Otolaryngology Researchers Develop New Approach to Improve Efficacy of Cochlear Implantation

A team of researchers in the Department of Otolaryngology led by Suhrud M. Rajguru, Ph.D., assistant professor of biomedical engineering and otolaryngology, has developed a novel system for delivering therapeutic hypothermia locally to the inner ear in an animal model to conserve residual hearing following cochlear implant surgical trauma. Their approach has the potential to ensure that the sensory structures in the cochlea are left undamaged, enabling patients to benefit from future technologies and therapies.

Rajguru and his colleagues reported on the safety and efficacy of the procedure in a recently published article, “A Cool Approach to Reducing Electrode-Induced Trauma: Localized Therapeutic Hypothermia Conserves Residual Hearing in Cochlear Implantation,” in the journal Hearing Research.

During cochlear implantation, trauma can lead to cell death and a loss of residual hair cells in the cochlea. While various therapeutic approaches have been studied to prevent implant-induced residual hearing loss, they have shown limited success.

“Long-term preservation of a patient’s residual hearing and sensitive neural structures post-implantation is critical,” said Rajguru. “We knew that mild therapeutic hypothermia, exposing nerve cells to low temperatures after trauma and injury, could protect them from damage.”

To develop a device to deliver hypothermia that does not require any modifications to the cochlear implant or the surgical procedure, Rajguru and Ilmar Tamames, a doctoral student in his lab, collaborated with Lucent Medical Systems and other Miller School researchers. Once the technology was created, they tested the “cool approach” by delivering localized hypothermia to the middle turn of the cochlea in animal models for 20 minutes before and after implantation using a custom-designed probe perfused with cooled fluorocarbon.

Auditory brainstem responses were recorded to assess the hearing function before and after cochlear implantation, up to 30 days following the procedure. At the conclusion of the trials, inner ears were harvested for histology and cell count. The team discovered a significant loss of residual hearing in the normothermic implant group. By contrast, the residual hearing in the cochleae receiving therapeutic hypothermia was significantly conserved. Histology confirmed a significant loss of outer hair cells in normothermic cochleae receiving the surgical trauma when compared to the hypothermia treated group.

To test the potential for clinical translation, the approach was extended to cadaver temporal bones to study the potential surgical approach and efficacy of the device. In this case, the hypothermia probe was placed next to the round window niche via the facial recess or a myringotomy.

“We successfully achieved a controlled and effective cooling of the cochleae using our approach,” Rajguru said.

These results suggest that therapeutic hypothermia during cochlear implantation may reduce traumatic effects of electrode insertion and improve conservation of residual hearing, and can be extended to all inner ear related surgeries.

“Conservation of residual hearing and reduction trauma has always been an important goal during inner ear surgeries, especially during cochlear implantation,” said Rajguru. “Patients with residual hearing are now being implanted to take advantage of bimodal electroacoustic stimulation.”

The Food and Drug Administration-approved indications for cochlear implantation now permit bilateral implants in young children in whom residual hearing levels are difficult to ascertain. In recent years, novel electrode designs have improved efficiency and performance by locating stimulation sites closer to spiral ganglion neurons and deeper into the scala tympani. Looking ahead, the number of recipients with some degree of usable hearing is likely to increase.

The current approach, using hypothermia therapy to reduce inflammation and oxidative stress leading to neural degeneration, hair cell loss and loss of residual hearing, can potentially provide significant benefits to these patients. Funded by grants from the NIH National Institute on Deafness and Other Communication Disorders, the team is developing a hypothermia device for humans and to determine the mechanisms by which hypothermia therapy protects the inner ear sensory cells.

The UHealth Ear Institute, part of the Department of Otolaryngology, in collaboration with the Barton G Kids Hear Now Foundation Cochlear Implant Family Resource Center, is one of the busiest programs in the country for placing cochlear implants in adults and children with severe to profound hearing loss, and is a leader in cochlear implant research.

“Dr. Rajguru has applied hypothermia cooling to the inner ear and found good evidence to suggest that this method of organ preservation can help us to preserve residual hearing during cochlear implantation of deaf patients,” said Fred F. Telischi, M.D., professor and James R. Chandler Chair of Otolaryngology. “We are also finding that these auditory implant devices have potential for patients with an expanded range of hearing loss, even those with significant natural residual hearing. Dr. Rajguru’s innovative research is one of many strategies under investigation at the UM Ear Institute to accomplish this important goal.”

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