Clinical application of non-invasive electrocochleography

Computational modeling of the human compound action potential

The auditory nerve (AN) compound action potential (CAP) is an important tool for assessing auditory disorders and monitoring the health of the auditory periphery during surgical procedures. The CAP has been mathematically conceptualized as the convolution of a unit response (UR) waveform with the firing rate of a population of AN fibers. Here, an approach for predicting experimentally recorded CAPs in humans is proposed, which involves the use of human-based computational models to simulate AN activity. CAPs elicited by clicks, chirps, and amplitude-modulated carriers were simulated and compared with empirically recorded CAPs from human subjects. In addition, narrowband CAPs derived from noise-masked clicks and tone bursts were simulated. Many morphological, temporal, and spectral aspects of human CAPs were captured by the simulations for all stimuli tested. These findings support the use of model simulations of the human CAP to refine existing human-based models of the auditory periphery, aid in the design and analysis of auditory experiments, and predict the effects of hearing loss, synaptopathy, and other auditory disorders on the human CAP.

The role of summating potential in the diagnosis and management of Menière's disease

To assess the role of a negative summating potential (-SP) in the clinical diagnosis and management of Menière's disease, the relationship of -SP abnormality to clinical symptoms, hearing level and caloric test results was examined in 70 patients with unilateral Meniere's disease. The click-induced -SP and action potential (AP) were recorded by extratympanic electrocochleography. When SP/AP ratio exceeded 0.43, the -SP was considered to be abnormal. No significant relationship was found between abnormal -SP and clinical symptoms (the duration of cochlear and vestibular symptoms, recent hearing fluctuation and recent vertigo attack). Ears with abnormal -SP had a significantly worse hearing loss at high frequencies (2-8 kHz) than ears with normal -SP, whereas there was no significant difference in hearing loss at low frequencies (0.25-1 kHz) between both ears. No significant relation was found between abnormal -SP and abnormal unilateral weakness in caloric test. The results indicate that the click-induced -SP reflects the pathophysiology of Menière's disease basically in the cochlear partition at high frequencies.

Change in the summating potential and action potential during the fluctuation of hearing in Ménière's disease

Summating potential (SP) and action potential (AP) were monitored by extratympanic electrocochleography (ECoG) during the fluctuation of hearing in 8 patients with Ménière's disease. The relationship of SP and AP parameters to pure-tone hearing threshold level was examined. The correlational analysis revealed the following: AP amplitude decreases with increase in the hearing threshold level at higher frequencies (2-8 kHz), whereas it alters independently of the change in the hearing threshold level at lower frequencies (0.25-1 kHz). -SP amplitude is unchanged irrespective of changes in the hearing threshold level at any frequency. The ratio of -SP to AP amplitude increases with increase in the hearing threshold level at higher frequencies (2-8 kHz), whereas it alters independently of the change in the hearing threshold level at lower frequencies (0.25-1 kHz).

Prolonged electrode implantation in experimental studies. Critical evaluation of a technique

Stainless steel electrodes were chronically implanted through the right facial canal of 30 guinea pigs, close to the potential generator (VIII nerve). Compound action potential (CAP) thresholds, N1 latencies and input-output curves were recorded on day of implantation and 2, 4 and 8-12 weeks later. In the same sitting, auditory evoked brain stem response (ABR) thresholds, latencies and inter-peak-latencies were measured on both sides as a control. N1 thresholds and latencies at low and high intensities were stable. N1 amplitudes, however, showed some variation. Rate of infection was low and reimplantation was successful. Preserving the facial nerve as a land mark was found advantageous, particularly on reimplantation, and did not affect the CAP recording. The technique, originally described by Hildesheimer et al., proved to be reproducible. A few technical difficulties are pointed out and the implication of some interesting findings are discussed.

The relationship of SP and AP findings to hearing level in Menière's disease

The relationship of summating potential (SP) and action potential (AP) to hearing threshold level was examined in 46 patients with a unilateral Ménière's disease. The SP and AP were recorded with the extratympanic method. The ratio of -SP and AP amplitudes in affected ears to those in contralateral ears (-SP and AP amplitude ratio) at 80 dB nHL of click stimuli was used as parameters of analysis in order to diminish the variability of SP and AP amplitudes among individuals. The results revealed that there is no relationship between -SP amplitude ratio and the hearing threshold level at any frequency, whereas AP amplitude ratio has a significant negative correlation (r = -0.419, p less than 0.01) to the average hearing threshold level at 2-8 kHz, but not at 0.25-1 kHz (p greater than 0.05). The results indicate that an increase in the ratio of -SP amplitude to AP amplitude with the deterioration of the hearing at higher frequencies reported by our previous study (Mori et al., 1987) results from a decrease in AP amplitude rather than an increase in -SP amplitude. The dependence of AP amplitude on hearing threshold level and the independence of -SP amplitude on hearing threshold level suggests that the mechanism underlying the increase in -SP amplitude may be different from that causing the hearing loss in Ménière's disease.

Auditory brainstem responses and extratympanic electrocochleography. A threshold comparison in children

Electrocochleography (ECoG) and auditory brainstem response (ABR) have been recorded simultaneously in 23 children referred for threshold evaluation. The ECoG electrode is an extratympanic silver ball (Life-Tech) whereas the ABR is recorded with Ag-AgCl surface electrodes. Of the 30 ears investigated according to this protocol, 11 had no response with either technique, and in a further 11 no difference was found between ECoG and ABR thresholds. In the remaining 8 ears, ABR threshold was lower in 6 and the ECoG in 2. We conclude that the extra time needed for cleansing the ear canal and inserting the electrode does not justify the use of ECoG in threshold evaluations, since the ABR alone has the necessary sensitivity.

Comparison between electrocochleography and glycerol test in the diagnosis of Meniere's disease

Electrocochleography (ECoG) and glycerol test were performed in 51 Meniere ears. The positive rate of both tests was compared. The positive rate of ECoG and glycerol test was 63% and 51%, respectively. The ears with positive result of both tests and of either test were 15 of 51 ears (29%) and 43 of 51 ears (84%), respectively. The positive rate of ECoG was higher in ears with a moderate to severe hearing loss at high frequencies, while the positive rate of glycerol test was higher in ears with a moderate to severe hearing loss at low frequencies. The present study has demonstrated that ECoG is different in selectivity of detection of the endolymphatic hydrops from glycerol test and that the combination of both tests increases the detection rate of the endolymphatic hydrops in Meniere's disease.

Comparison between AP and SP parameters in trans- and extratympanic electrocochleography

Results of the comparison of action potential (AP) and summating potential (SP) parameters in trans- (TT) and extratympanic (ET) methods in 2 normal-hearing ears and 20 hearing-impaired ears with various etiologies and audiogram shapes are reported. In normal and impaired ears the TT/ET ratio of N1 amplitude was intensity dependent and was greater at higher intensities than at lower intensities. N1 latency was identical in both methods. The AP waveform was almost identical in both methods in ears except in a noise-induced hearing loss: N1/N2 ratio was greater in the TT method than in the ET method. In the TT method +SP at high frequency tone bursts and -SP at low frequency tone burst were recorded in Menière's disease and progressive sensorineural hearing loss, while in the ET method only -SP was recorded at a tone burst of each frequency. Origins of N1 and N2 and a clinical value of -SP and +SP are discussed.