Transtympanic versus tympanic membrane electrocochleography in examining cochleovestibular disorders

Human Summating Potential Using Continuous Loop Averaging Deconvolution: Response Amplitudes Vary with Tone Burst Repetition Rate and Duration

Electrocochleography (ECochG) to high repetition rate tone bursts may have advantages over ECochG to clicks with standard slow rates. Tone burst stimuli presented at a high repetition rate may enhance summating potential (SP) measurements by reducing neural contributions resulting from neural adaptation to high stimulus repetition rates. To allow for the analysis of the complex ECochG responses to high rates, we deconvolved responses using the Continuous Loop Averaging Deconvolution (CLAD) technique. We examined the effect of high stimulus repetition rate and stimulus duration on SP amplitude measurements made with extratympanic ECochG to tone bursts in 20 adult females with normal hearing. We used 500 and 2,000 Hz tone bursts of various stimulus durations (12, 6, 3 ms) and repetition rates (five rates ranging from 7.1 to 234.38/s). A within-subject repeated measures (rate x duration) analysis of variance was conducted. We found that, for both 500 and 2,000 Hz stimuli, the mean deconvolved SP amplitudes were larger at faster repetition rates (58.59 and 97.66/s) compared to slower repetition rates (7.1 and 19.53/s), and larger at shorter stimulus duration compared longer stimulus duration. Our concluding hypothesis is that large SP amplitude to short duration stimuli may originate primarily from neural excitation, and large SP amplitudes to long duration, fast repetition rate stimuli may originate from hair cell responses. While the hair cell or neural origins of the SP to various stimulus parameters remains to be validated, our results nevertheless provide normative data as a step toward applying the CLAD technique to understanding diseased ears.

Non-invasive Wet Electrocochleography

To detect electrocochleographic (ECochG) potentials generated by the cochlea in response to auditory stimuli, either transtympanic or tympanic/extratympanic electrodes are currently used. The first are invasive, while the second are arranged in contact or very close to the tympanic membrane (TM). To avoid the discomfort and the risks inherent to the application of such conventional electrodes, this Letter presents an alternative technique. A conducting liquid is inserted into the ear canal to act as a distributed electrical interface between the TM and an external electrode. Thus, ECochG potentials are detected without any direct contact between the solid electrode and the sensitive TM. This technique was tested on ten volunteers with single-click auditory stimuli. Results showed its efficacy to noninvasively detect useful ECochG responses, with accurate morphology and significant amplitude. The technique is comfortable, sedation/anesthesia-free, inherently safe, and easy to perform. It also favors improvements of contact stability, reductions of contact impedance, and relative tolerance to misplacements. As a contraindication, the liquid prevents use on subjects affected by tympanic perforation. All these features encourage further investigations on this technique as a possible additional tool for the ECochG practice.

The effects of high stimulus rate on the electrocochleogram in normal-hearing subjects

The use of high stimulus rates has the potential to improve the electrocochleogram's (ECochG) sensitivity and specificity in endolymphatic hydrops and Menière's disease, but is currently hindered by the absence of an acceptable normative database. In response, this study recorded click-evoked ECochG tracings from 51 normal-hearing subjects (102 ears), between 18 and 60 years of age, at 7.1, 51.1, 101.1 and 151.1 clicks/s using a tympanic membrane electrode. As stimulus rate increased, various statistically significant (p < 0.05) changes were observed. In general, summating potential (SP) latency and amplitude and action potential (AP) latency increased, SP/AP amplitude ratio and waveform width increased but then plateaued, and AP amplitude fluctuated. While providing the largest contribution to a high-stimulus-rate ECochG normative database published to date, potential clinical limitations were identified and a possible solution proposed.