Electrically Evoked Stapedius Reflex Measurements in Cochlear Implantation and Its Application in the Postoperative Fitting Process

We are interested in improving the hearing performance of cochlear implants through optimizing fitting procedures and also through advanced speech coding strategies. And one particular focus of our research is to develop objective methods for the fitting of very young children from the age one to 10 years, and also for patients who are not able to provide feedback on electrical stimulation by the implant. Recently, we studied the influence of a delay in the stimulation by the cochlear implant in patients with single-sided deafness and in patients with bimodal hearing, and the effect was seen in the localization abilities.

Now results from that study led to the introduction of a new parameter in the speech coding protocol. The main experimental challenge is reducing the time consumptions when you are performing reliable tests in different age groups. And with that respect, also ergonomic aspects and ease of testing has to be taken into account.

And this is particularly important when they're testing children, because when working with children, time runs over short. The aim of our study was to develop a clinically feasible method for the objective fitting of proclaim plants. And the real challenge of all this work was to transfer results from basic research to clinical practice.

One interesting research question for the future will be to study the long-term development of cochlear implant fitting parameters and hearing performance. This is particularly interesting also for the development of children when they start here with the implant for the first time in their life. To begin, cover the patient with surgical drapes at the implant coil site.

On the cochlear implant or CI manufacturer software, add the patient data to perform in package tests on the implant as suggested by the manufacturer. After inserting the CI electrode array into the cochlea of the anesthetized patient, place the measurement coil of the CI manufacturer in sterile packaging. While the surgeon places the measurement coil on the patient's skin over the implant housing, check the coupling between the measurement coil and the implant.

Then, click on the program tab IFT to verify the proper functioning of the implant. And to measure the telemetric electrical impedances of all CI electrodes. Select the program tab ESRT to initiate stimulation at moderate values while the surgeon observes the stapedius tendon under an operating microscope.

Deliver single stimuli with a burst duration of approximately 500 to 700 milliseconds and monitor for any stapedial tendon movement. Once the maximum allowed stimulation intensity is reached, stop increasing stimulation. After discussing the eSRT testing procedure with the patient, perform tympanometry to verify the normal status of the middle ear, showing regular compliance at zero pressure indicative of Type A tympanogram.

Ensure the patient is sitting comfortably for measurements taken while awake. Place the audio processor and its coil in the proper position and check coupling with the patient's implant. Using a single use ear tip, place the ear probe of the acoustic impedance meter in the ear canal of the patient.

Then, fasten the probe cable to the patient's head to reduce acoustic interference. After starting the CI fitting software in normal fitting mode, load the programming of the CI currently in use by the patient. Use electrical stimulation bursts for at least 300 milliseconds duration, followed by a pause of 700 milliseconds.

Select an electrode in the middle of the electrode array and start stimulation at a moderate loudness level. If an ESR is detected by a change in acoustic impedance in response to the stimulation, reduce the stimulation level further. Gradually increase the stimulation level in 3%steps until a change is detected in acoustic impedance.

Carefully observe the patient to avoid uncomfortable loudness. Upon first observation of the ESR, increase the stimulation intensity by a further 3%step and then decrease it until the ESR is no longer detected. Record the lowest stimulation levels that trigger the ESR in both the increasing and decreasing sequences.

Bilateral cochlear implant users showed improved hearing with eSRT-based programming, achieving similar hearing thresholds across ears indicating high hearing symmetry. The aided hearing thresholds on the left and right sides are almost symmetrical, whereas the eSRT-based stimulation levels show a large asymmetry between the left and right ears. A case study for sound localization demonstrated nearly perfect sound localization symmetry for broadband acoustic stimuli at high percentages, showcasing no bias.