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

Low-frequency and high-frequency distortion product otoacoustic emission suppression in humans

Distortion product otoacoustic emission suppression (quantified as decrements) was measured for f(2)=500 and 4000 Hz, for a range of primary levels (L(2)), suppressor frequencies (f(3)), and suppressor levels (L(3)) in 19 normal-hearing subjects. Slopes of decrement-versus-L(3) functions were similar at both f(2) frequencies, and decreased as f(3) increased. Suppression tuning curves, constructed from decrement functions, were used to estimate (1) suppression for on- and low-frequency suppressors, (2) tip-to-tail differences, (3) Q(ERB), and (4) best frequency. Compression, estimated from the slope of functions relating suppression "threshold" to L(2) for off-frequency suppressors, was similar for 500 and 4000 Hz. Tip-to-tail differences, Q(ERB), and best frequency decreased as L(2) increased for both frequencies. However, tip-to-tail difference (an estimate of cochlear-amplifier gain) was 20 dB greater at 4000 Hz, compared to 500 Hz. Q(ERB) decreased to a greater extent with L(2) when f(2)=4000 Hz, but, on an octave scale, best frequency shifted more with level when f(2)=500 Hz. These data indicate that, at both frequencies, cochlear processing is nonlinear. Response growth and compression are similar at the two frequencies, but gain is greater at 4000 Hz and spread of excitation is greater at 500 Hz.

Transient and distortion product evoked oto-acoustic emissions in normal hearing patients with and without tinnitus

Objective

To test the hypothesis that tinnitus begins with outer hair cell dysfunction by recording transient (TEOAE) and distortion product evoked (DPOAE) oto-acoustic emissions in patients with normal hearing with (study group, SG) and without tinnitus (control group, CG).

Study Design

Case control study.

Subjects and Methods

SG had 32 patients with pure tone thresholds below 25 dB in the 500 to 8000 Hz interval. CG had 37 age- and gender-matched patients with similar thresholds. All patients had normal tympanograms and stapedial reflexes. TEOAE were recorded with wide band click in continuous mode at 80-dB peak SPL. DPOAE were recorded with f1/f2 = 1.22 and intensities of 65 dB (f1) and 55 dB (f2) SPL.

Results

DPOAE were abnormal in 68.4% of SG and in 50% of CG ( P = 0.036). TEOAE were abnormal in 70.2% of SG and in 16.10% of CG ( P = 0.0001).

Conclusion

SG had significantly higher prevalence of abnormal TEOAE and DPOAE than CG.

Subclinical Dysfunction of Cochlea and Cochlear Efferents in Migraine: An Otoacoustic Emission Study

Otoacoustic emission (OAE) testing enables us to identify the cochlear component of a hearing disorder and to monitor objectively minute changes in cochlear status undetectable by other audiological methods. Contralateral sound-induced suppression is mediated by medial superior olivary complex efferents which induce hyperpolarization counteracting the amplifying effects of outer hair cell (OHC) activity. The aim of this study was to assess functions of cochlea and its efferents in migraine using OAE testing and contralateral suppression of transiently evoked OAEs (TEOAE). Fifty-three migraineurs (106 ears) and 41 healthy subjects (82 ears) were included and pure tone audiometry (PTA), speech discrimination scores (SDS), distortion product OAE (DPOAE), TEOAE and contralateral suppression of TEOAEs were tested. PTA and SDS of migraineurs and controls were not different ( P > 0.05). DPOAEs were tested between 1 and 6 kHz and a significant difference was detected only at 5 kHz frequency, where DPOAE amplitudes in migraine with aura (MA) were lower than in controls ( P < 0.03). The mean amplitudes of TEOAEs were statistically insignificant between controls and migraine groups. Contralateral sound stimulus induced significant decrease in amplitudes of TEOAE ( P = 0.005) in controls. In patients with migraine without aura and MA, mean amplitudes of TEOAEs were not suppressed by contralateral sound stimulus ( P > 0.05). As PTA, SDS and DPOAE tests demonstrate normal functioning of inner ear between 1 and 4 kHz, absence of suppression of the TEOAEs by contralateral sound stimulation indicates the presence of dysfunction either in the medial olivocochlear complex in the brainstem or at the synaptic transmission between olivocochlear efferents and OHCs in the cochlea. Disruption in the contralateral suppression may be one of the mechanisms predisposing to the phonophobia symptom associated with migraine headache.

Using otoacoustic emissions to screen for hearing loss in early childhood care settings

OBJECTIVE

Until recently, no objective tool has been available to help health and early childhood education providers screen young children for hearing loss. The aim of this study was to screen underserved children <or=3 years of age for hearing loss using otoacoustic emissions (OAE) technology and to systematically document multi-step screening and diagnostic outcomes.

METHODS

A total of 4,519 children, <or=3 years of age in four states were screened by trained lay screeners using portable OAE equipment set to deliver stimuli and measurement levels sensitive to mild hearing loss as low as 25 decibels (dB) hearing level. The screening and follow-up protocol specified that children not passing the multi-step OAE screening be evaluated by local physicians and hearing specialists.

RESULTS

Of the 4,519 children screened as a part of the study, 257 (6%) ultimately required medical or audiological follow-up. One hundred and seven children were identified as having a hearing loss or disorder of the outer, middle or inner ear requiring treatment or monitoring. Of these 107 children, 5 had permanent bilateral and 2 had permanent unilateral hearing loss. The seven children with permanent hearing loss included four who had passed newborn screening, two who were not screened at birth and one who did not receive follow-up services after referring from newborn screening.

CONCLUSIONS

OAE screening, using a multi-step protocol, was found to be a feasible and accurate practice for identifying a wide range of hearing-health conditions warranting monitoring and treatment among children <or=3 years of age in early childhood care programs. Future studies are needed to: (1) further examine barriers to effective OAE screening in early childhood care settings and (2) explore the value of extending early childhood OAE hearing screening into health care clinics and settings where young children receive routine care.

Distortion product otoacoustic emissions in sheep before and after hyperinsulinemia induction

Transient evoked otoacoustic emissions and distortion product otoacoustic emissions have gained significant importance in the identification of cochlear alterations.

AIM

To record distortion product thresholds through the monitoring of otoacoustic emissions in normal conditions and in the presence of electrophysiologic changes in cochlear outer hair cells in sheep after hyperinsulinemia induction.

MATERIAL AND METHODS

Experimental study, with seven sheep in the control group and seven in the study group. Insulin and glucose concentrations were measured simultaneously for the recording of distortion product otoacoustic emission every 10 minutes, all the way to 90 minutes. The control group received saline solution, and the study group received a bolus injection of 0.1 U/kg of regular human insulin.

RESULTS

There was a significant reduction in distortion product thresholds in the study group when compared to the control group at frequencies greater than 1,500 Hz and after 60 minutes (P < 0.001).

CONCLUSION

This study established distortion product otoacoustic emission thresholds in sheep with constant reproducibility, demonstrating that the method is adequate for use in audiology and otology investigations. Results also fully confirm that acute hyperinsulinemia may cause important changes in these thresholds.

Distortion product otoacoustic emissions: cochlear-source contributions and clinical test performance

It has been proposed that the clinical accuracy of distortion product otoacoustic emissions (DPOAEs) is affected by the interaction of distortion and reflection sources contributing to the response. This study evaluated changes in dichotomous-decision test performance and threshold-prediction accuracy when DPOAE source contribution was controlled. Data were obtained from 205 normal and impaired ears with L(2) ranging from 0 to 80 dB SPL and f(2)=2 and 4 kHz. Data were collected for control conditions (no suppressor, f(3)) and with f(3) presented at three levels that previously had been shown to reduce the reflection-source contribution. The results indicated that controlling source contribution with a suppressor did not improve diagnostic accuracy (as reflected by relative operating characteristic curve area) and frequently resulted in poorer test performance compared to control conditions. Likewise, correlations between DPOAE and behavioral thresholds were not strengthened when using the suppressors to control source contribution. While improvements in test accuracy were observed for a subset of subjects (normal ears with the smallest DPOAEs and impaired ears with the largest DPOAEs), the lack of improvement for the larger, unselected subject group suggests that DPOAEs should be recorded in the clinic without attempting to control the source contribution with a suppressor.

Otoacoustic emissions, ear fullness and tinnitus in the recovery course of sudden deafness

OBJECTIVE

This study aimed to investigate how the symptoms of ear fullness, tinnitus and otoacoustic emissions (OAE) change in relation to the recovery course of pure tone audiometry thresholds (PTA) in sudden deafness (SD).

METHODS

This study analyzed follow-up data on ear fullness, tinnitus and otoacoustic emissions of eight SD patients with good hearing improvement (Group A) and eight SD patients with poor hearing improvement (Group B) in an attempt to elucidate the behavior of these symptoms in their recovery course. This study was done until there was no change in the PTA for more than 1 week and hearing recovery was no longer expected.

RESULTS

All patients from both groups had ear fullness and tinnitus in association with the onset of SD. However, these symptoms improved only in Group A. showing a significant relationship between PTA recovery and the improvement of ear fullness annoyance (P<0.05), presence of tinnitus (P<0.01), improvement in tinnitus loudness (P<0.01) and in tinnitus annoyance (P<0.01). No patients (Group A or B) had OAE responses at their first examination. In Group A, OAE responses appeared simultaneously with improvement of hearing levels in five patients (63%) and it appeared later than hearing levels improvement in the other three patients (37%) from Group A. No patient from Group B showed OAE response on follow-up.

CONCLUSION

SD patients with good hearing improvement (Group A) tended to have OAE responses and the sensations of the ear fullness and tinnitus improved almost simultaneously with hearing level improvement. Their PTA improvement occurred primarily in the low to mid frequencies, with high frequencies showing less recovery. When hearing recovery was not full, OAEs did not reappear for these frequencies. Patients with poor hearing improvement tended to have absent OAEs and persistent ear fullness and tinnitus.

Perception of temporally processed speech by listeners with hearing impairment

OBJECTIVES

The purpose of this study was to assess a new signal-processing strategy, Spatiotemporal Pattern Correction (SPC), for a group of listeners with varying degrees of sensorineural hearing loss. SPC is based on a physiological model of the level-dependent temporal response properties of auditory nerve (AN) fibers in normal and impaired ears. SPC attempts to "correct" AN response patterns by introducing time-varying group delays that differ across frequency channels. Listeners' speech intelligibility and preference judgments were obtained at different strengths of SPC processing.

DESIGN

Fifteen listeners, 12 with bilateral sensorineural hearing loss and 3 with normal hearing, participated in this study. Listeners with hearing impairment were separated into 3 groups (mild, moderate, and moderate-to-severe), based on their pure-tone averages at 0.5, 1, 2, and 4 kHz. All preference judgments were made using sentences from the Hearing-In-Noise-Test (HINT). The sentences were processed at five SPC strengths (1.0, 1.1, 1.2, 1.3, and 1.4). At an SPC strength of 1.0, the speech was processed through the SPC signal processor, becoming bandlimited, but no dynamic group delays were added to the signal. On each trial, listeners were presented a single sentence at two different SPC strengths, 1.0 (uncorrected) and a randomly selected SPC strength. Listeners were instructed to identify which of the two sentences they preferred. Sixteen vowel-consonant syllables, a subset of the Nonsense Syllable Test (NST), were used to assess speech intelligibility at three SPC strengths (1.0, 1.1, and 1.2). Listeners were asked to push one of 16 buttons on a response box that corresponded to the vowel-consonant syllable they heard. The moderate-to-severe hearing loss group was also tested using the low-probability sentences of the Speech-Perception-In-Noise (SPIN) test.

RESULTS

Listeners with normal hearing and listeners with mild hearing loss preferred the quality of uncorrected sentences (SPC strength of 1.0) compared with SPC-processed sentences. As the strength of SPC increased, listeners' preference for uncorrected sentences also increased. Listeners with moderate and moderate-to-severe hearing loss had difficulty differentiating between uncorrected and lower strength SPC-processed sentences but strongly preferred the uncorrected sentences as compared with high strength SPC-processed sentences. Vowel-consonant intelligibility was not improved or degraded by SPC. Sentence recognition scores for listeners with moderate-to-severe hearing loss decreased with SPC processing.

CONCLUSIONS

Although SPC-processed speech was not preferred by listeners with hearing loss, the listeners with a more moderate degree of impairment could not differentiate the unprocessed sentences from the SPC processed sentences. Speech intelligibility was not improved by SPC processing.

Otoacoustic Emissions in Early Noise-Induced Hearing Loss

OBJECTIVE

To follow changes in transient evoked and distortion product otoacoustic emissions (TEOAEs, DPOAEs) as they relate to pure-tone audiometry (PTaud) thresholds during the first 2 years of occupational noise exposure.

DESIGN

Prospective controlled.

METHODS

Pure-tone audiometry thresholds, TEOAE and DPOAE amplitudes, and contralateral medial olivocochlear reflex strength were repeatedly evaluated during 2 years and compared between and within a cohort of 135 ship engine room recruits and a control group of 100 subjects with no noise exposure.

RESULTS

Pure-tone audiometry thresholds for 2,000, 3,000 and 4,000 Hz in both ears were significantly elevated in the study group after 2 years of noise exposure. Significantly lower TEOAE amplitudes were found at 2,000 Hz in the right ear and 2,000 and 4,000 Hz in the left ear. Longitudinal intrasubject analysis of the study group revealed significant reductions of TEOAE amplitudes at 2,000 to 4,000 Hz in both ears and reduced DPOAE amplitudes for 5,957 Hz in the right ear and 3,809, 4,736, and 5,957 Hz in the left ear in the second follow-up evaluation. Baseline medial olivocochlear reflex strength showed no correlation to PTaud thresholds after 2 years of noise exposure. Poor to moderate negative linear correlations (r = -0.07 to -0.37) were found between the DPOAE-averaged amplitudes at 2,979 to 5,957 Hz and PTaud threshold means at 3,000 to 6,000 Hz. Abnormal TEOAE parameters after the first year of noise exposure had high sensitivity (86-88%) and low specificity (33-35%) for the prediction of noise-induced hearing loss (NIHL) after 2 years.

CONCLUSION

The DP-gram is not significantly correlated with PTaud and cannot be used as an objective measure of pure-tone thresholds in early NIHL. Medial olivocochlear reflex strength before the beginning of chronic exposure to occupational noise has no relation to individual vulnerability to NIHL. Although TEOAEs changes after 1 year showed high sensitivity in predicting NIHL after 2 years of exposure, they cannot be recommended as an efficient screening tool due to high false-positive rates.

Otoacoustic emission sensitivity to low levels of noise-induced hearing loss

With the aim of investigating the capability of otoacoustic emission (OAE) in the detection of low levels of noise-induced hearing loss, audiometric and otoacoustic data of young workers (age: 18-35) exposed to different levels of industrial noise have been recorded. These subjects are participating in a long-term longitudinal study, in which audiometric, exposure (both professional and extra-professional), and OAE data (transient evoked and distortion product) will be collected for a period of several years. All measurements have been performed, during routine occupational health surveillance, with a standard clinical apparatus and acquisition procedure, which can be easily used in the occupational safety practice. The first study was focused on the correlation between transient evoked OAE signal-to-noise ratio and distortion product (DPOAE) OAE level and the audiometric threshold, investigating the causes of the rather large intersubject variability of the OAE levels. The data analysis has shown that, if both OAE data and audiometric data are averaged over a sufficiently large bandwidth, the correlation between DPOAE levels and audiometric hearing threshold is sufficient to design OAE-based diagnostic tests with good sensitivity and specificity also in a very mild hearing loss range, between 10 and 20 dB.

Emissões otoacústicas: produto de distorção em lactentes até dois meses de idade

TEMA: na Audiologia clínica há uma necessidade de se estabelecer parâmetros para análise da emissão otoacústica - produto de distorção (EOAPD) em lactentes, com a finalidade de utilizá-los como critério clínico na avaliação audiológica. OBJETIVO: descrever os achados do registro das EOAPD em lactentes até dois meses de idade por meio da análise do nível de resposta, do nível de ruído e da relação sinal/ruído em todas as bandas de freqüências; da análise do nível de resposta em relação às variáveis: gênero, pico de pressão na timpanometria e estado do lactente durante o exame e da distribuição do percentil do nível de resposta. MÉTODO: foram avaliados 138 lactentes sem indicadores de risco para perda auditiva e que passaram na triagem auditiva. Os parâmetros foram: L1 = 65dBNPS e L2 = 50dBNPS no equipamento ILO292 - Otodynamics. RESULTADOS: Foram avaliados 70 lactentes do gênero masculino e 68 do feminino. As medianas do nível de resposta das EOAPD por freqüência (f2) variaram entre 6,0dB NPS e 16,3dBNPS. As medianas do nível de ruído das EOAPD por freqüência (f2) variaram entre -12,5dB NPS e -2,1dBNPS. As medianas da relação sinal/ruído das EOAPD por freqüência (f2) variaram entre 10,5dBNPS e 25,5dBNPS. CONCLUSÕES: Não houve diferença estatisticamente significante entre gêneros e entre orelhas para o nível de resposta. O pico de pressão na timpanometria definido por três grupos (entre -50 e +50daPa; < -50daPa e > +50daPa) não influenciou no registro do nível de resposta. Para uma interpretação clínica, o percentil 5 pode sugerir perda auditiva e o percentil 95 pode sugerir audição dentro da normalidade. É importante a realização de estudos com lactentes com perda auditiva para que se possa complementar o critério clínico no caso de presença de EOAPD e perda auditiva.

Distortion Product Otoacoustic Emission Findings in Behçet’s Disease and Rheumatoid Arthritis

BACKGROUND AND OBJECTIVE

This study aimed to assess cochlear functions in Behçet's disease and rheumatoid arthritis (RA) using otoacoustic emission testing (OAE), which objectively assesses outer hair cells in the cochlea.

METHODS

Patients with Behçet's disease (n = 16) and RA (n = 11) as well as 20 controls were tested using pure tone audiometry and transiently evoked (TEOAEs) and distortion product OAEs (DPOAEs).

RESULTS

Pure tone results in the Behçet's group were not significantly different from controls (p > 0.05). Pure tone results in the RA group were significantly different than in controls at 250, 500 and 6,000 Hz (p < 0.05). TEOAEs could be obtained in all participants. DPOAE amplitudes in the RA group and controls were similar (p > 0.05). DPOAE amplitudes were significantly higher in the Behçet's group than in controls at 1 and 2 kHz (p < 0.05).

CONCLUSION

A subtle deterioration in hearing can be seen at low and high frequencies in RA, which is not related to outer hair cell dysfunction as detected by DPOAE testing. In the patients with Behçet's disease who have hearing thresholds within the normal limits, outer hair cell functions seem spared with an increased activity in the apical regions of the cochlea.

High frequency distortion product otoacoustic emissions in children with and without middle ear dysfunction

OBJECTIVE

Distortion product otoacoustic emissions (DPOAEs) (9-16kHz) are a useful measure of the function of the cochlea, which may be damaged by ototoxic drugs during anticancer chemotherapy. As children undergoing chemotherapy may also have middle ear problems, it is necessary to know if middle ear problems would have a confounding effect on the ability of DPOAEs to assess cochlear function in the extend high frequency region (9-16kHz). The present study aimed to investigate the effect of middle ear dysfunction on DPOAEs in the extended high frequency region in young children.

METHODS

The sample was comprised of 100 ears of 50 school-aged children (21 boys and 29 girls) with a mean age of 6.3 years (S.D.=0.5; range 5.3-7.3). Otoscopy, pure tone hearing screening, tympanometry, acoustic reflexes and DPOAEs for both the conventional and extended high frequencies were administered to each child under typical school screening conditions. Participants were classified into one of three groups based on immittance (tympanometry and acoustic reflex) results. They included a "pass immittance" group, a "fail immittance" group and an "undetermined" group (with a pass in either tympanometry or acoustic reflexes, but not both). DPOAE amplitudes and signal-to-noise ratios (SNRs) were measured and compared across the three groups of participants.

RESULTS

The fail immittance group showed significantly smaller DPOAE amplitudes and SNRs when compared to the other two groups at frequencies ranging from 1 to 9.5kHz and at 13kHz, but not at 10, 11, 12 and 14kHz. There was no significant difference in DPOAE results between the pass immittance and undetermined groups.

CONCLUSIONS

Despite the adverse effects of middle ear dysfunction, its effect on DPOAEs in the extended high frequency region was not as severe as that in the lower frequency region. Hence, assessment of cochlear function in children with a middle ear lesion in the extended high frequencies using DPOAEs should be made with caution.

A validation and potential clinical application of multivariate analyses of distortion-product otoacoustic emission data

OBJECTIVE

To test the generalizability of multivariate analyses of distortion-product otoacoustic emission (DPOAE) data. Previously published multivariate solutions were applied to a new set of data to determine if test-performance improvements, evident in previous reports, are retained. An additional objective was to provide an alternative approach for making multivariate dichotomous decisions of hearing status in the clinic, based on DPOAE measurements.

DESIGN

DPOAE level and noise were obtained in 345 ears of 187 subjects. Approximately one third of the subjects had normal hearing, whereas the remainder had hearing loss, ranging from 25 to more than 120 dB HL. DPOAE data were collected at each of nine frequencies. After data collection, clinical decision theory, in combination with univariate (DPOAE level and signal-to-noise ratio [SNR]) and multivariate (logistic regression) analyses, was used to construct relative operating characteristic (ROC) curves and to generate ROC curve areas. In addition, test performance was assessed by fixing the false-alarm rate and comparing different approaches to analyses in terms of their failure rates as a function of magnitude of hearing loss. The DPOAE test results were compared with either single-frequency or multifrequency gold standards. The multivariate solutions were taken from previously published work (Dorn et al., 1999; Gorga, et al., 1999).

RESULTS

DPOAE level and SNR resulted in roughly equivalent test performance (ROC curve areas and failure rates among ears with hearing loss), although DPOAE level performed better for frequencies above 1 kHz, and SNR performed better for frequencies at 0.75 and 1 kHz. Multivariate analyses resulted in better test performance for nearly all conditions, compared with the univariate approaches that used either DPOAE level or SNR. The improvements in test performance were greatest for the frequencies at which the univariate analyses performed poorest (0.75 kHz, 1 kHz, and 8 kHz). Less difference was observed between univariate and multivariate approaches when multifrequency gold standards were used; however, even for the multifrequency cases, multivariate analyses generally resulted in better performance. An approach that might facilitate the interpretation of multifrequency DPOAE measurements in the clinic is described.

CONCLUSIONS

Previously described multivariate analyses were robust in that they improved test performance when applied to an entirely new set of DPOAE data. This, in turn, suggests that the previously described multivariate solutions may have clinical utility in that they are expected to improve test performance at no additional cost in terms of data-acquisition or data-analysis time. In addition to demonstrating that these solutions generalized to new data, an alternative approach to interpreting multifrequency DPOAE measurements is provided that includes the advantages of using multivariate analyses. This new metric may be useful when DPOAEs are used for screening purposes.

Distortion product otoacoustic emissions and tympanometric measurements in an adult population-based study

OBJECTIVE

Otoacoustic emissions (OAEs) are useful clinical tools that can be used as a test to reflect hearing, especially cochlear function. When OAEs are recorded, the sound energy is conducted inwards and outwards through the middle ear system, but the degree to which the middle ear condition affects the OAEs level remains obscure. The objectives of the present study were to estimate the effect of the condition of the middle ear expressed by multifrequency tympanometry on the distortion product otoacoustic emissions (DPOAEs) adjusting for age and the corresponding pure-tone thresholds.

SUBJECTS AND METHODS

The evaluation was conducted using 1,043 subjects without a history of ear disease or occupational noise exposure out of a population-based sample of 2,259 adults aged 40-82 years. Multifrequency tympanometry, DPOAEs, and pure-tone audiometry were administered. The resonance frequency (RF), static admittance (SA) and tympanometric peak pressure (PP) were taken as variables representing middle ear function. Subjects were categorized into three groups of variables < or = 5th percentile, between 5th and 95th percentile, and > or = 95th percentile. The signal-to-noise ratio in DPOAE levels were compared among three groups adjusting for age and the pure-tone threshold level.

RESULTS

Both abnormally high and low RF exerted a negative effect on DPOAEs. Smaller RF values were related to smaller DPOAEs for the frequency around 1000 Hz, and greater RF values were related to smaller DPOAEs for the frequency around 4000 Hz. The tendency was similar between genders. Abnormally high SA had a negative influence on DPOAEs, while abnormally low SA had no significant effect on either gender. Smaller PP values were significantly related to smaller DPOAEs.

CONCLUSIONS

We interpreted the findings of the present study as verification of the effect of the condition of the middle ear on DPOAEs after adjustment for age and the pure-tone threshold level, although ears out of normal range in tympanometric variables might conceivably include not only middle ear dysfunction but also inner ear abnormality. Tympanometric assessment must always be taken into account when OAEs are analyzed for an estimation of the cochlea function.

Modeling distortion product otoacoustic emission input/output functions using segmented regression

Distortion product otoacoustic emissions (DPOAEs) are low-level acoustic signals, the detection of which involves extraction from a background of noise. Boege and Janssen [J. Acoust. Soc. Am. 111, 1810-1818 (2002)] described a method for modeling the presence and growth of these responses. While improving growth function parameter estimation, this technique excludes a significant fraction of the data (especially low-level responses), and relies on ad hoc model fit acceptance criteria. The statistical difficulties associated with these limitations are described, and a weighted segmented linear regression model that avoids them is proposed. A simple test is presented for the presence of DPOAE growth. This technique is compared to that of Boege and Janssen in a dataset of 9 556 input/output (I/O) functions collected over 4 years on 866 ears from 379 construction apprentices and 63 age-matched controls. Comparisons are made on the entire dataset and within audiometric hearing loss categories. Segmented regression avoids the statistical pitfalls of the previous method, allows estimation of the threshold and slope of auditory response on a far greater number of I/O functions, and improves estimation of these parameters in this dataset. The potential for this method to yield more sensitive metrics of hearing function and compromise is discussed.

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.

Insights into elevated distortion product otoacoustic emissions in sickle cell disease: Comparisons of hydroxyurea-treated and non-treated young children

Distortion product otoacoustic emissions (DPOAEs) were examined in 15 normal-hearing African-American children between the ages of 6 and 14 years with homozygous sickle cell disease (SCD), who were on a regimen of hydroxyurea (HDU), a drug that reduces inflammatory processes and symptoms of SCD; a matched group of 15 African-American children with homozygous SCD not on HDU; and 15 African-American children with normal hemoglobin. DPOAEs were evoked by 13 primary tone pairs with f2 frequencies ranging from 1000 to 4500 Hz. Increased DPOAE amplitudes, believed to be a precursor of eventual hearing loss, were evident in children with SCD who were not receiving HDU. Those taking HDU had DPOAE amplitudes similar to normal controls. These findings suggest that HDU, in addition to reducing symptoms of SCD, may play a role in inhibiting or preventing cochlear pathology and hearing loss in individuals with SCD.

Distortion product otoacoustic emission (DPOAE) in tinnitus patients

The aim of this study was to determine the effect of tinnitus (experiment I) and the combined effect of tinnitus and sensorineural hearing loss (experiment II) on the distortion product otoacoustic emission (DPOAE) for two age groups of tinnitus patients. Tinnitus patients with normal earing, along with normal-hearing control subjects, participated in experiment I. They were divided into two age groups, below 50 and above 50 years. Experiment I showed that the DPOAE levels in the tinnitus patients were lower than those in the normal-hearing (nontinnitus) subjects. The differences depended on the frequency and the age of the patients, suggesting the confounding influence of presbyacusis. The second group of tinnitus patients with increasing and notch-like hearing loss participated in experiment II. They were also divided into two age groups, below 50 and above 50 years. The data from experiment II showed that DPOAE activity well reflects the increasing and notch-like hearing loss functions up to about 40 dB HL. The effect of age on the DPOAE level was clearly noted only for the tinnitus patients with clinically normal-hearing thresholds and was ambiguous for the tinnitus patients with hearing loss.

Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissions

The combined influence of primary-level differences (L1-L2) and primary-frequency ratio (f2/f1) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248-1259 (2005)] for the following stimulus conditions: f2= 1, 2, 4, and 8 kHz and f2/f1=1.05 to 1.4; various L1-L2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L2 levels, the largest DPOAEs were recorded when L1 was much higher than L2, with L1 remaining relatively constant as L2 increased. As f2/fl decreased, the largest DPOAEs were observed when L1 was closer to L2 and increased as L2 increased. Optimal values for L1-L2 and f2 f1 were derived from these data. In general, average DPOAE levels for the new L1-L2 and f2/f1 were equivalent to or larger than those observed for other stimulus combinations, including the L1-L2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] and those defined by Neely et al. in which L1-L2 was evaluated, but f2/f1 was fixed at 1.2.

A Multisite Study to Examine the Efficacy of the Otoacoustic Emission/Automated Auditory Brainstem Response Newborn Hearing Screening Protocol

Purpose: This article examines whether changes in hearing screening practices are warranted based on the results of the recent series of studies by J. L. Johnson, K. R. White, J. E. Widen, J. S. Gravel, B. R. Vohr, M. James, T. Kennalley, A. B. Maxon, L. Spivak, M. Sullivan-Mahoney, Y. Weirather, and S. Meyer (Johnson, White, Widen, Gravel, James, et al., 2005; Johnson, White, Widen, Gravel, Vohr, et al., 2005; White et al., 2005; Widen et al., 2005) that found a significant number of infants who passed an automated auditory brainstem response (A-ABR) screening after failing an initial otoacoustic emission (OAE) screening later were found to have permanent hearing loss in one or both ears.

Method: Similar to the approach used by F. H. Bess and J. Paradise (1994), this article addresses the public health tenets that need to be in place before screening programs, or in this case, a change in screening practice (use of a 2-step screening protocol) can be justified.

Results: There are no data to suggest that a 2-step OAE/A-ABR screening protocol should be avoided.

Conclusion: Research is needed before any change in public policy and practice surrounding current early hearing detection and intervention programs could be supported.

Audiometric predictions using stimulus-frequency otoacoustic emissions and middle ear measurements

OBJECTIVE

The goals of the study are to determine how well stimulus-frequency otoacoustic emissions (SFOAEs) identify hearing loss, classify hearing loss as mild or moderate-severe, and correlate with pure-tone thresholds in a population of adults with normal middle ear function. Other goals are to determine if middle ear function as assessed by wideband acoustic transfer function (ATF) measurements in the ear canal account for the variability in normal thresholds, and if the inclusion of ATFs improves the ability of SFOAEs to identify hearing loss and predict pure-tone thresholds.

DESIGN

The total suppressed SFOAE signal and its corresponding noise were recorded in 85 ears (22 normal ears and 63 ears with sensorineural hearing loss) at octave frequencies from 0.5 to 8 kHz, using a nonlinear residual method. SFOAEs were recorded a second time in three impaired ears to assess repeatability. Ambient-pressure ATFs were obtained in all but one of these 85 ears and were also obtained from an additional 31 normal-hearing subjects in whom SFOAE data were not obtained. Pure-tone air and bone conduction thresholds and 226-Hz tympanograms were obtained on all subjects. Normal tympanometry and the absence of air-bone gaps were used to screen subjects for normal middle ear function. Clinical decision theory was used to assess the performance of SFOAE and ATF predictors in classifying ears as normal or impaired, and linear regression analysis was used to test the ability of SFOAE and ATF variables to predict the air conduction audiogram.

RESULTS

The ability of SFOAEs to classify ears as normal or hearing impaired was significant at all test frequencies. The ability of SFOAEs to classify impaired ears as either mild or moderate-severe was significant at test frequencies from 0.5 to 4 kHz. SFOAEs were present in cases of severe hearing loss. SFOAEs were also significantly correlated with air conduction thresholds from 0.5 to 8 kHz. The best performance occurred with the use of the SFOAE signal-to-noise ratio as the predictor, and the overall best performance was at 2 kHz. The SFOAE signal-to-noise measures were repeatable to within 3.5 dB in impaired ears. The ATF measures explained up to 25% of the variance in the normal audiogram; however, ATF measures did not improve SFOAEs predictors of hearing loss except at 4 kHz.

CONCLUSIONS

In common with other OAE types, SFOAEs are capable of identifying the presence of hearing loss. In particular, SFOAEs performed better than distortion-product and click-evoked OAEs in predicting auditory status at 0.5 kHz; SFOAE performance was similar to that of other OAE types at higher frequencies except for a slight performance reduction at 4 kHz. Because SFOAEs were detected in ears with mild to severe cases of hearing loss, they may also provide an estimate of the classification of hearing loss. Although SFOAEs were significantly correlated with hearing threshold, they do not appear to have clinical utility in predicting a specific behavioral threshold. Information on middle ear status as assessed by ATF measures offered minimal improvement in SFOAE predictions of auditory status in a population of normal and impaired ears with normal middle ear function. However, ATF variables did explain a significant fraction of the variability in the audiograms of normal ears, suggesting that audiometric thresholds in normal ears are partially constrained by middle ear function as assessed by ATF tests.

Detection of hearing loss using 2f2-f1 and 2f1-f2 distortion-product otoacoustic emissions

Although many distortion-product otoacoustic emissions (DPOAEs) may be measured in the ear canal in response to 2 pure tone stimuli, the majority of clinical studies have focused exclusively on the DPOAE at the frequency 2f1-f2. This study investigated another DPOAE, 2f2-f1, in an attempt to determine the following: (a) the optimal stimulus parameters for its clinical measurement and (b) its utility in differentiating between normal-hearing and hearing-impaired ears at low-to-mid frequencies (<or=2,000 Hz) when measured either alone or in conjunction with the 2f1-f2 DPOAE. Two experiments were conducted. In Experiment 1, the effects of primary level, level separation, and frequency separation (f2/f1) on 2f2-f1 DPOAE level were evaluated in normal-hearing ears for low-to-mid f2 frequencies (700-2,000 Hz). Moderately high-level primaries (60-70 dB SPL) presented at equal levels or with f2 slightly higher than f1 produced the highest 2f2-f1 DPOAE levels. When the f2/f1 ratio that produced the highest 2f2-f1 DPOAE levels was examined across participants, the mean optimal f2/f1 ratio across f2 frequencies and primary level separations was 1.08. In Experiment 2, the accuracy with which DPOAE level or signal-to-noise ratio identified hearing status at the f2 frequency as normal or impaired was evaluated using clinical decision analysis. The 2f2-f1 and 2f1-f2 DPOAEs were measured from both normal-hearing and hearing-impaired ears using 2 sets of stimulus parameters: (a) the traditional parameters for measuring the 2f1-f2 DPOAE (f2/f1 = 1.22; L1, L2 = 65, 55 dB SPL) and (b) the new parameters that were deemed optimal for the 2f2-f1 DPOAE in Experiment 1 (f2/f1 = 1.073, L1 and L2 = 65 dB SPL). Identification of hearing status using 2f2-f1 DPOAE level and signal-to-noise ratio was more accurate when the new stimulus parameters were used compared with the results achieved when the 2f2-f1 DPOAE was recorded using the traditional parameters. However, identification of hearing status was less accurate for the 2f2-f1 DPOAE measured using the new parameters than for the 2f1-f2 DPOAE measured using the traditional parameters. No statistically significant improvements in test performance were achieved when the information from the 2 DPOAEs was combined, either by summing the DPOAE levels or by using logistic regression analysis.

Otoacoustic emissions in the general adult population of Nord-Trøndelag, Norway: III. Relationships with pure-tone hearing thresholds

This study aims to describe the association between otoacoustic emissions (OAEs) and pure-tone hearing thresholds (PTTs) in an unscreened adult population (N =6415), to determine the efficiency by which TEOAEs and DPOAEs can identify ears with elevated PTTs, and to investigate whether a combination of DPOAE and TEOAE responses improves this performance. Associations were examined by linear regression analysis and ANOVA. Test performance was assessed by receiver operator characteristic (ROC) curves. The relation between OAEs and PTTs appeared curvilinear with a moderate degree of non-linearity. Combining DPOAEs and TEOAEs improved performance. Test performance depended on the cut-off thresholds defining elevated PTTs with optimal values between 25 and 45 dB HL, depending on frequency and type of OAE measure. The unique constitution of the present large sample, which reflects the general adult population, makes these results applicable to population-based studies and screening programs.

Frequency-specific cochlear damage in guinea pig after exposure to different types of realistic industrial noise

For the causal evaluation of occupational hearing damage it is important to identify definitely the noise source. Here we tested, whether recordings of distortion product otoacoustic emissions (DPOAEs) in awake guinea pigs can distinguish the effects of different industrial noises. Six groups of 12 animals each were investigated before and over four months after a single 2 h exposure to specific, played-back industrial noise as well as before and for 2 months after impulse noise exposure. We compared broadband noise (buzz saw, bottle washing machine), low frequency noise (drawing press), and mid-frequency noise (bottle filling machine). All animals had stable DPOAE levels before noise exposure. Frequency specific decreases in DPOAEs were found after exposure to the different noises. Broadband noise diminished mostly all frequencies tested, whereas low- or mid-frequency noise had a greater effect on DPOAE evoked by middle and higher frequencies, respectively. DPOAE evoked by middle and higher frequencies were obliterated after impulse noise. Morphological analysis of the cochleae confirmed these alterations. OHC loss was found in the middle turns of the cochleae corresponding to the diminution of DPOAE. We conclude that different kinds of industrial noise tend to produce typical changes in DPOAE levels.

Effects of aspirin on distortion product otoacoustic emission suppression in human adults: a comparison with neonatal data

One of the distortion product otoacoustic emission (DPOAE) paradigms used to study cochlear function is DPOAE (2f1-f2) ipsilateral suppression. Newborns do not have adultlike DPOAE suppression. At 6000 Hz, infants show excessively narrow DPOAE suppression tuning and shallow growth of suppression for low-frequency suppressor tones. The source of this immaturity is not known but the outer hair cell (OHC) is one possible locus. In the present study, DPOAE suppression was measured at f2 = 1500 and 6000 Hz from two groups with impaired OHC function in an attempt to model the observed immaturity in neonates: adults with aspirin-induced OHC dysfunction and subjects with sensorineural hearing loss (SNHL). Their DPOAE suppression results were compared to those obtained from a group of term newborns to address whether infant DPOAE suppression resembles suppression from individuals with known OHC dysfunction. Results indicate that aspirin systematically alters DPOAE suppression in adults at f2 = 6000 Hz, but not 1500 Hz. However, neither aspirin-induced OHC dysfunction nor naturally occurring SNHL produces "neonatal-like" DPOAE suppression at either test frequency. This finding does not support the hypothesis that non-adultlike DPOAE suppression characterizing newborns can be explained by minor impairments or alterations of OHC function.

Distortion-product otoacoustic emission measured with continuously varying stimulus level

Distortion-product otoacoustic emissions (DPOAE) are measured by stimulating the ear with two simultaneous tones. A novel method for measuring DPOAEs has been developed in which the tone levels vary continuously instead of in discrete steps. Varying the tone levels continuously may offer advantages for characterizing DPOAE level as a function of stimulus level. For equivalent primary levels, DPOAE levels measured with the continuous-level method were the same as levels obtained with the discrete-level method, thus validating the new method. Continuous-level measurements were used to determine the optimal L1 for each L2 in individual subjects (N= 20) at f2 = 1, 2, 4, and 8 kHz by using a Lissajous path that covered a wide range of stimulus levels. The optimal L1 (defined as the L1 that resulted in the largest DPOAE for each L2) varied across subjects and across frequency. The optimal difference between L1 and L2 decreased with increasing L2 at all frequencies, and increased with frequency when L2 was low. When the optimal L1 was determined individually for each ear, the DPOAE levels were larger and less variable than those obtained using the equation for L1 suggested by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)].

Auditory neuropathy/dys-synchrony and its perceptual consequences

Auditory neuropathy/dys-synchrony is a form of hearing impairment in which cochlear outer hair cell function is spared but neural transmission in the auditory pathway is disordered. This condition, or group of conditions with a common physiologic profile, accounts for approximately 7% of permanent childhood hearing loss and a significant (but as yet undetermined) proportion of adult impairment. This paper presents an overview of the mechanisms underlying auditory neuropathy/dys-synchrony-type hearing loss and the clinical profile for affected patients. In particular it examines the perceptual consequences of auditory neuropathy/dys-synchrony, which are quite different from those associated with sensorineural hearing loss, and considers currently available, and future management options.

Sensorineural hearing loss in children and adults with Williams syndrome

Williams syndrome (WS) is a genetic neurodevelopmental disorder, most often accompanied by mild-to-moderate mental retardation. Individuals with WS show unique communication strengths and impairments that are challenging to treat in community, educational, and vocational settings. Many issues regarding characteristics of auditory sensitivity in WS remain to be resolved. Our purpose was to obtain behavioral (screening and pure-tone audiometry) and objective (distortion product otoacoustic emission-DPOAE) measures of auditory system function from a group of 27 individuals with WS, 6-48 years of age. These measures were gathered both at an international professional conference (n = 19) and in a clinic setting (n = 8). In the behavioral screening conditions, 16/19 (84%) of the individuals failed the hearing screening; and in the behavioral diagnostic hearing condition, 6/8 (75%) demonstrated sensorineural hearing loss (SNHL) and 1/8 demonstrated a hearing loss of undetermined type. In the objective DPOAE testing, 19/25 (76%) had DPOAE absolute amplitudes below the 5th percentile for ears with normal hearing [Gorga et al. (1997); Ear Hear 18(6):440-455]. We report SNHL in 14/18 (78%) of school-age children with WS. Post hoc analyses revealed a significant effect for age, suggesting a pattern of progressive hearing loss. An effect size analysis indicated a clinically meaningful difference in the hearing sensitivity between school-aged children and adults in the high frequencies (4,000 and 8,000 Hz). Similar hearing loss phenotype was observed in patients with familial nonsyndromic supravalvular aortic stenosis (SVAS), suggesting that molecular defects in the elastin gene in the pathogenesis of SNHL in WS. This study highlights the importance of early and regular hearing testing for WS patients and suggests that elastin may have a previously unappreciated function in maintaining hearing sensitivity.

Outer and middle ear status and distortion product otoacoustic emissions in children with sickle cell disease

The purpose of this study was to investigate distortion product otoacoustic emissions (DPOAEs) and outer/middle ear status in 12 African American children with normal hearing and homozygous sickle cell disease (SCD) and age-, gender-, and ear-matched African American controls. C. R. Downs, A. Stuart, & D. Holbert (2000) reported that DPOAE amplitudes were significantly larger for children with SCD. Because the integrity of the middle ear system directly influences OAE characteristics, it was felt that concurrent investigation of DPOAE amplitudes and outer/middle ear function in children with SCD was warranted. DPOAEs were evoked by 13 primary-tone pairs with f2 frequencies ranging from 1000 to 4500 Hz. Outer/middle ear status was assessed with tympanometry through indices of peak compensated static acoustic admittance, tympanometric width, tympanometric peak pressure, ear canal volume, and middle ear resonance frequency. Tympanograms were recorded with probe-tone frequencies of 226 and 678 Hz. DPOAE amplitudes were significantly larger for children with SCD (p < .05). There were no group differences in any of the middle ear indices (p > .05). These findings suggest that increased DPOAE amplitudes for children with SCD cannot be attributed to differences in outer/middle ear function as assessed with tympanometry.

Effects of a Suppressor Tone on Distortion Product Otoacoustic Emissions Fine Structure: Why a Universal Suppressor Level Is Not a Practical Solution to Obtaining Single-Generator DP-Grams

OBJECTIVES

The use of a suppressor tone has been proposed as the method of choice in obtaining single-generator distortion product (DP) grams, the speculation being that such DP grams will be more predictive of hearing thresholds. Current distortion product otoacoustic emissions (DPOAE) theory points to the ear canal DPOAE signal being a complex interaction between multiple components. The effectiveness of a suppressor tone is predicted to be dependent entirely on the relative levels of these components. We examine the validity of using a suppressor tone through a detailed examination of the effects of a suppressor on DPOAE fine structure in individual ears.

DESIGN

DPOAE fine structure, recorded in 10 normal-hearing individuals with a suppressor tone at 45, 55, and 65 dB SPL, was compared with recordings without a suppressor. Behavioral hearing thresholds were also measured in the same subjects, using 2-dB steps.

RESULTS

The effect of the suppressor tone on DPOAE fine structure varied between ears and was dependent on frequency within ears. Correlation between hearing thresholds and DPOAE level measured without a suppressor was similar to previous reports. The effects of the suppressor are explained in the theoretical framework of a model involving multiple DPOAE components.

CONCLUSIONS

Our results suggest that a suppressor tone can have highly variable effects on fine structure across individuals or even across frequency within one ear, thereby making the use of a suppressor less viable as a clinical tool for obtaining single-generator DP grams.

Occupational hearing loss: screening with distortion-product otoacoustic emissions

Hearing assessment of applicants for occupational hearing loss compensation can be a time-consuming process. An accurate screening procedure that is sensitive to occupational hearing loss may have application in many situations. The present study developed distortion-product otoacoustic emission (DPOAE) screening criteria to identify subjects likely to meet the Hong Kong requirements for occupational hearing loss compensation, namely a bilateral sensorineural loss > or = 40 dB HL (average of 1000, 2000 and 3000 Hz). The screening criteria of 1500 and/or 2000 Hz, with a signal-to-noise ratio of > 0 or 3 dB, yielded high sensitivity and specificity. DPOAE measures therefore have the potential to accurately indicate possible occupational hearing loss. However, DPOAEs should be used as a screening tool only, as conventional puretone audiometry remains the more comprehensive measure of hearing sensitivity.

Periodogram based tests for distortion product otoacoustic emissions

Distortion product otoacoustic emissions (DPOAEs) are an important nonbehavioral measure of cochlear function, which provides a close analogue of the behavioral pure-tone audiogram. DPOAEs are sinusoidal distortion products (DPs) produced by nonlinearities in the healthy cochlea. Detection of DPs is accomplished in the Fourier domain with a periodogram based test. The test compares the power in the DP periodogram bin to a noise estimate derived from a certain number of the surrounding bins. Statistical properties of this test to date have only been examined by constructing receiver operator characteristics curves derived from DPOAE measurements in normal and hearing impaired individuals. In this paper the null distribution of this order-statistic based test is explicitly derived, and via simulations intended to mimic the nonwhite features of real-ear noise measurements, the power of the test is demonstrated. These simulations demonstrate that a local F test is more powerful than this DPOAE test, with critical values that are easier to calculate. Although the power of both tests increase with an increasing number of bins, the improvement is negligible at around four bins. Since the power of both tests decrease at lower DP frequencies, it is not recommended to use a large number of bins.

Randomized controlled trial of once- versus thrice-daily tobramycin in febrile neutropenic children undergoing stem cell transplantation

BACKGROUND

The benefits of aminoglycoside antibiotics, such as tobramycin, administered as a once-daily dose to manage febrile neutropenia, have been demonstrated in many patient populations. However, toxicity and safety data are lacking for pediatric stem cell transplant recipients, who are at especially high risk for aminoglycoside-related toxicity and infectious morbidity. In particular, the relative nephrotoxicity and efficacy of tobramycin administered as a single daily dose or as three daily doses among this patient population is not known.

METHODS

We conducted a randomized, double-blind controlled study of tobramycin dosing among children 18 years or younger who had fever and neutropenia while undergoing stem cell transplantation. From October 2000 through November 2002, 60 children were randomly assigned to receive intravenous tobramycin, as either a single daily dose (n = 29) or every 8 hours (n = 31), in combination with either piperacillin or ceftazidime (intravenous). Tobramycin doses were adjusted to achieve pharmacokinetic targets. The primary outcome was nephrotoxicity, as represented by the maximal percent increase in serum creatinine concentration throughout the episode of febrile neutropenia relative to the baseline serum creatinine concentration. Efficacy was a secondary outcome and was defined as survival of the episode without modification of the antibacterial regimen. All statistical tests were two-sided.

RESULTS

In a modified intent-to-treat analysis, the mean maximal percent increase in serum creatinine concentration was 32% (N = 26) in the once daily dose group and 51% (N = 28) in the every 8 hours dose group (difference = 19%, 95% confidence interval [CI] = 0% to 38%; P =.054). Among patients evaluable for efficacy, 12 (46%) of 26 patients in the once daily dose group and five (19%) of 27 patients in the every 8 hours dose group survived the episode of febrile neutropenia without requiring antibacterial treatment modification (difference = 27%, 95% CI = 4% to 52%; P =.03). There was one death in each group.

CONCLUSIONS

In febrile neutropenic children undergoing stem cell transplantation, tobramycin may be less nephrotoxic and more efficacious when administered as a once daily dose than when administered every 8 hours.

The use of distortion product otoacoustic emissions in the estimation of hearing and sensory cell loss in noise-damaged cochleas

Distortion product otoacoustic emissions (DPOAE), permanent threshold shifts (PTS) and outer hair cell (OHC) losses were analyzed in a population of 187 noise-exposed chinchillas to determine the predictive accuracy (sensitivity and specificity) of the DPOAE for PTS and OHC loss. Auditory evoked potentials (AEP) recorded from the inferior colliculus of the brainstem were used to estimate hearing thresholds and surface preparation histology was used to determine sensory cell loss. The overlapping cumulative distributions and high variability in emission responses for both PTS and OHC loss made it difficult to predict AEP threshold and OHC loss from DPOAE level measurements alone. Using a strict criterion (i.e. emissions better than the 5th percentile of the preexposure DPOAE level, and PTS< or = 5 dB or OHC loss< or = 5%), it was found that the postexposure DPOAE level could be used with reasonable confidence to determine if the status of peripheral auditory system was either normal (i.e. PTS< or = 5 dB) or abnormal (PTS>30 dB or OHC loss>40%). However, the high variability of individual DPOAE responses resulted in a broad region of 'uncertainty' (i.e. 5<PTS< or = 30 dB and 5%<OHC loss< or = 40%) making it difficult in the chinchilla model to use the postexposure DPOAE level with confidence to predict in individual subjects the amount of PTS or OHC loss. Our results also indicate that significant reductions in the amplitude of the DPOAE are related primarily to a systematic loss of OHCs, and that a postexposure DPOAE level< or = 10 dB SPL, obtained with a low frequency primary level of 65 dB SPL, represents a criterion value which can serve as an indication of significant OHC loss (> or = 50%) or PTS (> or = 35 dB) in noise-exposed chinchillas. Based on an exponential regression analysis of individual subjects, correlations were higher for PTS/DPOAE than for OHC loss/DPOAE.

Distortion product otoacoustic emissions and auditory evoked potentials in the hedgehog tenrec, Echinops telfairi

The hedgehog tenrec, Echinops telfairi, has certain basal mammalian features, like a cloaca and a sparsely differentiated brain with smooth cerebral hemispheres. The peripheral auditory capabilities of this species were investigated by means of distortion product otoacoustic emissions (DPOAE). For comparison, we determined auditory evoked potentials (AEP) in the inferior colliculus and the auditory cortex. Both methods show that the auditory range of E. telfairi extends well into ultrasonic frequencies, with a region of highest sensitivity at around 16 kHz. The total auditory range spans about 4 octaves at 40 dB SPL. The low-frequency limit of auditory processing is found at frequencies of about 2-3 kHz. The DPOAE and the AEP thresholds of E. telfairi do not run fully parallel in the high-frequency range. For a threshold value of 40 dB SPL, cochlear mechanical thresholds as measured with DPOAE extend up to 50 kHz, whereas neuronal thresholds reach the high-frequency limit at about 30 kHz. Frequency tuning, as assessed from DPOAE suppression tuning curves, was low to moderate with Q(10 dB) values ranging from 1.7 to 8. The lack of discontinuity in the group delay (derived from DPOAE measurements) reveals that cochlear frequency representation is tonotopic without any region of specialized mechanical tuning.

Sources and Mechanisms of DPOAE Generation: Implications for the Prediction of Auditory Sensitivity

Otoacoustic emissions (OAEs) have become a commonly used clinical tool for assessing cochlear health status, in particular, the integrity of the cochlear amplifier or motor component of cochlear function. Predicting hearing thresholds from OAEs, however, remains a research challenge. Models and experimental data suggest that there are two mechanisms involved in the generation of OAEs. For distortion product, transient, and high-level stimulus frequency emissions, the interaction of multiple sources of emissions in the cochlea leads to amplitude variation in the composite ear canal signal. Multiple sources of emissions complicate simple correlations between audiometric test frequencies and otoacoustic emission frequencies. Current research offers new methods for estimating the individual components of OAE generation. Input-output functions and DP-grams of the nonlinear component of the 2f2-f2 DPOAE may ultimately show better correlations with hearing thresholds. This paper reviews models of OAE generation and methods for estimating the contribution of source components to the composite emission that is recorded in the ear canal. The clinical implications of multiple source components are discussed.

Distortion product otoacoustic emission suppression tuning curves in normal-hearing and hearing-impaired human ears

Distortion product otoacoustic emission (DPOAE) suppression measurements were made in 20 subjects with normal hearing and 21 subjects with mild-to-moderate hearing loss. The probe consisted of two primary tones (f2, f1), with f2 held constant at 4 kHz and f2/f1 = 1.22. Primary levels (L1, L2) were set according to the equation L1 = 0.4 L2 + 39 dB [Kummer et al., J. Acoust. Soc. Am. 103, 3431-3444 (1998)], with L2 ranging from 20 to 70 dB SPL (normal-hearing subjects) and 50-70 dB SPL (subjects with hearing loss). Responses elicited by the probe were suppressed by a third tone (f3), varying in frequency from 1 octave below to 1/2 octave above f2. Suppressor level (L3) varied from 5 to 85 dB SPL. Responses in the presence of the suppressor were subtracted from the unsuppressed condition in order to convert the data into decrements (amount of suppression). The slopes of the decrement versus L3 functions were less steep for lower frequency suppressors and more steep for higher frequency suppressors in impaired ears. Suppression tuning curves, constructed by selecting the L3 that resulted in 3 dB of suppression as a function of f3, resulted in tuning curves that were similar in appearance for normal and impaired ears. Although variable, Q10 and Q(ERB) were slightly larger in impaired ears regardless of whether the comparisons were made at equivalent SPL or equivalent sensation levels (SL). Larger tip-to-tail differences were observed in ears with normal hearing when compared at either the same SPL or the same SL, with a much larger effect at similar SL. These results are consistent with the view that subjects with normal hearing and mild-to-moderate hearing loss have similar tuning around a frequency for which the hearing loss exists, but reduced cochlear-amplifier gain.

"Auditory neuropathy": physiologic and pathologic evidence calls for more diagnostic specificity

The term "auditory neuropathy" is being used in a rapidly increasing number of papers in the audiology/otolaryngology literature for a variety of individuals (mostly children) who fulfill the following criteria: (1) understanding of speech worse than predicted from the degree of hearing loss on their behavioral audiograms; (2) recordable otoacoustic emissions and/or cochlear microphonic; together with (3) absent or atypical auditory brain stem responses. Because of the general lack of anatomic foundation for the label "auditory neuropathy" as currently used, we review the anatomy of the auditory pathway, the definition of neuropathy and its demyelinating, axonal, and mixed variants. We submit that the diagnostic term "auditory neuropathy" is anatomically inappropriate unless patients have documented evidence for selective involvement of either the spiral ganglion cells or their axons, or of the 8th nerve as a whole. In view of biologic differences between peripheral nerves and white matter tracts in the brain, the term "auditory neuropathy" is inappropriate for pathologies affecting the central auditory pathway in the brainstem and brain selectively. Published reports of patients with "auditory neuropathy" indicate that they are extremely heterogeneous in underlying medical diagnosis, age, severity, test results, and that only a small number have undergone the detailed investigations that would enable a more precise diagnosis of the locus of their pathologies. The electrophysiology of peripheral neuropathies and the deficits expected with pathologies affecting the hair cells, spiral ganglion cells and their axons (auditory neuropathy sensu stricto), and brain stem relays are reviewed. In order to serve patients adequately, including potential candidates for cochlear implants, and to increase knowledge of auditory pathologies, we make a plea for more comprehensive evaluation of patients who fulfill the currently used audiologic criteria for "auditory neuropathy" in an effort to pinpoint the site of their pathologies. We suggest that the term auditory neuropathy be limited to cases in which the locus of pathology is limited to the spiral ganglion cells, their processes, or the 8th nerve, and that the term neural hearing loss be considered for pathologies that affect all higher levels of the auditory pathway, from the brainstem to the auditory cortex.

Further efforts to predict pure-tone thresholds from distortion product otoacoustic emission input/output functions

Recently, Boege and Janssen [J. Acoust. Soc. Am. 111, 1810-1818 (2002)] fit linear equations to distortion product otoacoustic emission (DPOAE) input/output (UO) functions after the DPOAE level (in dB SPL) was converted into pressure (in microPa). Significant correlations were observed between these DPOAE thresholds and audiometric thresholds. The present study extends their work by (1) evaluating the effect of frequency, (2) determining the behavioral thresholds in those conditions that did not meet inclusion criteria, and (3) including a wider range of stimulus levels. DPOAE I/O functions were measured in as many as 278 ears of subjects with normal and impaired hearing. Nine f2 frequencies (500 to 8000 Hz in 1/2-octave steps) were used, L2 ranged from 10 to 85 dB SPL (5-dB steps), and L1 was set according to the equation L1 = 0.4L2 + 39 dB [Kummer et al., J. Acoust. Soc. Am. 103, 3431-3444 (1998)] for L2 levels up to 65 dB SPL, beyond which L1 = L2. For the same conditions as those used by Boege and Janssen, we observed a frequency effect such that correlations were higher for mid-frequency threshold comparisons. In addition, a larger proportion of conditions not meeting inclusion criteria at mid and high frequencies had hearing losses exceeding 30 dB HL, compared to lower frequencies. These results suggest that DPOAE I/O functions can be used to predict audiometric thresholds with greater accuracy at mid and high frequencies, but only when certain inclusion criteria are met. When the SNR inclusion criterion is not met, the expected amount of hearing loss increases. Increasing the range of input levels from 20-65 dB SPL to 10-85 dB SPL increased the number of functions meeting inclusion criteria and increased the overall correlation between DPOAE and behavioral thresholds.

Distortion product otoacoustic emission response characteristics in older adults

OBJECTIVE

The primary purpose of this study was to determine the distortion product otoacoustic emission (DPOAE) and noise response characteristics in a large sample of older adults. Another purpose was to evaluate how specific absolute DPOAE levels or DPOAE/Noise ratios differentiated hearing status in these individuals.

DESIGN

A cross-sectional design was utilized for this study. As a part of the Epidemiology of Hearing Loss Study (EHLS), DPOAEs were measured in 937 of the 3,429 participants aged 48 to 92 yr. The DPOAE and noise response characteristics were evaluated at 1,000, 2,000, 4,000, and 8,000 Hz. Absolute DPOAE level and DPOAE/Noise ratios were measured in the participants. The DPOAE data were compared with individual pure-tone frequencies (1,000, 2,000, 4,000, and 8,000 Hz) in the participants to investigate how DPOAE responses differentiated ears with normal hearing from impaired ears. Sensitivity, specificity, positive and negative predictive values, and accuracies were calculated for various absolute DPOAE levels and DPOAE/Noise ratios.

RESULTS

Due to the considerable overlap between DPOAE responses and the noise levels at 1,000 Hz, this frequency was not used for any analyses. Sensitivity and specificity were calculated for various DPOAE responses. Sensitivity and specificity varied by frequency for absolute DPOAE levels and DPOAE/Noise ratios. Receiver operator characteristic (ROC) analyses were used to determine which DPOAE responses differentiated normal hearing from hearing loss. The ROC analyses demonstrated that -6 dB SPL at 2,000 Hz, -14 dB SPL at 4,000 Hz, and -22 dB SPL at 8,000 Hz and a +9 dB DPOAE/Noise ratio at each of these frequencies yielded the highest discrimination.

CONCLUSIONS

Sensitivity and specificity varied by DPOAE response characteristics and frequency. The decision as to which DPOAE response criterion used should be based on careful consideration of objectives and the possible consequences of misdiagnosis. The results of this study support the use of DPOAEs as a clinical measure for older adults.

Differential responses to acoustic damage and furosemide in auditory brainstem and otoacoustic emission measures

Characteristics of distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs) were measured in Mongolian gerbil before and after the introduction of two different auditory dysfunctions: (1) acoustic damage with a high-intensity tone, or (2) furosemide intoxication. The goal was to find emission parameters and measures that best differentiated between the two dysfunctions, e.g., at a given ABR threshold elevation. Emission input-output or "growth" functions were used (frequencies f1 and f2, f2/f1 = 1.21) with equal levels, L1 = L2, and unequal levels, with L1 = L2 + 20 dB. The best parametric choice was found to be unequal stimulus levels, and the best measure was found to be the change in the emission threshold level, delta x. The emission threshold was defined as the stimulus level required to reach a criterion emission amplitude, in this case -10 dB SPL. (The next best measure was the change in emission amplitude at high stimulus levels, specifically that measured at L1 x L2 = 90 x 70 dB SPL.) For an ABR threshold shift of 20 dB or more, there was essentially no overlap in the emission threshold measures for the two conditions, sound damage or furosemide. The dividing line between the two distributions increased slowly with the change in ABR threshold, delta ABR, and was given by delta x(t) = 0.6 delta ABR + 8 dB. For a given delta ABR, if the shift in emission threshold was more than the calculated dividing line value, delta x(t), the auditory dysfunction was due to acoustic damage, if less, it was due to furosemide.

Patients affected with Fabry disease have an increased incidence of progressive hearing loss and sudden deafness: an investigation of twenty-two hemizygous male patients

BACKGROUND

Fabry disease (FD, OMIM 301500) is an X-linked inborn error of glycosphingolipid metabolism due to the deficient activity of alpha-galactosidase A, a lysosomal enzyme. While the progressive systemic deposition of uncleaved glycosphingolipids throughout the body is known to have protean clinical manifestations, few data are available regarding the cochlear involvement.

METHODS

We non-invasively investigated cochlear functions in 22 consecutive hemizygous males (age 19-64 years, mean 39) affected with classic FD. Conventional audiometry, tympanometry, ABR audiometry, otoacoustic emissions were performed in all patients, together with medical history record and physical examination as part of an exhaustive baseline evaluation prior to enzyme replacement therapy.

RESULTS

A total of 12 patients (54.5%) with classic FD were found to have abnormal audition. Five patients had progressive hearing loss and seven patients (32%) experienced sudden deafness. In addition, a hearing loss on high-tone frequencies was found in 7 out of the 10 remaining patients without clinical impairment, despite their young age at time of examination. The incidence of hearing loss appeared significantly increased in FD patients with kidney failure (P < 0.01) or cerebrovascular lesions (P < 0.01), whereas there was no correlation with left ventricular hypertrophy. In addition, tinnitus aurium was also found in six patients (27%).

CONCLUSION

This is the first evidence of a high incidence of both progressive hearing loss and sudden deafness in a cohort of male patients affected with classic Fabry disease. The exact pathophysiologic mechanism(s) of the cochlear involvement deserves further studies.

DPOAEs in young normal-hearing subjects with histories of otitis media: evidence of sub-clinical impairments

To investigate the origin of the susceptibility to noise in subjects with histories of otitis media (OM), we assessed early sub-clinical impairments in normally hearing subjects with a history of OM using distortion product otoacoustic emissions (DPOAEs). DPOAEs of 213 normal-hearing subjects aged 18-24 years were obtained and comparisons of DPOAE levels in several groups as a function of OM past infections were tested by ANOVA. A main finding was that young normal-hearing subjects with a history of OM had significantly lower DPOAEs over all octaves tested compared to normal-hearing subjects without antecedent of OM. The mean difference was 3.5+/-1.1 dB in the 2-4 kHz zone, which was especially marked in subjects (n=21) that had undergone a myringotomy (6.6+/-1.5 dB) in the 4 kHz zone. The level of impairment seemed to depend on the severity of the past infection as characterised by the importance and the duration of the infectious effusions.

Pure-tone threshold estimation from extrapolated distortion product otoacoustic emission I/O-functions in normal and cochlear hearing loss ears

A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f1-f2 distortion products and pure-tone threshold at f2 were measured at 51 frequencies between f2=500 Hz and 8 kHz at up to ten primary tone levels between L2=65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss ears. Using an optimized primary tone level setting (L1 = 0.4L2 + 39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f2, the pressure of the 2 f1-f2 distortion product pDP is a linear function of the primary tone level L2. Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and impaired hearing. This suggests that the observed linear functional dependency is quite general. Extrapolating towards pDP=0 yields the DPOAE threshold for L2. There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of an essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data.

Sources of DPOAEs revealed by suppression experiments, inverse fast Fourier transforms, and SFOAEs in impaired ears

DPOAE sources are modeled by intermodulation distortion generated near the f2 place and a reflection of this distortion near the DP place. In a previous paper, inverse fast Fourier transforms (IFFTs) of DPOAE filter functions in normal ears were consistent with this model [Konrad-Martin et al., J. Acoust. Soc. Am. 109, 2862-2879 (2001)]. In the present article, similar measurements were made in ears with specific hearing-loss configurations. It was hypothesized that hearing loss at f2 or DP frequencies would influence the relative contributions to the DPOAE from the corresponding basilar membrane places, and would affect the relative magnitudes of SFOAEs at frequencies equal to f2 and fDP. DPOAEs were measured with f2 = 4 kHz, f1 varied, and a suppressor near fDP. L2 was 25-55 dB SPL (L1 = L2 + 10 dB). SFOAEs were measured at f2 and at 2.7 kHz (the average fDP produced by the f1 sweep) for stimulus levels of 20-60 dB SPL. SFOAE results supported predictions of the pattern of amplitude differences between SFOAEs at 4 and 2.7 kHz for sloping losses, but did not support predictions for the rising- and flat-loss categories. Unsuppressed IFFTs for rising losses typically had one peak. IFFTs for flat or sloping losses typically have two or more peaks; later peaks were more prominent in ears with sloping losses compared to normal ears. Specific predictions were unambiguously supported by the results for only four of ten cases, and were generally supported in two additional cases. Therefore, the relative contributions of the two DPOAE sources often were abnormal in impaired ears, but not always in the predicted manner.

The use of distortion product otoacoustic emission suppression as an estimate of response growth

Distortion product otoacoustic emission (DPOAE) levels in response to primary pairs (f2 = 2 or 4 kHz, L2 ranging from 20 to 60 dB SPL, L1 = 0.4L2 + 39 dB) were measured with and without suppressor tones (f3), which varied from 1 octave below to 1/2 octave above f2, in normal-hearing subjects. Suppressor level (L3) varied from -5 to 85 dB SPL. DPOAE levels were converted into decrements by subtracting the level in the presence of the suppressor from the level in the absence of a suppressor. DPOAE decrement vs L3 functions showed steeper slopes when f3 < f2 and shallower slopes when f3 > f2. This pattern is similar to other measurements of response growth, such as direct measures of basilar-membrane motion, single-unit rate-level functions, suppression of basilar-membrane motion, and discharge-rate suppression from lower animals. As L2 increased, the L3 necessary to maintain 3 dB of suppression increased at a rate of about 1 dB/dB when f3 was approximately equal to f2, but increased more slowly when f3 < f2. Functions relating L3 to L2 in order to maintain a constant 3-dB reduction in DPOAE level were compared for f3 < f2 and for f3 approximately = f2 in order to derive an estimate related to "cochlear-amplifier gain." These results were consistent with the view that "cochlear gain" is greater at lower input levels, decreasing as level increases.

Effects of age on the distortion product otoacoustic emission growth functions

Age-related hearing loss (presbycusis) is thought to result from age-related degeneration (aging) of the cochlea plus the cumulative effects of extrinsic damage (noise and other ototoxic agents) and intrinsic disorders (e.g. systemic diseases). Previous studies have implicated dysfunction of the hair cells (sensory presbycusis) as the principal mechanism of age-related hearing loss. However, recent evidence from quiet-reared gerbils suggests that cochlear aging results primarily from atrophy of the stria vascularis, which is associated with diminished endocochlear potential (EP), spiral ganglion atrophy, and a relatively flat audiometric loss, termed metabolic presbycusis. Because it is not currently possible to measure EP directly in the clinical setting, we wondered if cochlear metabolic dysfunction might be evidenced indirectly from existing clinical tests, specifically, the input-output (IO) growth function of the distortion product (DP) otoacoustic emissions in relation to behavioral hearing threshold levels (HTL). We anticipated finding discordance between the IO functions and HTL with either a greater decline with age in HTL than in IO functions if an age-related metabolic dysfunction of the cochlea was operant, or a greater loss of IO function than HTL if outer hair cell dysfunction was the dominant pathology. To address this supposition we analyzed existing auditory data from a large cohort of adults to determine the change with age in three aspects of the DP IO function: area under the curve, threshold, and slope. The analyses demonstrated a greater effect of age on HTL than on the DP IO measures. This effect supports the hypothesis that strial dysfunction is a substantive factor in cochlear aging. The etiology and mechanisms for this dysfunction are conjectural at present.

Distortion product otoacoustic emission input/output functions in normal-hearing and hearing-impaired human ears

DPOAE input/output (I/O) functions were measured at 7f2 frequencies (1 to 8 kHz; f2/f1 = 1.22) over a range of levels (-5 to 95 dB SPL) in normal-hearing and hearing-impaired human ears. L1-L2 was level dependent in order to produce the largest 2f1-f2 responses in normal ears. System distortion was determined by collecting DP data in six different acoustic cavities. These data were used to derive a multiple linear regression model to predict system distortion levels. The model was tested on cochlear-implant users and used to estimate system distortion in all other ears. At most but not all f2's, measurements in cochlear implant ears were consistent with model predictions. At all f2 frequencies, the ears with normal auditory thresholds produced I/O functions characterized by compressive nonlinear regions at moderate levels, with more rapid growth at low and high stimulus levels. As auditory threshold increased, DPOAE threshold increased, accompanied by DPOAE amplitude reductions, notably over the range of levels where normal ears showed compression. The slope of the I/O function was steeper in impaired ears. The data from normal-hearing ears resembled direct measurements of basilar membrane displacement in lower animals. Data from ears with hearing loss showed that the compressive region was affected by cochlear damage; however, responses at high levels of stimulation resembled those observed in normal ears.