Distortion product otoacoustic emissions in patients with King-Kopetzky syndrome

In the present study, mild impairment of cochlear function in patients with King-Kopetzky syndrome was investigated using DPOAEs. A significant decrease in DPOAE levels in both ears was found in patients with King-Kopetzky syndrome compared with the controls after considering the thresholds as a co-variable. It is noteworthy that the global mean levels of DPOAEs were still significantly greater in controls than in patients with matched thresholds. Further frequency analyses showed a significant decrease in DPOAE levels over the mid- and high-frequency range in patients with better hearing thresholds when compared with those in the control group. Moreover, significantly smaller DPOAEs were found in the ears of patients with King-Kopetzky syndrome and without SOAEs, than in such ears of control subjects after considering the thresholds as a co-variable. However, when SOAEs were present there was no difference. Decreases in DPOAE level appear to represent evidence of minor cochlear pathology, and provide a pathological basis for the difficulty of hearing speech in the presence of background noise, which characterizes King-Kopetzky syndrome.

Sumario

En el presente estudio, se investigó una leve alteración en la función coclear en pacientes con el síndrome de King-Kopetzky usando DPOAE. Se encontró una disminución significativa en los niveles de intensidad de las DPOAE en ambos oídos en pacientes con este síndrome, al compararlos con los controles, luego de considerar el umbral como una co-variable. Es digno de resaltar que los niveles globales medios de las DPOAE fueron aún significativamente mayores en los controles que en los pacientes con umbrales correspondientes. Un análisis de frecuencia ulterior mostró una disminución significativa en los niveles de las DPOAE, en el rango de frecuencias medias y altas, en pacientes con los mejores umbrales auditivos, al compararlos con aquellos del grupo control. Más aún, se encontraron DPOAE significativamente menores en la audición de pacientes con el síndrome de King-Kopetzky y ausencia de SOAE, comparados con los oídos de sujetos control, luego de considerar el umbral como una co-variable. Sin embargo, cuando las SOAE estuvieron presentes, no hubo diferencia. La disminución en el nivel de intensidad de las DPOAE parece representar evidencia de patología coclear menor, y aporta una base patológica para explicar la dificultad para entender el lenguaje en presencia de ruido de fondo, que caracteriza al síndrome de King-Kopetzky.     

An objective method of analyzing cochlear versus noncochlear patterns of distortion-product otoacoustic emissions in patients with acoustic neuromas

OBJECTIVES: To objectify the effects of retrocochlear disease on distortion-product otoacoustic emissions (DPOAEs) by developing a computer-based software strategy for classifying DPOAE patterns as cochlear or noncochlear and to evaluate the sensitivities of these techniques in a large series of patients with unilateral acoustic neuromas. STUDY DESIGN: Development of a novel, software-based method of DPOAE analysis, which was evaluated with data obtained from a retrospective review of the results from audiometric tests performed in a series of patients. METHODS: A computer-based software strategy was developed, using frequency-specific data from normal-hearing adults, for the purpose of distinguishing cochlear from noncochlear patterns of hearing loss, by determining the discrepancies between DPOAEs and behavioral audiometry. Preoperative pure-tone thresholds and DPOAEs from 97 patients with surgically confirmed acoustic neuroma were compared using an objective method and a standard, subjective technique that was considered to be the gold standard. The effects of bilateral hearing losses, such as noise-induced hearing loss and presbycusis, were accounted for during the analysis to isolate the effects of the tumors on hearing thresholds and DPOAEs. RESULTS: Overall, 55 (57%) of the tumor ears were assigned to the cochlear group (i.e., DPOAEs consistent with hearing thresholds), 40 (41%) to the noncochlear group (i.e., DPOAEs inconsistent with hearing thresholds), and 2 (2%) to an indeterminate group, using the subjective technique for classifying DPOAEs. There was no significant difference in the categorization of the patients with acoustic neuroma when employing the objective strategy. The objective algorithm, when modified to maximize the number of noncochlear identifications, led to assignments of 36 (37%) to the cochlear, 57 (59%) to the noncochlear, and 4 (4%) to the indeterminate categories. CONCLUSIONS: Subjective analysis of a large series patients with acoustic neuromas showed that the majority of ears with tumors demonstrated cochlear (57%), rather than non-cochlear (41%), patterns of DPOAEs. The computerized, software-based algorithm developed for differentiating cochlear from noncochlear patterns of DPOAEs in patients with retrocochlear disease had a maximum sensitivity of 59%. This value was significantly higher than that reported in previous studies.     

Hearing evaluation with distortion-product otoacoustic emissions in young patients undergoing haemodialysis.

Sensorineural hearing loss is frequently reported in young patients with chronic renal failure having haemodialysis. The effect of a single session of haemodialysis on hearing acuity was assessed prospectively in nine children with end-stage renal disease using pure-tone audiometry (PTA) and distortion-product otoacoustic emissions (DPOAEs). Results were compared with those obtained from nine audiologically normal healthy children also tested with PTA and DPOAEs twice during a 4-h interval. Sensorineural hearing loss of unknown aetiology was found in 55.5% of renal patients, mainly in the higher frequencies. Patients on HD had mean PTA thresholds significantly poorer than those of the control group in the frequency range 1000-12 000Hz (P < 0.05). Their mean DPOAE amplitudes were significantly lower in all frequencies > 1184 Hz (P < 0.05). Furthermore, patients' ears with normal PTA thresholds between 250 and 4000 Hz also had decreased DPOAE amplitudes. No significant changes in PTA thresholds or DPOAE amplitudes were encountered in renal patients before and after a HD session (P > 0.05). Changes in PTA thresholds or DPOAE amplitudes were not significantly different than those in the control group (P > 0.05). In conclusion, sensorineural hearing loss of unknown origin, especially in high frequencies, is frequent in young renal patients under HD and single HD sessions do not seem to alter the hearing acuity of these patients. DPOAEs seem to be more sensitive to incipient cochlear damage than behaviour thresholds in monitoring renal patients.     

The clinical use of oto-acoustic emissions of cochlear distortion products

Otoacoustic emissions of cochlear distortion products (DPOAEs) were measured in normally hearing and hearing-impaired human ears. A total of 133 subjects (231 ears) were tested. Two puretone stimuli f1 and f2 were delivered to a sound probe fixed in the outer ear canal. The frequencies of the two primaries were chosen so that their geometric mean represented pure-tone audiometric frequencies. The otoacoustic emission was measured at the distortion product frequency 2f1-f2 by spectral averaging. For 199 ears, the levels of the primaries were 73 dBHL for L1 and 67 dBHL for L2. Statistical analysis was carried out in 77 ears of 46 subjects with normal hearing (average hearing levels at pure-tone audiometric thresholds less than or equal to 10 dBHL) and 36 ears of 25 subjects exhibiting near-normal hearing (average hearing levels at pure-tone audiometric thresholds less than or equal to 20 dBHL). The mean DPOAE amplitudes were similar in these two groups of ears. In 111 of these 113 ears (98.2%), DPOAEs were detected at three or more of the six tested frequencies between 1 and 6 kHz. DPOAEs were measured in more than 75% of ears at each frequency between 1-6 kHz and in more than 86% between 1-4 kHz. Eighty-six hearing-impaired ears of 44 subjects with sensorineural hearing loss formed the patient group. A highly significant correlation between pure-tone audiometric thresholds and DPOAE amplitudes was demonstrated in the frequency range of 1-4 kHz. Percentiles of DPOAE amplitudes were calculated in 22 ears with a mean pure-tone threshold less than or equal to 5 dBHL and in 12 specially selected pathological ears.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distortion-product otoacoustic emissions in humans with high frequency sensorineural hearing loss

Distortion-product otoacoustic emissions (DPOAEs) and pure-tone behavioral thresholds were compared in 20 ears with normal hearing and in 20 ears with high-frequency sensorineural hearing loss. The purpose was to determine if DPOAE amplitude is associated with pure-tone behavioral threshold. Comparison of results from the two groups of ears indicated that DPOAEs were reduced in amplitude or were absent in ears with high-frequency hearing loss. The differences occurred at frequencies above 1,500 Hz. Comparing results from 750 to 8,000 Hz within the same ear revealed a frequency-related correspondence of elevated behavioral threshold to reduced DPOAE amplitude. When behavioral thresholds were better than 20 dB HL, DPOAE amplitude was within the range (+/- 2 SDs) determined for the ears with normal hearing. When pure-tone threshold was greater than 50 dB HL, DPOAEs were absent or were significantly attenuated in 16/17 subjects (94%). The association of emission level with behavioral threshold level was variable when threshold was between these two extremes. Results imply that the measurement of DPOAEs has clinical potential as a means of detecting hearing loss by frequency.     

Otoacoustic Emissions in Smoking and Nonsmoking Young Adults

Objectives

The present study investigates the usefulness of transiently evoked otoacoustic emissions (TEOAEs) and distortion product OAEs (DPOAEs) in detecting small changes in the hearing of young smoking adults.

Methods

Otoacoustic emissions were acquired from the ears of 48 young adults (age, 20 to 27 years). The dataset was divided into two groups, smoking (24 persons/48 ears) and nonsmoking (24 persons/48 ears). The level of smoking was relatively small in comparison to previous studies, an average of 3.8 years and 8.7 cigarettes per day. In each ear three OAE measurements were made: TEOAEs, DPOAEs, and spontaneous OAEs (SOAEs). Pure tone audiometry and tympanometry were also conducted. Audiometric thresholds did not differ significantly between the datasets. Half-octave-band values of OAE signal to noise ratios and response levels were used to assess statistical differences.

Results

Averaged data initially revealed that differences between the two study groups occurred only for TEOAEs at 1 kHz. However when the datasets were divided into ears with and without SOAEs more differences became apparent, both for TEOAEs and DPOAEs. In ears that exhibited SOAEs, both smokers and nonsmokers, there were no statistically significant differences between evoked OAEs; however in all ears without SOAEs, evoked OAEs were higher in the ears of nonsmokers, by as much as 5 dB. These differences were most prominent in the 1-2 kHz range.

Conclusion

A general decrease in OAE levels was found in the group of smokers. However, in ears which exhibited SOAEs, there was no difference between the evoked OAEs of smokers and nonsmokers. We conclude that smoking had not yet measurably affected the ears of those with acute hearing (i.e., those who exhibit SOAEs). However, in ears without SOAEs, smokers exhibited smaller evoked OAE amplitudes than nonsmokers, even though their audiometric thresholds were within the norm.     

Hearing evaluation with distortion-product otoacoustic emissions in young patients undergoing haemodialysis

Sensorineural hearing loss is frequently reported in young patients with chronic renal failure having haemodialysis. The effect of a single session of haemodialysis on hearing acuity was assessed prospectively in nine children with end-stage renal disease using pure-tone audiometry (PTA) and distortion-product otoacoustic emissions (DPOAEs). Results were compared with those obtained from nine audiologically normal healthy children also tested with PTA and DPOAEs twice during a 4-h interval. Sensorineural hearing loss of unknown aetiology was found in 55.5% of renal patients, mainly in the higher frequencies. Patients on HD had mean PTA thresholds significantly poorer than those of the control group in the frequency range 1000–12 000Hz (P < 0.05). Their mean DPOAE amplitudes were significantly lower in all frequencies > 1184 Hz (P < 0.05). Furthermore, patients' ears with normal PTA thresholds between 250 and 4000 Hz also had decreased DPOAE amplitudes. No significant changes in PTA thresholds or DPOAE amplitudes were encountered in renal patients before and after a HD session (P > 0.05). Changes in PTA thresholds or DPOAE amplitudes were not significantly different than those in the control group (P > 0.05). In conclusion, sensorineural hearing loss of unknown origin, especially in high frequencies, is frequent in young renal patients under HD and single HD sessions do not seem to alter the hearing acuity of these patients. DPOAEs seem to be more sensitive to incipient cochlear damage than behaviour thresholds in monitoring renal patients.     

Changes in otoacoustic emissions and high-frequency hearing thresholds in children and adolescents

With the aim of characterizing the loss of high frequency hearing sensitivity in children, hearing thresholds and otoacoustic emissions were measured in a group of 126 normal hearing children and adolescents aged from 6 to 25 years. The subjects were divided into four 5-year age groups. Hearing thresholds over a range of 125 Hz-12.5 kHz were similar in all age groups, the average hearing threshold at 16 kHz was significantly elevated in the oldest age group. The response values of transiently evoked otoacoustic emissions (TEOAEs) significantly declined with age; the decline was negatively correlated with the hearing loss at 16 kHz. Significantly larger TEOAE responses and average distortion-product otoacoustic emission (DPOAE) values at 6.3 kHz were present in the youngest group in comparison with the other three older groups. Spontaneous otoacoustic emissions (SOAEs) were present in 70.8% of the children (in either one or both ears) with the greatest prevalence in the 11-20-year-old subjects. In the 21-25-year-old group, the hearing loss at 16 kHz was significantly smaller in ears with SOAEs than in ears without SOAEs. The results demonstrate that the increase in the high frequency hearing threshold at 16 kHz, which starts at ages over 20 years, is correlated with a decrease in the TEOAE responses at middle frequencies.     

Cochlear ischemia induced by circulating iron particles under magnetic control: an animal model for sudden hearing loss

PURPOSE: To correlate the absence of distortion-product otoacoustic emissions observed in sudden hearing loss (SHL) with a possible thromboembolic vascular cause, using an animal model. BACKGROUND: Distortion-product otoacoustic emissions (DPOAEs) are sensitive to cochlear disorders and are absent in cochlear injury. In a previous study, the authors showed that 75% of patients with SHL who have no measurable emissions do not recover hearing. The underlying cause of the loss of emissions is unknown, but it may be secondary to cochlear ischemia. METHODS: Six New Zealand white rabbits underwent unilateral cochlear embolization through the use of circulating iron particles under magnetic control. Cochlear function was monitored through DPOAE recordings of the experimental and control ears. Results: In all animals, a rapid decrease in emissions was noted, which fluctuated but returned to baseline within 2 hours to 3 weeks after embolization, leaving no measurable residual defects. The DPOAEs were suppressed by 5 to 19 dB within 10 minutes of injection of iron solution and magnet placement. The lowest emissions were obtained at 30 minutes and again at 120 minutes, which were 12 to 37 dB below preembolization levels. Two animals returned to baseline DPOAE levels at 1 to 3 weeks, with no identifiable residual deficits. CONCLUSION: It is likely that the loss of emissions seen in the present study is related to cochlear ischemia. The early suppression of DPOAEs in the rabbit cochlea after embolization may parallel that in SHL patients with absence of DPOAEs on presentation.     

High-frequency hearing influences lower-frequency distortion-product otoacoustic emissions

OBJECTIVES: The primary goal of this study was to test the ability of 2f1-f2 distortion-product otoacoustic emissions (DPOAEs) to detect reduced cochlear function in the presence of normal behavioral sensitivity. DESIGN: A prospective study was performed in normal-hearing young adults using simple and complex regression analyses to clarify the relationship between ultra-high frequency (UHF) hearing and DPOAE levels at lower frequencies, as well as the influence of hearing levels for frequencies within the conventional test range and subject age on this association. METHODS: Average DPOAE levels between 4 to 8 kHz, which were elicited by equilevel primary tones of low to moderate levels, were measured as level-frequency functions, or distortion-product (DP) grams, and related to the mean UHF hearing levels from 11.2 to 20 kHz. The median hearing level for the UHF hearing was used to separate subjects into good and poor UHF hearers. This distinction was then used to compare DPOAE levels from 4 to 8 kHz for the 2 groups to determine if UHF hearing status influenced DPOAE levels at lower frequencies. RESULTS: Simple regression analysis revealed that the 4-to 8-kHz DPOAE levels were significantly correlated with the pure-tone average (PTA) from 11.2 to 20 kHz. However, the PTA for 4 and 8 kHz was also significantly correlated with the PTA for UHF hearing. Further multiple regression analyses revealed that UHF hearing significantly and uniquely accounted for approximately 14% of the variance in DPOAE levels from 4 to 8 kHz for most of the primary-tone level combinations. In contrast, neither the PTA for the conventional hearing range nor subject age contributed significantly to the DPOAE variance. CONCLUSIONS: The findings suggest that UHF hearing influences DPOAEs at significantly lower frequencies because emissions are sensitive to subtle changes in outer hair cells not yet detected by pure-tone thresholds in this region or because alterations in the basal cochlea affect the generation of lower-frequency DPOAEs originating from more apical cochlear regions.     

CD1 hearing-impaired mice. II: Group latencies and optimal f2/f1 ratios of distortion product otoacoustic emissions, and scanning electron microscopy

In our companion paper (Le Calvez et al., 1998), the levels of distortion product otoacoustic emissions (DPOAE) were collected in the ears of CD1 mice with progressive degeneration of cochlear outer hair cells (OHC). Their comparison to standard functional measurements such as auditory-evoked brainstem responses (ABR) showed that CD1 ears could be classified as normal or impaired in a frequency-specific manner using DPOAE levels. The present work reports how DPOAE phases and levels of young CD1 mice were affected by varying the frequency ratio of eliciting stimuli at frequencies f₁ and f₂. Normally hearing CBA/J mice served as controls. The rate of phase change of DPOAE when f₁ was varied and f₂ was fixed allowed the group delay of DPOAE to be derived. The changes of DPOAE levels during this procedure disclosed bandpass characteristics that several reports (Fahey and Allen, 1986; Brown and Gaskill, 1990) assumed to be the reflection of important features of cochlear micromechanics, possibly in relation to the coupling of OHCs to the tectorial membrane. Group delays became significantly shorter when ABR thresholds exceeded 40 dB elevation. The bandpass filter characteristics strikingly depended on auditory function so that the optimal ratio f₂/f₁ progressively shifted from 1.24 to 1.50 or more when hearing loss increased. A difference was also noted between CD1 ears whose ABR thresholds were not yet increased and control CBA/J (optimal ratio 1.20). Scanning electron microscopy disclosed a variety of often minor OHC lesions that were only roughly correlated with cochlear function. However, the presence of abnormalities in the reticular lamina associated with early changes of DPOAE fine structure as a function of f₂/f₁ supported the hypothesis of some involvement of micromechanical features in the bandpass filter characteristics of DPOAE. The sensitivity of their measurement in pathological situations is potentially interesting.     

Impaired cochlear function correlates with the presence of tinnitus and its estimated spectral profile

The presence of tinnitus often coincides with hearing loss. It has been argued that reduced peripheral input leads to frequency-specific increase in neuronal gains resulting in tinnitus-related hyper-activity. Following this gain-adaptation hypothesis, impaired cochlear function should be predictive of the presence and spectral characteristics of tinnitus. To assess cochlear function, perceptual thresholds and distortion product otoacoustic emissions (DPOAEs) were measured with high frequency resolution for subjects with tinnitus and non-tinnitus control subjects (N?=?29 and N?=?18) with and without hearing loss. Subjects with tinnitus also provided a 'tinnitus likeness spectrum' by rating the similarity of their tinnitus to tones at various frequencies. On average, subjects with tinnitus had elevated thresholds, reduced DPOAE, and increased slope of the DPOAE input-output function in the range from 4 to 10?kHz. These measures were strongly correlated and were equally predictive of the presence of tinnitus. Subjects with a pronounced edge to their hearing loss profile were very likely to have tinnitus. In the group average, the tinnitus likeness spectrum was correlated with perceptual thresholds (r?=?0.98, p?相似文献   

畸变产物耳声发射在军事噪声致爆震性聋早期监测中的作用

目的探讨畸变产物耳声发射(DPOAE)在军事噪声致爆震性聋早期监测中的作用。方法将听力正常的炮兵某部男性官兵88例(176耳)随机分成两组,每组44例(88耳),实验组参加火炮实弹射击训练,对照组未参加火炮实弹射击训练。对照组及实验组训练前后进行纯音测听及DPOAE测试,对两组结果进行比较分析。结果实验组训练后80耳中耳传导功能无障碍,其中13耳纯音听阈示感音神经性听力损失,DPOAE检查亦异常;67耳纯音听阈正常,其中15耳DPOAE幅值在4kHz处降低。与训练前、对照组比较,实验组训练后2、4及8kHz纯音听阈升高(P<0.05或P<0.01),以4kHz处升高最为明显;实验组训练后2、3、4、6及8kHzDPOAE幅值降低(P<0.05或P<0.01),其中以4kHz处降低最为明显。结论畸变产物耳声发射在军事噪声致爆震性聋早期监测中有一定应用价值,可对其防护、诊断和治疗提供指导和帮助。     

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.     

CD1 hearing-impaired mice. I: Distortion product otoacoustic emission levels, cochlear function and morphology

The levels of distortion product otoacoustic emissions (DPOAEs) were measured in a strain of hearing-impaired mutant mice (CD1) at various stages of outer hair cell impairment and compared to those of a control inbred strain (CBA/J). Parallel measurements of cochlear potentials and auditory brainstem evoked responses (ABRs) were performed and surface preparations of organs of Corti were observed using phalloidin staining of filamentous actin. Comparison of DPOAEs (elicited by stimulus levels of 60 and 70 dB SPL) with standard functional tests allowed the categorization of CD1 ears into two groups on the basis of the presence or absence of DPOAE, which corresponded to mean ABR thresholds greater or less than 40 dB nHL respectively. When adopting ABR threshold as the gold standard, this procedure yielded rates of false-positives and -negatives ranging from 5 to 16%. However, individual predictions of electrophysiological function from DPOAE levels were not accurate, owing to their large variance, and attempts to optimize stimulus levels did not reduce this variance. In contrast, the profiles of DPOAE level vs. f₂ exhibited large correlations with ABR threshold profiles as a function of f₂. It was also noteworthy that the mean levels of DPOAEs in CD1 mice recorded in frequency intervals with normal ABR thresholds were significantly smaller than those of CBA/J mice. Although hearing loss was revealed early both by DPOAEs and by other functional tests, surface preparations often remained normal until about 3–4 months of age.     

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.     

Audiogram fine structure and spontaneous otoacoustic emissions in patients with Menière's disease.

The incidence of and inter-relationship between audiogram fine structure and spontaneous otoacoustic emissions (SOAEs) was investigated in patients with Menière's disease. This project is a part of a comprehensive longitudinal study in which a range of tests of cochlear and vestibular function in patients who suffer from Menière's disease, is carried out and repeated over time. In this paper we present preliminary data from both ears (in most cases an affected and an unaffected ear) of 13 patients. The thresholds in these 26 ears ranged from normal to 80 dB HL. SOAEs could be measured in only four ears; these ears had near-normal thresholds. Data from seven ears had to be excluded because of the possibility of cross-over effects. In 16 out of the 19 remaining ears, audiogram fine structure was found. Our data confirm that (1) SOAEs correspond to behavioural sensitivity peaks. (2) There is no simple relationship between SOAE level and height of sensitivity peaks. (3) Sensitivity peaks may occur at frequencies without measurable SOAEs. In addition, our data show that: (1) Audiogram fine structure may occur in ears without observable SOAEs. (2) Fine structure can be present in ears without normal thresholds. (3) There is a weak tendency for fine structure to be more pronounced in ears with milder hearing loss.     

Diagnostics of the cochlear amplifier by means of distortion product otoacoustic emissions

Distortion product otoacoustic emission (DPOAE) growth functions reflect the active nonlinear cochlear sound processing when using a primary-tone setting which accounts for the different compressions of the two primaries at the DPOAE generation site and hence provide a measure for objectively assessing cochlear sensitivity and compression. DPOAE thresholds can be derived from extrapolated DPOAE input/output (I/O) functions independently of the noise floor and consequently can serve as a unique measure for reading DPOAE measurements. The thus-estimated DPOAE thresholds exhibit a close correspondence to behavior audiometric thresholds and thus can be used for reconstructing an audiogram, i.e., a DPOAE audiogram. The DPOAE I/O functions' slope increases with cochlear hearing loss and thus provides a measure for assessing recruitment. Hence, DPOAE I/O functions can give more information for diagnostic purposes than those of DP grams, transiently evoked OAEs (TEOAEs), or auditory brain stem responses (ABRs). DPOAE audiograms can be applied in pediatric audiology to assess cochlear dysfunction in a couple of minutes. In newborn hearing screening, they are able to detect transitory sound-conductive hearing loss and thus can help to reduce the rate of false-positive TEOAE responses in the early postnatal period. Since DPOAE I/O functions are correlated with loudness functions, DPOAEs offer the possibility of basic hearing aid adjustments, especially in infants and children. Extrapolated DPOAE I/O functions provide a tool for a fast automated frequency-specific and quantitative evaluation of hearing loss.     

Magnitudes and phases of human distortion-product otoacoustic emissions at 2f(1)-f(2) against f(2)/f(1): effects of an audiometric notch

The influence of the frequency ratio f(2)/f(1) of two pure-tone stimuli on the distortion-product otoacoustic emissions (DPOAEs) at 2f(1)-f(2) was assessed in 14 hearing-impaired human ears exhibiting a narrow audiometric notch at 4 kHz, whereas 11 normally hearing ears served as controls. A fixed-f(2) paradigm was used, with f(2) values varying from 2 to 8 kHz in 1-kHz steps. The intensities of the two stimuli were either 60 or 70 dB SPL. The magnitudes and phases of DPOAEs were extracted so that the bandpass filter-like profile of DPOAE magnitude against f(2)/f(1) (f(2)/f(1) magnitude function) could be characterized by the presence and position of its maximum, and DPOAE group delays were derived from the phase gradient of the DPOAE when f(1) varied. The main difference between normal and impaired ears occurred at 4 kHz in that, in contrast with normal ears, nine impaired ears out of 14 did not present any peak in their f(2)/f(1) magnitude function, while the remaining five ears only differed from normal ones by a slightly shifted maximum toward larger f(2)/f(1)s. Group delays were significantly shortened in all impaired ears, with a tendency to be shorter in the subset of ears with flat DPOAE magnitude profiles with f(2)/f(1). No clear effect of notch depth was observed, and with the chosen stimulus characteristics, no abnormal DPOAE result was observed whenever f(2) fell outside the audiometric notch. It is concluded that DPOAE group delays apparently provide useful objective clues of cochlear dysfunction, more sensitive than DPOAE magnitudes inasmuch as many of them remained near the normal range. Although a majority of f(2)/f(1) magnitude functions were clearly flattened when f(2) was impaired, this feature was less systematic.