Wk11-26: eCAp and eABR Flashcards
What does eCAP stand for?
Electrically evoked compound action potentials
eCAPs are measured by delivering biphasic electrical pulses to an intracochlear electrode contact to stimulate the AN, and using a nearby intracochlear electrode contact to record neural response.
What is this process called?
Reverse telemetry
What are “eCAPs”?
Synchronous physiological responses from an aggregate population of auditory nerve fibers in response to electrical stimulation
eCAP measurements are basically a near-field version of which ABR wave?
Wave I
Approximately which time frame would we expect to find the N1 and P1 of eCAPs?
~0.2 - 0.8 ms post-stimulus
What CI equipment is used to generate/record eCAPs?
- Standard programming soft and hardware
- monopolar coupling to deliver a single biphasic current pulse
- CI electrodes to record the response
What are the advantages of eCAP over ABR?
- immune to anesthesia effects
- no myogenic noise
- larger responses d/t proximity
- fewer averages needed (d/t larger responses)
- can be measured reliably w/in first year of life
What measurements can be performed with eCAPs?
- amplitude growth function (slope and threshold of stimulation)
- refractory recovery (measured using eCAP amplitude in response to masked probe; reflects size of underlying neural pop’n)
- spread of excitation (using spatial spread c/ fixed stimulation electrode and diff recording electrodes, or spatial masking using forward masking subtraction)
What is spatial masking?
When a masker elevates the threshold of a subsequent stimulus
What are eCAP measurement used for in clinic?
- to confirm device function
- to confirm AN function
- to assist c/ sound processor programming
- to verify questionable behaviour responses
Can eCAPs predict MAP (M and C) levels alone? Why or why not?
No - eCAP thresholds are above behavioural thresholds, sometimes exceeding upper comfort levels; they correlate with MAP levels better with lower stimulation rates
- still, useful when combined with other results
What is an electrically evoked auditory brainstem response (eABR)? How does it differ from eCAP?
- a synchronous physiological response from the AN to structures in the brainstem
- Waves I-V with focus on Wave V (vs Wave I for eCAP)
Are eABR waves earlier or later than ABR waves? Why?
Earlier (by ~1.5 ms)
- because we stimulate directly in the cochlea
What equipment do we need to measure eABRs?
- standard programming soft and hardware for the stimulus
- standard ABR system for recording
- trigger pulse output from the programming interface to synchronize the recording system
- single biphasic current pulse delivered using monopoly coupling
- scalp electrodes for recording
What are the advantages of eABR?
- no need for reverse telemetry (good since only the newer internal components are capable of this)
- goes up to the brainstem, so covers more of the auditory pathway
- can be used when eCAP STIMULUS noise (not muscle noise) is too noisy (since eCAP is recorded only 0.4 ms after the stimulus, sometimes the stimulus itself interferes)
- Wave V is easier to locate d/t higher amplitude and longer latency than Wave I
