Assessment of the medial olivocochlear efferent system in children. pure tone 1.0 kHz and 2.0 kHz suppressive effects on transient evoked otoacoustic emission

The role of medial efferent system in regulating outer hair cell function has been studied by many investigators. Usually narrow band noise or white noise as contralateral stimulation (CS) suppressors have been used and changes in OAE amplitudes estimated. Thirty children aged 6-15 years (mean 12.5 +/- 4.7), without any changes in tonal and impedance audiometry and with negative history regarding otiatric diseases were examined. Transient evoked otoacoustic emissions (TEOAE) were recorded using ILO 92 Otodynamics Analyser. CS was performed using 1.0 kHz and 2.0 kHz continuous pure tones of 30 dB SL or 50 dB SL. Effects of CS on TEOAE evoked by click of 80, 70 and 60 dB SPL were investigated. TEOAE analysis included assessment of TEOAE amplitude of half octave frequency bandwidth (HOFBW-1.0; HOFBW-1.5; HOFBW-2.0; HOFBW-3.0 and HOFBW-4.0 kHz) and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes centred at 1.0; 2.0; 3.0; 4.0 and 5.0 kHz. TEOAE amplitude recorded for stimuli 80, 70 and 60 dB SPL without CS decreased: mean values respectively 6.1 +/- 4.2; 5.4 +/- 4.5 and 3.3 dB SPL +/- 4.3. CS effect on TEOAE was observed for all CS options, however, larger suppressive effect was recorded on TEOAE elicited by 70 dB SPL stimulus using 1 kHz/50 dB SL tone as a suppressor and on TEOAE elicited by 60 dB SPL stimulus using 2 kHz/50 dB SL tone as a suppressor. HOFBW and 0.8-FBW analyses showed the association between the frequency/intensity of the suppressors and decreasing of amplitudes of adequate frequency bands. It is concluded that the described method of investigating of the medial olivocochlear efferent system seems to be sensitive and confirms frequency-dependent suppressive effect on OAE.     

背景噪声对新生儿瞬态诱发耳声发射的影响

目的 分析背景噪声对新生儿瞬态诱发耳声发射(TEOAE)的影响.方法 对122例通过听力筛查的新生儿(244耳,女62例,男60例)分别以短声刺激行TEOAE检测,用quick TEOAE模式,叠加次数大于100次.并以背景噪声分组,比较安静组与噪声组之间TEOAE差异.结果 ①新生儿TEOAE的背景噪声为(33.94...     

新生儿与成人瞬态诱发耳声发射差异的频谱特性分析

目的 比较新生儿与成人瞬态诱发耳声发射(TEOAE)的差异,并分析其频谱特性.方法 以短声刺激分别对120名通过听力筛查的新生儿(男58,女62)和32名平均纯音听阈(听力级)在20 dB以内的成年人(男15,女17)行TEOAE检测,对于测试结果 行频谱分析和半倍频程分析.结果 ①新生儿组TEOAE总强度(声压级,下同)为(15.18±4.39)dB,高于成人组的(9.51±4.12)dB,差异具有统计学意义(t=9.303,P<0.05).②新生儿的频带重复率、频带重复率非0比例、频带信噪比检出率及频带信噪比在第1频带(0.8 kHz)最低,在3.2 kHz最大;而成人在第5频带(4.0 kHz)处最低,在1.5 kHz最大.③新生儿与成人最大频带信噪比强度差为7.09 dB,二者出现的频率位置相差约1.7 kHz.④半倍频程分析显示新生儿TEOAE最大能量为(10.50±5.09)dB,在2828 Hz处,而成人为(2.84±5.33)dB,在1414 Hz处;二者最大反应在强度上相差7.66 dB,出现的频率位置相差1414 Hz.⑤成人1.5 kHz区的TEOAE信号最强,之后其信噪比随频带增高而降低,而新生儿信噪比却呈现随频带增高而增强的特征;从第1频带到第5频带,新生儿与成人TEOAE强度的差值随频带增高也逐渐增大.结论 成人TEOAE总强度低于新生儿.新生儿频带信噪比及半倍频程能量反应峰的分布频率及反应强度均高于成人.     

The effect of various durations of noise exposure on auditory brainstem response, distortion product otoacoustic emissions and transient evoked otoacoustic emissions in rats

This study was designed to investigate the effect of various durations of noise exposure in animals on physiological responses from the cochlea which are also used clinically in humans: auditory brainstem response (ABR), transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs). Rats were exposed to 113 dB SPL broad-band noise (12 h on/12 h off) for durations of 3, 6, 9, 12, 15 and 21 days, and tested 24 h after cessation of the noise and again after a period of 6 weeks. ABR threshold to click stimuli and to a 2-kHz tone burst (TB), TEOAE energy content and DPOAE amplitude in the exposed rats were compared to those in a group of control rats not exposed to noise. ABR thresholds (click and TB) were significantly elevated in all exposure duration groups compared to control rats. DPOAE amplitudes and TEOAE energy content were significantly reduced. The mean ABR thresholds following 21 days exposure were significantly greater (click = 100 dB pe SPL; TB = 115 dB pe SPL) than those following 3 days exposure (click = 86 dB pe SPL; TB = 91 dB pe SPL). Linear regression analysis between recorded responses and duration of noise exposure (days) showed a significant increase in ABR thresholds of approximately 0.8-- 1.4 dB/day. TEOAE and DPOAE responses showed no such dependence on noise duration and were already maximally reduced after only 3 days of exposure. This can be explained by the possibility that short noise exposures may cause damage to the early, more active stages of cochlear transduction (as shown by TEOAEs and DPOAEs). As the noise exposure continues, further damage may be induced at additional, later stages of the cochlear transduction cascade (as shown by ABR). Thus, ABR seems more sensitive to noise duration than OAE measures.     

Ototoxic effects of cisplatin in a Sprague-Dawley rat animal model as revealed by ABR and transiently evoked otoacoustic emission measurements

The ototoxic effects of cisplatin in a Sprague–Dawley rat model were evaluated by recordings of auditory brainstem responses (ABR) and transiently evoked otoacoustic emissions (TEOAEs). The ABR responses were evoked from alternating clicks and 8, 10, 12, 16, 20 and 30 kHz tone pips in a range from 40 to 100 dB SPL range. The TEOAEs were recorded with a non-linear protocol, and were evoked by a 63.5 dB SPL click stimulus. Twenty five male Sprague–Dawley rats were used in the study, 20 animals were treated with cisplatin (16 mg/kg, body weight) and five animals served as controls. The data showed that 72 h after the cisplatin administration, the TEOAE and ABR variables were significantly altered. The relationship between the ABR and TEOAE variables was shown to be non-linear. The most significant relationships were observed between the TEOAE correlation and the ABR threshold values at 10, 12, and 16 kHz.     

Efficient Otoacoustic Emission Protocols Employed in a Hospital-based Neonatal Screening Program

Within the context of a hospital-based newborn hearing screening program, we have studied the application of two OAE protocols (TEOAE and DPOAE) on a group of 250 well babies. The main goal of this study was to evaluate the performance of DPOAE protocol in a relatively large population sample, using a preset number of five tested frequencies, in comparison with a default TEOAE screening protocol. The data were collected on the second day of life and during spontaneous sleep. The TEOAE recordings were acquired with linear protocols using click stimuli of 70-75 dB SPL and were used as indicators of normal cochlear function. The cubic distortion product DPOAE responses were evoked by an asymmetrical 75-65 dB SPL protocol, with a frequency ratio of 1.22. Five frequencies (referring to F₂) were tested at 1.5, 2.0, 3.0, 4.0 and 5.0 kHz. The data from the DPOAE responses show a similar pass rate (similarity=0.98) to the linear TEOAE protocol. The data presented suggest that a DPOAE cochlear evaluation, at 5 pre-selected frequencies, has clinical potential.     

Efficient otoacoustic emission protocols employed in a hospital-based neonatal screening program

Within the context of a hospital-based newborn hearing screening program, we have studied the application of two OAE protocols (TEOAE and DPOAE) on a group of 250 well babies. The main goal of this study was to evaluate the performance of DPOAE protocol in a relatively large population sample. using a preset number of five tested frequencies, in comparison with a default TEOAE screening protocol. The data were collected on the second day of life and during spontaneous sleep. The TEOAE recordings were acquired with linear protocols using click stimuli of 70-75 dB SPL and were used as indicators of normal cochlear function. The cubic distortion product DPOAE responses were evoked by an asymmetrical 75-65 dB SPL protocol, with a frequency ratio of 1.22. Five frequencies (referring to F2) were tested at 1.5, 2.0, 3.0, 4.0 and 5.0 kHz. The data from the DPOAE responses show a similar pass rate (similarity = 0.98) to the linear TEOAE protocol. The data presented suggest that a DPOAE cochlear evaluation, at 5 pre-selected frequencies, has clinical potential.     

A TEOAE screening protocol based on linear click stimuli: performance and scoring criteria.

In order to improve the quality of current TEOAE recording methodologies, we have conducted a comparison of TEOAE neonatal recordings acquired with linear protocols using click stimuli of 68 dB SPL and non-linear protocols using the ILO default stimulus values. From a theoretical standpoint it was expected that the linear recordings would generate responses characterized by higher S/N ratios due to the fact that the stimulus sequence contains four clicks of the same intensity and polarity. The project included recordings from 1,416 neonatal ears (age 48 h). The TEOAE data were compared in terms of correlation, response amplitude, noise, corrected response and S/N ratio in the 1.0-, 2.0-, 3.0-, 4.0- and 5.0-kHz bands, using a paired t-test criterion. We found that windowed (4-14 ms) responses evoked by a linear TEOAE protocol generated superior S/N estimates in the 2.0-, 3.0-, 4.0- and 5.0-kHz TEOAE bands, in addition to superior correlation estimates, and demonstrated lower levels of noise. Clear-cut scoring criteria were established for the S/N ratios at 2.0, 3.0 and 4.0 kHz, by constructing one-sided distribution-free tolerance boundaries.     

TEOAE-based estimation of the auditory threshold in the mid-octave frequencies

The purpose of this study was to estimate the hearing levels, at the mid-frequencies, of 233 ears with sensorineural hearing loss by classifying the corresponding transiently evoked otoacoustic emissions (TEOAE) recordings into three threshold groups. A classification algorithm was based upon a discriminant analysis of fast Fourier transform (FFT) data, evoked by non-linear click stimuli of 80 (+/-2) dB SPL per ear. To validate the efficiency of the proposed methodology TEOAE recordings were initially grouped by mean hearing level values of the 1 kHz and 2 kHz octaves into three threshold ranges according to two strategy schemes: in the first, TEOAE data were assigned into 10-19 dB HL, 20-39 dB HL or > or = 40 dB HL groups. In the second, TEOAE data were assigned into 10-29 > dB H >, 30-39 dB HL or > or = 40 dB HL groups. The most accurate prediction estimates were obtained from the second strategy scheme with a 90.9% accuracy in the 10-29 dB HL group, 82% in the 30-39 dB HL group and 71.4% in the > or = 40 dB HL group.     

Identification of neonatal hearing impairment: transient evoked otoacoustic emissions during the perinatal period

OBJECTIVES: 1) To describe transient evoked otoacoustic emission (TEOAE) levels, noise levels and signal to noise ratios (SNRs) for a range of frequency bands in three groups of neonates who were tested as a part of the Identification of Neonatal Hearing Impairment multi-center consortium project. 2) To describe the relations between these TEOAE measurements and age, test environment, baby state, and test time. DESIGN: TEOAEs were measured in 4478 graduates of neonatal intensive care units (NICUs), 353 well babies with at least one risk indicator, and 2348 well babies without risk factors. TEOAE and noise levels were measured for frequency bands centered at 1.0, 1.5, 2.0, 3.0, and 4.0 kHz for a click stimulus level of 80 dB SPL. For those ears not meeting "passing" stopping criteria at 80 dB pSPL, a level of 86 dB pSPL was included. Measurement-based stopping rules were used such that a test did not terminate unless the response revealed a criterion SNR in four out of five frequency bands or no response occurred after a preset number of averages. Baby state, test environment, and other test factors were captured at the time of test. RESULTS: TEOAE levels, noise levels and SNRs were similar for NICU graduates, well babies with risk factors and well babies without risk factors. There were no consistent differences in response quality as a function of test environment, i.e., private room, unit, open crib, nonworking isolette, or working isolette. Noise level varied little across risk group, test environment, or infant state other than crying, suggesting that the primary source of noise in TEOAE measurements is infant noise. The most significant effect on response quality was center frequency. Responses were difficult to measure in the half-octave band centered at 1.0 kHz, compared with higher frequencies. Reliable responses were measured routinely at frequencies of 1.5 kHz and higher. CONCLUSIONS: TEOAEs are easily measured in both NICU graduates and well babies with and without risk factors for hearing loss in a wide variety of test environments. Given the difficulties encountered in making reliable measurements for a frequency band centered at 1.0 kHz, its inclusion in a screening program may not be justified.     

Bilaterally Preserved Otoacoustic Emissions in Four Children with Profound Idiopathic Unilateral Sensorineural Hearing Loss

Severe to profound unilateral sensorineural hearing loss of the left ear was discovered by screening in four healthy children without any family history of hearing loss. Three of the children were four years old and one child was seven years old at the time of discovery. The PTA0.5–2 was 66–75 dB HL for three of the children and one child was without any hearing reactions on the affected ear. The hearing of the right ear was normal in all four cases. The hearing thresholds have been stable during an observation period of 3–12 years. No certain auditory-evoked brainstem responses were recorded with stimulation of the affected ear. Electronystagmography was normal in all cases and magnetic resonance imaging gave no explanation of the hearing loss. Repeated recordings of the transiently evoked otoacoustic emissions (TEOAE) have shown clear bilateral responses using different instrumentation systems. Recently the hearing levels were unchanged and the TEOAE responses of the affected ears were 6.7–19.9 dB SPL (waveform reproducibility: 88–98 per cent) recorded on the ILO88 OAE Analyser (stimulus: 82.2–83.4 dB peak). The collected results suggest that the children suffer from a similar disorder with a unilateral affection of the cochlea, involving the inner hair cells and/or the first neuron. The TEOAE recordings indicate substantially preserved outer hair cell function independent of the profound hearing loss.     

Effect of infrasound on cochlear damage from exposure to a 4 kHz octave band of noise

Infrasound (i.e., <20 Hz for humans; <100 Hz for chinchillas) is not audible, but exposure to high-levels of infrasound will produce large movements of cochlear fluids. We speculated that high-level infrasound might bias the basilar membrane and perhaps be able to minimize noise-induced hearing loss. Chinchillas were simultaneously exposed to a 30 Hz tone at 100 dB SPL and a 4 kHz OBN at either 108 dB SPL for 1.75 h or 86 dB SPL for 24h. For each animal, the tympanic membrane (TM) in one ear was perforated ( approximately 1 mm(2)) prior to exposure to attenuate infrasound transmission to that cochlea by about 50 dB SPL. Controls included animals that were exposed to the infrasound only or the 4 kHz OBN only. ABR threshold shifts (TSs) and DPOAE level shifts (LSs) were determined pre- and post-TM-perforation and immediately post-exposure, just before cochlear fixation. The cochleae were dehydrated, embedded in plastic, and dissected into flat preparations of the organ of Corti (OC). Each dissected segment was evaluated for losses of inner hair cells (IHCs) and outer hair cells (OHCs). For each chinchilla, the magnitude and pattern of functional and hair cell losses were compared between their right and left cochleae. The TM perforation produced no ABR TS across frequency but did produce a 10-21 dB DPOAE LS from 0.6 to 2 kHz. The infrasound exposure alone resulted in a 10-20 dB ABR TS at and below 2 kHz, no DPOAE LS and no IHC or OHC losses. Exposure to the 4 kHz OBN alone at 108 dB produced a 10-50 dB ABR TS for 0.5-12 kHz, a 10-60 dB DPOAE LS for 0.6-16 kHz and severe OHC loss in the middle of the first turn. When infrasound was present during exposure to the 4 kHz OBN at 108 dB, the functional losses and OHC losses extended much further toward the apical and basal tips of the OC than in cochleae exposed to the 4 kHz OBN alone. Exposure to only the 4 kHz OBN at 86 dB produces a 10-40 dB ABR TS for 3-12 kHz and 10-30 dB DPOAE LS for 3-8 kHz but little or no OHC loss in the middle of the first turn. No differences were found in the functional and hair-cell losses from exposure to the 4 kHz OBN at 86 dB in the presence or absence of infrasound. We hypothesize that exposure to infrasound and an intense 4 kHz OBN increases cochlear damage because the large fluid movements from infrasound cause more intermixing of cochlear fluids through the damaged reticular lamina. Simultaneous infrasound and a moderate 4 kHz OBN did not increase cochlear damage because the reticular lamina rarely breaks down during this moderate level exposure.     

Medial Olivocochlear-Induced Transient-Evoked Otoacoustic Emission Amplitude Shifts in Individual Subjects

Activation of the medial olivocochlear reflex (MOCR) can be assessed indirectly using transient-evoked otoacoustic emissions (TEOAEs). The change in TEOAE amplitudes when the MOCR is activated (medial olivocochlear (MOC) shift) has most often been quantified as the mean value in groups of subjects. The usefulness of MOC shift measurements may be increased by the ability to quantify significant shifts in individuals. This study used statistical resampling to quantify significant MOC shifts in 16 subjects. TEOAEs were obtained using transient stimuli containing energy from 1 to 10 kHz. A nonlinear paradigm was used to extract TEOAEs. Transient stimuli were presented at 30 dB sensation level (SL) with suppressor stimuli presented 12 dB higher. Contralateral white noise, used to activate the MOCR, was presented at 30 dB SL and was interleaved on and off in 30-s intervals during a 7-min recording period. Confounding factors of middle ear muscle reflex and slow amplitude drifts were accounted for. TEOAEs were analyzed in 11 1/3-octave frequency bands. The statistical significance of each individual MOC shift was determined using a bootstrap procedure. The minimum detectable MOC shifts ranged from 0.10 to 3.25 dB and were highly dependent on signal-to-noise ratio at each frequency. Subjects exhibited a wide range of magnitudes of significant MOC shifts in the 1.0–3.2-kHz region (median?=?1.94 dB, range?=?0.34–6.51 dB). There was considerable overlap between the magnitudes of significant and nonsignificant shifts. While most subjects had significant MOC shifts in one or more frequency bands below 4 kHz, few had significant shifts in all of these bands. Above 4 kHz, few significant shifts were seen, but this may have been due to lower signal-to-noise ratios. The specific frequency bands containing significant shifts were variable across individuals. Further work is needed to determine the clinical usefulness of examining MOC shifts in individuals.     

瞬态诱发耳声发射检测职业性听力损伤的可行性研究

目的 :探讨瞬态诱发耳声发射 (TEOAE)检测职业性听力损伤的可行性及临床应用价值。方法 :选择 90例 (180耳 )噪声暴露工人为实验总组 ,按噪声暴露时间长短又分为 1、2、3组 ;另选 11例 (2 2耳 )正常听力青年人作为对照组 ,行纯音听阈和TEOAE测试。结果 :各实验组纯音听阈值明显高于对照组 ,TEOAE总重复率、幅值和信噪比及各频段重复率、幅值和信噪比明显低于对照组 (P <0 .0 5或P <0 .0 1)。实验 1、2、3组间比较 ,随着噪声接触时间的增加 ,各频率点纯音听阈提高 ,TEOAE总重复率、幅值和信噪比及各频段重复率、幅值和信噪比变小 ,在 2 .5 0～ 3.5 0kHz和 3.5 0～ 4 .5 0kHz频段最明显。结论 :用TEOAE检测职业性听力损伤是可行的 ,有临床应用价值 ,最敏感频段为 2 .5 0～ 3.5 0kHz和 3.5 0～ 4 .5 0kHz频段。     

Audibility and speech perception of children using wide dynamic range compression hearing AIDS

PURPOSE: This study examined the relation of audibility for frequency-specific sounds and the Speech Intelligibility Index (SII) to speech perception abilities of children with sensorineural hearing loss using digital signal-processing hearing aids with wide dynamic range compression. METHOD: Twenty-six children age 5-15 years with pure-tone averages (0.5, 1.0, and 2.0 kHz) from 60-98 dB HL participated. Three subgroups were created based on the compression characteristics of each hearing aid. Minimum audibility was determined using aided thresholds for frequency-modulated tones and the SII calculated at 55 and 70 dB SPL using the simulated real-ear output of the hearing aid. The Lexical Neighborhood Test (LNT; K. I. Kirk, D. B. Pisoni, & M. J. Osberger, 1995) was presented at 50 and 70 dB SPL. RESULTS: LNT scores at 70 dB SPL were significantly higher than at 50 dB SPL. Average aided thresholds at 0.5, 1.0, and 2.0 kHz were negatively correlated with LNT scores at 50 dB SPL, and SIIs at 55 and 70 dB SPL were positively correlated with LNT scores at 50 and 70 dB SPL. CONCLUSIONS: Results support using aided thresholds and speech test scores at soft to loud levels as part of the amplification fitting process.     

Noise-induced hearing loss in the noise-toughened auditory system

The auditory system, toughened by an interrupted noise exposure, has been shown in several reports to be less affected by (or protected from) a subsequent high-level noise exposure. Exposure to 115 dB peak SPL, 1 kHz narrow band (400 Hz) transients presented l/s, 6 h/day, to four groups of chinchillas produced a 10-28 dB toughening effect across the 0.5-8.0 kHz test frequency range. Following either a 30 day or an 18 h recovery period the animals were exposed to the same impulses but presented at 121 or 127 dB peak SPL for five uninterrupted days, thus producing an asymptotic threshold shift (ATS) condition. Comparisons between toughened and untoughened control subjects showed: (1) During the 121 dB exposure there was a statistically significant reduction of 10-25 dB in ATS across the entire test frequency range. Thirty days following the 121 dB exposure there were no significant differences in the postexposure permanent effects on thresholds and sensory cell loss. (2) During the 127 dB exposure only the group with the 30 day interval between the toughening and traumatic exposures showed a small (approximately 10 dB), statistically significant, frequency-specific (8 kHz), reduction in ATS. Thirty days following the 127 dB exposure a statistically significant protective effect on threshold was measured only at 16.0 kHz. However, both toughened groups showed less inner hair cell loss at and above 1.0 kHz, while only the group with the 18 h interval between the toughening and traumatic exposures showed less outer hair cell loss at and above 1.0 kHz. There were no systematic differences in the response of the toughened animals that could be attributed to the 30 day or 18 h post-toughening interval.     

Transient evoked otoacoustic emissions and contralateral suppressions in children with auditory listening problems

Objectives

Transient evoked otoacoustic emissions (TEOAEs) are reflections of cochlear energy produced during the processing of sound. The suppression effect identified as the decrease with the additional tone stimulator of the otoacoustic emission amplitude is use for assessing efferent auditory system function. The aim of this study is to investigate the contralateral suppression effect (CSE) of transient evoked otoacoustic emissions (TEOAEs) in children with auditory listening problems (ALPs) compared to normal hearing children.

Method

The study group (Group 1) was consisted of 12 ALP children (8 males and 4 females), aged 5–10 years, and associated with receptive and expressive language delay. The control group was consisted of (Group 2) 12 children with normal hearing levels, matched according to gender and age of TEOAEs and CSE of TEOAEs were investigated at 1.0–4.0 kHz in both groups.

Results

For right ear, at 1.0 and 3.0 kHz, TEOAE amplitudes of the ALP group were significantly lower than the control group. At 2.0, 4.0 and 5.0 kHz of the right ear and at 1.0–5.0 kHz of the left ear, TEOAE amplitudes were found as not different between ALP and control groups. Suppression values of the ALP group were significantly lower than the control group at 1.0–2.0 kHz of the right ear and at 2.0 kHz of the left ear. At the other frequencies, there was no significant difference between the suppression values of the ALP and control groups.

Conclusion

Lower suppression values in ALP group at all frequencies (significant at 1.0–2.0 and 2.0 kHz in the right and left ears, respectively) showed that cochlear and cranial maturation of the ALP group may lower than the control group. Since the age profile in both group is similar, we thought that age's effect on this results is not important. Our results showed that children with ALP have auditory processing difficulties in noisy environment. For understanding the efferent auditory system, patients with auditory processing disorders may be evaluated by the help of background noise.     

Quantitative analysis of cochlear active mechanisms in tinnitus subjects with normal hearing sensitivity: multiparametric recording of evoked otoacoustic emissions and contralateral suppression

Objective

Aim of this study was to investigate the possible role played by outer hair cells and cochlear efferent system functionality when tinnitus develops in normal hearing ears. A multiparametric approach was used, entailing recording and analysis of a set of otoacoustic emissions (OAEs): distortion product (DPOAEs), transient evoked (TEOAEs) and efferent-mediated TEOAE suppression in the presence of contralateral acoustic stimulation (CAS).

Methods

Fifty-four subjects with normal hearing sensitivity participated in the study. Twenty-three suffered from chronic subjective tinnitus whereas thirty-one did not have tinnitus and acted as control subjects. DPOAEs were measured with eliciting tones of frequency ratio 1.22 and intensity 65 and 55 dB SPL in the frequency range 0.5–8 kHz. TEOAEs were recorded with the ‘linear’ protocol using clicks at 60 dB peak SPL both in the absence and in the presence of CAS at two different intensities. DPOAE amplitude, TEOAE amplitude, and TEOAE suppression were analysed as relevant parameters.

Results

Significantly reduced DPOAE amplitude in the frequency range 1.5–8 kHz, lower TEOAE amplitude, and slightly decreased TEOAE suppression were measured in tinnitus subjects compared to non-tinnitus controls. In particular, 74% of tinnitus subjects exhibited abnormal DPOAEs, 13% had abnormal TEOAEs, whereas abnormal TEOAE suppression was found in 9% of patients.

Conclusion

Overall, the present work revealed the presence of abnormal OAEs, in particular at higher frequencies, in tinnitus subjects with normal hearing sensitivity. A minor (i.e., sub-clinical) outer hair cell dysfunction, particularly in high-frequency cochlear regions, might thus be assumed in normal hearing tinnitus subjects. In order to better put in light the possible role played by outer hair cells in low-frequency cochlear regions, or by the cochlear efferent system, additional analyses would be needed.     

Noise suppression of transient-evoked otoacoustic emissions. I. A comparison with the non-linear method

A new method to record transient-evoked otoacoustic emissions (TEOAEs) is introduced. Click stimuli were presented both with and without a simultaneously presented wide-band noise burst. Subtraction of the recorded signal evoked by the noise burst plus click from the signal evoked by the click alone, cancelled the eardrum reflection components of the response and resulted in a measure of the emission. This was used to obtain the TEOAEs from 21 subjects for peak click stimulus levels of 48-66 dB SPL. The root-mean-square (RMS) level of the noise burst was set 10 dB higher than the peak click level, and resulted in suppression of the TEOAE by up to 20 dB. The TEOAE waveforms obtained by the new method were compared to those obtained with Kemp's non-linear method, and were indistinguishable in 20 of the 21 subjects. On basis of the emission spectra, they were indistinguishable in 18 out of 21 subjects. The latencies of narrow-band filtered components from the TEOAEs obtained with the two methods were also similar. This suggests that this noise-suppression method produces similar results as Kemp's non-linear method with the advantage that emission components with very short latencies can be obtained.     

TEOAE recording protocols revised: data from adult subjects

The objective of this study was the experimental re-evaluation of the current clinical transiently evoked otoacoustic emission (TEOAE) protocols, based on linear and non-linear protocol paradigms from a population of 42 adult subjects serving as a normative database. The linear and non-linear TEOAE responses were elicited by clicks with average intensities of 72 and 84 dB p.e. SPL respectively. An initial comparison between non-processed non-linear and linear recordings, at early recording segments from 3.2 to 5.2 ms, showed that the responses had highly similar contours and no statistically significant mean differences. The stimulus-induced artefact in the linear TEOAE responses was suppressed by post-processing the data with a window function (3.8-13.8 ms) and by a high-pass filter at 830 Hz. A repeated-measures model was used to evaluate the differences between post-processed linear and non-linear responses across clinical variables of interest (such as TEOAE response, noise, correlation, and signal-to-noise ratios (SNRs) at 1.0-5.0 kHz). The data indicated that the linear recordings demonstrate significantly lower levels of noise (and thus superior SNRs) and higher values of reproducibility. Normative adult scoring criteria were calculated from free distribution tolerance intervals for the TEOAE correlation and the SNRs at 2.0 and 3.0 kHz.