A model of real time monitoring of the cochlear function during an induced local ischemia

The aim of this study was to investigate the utility of distortion product otoacoustic emissions (DPOAEs) in intraoperative monitoring (IM) of cochlear ischemic episodes in animals during internal auditory artery (IAA) compression. The IAA was exposed using the posterior fossa approach and then compressed for 3 and 5 min intervals to effect ischemia. DPOAE amplitudes and phases were measured at 4, 8, and 12 kHz geometric mean frequency (GMF). In each monitored ear, laser-Doppler cochlear blood flow (CBF) was measured. All IAA compressions resulted in rapid decrease of DPOAE amplitude and CBF, with simultaneous DPOAE phase increase. DPOAE phase changes were found to increase consistently within several seconds of IAA compression, while corresponding DPOAE amplitudes changed more slowly, with up to 30-40 s delays. Following IAA release, DPOAEs at 12 kHz GMF were characterized by longer delays in returning to baseline than those measured at lower frequencies. In some cases, CBF did not return to baseline. In this animal model, DPOAEs were found to be sensitive measures of cochlear function during transient cochlear ischemic episodes, suggesting the utility of DPOAE monitoring of auditory function during surgery of cerebello-pontine angle tumors.     

Ototoxicity caused by topical administration of gentamicin versus tobramycin in rabbits

Aim

To investigate the possible differences in cochleotoxic effects in rabbits between twice-daily administration of topical gentamicin and tobramycin throughout the perforated tympanic membrane with the use of distortion-product otoacoustic emissions (DPOAEs).

Materials and methods

Twenty female rabbits were studied prospectively daily for 21 days. The rabbits’ ears were divided into two groups: right and left ear groups. Twice-daily for 21 days after paracentesis, 0.3% gentamicin was administered topically in the left ears, and 0.3% tobramycin was administered topically in the right ears. For 21 days, the cochlear activity of the right and left ears of all rabbits was examined every 7 days using DPOAEs. The numerical values of the distortion product (DP) intensity recorded on days 7, 14 and 21 of drug administration were compared between the two groups.

Results

Cochlear activity was reduced earlier in the gentamicin group in the 2-4 kHz frequencies compared to the tobramycin group in the second DPOAE measurement (day 7 of the experiment). In two rabbits in the gentamicin group, the third DPOAE measurement showed that cochlear activity was reduced in all frequencies. In six rabbits in the tobramycin group, the third DPOAE measurement showed that cochlear activity was reduced in all frequencies. There was no statistical significance between the two groups except day 7 in the 2 and 3 kHz frequencies (p < 0.05).

Conclusion

We concluded that low frequencies (2 and 3 kHz) are more sensitive to the administration of topical gentamicin than to topical tobramycin. Early cessation of tobramycin drops may be minimally cochlear toxic compared to gentamicin within the first 7 days when these drugs are misused in treating chronic otitis media.     

Comparison of the Auditory-Evoked Brainstem Response Wave I to Distortion-Product Otoacoustic Emissions Resulting From Changes to Inner Ear Blood Flow

Objective/Hypothesis: Examine and compare in detail the time courses of the auditory brainstem response (ABR) wave I amplitude and latency to the distortion-product otoacoustic emission (DPOAE) amplitude and phase measured in the rabbit model following deliberate obstruction of cochlear blood flow (CBF). Methods: Using a posterior fossa craniotomy in five rabbits, the internal auditory artery (IAA) was compressed with a probe. ABR and otoacoustic emission were continuously monitored before, during, and after the compressions. Results: ABR wave I amplitudes demonstrated measurable decreases at a mean of 28.3 s after IAA compression, whereas DPOAE amplitudes decreased after a mean of 14.8 s. Wave I latencies began to increase at a mean of 18.3 s after occlusion, while DPOAE phase measures changed after a mean of only 4.8 s following IAA compression. The time-course patterns were similar for the amplitudes of both ABR wave I and DPOAE. Conclusions: ABR wave I amplitude follows a similar, though delayed (by approximately 10 s) time-course pattern to that of the DPOAE following IAA compression. The implication of these findings for intraoperative auditory monitoring is that changes in many currently employed measures will lag actual surgically induced alterations in CBF by at least 20 to 30 s.     

Influence of Ketamine–Xylazine Anaesthesia on Cubic and Quadratic High-Frequency Distortion-Product Otoacoustic Emissions

Ketamine is a dissociative anaesthetic, analgesic drug as well as an N-methyl-d-aspartate receptor antagonist and has been reported to influence otoacoustic emission amplitudes. In the present study, we assess the effect of ketamine–xylazine on high-frequency distortion-product otoacoustic emissions (DPOAE) in the bat species Carollia perspicillata, which serves as model for sensitive high-frequency hearing. Cubic DPOAE provide information about the nonlinear gain of the cochlear amplifier, whereas quadratic DPOAE are used to assess the symmetry of cochlear amplification and potential efferent influence on the operating state of the cochlear amplifier. During anaesthesia, maximum cubic DPOAE levels can increase by up to 35 dB within a medium stimulus level range from 35 to 60 dB SPL. Close to the -10 dB SPL threshold, at stimulus levels below about 20-30 dB SPL, anaesthesia reduces cubic DPOAE amplitudes and raises cubic DPOAE thresholds. This makes DPOAE growth functions steeper. Additionally, ketamine increases the optimum stimulus frequency ratio which is indicative of a reduction of cochlear tuning sharpness. The effect of ketamine on cubic DPOAE thresholds becomes stronger at higher stimulus frequencies and is highly significant for f2 frequencies above 40 kHz. Quadratic DPOAE levels are increased by up to 25 dB by ketamine at medium stimulus levels. In contrast to cubic DPOAEs, quadratic DPOAE threshold changes are variable and there is no significant loss of sensitivity during anaesthesia. We discuss that ketamine effects could be caused by modulation of middle ear function or a release from ipsilateral efferent modulation that mainly affects the gain of cochlear amplification.     

Cochlear origin of early hearing loss in vestibular schwannoma

OBJECTIVE: To test whether early hearing loss (HL) is cochlear in origin in patients with vestibular schwannoma (VS). STUDY DESIGN: Retrospective case review in an academic tertiary referral center. METHODS: A group of 19 VS patients with normal/symmetrical hearing and a group of 20 VS patients with mild HL (threshold at any tested frequency better than 45 dB HL) on the tumor ear side. Differences of the amplitudes of the distortion products of otoacoustic emissions (DPOAEs) between the tumor ear and the nontumor ear were studied at frequencies of 1, 1.4, 2, 2.8, and 4 kHz. The Wilcoxon test was used to compare the ears for both groups and to test for possible differences in tumor size between groups. RESULTS: DPOAE amplitudes do not differ strongly between the ears in VS patients with normal/symmetrical hearing (two-sided P values: .050 at 1 kHz, .182 at 1.4 kHz, .378 at 2 kHz, .293 at 2.8 kHz, and .238 at 4 kHz) but are decreased compared with the nontumor ear at frequencies 1, 1.4, 2, and 2.8 kHz in VS patients with even mild HL (two-sided P values: .013 at 1 kHz, .007 at 1.4 kHz, .033 at 2 kHz, .010 at 2.8 kHz, and .156 at 4 kHz). Tumor size did not differ significantly between the two groups (P = .436). CONCLUSION: Amplitudes of DPOAEs begin to decrease even at the early stages of HL in VS patients, which suggests a cochlear origin of early HL in these patients. DPOAEs may be used in a clinical setting to monitor progression of cochlear damage at the early stages of hearing impairment in VS patients.     

豚鼠畸变产物耳声发射潜伏期的对侧抑制效应现象

目的 通过观察对侧抑制效应中畸变产物耳发射（distortion productotoacousticemissions,DPOAE)各指标的改变,探讨耳蜗生理机制及传出神经的调节机能。方法 12只健康杂色豚鼠分A、B2组,在对侧耳无声刺激及给予70dB SPL宽带噪声条件下,分别使用不同的原始纯音强度组合测定在f2＝2、4、6kHz时测试耳DPOAE之幅值及潜伏期。次日,A组动物背侧径路开放右耳听泡,圆窗膜给予60mmol/L卡因酸1μL,作用3h后拭去。给药后6h测试右耳无声刺激和给予70dB SPL宽带噪声刺激下,左耳的DPOAE幅值、潜伏期等指标。结果 ①用药前,A组对侧耳给声时以等强度原始音诱发的测试耳DPOAE各频率幅值与给声前基本无变化,而潜伏期显著延长;②用药前,B组对侧耳给声以差强度原始音（L2＝L1－10dB)诱发的测试耳DPOAE在2、4kHz的幅值与给声前相比有显著减小,潜伏期也显著延长;③A组用药后,对侧耳给声对测试耳DPOAE幅值和潜伏期均无显著影响。结论 潜伏期亦是对侧抑制研究中的敏感指标。对侧抑制效应在调制耳蜗转导机制中发挥负反馈作用。     

Middle ear and cochlear disorders result in different DPOAE growth behaviour: implications for the differentiation of sound conductive and cochlear hearing loss

Input/output functions of distortion product otoacoustic emissions (DPOAE I/O-functions) give an insight into the compressive, non-linear sound processing of the cochlea. With an inner ear dysfunction a steeper I/O-function is observed. Due to the linear sound processing of the middle ear, one can assume that the DPOAE growth behaviour remains unaltered with a sound conduction dysfunction. If that is true, a differentiation between middle and inner ear dysfunction will be possible by using the slope of DPOAE I/O-functions as a means for assessing cochlear compression. In order to test that hypothesis, DPOAE I/O-functions were recorded in a wide primary tone level range at up to 8 f2 frequencies between 2.0 and 8.0 kHz (15 dB SPL < L2< 60 dB SPL; L1=0.46 L2 + 41 dB SPL; f2/f1=1.2) in guinea pigs in which middle (saline solution in the bulla) and inner ear (exposure to loud broadband noise) disorders were induced. Middle ear dysfunction resulted in a reduction of the DPOAE amplitude independent of the primary tone level. Consequently, DPOAE growth behaviour was not affected. In contrast to that, during cochlear impairment, steepened DPOAE I/O-functions were observed reflecting loss of compression of the cochlear amplifier. Accordingly, DPOAE I/O-functions allow a differentiation between middle and inner ear dysfunction. Further studies will have to show the usability of this method for clinical diagnostics, e.g. for detecting sound conduction disturbances in newborn hearing screening due to amniotic fluid or Eustachian tube dysfunctions during the early postnatal period.     

Effect of middle ear effusion on distortion product otoacoustic emission

OBJECTIVES: It is well documented that children, particularly between the ages of about 2 and 6 years, exhibit a high prevalence and incidence of otitis media. Distortion product otoacoustic emissions (DPOAEs) offer great potential for clinical testing of cochlear function in children. The aim of the present study was to determine the influence of middle ear effusion and physical properties of the effusion on the recording of DPOAE. METHODS: Nineteen children (38 ears) undergoing myringotomy and/or tympanostomy tube insertion for secretory otitis media were studied. Pre-operative and post-operative first day DPOAE signal to noise ratios were compared. The results were analyzed by paired samples test and ANOVA statistical methods. RESULTS: We were found significant differences between pre-operative and post-operative first day DPOAE signal to noise at 1, 1.5, 2 and 4kHz. In addition, comparison of the pre-operative DPOAE signal to noise ratio and per-operative middle ear findings are shown significant differences between glue (thick mucous) and the other three groups (mucous, serous and no-effusion groups) at 2 and 4kHz, and between glue and no effusion group at 8kHz. Also post-operative DPOAE signal to noise ratio in relation to per-operative middle ear findings were significantly different at 2, 4 and 8kHz. The most increase of emissions at the post-operative first day was seen in ears with glue effusion at 1 and 2kHz. CONCLUSIONS: Otitis media with effusion can be monitored by DPOAE measurement pre-operatively and post-operatively. In the pre-operative evaluation, glue effusion may cause a reduction in the emissions at 2, 4 and 8kHz more than the other kind effusions.     

畸变产物耳声发射测试对噪声性聋诊断的敏感度和特异度

目的 探讨畸变产物耳声发射测试对噪声性聋的诊断价值。方法 对115名军人（204耳）进行DPOAE幅值测试,采用两个等强度L1＝L2＝70dB SPL的纯音信号f1、f2＝1．2。测试1、2、4kHz和6kHz DPOAE幅值,根据DPOAE幅值是否大于或小于标准值,判断听力正常与否。并同纯音听阈进行对照。结果 1、2、4和6kHz各频率的敏感度分别是70％、67％、85％和73％;特异度分别是71％、66％、84％和75％。结论 DPOAE幅值测试用于诊断噪声性聋,缺乏足够的敏感性和特异性,单一的DPOAE幅值测试,不能诊断噪声性聋。     

短时纯音暴露对畸变产物耳声发射的影响

畸变产物耳声发射（ＤＰＯＡＥ）测试中所采用的参数可以对测试结果有明显影响，为研究改变ＤＰＯＡＥ测试参数对反映耳蜗功能变化是否有影响，使１０只大白兔（１６耳）接触短时（３分钟）、中等强度（８２ｄＢＳＰＬ）的纯音暴露后发现，以等强原始音（Ｌ１＝Ｌ２）诱发的ＤＰＯＡＥ的幅度变化小于以差强原始音（Ｌ２＝Ｌ１－１２ｄＢ）诱发的ＤＰＯＡＥ（相差１０．１１ｄＢ），而其恢复过程也短于后者（相差１００．７１秒）。这种差别可能提示在ＤＰＯＡＥ的产生过程中有多个生理机制发挥作用，而变化测试参数则可以选择性地突出表现其中某一个机制     

短时纯音暴露对畸变产物耳声发射的影响

畸变产物耳声发射（ＤＰＯＡＥ）测试所采用的参数可以对测试结果有明显影响，为研究改变ＤＰＯＡＥ测试参数对反映耳蜗功能变化是否有影响，使１０只大白兔（１６耳）接触短时（３分钟）、中等强度（８２ｄＢ ＳＰＬ）的纯音暴露后发现，以等强原始音（Ｌ１＝Ｌ２）诱发的ＤＰＯＡＥ的幅度变化小于以差强原始音（Ｌ２＝Ｌ１－１２ｄＢ）诱发的ＤＰＯＡＥ（相差１０．１１ｄＢ），而其恢复过程也短于后者（相差１００．７１秒）。这     

Otoacoustic emission examinations in soldiers before and after shooting

Firearms are a common source of impulse noise that may potentially damage hearing organ. The purpose of this study was evaluation of the click evoked otoacoustic emission (TEOAE) and distortion-product otoacoustic emission (DPOAE) before and after shooting and comparison with conventional pure tone audiometry. Standard pure tone audiometry, tympanometry, TEOAE and DPOAE were made before and 10-15 minutes after shooting. Ten male soldiers (20 ears) were exposed to impulse noise from automatic gunfire (15 single rounds of live ammunition). They did not use any earplugs. The reduction amplitude of the TEOAE after shooting was found especially for the frequency 3,4 kHz for the right ear and 1 and 2 kHz for the left ear. The DPOAE greatest reduction concerned frequency 2,5 and 4 kHz for the left ear. All our shooters were right-handed and probably the asymmetrical effect resulted from the shooting posture. Any differences existing between the audiometric threshold before and after shooting were not noticed. Clinical experience with OAE indicates that it may play a role as a screening method for the soldiers exposed to noise and as a tool for monitoring early changes in cochlea. Emissions seem to be more sensitive for monitoring early cochlear changes after shooting than pure tone audiometry.     

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。     

急性低频感音神经性耳聋的临床观察

目的探讨急性低频感音神经性耳聋(acute low-tone sensorineural hearing loss,ALHL)的临床特点和疗效,提高对该疾病的诊断和认识。方法回顾性分析62例ALHL患者的临床表现、听力学检查和治疗情况,总结其临床发展规律。结果发病年龄以青中年为主,女性明显多于男性,多为单耳发病,表现为耳闷或伴耳鸣,听力下降,不伴眩晕,所有患者纯音听阈均表现为轻中度低频感音神经性耳聋,治疗前后分别为(38.71±6.82)dB和(20.56±9.44)dB,两者比较差异具有统计学意义(P<0.05)。鼓室图"A"型,49例(80.9%)镫骨肌反射引出,40例(64.5%)Metz试验阳性,62例ABR均正常。62例患者治疗前DPOAE在0.5～1 kHz的引出率仅为18.7%,反应幅值明显降低,治疗后DPOAE在0.5～1 kHz的引出率提高至43.8%,幅值亦有所提高。结论 ALHL以突发的耳闷和(或)伴耳鸣为主要表现,常单耳发病,青中年女性为主,听力学定位诊断为蜗性聋,仅累及低频区,皮质类固醇激素治疗有较好的疗效。     

Cochlear microphonics and otoacoustic emissions in chronically de-efferented chinchilla

The effects of eliminating the olivocochlear bundle (OCB) on cochlear electromechanical properties were examined by measuring cochlear microphonics (CM) and distortion product otoacoustic emissions (DPOAEs) in chronically de-efferented chinchillas. The OCB fibers to the right ears were successfully sectioned in six out of 15 adult chinchillas via a posterior paraflocular fossa approach. At the end of the experiment, these ears were histologically verified as being deprived of both lateral and medial OCB fibers. The opposite (left) ears from the animals served as controls. Following de-efferentation, changes of the inter-modulation distortion components (2f(1)-f(2), f(2)-f(1), 3f(1)-2f(2), 3f(2)-2f(1)) varied, depending on the frequencies and levels of the stimuli. DPOAE amplitudes to low-level stimuli were within the 95% confidence intervals around mean DPOAE amplitudes of the control ears at all the frequencies (1-8 kHz). At high stimulus levels, DPOAE amplitudes increased by 5-20 dB at 1 and 2 kHz while remaining in the normal range at 4 and 8 kHz. In contrast, the CM input/output functions to stimuli from 1 to 8 kHz were significantly reduced by approximately 40-50% at all input levels. The results suggest that the OCB may play a role in modulating electrical properties of the outer hair cells and in reducing the magnitude of cochlear distortion to high-level stimuli.     

耳蜗性聋的畸变产物耳声发射测试

目的：通过畸变产物耳声发射(DPOAE)测试耳蜗性聋的敏感性、特异性和符合率来评估其测试效能。方法：测试听力正常人86耳和耳蜗性聋98耳的DPOAE，其1～6kHz各个频率的幅值与对应频率的电测听纯音听阈相比较，用所得到患耳蜗性聋敏感性和特异性值作受试者作业特征曲线。并计算其面积。其面积值并不因为DPOAE用于区别听力正常与否的取值标准不同而发生变化。用所得到的面积值来判断DPOAE的测试效能。结果：1～6kHz从低到高各个频率对应的受试者特征曲线面积分别为0．677，0．777，0．818，0．890，0．873。结论：DPOAE可以作为测试耳蜗性聋的一种频率特异性的客观方法。     

Effects of GSM-like Radiofrequency on distortion product otoacoustic emissions of rabbits: Comparison of infants versus adults

Objectives

The aim of this study is to investigate the potential hazardous effects of 1800 MHz Global System for Mobile Communications-like (GSM-like) Radiofrequency (RF) exposure on the cochlear functions of female infant and adult rabbits by measuring Distortion Product Otoacoustic Emission (DPOAE) response amplitudes.

Methods

Eighteen each one-month-old New Zealand White female rabbits and eighteen each 13-month-old adult rabbits were included into the study. They were randomly divided into four groups. Nine infant rabbits (Group 1) were not exposed to 1800 MHz GSM-like RF (Infant Control, C-In). Nine infant rabbits (Group 2) were exposed to 1800 MHz GSM-like RF, 15 min daily for 7 days after they reached one-month of age (Infant RF, RF-In). Nine adult rabbits were not exposed to 1800 MHz GSM-like RF, 15 min daily for 7 (Adult Control, C-Ad). Nine adult rabbits were exposed to 1800 MHz GSM-like RF, 15 min daily for 7 days (Adult RF, RF-Ad). Cochlear functions were assessed by DPOAEs at 1.0-8.0 kHz.

Results

At 1.0-2.0 and 6.0 kHz, the mean DPOAE values of Group 2 were significantly higher than that of Group 1. At 3.0-8.0 kHz, the mean DPOAE values of Group 4 were significantly lower than that of Group 1. At 6.0-8.0 kHz, the mean DPOAE values of Group 2 were significantly higher than that of Group 3. At 1.0-8.0 kHz, the mean DPOAE values of Group 4 were significantly lower than that of Group 2. At 1.0-8.0 kHz, the mean DPOAE values of Group 4 were significantly lower than that of Group 3.

Conclusion

Harmful effects of GSM-like 1800 MHz RF exposure was detected more in the adult female rabbits than infant female rabbits by DPOAE measurement. Prolonged exposure and hyperthermia related to the power density of applied RFR, increasing the temperature in the ear canal, may decrease the DPOAE amplitudes. Water containing medium in the middle ear of infant rabbits may play the protective role **from the RF damage.     

畸变产物耳声发射甘油试验在内淋巴积水早期诊断中的价值

目的　用畸变产物耳声发射 (DPOAE)甘油试验来观察可疑梅尼埃病患耳内淋巴积水早期对耳蜗功能的影响。方法　对可疑梅尼埃病患者组 (4 0耳 )及正常组 (34耳 ) ,于服用甘油 1小时前后分别进行DPOAE测试。结果　正常组甘油试验前后比较DPOAE各频率点幅值及信噪比无明显变化 (P >0 .0 5 ) ;患者组甘油试验前后比较以 0 .5kHzDPOAE幅值及信噪比变化最为显著 (P <0 .0 5 )。与正常组比较 ,患者组DPOAE 0 .5kHz幅值和信噪比变化、1.0kHz信噪比变化明显提高 (P <0 .0 5 )。研究还发现DPOAE幅值变化与信噪比变化有一定的线性增长趋势。结论　畸变产物耳声发射甘油试验可为临床表现无听力下降的可疑梅尼埃病患者的早期诊断提供一定的客观依据 ;在分析耳声发射甘油试验结果时应重视信噪比的变化     

Rapid adaptation of the 2f1-f2 DPOAE in humans: binaural and contralateral stimulation effects

The present data were collected in humans to characterize the effects of monaural and binaural stimulation and contralateral noise on the 2f1-f2 distortion-product otoacoustic emission (DPOAE) adaptation response. DPOAE levels (f2/f1=1.21, L1=70 dB SPL, L2=65 dB SPL) were measured in both ears for a range of f2 frequencies (1.2 to 10.0 kHz). The f2 frequency producing the largest amplitude DPOAE was used for further testing employing three different stimulus conditions: the primary tones were presented to only one ear for 4 s; the two tones were presented simultaneously in both ears; and, contralateral broadband noise (60 dB SPL) was presented for 5 s, beginning 4 s after the onset of the monaural primaries in the test ear. Acoustic reflex thresholds were measured to verify that the middle-ear muscles played no systematic role in the measured DPOAE reductions. Estimates of monaural rapid adaptation levels and time constants agreed well with previous human findings. The magnitude of the rapid adaptation under binaural stimulation, as compared with monaural primaries, was 25% greater on average, though adaptation time constants were comparable. With added contralateral noise, the average DPOAE suppression was 1.1 dB (0.3-2.7 dB). The magnitude of the monaural adaptation and the effects of binaural and contralateral stimulation, however, were smaller than those measured previously in experimental animals, though the time constants were in good agreement.