTIVES

Although ethnicity effect on wideband absorbance (WBA) findings was evident for adults, its effect on neonates has not been established yet. This study aimed to investigate the influence of ethnicity on WBA measured at 0 daPa from neonates with healthy middle ear functions.

SUBJECTS AND METHODS

Participants were 99 normal, healthy, full-term newborn babies with chronological age between 11 and 128 hours of age (mean=46.73, standard deviation=26.36). A cross-sectional study design was used to measure WBA at 16 one-third octave frequency points from 99 neonates comprising of three ethnic groups: Malays (n=58), Chinese (n=13) and Indians (n=28). A total of 165 ears (83.3%) that passed a battery of tests involving distortion product otoacoustic emissions, 1 kHz tympanometry and acoustic stapedial reflex were further tested using WBA. Moreover, body size measurements were recorded from each participant.

RESULTS

The Malays and Indians neonates showed almost identical WBA response across the frequency range while the Chinese babies showed lower absorbance values between 1.25 kHz and 5 kHz. However, the differences observed in WBA between the three ethnic groups were not statistically significant (p=0.23). Additionally, there were no statistically significant difference in birth weight, height and head circumference among the three ethnic groups.

CONCLUSIONS

This study showed that Malays, Chinese and Indians neonates were not significantly different in their WBA responses. In conclusion, to apply for the ethnic-specific norms is not warranted when testing neonates from population constitute of these three ethnicities.

Pressurized Wideband Absorbance Findings in Healthy Neonates: A Preliminary Study

PURPOSE

The present study aimed to establish normative data for wideband absorbance (WBA) measured at tympanometric peak pressure (TPP) and 0 daPa and to assess the test-retest reliability of both measurements in healthy neonates.

METHOD

Participants of this cross-sectional study included 99 full-term neonates (165 ears) with mean chronological age of 46.7 hrs (SD = 26.3 hrs). Of the 99 neonates, 58 were Malay, 28 were Indian, and 13 were Chinese. The neonates who passed high-frequency (1 kHz) tympanometry, acoustic stapedial reflex, and distortion product otoacoustic emission screening tests were assessed using a pressurized WBA test (wideband tympanometry). To reduce the number of measurement points, the WBA responses were averaged to 16 one-third octave frequency bands from 0.25 to 8 kHz. A mixed-model analysis of variance was applied to the data to investigate the effects of frequency, ear, gender, and ethnicity on WBA. The analysis of variance was also used to compare between WBA measured at TPP and 0 daPa. An interclass correlation coefficient test was applied at each of the 16 frequency bands to measure the test-retest reliability of WBA at TPP and 0 daPa.

RESULTS

Both WBA measurements at TPP and 0 daPa exhibited a multipeaked pattern with 2 maxima at 1.25-1.6 kHz and 6.3 kHz and 2 minima at 0.5 and 4 kHz. The mean WBA measured at TPP was significantly higher than that measured at 0 daPa at 0.25, 0.4, 0.5, 1.25, and 1.6 kHz only. A normative data set was developed for absorbance at TPP and at 0 daPa. There was no significant effect of ethnicity, gender, and ear on both measurements of WBA. The test-retest reliability of WBA at TPP and 0 daPa was high with the interclass correlation coefficient ranging from 0.77 to 0.97 across the frequencies.

CONCLUSIONS

Normative data of WBA measured at TPP and 0 daPa for neonates were provided in the present study. Although WBA at TPP was slightly higher than the WBA measured at 0 daPa at some frequencies below 2 kHz, the WBA patterns of the 2 measurements were nearly identical. Moreover, the test-retest reliability of both WBA measurements was high.

Otoacoustic emissions in young adults exposed to drums noise of a college band

ABSTRACT Purpose: to identify cochlear dysfunction and occurrence of tinnitus in young adults exposed to drums noise of a college band. Methods: the sample included 50 subjects: 25 musicians (study group) and 25 non-musicians (control group). The procedures included anamnesis, pure tone audiometry, acoustic impedance and Transient Evoked Otoacoustic Emissions, Distortion Product Otoacoustic Emissions and Distortion Product Otoacoustic Emissions Input-Output function. Results: positive correlation between the occurrence of tinnitus and the variables exposure time and use of personal stereos was found. Overall, the study group showed significantly lower Transient Evoked Otoacoustic Emissions, when compared to the control group. In the study group, there was a tendency toward worse response in 6 kHz(f2) in Distortion Product Otoacoustic Emissions in both ears. The Distortion Product Otoacoustic Emissions Input-Output function did not differ between groups nor did its slope. Conclusion: in general, otoacoustic emissions were worse in noise-exposed young people (study group) when compared to the unexposed (control group), indicating that the test may be important in early identification of cochlear changes.

Towards a joint reflection-distortion otoacoustic emission profile: Results in normal and impaired ears

Otoacoustic emissions (OAEs) provide salient information about cochlear function and dysfunction. Two broad classes of emissions, linear reflection and nonlinear distortion, arise via distinct cochlear processes and hence, appear to provide independent information about cochlear health and hearing. Considered in combination, these two OAE types may characterize sensory hearing loss most effectively. In this study, the level-dependent growth of stimulus-frequency OAEs (a reflection-type emission) and distortion-product OAEs (a distortion-type emission) were measured in ten normal-hearing ears and eight ears with slight-to-moderate sensorineural hearing loss. Metrics of OAE strength and compression were derived from OAE input/output functions and then considered in a combined fashion. Results indicate that SFOAEs and DPOAEs differ significantly in their strength and compression features. When SFOAE and DPOAE metrics are displayed together on a two-dimensional plot, relatively well-defined data clusters describe their normative relationship. In hearing-impaired ears, this relationship is disrupted but not in a uniform way across ears; ears with similar audiograms showed differently altered joint-OAE profiles. Hearing loss sometimes affected only one OAE or one more than the other. Results suggest a joint-OAE profile is promising and warrants study in a large group of subjects with sensory hearing loss of varied etiologies.

Detection of Deafness in Puppies Using a Hand-Held Otoacoustic Emission Screener

The purpose of this study was to evaluate the use of a hand-held otoacoustic emissions screener to detect deafness in puppies. Specifically, distortion product otoacoustic emissions were recorded from 34 puppies (both sexes) of a variety of breeds, from 6-10 wk of age, and the results were compared to brainstem auditory evoked responses (BAER) recorded from the same puppies. Recordings were obtained from both ears in awake or lightly anesthetized puppies, and the results from each ear were compared. In all 62 ears that had normal BAERs, the distortion product otoacoustic emissions screener gave a response of "Pass." The three puppies that had flat BAER recordings in one or both ears provided a screener result of "Refer." In two ears with unusual BAERs (waveforms with reduced amplitudes and prolonged latencies) and a "Refer" response from the screener, there was compacted debris in one external ear canal, and the other ear canal was normal. The screener technology has proven application in human infants and is an attractive alternative to BAER testing in puppies because of expense and ease of use.

Transient evoked otoacoustic emissions in rock musicians

OBJECTIVE

Our focus in this study was the assessment of transient evoked otoacoustic emissions (TEOAEs) in a large group of rock musicians. A further objective was to analyse tinnitus among rock musicians as related to TEOAEs.

DESIGN

The study was a cross-sectional survey of rock musicians selected at random. A control group was included at random for comparison.

STUDY SAMPLE

We recruited 111 musicians and a control group of 40 non-musicians. Testing was conducted by using clinical examination, pure tone audiometry, TEOAEs and a questionnaire.

RESULTS

TEOAE SNR in the half-octave frequency band centred on 4 kHz was significantly lower bilaterally in musicians than controls. This effect was strongly predicted by age and pure-tone hearing threshold levels in the 3-6 kHz range. Bilateral hearing thresholds were significantly higher at 6 kHz in musicians. Twenty percent of the musicians had permanent tinnitus. There was no association between the TEOAE parameters and permanent tinnitus.

CONCLUSIONS

Our results suggest an incipient hearing loss at 6 kHz in rock musicians. Loss of TEOAE SNR in the 4 kHz half-octave frequency band was observed, but it was related to higher mean 3-6 kHz hearing thresholds and age. A large proportion of rock musicians have permanent tinnitus.

Outer Hair Cell and Auditory Nerve Function in Speech Recognition in Quiet and in Background Noise

The goal of this study was to describe the contribution of outer hair cells (OHCs) and the auditory nerve (AN) to speech understanding in quiet and in the presence of background noise. Fifty-three human subjects with hearing ranging from normal to moderate sensorineural hearing loss were assayed for both speech in quiet (Word Recognition) and speech in noise (QuickSIN test) performance. Their scores were correlated with OHC function as assessed via distortion product otoacoustic emissions, and AN function as measured by amplitude, latency, and threshold of the VIIIth cranial nerve Compound Action Potential (CAP) recorded during electrocochleography (ECochG). Speech and ECochG stimuli were presented at equivalent sensation levels in order to control for the degree of hearing sensitivity across patients. The results indicated that (1) OHC dysfunction was evident in the lower range of normal audiometric thresholds, which demonstrates that OHC damage can produce “Hidden Hearing Loss,” (2) AN dysfunction was evident beginning at mild levels of hearing loss, (3) when controlled for normal OHC function, persons exhibiting either high or low ECochG amplitudes exhibited no statistically significant differences in neither speech in quiet nor speech in noise performance, (4) speech in noise performance was correlated with OHC function, (5) hearing impaired subjects with OHC dysfunction exhibited better speech in quiet performance at or near threshold when stimuli were presented at equivalent sensation levels. These results show that OHC dysfunction contributes to hidden hearing loss, OHC function is required for optimum speech in noise performance, and those persons with sensorineural hearing loss exhibit better word discrimination in quiet at or near their audiometric thresholds than normal listeners.

Distortion product otoacoustic emissions in young adult and geriatric cats

Recordings of distortion product otoacoustic emissions (DPOAEs) were taken from 15 geriatric cats (mean age ± standard deviation, SD, 13.6 ± 2.7 years; range 10.2-19.4 years) and 12 young adult control cats (mean ± SD 4.6 ± 0.5 years; range 3.4-5 years) to identify frequency-specific age-related changes in cochlear responses. Recordings were performed for primary frequencies from 2 to 12 kHz in 2 kHz increments. Cats were considered to be geriatric > 11.9 ± 1.9 years of age. Brainstem auditory evoked response (BAER) recordings were also made for subjective comparison with DPOAE responses. No differences in DPOAE response amplitudes were observed at any tested frequency in geriatric cats compared to control cats, reflecting an apparent absence of loss of cochlear outer hair cells along the length of the cochlea. No linear regression relationships were found for DPOAE response amplitude versus age in geriatric cats, despite the progressive nature of age-related hearing loss in other species. The absence of reductions in response at any of the tested frequencies in cats within the age span where cats are considered to be geriatric indicates that age-related hearing loss, if it does develop in cats, begins later in the life span of cats than in dogs or human beings.

Concurrent measures of contralateral suppression of transient-evoked otoacoustic emissions and of auditory steady-state responses

Contralateral suppression of otoacoustic emissions (OAEs) is frequently used to assess the medial olivocochlear (MOC) efferent system, and may have clinical utility. However, OAEs are weak or absent in hearing-impaired ears, so little is known about MOC function in the presence of hearing loss. A potential alternative measure is contralateral suppression of the auditory steady-state response (ASSR) because ASSRs are measurable in many hearing-impaired ears. This study compared contralateral suppression of both transient-evoked otoacoustic emissions (TEOAEs) and ASSRs in a group of ten primarily older adults with either normal hearing or mild sensorineural hearing loss. Responses were elicited using 75-dB peak sound pressure level clicks. The MOC was activated using contralateral broadband noise at 60 dB sound pressure level. Measurements were made concurrently to ensure a consistent attentional state between the two measures. The magnitude of contralateral suppression of ASSRs was significantly larger than contralateral suppression of TEOAEs. Both measures usually exhibited high test-retest reliability within a session. However, there was no significant correlation between the magnitude of contralateral suppression of TEOAEs and of ASSRs. Further work is needed to understand the role of the MOC in contralateral suppression of ASSRs.

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.

Estrogen Blockade Reduces Auditory Feedback in CBA Mice

OBJECTIVE: To examine the effects of estrogen suppression on age-related changes in distortion product otoacoustic emissions (DPOAEs) and contralateral suppression (CS) of DPOAEs in CBA mice.

STUDY DESIGN AND SETTING: Young CBA mice received a slow-release shoulder implantation of either tamoxifen or placebo. Serial DPOAEs and CS of DPOAEs were obtained at 3-week intervals over a period of 9 weeks.

RESULTS: Although DPOAEs were maintained over the study interval, CS of DPOAEs decreased significantly with age in the experimental group. No such declines were observed in either the control animals or the untreated male mice.

CONCLUSIONS: Estrogen suppression negatively affects the MOC efferent feedback system.

SIGNIFICANCE: Our results support the hypothesis that estrogen plays an important role in the maintenance of auditory integrity. Additionally, our findings raise intriguing questions about auditory effects of hormonal shifts in humans resulting from menopause, hormone supplements such as oral contraceptives, and hormone replacement therapy as well as antiestrogens.

Audiometric Thresholds: Stimulus Considerations in Sound Field and Under Earphones

PURPOSE

This study evaluates a new stimulus, FREquency Specific Hearing assessment (FRESH) noise, to obtain hearing thresholds and reviews the potential pitfalls of using narrow band noise.

METHOD

Twelve adults with simulated gradually sloping hearing loss and 12 adults with steeply sloping hearing loss participated. Hearing thresholds were measured in sound field and under a supraaural earphone for FRESH noise, warbled tones, and narrowband noise. Pure-tone thresholds were also measured under the supraaural earphone.

RESULTS

FRESH noise thresholds were similar to pure-tone and warbled-tone thresholds regardless of audiometric configuration. For the group with gradually sloping hearing loss, thresholds obtained with narrowband noise were approximately 4 dB better than those obtained with the other test stimuli. For the group with steeply sloping hearing loss, narrowband noise significantly underestimated hearing thresholds-the steeper the hearing loss, the greater the underestimation.

CONCLUSIONS

When hearing loss is suspected, FRESH noise is appropriate for accurately determining audiometric thresholds in sound field and under earphones. A wider band, attention-getting stimulus such as narrowband noise can result in thresholds that are inaccurate. Clinical decision making regarding choice of test stimulus is discussed.

Service Learning in Undergraduate Audiology Education

PURPOSE

The purpose of this study was to incorporate a service learning project in an undergraduate audiology course and evaluate how it affected student learning in the class.

METHOD

The study involved partnering with a group of students enrolled in a band learning community. Students in the audiology course learned about hearing assessment procedures in class and practiced the procedures on each other in labs. Toward the end of the semester, they assessed the hearing of the band students and provided counseling regarding the importance of hearing protection. Qualitative data were obtained in the form of preflections and final reflection papers completed by the students in the audiology course at the start and conclusion of the semester. Quantitative data included completion of the Community Service Attitudes Scale (CSAS; Shiarella, McCarthy, & Tucker, 2000) prior to and at the conclusion of the course.

RESULTS

Results revealed overwhelmingly positive comments from the students in their final reflections, although there were no significant changes in the pre- and post-administration of the CSAS.

CONCLUSION

Incorporating service learning projects into undergraduate curricula in speech and hearing has the potential to enhance academic and civic learning while also benefitting the community.

Comparative multivariate analyses of transient otoacoustic emissions and distorsion products in normal and impaired hearing

BACKGROUND AND AIM

The clinical utility of otoacoustic emissions as a noninvasive objective test of cochlear function has been long studied. Both transient otoacoustic emissions and distorsion products can be used to identify hearing loss, but to what extent they can be used as predictors for hearing loss is still debated. Most studies agree that multivariate analyses have better test performances than univariate analyses. The aim of the study was to determine transient otoacoustic emissions and distorsion products performance in identifying normal and impaired hearing loss, using the pure tone audiogram as a gold standard procedure and different multivariate statistical approaches.

METHODS

The study included 105 adult subjects with normal hearing and hearing loss who underwent the same test battery: pure-tone audiometry, tympanometry, otoacoustic emission tests. We chose to use the logistic regression as a multivariate statistical technique. Three logistic regression models were developed to characterize the relations between different risk factors (age, sex, tinnitus, demographic features, cochlear status defined by otoacoustic emissions) and hearing status defined by pure-tone audiometry. The multivariate analyses allow the calculation of the logistic score, which is a combination of the inputs, weighted by coefficients, calculated within the analyses. The accuracy of each model was assessed using receiver operating characteristics curve analysis. We used the logistic score to generate receivers operating curves and to estimate the areas under the curves in order to compare different multivariate analyses.

RESULTS

We compared the performance of each otoacoustic emission (transient, distorsion product) using three different multivariate analyses for each ear, when multi-frequency gold standards were used. We demonstrated that all multivariate analyses provided high values of the area under the curve proving the performance of the otoacoustic emissions. Each otoacoustic emission test presented high values of area under the curve, suggesting that implementing a multivariate approach to evaluate the performances of each otoacoustic emission test would serve to increase the accuracy in identifying the normal and impaired ears. We encountered the highest area under the curve value for the combined multivariate analysis suggesting that both otoacoustic emission tests should be used in assessing hearing status. Our multivariate analyses revealed that age is a constant predictor factor of the auditory status for both ears, but the presence of tinnitus was the most important predictor for the hearing level, only for the left ear. Age presented similar coefficients, but tinnitus coefficients, by their high value, produced the highest variations of the logistic scores, only for the left ear group, thus increasing the risk of hearing loss. We did not find gender differences between ears for any otoacoustic emission tests, but studies still debate this question as the results are contradictory. Neither gender, nor environment origin had any predictive value for the hearing status, according to the results of our study.

CONCLUSION

Like any other audiological test, using otoacoustic emissions to identify hearing loss is not without error. Even when applying multivariate analysis, perfect test performance is never achieved. Although most studies demonstrated the benefit of using the multivariate analysis, it has not been incorporated into clinical decisions maybe because of the idiosyncratic nature of multivariate solutions or because of the lack of the validation studies.

Hearing Thresholds, Minimum Response Levels, and Cross-Check Measures in Pediatric Audiology

PURPOSE

Pediatric audiologists must identify hearing loss in a timely manner so that early intervention can be provided. In this article, the methods important for differentiating between a hearing threshold and minimum response level (MRL), important for an accurate diagnosis, are described.

METHOD

Operant conditioning procedures, used during visual reinforcement audiometry and conditioned play audiometry, are reviewed. Case examples are provided that demonstrate the importance of using evidence-based procedures, evaluating the success of such procedures, and using cross-check measures for interpreting responses as thresholds or MRLs.

RESULTS

Behavioral-hearing thresholds can be obtained when operant conditioning procedures are successful and cross-check measures corroborate the audiometric results. When MRLs are obtained, cross-check measures are critical in determining the likelihood of hearing loss and making follow-up recommendations.

CONCLUSIONS

Early diagnosis of hearing loss is important so that intervention can be initiated within critical periods during infant and childhood learning. Accurate diagnosis depends on the audiologist, who must adhere to evidence-based procedures, use cross-check measures, and evaluate the validity of each procedure. Future research and guidelines are needed to examine decision-making processes in pediatric audiology that ensure diagnostic accuracy and timely intervention for infants and children identified with hearing loss.

Auditory function in normal-hearing, noise-exposed human ears

OBJECTIVES

To determine whether suprathreshold measures of auditory function, such as distortion-product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs), are correlated with noise exposure history in normal-hearing human ears. Recent data from animal studies have revealed significant deafferentation of auditory nerve fibers after full recovery from temporary noise-induced hearing loss. Furthermore, these data report smaller ABR wave I amplitudes in noise-exposed animal ears when compared with non-noise-exposed control animals or prenoise exposure amplitudes in the same animal. It is unknown whether a similar phenomenon exists in the normal-hearing, noise-exposed human ear.

DESIGN

Thirty normal-hearing human subjects with a range of noise exposure backgrounds (NEBs) participated in this study. NEB was quantified by the use of a noise exposure questionnaire that extensively queried loud sound exposure during the previous 12 months. DPOAEs were collected at three f2s (1, 2, and 4 kHz) over a range of L2s. DPOAE stimulus level began at 80 dB forward-pressure level and decreased in 10 dB steps. Two-channel ABRs were collected in response to click stimuli and 4 kHz tone bursts; one channel used an ipsilateral mastoid electrode and the other an ipsilateral tympanic membrane electrode. ABR stimulus level began at 90 dB nHL and was decreased in 10 dB steps. Amplitudes of waves I and V of the ABR were analyzed.

RESULTS

A statistically significant relationship between ABR wave I amplitude and NEB was found for clicked-evoked ABRs recorded at a stimulus level of 90 dB nHL using a mastoid recording electrode. For this condition, ABR wave I amplitudes decreased as a function of NEB. Similar systematic trends were present for ABRs collected in response to clicks and 4 kHz tone bursts at additional suprathreshold stimulation levels (≥70 dB nHL). The relationship weakened and disappeared with decreases in stimulation level (≤60 dB nHL). Similar patterns were present for ABRs collected using a tympanic membrane electrode. However, these relationships were not statistically significant and were weaker and more variable than those collected using a mastoid electrode. In contrast to the findings for ABR wave I, wave V amplitude was not significantly related to NEB. Furthermore, there was no evidence of a systematic relationship between suprathreshold DPOAEs and NEB.

CONCLUSIONS

A systematic trend of smaller ABR wave I amplitudes was found in normal-hearing human ears with greater amounts of voluntary NEB in response to suprathreshold clicks and 4 kHz tone bursts. These findings are consistent with the data from previous work completed in animals, where the reduction in suprathreshold responses was a result of deafferentation of high-threshold/low-spontaneous rate auditory nerve fibers. These data suggest that a similar mechanism might be operating in human ears after exposure to high sound levels. However, evidence of this damage is only apparent when examining suprathreshold wave I amplitude of the ABR. In contrast, suprathreshold DPOAE level was not significantly related to NEB. This was expected, given noise-induced auditory damage findings in animal ears did not extend to the outer hair cells, the generator for the DPOAE response.

Most individuals with either segmental or non-segmental vitiligo display evidence of bilateral cochlear dysfunction

BACKGROUND

Vitiligo has been classified clinically into segmental vitiligo (SV) and nonsegmental vitiligo (NSV) and may also be associated with audiological abnormalities.

OBJECTIVES

We examined cochlear function in ears of individuals with SV and NSV, including subjects with facial and nonfacial lesions, and in patients who have SV with unilateral facial involvement.

METHODS

This study included 25 patients with SV and 28 patients with NSV. Fifteen age- and sex-matched healthy individuals served as controls. Cochlear function was studied using the distortion product otoacoustic emissions (DPOAEs). Data were analysed using SPSS.

RESULTS

Sixty-four ears (60%) of patients with vitiligo had cochlear dysfunction while the control group exhibited no abnormalities. On comparing the cochlear dysfunction of patients with SV with patients with NSV, no statistically significant difference was found. The ears on both sides, affected and unaffected by vitiligo, in patients with SV showed cochlear dysfunction with no statistically significant difference in DPOAE. To determine the effect of the lesion side on cochlear function, we compared DPOAE amplitude using Student's t-test. The comparisons included NSV of the face vs. NSV on other areas, NSV of the face vs. SV of the face and SV of the face vs. SV of other areas. No statistically significant difference was found in these comparisons.

CONCLUSIONS

Bilateral cochlear dysfunction is common in both NSV and SV and does not reflect the appearance of vitiligo in the skin. Our results underscore the important role of melanocytes and melanin in cochlear function, and suggest that the cochlear abnormalities in SV point to the presence of additional nonsegmental pathophysiological events underlying all forms of vitiligo.

A test protocol for assessing the hearing status of students with special needs

OBJECTIVES

Individuals with disabilities are often reported to have a high prevalence of undetected hearing disorders/loss, but there is no standardized hearing test protocol for this population. The purposes of this study were (1) to examine the hearing status of students with special needs in Taiwan, and (2) to investigate the use of an on-site hearing test protocol that would adequately detect hearing problems in this population and reduce unnecessary referrals for off-site follow-up services.

METHODS

A total of 238 students enrolled in two schools for special education and one habilitation center participated in the study. Most students had intellectual disabilities and some also had additional syndromes or disorders. A hearing screening protocol including otoscopy, tympanometry, and distortion product otoacoustic emissions was administered to examine students' outer, middle, and inner ear functions, respectively. Pure tone tests were then administered as an on-site follow-up for those who failed or could not be tested using the screening protocol.

RESULTS

Only 32.4% of students passed. When administered alone, the referral rate of otoscopy, tympanometry, and otoacoustic emissions were 38.7%, 46.0%, and 48.5%, respectively. The integration of these subtests revealed 52.1% of students needed follow-up services, 11.8% could not be tested, 2.5% had documented hearing loss, and 1.3% needed to be monitored because of negative middle ear pressure. The inclusion of pure tone audiometry increased the passing rate by 9.9% and provided information on hearing sensitivity for an additional 8.6% of students.

CONCLUSION

Hearing assessments and regular hearing screening should be provided as an integral part of health care services for individuals with special needs because of high occurrences of excessive cerumen, middle ear dysfunction, and sensorineural hearing loss. The training of care-givers and teachers of students with special needs is encouraged so that they can help identify hearing problems and reduce the negative impact of hearing disorders and hearing loss. The screening protocol needs to include subtests that examine the status of different parts of their auditory system. The addition of pure tone audiometry as an on-site follow-up tool reduced the rate of off-site referrals and provided more information on hearing sensitivity.