Comparison of distortion product otoacoustic emissions in 28 inbred strains of mice

Cochlear function was evaluated in a longitudinal study of 28 inbred strains of mice at 3 and 5 mo of age using measures of distortion product otoacoustic emissions (DPOAEs) in response to a federal initiative to develop rapid mouse phenotyping methodologies. DP-grams at f(2) frequencies ranging from 6.3 to 54.2kHz were obtained in about 3min/ear by eliciting 2f(1)-f(2) DPOAEs in 0.1-octave steps of f(2) with primary tones at L(1)=L(2) =55, 65, and 75dB SPL. CBA/CaJ mice exhibited average levels of approximately 26dB SPL and this strain was selected as the normal reference strain against which the others were compared. Based upon the configurations of their DP-grams, the 28 mouse strains could be categorized into four distinct groups. That is, nine of the strains including the CBA were designated as the CBA-like group because these mice displayed robust DPOAE levels across frequency. In contrast, the remaining three groups all exhibited irregular DP-gram patterns. Specifically, eight of the remaining 19 strains showed a progressive high- to low-frequency reduction in DPOAE levels that was typical of age-related hearing loss (AHL) associated with mouse strains homozygous for the ahl allele and were labeled as AHL-like strains. Seven strains demonstrating relatively even patterns of reduced DPOAE levels across the frequency-test range were designated as Flat-loss strains. Finally, the remaining four strains exhibited no measurable DPOAEs at either 3 or 5 mo of age and thus were classified as Absent strains. Extending the f(2) test frequencies up to approximately 54kHz led to the detection of very early-onset reductions in cochlear function in non-CBA-like groups so that all strains could be categorized by 3 mo of age. Predictably, the AHL-like strains showed more pronounced DPOAE losses at 5 mo than at 3 mo. A similar deterioration in DPOAE levels was not apparent for the Flat-loss strains. Both the AHL-like and Flat-loss strains showed considerably more variability in DPOAE levels than did the CBA-like strains. Together, these findings indicate that DP-grams adequately reveal both frequency-specific loss patterns and details of inbred strain variability.     

Alternative distortion product otoacoustic emissions and hearing loss in a clinical population

Parameters of the alternative distortion product otoacoustic emissions (DPOAEs) 4f1-3f2, 3f1-2f2, 2f2-f1, 3f2-2f1 and 4f2-3f1 as well as the cubic distortion product 2f1-f2 were extracted from the ILO 92 binary files of patients reported on earlier (Lind, 1998). The DPOAEs were recorded at 18 stimulus levels between 19 and 70 dB SPL. The prevalence of at least one valid DPOAE data-point varied from 74% at 4f1-3f2 to 100% at 2f2-f1. The mean number of valid points was six for 2f2-f1, but generally below four for the others. The mean maximum amplitude for the alternative DPOAEs was 6-12 dB below that of the 2f1-f2. The mean maximum signal-to-noise-ratio (SNR) was between 2.5 and 3.5 dB SPL for the four most peripheral emissions and increased to 6.7 dB SPL for the 2f2-f1. As reported earlier, the 2f1-f2 distortion was fairly well correlated with hearing threshold at 2 kHz. The 2f2-f1 shows some correlation with hearing loss at frequencies above f2, but the other DPOAEs were not correlated with hearing loss at any frequency, which may suggest different generating mechanisms and/or sites. The inf1uence of age on maximum amplitude was small but significant for all DPOAEs.     

Test-retest repeatability of distortion product otoacoustic emissions

OBJECTIVES: Distortion product otoacoustic emissions (DPOAE) have become part of routine audiological diagnostics. The large scale of clinical DPOAE applications, such as screening of hearing in infants, objective estimation of hearing status, distinction between cochlear and retrocochlear origin of sensorineural hearing loss, exclusion of psychogenic hearing loss, monitoring of hearing during administration of ototoxic drugs, and others illustrates the significance of this audiological tool. In all diagnostic tests, knowledge about the procedure's test-retest repeatability is of crucial importance, to allow for distinction between measurement deviations and true physiological or pathological changes in monitoring over time. DESIGN: Measurements of DPOAE were performed in triplicate in 80 normally hearing ears of 40 subjects. Both immediate remeasurements with the ear probe left in place [single-fit mode (SF-mode)] and remeasurements after approximately 5 to 10 days [multiple-fit mode (MF-mode)] were included. DPOAE primary tone levels were varied in 5 dB steps from L2 = 60 to 20 dB SPL (L1 = L2 x 0.4 + 39 dB SPL) and within the frequency range f2 = 1 to 6 kHz. Repeatability of DPOAE was evaluated by the standard error of measurement (Sm), reliability (Cronbach alpha), absolute differences between measurements, 95% confidence intervals, and repeatability standard deviations. RESULTS: Sm averaged 0.67 dB over all frequencies and primary tone levels in the SF-mode, and 1.44 dB in the MF-mode, respectively. As expected, test-retest repeatability declined with decreasing primary tone levels; however, repeatability values were still mostly satisfactory with the lower primary tone levels. For the exemplary primary tone level combination of L1/L2 = 63/60 dB SPL, which is close to common clinical paradigms, the difference between two DPOAE measurements under the reported test conditions could be considered statistically significant (p = 0.05) if it exceeded 0.7 to 1.3 dB in the range 1 to 5 kHz and 2.3 dB for 6 kHz in the SF-mode, when compared with 1.8 to 2.7 dB for 1 to 5 kHz and 3.7 dB for 6 kHz in the MF-mode. Signal to noise ratio (SNR) did not seem to have a large influence on repeatability, as long as SNR was within 6 to 35 dB, which covers the range of most clinical DPOAE measurements. CONCLUSIONS: The DPOAE-test-retest study presented here is to our knowledge the first, which combines variation of primary tone levels, assessment of both SF- and MF-modes, and comparison of the two modalities within the same subjects. Although the measurements were conducted under practical conditions resembling the clinical setting, repeatability was generally good. The widely used minimum SNR of 6 dB seems to be a recommendable criterion when considering both practicability and measurement quality under clinical conditions. The current findings underline the suitability of DPOAE as a monitoring tool of cochlear status over time. The data are intended to assist the clinician and the scientist in the correct interpretation of DPOAE level changes in the test-retest situation.     

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.     

畸变产物耳声发射的临床研究

畸变产物耳声发射（distortionProductotoacousticemissions，DPOAEs）为由两个纯音（F_1，F_2）同时刺激诱发的、由耳蜗外毛细胞能动活动产生的、在外耳道记录到的一种声能。与其它耳声发射相比其用于临床有以下优点：①潜伏期短；②可以连续评价任何频率，尤其是1～8kHz频率范围耳蜗功能；③可以完全评价刺激阈或刺激阈上水平的耳蜗功能（输入／输出功能曲线）；④听阈高达45～55dBHL，患者可以检测出，而瞬态诱发耳声发射（TEOAES）当听阈大于30dBHL时则测不出’‘’。所以DPOAES越来越多地受到人们的重视。巨DPOAES用于临…     

畸变产物耳声发射在伪聋和夸大性聋检测中的应用

目的：探讨畸变产物耳声发射（DPOAE）对伪聋和夸大性聋的鉴别诊断作用。方法：采用ILO 96耳动态分析仪对外伤后诉听力下降,而又不配合纯音听阈（PTT）检测的患者进行DPOAE检测与分析。结果：经PTT检测的129例（150耳）外伤性听力下降患者中,有102例（121耳）,作DPOAE检测结果显示伪聋占66．12％（80／121）,夸大性聋占33．88％（41／121）。经ABR检测反应阈值,证实DPOAE检测结果客观、可靠。结论：DPOAE作为外伤后听力损失鉴别诊断的常规检测方法,可对伪聋和夸大性聋作出客观、可靠的诊断和鉴别诊断。     

Sensitivity of distortion product otoacoustic emissions in noise-exposed chinchillas

The present study investigates the effect of small amounts of outer hair cell (OHC) loss on distortion product otoacoustic emission (DPOAE) levels and evoked potential permanent threshold shifts (PTS) in a population of 12 noise-exposed chinchillas. The group mean DPOAE level, which decreased by up to approximately 15 dB in the presence of less than 8 dB PTS and 15% OHC loss, indicates that DPOAEs can detect an underlying cochlear pathology (i,e., OHC damage/loss) despite the presence of normal to near normal thresholds. The sensitivity of DPOAEs in detecting OHC loss makes this test measure suited for diagnosing sensorineural hearing impairment, particularly when abnormal auditory symptoms (i.e., speech discrimination problems) are associated with a normal audiogram in the clinical setting and as part of a hearing conservation program.     

Influence of spontaneous otoacoustic emissions on distortion product otoacoustic emission amplitudes

Although the influence of the levels and ratios of the primary stimulus on the amplitude of distortion product otoacoustic emissions (DPOAEs) has been studied intensely, the influence of the presence of spontaneous otoacoustic emissions (SOAEs) has been investigated less thoroughly. The present investigation analysed whether the unilateral presence of 58 SOAEs in 43 normal-hearing adults was related to larger DPOAEs in the ear with SOAEs compared to the contralateral ear having no SOAEs. The study was designed such that the only factor that could influence the amplitude of DPOAEs was the presence of SOAEs. Input/output (I/O) functions were collected in response to primary tones that were presented in 5-dB steps from 70 to 40 dB SPL at the frequency of the unilaterally recorded SOAE of each subject. The primary outcome was the demonstration of statistically significant (P<0.05) larger DPOAEs in ears exhibiting SOAEs than in ears without measurable SOAEs, except at the highest stimulus level of 70 dB SPL. These results suggest that SOAEs play an additive role in the measurement of DPOAEs. The enhancing effect of the unilateral presence of SOAEs on DPOAEs was statistically significant for 65 dB SPL and lower levels of primary tones. The authors speculate that passive cochlear properties begin to participate in the generation of DPOAEs at primary-stimulus levels greater than 65 dB SPL.     

豚鼠畸变产物耳声发射的检测

目的 :建立稳定可靠的检测动物畸变产物耳声发射的方法。方法 :采用预先手术切除耳屏软骨 ,加用自制探头套管 ,选择复合麻醉等改良方法 ,测量健康杂色豚鼠 7只 ( 13耳 ) 2、4、6k Hz畸变产物耳声发射( DPOAE)输入输出 ( I/ O )曲线、潜伏期等指标。结果 :各频率 DPOAE引出率均为 10 0 % ,I/ O曲线最大幅值分别为 ( 2 7.2 4± 4 .15 ) d B SPL ,( 2 7.98± 4 .0 5 ) d B SPL和 ( 4 1.4 5± 1.2 0 ) d B SPL ;潜伏期为 ( 2 .0 6± 0 .2 1) m s,( 1.5 2±0 .16) ms和 ( 1.3 7± 0 .0 8) m s。结论 :改良法豚鼠 DPOAE检出率高 ,振幅大 ,各指标结果重复性好 ,适用于动物DPOAE的研究。     

Isoflurane anesthesia suppresses distortion product otoacoustic emissions in rats

A commonly used anesthetic, isoflurane, can impair auditory function in a dose-dependent manner. However, in rats, isoflurane-induced auditory impairments have only been assessed with auditory brainstem responses; a measure which is unable to distinguish if changes originate from the central or peripheral auditory system. Studies performed in other species, such as mice and guinea-pigs, suggests auditory impairment stems from disrupted OHC amplification. Despite the wide use of the rat in auditory research, these observations have yet to be replicated in the rat animal model. This study used distortion product otoacoustic emissions to assess outer hair cell function in rats that were anesthetized with either isoflurane or a ketamine/xylazine cocktail for approximately 45?min. Results indicate that isoflurane can significantly reduce DPOAE amplitudes compared to ketamine/xylazine, and that responses were more variable with isoflurane than ketamine/xylazine over the 45-min test period. Based on these observations, isoflurane should be used with caution when assessing peripheral auditory function to avoid potentially confounding effects.     

The evaluation of distortion product otoacoustic emissions after stapedotomy

34 patients with otosclerosis operated at the ENT Clinic, were enrolled in this study. Prior and 4 months after stapedotomy the signal of DPOAE and the threshold levels for air and bone conduction were evaluated. No signal of otoacoustic emissions was registered in any of the patients prior stapedotomy. After operation DPOAE was registered in 23 out of 34 examined patients (67.6%).     

Effects of cigarette smoking on distortion product otoacoustic emissions

This study measured distortion product otoacoustic emissions (DPOAEs) and DPOAE input/output (I/O) curves to assess the effects of smoking on cochlear function. Twenty-four healthy adults, 12 smokers and 12 nonsmokers in the 20-30 years age range were selected based on self-reported histories of five to eight years of smoking or no smoking, respectively. All subjects received tympanometric screening to rule out middle ear pathology. Conventional (0.25-8 kHz) and ultra high frequency (UHF; 10-20 kHz) audiometry showed normal or age-appropriate thresholds across both groups. DPOAE results showed small, but significant, decline in DPOAE levels without concomitant changes in noise floors in smokers as compared to nonsmokers. I/O detection thresholds were also significantly elevated at high frequencies in smokers as compared to their nonsmoking counterparts. These findings indicate that smokers are at greater risk for cochlear damage than nonsmokers, and that DPOAE amplitudes and I/O detection thresholds may identify early changes in cochlear function in smokers.     

早产儿畸变产物耳声发射的特性分析

目的 :研究早产儿畸变产物耳声发射 (DPOAE)的幅值、信噪比、本底噪声等基本特性。方法 :应用DP2 0 0 0型耳声发射仪对 31例早产儿 (5 9耳 )和 19例足月新生儿 (35耳 )在出生后 3d～ 1周内行DPOAE检测。结果 :早产儿DPOAE反应幅值曲线有一峰点 (f2 =15 87Hz)和一谷点 (f2 =4 0 0 0Hz) ,早产儿各频率反应幅值均低于足月新生儿相应频率 (P <0 .0 5 ) ;早产儿DPOAE信噪比SNR于f2 =4 0 0 0Hz处最高 ,f2 =10 0 0Hz处最低 ,4 0 0 0Hz、3175Hz及 15 87Hz、12 6 0Hz、10 0 0Hz处SNR均低于足月儿相应水平 (P <0 .0 5 ) ;早产儿DPOAE本底噪声在低频段 (f2 =12 6 0Hz、10 0 0Hz)显著高于其他频率 ,4 0 0 0Hz处噪声水平最低 (P <0 .0 1) ,3175Hz、2 5 2 0Hz及 2 0 0 0Hz处早产儿组噪声水平均低于足月儿组 (P <0 .0 5 )。结论 :早产儿DPOAE反应幅值、信噪比及本底噪声与足月儿相比差异均有统计学意义。该差异与耳蜗外毛细胞发育过程相关 ,还可能与中耳及外耳的发育有关     

选择注意对畸变产物耳声发射的影响

为研究高级中枢对耳蜗微机制的调控作用，对正常人１６例（３２耳）进行有和无视觉选择任务条件下的畸变学产物耳声发射（ＤＰＯＡＥ）测试，结果显示视觉任务了出现时ＤＰＯＡＥ幅值下降，Ｆ２为１，２ｋＨｚ处的ＤＰＯＡＥ幅值下降达显著性水平（Ｐ〈０．０５）。讨论了调控作用的可能机制，认为研究高级中枢和橄榄耳蜗传出神经系统对耳蜗功能的影响将有十分重要的生理和病理意义。     

Age-related declines in distortion product otoacoustic emissions utilizing pure tone contralateral stimulation in CBA/CaJ mice

One role of the medial olivocochlear (MOC) auditory efferent system is to suppress cochlear outer hair cell (OHC) responses when presented with a contralateral sound. Using distortion product otoacoustic emissions (DPOAEs), the effects of active changes in OHC responses due to the MOC as a function of age can be observed when contralateral stimulation with a pure tone is applied. Previous studies have shown that there are age-related declines of the MOC when broad band noise is presented to the contralateral ear. In this study, we measured age-related changes in CBA/CaJ mice by comparing DPOAE generation with and without a contralateral pure tone at three different frequencies (12, 22, and 37 kHz). Young (n = 16), middle (n = 10) and old-aged (n = 10) CBA mice were tested. DPOAE-grams were obtained using L1 = 65 and L2 = 50 dB SPL, F1/F2 = 1.25, using eight points per octave covering a frequency range from 5.6-44.8 kHz. The pure tone was presented contralaterally at 55 dB SPL. DPOAE-grams and ABR levels indicated age-related hearing loss in the old mice. In addition, there was an overall change in DPOAEs in the middle-aged and old groups relative to the young. Pure tone stimulation was not as effective as a suppressor compared to broadband noise. An increase in pure tone frequency from 12 to 22 kHz induced greater suppression of DPOAEs, but the 37 kHz was least effective. These results indicate that as the mouse ages, there are significant changes in the efficiency of the suppression mechanism as elicited by contralateral narrowband stimuli. These findings reinforce the idea that age-related changes in the MOC or the operating points of OHCs play a role in the progression of presbycusis - age-related hearing loss in mammals.     

Distortion product otoacoustic emissions in sensorineural hearing loss

The measurement of distortion product otoacoustic emissions (DPOE), one of the types of otoacoustic emissions (OES) gives the possibility of frequency--specific, objective assessment of cochlear function. Data were collected from 67 ears with sensorineural hearing loss and 30 normally hearing ears as a control group. Percentage of DPOE response detected above the noise floor level was evaluated in relation to the pure-tone audiometric thresholds. Analysis of correlation coefficient between amplitude of DPOE and degree of hearing loss for respective frequencies was performed. DPOE were detected in significantly lower percentage in the group of ears with sensorineural hearing loss exceeding 60 dB HL. The amplitude of DPOE decreased with the degree of hearing loss detected in pure-tone audiometry. There was statistically significant correlation (r -0.65(-)-0.85) in all examined frequencies between DPOE and hearing loss (1-6 kHz).     

畸变产物耳声发射与瞬态诱发耳声发射的相关性观察

目的：探讨畸变产物耳声发射（DPOAE)和瞬态诱发耳声发射(TEOAE)的特点和相关性。方法：以20例（40耳）耳科正常青年人观察噪声暴露前后在无对侧抑制（NCS)状态下和有对侧抑制（CS)状态下TEOAE的频带信噪比、频带反应幅值，与DPOAE的2f1-f2幅值、信噪比相互间的相关性。结果：DPOAE与TEOAE虽由不同的刺激声所引出，有各自的图形特征，但在绝大多数相近频率点上，其测量值有较好的相关性，形成一定的数量关系。结论：TEOAE测试较为快捷并有中频优势，而DPOAE则有很好的频率特异性和高频优势。二者幅值及信噪比间有良好的相关性，可得出有统计意义的线性回归方程参数，听觉损害，噪声性。     

Changes in distortion product otoacoustic emissions during prolonged noise exposure

The aim of this study was to evaluate the reduction in 2f₁−f₂ distortion product otoacoustic emission (DPOAE) amplitude resulting from prolonged noise exposures. A group of five chinchillas was exposed continuously to an octave-band noise centered at 4.0 kHz for a total of 42 days, 6 days at each of seven exposure levels. Exposure level increased in 8-dB steps from 48 to 96 dB SPL. DPOAE input-output (I/O) functions were measured at octave intervals over a range of primary tone f₂ frequencies between 1.2 and 9.6 kHz. Measurements were obtained (1) pre-exposure, (2) during days 3–6 of each 6-day exposure, and (3) 4 weeks after the final exposure. Continuous noise exposure caused a reduction in DPOAE amplitude that was greatest at f₂ frequencies within and above (3.4–6.8 kHz) the octave-band noise exposure. For these f₂ frequencies, DPOAE amplitudes decreased as exposure level increased up to approximately 72–80 dB SPL; higher exposure levels failed to cause any further reduction in DPOAE amplitude. The noise level at which DPOAE amplitude began to decrease was approximately 50 dB SPL. Above this critical level, DPOAE amplitude decreased 1.3 dB for every dB increase in noise level up to approximately 75 dB SPL.     

The effect of impulse noise on distortion product otoacoustic emissions

The aim of this study was the evaluation of distortion product otoacoustic emissions (DPOAEs) before and after noise exposure from shooting, and the comparison of DPOAEs with pure-tone audiometry. Thirteen young male police officers were exposed to impulse noise from shooting, without using earplugs. Standard pure-tone audiometry, tympanometry, and DPOAEs were performed before exposure and at one hour post- and 24 hour post-exposure. In the one hour post-exposure testing mean pure-tone thresholds were elevated in the 1-8 kHz frequency zone and DPOAE levels were reduced at several frequencies. DPOAEs were more affected at 3 kHz or lower, whereas pure-tone thresholds were more affected at higher frequencies. After the final examination, non-significant partial shifts at high frequencies on both tests remained. Pure-tone audiometry was overall more sensitive, but DPOAEs provided additional information about the cochlear status of certain ears. These data suggest that besides behavioral testing, DPOAEs may play a role as a fast, objective, and easy to perform test for monitoring subjects exposed to impulse noise.     

Screening of high-risk infants using distortion product otoacoustic emissions.

Otoacoustic emissions have been used as an objective and noninvasive test of cochlear function. Due to its ease of use, accuracy, and test-retest reliability, otoacoustic emissions testing is considered an excellent tool for evaluating difficult-to-test patients. This project involved screening infants at high risk of congenital hearing loss. These infants were selected from the Special Infant Clinic at Queen's University, Kingston, Ontario. The first part of this project was to establish a distortion product otoacoustic emissions (DPOAEs) "norm" as the reference for this group of patients. A prospective study was then conducted to compare DPOAE and auditory brainstem response (ABR) as screening tools for this group of patients. Auditory brainstem response has been the gold standard for evaluating the hearing status of these infants. We will also present our experience in testing over 50 patients at high risk of congenital hearing loss using DPOAEs.