Optimizing the Simultaneous Recording of Electrocochleography and Auditory Brainstem Response Measurements

In 1998, I was doing my clinical fellowship year (CFY) at Henry Ford Hospital. During this time, I was also a PhD student at The Ohio State University, where I was learning about auditory electrophysiology. As a student clinician, of course, there is so much you are trying to learn all at once and it can seem overwhelming.

Electrophysiology was the focus area for my doctoral research and I was very excited to learn from Gary Jacobson, who was the director at Henry Ford Hospital at the time and had a background in auditory evoked potentials (EPs). One of the auditory EPs that we were responsible for recording was electrocochleography (EcochG)

Now, when one reads about how to record an EcochG, it seems straightforward and easy to interpret. The seminal auditory textbooks at the time (e.g., Hall and Jacobson) would show illustrations of beautifully robust and clear EcochG waveforms. As a student, you would look at them and say to yourself “how hard can that be.” Well, come to find out, it can be, in some instances, very hard to record a clear and robust EcochG.

After working in the area of clinical auditory electrophysiology for 20+ years, I have come to realize that there are two big factors that play a role in how well your EcochG recording is going to go. First, the amount of hearing loss is going to have a big effect and, second, the type (and correct placement) of the electrode you use will also have an effect.

For the first factor (hearing loss), it is incumbent upon the clinician to understand how the degree and shape of hearing loss will alter the morphology and threshold of the responses. The second factor, however, is completely under the control of the clinician and (assuming the recording and stimulating parameters are optimal) will play a crucial role in obtaining measurable responses and correct interpretation.

When I was learning to record EcochGs during my CFY, Gary Jacobson showed up in the EP laboratory with a fishing tackle box. Inside this tackle box was all sorts of teflon-coated silver wire, old cup electrodes, otoblocks, a soldering iron, and an impedance meter.

Sadly, Gary did not take me fishing that day. Instead, I learned to make my own EcochG electrodes that we would use in clinic. This electrode-manufacturing skill is not taught in many audiology programs today (at least that I know of) and represents somewhat of a lost art in audiology.

The EcochG really began as a way to evaluate patients who presented with symptoms of Meniere's disease and to enhance the Wave I on an auditory brainstem response (ABR) when there was a fair bit of high-frequency hearing loss. What has happened more recently is that new applications have been set forth for the response. For example, Paul Kileny and his colleagues here at the University of Michigan described how to use EcochG to evaluate those patients with superior semicircular canal dehiscence. Other groups have shown its clinical utility in investigating suspected cochlear synaptopathy.

In this issue of the Journal of the American Academy of Audiology, we revisit the age-old skill of making homemade electrodes and compare the performance with two other extratympanics, including commercially available Lilly TM-Wick Electrodes and TipTrodes. Lefler, Kar, and Ferraro evaluated several different EcochG response measurements such as the SP/AP amplitude ratio, SP/AP area ratio, and AP amplitude, among others. The results from the study are heavily weighted in favor of two of the electrodes and may warrant those of us recording EcochGs to go buy a fishing tackle box.

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Artikel online veröffentlicht:
03. November 2021