Science Spotlight: Electrode Insertion and Positioning

As the field of cochlear implants continues to advance, researchers and clinicians are increasingly focused on understanding the factors that influence performance outcomes. One critical area of investigation centers around electrode selection and the impact of electrode positioning within the cochlea on both short- and long-term results.

Recent trends in cochlear implant technology have introduced innovative approaches to reduce trauma during electrode insertion. These include techniques such as electrocochleography (ECochG), robotic-assisted insertion, drug delivery systems, and long-term histological studies of the cochlea.

Please take a moment to read this article which delves into the multifaceted impact of electrode insertion and positioning on cochlear health. Specifically, it explores how perimodiolar electrode placement can contribute to a lifetime of improved hearing performance.

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Cochlear Case Studies: Electrode selection

July 19, 2021

Cochlear Case Studies is a series on Cochlear ProNews that highlights relevant clinical and surgical scenarios surrounding the latest hearing industry topics and research. We’re excited to partner with professionals to highlight their experiences surrounding specific patients.

This first installment features five surgeons, their cases and contributing factors for use of different electrodes:

Use of Slim Straight Electrode with Dr. Daniel Zeitler

Daniel Zeitler, board-certified Otologist/Neurotologist and Skull Base Surgeon at Virginia Mason Medical Center in Seattle, presents a case where the patient had significant right-sided tinnitus along with extensive noise exposure for many years. Due to the inability to completely visualize nor access the round window, the surgeon determined that the silicone sheath of the CI632 would not fit in the small opening making the use of this electrode impossible. Fortunately, the CI622 had been ordered as backup, and the intraoperative decision was made to use the CI622 electrode instead due to its small diameter.

Use of Cochlear Nucleus® Profile™ Plus with Slim 20 Electrode with Dr. Marlan Hansen

Marlan Hansen, MD, is a Professor in the Departments of Otolaryngology-Head and Neck Surgery, Neurosurgery and Molecular Physiology and Biophysics. He presents a young adult male with hearing loss identified at age five. Dr. Hansen elected to use a Nucleus® Profile™ Plus with Slim 20 Electrode (CI624), as the patient presented with aidable low frequency hearing and there was a desire to preserve the structure of the cochlea while providing a full-length electrode option.

Use of Contour Advance Electrode with Dr. David Friedmann

David Friedmann, MD, MSc, is a neurotologist, cochlear implant surgeon and clinical investigator at NYU Grossman School of Medicine. He presented a middle-aged male with a long history of bilateral otosclerosis first diagnosed in his 20’s when he began wearing hearing aids. He chose to use Contour Advance™ (CI512) for the stiffness of the stylet and perimodiolar preference.

Benefit of cochlear implantation with use of Contour Advance® Electrode

Lisa Bell, AuD, and Sujana Chandrasekhar, MD, FACS, from ENT and Allergy Associates presented a middle-aged female with developmental delays. The Cochlear™ Nucleus® Profile™ with Contour Advance® Electrode (CI512) was selected for implantation due to the normal anatomy determined via pre-operative CT scan. Read more on the clinical and surgical perspective of this case.

CI632 trauma case with Dr. Sarah Mowry

Sarah Mowry, MD at University Hospitals, presented a 52-year-old male who had sustained direct head trauma after falling down a flight of stairs. She chose the CI632 for its perimodiolar position, MRI compatibility and slim profile to help minimize trauma in this already traumatized cochlea.

To hear more , listen to our Cochlear Case Studies surgeon panel webinar!

Clinical Programming Series: Impedances

August 7, 2024

Approximately 5 minutes to read
Learning objectives:
- Understand why and how impedances provide valuable clinical information
- Understand what factors impact impedances
- Understand how the clinician can use impedance measurements to determine the need for programming changes

Why are we talking about impedances?

As cochlear implant audiologists, the concept of impedances is integral to our clinical lexicon. Due to the growing interest in a more in-depth understanding of impedances, our clinical team has compiled a summary that delves into the science of impedances in cochlear implant care and outlines the essential information for programming cochlear implants.

What are impedances?

When electrical current flows in a conductor (in this case, the cochlea) there is a force that opposes the flow of the electrical current through the cochlea to the spiral ganglion cells. This is known as resistance. All materials naturally contain some resistance to the flow of an electrical current. Electrode impedances measures this resistance to the flow of electrical current from the cochlear implant electrode to the spiral ganglion cells.

Electrical impedance is calculated as the ratio of the applied voltage (driving force) to the resulting current that flows through the material or solution.

How does Cochlear calculate impedances?

Cochlear calculates the total impedance which includes the Polarization Impedance and the Access Impedance. Polarization Impedance looks at the electrode-electrolyte interface. Polarization impedances are caused by electrochemical effects at the electrode’s electrode-fluid interface. Access Impedance looks at the bulk material around the electrode. High access impedances are caused by the presence of fibrous tissue or new bone growth around the electrode array. To have an accurate understanding of the surface quality change of the electrodes, it’s necessary to assess both Access and Polarization Impedances. Total impedance offers the most complete picture of impedance and its effect on compliance, power requirements, and MAP parameters.

Impedance in a tissue-stimulating system is more complex than a simple material or solution due to the dynamic behavior of the electrode-tissue interface. Biological processes at a cellular level can change the electrode-tissue interface and therefore also affect the impedance of the system over time frames ranging from seconds to minutes to much longer periods.

Impedance measurements are included in Cochlear™ Nucleus® implants to perform three functions:

To confirm the integrity of the electrode contacts through detection of open and short circuits.
To ensure the map is set to maintain electrodes in compliance.
To provide some insight into the characteristics of the local environment around the electrode to assist with clinical management.

What factors can impact impedances?

Conditions unrelated to a patient’s hearing have been associated with changes in hearing outcomes or impedance. In these cases, it may take an extended time for clinicians to find out that a recipient is on contributing drug therapy since the recipient may not associate other health conditions with challenges in their hearing. Papers have associated impedance rises to Meniere’s disease and tinnitus¹, labyrinthitis², otitis media^{3, 4}, delayed hearing loss⁵, and episodes of vertigo^{2, 6}. In these instances, the impedance change is an indicator of some process that is happening in the inner ear.

There are reports involving bilateral recipients where impedances are seen to rise in a single ear¹, and others where the process involves both ears² suggesting a more systemic involvement. Interestingly one bilateral case with different model implants experienced increased impedance in both implants at the same time².

A number of papers report on the potential for pharmaceuticals to reduce electrode impedance. In one case treatment with cortisone, antibiotics and widening pulse widths resulted in impedances falling over 25 kohm to under 14 kohm within 24 hours².

Why is it important to monitor impedances?

Alterations in impedance can lead to reduced performance in patients. By managing these changes through medical intervention or by adjusting the pulse width, these issues can be addressed, resulting in optimization of the recipient’s programming.

How do we use this information clinically?

Regular measurement of electrode impedances is considered good clinical practice, typically performed at each programming session. For adults and children capable of providing feedback on their cochlear implant’s sound quality, routine monitoring of the impedance profile, alongside speech perception measures and other case information, constitutes a best management approach. This practice establishes a historical record of impedance measurements, facilitating correlation with additional recipient data collected over time. Should any electrodes fall out of compliance, it is common practice to increase the pulse width across the array to return these channels to compliance, rather than deactivating.

Additionally, electrode impedance measurements detect circumstances under which certain electrodes should not be used, such as open or short circuits. Since each electrode interacts with its local environment, impedances can vary from electrode to electrode across the array. An unexpected impedance pattern calls for a detailed review of the electrode impedance data in context with the recipient’s imaging, programming, medical history, and auditory performance.

Please reach out to your local Cochlear representative to learn more about what impedance measurements can tell you about your patient’s cochlear implant.

¹McNeill, A., & Eykamp, K. (2016). Cochlear Implant Impedance Fluctuation in Meniere’s Disease: A Case Study. Otology & Neurotology, 37(7), 873-877.

²Neuburger, J., Lenarz, T., Lesinski-Schiedat, A., & Büchner, A. (2009). Spontaneous increases in impedance following cochlear implantation: Suspected causes and management. International Journal of Audiology, 48(5), 233-239.

³Vargas, J.L., Sainz, M., Roldan, C., Alvarez, I., & Torre, A. (2012) Long-tern evolution of the electrical stimulation levels for cochlear implant patients. Clinical and Experimental Otorhinolaryngology, 5(4), 194-200.

⁴Dixon, J.F., Shinn, J.B., Adkins, M., Hardin, B.D., & Bush, M.L. (2015). Middle Ear Disease and Cochlear Implant Function: A Case Study. Hearing Balance and Communication, 12, 155-158.

⁵Scheperle, R.A., Tejani, V.D., Omtvedt, J.K., Brown, C.J., Abbas, P.J., Hansen, M.R., Gantz, B.J, Oleson, J.J, & Ozanne, M.V. (2017). Delayed changes in auditory status in cochlear implant users with preserved acoustic hearing. Hearing Research, 350, 45-57.

⁶Plontke, S.K., Götze, G., Rahne, T., & Liebau, A. (2017). Intracochlear drug delivery in combination with cochlear implants. HNO, 65, 19-28.