Cochlear Implant Programming Flashcards
What is the dynamic range of hearing and its relationship to the MAP?
- NH: ~120 dB
- CI: up to 20 dB
- Acoustic to electrical transformation is determined by the MAP
Define MAPs.
-Configuration of current units (CUs), processing strategies, stimulation rate, etc.
Define programs.
- Configuration of MAPs
- Use of different programs
- May be progressive over first to increase current levels
- Similar to heading aid programs after first week/month (i.e., noise, school)
What would warrant an interim mapping appointment?
- Changes in auditory discrimination
- Increased request repetition
- Addition/omission of syllables
- Prolongation of vowels
- Changes in vocal quality
What is most likely to warrant an interim mapping appointment for a child?
- Prolongation of vowels
- Changes in vocal quality
What do you do to connect the equipment before programming?
- Verify 4 components:
1. Computerized processing unit (CPU)
2. Implant
3. Processor
4. Patient
How do you prepare the equipment for programming?
- Verify connection of components
- Initialize processor
- Condition electrode array
Describe how to initialize the processor.
- For AB only
- Dictate in the software: which ear, how it’s being used (i.e., AD, AU, bimodal)
- Only needs to be done initially
- May need to reset processor (for Cochlear)
Describe how to condition the electrode array.
- For AB only
- Send stimulation to all channels at the same time
What measurements should be performed during programming?
- Telemetry
- Neural response assessment
- T- levels
- C- or M-levels
- Speech strategies
What is telemetry?
- Aka impedance
- Confirms proper communication between the processor and the electrodes
- Always performed
What is neural response assessment?
- Electrophysiologic response from the nerve in response to electrode stimulation
- Essentially an eABR
- Useful for children who cannot give subjective measurements
What are speech encoding strategies?
- Different methods of stimulation that can produce different perceptions from the patient
- Method by which the implant translates the incoming acoustic signal into patterns of electrical pulses
- Can be simultaneous and/or sequential
- Provide spectral and envelope information
What is impedance?
- Measure of the opposition to electrical current flow
- Impedance = voltage/current
- Reported in kOhms
What can cause electrode impedance?
- Fibrous tissue
- Electrolytes
- Macrophages
- Proteins
What are the stimulus parameters of electrode impedance?
- Current
- Voltage
- Stimulus width
What should be checked when measuring impedances?
- Do electrodes have normal impedances?
- Have the impedances changed?
- Impedance of deactivated electrodes
What could cause abnormally low impedance?
<1 kOhm
- Short circuit = short electrodes
- Likely to send stim across all channels (happens in pairs)
- May be caused by wires touching
- If the case, deactivate and never turn back on
What could cause abnormally high impedance?
> 30 kOhms
- Open circuit
- Likely a single channel
- May be caused by: air bubble, broken wire, electrodes in contact with air
- Can recover over time, so want to keep trying them
How should high impedances be addressed?
- May decrease with use or by increasing pulse width
- Initially, open circuits may be due to air bubbles in the cochlea (re-measure after stimulation)
- Short circuits will never be activated
What is the electrically evoked compound action potential (ECAP)?
- Gross potential that reflects synchronous firing of a large # of electrically stimulated nVIII fibers
- Want to instruct patient to try to tolerate sounds but let the Au.D. if it’s too uncomfortable (want to look for nVII stim)
What is the utility of the ECAP?
- Corresponds to wave I of the acoustic ABR
- Corresponds to upper limit of eDR (M or C)
How is Auto NRT (Cochlear) measured?
- Select # channels to run (3, 5, 9, or all–usually adults: ~5; kids: ~9)
- Click measure
- Watch measurements and patient reaction
- Prepare to skip channels if patient reports discomfort
- Software will move on to another channel if stimulation reaches compliance without achieving a response
How is Flex NRI (AB) measured?
- Select channels to stimulate (3, 7, 11, 15–avoiding basal channels)
- Recording channel is 2 apical from stim
- Select level of ordering (low to high if patient is conscious; high to low if patient is sedated)
- Set min and max stim levels (-100 to 250 uV)
- Look for 3 repetitions of response per channel (can change levels while running, skip to next data point, skip to next electrode)
- Creates EP Growth Function
- tNRI corresponds to M-levels
How is NRI measured for MED-EL?
-It can’t be measured manually
What is the clinical utility of NRT/NRI?
- Relatively stable over time
- Used with impedances to tell if change in performance if due to device function or neural responsiveness (i.e., integrity of internal device)
- Establishing a baseline for monitoring (every 6-12 months)
- Establishing appropriate programming levels
- Assess pitch perception at activation (i.e., same vs. different, pitch quality)
What is the electrically evoked stapedial reflex threshold (ESRT)?
- Electrical stimulation to implant
- Measure SRT in non-implanted ear (via immittance bridge)
- SRT occurs at/near max levels used by speech processor
- Not recorded in 25-35% CI patients
- Requires some cooperation on the part of the patient
How is the ESRT measured?
- Probe placed in contralateral ear
- Continuously record acoustic admittance with 226 Hz probe tone
- Present programming stimulus used for upper limit of DR (M-/C-levels)
- Change in admittance occurs time-locked with stimulus when presentation level is of the ideal intensity for the upper limit of the DR
What is stimulation mode?
- Location of the reference electrode to the active electrode
- Can be monopolar or bipolar
What is monopolar stimulation mode?
- Ground electrode is outside the cochlea
- Wider spread for stim (problematic for strange anatomy)
- Allows for lower thresholds (due to greater separation between ground and active)
- Better battery life
- More consistent thresholds for adjacent electrodes (can interpolar, don’t need to measure each)
What is bipolar stimulation mode?
- All stimulation occurs within the cochlea
- Better when there are concerns about spread of excitation
What stimulation modes are available for the 3 manufacturere?
- Cochlear and AB: either monopolar or bipolar
- MED-EL: monopolar mode only
What is the input dynamic range (IDR)?
- CI selects the range of intensities of input to code
- What we try to mimic in CI output
- Want a minimum DR of 30 or 60 CUs
- Number of changes that happen to signals with CIs is significantly higher than with hearing aids (why brain/adaptation is so important)
What are threshold levels (T-levels)?
- Ensure that speech sounds are audible
- Soundfield responses to NBN should be in line with specs ( 20-25 dB for Cochlear, 30-35 dB for MED-EL & AB)
- If ~10 dB HL, too much stimulation (need to lower T’s to reduce stimulation)
What would happen if T’s are too high?
- Patient might be able to hear the processor
- Turn off mic and see if noise goes away
- If yes, then lower T’s
- Want to ask what kinds of sounds are too loud
What would happen if T’s are too low?
- Patient can’t detect soft sounds (i.e. LING sounds)
- If yes, then raise T’s
How are T-levels established for Cochlear?
- Measured manually
- Set at or just above threshold
- Can be obtained via: ascending, bracketing, loudness growth chart
How are T-levels established for AB & MED-EL?
- Interpolated based on M-levels
- Highest stim where no sound is perceived
What is a t-tail?
- Doesn’t decrease in perceived level by patient but different in programming level
- Want to set at highest stim level
How should T-levels be measured in pediatrics?
- May use with objective offset programming method (want threshold in at least 1 channel to see DR, then can apply DR to rest of MAP)
- Can measure behaviorally via BOA, VRA, CPA in office or soundbooth (but with stim as stimulus)
What are some considerations for setting T-levels in tinnitus patients?
- Presence of tinnitus causes difficulties detecting stimulus during measurement (need to move quickly because there is no ambient noise to mask tinnitus when implant is off)
- Multiple presentations of stim can help in perception over tinnitus
How should T-levels be set in tinnitus patients?
- Set T’s over level of tinnitus and then decrease globally
- Loudness balancing at 50% over T’s
What is the significance of T-levels?
- Artificially raised T’s results in better performance (also preferred by participants)
- Progressively louder T’s, effectively reducing the DR (very little difference in performance)
What are comfort levels?
- Upper limit of the DR
- Cochlear: set below max comfort (due to summation across electrodes)
- AB: most comfortable level
- MED-EL: highest stim level at which sound is loud but comfortable
How should M-levels be measured for AB?
- Channels are grouped by 4
- Want a flap MAP across all channels (can flatten by doing single-channel measurements)
- Measure groups of 4 channels with speech bursts
- Measure single channels with tone bursts
How should M-levels be measured for MED-EL?
- Want a flap MAP across all channels
- EX: start with all even channels, then odds
- EX: 6, 12, 4, 16 (alternate so no residual stim)
- Measure M-levels with tone bursts
What are methods of measuring C- and M-levels?
- Ascending technique (w/ multiple presentations at each levels)
- Loudness growth charts
What are some programming methods?
- Behavioral
- Objective preset
- Objective with behavioral offset
What is objective preset programming?
-Take NRIs/NRTs and have programming may you a MAP from it
What is objective w/ behavioral offset programming?
-Use objective preset for T’s and C’s/M’s and then do behavioral measurements on at least 1 channel
What influences current levels?
- Speech processing strategies
- Bipolar vs. monopolar mode
- Stimulation rates
- Proximity of electrode array to modiolus
What is the effect of stim rate on current levels?
- As rate increases, level decreases
- But doesn’t preserve battery life
What are compliance levels?
- The amount of voltage allowed for each electrode
- Ran first thing on new or transfer patients
What does it mean to be “out fo compliance”?
- Maximum voltage available from the implant is not sufficient to generate the desired current level
- No further perception of loudness growth
- Increase pulse width or decrease stim rate
- Will then need to redo entire MAP
What are the consequences of being out of compliance?
- Insufficient loudness growth, variable loudness, lack of loudness growth
- Sound may be distorted
- Poor battery life
- Decreased performance in general
What is Automatic Pulse Width (APW)?
- AB
- Optimizes PW and rate during programming
- Designed to maintain the narrowest PW and fastest rate for a selected HiRes strategy
- APW calculates and adjusts PW and rate based on compliance and M-level requirements
- May help to determine which manufacturer to select for a patient
What are the two versions of APW?
- APW I: most narrow PW for fastest rates
- APW II: more compliance headroom to allow for fluctuating impedances (default)
What patients may benefit from APW?
- Patients whose body chemistry may change
- EX: transfusions, arthritis
When should manual PW be used?
- Poor sound quality
- Cannot obtain adequate loudness due to nVII stim
- Increase PW (decrease rate)
What is radio frequency (RF) transmission?
- CIs have no internal batteries
- All power comes across the skin from the transmitter coil
- Burden of power rests upon what power it receives from the SP
- Many intermittencies and sound quality problems arise from issues that surround transmission of power (disturbances between external and internal devices)
What contributes to successful RF transmission?
- Flap thickness/thinness
- RF power level in software
- Transmitter cable length
- Battery option
- Compliance levels
- C-levels
- Rate/maxima
- Listening environment/input level
How does flap thickness impact RF transmission?
- Thick/fat head = hard to transmit signal
- Thin skin = ex/internal device are too close together (touchy transmission)
What is power optimization?
- The need for power
- Voltage and Power dictate the user’s power level
- Can the battery type provide sufficient voltage to deliver requested amount of current?
- System calculated how much power is consumed by the “worst-case condition” (i.e., ambient room noise >65 dB)
- Measurement done for each MAP (but only on main processor)
What is indicated by power optimization across the skin?
- Sufficient voltage available to the implant to ensure all electrodes remain in compliance
- Sufficient power (voltage and current) for the demands of the chosen MAP
What is voltage impacted by?
- Skin flap thickness
- T’s and C’s (current levels)
- Impedances
As required voltage increases, battery life life decreases. How can this be addressed?
- Decrease pulse rate
- Want to use automatic power as much as possible
When should compliance and power status be checked?
- New MAP
- New SP
- Reported intermittences
- Poor battery life
- Change in sound quality
- Transfer patient
- > 6 months since last visit
- Lost/gained weight
- Significant growth/shortening of hair
How should problems with battery life be addressed?
- Decrease rate/maxima if high stim levels or OOC conditions are not an issue
- Increase PW
- Move to body worn SP
What are some live voice modifications?
- Tilting
- Increasing/decreasing levels on all channels
- Gain
- Frequency adjustments
What are some options for noise reductions?
- AGC autosensitivity
- Adaptive directional range optimization (ADRO–Coclear)
- BEAM: multi-microphone technology
What is ADRO?
- Cochlear
- Adjusts gain at each frequency band to optimize the signal
What is loudness balancing?
- Ensure equal loudness on all electrodes
- Need to make sure the patient understands the tasks (must understand pitch vs. loudness)
- Incorrect loudness balancing can be detrimental to performance
- Not always necessary due to use of loudness charts (may be warranted if MAP looks funny/not balanced, or if patient is getting artifact with live voice)
- Can be done via balancing or sweeping
What is pitch ranking?
- If the electrode array is rolled over on itself, pitch does not increase from low to high on sequential electrodes
- Usually identified in post-op X-ray
- Balance neighboring electrodes
- Reorder channels
Describe counseling re: patient controls.
- Programs: microphone modes
- Volumes: modifies C-levels
- Sensitivity: distance of hearing
