Distortion product otoacoustic emissions: a normative study

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.

Auditory function and prevalence of specific ear and hearing related pathologies in the general population at age 70

Objective: To describe the auditory function in early old age in detail based on both psychoacoustic and physiological measures, and to investigate the prevalence of specific audiological and otological pathologies.Design: An unscreened subsample from a population-based geriatric investigation was examined with otoscopy; tympanometry; pure-tone audiometry; word-recognition-in-noise test; distortion-product otoacoustic emissions; and auditory-evoked brainstem responses. Audiometric subtypes and diagnoses were established based on set criteria. The association between word scores and ABR was examined with linear regression analysis.Study Sample: 251 persons aged 70 (113 men, 138 women, born in 1944) that were representative of the inhabitants of the city of Gothenburg.Results: The prevalence of conductive pathology was 2% versus 49% for cochlear and 2% for auditory-neural pathology. Four percent had indeterminate type. Cochlear dysfunction was present in the majority of ears and around 20% performed worse-than-expected on speech testing. Poor performance on the speech in noise test was associated with prolonged interpeak latency interval of ABR waves I-V.Conclusion: Specific otological and audiological pathologies, other than cochlear hearing loss, are rare in the general population at age 70. Additionally, there is subtle evidence of age-related decline of the auditory nerve. Longitudinal follow-up would be of great interest.

Longitudinal analysis of the audiological phenotype in osteogenesis imperfecta: a follow-up study

Objective

This prospective study involved a longitudinal analysis of the progression of hearing thresholds in patients with osteogenesis imperfecta.

Methods

Audiometric results from 36 osteogenesis imperfecta patients (age range, 6–79 years) were compared between two test times with an average interval of 4 years. Audiometric evaluation included acoustic admittance measurements, acoustic stapedial reflex measurements, pure tone audiometry and otoacoustic emissions testing.

Results

Air conduction pure tone average, corrected for sex and age, and bone conduction pure tone average increased significantly in the study population (p < 0.05 and p < 0.001, respectively). In 14.3 per cent of the evaluated ears, an alteration in type and/or severity of hearing loss was observed.

Conclusion

After an average time interval of four years, significant changes in hearing status occurred in a population of osteogenesis imperfecta patients. These findings highlight the importance of regular audiological follow up in osteogenesis imperfecta patients, including audiometry, and measurements of acoustic admittance, acoustic stapedial reflexes and otoacoustic emissions.

Distortion-product otoacoustic emissions in workers exposed to urban stressors

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

A systematic review of stimulus parameters for eliciting distortion product otoacoustic emissions from adult humans

OBJECTIVE

The objective of this study is to review the scientific literature to determine if a set of stimulus parameters can be described to elicit distortion product otoacoustic emissions (DPOAEs) of higher absolute level and/or greater reliability in healthy adult humans and higher sensitivity and specificity in adults with cochlear lesions.

DESIGN

Systematic review.

STUDY SAMPLE

Searches of four electronic databases yielded 47 studies that had used different parameters to elicit DPOAEs from within or between-groups of adult humans.

RESULTS

The wide range of stimulus parameters used in the reviewed studies saw a wide range of reported values for DPOAE level, reliability, and sensitivity and specificity to cochlear lesions.

CONCLUSION

The most commonly used stimulus parameters for eliciting DPOAEs from adult humans have included frequency ratios for the two primary tones (f₂/f₁) of between 1.04 and 1.4 and levels (L₁/L₂) of 65/55 dB SPL. The most commonly used parameters for eliciting DPOAEs of higher level in healthy adults appear to be linked to f₂/f₁ values between 1.20 and 1.22 and L₁/L₂ levels of 75/75 dB SPL. The stimulus parameters for eliciting DPOAEs of greater reliability in healthy adults and higher sensitivity and specificity in adults with cochlear lesions have yet to be clearly determined.

TE and DP otoacoustic emission data from an Australian cross-sectional hearing study

OBJECTIVE

This paper presents a summary of otoacoustic emission (OAE) data collected as part of an Australian hearing health survey ( Carter, 2011 ; Williams et al, 2014 ) designed to: (1) examine the relationship between audiological indicators and participant characteristics, and (2) extract audiological data suitable for reference use.

DESIGN

Cross-sectional cohort study. Distortion product (DP) OAE and transient evoked (TE) OAE measures.

STUDY SAMPLE

Age range 11-35 years; N = 1386 participants (2672 test ears).

RESULTS

Descriptive statistics for amplitude and signal-to-noise ratio (SNR) were calculated for 327 participants (589 test ears; age 13 to 32 years). DPOAE amplitudes down to the 25th percentile were > 0 dB SPL for test frequencies up to 6 kHz. TEOAE SNRs down to the 25th percentile were > 6 dB SPL up to 4 kHz.

SUMMARY

This dataset can be used as a clinical reference for similar populations, providing that the same test parameters are used.

CONCLUSIONS

The clinical significance of OAE testing would be greater if agreed criteria were available. These data could be pooled with other datasets to build a substantial OAE database, similar to the existing international standards for pure-tone hearing threshold levels (HTLs) ( ISO, 2000 ).

Effect of age on click-evoked otoacoustic emission: A systematic review

OBJECTIVE:

The aims of this study were to investigate the changes of the total intensity of transient evoked otoacoustic emission (TEOAE) and signal-to-noise ratio in various frequency bands as a function of aging, and to explore the role of age-related decline of cochlear outer hair cells.

DATA SOURCES:

The literature was searched using the PubMed database using ‘transient-evoked otoacoustic emissions’ as a keyword. Articles were limited as follows: Species was ‘Humans’; languages were ‘English and Chinese’; publication date between 1990-01-01 and 2010-12-31. The references of the found were also searched to obtain additional articles.

DATA SELECTION:

Inclusion criteria: (1) Articles should involve the total TEOAE level or signal-to-noise ratio. (2) The measurement and analysis system used was Otodynamics ILO analysis system (ILO88, ILO92, ILO96 or ILO292). (3) Studies involved groups of greater than 10 subjects and TEOAE results were from normally hearing ears. (4) If more papers from the same author or laboratory analyzed the same subjects, only one was used.

MAIN OUTCOME MEASURES:

The correlations of the age scale with the total level and signal-to-noise ratio of TEOAE was determined, respectively.

RESULTS:

(1) TEOAE total level gradually increased until 2 months of age, and then decreased with increasing age. Significant negative correlations between total TEOAE level and age were found (r = –0.885, P = 0.000). (2) The most rapid decrease of TEOAE amplitude occurred at 1 year old. The total TEOAE level decreased about 4.25 dB SPL between 2 months to 1 year old, then about 0.26–0.52 dB SPL from 1 year to 10 years old, about 0.23 dB SPL from 11 years to 25 years old, and about 0.14 dB SPL from 26 years to 60 years old. (3) The signal-to-noise ratio in the frequency bands centered at 1.5, 2, 3 and 4 kHz decreased with increasing age after 2 months of age. Significant negative correlations between the signal-to-noise ratio and age were found for frequency bands ranging from 1.5 kHz to 4 kHz, with the highest correlations at 4 kHz (r = –0.890, P < 0.01), then at 3 kHz (r = –0.889, P < 0.01), at 2 kHz (r = –0.850, P < 0.01) and at 1.5 kHz (r = –0.705, P < 0.05). Conversely, a positive correlation between the signal-to-noise ratio centered at 1 kHz and age was found, but was not statistically significant (r = 0.298, P = 0.374).

CONCLUSION:

The total TEOAE response level decreased with increasing age after the first 2 months of age. The signal-to-noise ratio also decreased with increasing age in frequency bands above 1.5 kHz. The signal-to-noise ratio in higher frequencies decreased faster than in lower frequencies, leading to the maximum signal-to-noise ratio shift form 3.2–4.0 kHz in neonates to 1.5 kHz in adults, and further decreasing the total TEOAE response level. The age-related TEOAE spectrum peak shift is most likely because the outer hair cells functioning in higher frequencies are more prone to damage than those for lower frequencies.

Distortion product otoacoustic emissions: An objective technique for the screening of hearing loss in children treated with platin derivatives

In order to develop a sensitive audiometric protocol for identifying ototoxicity in children, a retrospective study of 16 children treated with cisplatin and/or carboplatin was performed. Audiometric testing was done by means of pure-tone threshold audiometry (PTA), high-frequency audiometry (HFA), and distortion product otoacoustic emissions (DPOAEs). Cisplatin caused a sensorineural high-frequency hearing loss in the study group compared to the controls (p < 0.01). Sixty-six percent of the cisplatin patients had a grade 2 or 3 ototoxicity. However, ototoxicity was not found in the patients treated with carboplatin. An excellent correlation was found between DPOAE levels and results obtained by audiometry (r = 0.82). Patients exposed to cisplatin are at significant risk for the development of drug-induced sensorineural hearing loss. Because of the several advantages of DPOAEs (noninvasive, objective, rapid, easy to use, sensitive) this method should be added in the audiological follow-up in infants and toddlers.

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.

Cortical responses to the 2f1-f2 combination tone measured indirectly using magnetoencephalography

The simultaneous presentation of two tones with frequencies f(1) and f(2) causes the perception of several combination tones in addition to the original tones. The most prominent of these are at frequencies f(2)-f(1) and 2f(1)-f(2). This study measured human physiological responses to the 2f(1)-f(2) combination tone at 500 Hz caused by tones of 750 and 1000 Hz with intensities of 65 and 55 dB SPL, respectively. Responses were measured from the cochlea using the distortion product otoacoustic emission (DPOAE), and from the auditory cortex using the 40-Hz steady-state magnetoencephalographic (MEG) response. The perceptual response was assessed by having the participant adjust a probe tone to cause maximal beating ("best-beats") with the perceived combination tone. The cortical response to the combination tone was evaluated in two ways: first by presenting a probe tone with a frequency of 460 Hz at the perceptual best-beats level, resulting in a 40-Hz response because of interaction with the combination tone at 500 Hz, and second by simultaneously presenting two f(1) and f(2) pairs that caused combination tones that would themselves beat at 40 Hz. The 2f(1)-f(2) DPOAE in the external auditory canal had a level of 2.6 (s.d. 12.1) dB SPL. The 40-Hz MEG response in the contralateral cortex had a magnitude of 0.39 (s.d. 0.1) nA m. The perceived level of the combination tone was 44.8 (s.d. 11.3) dB SPL. There were no significant correlations between these measurements. These results indicate that physiological responses to the 2f(1)-f(2) combination tone occur in the human auditory system all the way from the cochlea to the primary auditory cortex. The perceived magnitude of the combination tone is not determined by the measured physiological response at either the cochlea or the cortex.

Overexposure effects of a 1-kHz tone on the distortion product otoacoustic emission in humans

The effects of overexposure on the properties of distortion product otoacoustic emissions (DPOAEs) are investigated. In total, 39 normal-hearing humans were monaurally exposed to a 1-kHz tone lasting for 3 min at an equivalent threshold sound-pressure level of 105.5 dB. The effects of overexposure were studied in two experiments (1) on the broadband DPOAE and (2) on the DPOAE fine structure, measured using a higher frequency resolution in a narrower frequency range. The obtained DPOAE shifts were compared to temporary threshold shift (TTS) obtained after a similar exposure. Similarities between DPOAE shifts and TTS were found in the affected frequency range and the time course of recovery. The amount of TTS was higher in the early recovery time (1-4-min postexposure), but similar to the DPOAE shift (even in absolute terms) at later recovery times (5-20-min postexposure). The DPOAE fine structure was not systematically changed after the exposure.

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.

Evidence of Subtle Auditory Deficit in a Group of Patients Recovered from Bacterial Meningitis

OBJECTIVES

Sensorineural hearing loss of greater than 30 dB hearing loss occurs in up to 30% of patients after acute bacterial meningitis. This study investigated whether postbacterial meningitic patients with no apparent clinical sensorineural hearing loss had any evidence of more subtle subclinical cochlear deficit.

DESIGN

Prospective case-controlled clinical trial.

SETTING

Departments of Otolaryngology in Leicester and Nottingham, England, UK.

PATIENTS

Fifty-eight controls and 20 postbacterial meningitic patients aged between 18 and 38 years were screened by a questionnaire and tympanometry to exclude hearing loss attributable to other causes. All participants fell below the 90th percentile pure-tone audiometry threshold of the Lutman and Davis UK data sets.

MAIN OUTCOME MEASURES

In both ears, standard (0.25-8 kHz) pure-tone audiometry, high-frequency pure-tone audiometry (10-16 kHz), and distortion product otoacoustic emissions at 2, 4, and 6 kHz were measured.

RESULTS

Mean thresholds over the range of standard pure-tone audiometry (analyzed independently) for the postbacterial meningitic patients were significantly elevated at most frequencies (p < 0.05-p < 0.001) between 4 and 7 dB in both ears above control group values. There was no evidence of significant high-frequency threshold elevation (10-16 kHz). The mean iso-distortion product values at 2, 4, and 6 kHz were elevated in both ears in the meningitis group; significantly so (p < 0.05-p < 0.01) at all three frequencies in the right ear and at 4 kHz in the left.

CONCLUSIONS

Postbacterial meningitic patients with hearing below the 90th percentile range had a slight but significant subclinical threshold elevation over the standard pure-tone audiometry. This may reflect a real effect of the infection at the level of the cochlea, or it may be attributable to a mild residual cognitive defect. The moderate increases in iso-distortion product values are more likely to be real and reflect an effect on outer hair cell function in response to lower stimulus intensities.

A normative study of distortion-product otoacoustic emissions in 6-year-old schoolchildren

Evoked otoacoustic emissions have demonstrated potential for application in the community-based hearing screening of paediatric populations. Distortion-product otoacoustic emissions (DPOAEs), as opposed to transient evoked otoacoustic emissions (TEOAEs), have not been extensively researched in this regard. The current study aimed to describe the range of DPOAE values obtained in a large cohort (1576 ears) of 6-year-old children in school settings and to examine possible ear asymmetry, gender and history of ear infection effects on the data. Results indicated a variety of significant effects, particularly in the high frequencies, for DPOAE signal-to-noise ratio. The measurement parameter, DPOAE amplitude (DP-amp), was found to display potentially less clinical applicability due to large standard deviation values. Use of descriptive normative data, as derived in the present investigation, may contribute toward future improvements in the hearing screening of 6-year-old schoolchildren.

Contralateral suppression of transient evoked otoacoustic emissions in patients with cerebello-pontine angle tumor

OBJECTIVE

During measurement of transient evoked otoacoustic emissions (TEOAEs), acoustic stimulation of the contralateral ear reduces or suppresses TEOAE amplitude. This is thought to be due to the inhibitory control that the medial efferent auditory nerve exerts on outer hair cell (OHC) function. The main aim of this study was to investigate the effect of cerebello-pontine angle (CPA) tumor on the medial efferent nerve pathways to both tumor and non-tumor ears by examining alterations in TEOAE amplitude that result from contralateral acoustic stimulation.

DESIGN

Contralateral suppression of TEOAEs using broadband noise was measured preoperatively in 17 patients with unilateral CPA tumor and 17 normally hearing controls, matched for age and gender.

RESULTS

The control ears demonstrated significantly more suppression than the tumor and non-tumor ears in the patient group. There was, however, no significant difference in suppression between the tumor and non-tumor ears, and the statistical correlation for suppression between them was high. There was no effect of gender, hearing threshold levels, or size and type of tumor on suppression, although there was an effect of age on suppression in both the control and patient groups where suppression reduced as age increased. Four of the 17 patients had TEOAEs, which were clearly present in the tumor ear despite substantial hearing loss, three of which had no measurable hearing.

CONCLUSIONS

It is hypothesized that neural compression by CPA tumor disrupts the medial efferent nerve control mechanism to the OHCs of tumor ears. It also is hypothesized that neural compression reduces transmission of afferent nerve impulses from the tumor ear, which cross over to the medial olivo-cochlear complex and reduce the inhibitory control of OHC function in the non-tumor cochlea.

Evoked otoacoustic emissions--an approach for monitoring cisplatin induced ototoxicity in children

OBJECTIVES

Cisplatin chemotherapy is associated with an increased risk of ototoxic changes. The incidence of hearing loss after the 1st cisplatin-infusion session is only scarcely mentioned in the international literature. With increasing survival rates, prevention and/or early detection of ototoxicity are important for providing management options. The predictive value of pure-tone audiometry in early detection of ototoxicity has been questioned, particularly in the higher frequencies. Otoacoustic emissions appear to be more sensitive to cochlear insult than the conventional pure-tone audiometry. The aims of our study was (a) to define the extent of hearing damage in children after the 1st cisplatin-infusion session (50 mg/m(2)); and (b) to compare the efficacy of otoacoustic emissions (transient evoked otoacoustic emissions, distortion-product otoacoustic emissions) with that of pure-tone audiometry as methods of audiological monitoring.

METHODS

Baseline audiometric (0.25-8 kHz) and otoacoustic emission testing (transient evoked otoacoustic emissions, distortion-product otoacoustic emissions) was conducted in 19 children, 12 of whom met the criteria for inclusion in the final study. Comparisons were performed between baseline measurements and those recorded after the 1st cisplatin course. Transient evoked otoacoustic emissions were analyzed in terms of emission level and reproducibility as a function of frequency (0.8-4 kHz). Distortion-product otoacoustic emissions were obtained as DP-grams and I/Q functions at 4,6 and 8 kHz. The DP-gram amplitude, the dynamic range and the detection thresholds from the I/Q functions were determined for each child.

RESULTS

Threshold changes from baseline were founded to be statistically significant from 4-8 kHz in 50% of the children (P<0.01). Transient evoked otoacoustic emissions revealed a significant decrease in the emission level and in the reproducibility at the highest frequency tested (4 kHz, P<0.01), reflecting the results seen in pure-tone audiometry. Distortion-product otoacoustic emissions demonstrated a significant threshold shift, a reduced dynamic range and a decreased amplitude in the frequencies >3 kHz (P<0.05). Furthermore, DP-gram amplitude also reduced significantly at 3 kHz (P<0.05) without any similar change in pure-tone audiometry.

CONCLUSIONS

A significant high-frequency hearing loss is identified in children even after one low-dose cisplatin-infusion session. As ototoxicity screening tools DP-grams were extremely sensitive and superior to pure-tone audiometry and/or transient evoked otoacoustic emissions. Their use is recommended for regular monitoring of cochlear function, aiming in prevention of permanent damage. Some suggestions for reducing the potential for cisplatin ototoxicity (chemoprotective agents, gene therapy, inhibition of apoptosis) are also discussed.

Effects of spontaneous otoacoustic emissions on distortion product otoacoustic emission

OBJECTIVE

It has been reported that spontaneous otoacoustic emission (SOAE) can prolong the responses or increase the echo power of transiently evoked otoacoustic emission (TEOAE), yet the effects of SOAE on distortion product otoacoustic emission (DPOAE) have been studied less thoroughly. As most of the previous studies have not paid attention to the patient's age, sex and hearing level, they have not reflected possible effects of those factors. We studied the effects of SOAE specifically on DPOAE in the following subjects.

SUBJECTS AND METHODS

The subjects were all females ranging in age from 19 to 24 (average: 21.4) and the 78 ears had a hearing threshold under 15 dB for 1.2, and 4 kHz on pure-tone hearing test. IL088 (Otodynamics) was used for measurement of SOAE and IL092 (Otodynamics) for DPOAE. SOAEs were measured by time-averaging over 100 of the responses, of which those showing a clear peak 3 dB above the noise floor and being reproducible were considered as SOAE-positive. In all the ears. DPOAE responses were measured at L1 = L2 = 70 dB, and in 42 ears also at L1 = L2 = 60 dB and L1/L2 = 60/50 dB. The subjected ears were grouped into two by the presence or the absence of SOAE, and DPOAE amplitudes of 1, 2, and 4 kHz were compared. respectively.

RESULTS

Of the total, 39 ears were SOAE-positive and 39 SOAE-negative. Statistically no significant difference was observed in the average hearing level between the SOAE-positive and SOAE-negative groups. The hearing levels did not significantly differ in the frequencies of 1, 2. and 4 kHz, respectively, indicating that influence of the hearing level on DPOAE could be excludable. DPOAE amplitudes at L1 = L2 = 70 dB in the frequencies of 1, 2, and 4 kHz were higher in the SOAE-positive group than in the SOAE-negative group. And DPOAE amplitudes were also higher in SOAE-positive group at L1 = L2 = 60 dB and L1/L2 = 60/50 dB in the frequency of 1.2, and 4 kHz, but significant differences were observed only in the frequencies of 4 kHz. By grouping the ears by the number of SOAE. we revealed the tendency that the larger the number of SOAE, the higher the DPOAE amplitudes.

CONCLUSIONS

We evidenced that SOAE has significant effects on DPOAE responses. In clinical application of DPOAE measurement, therefore, the effects should be seriously taken into account.

Optimal stimulus level conditions for measurements of distortion product otoacoustic emissions

OBJECTIVE

Distortion product otoacoustic emission (DPOAE) is a tool for an objective examination of the cochlea function. While the clinical application of DPOEA test is in progress, the measurements vary depending on the stimulus conditions. We aimed to determine the most appropriate stimulus level in the clinical application of DPOAE test.

METHODS

Ninety-seven normal hearing ears and 80 hearing-impaired ears (total 177) were subjected to this study. Two levels of stimulations (L1 and L2) were applied as follows: L1 = L2 = 70 dB; L1 = L2 = 60 dB and L1 = 60/L2 = 50 dB, and DP level was measured at each stimulation, and compared with hearing level.

RESULTS

DP level was highest at L1 = L2 = 70 dB. Normal hearing ears and hearing-impaired ears were well differentiated at L1 = L2 = 60 dB.

CONCLUSION

In clinical application of DPOAE test, DP levels should be measured at the stimulus level most appropriate for the purposes.

Effects of industrial noise exposure on distortion product otoacoustic emissions (DPOAEs) and hair cell loss of the cochlea--long term experiments in awake guinea pigs

Distortion product otoacoustic emissions (DPOAEs), a sensitive detector of outer hair cell (OHC) function, cochlear microphonics (CM), and hair cell loss have been monitored in 12 awake guinea pigs before and after 2 h exposure to specific, played-back industrial noise (105 dB SPL maximal intensity). All animals had stable DPOAE levels before noise exposure. In the first hours after noise exposure DPOAE levels were reduced significantly. In about 70% a partial recovery of the DPOAEs was found within 4 months after noise exposure. In 16% of the investigated ears no recovery of DPOAEs was observed. However, in a few ears increased DPOAEs were observed after noise exposure. Exposure to industrial noise caused both morphological changes in the middle turns of the cochlea and electrophysiological changes in the middle frequency range. A close correlation existed between reduced DPOAE levels, loss in CM potentials, and area of damaged or lost OHCs, but not with the numbers of damaged or lost OHCs in the cochlea. It can be concluded that continuous industrial noise causes a damage to OHCs which differs form the damage caused by impulse noise.

[Scanning electron microscopic findings concerning the formation of the organ of Corti near the helicotrema in guinea pigs]

We report on findings in guinea pigs with objectively tested normal hearing ability. At the apical end of the Corti organ only in the inner row of hair cells the stereociliae are detectable by scanning electron microscopy. Here the row is interrupted several times. Near the helicotrema we find first the inner row of the outer hair cells, then the middle row and finally the outer row. At the beginning of the D-turn their arrangement is disordered. Normally, at the basal end of the D-turn all rows of inner and outer hair cells show their typical formation. This finding should be taken into consideration when making a cochleogram for proving of experimental noise damages.

Test-retest variability of distortion-product otoacoustic emissions in human ears with normal hearing

In the present study, the test-retest variability of distortion product otoacoustic emissions (DPOAEs) due to various causes has been assessed quantitatively at individual frequencies using the ILO88/92 system. The short-term variance was generally lower than 3 dB2. Changing the position and the fit of the probe may affect the level of background noise in the ear canal, which interferes with the responses of the DPOAEs mainly at low frequencies and can also influence the interaction of the resonances of the outer ear and acoustic stimuli. The long-term variance was significantly greater than short-term variance, but did not differ significantly from variance of refitting the probe. The total DPOAE variance was small across all the frequencies above 1000 Hz except for a small peak in the 2500 Hz range. This may be related to the low response amplitudes in this region. The limitation of DPOAE detection at frequencies below 1000 Hz must lead to caution in the interpretation of results in this frequency range. The magnitude of the total variance was similar to that found in audiometric studies.

Sensitivity of transient evoked and distortion product otoacoustic emissions to the direct effects of noise on the human cochlea

Measurement of otoacoustic emissions (OAEs) has been proposed as a sensitive test to reliably assess the effects of noise exposure. The present study in humans was designed to evaluate the sensitivity and applicability of transient evoked OAEs (TEOAEs) and 2f1-f2 distortion product OAEs (DPOAEs) as quantitative indices of the functional integrity of the outer hair cells (OHC) during growth of and recovery from temporary threshold shift (TTS). This was examined in two different groups of volunteers by measuring the per- and post-stimulatory effects of a one hour BBN and an on-site five hour exposure to loud music from a discotheque. The results of both experiments show consistent growth and recovery patterns for both DPOAEs and TEOAEs. For TEOAEs, both the reproducibility scores and signal to noise ratio values for the 4 kHz frequency band exhibited the greatest sensitivity. The DPOAEs, on the other hand, showed the greatest sensitivity between 2 and 5.5 kHz. Thus, both the TEOAEs and DPOAEs have a great potential in the detection of TTS after noise exposure.

Mechanisms in noise-induced permanent hearing loss: an evoked otoacoustic emission and auditory brainstem response study

In this study 22 patients (44 ears) with noise-induced permanent hearing loss were audiologically evaluated using transient-evoked otoacoustic emissions (TEOAE) and auditory brain-stem response (ABR). Twenty-one normal subjects (42 ears) without exposure to occupational noise were used as controls. Based upon the hearing loss at 4, 3, 2 and 1 kHz on the pure-tone audiogram, they were classified into four groups. In group 1 (eight ears), emissions were present in all ears but their TEOAE-noise level and their reproducibility (percentage) proved to be weak. The auditory brain-stem response (ABR) indicated that the I/V amplitude ratio, the latency values of wave V and the I-V intervals fell within the normal range in all ears. In Group 2 (14 ears), 40 per cent had no emissions, whereas the remaining ears showed weak emissions. The ABR revealed that in all ears the I/V amplitude ratio became small while wave V peak latency as well as I-V intervals were within the normal range. In Group 3 (10 ears), emissions were absent in 50 per cent, while in the other ears the emissions were very weak. The ABR revealed that the I/V amplitude ratio, which could be calculated in the 60 per cent in which wave I was present, was smaller than in Group 2. Wave V latency as well as I-V intervals were within the normal range. In Group 4 (12 ears), none of the ears showed emissions. The ABR indicated that the I/V amplitude ratio was much smaller when wave I was present (27 per cent) as well as I-V interval values being within the normal range. Wave V absolute latency value (delta V index) indicated a positive index in 17 per cent of this group (two ears) when wave I was absent. In the present study a dynamic process from cochlear outer hair cells to cochlear neurons was seen, correlating with an increasing hearing loss.