CIs (Exam 1)

Neural prostheses

A general class of devices that replace dysfunctional systems within the body

Types of neural prostheses (4)

• Motor

• Sensory

• Cognitive modality

• Anything that has been injured

Implantable auditory prostheses

A general category of neural prostheses that address hearing losses

Implantable auditory prostheses may be placed where?

• Cochlea

• Auditory brainstem

Cochlear prosthesis

A device that replaces a malfunctioning cochlea

A CI is based on what premise? What is required?

• Is based on the premise that the cochlea is the site of lesion

• Requires that the auditory nerve fibers exist and are capable of being stimulated

Explain hearing with a CI

Electrical hearing rather than acoustic hearing

• HF selective and HC transaction process with cochlear hearing. BM fibers mechanically stimulated

• Electrical stimulation induces neural synchrony

T/F: You don’t need surviving nerual untis depsite haveing a damaged cochlea

F

• You need surviving spiral ganglion cells (SGC) BUT survival can be patchy and there is now way to know until postmortem

The SGC do what?

Transmit information about the auditory signal to the cortex

Why does a CI work?

• Auditory nerve fibers survive even when the cochlea is damaged

• The stimulation of nerve fibers electrically causes the perception of sound at the cortex

CI parts include (5)

• Microphone

• External speech processor

• Transmission link

• Internal processor

• Electrode array

Microphone

Changes acoustic signal to an electrical signal. Out put goes to the external processor.

• Typically directional

• Head mounted

• Will be different across devices

Characteristics of good mics for CIs include

• Broad frequency response

• Minimize responses to low frequency vibrations

• Directionality

External speech processor

Input from the mic is transformed. Contains signal processing hardware and software

• House in a BTE type casing

• Is programmed by the AuD

Transmission link

Transcutaneous (signal transmitted across the scalp via radio frequency transmission through two magnets between the skull)

Internal processor

With its electronic package, the signal is decoded and generates electrical impulses with information received from the radio frequency signal from the external transmitter coil. Consists of:

• Radio frequency antenna

• Magnent (for transcutaneous connection)

• Electronics package connected to the electrode array

• Packaged in a biocompatible container

Electrode array

Is designed to be placed tonotopically

• Basal electrodes stimulate HF

• Apical electrodes stimulate low freuqneices

External portion of CI includes

• Microphone- worn on the head

• Speech processor- microcomputer that analyzes speech

• Headpiece with magnet

Internal portion of CI includes

• Internal receiver and coil with a magnet

• Electrode array- inserted into the scala tympani

Types of transmission links

• Percutaneous (only part implanted was the electrodes)

• Transcutaneous

Percutaneous link

Allows direct access to the electrode array

• Is the ideal research device bc one can change the processing strategy online

• ONLY in the Ineraid device (formerly Symbion)

Transcutaneous link

Radio frequency signal is transmitted by induction across the skin

• Current technology

Insertion of the electrode array

• Each intracochlear electrode array, regardless of type, is placed in the scala tympani

• The electrodes are then close to the neural units in the modiolus

Electrodes

Refers to the contacts implanted in the scala tympani. May vary in

• Number

• Spacing

• Vary with respect to orientation to the excitable tissue

• May be monopolar or bipolar (describes how the electric current loop is closed)

Mono- vs Bi- polar activation

• Mono- every electrode has the same ground electrode (allows BROADER ACTIVATION)

• BI- electrode next to the stimulated electrode becomes the ground electrode (allows FOCAL ACTIVATION)

Types of electrode stimulation

• Mono (MP)

  • MP1, MP2, MP1+2

• Bi (BP)

  • BP, BP +1, BP+2

• Tripolar

• Partial tripolar

Monopolar stimulation

Once current source and one current sink (ground electrode). Current spreads out symmetrically from the active electrode (this may stimulate unintended areas)

• Usually the ground electrode is extracochlear - in the temporalis muscle

• The active electrodes are in the cochlea

• Can be used with one electrode or many

Bipolar stimulation

Uses pairs of electrodes close together

• Current spreads out over a discrete area

• Electrode arrangement can be longitudinal or radial

Electrode channel

A channel is a pathway of information

Multi-channel system

Sends directly processed information to different electrodes through separate pathways or channels

Electrode placement (4)

• Extracochlear- any electrode outside of the cochlea

• Intracochlear

• Modiolar

• Auditory brainstem- on cochlear nucleus

What are the challenges of CI design?

All nerve fibers are bathed in the same conducting fluid and tissue - we want FREQUNECY SELECTIVITY

Who oversees CIs?

Center of Devices and Radiological Health (CDRH)

• Regulates manufactures

CDRH three regulatory classes for medical devices

• Class I: Prescription of HA (now deregulated)

• Class II: Osseointegrated hearing implant systems (e.g BAHA)

• Class III: CIs

Original audiological criteria for adult candidacy

• Adults 18+ only

• Profound SNHL AU

• Postlingual onset

• No benefit from HA

  • 0% auditory only speech rec

Who determines CI criteria?

Manufacturers submit an application for pre-market approval (PMA) outlining indications for the device

• The FSA either approves or denies the application

• Clinical trial is completed

• If acceptable to the FDA, the manufacturer-defined indications for implantation are then listed as the FDA criteria for use of that particular device

Who approves and sets “FDA labeled indications?”

Approved by the FDA but are NOT set by the FDA

Cochlear audiometric thresholds and speech-rec CI candidiacy criteria for ADULTS

• Moderate to profound bilateral SNHL in low frequencies, profound SNHL in mid to HF

• Prelingual or postlingual onset

• Less than or equal to 50% on a test of open-set sentence rec in ear to be implanted

• Less than or equal to 60% in the best aided condition on test of open-set sentence rec

When should you refer for a CI eval for an adult?

60/60 guideline

• Greater than 60 dB PTA in the better ear (500, 1k, and 2k Hz)

• Less than or equal to 60% on CNC words in the better ear (unaided)

Limited benefit from HA or poor quality of life

A CI candidacy eval what areas in the pt?

• Audiogram

• Medical hx

• Lifestyle/demographics

• Hearing hx and etiology

• Speech rec

A CI team consists of who (6)

• AUD

• SLP

• Otologist

• Neuroradiologist

• Psychologist/neuropsychologist

• Family members/caregivers

• Social workers

Candidacy: lifestyle and demographics considerations

• Commitment to the CI process (access to care, transportation)

• Family support

• Pt lifestyle and communication goals

• Feasibility of care

Candidacy: HA hx

• Experience w/ HA

• Etiology of deafness

• Duration of deafness

• Impact of HL on daily life

CI candidacy protocol: comprehensive audiological evaluation criteria (audio, immittance, speech)

• Audio

  • Air 125-8k Hz including interoctaves

  • BC: 250, 500, 1k, 1500, 2k, 4k Hz

• Immitance

  • Tymps: ME anomoly will delay surgery

  • ART

• Speech

  • SRTs

  • Word rec (1 50-word CNC list in each ear (recorded)

CI candidacy protocol: HA verification

• HA programmed based on most recent audiogram

• Electroacoustic eval

  • Test box verification

• REM

  • Validate prescribed gain using probe mic

  • 60 dB SPL input

  • Functional gain measures not rec

CI candidacy protocol: aided speech rec testing

Minimum Speech Test Battery (MSTB-3)

• Streamlined test batteries for all pts

• For traditional, SSD/asymmetrical, bimodal/EAS

• Additional measures used when needed (e.g. cognitive screeners, additional referrals etc.)

MSTB-3 caveats

• Is not designed to align with current FDA or insurer indications

  • Focuses on measures that will assist clinicians in making clinical decisions and recommendations

  • Once a clinical decision is made, additional tests can be administered to determine if the pt qualifies for a CI based on their insurer’s indications

• It is not a guideline for test scores to determine candidacy

  • Rec test measures for evaluating candidacy and post-operative performance

  • Encourages that clinics come up w/ own candidacy criteria

MSTB-3 recorded materials and pres lvl

• AzBio sentences

  • Sentences presented in multi-talker babble

• Consonant-nucleus-consonant (CNC) words

  • Monsyllabic words in quiet

• Stimuli presented at 60 dB A

Why aren’t HINT sentences used for CI candidacy?

Ceiling effects occur

MSTB-3: Best Aided

Testing using a hearing aid that has been optimized for HL in the ear to be implanted

MSTB-3: Everyday Listening Condition

Testing with the optimized hearing configuration typical of everyday listening

When are the CNC and AzBio used?

The CNC is used as te clinical basis for determining candidacy. The AzBio is obtained for the ear to be implanted in the best aided condition as a basis for insurer’s requriements, as needed.the

What should be done for pts with residual hearing in the non-test ear?

Isolate the test ear by

• Plugging and placing the circumaural phone over NTE

• Use of effective masking in NTE

• NTE should NOT contribute to the score

Speech rec testing setup

• Loud speaker 1m from subject

• 0 degrees azimuth

• Recorded stimuli

• 60 dBA presentation level

• Calibration of input and output of audiometer

CNC

• Assess aided CNC word rec in QUIET first (50 word list, each ear tested separately)

  • Clinic decides what CNC cutoff score is used to determine initial candidacy (40-60%)

AzBio

• Administer one list at +10 dB SNR

• If pt does well

  • Administer at +5 dB SNR

• If pt obtains a 0%

  • Administer in quiet

Medical and surgical evaluation (at pre op) includes

Pre-implant eval should show general good health

• Examine otologic/neurotologic history and physical

• ENT exam

• MRI/CT scan to show pt cochlea

• Vaccination

• Cognitive testing
  

What percentage of adults >40 yrs have vestib dysfunction?

35%

• Vestib testing may be done

ABSOLUTE contraindications

• Cochlear/VIII nerve aplasia (absent nerve)

• Medical/psychiatric

• HA benefits exceed expected CI benefits

• Pt does not want surgery

Relative contraindications

• ASL/Deaf culture

• Chronic

• OME

• Prelinguistic HL

• Scalar obstruction

• Medical comorbidities

Factors to decide which ear to implant include

• Pt preference

• Medical eval

• Imaging

• Audiometric results

Adult EAS candidacy: Cochlear Nucleus Hybrid

Audio thresholds

• < 60 dB HL 125-500 Hz

•  > 70 dB HL 2k+ Hz

Speech rec

• CNC < 60% in ear to be implanted

• < 80% in non-CI ear

Adult SSD and asymmetric candidacy: Cochlear nucleus hybrid

Audio thresholds

• < 60 dB HL 125-500Hz; >75 dB HL 2000+ Hz

Speech rec

• CNC < 60 % in ear to be implanted; <80% correct in non-CI ear

Adult CI candidacy consideration protocol for SSD

• Etiology

• Potential contraindications

• Imaging

• Duration of SSD

• Age at implantation

• Tinnitus

• Experience with alternative hearing tech

• Subjective benefit/quality of life

Adult CI candidacy for SSD: Etiology considerations

• SSD is often due to sudden SNHL, BUT should not be implanted too soon due to spontaneous recovery

• Meneire’s

• Trauma

• Retrocochlear

• Congenital

• Must consider the likelihood of acquiring hearing loss in the other ear

Adult CI candidacy for SSD: Contraindications

• Severe ossification of cochlea

• Cochlear nerve aplasia

• Retrocochlear issues

Adult CI candidacy for SSD: Imaging

• MRI (sensitive to VS)

• CT of temporal bone

Adult CI candidacy for SSD: Duration

• Longer duration = possible poorer outcomes

• Relationship b/w duration of deafness and subjective benefit

• Congenital SSD vs adult-onset considerations

Adult CI candidacy for SSD: Age

Advanced age is NOT a contraindication

Adult CI candidacy for SSD: Tinnitus severity

• Often reduction in tinnitus with implantation

Adult CI candidacy for SSD: Experience w/ alternative amplification

• CROS

• Bone conduction device

Adult CI candidacy for SSD: Aided speech rec testing with MSTB-3

• Assess aided CNC word rec in QUIET for the ear to be implanted using 50 word list

  • Must isolate the ear - plug and muff NTE

• Aided sentence testing in everyday listening conditions (65 dB A at 0 SNR)

  • Additional sentence lists presented in a variety of configurations to evaluate and document difficulties pts w/ SSD or AHL have in different listening conditions

If the best aided CNC score for the ear being considered exceeds the clini’s cut-off score for candidacy what should the pt do?

Return in one year for retesting

Why should questionnaires be administered for CI candidacy?

To assess subjective benefit, performance, and quality of life

MSTB-3 questionnaires

• CI-QoL 10 (The cochlear implant quality of life)

• SSQ-12 (Speech, Spatial, and Qualities of Hearing Scale

• Tinnitus Handicap Inventory (when sign tinnitus rptd)

Outcomes of older pts implanted compared to younger pts

• Word recognition did not differ significantly in older vs. younger patients

• Both groups had significant increases from their pre-implant scores