Gender effects on high frequency distortion product otoacoustic emissions in humans

Associations Between Noise Exposure Level, Noise Kurtosis, and Distortion Product Otoacoustic Emissions in Young Workers With Normal Hearing

OBJECTIVES

Growing evidence has suggested that, in addition to noise exposure level, noise temporal structure (i.e., kurtosis) plays an important role in the development of noise-induced hearing loss, while most of the relevant research has been on the results of pure-tone audiometry. This study focuses on the combined effect of noise exposure level and noise kurtosis on distortion product otoacoustic emissions (DPOAEs) in young workers with normal hearing.

DESIGN

A cross-sectional study among young workers in manufacturing industries was conducted in Zhejiang Province, China. Individual noise exposure measurements were performed on participants to obtain an A-weighted noise exposure level normalized to 8 hr ( LAeq, 8hr ), cumulative noise exposure (CNE), kurtosis, and kurtosis-adjusted CNE (CNE-K). The DPOAE test was performed on the participants and DPOAE levels were obtained. The relationships between noise exposure level, kurtosis, and DPOAE levels were explored by univariate analyses. Furthermore, multivariate regression models were conducted to estimate the combined effects of exposure level and kurtosis after adjusting for age, gender, and use of hearing protection devices.

RESULTS

The overall DPOAE curves across frequency bands presented a fluctuating downward trend with increasing frequency. Both exposure level and kurtosis were found to be associated with decreases in DPOAE levels. The multivariate regression model including CNE-K as a joint indicator of complex noise showed an increased R2 compared with the model including CNE. After adjustment for age, gender, and the use of hearing protection devices, significant effects of CNE-K on DPOAE levels were observed at 3, 4, and 5 kHz frequencies, with maximum effect presented at 4 kHz.

CONCLUSIONS

DPOAE is a sensitive test that can detect cochlear damage in limited areas that cannot be detected by conventional audiometry. The present study provided a more comprehensive understanding of the impact of complex noise on the DPOAE levels. It also suggested that CNE-K was an effective metric in assessing DPOAE levels associated with complex noise.

Expression profiling of cochlear genes uncovers sex-based cellular function in mouse cochleae

Sex is a pivotal biological factor that significantly impacts tissue homeostasis and disease susceptibility. In the auditory system, sex differences have been observed in cochlear physiology and responses to pathological conditions. However, the underlying molecular mechanisms responsible for these differences remain elusive. The current research explores the differences in gene expression profiles in the cochlea between male and female mice, aiming to understand the functional implication of sex-biased gene expression in each sex. Using RNA-sequencing analysis on cochlear tissues obtained from male and female mice, we identified a significant number of genes exhibiting sex-biased expression differences. While some of these differentially expressed genes are located on sex chromosomes, most are found on autosomal chromosomes. Further bioinformatic analysis revealed that these genes are involved in several key cellular functions. In males, these genes are notably linked to oxidative phosphorylation and RNA synthesis and processing, suggesting their involvement in mitochondrial energy production and regulatory control of gene expression. In contrast, sex-biased genes are associated with mechano-transduction and synaptic transmission within female cochleae. Collectively, our study provides valuable insights into the molecular differences between the sexes and emphasizes the need for future research to uncover their functional implications and relevance to auditory health and disease development.

Comparison of Two Clinical Devices for the Measurement of Distortion Product Otoacoustic Emissions in Normal-Hearing Adults

BACKGROUND AND OBJECTIVES

Otoacoustic emissions (OAEs) are low-intensity sounds generated by the cochlea and associated with the function of the outer hair cells. Since OAE measurements do not require active participation of a listener, OAEs are considered an objective measure of cochlear function. While distortion-product OAEs (DPOAEs) are commonly used in clinical practice, limited information is available on the performance of various clinical devices. This study compared two commercial clinical devices, Titan and Eclipse from Interacoustics, and collected normative data for DPOAEs in people with normal hearing. The data collection and analysis were focused on signal and noise amplitudes as well as signal-to-noise ratios (SNRs).

SUBJECTS AND METHODS

Sixty-three participants with normal hearing (age 23.2±2.0 years) were included in the study. DPOAEs were measured at 31 frequencies ranging from 500 to 10,000 Hz.

RESULTS

DPOAE amplitude differed across frequencies. Additionally, a high number of unreliable responses were observed at the edge frequencies (<828 Hz and >6,072 Hz). There were no significant differences between the two devices in terms of DPOAE amplitudes, but the recorded-noise levels (amplitude) differed significantly. SNRs of the recorded OAEs were frequency dependent (higher frequencies showed larger SNRs), and significant differences in terms of SNR were found between the two devices.

CONCLUSIONS

Despite the above-mentioned differences, the OAEs recorded with both devices met the pass criteria for the SNR (≥6 dB) consistently across frequencies, and thus the differences do not compromise the test outcomes. The frequency dependence of the OAE amplitudes and the corresponding SNRs may be relevant for clinical practice.

Descriptive Characterization of High-Frequency Distortion Product Otoacoustic Emission Source Components in Children

PURPOSE

Distortion product otoacoustic emissions (DPOAEs) provide an objective assessment of cochlear function and are used for serial ototoxicity monitoring in pediatric cancer patients. DPOAEs are modeled as having distortion (near f2) and reflection (near 2f1-f2) component sources, and developmental changes are observed in these components' relative strengths in infants compared with adults. However, little is known about source component strengths in childhood or at extended high frequencies (EHFs; > 8 kHz). Thus, the purpose of this study was to describe the effects of age and stimulus frequency on DPOAE components in children.

METHOD

DPOAEs were collected with varied frequency ratios (f2/f1 = 1.1-1.25) for a wide range of frequencies (2-16 kHz) in 39 younger (3-6 years) and 41 older (10-12 years) children with constant levels (L1/L2) of 65/50 dB SPL. A depth-compensated simulator sound pressure level method of calibration was employed. A time waveform representation of the results across various ratios was created to estimate peak pressures and latencies of each DPOAE component.

RESULTS

Estimated peak pressures of DPOAE components revealed the greatest differences in DPOAE sources between children occurring at the highest frequencies tested, where the peak pressure of both components was largest for younger compared with older children. Latency differences between the children were only noted at higher frequencies for the distortion component.

CONCLUSIONS

These results suggest that DPOAE levels decrease with age and reflection emissions are vulnerable to cochlear change. This work guides optimization of protocols for pediatric ototoxicity monitoring, whereby including EHF otoacoustic emissions is clearly warranted and choosing to isolate DPOAE sources may prove beneficial.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.23669214.

Ultra-High Frequency Distortion Product Otoacoustic Emissions for Detection of Hearing Loss and Tinnitus

Several studies have suggested that distortion product otoacoustic emissions (DPOAEs) may be an early marker not only of hearing loss (HL) but also of tinnitus. The purpose of this study was to investigate whether DPOAEs measured up to 16 kHz are affected by the presence of tinnitus. Pure tone thresholds and DPOAEs were measured in two groups: 55 patients with tinnitus and 63 subjects without tinnitus. The subjects were divided into three groups according to their audiometric results-better than 25 dB HL at all tested frequencies from 0.125 to 16 kHz, better than 25 dB up to 8 kHz, and hearing impaired. Receiver operator characteristics (ROCs) were used to test whether DPOAEs could differentiate between normal hearing, hearing loss, and tinnitus. Comparison of tinnitus subjects with the control group, matched accurately according to thresholds, did not yield any significant difference in DPOAEs. However, in both these groups hearing loss was accompanied by a decrease in DPOAEs, specifically, at 2-6 kHz and 16 kHz. The results suggest that any decrease in DPOAEs seems to be related only to hearing loss and there is no additional effect from tinnitus.

Association Analysis of Candidate Gene Polymorphisms and Audiometric Measures of Noise-Induced Hearing Loss in Young Musicians

INTRODUCTION

This study aimed to investigate the association between candidate genetic variants and audiometric measures of noise-induced hearing loss (NIHL) in young musicians.

METHODS

The study analyzed a database by Phillips et al. (Feasibility of a bilateral 4000-6000 Hz notch as a phenotype for genetic association analysis. Int J Audiol 2015;54:645-52.) which included behavioral hearing thresholds, distortion-product otoacoustic emissions (DPOAE), tympanometric, and genetic data of 166 participants meeting the inclusion criteria. Nineteen single nucleotide polymorphisms (SNPs) in 13 cochlear genes previously associated with NIHL in factory workers were included in the present investigation. The average hearing threshold at 3000 and 4000 Hz (AHT) and average DPOAE signal to noise ratio (DPOAE SNR) in both ears were calculated.

RESULTS

The regression analyses showed that two SNPs- one in KCNE1 (rs2070358) and the other in CAT (rs12273124) revealed a statistically significant relationship with DPOAE SNR in both ears. Two SNPs in MYH14 and one in GJB4 revealed a significant association with DPOAE SNR in the left ear. Two SNPs in HSP70, one in CDH23 and one in KCNJ10 showed significant association with DPOAE SNR in the right ear. None of the included SNPs showed association with AHT in both ears.

CONCLUSIONS

A genetic variant in KCNE1 was associated with the strength of the cochlear amplifier as assessed by DPOAE SNR. Musicians carrying causal genetic variants to NIHL might exhibit changes in their auditory functions early in the lifespan even when most subjects had their hearing thresholds within normal limits. These participants are likely to show the clinical manifestation of NIHL in the future if no preventive measures are applied.

Audiological assessment and otoacoustic emissions in patients with head and neck cancer

ABSTRACT Purpose: to describe the audiological and otoacoustic emission findings in patients who had head and neck cancer and compare them with individuals without the disease. Methods: a comparative, cross-sectional, observational study encompassing two groups: Study: individuals with a history of head and neck cancer, submitted to chemotherapy and/or radiotherapy; Control: individuals without the disease. The sample comprised 23 individuals in each group, matched for age and gender. Procedures in which the groups were compared: meatoscopy; pure-tone threshold and high-frequency audiometry; speech audiometry; transient-evoked otoacoustic emissions. Statistical tests: Pearson’s chi-square; Fisher’s exact; two-proportion Z-test; Wilcoxon; Mann-Whitney; Student’s t-test. Results: the comparison between the groups revealed statistically significant differences at the 3, 6, 8, 10, and 12.5 kHz frequencies in the pure-tone threshold audiometry, with better pure-tone auditory thresholds in the control group. No significant differences were observed between the groups in the otoacoustic emissions regarding the general response and frequency band. Conclusion: individuals with a history of head and neck cancer had higher pure-tone auditory thresholds than their controls, especially at the higher frequencies. This evidences the deleterious effect of ototoxicity on the peripheral auditory system of adults. The otoacoustic emissions were similar in the two groups.

High-frequency otoacoustic emissions in universal newborn hearing screening

OBJECTIVE

Distortion-product otoacoustic emissions (DPOAEs) are currently used in many newborn hearing screening programs as the initial hearing test, typically testing frequencies between 1 and 4 or 6 kHz, but they have been associated with high false-positive rates. The objective was to investigate the possible benefit of high-frequency DPOAEs for reducing false-positive rates.

METHODS

255 healthy newborns (138 males and 117 females) undergoing conventional hearing screening based on DPOAE and automated auditory brainstem response (AABR) testing were recruited. High-frequency DPOAE amplitudes, noise floors and signal-to-noise ratios (SNRs) were measured for f2 frequencies up to 12 kHz.

RESULTS

Of the 255 newborns who participated in this study, 23 (9%) failed the conventional DPOAE test but passed the AABR test, and 8 (3%) failed both tests. For an SNR threshold of 6 dB, high-frequency DPOAE tests at f2 = 4, 6, 8 and 10 kHz resulted in a reduction in the false-positive rate from 9% to 0.4%, or to zero if only three of the four frequencies were required to exceed the threshold. SNRs were lower in newborns with birth weights greater than 4000 g; lower at 2 kHz in newborns with a gestational age of 41 weeks; slightly higher in vaginally-delivered newborns; and higher at 2 kHz with increasing age in the group that failed the conventional DPOAE test but passed AABR.

CONCLUSION

High-frequency DPOAEs resulted in a reduction in the DPOAE failure rate and the false-positive rate. These findings may be helpful in universal newborn hearing screening programs.

Distortion product otoacoustic emissions in college music majors and nonmusic majors

The presence and absence of distortion product otoacoustic emissions (DPOAEs) as well as DPOAE amplitudes were compared between college music majors and a control group of nonmusic majors. Participants included 28 music majors and 35 nonmusic majors enrolled at a university with ages ranging from 18-25 years. DPOAEs and hearing thresholds were measured bilaterally on all the participants. DPOAE amplitudes were analyzed at the following f2 frequencies: 1,187 Hz, 1,500 Hz, 1,906 Hz, 2,531 Hz, 3,031 Hz, 3812 Hz, 4,812 Hz, and 6,031 Hz. Significantly more music majors (7/28) than nonmusic majors (0/35) exhibited absent DPOAEs for at least one frequency in at least one ear. Both groups of students reported similar histories of recreational and occupational noise exposures that were unrelated to studying music, and none of the students reported high levels of noise exposure within the previous 48 h. There were no differences in audiometric thresholds between the groups at any frequency. At DPOAE f2 frequencies from 3,031 Hz to 6,031 Hz, nonsignificantly lower amplitudes of 2-4 dB were seen in the right ears of music majors versus nonmajors, and in the right ears of music majors playing brass instruments compared to music majors playing nonbrass instruments. Given the greater prevalence of absent DPOAEs in university music majors compared to nonmusic majors, it appears that early stages of cochlear damage may be occurring in this population. Additional research, preferably longitudinal and across multiple colleges/universities, would be beneficial to more definitively determine when the music students begin to show signs of cochlear damage, and to identify whether any particular subgroups of music majors are at a greater risk of cochlear damage.

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.

Distortion-product otoacoustic emissions at ultra-high frequencies in parents of individuals with autosomal recessive hearing loss

Purpose: To evaluate the cochlear function of parents of individuals with autosomal recessive gene Gap Junction Protein Beta-2 hearing loss by ultra-high frequencies distortion-product otoacoustic emissions (DPOAEs), compared with responses of a control group matched for age and gender. Methods: We studied 56 subjects aged from 20 to 58 years, divided into two groups. The study group comprised 28 parents of hearing-impaired patients due to autosomal recessive inheritance, 14 females aged 20.0-55.0 years (mean 32.8 years) and 14 males aged 20.0-58.0 years (mean 35.2 years). Control group was composed of normal hearing individuals, 14 males and 14 females age-matched to the study group. The subjects underwent tests for audiometry, tympanometry, and DPOAE in the frequency range of 9.000-16.000 Hz. Results: We found 64.3% of normal results of DPOAE in the study group compared to 91.1% in the control. There were significant differences between groups in the ears and DPOAE responses, and the mean level of response was in 10 dBNPS in study group and 14 dBNPS in the control. The Pearson's correlation between age and DPOAE in ultra-high frequencies showed no statistical significance. Conclusion: DPOAE at ultra-high frequencies were able to identify individuals from both groups, suggesting that heterozygous individuals for the Gap Junction Protein Beta-2 gene mutation may have damage to the cochlear function before clinical manifestation in audiometry.

Behavioral hearing thresholds between 0.125 and 20 kHz using depth-compensated ear simulator calibration

OBJECTIVES

The purpose of this study was to obtain behavioral hearing thresholds for frequencies between 0.125 and 20 kHz from a large population between 10 and 65 yr old using a clinically feasible calibration method expected to compensate well for variations in the distance between the eardrum and an insert-type sound source. Previous reports of hearing thresholds in the extended high frequencies (>8 kHz) have either used calibration techniques known to be inaccurate or specialized equipment not suitable for clinical use.

DESIGN

Hearing thresholds were measured from 352 human subjects between 10 and 65 yr old having clinically normal-hearing thresholds (<20 dB HL) up to 4 kHz. An otoacoustic emission probe fitted with custom sound sources was used, and the stimulus levels individually tailored on the basis of an estimate of the insertion depth of the measurement probe. The calibrated stimulus levels were determined on the basis of measurements made at various depths of insertion in a standard ear simulator. Threshold values were obtained for 21 frequencies between 0.125 and 20 kHz using a modified Békésy technique. Forty-six of the subjects returned for a second measurement months later from the initial evaluation.

RESULTS

In agreement with previous reports, hearing thresholds at extended high frequencies were found to be sensitive to age-related changes in auditory function. In contrast with previous reports, no gender differences were found in average hearing thresholds at most evaluated frequencies. Two aging processes, one faster than the other in time scale, seem to influence hearing thresholds in different frequency ranges. The standard deviation (SD) of test-retest threshold difference for all evaluated frequencies was 5 to 10 dB, comparable to that reported in the literature for similar measurement techniques but smaller than that observed for data obtained using the standard clinical procedure.

CONCLUSIONS

The depth-compensated ear simulator-based calibration method and the modified Békésy technique allow reliable measurement of hearing thresholds over the entire frequency range of human hearing. Hearing thresholds at the extended high frequencies are sensitive to aging and reveal subtle differences, which are not evident in the frequency range evaluated regularly (≤8 kHz). Previously reported gender-related differences in hearing thresholds may be related to ear-canal acoustics and the calibration procedure and not because of differences in hearing sensitivity.

Sex differences in distortion-product and transient-evoked otoacoustic emissions compared

Although several studies have documented the existence of sex differences in spontaneous otoacoustic emissions (SOAEs) and transient-evoked OAEs (TEOAEs) in humans, less has been published about sex differences in distortion-product OAEs (DPOAEs). Estimates of sex and ear differences were extracted from a data set of OAE measurements previously collected for other purposes. In accord with past findings, the sex differences for TEOAEs were substantial for both narrowband and wideband measures. By contrast, the sex differences for DPOAEs were about half the size of those for TEOAEs. In this sample, the ear differences were small for TEOAEs in both sexes and absent for DPOAEs. One implication is that the cochlear mechanisms underlying DPOAEs appear to be less susceptible to whatever influences are responsible for producing sex differences in TEOAEs and SOAEs in humans. We discuss the possibility that differences in the effective level of the stimuli may contribute to these outcomes.

Distortion-product otoacoustic emissions in the common marmoset (Callithrix jacchus): parameter optimization

Distortion-product otoacoustic emissions (DPOAEs) were measured in a New World primate, the common marmoset (Callithrix jacchus). We determined the optimal primary-tone frequency ratio (f(2)/f(1)) to generate DPOAEs of maximal amplitude between 3 and 24 kHz. The optimal f(2)/f(1), determined by varying f(2)/f(1) from 1.02 to 1.40 using equilevel primary tones, decreased with increasing f(2) frequency between 3 and 17 kHz, and increased at 24 kHz. The optimal f(2)/f(1) ratio increased with increasing primary-tone levels from 50 to 74 dB SPL. When all stimulus parameters were considered, the mean optimal f(2)/f(1) was 1.224-1.226. Additionally, we determined the effect of reducing L(2) below L(1). Decreasing L(2) below L(1) by 0, 5, and 10 dB (f(2)/f(1)=1.21) minimally affected DPOAE strength. DPOAE levels were stronger in females than males and stronger in the right ear than the left, just as in humans. This study is the first to measure OAEs in the marmoset, and the results indicate that the effect of varying the frequency ratio and primary-tone level difference on marmoset DPOAEs is similar to the reported effects in humans and Old World primates.

Racial and gender effects on pure-tone thresholds and distortion-product otoacoustic emissions (DPOAEs) in normal-hearing young adults

This study examined racial and gender effects on behavioral thresholds and distortion-product otoacoustic emissions (DPOAEs) in the same subjects. Pure-tone behavioral thresholds and DPOAEs were measured in 60 young normal-hearing adult subjects (20 Caucasian, 20 Asian, 20 African-American, with ten females and ten males in each group). Behavioral thresholds were measured from 1000 through 16,000 Hz using Békèsy tracking. A DPOAE frequency sweep was measured with primary stimulus levels of L(1)/L(2)=60/45 dB SPL, and an f(2)/f(1) of 1.2 at discrete f(2) frequencies between 2000 through 12,000 Hz for each subject. Significant racial and gender differences in behavioral thresholds were found at 14,000 and 16,000 Hz, with the African Americans and females having the best hearing sensitivity. Based on the current results, similar findings for DPOAE frequency sweeps can be expected amongst different racial groups given that no significant differences were identified between the groups. To further define the effects of race and gender on auditory measures, future studies should include larger numbers of subjects, measurement of body size and middle ear reflectance, and examine emission generators.

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.

Repeatability of High-Frequency Distortion-Product Otoacoustic Emissions in Normal-Hearing Adults

OBJECTIVES

Distortion-product otoacoustic emissions (DPOAEs) are repeatable over time at lower frequencies (<or=8 kHz). The purpose of this study was to examine the repeatability of DPOAEs measured with high-frequency stimuli in normal-hearing adult subjects. It was hypothesized that high-frequency DPOAEs would be repeatable over a minimum of 4 wk.

DESIGN

DPOAEs were measured in 25 subjects (14 female and 11 male) with normal behavioral thresholds, normal middle ear function, and present acoustic reflexes at 1 kHz evoked by contralateral stimulation. Behavioral thresholds were measured through 16 kHz, using Békèsy tracking. Each subject attended four trials, in which a complete set of data was collected. The four trials were separated by at least one, but no more than 2 wk. At each trial, two different DPOAE paradigms were completed. Frequency and ratio sweeps were used to measure DPOAE levels and calculate DPOAE group delay, respectively. Frequency sweeps were measured with varied stimulus level conditions (L1/L2 = 60/45, 60/50, 70/55, 70/60 dB SPL) and an f2/f1 of 1.2 at discrete f2 frequencies between 2 and 16 kHz. Ratio sweeps were obtained at f2 frequencies of 2, 4, 6, 8, 10, 12, 14, and 16 kHz, with L1 = 60 and L2 = 45 dB SPL, and the ratio (f2/f1) was varied from 1.05 to 1.3. Repeated-measures analysis of variance was performed.

RESULTS

Greater variability was found at the higher frequencies (>8 kHz) for DPOAE level measurements. The average DPOAE level differences-between-trials for the higher and lower frequencies for the four different stimulus level conditions was 5.15 (SD = 4.40 dB) and 2.80 (SD = 2.70 dB) dB, respectively. Individual subject analysis revealed that high-frequency DPOAE levels varied no more than 10 dB for 87.5 and 83.1% of young adult subjects for the 70/55 and 60/50 dB SPL stimulus level conditions, respectively. For low frequencies, repeated DPOAE level variations were within +/-10 dB for 98.4 and 96% of young adult subjects for the 70/55 and 60/50 dB SPL stimulus level conditions, respectively. For DPOAE group delay, greater variability was noted at lower frequencies (<or=8 kHz) and at 10 kHz. The average group-delay differences-between-trials for the higher (10 to 16 kHz) and lower (<or=8 kHz) frequencies was 0.22 (SD = 0.20 msec) and 0.28 (SD = 0.24 msec) msec, respectively. Individual subject analysis revealed that DPOAE group-delay values varied no more than 0.70 msec for the majority of young adult subjects (96.5 and 93.5% at high and low frequencies, respectively).

CONCLUSIONS

Even though the DPOAE level data obtained at frequencies greater than 8 kHz were more variable than at low frequencies, the higher frequencies were found to be repeatable for both paradigms tested. These results encourage the exploration of high-frequency DPOAE measures to be used as an objective test for monitoring ototoxicity in humans. Testing subjects receiving ototoxic therapies is a necessary step in determining if monitoring high-frequency DPOAEs will successfully predict ototoxic effects.

Latency of DPOAE in milliseconds and waves

The latency of Distortion Product Otoacoustic Emissions is defined as the time interval between the wave onset from initial stimulation and the return to the ear canal.

Aim

The aim of this research was to verify the latency of the distortion product otoacoustic emissions in normal hearing adults, analyzing the influence of the gender, ear, frequencies and measurements.

Study design

clinical prospective.

Material and method

The measurements had been taken in milliseconds and waves. It was an experimental study, conducted at São Paulo City in 2003. The sample consisted of 38 adults, 18 men and 20 women. Significant Differences for interactions between frequency, ear, gender and measurements were not observed in relation to the latency in milliseconds and waves. A high correlation between the latency measurements in milliseconds and waves was observed. It was concluded that the latency of distortion product otoacoustic emission diminishes as increases the frequency in milliseconds and the opposite occurs in waves. Statistical differences in latencies of distortion product otoacoustic emission were not observed between gender, ears and measurements.