Cochlear Implant

What is a Cochlear Implant?

Cochlear implants are medical devices that are used to give deaf or severely hard-of-hearing people a sense of sound. They consist of an external portion that sits on the wearer’s ear as well as a surgical implant under the skin. A microphone on the devices picks up audio signals and the transmitter on the device converts these signals to electrical impulses which directly stimulate the auditory nerve, unlike hearing aids which simply amplify sounds. Cochlear implants are most often used by adults with hearing loss who have not had success with hearing aids or by children who are deaf or severely hard of hearing as cochlear implants have been found to assist in the development of speech and language skills. [1]

Deafness and Hearing Loss

The World Health Organization has reported that about 466 million people (over 5% of the world’s population) have disabling hearing loss and 34 million of these are children. [2] Hearing loss has a wide variety of potential causes which can be either congenital or acquired throughout ones life.

Congenital causes:

• maternal rubella, syphilis, or another infection during pregnancy
• low birth weight
• birth asphyxia
• inappropriate use of aminoglycoside, cytotic drugs, antimalarial drugs, and diuretics during pregnancy
• severe neonatal jaundice

Acquired causes:

• diseases such as meningitis, measles, and mumps
• chronic ear infections
• otitis media
• use of medicines for neonatal infections, malaria, tuberculosis, or cancers
• head or ear injury
• excessive noise
• degeneration of sensory cells due to aging
• foreign bodies or wax blocking the ear canal

Qualifications for Cochlear Implants

Not all cases of hearing loss necessitate a cochlear implant and not everyone qualifies for one. Some of the qualifications for eligibility for a cochlear implant include:

• moderate to profound sensorineural hearing loss in both ears
• limited benefit from a hearing aid defined by test scores of less than or equal to 50% sentence recognition in the ear to be implanted and less than or equal to 60% in the opposite ear [3]

Surgery

Cochlear implant surgery is a routinely done surgery which requires general anesthesia. The surgery requires a small incision to be made behind the ear, which is later closed by resorbable sutures. Most patients are able to return to their normal routine within a few days of surgery, but the implant is not turned on until 3-4 weeks after surgery when the area has fully healed. A cochlear implant, however, does not restore the patient to normal hearing. It takes time and practice with speaking and listening for the patient to adapt to their new hearing and sometimes the assistance of a therapist is needed. [4]

Current Cochlear Implant Devices

3 major companies currently produce cochlear implants: Advanced Bionics, Cochlear Corporation, and Med-El.

Advanced Bionics HiRes™ Ultra 3D Cochlear implant

Cochlear Corporation’s Nucleus® Profile™ Plus Implant

Med-El’s Synchrony 2 Cochlear implant

 

Alternative Devices

While cochlear implants are the most common type of implant used to treat severe hearing loss or profound deafness, there are a couple of alternative implantable devices available.

The first alternative implant option is a Middle Ear Implant, or an MEI. This device is useful in patients with mild to severe hearing loss who have not benefitted from traditional hearing aids.  The MEI is implanted into the middle ear and works by transmitting sounds directly to the cochlea. The number of manufacturers of this device is comparable to the cochlear implant. The three most prominent manufacturers in the world currently are Med-El with the Vibrant Soundbridge, Cochlear Ltd. with the Carina MEI, and Medtronic which offers several different MEI devices. The Middle Ear Implant was first introduced in the 1930s, approximately 20 years before the cochlear implant was created. [5]

 

Middle Ear Implant

The ABI is another popular implantable device used for hearing loss. This device is only suitable for people who are not able to benefit from a cochlear implant due to auditory nerve damage. Where a cochlear implant bypasses the cochlea and transmits signals to the auditory nerve, the ABI bypasses both the cochlea and the auditory nerve. It is implanted directly into the brainstem so it requires a very complex operation and long recovery period, making the cochlear implant a more desirable option when damage to the auditory nerve is not present. Manufacturers of this device are much more limited than those of the Cochlear Implant and the Middle Ear Implant, this is because auditory nerve damage of the level needed to justify this device is fairly rare, and it requires a much more specialized production process. The main manufacturer of the ABI currently is Oticon Medical’s Digisonic ABI. This is the newest technology of the three devices discussed in this article, with production beginning in the 1970s. [6]

 

Auditory Brainstem Implant

Clinical Studies

Since cochlear implant surgery is most often done in deaf children at only a few months old and adults with profound hearing loss, it is important to evaluate the effectiveness of cochlear implants separately on each of these widely different age groups.

One clinical study evaluated the long term cognitive function of profoundly deaf adults with cochlear implants since mild cognitive impairment (MCI) is a significant problem for older adults with hearing loss. In the study, only 6% of patients with MCI prior to implantation developed dementia and 32% were able to return to normal cognition while the remainder stayed in stable condition. Of patients without MCI prior to implantation, 32% developed MCI but none developed dementia in the 5.5-8.5 years following surgery. [7]

Another study evaluated the correlation between the development of spoken language skills and the age of implantation in children. The study found that children implanted at 5‐11 months reached an age‐equivalent level of language understanding and better vocabulary outcome sooner than those implanted at 12-29 months. It concluded that cochlear implant surgery was safe at ages even earlier than 9 months and that implantation at a younger age may reduce the negative effects of auditory deprivation and promote more natural language development. [8]

Advantages and Disadvantages

Advantage as well as disadvantage about the cochlear implants with helping school-aged kids recognize emotion using the EmoHI test. Researches from the UK and the Netherlands conducted EmoHI test on 58 Dutch and 25 English kids. The EmoHI test is used to test the three core emotions (Happy, angry, and sad). When this test was conducted on normal hearing patients age ranging from 4-6 years old there was a 48.9% average of correctly identifying the emotions protracted by the speaker. The age group of 10-12 years-old had an average of 81.1% of identifying the correct emotion. The study goes on to say with children with normal hearing as their age increases so does their comprehension of emotion. However, children with Cochlear implants show no correlation to their age concerning the understating of emotions. The researchers go on to say that there was a range with the children’s test of 97.2-27.8 % comprehension of emotions with the cochlear implants. However, more than half of the children performed accordingly to their respective age groups. This shows that with the use of a cochlear implant children can understand emotions but at a limited capacity. [9]

One of the disadvantages of a cochlear implant is the microphone’s ability to clearly pick up the attended audience in different environments. A study was done by Chung King about the perceived sound quality of different signal processing algorithms cochlear implant listeners in real-world environments. The study conducted by King used 16 participants in three different environments.  For each of the 16 participants there were three different settings they could choose from and the participants would rate the ease of listening, the ability to understanding speech, and listening comfort on a scale from -100 to 100. The three different modes of the cochlear implants were no noise reduction with an omnidirectional microphone, moderate noise reduction with a combination of omnidirectional and adaptive directional microphones, and the last one is maximum noise reduction with adaptive directional microphones. From this study in a quiet location (hotel lobby) the omnidirectional microphone with no noise reduction produced the best result from the three different models tested. When the environment changed to a more busy and crowded place ( Noisy café and a Noisy restaurant ) so did the preference of the participants to the moderate noise reduction with a combination of omnidirectional and adaptive directional microphones as the preferred mode in this environment. This is a disadvantage to cochlear implants because there is not always a fixed solution to a problem in what types of programming and microphones to use. [10]

One of the advantages of cochlear implantation is that cochlear implantation can be done in young children. The study looks at the safety and effectiveness of cochlear implantation of young children including those with complicating conditions.  The study used 219 participants with the participants divided up into two age groups below 12 months old and 12-36 months old. The group of children’s with cochlear implants implanted under 12 months old, would start to use oral-only communication between the ages of 3.3 and 4.3 years at 88.2%. The group of children between 23-36 with cochlear implantation shows an increase of time 8.3-35% time delay before they started oral-only communication at 48.8% of the children using oral communication only. The study ends with saying that children under 37 months old can safely have cochlear implants implanted as well as children under 12 months old. The study then goes on to say that children that had the implant implanted under the age of 24 months would be more likely to use oral-only communication. [11]

Market

The market for cochlear implants is growing and is estimated to be worth $3.4 billion by 2026. The rise in demand for cochlear implants can be attributed to increased awareness of implantable hearing devices as well as technological improvements that have made devices more “efficient and user-friendly”. So far, the majority of implants have been unilateral, or only in one ear, because it is a more cost-effective option, but bilateral implantation has been increasing for its ability to help wearers, “recognize speech in noise”. There is also an increase in programs and government support for implanting cochlear devices in children at an early age so that they can readily adapt to the device and successfully recognize and interpret speech. [12] Despite the growing market, there is still a lack of awareness surrounding cochlear implants. Some healthcare providers were not informed about cochlear implants during their education and others simply aren’t trained in identifying and referring people who could be possible candidates. Awareness should increase as more and more people receive cochlear implants and further studies are conducted to evaluate their effectiveness. [13]

Resources

[1] “Cochlear Implants,” National Institute of Deafness and Other Communication Disorders, 14-Apr-2020. [Online]. Available: https://www.nidcd.nih.gov/health/cochlear-implants#c. [Accessed: 17-Apr-2020].

[2] “Deafness and hearing loss,” World Health Organization. [Online]. Available: https://www.who.int/news-room/fact-sheets/detail/deafness-and-hearing-loss. [Accessed: 22-Apr-2020].

[3] “Cochlear Implant Candidacy Information,” Cochlear, 03-Oct-2020. [Online]. Available: https://www.cochlear.com/us/en/professionals/products/cochlear-implants/candidacy. [Accessed: 22-Apr-2020].

[4] “Cochlear implant surgery,” Cochlear, 03-Oct-2020. [Online]. Available: https://www.cochlear.com/us/en/home/diagnosis-and-treatment/implant-preparation-and-procedures/cochlear-implant-surgery. [Accessed: 17-Apr-2020].

[5] “Middle Ear Implants: Bridging Sound Barriers,” Clarity Hearing Solutions. [Online]. Available: https://clarityhearingsolutions.com.au/implants/middle-ear-implants/. [Accessed: 23-Apr-2020].

[6] “Auditory brainstem implant,” Mayo Clinic, 19-Feb-2019. [Online]. Available: https://www.mayoclinic.org/tests-procedures/auditory-brainstem-implant/about/pac-20384649. [Accessed: 17-Apr-2020].

[7] Mosnier, I., Vanier, A., Bonnard, D., Lina‐Granade, G., Truy, E., Bordure, P., Godey, B., Marx, M., Lescanne, E., Venail, F., Poncet, C., Sterkers, O. and Belmin, J. (2018), Long‐Term Cognitive Prognosis of Profoundly Deaf Older Adults After Hearing Rehabilitation Using Cochlear Implants. J Am Geriatr Soc, 66: 1553-1561. doi:10.1111/jgs.15445

[8] Karltorp, E, Eklöf, M, Östlund, E, Asp, F, Tideholm, B, Löfkvist, U. Cochlear implants before 9 months of age led to more natural spoken language development without increased surgical risks. Acta Paediatr. 2020; 109: 332– 341. https://doi.org/10.1111/apa.14954

[9] Leanne, N., Etienne, G., Deborah, V., Marta Matos, L., Petra, H., & Deniz, B. (2020, April 2). Development of vocal emotion recognition in school-age children: The EmoHI test for hearing-impaired populations. Retrieved April 10, 2020, from https://apps-webofknowledge-com.prox.lib.ncsu.edu/full_record.do?product=WOS

[10] Chung, K. (2020, January/February). Perceived sound quality of different signal processing algorithms by cochlear implant listeners in real-world acoustic environments. Retrieved April 10, 2020, from https://www-sciencedirect-com.prox.lib.ncsu.edu/science/article/pii/S0021992419300814?via=ihub

[11] Hoff, S., Ryan, M., Thomas, D., Tournis, E., Kenny, H., Hajduk, J., & Young, N. M. (2019, April). Shibboleth -Safety and Effectiveness of Cochlear Implantation of Young Children, Including Those With Complicating Conditions. Retrieved April 10, 2020, from https://www-ncbi-nlm-nih-gov.prox.lib.ncsu.edu/pmc/articles/PMC6426352/

[12] “Cochlear Implants Market Size Worth $3.4 Billion By 2026: CAGR: 10.5%,” Market Research Reports & Consulting. [Online]. Available: https://www.grandviewresearch.com/press-release/global-cochlear-implants-market. [Accessed: 17-Apr-2020].

[13] D. L. Sorkin, “Cochlear implantation in the world’s largest medical device market: utilization and awareness of cochlear implants in the United States,” Cochlear implants international, Mar-2013. [Online]. Available: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3663290/. [Accessed: 17-Apr-2020].

FINAL VERSION