A comparison of extratympanic versus transtympanic recordings in electrocochleography.

Detection thresholds, amplitudes and input output curves of cochlear microphonics (CMs), and action potentials (APs) determined by extratympanic electrocochleography (ET ECochG) were compared with those determined by transtympanic (TT) ECochG in the same ears. Two groups were studied: 12 ears in 9 volunteers with normal hearing, and 6 ears in 6 subjects with sensorineural hearing loss. Short tone bursts with frequencies of 0.5, 1, 2 and 4 kHz were used as acoustic stimuli to evoke CMs, and a click was presented to measure the APs. In both groups, although the two approaches produced large differences in amplitudes, nearly identical values were obtained for the CM and AP detection thresholds. The CM and AP input-output curves obtained from mean amplitudes at each intensity in normally-hearing ears had similar slopes with the two approaches. These findings demonstrate the clinical usefulness of ET ECochG.     

A New Electrode (HIM-5) for CM Measurement in Extratympanic Electrocochleography

A new electrode (HN-5) for measuring cochlear microphonics (CMs) in extratympanic (ET) electrocochleography (ECochG) has been developed. The HN-5 electrode consists of a silver wire 2 mm in diameter and 5.0 cm in length connected to a low noise cable. The HN-5 electrode showed low impedance and excellent frequency characteristics. Using the dummy ear, artefact contamination tests, such as electromagnetic induction and mechanical vibration, were performed with the HN-5 electrode and various other electrodes. In the HN-5 electrode, artefact contaminations were kept within acceptable noise levels, whereas in the smaller electrodes, the measurable artefact contaminations were larger. The CMs were measured from subjects with normal hearing. CM findings obtained using the HN-5 electrode did not differ from those obtained by transtympanic (TT) ECochG, apart from their amplitude. HN-5 overcame the major disadvantage of the ET ECochG and provided a very favourable signal-to-noise ratio, resulting in repeatable response signals averaged from the same relatively small number of samples as those of TT ECochG. This resulted in successful CM measurements of ET ECochG.     

Hearing impairment in patients with acoustic neuroma—analysis by electrocochleography

Objective: In patients with acoustic neuroma, the site and severity of hearing impairment are important in discussing surgical approaches. Since the effectiveness of conventional auditory psychological testing is limited, we studied objectively hearing impairment of the cochlea and the cochlear nerve due to the tumor. Methods: Electrocochleography (ECochG) was carried out in 21 patients with acoustic neuroma. Cochlear microphonic potential (CM) and action potential (AP) in ECochG evoked with clicks and short tone bursts were recorded through a transtympanic needle electrode technique. Cochlear function was studied using the detection thresholds of CM, and cochlear nerve involvement was analyzed by differences between AP and CM detection thresholds. Results: The 1 kHz CM detection threshold was elevated in 17 (81.0%) of 21 patients indicating cochlear impairment. Of seven patients with normal hearing or mild sensorineural hearing loss in pure tone audiometry, three had a slightly elevated CM detection threshold. Of five patients with pronounced pure tone levels, four showed a CM response and were thought to have mild cochlear dysfunction. Cochlear nerve impairment was confirmed in three of four patients with well-developed CM based on elevated AP detection thresholds. Three patients had CM response but no AP response, suggesting severe cochlear nerve impairment. Conclusion: Disorders of the cochlea and the cochlear nerve can be evaluated with ECochG AP and CM measurement. The findings of ECochG are thought to be important information to judge hearing prognosis, thereby enhancing its clinical utility.     

Electrocochleography potentials evoked by condensation and rarefaction clicks independently derived by a new numerical filtering approach

The cochlear microphonic potential (CM) and the compound action potential (CAP) cannot be measured separately but only in combination. In the literature their individual estimates are conventionally recovered by the so-called CM cancellation technique. This method averages the potential obtained in response to rarefaction and condensation clicks under the assumption that changing the polarity of the clicks only affects the CM sign and does not alter the CAP in any way. However, both theory and evidence suggest that these hypotheses can be critical. In addition, recent contributions in the electrocochleography (ECochG) literature suggested that assessing the influence of stimulus polarity on the evoked CAP may constitute an indicator of clinical usefulness which the CM cancellation method cannot supply. In this work we propose a new algorithm to estimate the cochlear potentials evoked from positive clicks, CAP+ and CM+, and those evoked from negative clicks, CAP- and CM-, by processing the same kind and amount of data employed in the CM cancellation method. The application to real data taken from 3 subjects exhibiting quantitatively and qualitatively different ECochG responses at various levels of stimulation intensity is presented. In addition, simulated problems where the true CAP and CM are known are studied to permit a fair assessment of the proposed technique. Results suggest that the new algorithm is potentially able to point out small differences between CAP+ and CAP-. This encourages its further employment on a larger scale.     

Prognostic estimation of sudden deafness by cochlear microphonics of electrocochleography

Estimation of the prognosis of sudden sensorineural deafness is available by reviewing CM responses in electrocochleography (ECochG) even at an early stage of disease after the onset. The detection threshold of CM irrespective of the period of ECochG seems to be the most reliable tool to estimate the final hearing level in pure tone audiogram.     

纯音声场测听可行性研究报告

本文的目的是探讨纯音用于声场测听的可行性。普遍认为声场测听适宜刺激为啭音和窄带噪声，而纯音仅作为耳机测听和消声室中测试信号。本文通过对纯音声压分布、声场变异以及频率漂移对参考点声压级影响的研究发现，扩散场中纯音声压分布的均匀性虽不如啭音，但在某些范围其能量仍可充分扩散，这些区域声场测试结果受受试者头位改变和／或频率漂移影响轻微。对２０名重度感音神经性耳聋患者的测试结果证实了上述结论。由此认为，如在声场校正基础上合理选择参考点位置，用纯音进行声场测听是可行的。     

Compound Action Potential and Cochlear Microphonic Extracted from Electrocochleographic Responses to Condensation or Rarefaction Clicks

In electrocochleography (ECochG) compound action potential (CAP) and summation potential (SP) are usually separated from the cochlear microphonic (CM) by the CM cancellation technique consisting in averaging the responses evoked by rarefaction and condensation clicks. With the aim of analysing the ECochG responses evoked by monophasic clicks, we developed a numerical method based on the theory of optimal filtering, which makes no assumptions about the unknown potentials. The application of the filtering technique to the ECochG recordings obtained from 6 normally hearing children and 10 children with cochlear hearing loss allowed us to perform CAP extraction in cases where CM was not cancelled by the conventional method. Differences in SP amplitude and polarity were found between rarefaction and condensation click-evoked responses in cochlear hearing losses.     

Compound action potential and cochlear microphonic extracted from electrocochleographic responses to condensation or rarefaction clicks

In electrocochleography (ECochG) compound action potential (CAP) and summation potential (SP) are usually separated from the cochlear microphonic (CM) by the CM cancellation technique consisting in averaging the responses evoked by rarefaction and condensation clicks. With the aim of analysing the ECochG responses evoked by monophasic clicks, we developed a numerical method based on the theory of optimal filtering, which makes no assumptions about the unknown potentials. The application of the filtering technique to the ECochG recordings obtained from 6 normally hearing children and 10 children with cochlear hearing loss allowed us to perform CAP extraction in cases where CM was not cancelled by the conventional method. Differences in SP amplitude and polarity were found between rarefaction and condensation click-evoked responses in cochlear hearing losses.     

Lesion site in sudden deafness: study with electrocochleography and transiently evoked otoacoustic emission

We examined electrocochleogram (ECochG) and transiently evoked otoacoustic emission (TEOAE) on five cases of sudden sensorineural hearing loss which had no abnormalities detected on diagnostic imagings and showed complete recovery of hearing. At the initial examination, three cases showed a broadened wave 1 with prolonged latency in the auditory brainstem response (ABR) at 90 dB HL. The ECochG AP showed a broad waveform, low amplitude, and high threshold. CM threshold, although increased, was relatively well preserved compared with hearing threshold measured with conventional pure-tone audiometry. The thresholds in TEOAE examination were similar to those for CM and preserved better when compared with pure-tone audiometric thresholds. These findings suggest that the location of the disorder in these three cases involved not only the cochlea but also the retrocochlear auditory pathway. The other two cases showed normal ABR waveforms at 90 dB HL at the initial examinations. ECochG examination showed that a normal AP in one case and a smaller amplitude AP, an elevated threshold, and normal waveform of AP in the other ear. CM thresholds coincided with the conventional audiometry thresholds. These findings suggest that hearing loss in these two cases involved primarily the sensory hair cells.     

Cochlear microphonics recordable at the non-shielded bedside using a new tubal transducer

A new tubal transducer (NC-3) for measuring cochlear microphonics (CM) in extratympanic electrocochleography (ECochG) was developed by improving the common hearing aid earphone. Using a human forearm as a dummy ear, the artifact contamination generated from the NC-3 tubal transducer was tested and the possibility of measuring the CM at a non-shielded bedside was studied. An HN-5 electrode was fixed to a subject's forearm, and a sound stimulus of 90 dBnHL was delivered through the tube of the NC-3. When the earphone of the transducer was placed at a right-angle to the electrode on either a vertical or horizontal plane and the electrode was placed in direct contact with the tip of the tube, contamination from electromagnetic induction and CM-like mechanical vibration were prevented. Using the HN-5 electrode and NC-3, extratympanic ECochG-CM was recorded from normal-hearing subjects in both a shielded sound-proof room and a non-shielded ordinary, quiet room. No differences were found between CMs measured in the two rooms. These results suggest that the NC-3 overcomes the shortcomings of a loudspeaker system and allows CM to be recorded accurately at non-shielded bedsides.     

Electrocochleography in cochlear implantation: Development,applications, and future directions

Electrocochleography (ECochG) is an electrophysiological technique that records electrical potentials generated by different components of the inner ear and peripheral cochlear nerve in response to acoustic stimulation. ECochG responses can be analyzed into (1) cochlear microphonics (CM), (2) auditory nerve neurophonics, (3) summating potential, and (4) compound action potential. Over the past few decades, there have been ongoing refinements in technique and updates in the understanding of recorded potentials. Historically, ECochG found its main application in the diagnostic evaluation of Meniere’s disease (MD). However, in the last decade, the focus has shifted towards cochlear implantation (CI). In patients with residual hearing after CI, combined electric and acoustic stimulation has resulted in improved hearing and speech outcomes. Despite efforts to mitigate trauma during electrode insertion, hearing preservation rates vary after surgery. During implantation, real-time ECochG offers an opportunity to measure frequency specific CMs elicited from a localized region in the cochlea as the surgeon inserts the electrode array. In extracochlear ECochG recordings, the recording electrode can be placed on the promontory, the stapes, or the tympanic membrane. Intracochlear ECochG can be performed by inserting a recording electrode into the cochlea or by using one of the CI electrodes as the recording electrode. The loss of intraoperative ECochG signal may indicate cochlear trauma from electrode insertion, but the association between intraoperative ECochG changes and cochlear trauma remains controversial. The ability to monitor cochlear trauma during CI electrode placement holds promise to improve hearing preservation outcomes, modify surgical techniques, and change electrode design. The goal of this review is to provide a comprehensive overview of the electrophysiology and history of ECochG, discuss its recent applications in CI, and explore the ongoing research in this expanding field.     

Basis and some diagnostic implications of electrocochleography.

Electrocochleography (ECoG) involves the recording of electrical responses to sound from the vicinity of the cochlea. The technique, as we practice it, utilizes a trans-tympanic recording needle situated on the promontory of the middle ear. Filtered clicks in the frequency range between 500 and 8,000 Hz are presented to the ear under test at a rate of 10/sec. Repetitive clicks of a given frequency are first presented at high intensity and the responses summed (averaged) in a computer. The click is systematically lowered in intensity, and an average is collected at each level until the normal dynamic range of hearing has been explored. Two major electrical indices are present in the recording: these are 1. the whole-nerve action potential (AP) derived from the first-order auditory neurons, and 2. the cochlear microphonic (CM) derived from the hair cells. Inspection of the whole nerve AP as intensity is lowered allows the estimation of the response threshold, which correlates well with behavioral threshold. Inspection of the relation between the CM and the AP allows qualitative differentiation to be made between pathology arising in the hair cell (sensory) and in the nerve (neural).     

Measurement of basilar membrane vibrations and evaluation of the cochlear condition

The experimental procedure for measuring basilar membrane responses to acoustic signals is described. The surgical procedure developed for opening the cochlea with minimal trauma is presented. Each experiment included sound pressure level measurements to define the input signal, cochlear microphonic (CM) measurements to monitor the cochlear condition, interferometric measurements and histological evaluation of the cochleas. The characteristic frequency (CF) and the sensitivity at CF for the basilar membrane response is correlated with the change of CM response observed in six animals. It is demonstrated that both tuning characteristics are extremely sensitive to cochlear trauma as evidenced by changes of CM.     

Electrocochleography and symptoms of inner ear dysfunction

We examined the relationship between electrocochleographic test results and symptoms associated with Meniere's disease-endolymphatic hydrops (MD-ELH). Extratympanic electrocochleography (ECochG) was performed on 55 consecutive patients (110 ears) suspected of having MD-ELH, and the results compared with the clinical symptoms of the patients on the day of recording. Referring symptoms included sensorineural hearing loss, aural fullness or pressure, tinnitus, vertigo, and all combinations of these four. There was a statistically significant difference between ECochG findings when symptoms were absent compared with when one or more symptoms were present. Furthermore, the presence of hearing loss combined with aural fullness or pressure was the strongest predictor of a positive ECochG, as characterized by an enlarged summating potential action potential amplitude ratio.     

Electrocochleography in the diagnosis of perilymphatic fistula: intraoperative observations and assessment of a new diagnostic office procedure.

The intraoperative electrocochleogram (ECochG) was investigated during stapedectomy surgery and during cochleostomy surgery. This provided the justification for obtaining recordings with the oval window (OW) or round window (RW) intact and then when there was a definite fistula. It was noteworthy that no ECochG changes occurred on merely opening the OW or RW, but that marked changes occurred on removing perilymph, even by gentle suction. On raising the intrathoracic pressure and replacing the perilymph, the ECochG potentials usually recovered. Based on these intraoperative observations, an office procedure was designed. The subject was asked to raise the intrathoracic pressure on several occasions and changes in the amplitude of the ECochG potential were noted. An increase of over 15 percent in the action potential (AP), with or without a decrease in the negative summating potential (SP) during the period of raised intrathoracic pressure, was used as the diagnostic criteria for a perilymphatic fistula. A decrease in the AP with or without an increase in the negative SP immediately on relaxing after a period of raised intrathoracic pressure was also treated as a positive diagnostic criterion. Seventy-one normal ears were investigated and a positive result was recorded in two ears (false positive rate: 2.8%). Two hundred and six ears, strongly suspected as having a perilymph leak on the basis of the clinical history and vestibular signs have been investigated over the past 4 years. Ninety positive diagnoses have been reached and 46 of these ears have been surgically explored.(ABSTRACT TRUNCATED AT 250 WORDS)     

A study on the effect of infrasound

In order to examine the influence of infrasound that is becoming topical in society, human beings and guinea pigs were exposed to infrasound. After exposure, the hearing level, vestibular functions and autonomic nervous functions of human beings were examined, and endocochlear potential (EP) and cochlear microphonics (CM) of guinea pigs were examined. Next, after guinea pigs were exposed to intense audible low frequency sound that was born secondarily from infrasound and/or vibration of whole body concerning about air pressure change of infrasound, their EP and CM were examined. The results obtained were as follows: 1) By exposure of infrasound 10-15Ha 130-135dB LSPL for 30min. to human beings, their hearing level, vestibular functions and autonomic nervous functions were not changed. 2) After exposure of infrasound 15Hz 135-140dB LSPL for 24hrs.-72hrs. to guinea pigs, their EP and CM remained normal. 3) After each exposure of audible low frequency sound 90Hz 120dB SPL for 72hrs., 150Hz 110dB SPL for 72hrs. and 200Hz 100dB SPL for 72hrs. to guinea pigs, their EP became abnormal though their CM remained normal. 4) After exposure of 15Hz 500 mu +/- 30 mu vibration for 72hrs. to guinea pigs, both EP and CM remained normal. 5) After exposure of both audible low frequency sound 150Hz 100dB SPL and vibration 15Hz 500 mu +/- 30 mu for 72hrs. to guinea pigs, their EP became abnormal though their CM remained normal.     

Latencia de los microfónicos cocleares

Introduction and objectiveBy using appropriate instrumentation, we have found that cochlear microphonics (CM) advance or delay their appearance, depending on the sound pressure that generates them. This time variation is on the order of microseconds. We have not found any reference to this behaviour, which is why we make the finding known.Material and methodWe used the standard instrumentation specified for the study of CM. The method was based on the phase shift function of the CM according to the intensity of the stimulus.ResultsLatency was observed in CM, and we determined that latency time diminishes as the intensity of the stimulus increases.ConclusionsFrom the sound stimulus to the bioelectric potential transduction, there is a time period of microseconds, the shorter the more powerful the stimulus. This suggests that electromechanical transduction is not a simple mechanical process.     

The effect of 6 kHz tone exposure on inner ear function of the guinea pig: relation to changes in cochlear microphonics,action potential,endocochlear potential and chemical potentials of K+-ions and Na+-ions,using a double-barrel glass electrode

Using 97 male albino guinea pigs and applying electrophysiological methods, the effects of a 6 kHz tone were investigated at a moderate sound pressure level to the inner ear during a 24-h exposure time. Following exposure to the 6 kHz tone at 90 dB, cochleas showed decreased maximum output voltage of cochlear microphonics (CM) and action potential (AP). In the endolymph, K⁺ ion and Na⁺ ion concentrations remained unchanged during 40 min anoxia and 90 dB tone exposure. At 80 dB sound exposure decreases in maximum output voltage of CM and AP and decreases in the absolute value of EP could not be detected. Endolymph K⁺-ion Na⁺-ion concentrations were also unchanged. These findings indicate that diffusion potentials are induced at the same time as decreases of maximum output voltage in CM induced by exposure to sound at 90 dB.     

Cochlear microphonic potentials elicited by biosonar signals in flying bats, Pteronotus p. parnellii

Cochlear microphonic (CM) potentials were recorded from the bat, Pteronotus p. parnellii during tethered flight and during simulated flight on a pendulum. For each emitted signal the frequency of the ca. 61 kHz constant frequency (CF) component was compared with the frequency response characteristics of the animal's ear. The majority of ‘resting pulses’ had CF components with the maximum frequency approximately 200 Hz below the best frequency (BF) of the CM audiogram.Doppler shift compensation occurred only during forward swings of the pendulum and in such a way that the echo CF components were always maintained near the BF, but on the low frequency slope of the CM audiogram.CM responses to emitted pulses were usually small in amplitude and in some animals no responses were seen. Echoes Doppler shifted upward, however, evoked high amplitude potentials. Echo CF components estimated to be at least 43 dB fainter than the emitted pulses evoked higher amplitude CM potentials than the loud emitted pulses. Echoes from large surfaces up to 4.S-S.O meters away evoked CM potentials as high in amplitude as those elicited by emitted pulses, even when there was no Doppler shift. Beats in the CM were observed on many occasions and occurred as a result of pulse-echo and echo-echo interactions.     

Electrocochleographic effects of ear canal pressure change

A series of Swedish studies has shown that the application of middle ear over-pressure may be effective in ameliorating the symptoms associated with Meniere's disease. Other studies have shown that electrocochleography (ECochG) is an effective tool in the identification of Meniere's disease, especially in the presence of active symptoms. Based on the therapeutic potential of middle ear overpressure as a treatment for Meniere's symptoms and on the relationship between these symptoms and ECochG, we investigated the effects of ear canal pressure change on human electrocochleographic components in normally hearing subjects. An experimental system combining an immittance audiometer probe and ear canal electrode was utilized to record extratympanic ECochG when different atmospheric pressures were applied indirectly to the middle ear via the sealed ear canal. All ECochG parameters except for the duration of the whole nerve action potential (AP) of the auditory nerve were significantly affected by pressure changes in the ear canal. Effects included an enlargement of the summating potential (SP) amplitude and of the SP:AP amplitude ratio at pressures above and below 0 decaPa (daPa). An important implication of our findings is that the status of the middle ear must be taken into account in the interpretation of ECochG results.