07 Cochlear Implants

Question 1

Cochlear implant is the only device covering a specific area of the hearing map, what area is this?

Answer 1

profound hearing loss or complete deafness originating from the cochlea (sensorineural)

Question 2

what is tonotopy and why is it essential for cochlear implants?

Answer 2

tonotopy is the mapping between frequency and spatial position (in the cochlea). In profound hearing loss, frequency specific hearing is impaired, and the cochlear implant uses the tonotopy concept to restore hearing.

Question 3

What is the formula used by Greenwood to describe the tonotopy in the cochlea?

Answer 3

The formula correlates x distance from the round window with the anatomic location of hair cells and is valid for other species with adjusted constant values.

Question 4

What is a cochlear implant (CI)?

Answer 4

A cochlear implant (CI) is a surgically implanted neuroprosthetic device that provides individuals with moderate to profound sensorineural hearing loss a modified sense of sound.

Question 5

How does a cochlear implant function?

Answer 5

A cochlear implant bypasses the normal acoustic hearing process and replaces it with electric signals that directly stimulate the auditory nerve.

Question 6

What are the main components of a cochlear implant system?

Answer 6

The cochlear implant system consists of an external audioprocessor and an internal stimulator.

Question 7

What are the components of the external audioprocessor and what role do they play in a cochlear implant?

Answer 7

The external audioprocessor has properties similar to a conventional hearing aid; it contains:
- microphone: captures sound
- sound processor: processes sound and converts into digital signals
- transmitter coil: sends processed signals to internal implant (via radio frequency signals)

Question 8

What are the components of the internal stimulator and what role do they play in a cochlear implant?

Answer 8

• receiver antenna: receives digital signals from transmitter and converts them to electrical impulses
• electrode array: collects the impulses and sends them to the auditory nerve

Question 9

Up to how many electrode-cochlear duct contacts are there? what is the consequence for the frequency sensitivity?

Answer 9

up to 22 -> much lower frequency sensitivity (just like playing a piano with gloves)

It does maintin tonotopy (electrodes at the base are stimulated by high frequencies; apex by low frequencies)

Question 10

What configurations can be used in signal processing of cochlear implants?

Answer 10

Signal processing can use either monopolar or bipolar configurations for stimulation.

Question 11

What is monopolar stimulation in cochlear implants?

Answer 11

Monopolar stimulation involves the return of current to a distant extracochlear return electrode. The monopolar stimulation is preferred.

Question 12

What is bipolar stimulation in cochlear implants?

Answer 12

Bipolar stimulation involves current flowing between adjacent intracochlear electrodes.

Question 13

how is the transmitter coil attached to the head?

Answer 13

Magnetic attachment

Question 14

What is the role of a ground electrode in cochlear implants and where can it be located?

Answer 14

A ground electrode can be located on the implant or extracochlear. It is used to complete the electric circuit (together with the intracochlear electrode) stimulating auditory nerve/spiral ganglions.

Question 15

How does the spiral ganglion cell activation differ when using a cochlear implant compared to a normal ear physiology?

Answer 15

if implant: spread of electric field will activate many ganglions.
Physiologic hearing: inner hair cells activate only selected spiral ganglion cells.

Question 16

What is Continuous Interleaved Sampling (CIS) in cochlear implants?

Answer 16

CIS is a method where continuous brief pulses are introduced to electrodes in a nonoverlapping sequence called interleaved sampling.
The duration of each pulse is about 20 to 50 us, so 30’000-80’000 pulses per second.

Question 17

What is the purpose of biphasic pulses in cochlear implants?

Answer 17

Biphasic pulses apply both positive and negative charge to tissue to prevent DC currents.

Question 18

What does the individual fitting process for cochlear implant electrodes involve?

Answer 18

Each electrode is fitted individually to the patient’s sensation. The fitting includes determining the threshold and the most comfortable level, with a compression line applied between these two values (similar to conventional hearing aids).

Question 19

What are the main steps involved in cochlear implant surgery?

Answer 19

The surgery involves several steps, including an incision of the skin behind the ear.
Removal of mastoid bone.
Access to the middle ear cavity (tympanotomy).
Open the inner ear (cochleostomy).
Electrode insertion.

Question 20

What are the main two reasons for intraoperative testing during cochlear implant surgery?

Answer 20

To check the integrity of the implanted device and to confirm neural stimulation of the device.

Question 21

What are some tests that can be performed during surgery for cochlear implants?

Answer 21

Impedance testing, neural response telemetry (NRT), observation of the stapedial reflex (response to loud sound input) are examples of tests that can be performed.

Question 22

What is the normal impedance of an electrode?

Answer 22

The normal impedance of an electrode is approximately 5 kΩ.

Question 23

What are two abnormal electrode impedance cases?

Answer 23

1) Elevated impedance indicates that some contacts of the electrode are not inside the cochlea but are instead in the middle ear cavity.
2) short circuit -> impedance close to 0 and device needs to be replaced.

Question 24

Where are recording electrodes placed in Auditory Evoked Potentials (AEP) compared to Neural Response Telemetry (NRT)?

Answer 24

In AEP, recording electrodes are attached to the skin of the patient, while in NRT, one of the implant’s electrical contacts is used as the recording electrode.

Question 25

what is the stapedial reflex and how can it be observed?

Answer 25

The stapedial reflex is a protective reflex that involves the contraction of the stapedius muscle in response to loud sounds. The contraction of the stapedial nerve can be visually observed across the microscope.

Question 26

What milestone related to cochlear implants was noted in Switzerland in December 2023?

Answer 26

The implantation of 5000 cochlear implants (CIs).

Question 27

How do cochlear implants improve hearing as depicted in the audiogram?

Answer 27

Cochlear implants improve hearing significantly, as evidenced by the blue line on the diagram showing hearing with and without hearing aids. (about 90% recovery)

Question 28

Why is it particularly crucial to use cochlear implants in children at an early age?

Answer 28

Early usage of cochlear implants is crucial because hearing loss within the speech banana can affect a child’s ability to learn language.