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.     

畸变产物耳声发射在唇腭裂婴幼儿听力检查中的应用

目的探讨唇腭裂婴幼儿畸变产物耳声发射（distortion product otoacoustic emission,DPOAE）的特点,并将其与听性脑干反应（auditory brainstem response,ABR）阂值检查的结果加以对照,以探讨DPOAE在这类患儿听力检查中的应用价值。方法DPOAE检查63例（126耳）,年龄2个月-42个月,平均11.83个月。其中单纯腭裂组（以下简称腭裂组）23例（46耳）,腭裂并发唇裂及牙槽裂组（以下简称唇腭裂组）30例（60耳）,单纯唇裂组（以下简称唇裂组）10例（20耳）,每耳均检查8个频率,若2-5kHz4个频点有≥3个频点通过即为该耳通过。在上述患儿中,ABR阈值检查腭裂组17例（34耳）,唇腭裂组10例（20耳）,唇裂组6例（12耳）,以能重复引出V波的最小刺激强度为ABR阈值。结果DPOAE检查：腭裂组通过7耳,未通过39耳,通过率为15.22％;唇腭裂组通过6耳,未通过54耳,通过率为10.00％;唇裂组通过18耳,未通过2耳,通过率为90％。统计分析腭裂组与唇腭裂组无显著差异,而腭裂组与唇裂组,唇腭裂组与唇裂组均有显著差异。ABR阈值检查统计分析结果与DPOAE一致。将各组DPOAE通过率与ABR正常率进行比较,腭裂组及唇腭裂组中二者无差异（P〉0.05）,虽然唇裂组中二者有差异（P〈0.05）,但唇裂组ABR阈值反应的听力下降较轻（均≤50dB nHL）。从总体趋势上说,DPOAE与ABR阈值检查在检测的结果上是一致的。结论唇腭裂患儿DPOAE和ABR检测结果一致,与ABR相比,DPOAE具有快速、简便、易实施等特点,因此DPOAE可以作为唇腭裂婴幼儿听力检查的手段,但仍需进一步结合ABR及其他相关的听力检查,以明确听力损害的程度和类型。     

Sex differences in distortion product otoacoustic emissions as a function of age in CBA mice

Age-related hearing loss--presbycusis--is the number one communication problem of the aged. A major contributor to presbycusis is the progressive degeneration of cochlear outer hair cells (OHCs). Distortion product otoacoustic emissions (DPOAEs) are effective in vivo, physiological measures of hearing, assessing the health and functioning of the OHCs in mammals. We and others have previously demonstrated that DPOAE amplitudes decline with age in humans and mice. The present study's objective was to measure age-related declines in the OHCs in CBA mice (slow, progressive age-related hearing loss) by comparing DPOAEs and auditory brainstem responses (ABRs) generated from females and males. Young adult (2.1-2.9 months) and middle-aged CBA (14.0-16.4 months) mice were tested, as well as old CBAs (24.3-29.0 months). DPOAE-grams were obtained with L1 = 65 and L2 = 50 dB SPL, f1/f2 = 1.25, using eight points per octave covering a frequency range from 5.6 to 44.8 kHz (geometric mean frequency). ABRs ranged from 3 to 48 kHz. Analyses revealed that DPOAE levels decreased with age for middle-aged and old male CBAs, but for female CBAs, declines did not occur until old age - after menopause. In contrast, ABR amplitudes for female and male young adult and middle-aged CBAs were the same. Female ABR thresholds were lower than males for old CBAs. In conclusion, we discovered that pre-menopausal CBA female mice have healthier OHCs relative to middle-aged males, but much of this relative advantage is lost post-menopause. Understanding sex differences in age-related sensory disorders will be quite helpful for the goals of preventing, slowing or curing sensory problems in old age for both women and men.     

Distortion product otoacoustic emissions show exceptional resistance to noise exposure in MOLF/Ei mice

Baseline distortion-product otoacoustic emissions (DPOAEs) at several primary-tone levels were compared between naive 2- to 3-month old inbred CBA/CaJ (CBA) and wild-derived MOLF/Ei (MOLF) mice. Only minor DPOAE differences were noted between the two strains and these differences were not systematic across frequency or test levels. These emission findings were consistent with earlier results on auditory brainstem response thresholds reported by others [Zheng et al., Hear. Res. 130 (1999) 94-107] thus suggesting that both CBA and MOLF strains have normal hearing. Subsequent episodes of over-exposure to a 105-dB SPL, octave-band noise centered at 10 kHz for 8 h revealed that MOLF DPOAEs were exceptionally resistant to the adverse aftereffects of excessive noise exposure as compared to CBA mice. Unlike the noise-exposure resistant inbred 129/SvEvTac strain, which has reduced baseline DPOAE levels especially at high frequencies, MOLF mice have normal DPOAEs making the interpretation of noise-exposure effects more straightforward.     

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.     

Pattern of hearing loss in a rat model of cochlear implantation trauma.

HYPOTHESIS: Trauma caused by cochlear implant electrode insertion is attributable to the combination of direct physical trauma and the delayed cell death of oxidative stress-injured auditory sensory cells. BACKGROUND: Histologic evaluation of cochlear implant electrode trauma has demonstrated that the extent of sensory cell losses is proportional to the degree of injury. However, the impact of delayed oxidative stress within injured cochlear tissues and the progressive loss of injured hair cells by way of apoptosis are at present unknown. METHODS: Laboratory rats were evaluated for hearing acuity before and after electrode insertion, before and after round window membrane incision only. Hearing was measured before trauma or incision and over the next 7 days. Objective measurements of hearing function were distortion products of otoacoustic emissions (DPOAEs) in the frequency range of 2 to 32 kHz and tone-burst (i.e., 4-32 kHz) evoked auditory brain stem responses (ABRs). RESULTS: For the experimental cochleae, there were progressive increases in ABR thresholds and decreases in ABR amplitudes. The amplitude of the DPOAEs in the experimental cochleae also showed progressive decreases. For the contralateral control and round window membrane surgical control ears, there were no significant changes in either DPOAE or ABR thresholds. CONCLUSION: These results document a progressive loss of hearing acuity postimplantation and strongly suggest that electrode insertion trauma generated oxidative stress within injured cochlear tissues.     

obstructive sleep apnea-hypopnea syndrome and hearing in children

Objective To explore the relationship between hypoxemia and hearing in children with obstructive sleep apnea-hypopnea syndrome. Methods Auditory brainstem responses (ABRs) were recorded in 68 ears and distortion product otoacoustic emissions (DPOAEs) in 60 ears in children with OSAHS and type "A" tympanograms, and in 30 ears in normal children. Results ABR latencies of waves Ⅰ, Ⅲ and Ⅴ, and Ⅰ-Ⅲ, Ⅲ-Ⅴ and Ⅰ-Ⅴ intervals were not statistically different between OSAHS and normal children. Wave Ⅰlatency was delayed in children with OSAHS compared to normal children3 (P<0.05). DPOAE amplitudes in children with mild OSAHS were lower than normal children at 8 kHz (P<0.05). DPOAEs were lower at 6 kHz and 8 kHz in children with moderate/severe OSAHS than normal children (P<0.05). Conclusion Cochlear function was affected when AHI was at or greater than lO/hour. ABR and DPOAE can be used to detect early changes in auditory function in children with OSAHS.     

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.     

Protection against acoustic trauma by forward and backward sound conditioning

The purpose of the present study was to determine if short-term sound conditioning provides protection when delivered either before (forward sound conditioning) or after (backward sound conditioning) a traumatic exposure in the guinea pig. Two different sound conditioning paradigms were studied (1 kHz, 81 dB SPL, 24 h; 6.3 kHz, 78 dB SPL, 24 h). The 1-kHz forward sound conditioning paradigm (81 dB SPL, 24 h) protected distortion product otoacoustic emissions (DPOAEs) against a short-duration acoustic trauma (2.7 kHz, 103 dB SPL, 5 min) compared to the group exposed to the acoustic trauma alone. The 1-kHz forward sound conditioning paradigm (81 dB SPL, 24 h) also protected both the auditory brainstem response (ABR) thresholds and DPOAEs against a longer-duration acoustic trauma (2.7 kHz, 103 dB SPL, 30 min). The group exposed to the acoustic trauma alone showed ABR threshold shifts between 15 and 24 dB, and DPOAE amplitude shifts between 11 and 24 dB, while the group with 1-kHz forward sound conditioning showed statistically significant protection at all ABR frequencies and at all DPOAE frequencies. The 1-kHz backward sound conditioning paradigm protected against acoustic trauma (2.7 kHz, 103 dB SPL, 30 min). The ABR thresholds were protected at 1, 2 and 4 kHz, and DPOAEs at all frequencies (except 8 kHz) when compared to the group exposed only to the acoustic trauma. The 6.3-kHz forward sound conditioning paradigm protected against acoustic trauma (5.5 kHz, 109 dB SPL, 30 min) at 6.3, 8 and 10 kHz. The 6.3-kHz backward sound conditioning paradigm showed no protection against acoustic trauma at any DPOAE frequency. Taken together, these findings are important for understanding how the auditory system can be modulated by acoustic stimulation and highlights the importance of the acoustic environment during the recovery process of the auditory system.     

Strain-dependence of age-related cochlear hearing loss in wild and domesticated Mongolian gerbils

The Mongolian gerbil (Meriones unguiculatus) is one of the animal models in auditory research that has been used in several studies on age-related hearing loss. The standard laboratory strain is domesticated as it was bred in captivity for more than 70 years. We compared properties of distortion product otoacoustic emissions (DPOAEs) in domesticated gerbils with wild-type gerbils from F6-F7 generations of a strain originating from animals trapped in Central Asia in 1995. Up to an age of 9months, DPOAE thresholds were comparable between both strains and were below 10dB SPL for f2 frequencies between 4 and 44kHz. In older domesticated animals, the thresholds were increased by up to 12dB. Significant increases were found at stimulus frequencies of 2kHz, 12-20kHz, and 56-60kHz. The best frequency ratio f2/f1 to evoke maximum DPOAE amplitude was larger in domesticated animals at the age of 9 months or older. While these data show that there is a deterioration of cochlear sensitivity due to domestication, the magnitude of the described changes is small. Thus, the general suitability of domesticated gerbils for auditory research seems not to be affected.     

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)     

High frequency distortion product otoacoustic emissions in children with and without middle ear dysfunction

OBJECTIVE: Distortion product otoacoustic emissions (DPOAEs) (9-16kHz) are a useful measure of the function of the cochlea, which may be damaged by ototoxic drugs during anticancer chemotherapy. As children undergoing chemotherapy may also have middle ear problems, it is necessary to know if middle ear problems would have a confounding effect on the ability of DPOAEs to assess cochlear function in the extend high frequency region (9-16kHz). The present study aimed to investigate the effect of middle ear dysfunction on DPOAEs in the extended high frequency region in young children. METHODS: The sample was comprised of 100 ears of 50 school-aged children (21 boys and 29 girls) with a mean age of 6.3 years (S.D.=0.5; range 5.3-7.3). Otoscopy, pure tone hearing screening, tympanometry, acoustic reflexes and DPOAEs for both the conventional and extended high frequencies were administered to each child under typical school screening conditions. Participants were classified into one of three groups based on immittance (tympanometry and acoustic reflex) results. They included a "pass immittance" group, a "fail immittance" group and an "undetermined" group (with a pass in either tympanometry or acoustic reflexes, but not both). DPOAE amplitudes and signal-to-noise ratios (SNRs) were measured and compared across the three groups of participants. RESULTS: The fail immittance group showed significantly smaller DPOAE amplitudes and SNRs when compared to the other two groups at frequencies ranging from 1 to 9.5kHz and at 13kHz, but not at 10, 11, 12 and 14kHz. There was no significant difference in DPOAE results between the pass immittance and undetermined groups. CONCLUSIONS: Despite the adverse effects of middle ear dysfunction, its effect on DPOAEs in the extended high frequency region was not as severe as that in the lower frequency region. Hence, assessment of cochlear function in children with a middle ear lesion in the extended high frequencies using DPOAEs should be made with caution.     

DPOAE level shifts and ABR threshold shifts compared to detailed analysis of histopathological damage from noise

A detailed comparison of 2f(1)-f(2) distortion product otoacoustic emission (DPOAE) level shifts (LS) and auditory brainstem response (ABR) threshold shifts with noise-induced histopathology was conducted in chinchillas. DPOAE levels (i.e., L(1) and L(2)) at f(1) and f(2), respectively, ranged from 55-75 dB sound pressure level (SPL), with f(2)/f(1)=1.23, 6 points/octave, f(2)=0.41-20 kHz, and ABR thresholds at 0.5-20 kHz, 2 points/octave, were determined pre-exposure. The exposure was a 108 dB SPL octave band of noise centered at 4 kHz (1-1.75 h, n=6) or 80-86 dB SPL (24 h, n=5). DPOAE LSs (magnitude pre- minus post-exposure) and ABR threshold shifts (TS) were determined at 0 days and up to 28 days post-exposure. The cochleae were fixed, embedded in plastic and dissected into flat preparations. The length of the organ of Corti (OC) was measured; missing inner (IHC) and outer (OHC) hair cells counted; stereocilia damage rated; and regions of OC and nerve-fiber loss determined. Cytocochleograms were made showing functional loss and structural damage with the LS and TS overlaid. Some unexpected results were obtained. First, the best correlation of LS with histopathology required plotting the DPOAE data at f(1) with respect to the chinchilla-place map. The best correlation of TS was with IHC and nerve-fiber loss. Second, wide regions of up to 10% scattered OHC loss in the apical half of the OC showed little or no LS. Third, with the 108 dB SPL noise, there was 20-40 dB of recovery for DPOAEs at mid-high frequencies (3-10 kHz) in eight of 12 cochleae where there was 70-100% OHC loss in the basal half of the OC. The largest recovery at mid-high frequencies occurred in regions where the OC was entirely missing. Fourth, with the 80-86 dB SPL noise, there was no LS at small focal lesions (100% loss of OHCs over 0.4 mm) when the frequency place of either f(1) or f(2) was within the lesion but not both. There was no correlation of LS with OHC stereocilia loss, fusion or disarray. These results suggest that, after noise exposure, DPOAEs at mid-high frequencies can originate from or be augmented by generators located at someplace other than the frequency place of f(2), possibly the basal 20% of the OC when this region is intact. Also, noise-induced DPOAE LSs seemed to reflect differing mechanisms for temporary and permanent hearing loss.     

Comparison of cochlear morphology and apoptosis in mouse models of presbycusis

Objectives

Morphological studies on presbycusis, or age-related hearing loss, have been performed in several different strains of mice that demonstrate hearing loss with auditory pathology. The C57BL/6 (C57) mouse is a known model of early onset presbycusis, while the CBA mouse is characterized by relatively late onset hearing loss. We performed this study to further understand how early onset hearing loss is related with the aging process of the cochlea.

Methods

We compared C57 cochlear pathology and its accompanying apoptotic processes to those in CBA mice. Hearing thresholds and outer hair cell functions have been evaluated by auditory brainstem response (ABR) recordings and distortion product otoacoustic emission (DPOAE).

Results

ABR recordings and DPOAE studies demonstrated high frequency hearing loss in C57 mice at P3mo of age. Cochlear morphologic studies of P1mo C57 and CBA mice did not show differences in the organ of Corti, spiral ganglion, or stria vascularis. However, from P3mo and onwards, a predominant early outer hair cell degeneration at the basal turn of the cochlea in C57 mice without definitive degeneration of spiral ganglion cells and stria vascularis/spiral ligament, compared with CBA mice, was observed. Additionally, apoptotic processes in the C57 mice also demonstrated an earlier progression.

Conclusion

These data suggest that the C57 mouse could be an excellent animal model for early onset ''sensory'' presbycusis in their young age until P6mo. Further studies to investigate the intrinsic or extrinsic etiologic factors that lead to the early degeneration of organ of Corti, especially in the high frequency region, in C57 mice may provide a possible pathological mechanism of early onset hearing loss.     

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.     

ABR and DPOAE indices of normal loudness in children and adults

Loudness growth prediction using normal templates of loudness derived with ABR and DPOAE measures was investigated in 20 children 4 to 12 years and 20 adults with normal hearing. An ABR click latency-intensity function (LIF), ABR 2 kHz tone LIF, and DPOAE 2 kHz amplitude-intensity function (AIF) were recorded from each listener. A loudness-intensity function was also measured for each electrophysiologic stimulus. Children and adults exhibited similar intensity functions of ABR latency, DPOAE amplitude, and loudness. A statistically significant relationship was found between loudness and ABR latency and DPOAE amplitude. Loudness estimation equations derived with ABR latency and DPOAE amplitude accurately and reliably predicted the loudness-intensity functions of the listeners. Normative ABR and DPOAE templates of predicted loudness growth may have clinical application in site-of-lesion assessment or hearing aid fitting by distinguishing abnormal rates of loudness growth for individuals who cannot provide reliable behavioral measures.     

Relationship between distortion product otoacoustic emissions and frequency modulation difference limens

OBJECTIVE: To explore the relationship between distortion product otoacoustic emissions (DPOAEs) and frequency modulation difference limens (FMDLs) in normal-hearing subjects. DESIGN: Fifteen normal-hearing adult subjects (age range = 20 to 29 yr; mean age = 21 yr, 6 mo) participated in the study. Each subject met the following criteria: 1) hearing thresholds <20 dB HL bilaterally at frequencies 0.25 to 8 kHz; 2) type A tympanograms bilaterally; and 3) no history of otologic disease. To reduce gender-related differences, only female subjects were recruited as subjects. DPOAE amplitudes and FMDLs were measured in both ears of 15 female adults at 1, 2, and 4 kHz. Ears were classified on the basis of DPOAE amplitude into large DPOAEs and small DPOAEs. RESULTS: Results indicated that ears with larger DPOAEs showed better frequency discrimination (smaller FMDLs) than did ears with smaller DPOAEs at 2 kHz. CONCLUSIONS: Results of the current study support frequency discrimination models that predict a relationship between frequency selectivity and frequency discrimination.     

Electrophysiological findings in the Sprague-Dawley rat induced by moderate-dose carboplatin

Carboplatin is a second generation platinum-containing anti-tumor drug which selectively alters the micromechanical function of the inner hair cells (IHCs) of the organ of Corti in the chinchilla. Data from a recent study [Wake et al., Acta Otolaryngol. 116 (1996) 374-381], using the chinchilla model, have suggested that a moderate dose of carboplatin alters the efferent feedback loop gain of the OHCs. The present study was designed to evaluate the possible 'efferent feedback alteration mechanism' in the Sprague-Dawley rat using distortion product otoacoustic emissions (DPOAEs). A moderate dose of carboplatin (50 mg/kg body weight) was administered by a 30 min i.p. infusion. Pre- and 72-h post-treatment DPOAE and auditory brainstem response (ABR) recordings were acquired from a group of 12 rats. The animals were anesthetized with a ketamine-atropin anesthesia administered in two consecutive phases. The DPOAE responses (cubic distortion products) were recorded with four asymmetrical protocols: P1=60-50, P2=50-40, P3=40-30 and P4=30-20 dB SPL (sound pressure level), in the frequency range from 4.0 to 16 kHz. ABR responses were obtained for bipolar clicks and tone pips at the frequencies 8.0, 10.0, 20.0 and 30 kHz using stimuli in the range from 100 to 30 dB SPL. Significant ABR threshold shifts of 15 dB were observed at 30 kHz, and shifts of 10 dB at 20, 16 and 10 kHz. The comparison of pre- and post-treatment DPOAE responses did not reveal any significant changes for protocols P1, P2 and P4. Data from the P3 protocol indicated a decrease of the DPOAE amplitude. The findings from the rat model suggest that (a) moderate doses of carboplatin do not affect the efferent feedback loop OHC function and (b) the cochlear susceptibility to carboplatin across species is different, even at moderate-dose regimes.     

Utility of OAE screener (GSI 70) for the evaluation of distortion product otoacoustic emissions

The purpose of this study was to investigate the ability of the OAE screener GSI 70 to evaluate of cochlea function in neonates, infants and adults. Distortion product otoacoustic emissions (DPOAEs) were measured using the GSI 70 DPOAE Analyzer and evaluated in 123 human ears between December 1999 and June 2000. We performed the following four general clinical tests to determine the reliability of the GSI 70: 1) comparison of DPOAE levels measured using the ILO 92 and the GSI 70 in 55 adult ears, 2) comparison of DPOAE levels measured using the GSI 70 and hearing levels in 55 adult ears, 3) comparison of DPOAE levels measured using the GSI 70 and ABR levels in 45 neonate and infant ears, and 4) evaluation of the utility of DPOAE measurements obtained using the GSI 70 in functional deafness cases. The following results were obtained: 1) DPOAE levels measured with the ILO 92 and the GSI 70 were closely correlated (correlation coefficient, 0.773 at 2 kHz and 0.813 at 4 kHz). 2) The sensitivity of the GSI 70 in adult ears confirmed to have normal hearing was 80% at 2 kHz and 100% at 4 kHz; the specificity of hearing-impaired ears was 94% at 2 kHz and 94% at 4 kHz. 3) The sensitivity of the GSI 70 in normal neonate and infant ears with normal hearing was 100% at 2 kHz and 100% at 4 kHz; the specificity of hearing-impaired neonate and infant ears was 97% at 2 kHz and 94% at 4 kHz. 4) All of the functionally deaf ears showed excellent DPOAE responses. Examinations using the GSI 70 DPOAE analyzer were very easy and fast. Also, the results were highly reliable, with the exception of one adult who was classified as having normal hearing in an out-of-scale hearing level at 2 kHz. We suggest that specific criteria be established for the clinical usage of the GSI 70 in performing objective hearing evaluations.     

Intra- and intersubject variability of acoustically evoked otoacoustic emissions. II. Distortion product otoacoustic emissions]

BACKGROUND: Distortion product otoacoustic emissions (DPOAEs) are evoked by simultaneously stimulating the cochlea with two tones. The DPOAE with the highest amplitude (at the frequency 2f1-f2) is usually used for routine audiological evaluation. Any interpretation of DPOAEs in a clinical setting must consider their intra- and intersubject variability. METHODS: DPOAE measurements were performed in 36 normally hearing adults in three weekly test sessions. Each ear was tested twice per session, and the results were statistically analyzed. RESULTS: All test candidates had measurable DPOAEs. Statistically significant differences in absolute DPOAE amplitudes were neither found between two measurements at the same day, nor at weekly intervals, nor between right and left ear of the same candidate. Absolute DPOAE amplitudes in women were significantly higher in the 2-6 kHz range whereas they presented with significantly lower amplitudes below 2 kHz when compared to men. CONCLUSIONS: The present results indicate that monitoring of the inner ear status can be reliably performed using DPOAE measurements. Change in DPOAE amplitudes effectively indicate changes in the cochlear function with high sensitivity. Compared to TEOAE measurements, DPOAEs offer a higher frequency resolution in a broader frequency band and thus more detailed information about the cochlear condition.