Recording auditory-nerve potentials as an office procedure

ABR recordings in newborns using an ear canal electrode

The objective of this study was to improve the sensitivity of ABR recordings in newborns via a procedure that utilizes the ear canal as a recording site. Conventional recordings were compared to ear canal recordings of the ABR in 45 normally-hearing newborns who passed their newborn hearing screening. Responses were obtained at stimulus levels of 80, 60, 40, and 20 dBnHL using forehead (+) to ear canal (-), versus forehead (+) to mastoid (-) electrode configurations. ABR parameters evaluated included measurement of component amplitudes of wave I and V, absolute latencies of I and V, the I-V interwave interval, and amplitude ratio. At stimulus levels of 80, 60, and 40 dBnHL, wave I amplitude was significantly larger using the ear canal configuration. This investigation shows that the amplitude of wave I is significantly larger and easier to identify when the ear canal is used as one of the recording sites in comparison to more conventional scalp (mastoid) recordings.

A new electrode (HN-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, artifact contaminations were kept within acceptable noise levels, whereas in the smaller electrodes, the measurable artifact 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.

Quantitative assessment of inner ear pathology following ototoxic drugs or acoustic trauma

Techniques currently used in the assessment of structural and/or functional damage to the peripheral auditory system are summarized. Two histological approaches are described: one which allows light microscopic evaluation of all structures of the auditory periphery, and a second which concentrates on the sensory cells and their innervation. The latter technique allows electron microscopic analysis of selected regions after a thorough light microscopic survey. Two electrophysiological methods are described as well: a single-fiber approach which provides detailed information about cochlear condition at all frequency locations and a simpler and faster evoked-potential approach which is well suited to screening for cochlear changes. The correlations between structural and functional changes are described using examples from studies of acoustic injury of the inner ear.

Electrophysiology of the auditory system

This review has attempted to summarise the properties of electro physiological responses in the auditory system. The treatment was broad and consequently somewhat sketchy. For a more detailed recent treatment of the physiology of the auditory system the reader is referred to Pickles (1982), Møller (1983), or Altschuller et al (1986). The data on acoustic injury have been reviewed recently by Schmiedt (1984). Discussions of a number of topics such as development, hair cell function and speech encoding are found in Berlin (1984).

A comparison of transtympanic and ear canal recorded electrocochleography in clinical practice

Electrocochleograms were recorded in a routine clinic on 21 patients by the transtympanic method and from a surface electrode in the ear canal. This was to determine whether a non-invasive technique would give the same clinical information as the normal transtympanic technique. Taking the transtympanic technique as the standard for comparison, the ear canal technique produced a significant number of errors in compound action potential threshold and width. The summating potential/compound action potential ratio could only be measured in just over half the ear canal recordings compared with the transtympanic recordings. From these results and a retrospective study of the notes looking at the effect of electrocochleography on diagnosis and management, it was concluded that the ear canal technique was not a substitute for transtympanic electrocochleography where the use of an invasive technique is justified.

Clinical application of non-invasive electrocochleography

Non-invasive extratympanic electrocochleography (ECochG) was performed in normal-hearing subjects and patients with sensorineural deafness. Action potential (AP) threshold, N1 input-output function, waveform, summating potential (SP) are presented. AP thresholds were within 15 dB in normal-hearing ears and within 30 dB in hearing-impaired ears above subjective thresholds for the click. Correlational analysis showed that click-evoked AP thresholds are best correlated to pure tone thresholds at 2 to 4 kHz. Four types of N1 input-output functions were classified. Normal functions appeared in moderate high tone loss only at 8 kHz and low tone loss with almost normal threshold above at 4 kHz. Many ears with a flat loss had recruiting responses, while many ears with a high tone loss had either dissociated responses or responses with prolonged latency. Several types of waveforms were distinguished. Enhanced--SP was observed in Meniére's disease and late congenital syphilis to which endolymphatic hydrops is common. The clinical value of the non-invasive ECochG is discussed.

Auditory nerve and brainstem responses in the newborn and in preschool children

The practicability of recording auditory nerve and brainstem responses during early childhood is demonstrated. This paper reports our experience with two different electrode locations: ear-canal/ear-lobe and ear-lobe/vertex. The test is performed with a light portable stimulus-generating and response-recording system that can easily be brought into wards and nurseries. In most instances, the presence of responses can be assessed using ear-lobe/vertex recordings. There is seldom any need for sedation or general anaesthesia. Testing personnel can be limited to one trained technician. If responses are not detected, ear-canal/ear-lobe recording may be used to clarify the results. General anaesthesia may then be necessary and the presence of a physician will be required for the placement of the canal electrode.

Noninvasive chronic recording of auditory nerve potentials

A system is described which allows repeated, noninvasive recording of auditory nerve responses in the cat to transient acoustic stimuli using a closed acoustic system. N1 responses to clicks are recorded from a stainless steel ring electrode at the end of a hollow earbar, the tapered end of which is made of insulating plastic. Acoustic stimuli are generated by a dynamic earphone coupled to the earbar. A calibrated probe microphone is also imcorporated into the earbar to measure sound pressure near the tympanic membrane. This allows better stimulus control than is available with free-field systems. To facilitate insertion of the earbar, meatoplasties were performed on all animals. Responses recorded with this system in anesthetized cats are described and compared with those recorded at the round window. Good repeatability of measurements is described for an animal population of 20 domestic cats over a period of several months. For some of these animals, response amplitude varied from one session to another, but response latency, especially for condensation clicks, was consistent. By comparing statistics of multiple measurement of both N1 amplitude and latency for rarefaction and condensation clicks, it is concluded that the N1 latency vs click-level function for condensation clicks provides the most reliable measure of the cat's auditory nerve function.

Transtympanic electrocochleography in patients with syphilis and hearing loss

Transtympanic electrocochleography was carried out on 18 syphilitic patients (30 ears were tested) most of whom were suffering from the late onset congenital form of the disease. A diphasic action potential with a large negative summating potential on the descending limb was found in 77.7% of ears; the cochlear microphonic potential was always of small amplitude. While these findings are not pathognomonic of syphilis, they are characteristic and may be explained on pathological grounds.

Extra-tympanic electrocochleography

A non-invasive technique for recording the cochlear action potential in adults without recourse to sedation or local anaesthesia is presented. This technique has been assessed in two ways: (1) A group of normal subjects was tested to obtain distributions of response amplitude and latency as functions of stimulus intensity. (2) A group of patients with Meniere's disease was tested with trans- and extra-tympanic electrocochleography to compare the intensity amplitude functions and wave-forms obtained from the two methods. On the basis of this study the use of extra-tympanic electrocochleography as a replacement for the trans-tympanic method is discussed.

Transtympanic electrocochleography in the diagnosis of retrocochlear tumours

Transtympanic electrocochleography has been used as a diagnostic procedure in over 250 adult patients with sensorineural deafness. No complications have been encountered. Among these patients vestibulocochlear Schwannoma (acoustic neuroma) has been confirmed in 56 ears while 11 other ears have been found to be affected by other space-occupying lesions. As a result of our observations in these patients, we would like to propose that there are at least three separate criteria to be considered in reaching or strongly suspecting a diagnosis of such pathology. These are broadening of the action potential (loss of P1), observation of a clear microphonic response, and preservation of the action potential even when using stimulus intensities which are not audible in the patients' affected ears. The merits of each of these criteria are discussed and compared with other clinical and operative findings. With the electrocochleographic techniques now employed in searching for acoustic neuromas, false negative results are rare though false positive results are still obtained.

Clinical application of auditory nerve responses recorded from the ear canal

The practicality of recording auditory nerve responses in the routine practice of an otologist is demonstrated. Such recordings are particularly useful when the course of treatment requires a distinction between central or peripheral disorders. They are also helpful when it is difficult to obtain a valid audiogram. The electrical recordings from the auditory nerve can, in combination with standard audiological, otological and neurological examinations, present a more accurate picture of the patient's condition.

Auditory-nerve potentials from ear canals of patients with otologic problems

Summary--The feasibility of making rountine measurements of human auditory-nerve potentials in an office environment is demonstrated. Using a portable device for stimulus generating and response recording, auditory-nerve potentials are recorded from subjects with normal and abnormal hearing by means of an electrode placed on the skin of the ear canal. The results can be compared with those of others obtained under laboratory conditions. Preliminary results indicate that in many instances, the nature of the hearing deficit is related to the latency and size of the click-evoked auditory-nerve potentials. The precise relationships between nerve responses and specific disease conditions are still difficult to formulate.