CNIM: Guidelines 9C (Clinical) & 11C (IOM) Auditory Evoked Potentials

outer ear consists of __

pinna and external auditory canal

middle ear consists of __

tympanic membrane & ossicles (malleus, incus, stapes)

inner ear consists of __

vestibule, semicircular canals, cochlea

incoming sound enters the __

external acoustic meatus (auditory canal)

sound waves vibrate the ___ which cause the ossicles to vibrate

tympanic membrane

ossicles connect to the ___ via ___ which causes movement of fluid and hair cells

cochlea; oval window

hair cells generate what kind of AP?

depolarization

what 2 nerves form the vestibulocochlear nerve

cochlear & vestibular

hearing pathway

sound --> external acoustic meatus --> tympanic membrane --> ossicles --> cochlea --> hair cells --> vestibulocochlear nerve

brainstem is supplied by what arteries?

vertebral (2) & basilar = vertebrobasilar

cochlea is supplied by what arteries?

basilar/vertebrobasilar --> AICA (anterior inferior cerebellar artery) --> internal auditory artery (labyrinthine artery)

cochlear branch of vestibulo-cochlear artery

another name for cochlea

labyrinth

what branch of the basilar artery goes toward the cochlea

anterior inferior cerebellar artery

what is the main branch of the AICA that perfuses the cochlea

internal auditory artery/labyrinthine artery

short-latency auditory evoked potentials (SAEPs)

electrical responses of auditory pathways

consist of BAEP & ECoG

occur within 10-15 ms

brainstem auditory evoked potentials can also be referred to as?

BAER

ABR = auditory brainstem responses

AEP

SAEP = short latency auditory evoked potentials

ECoG records electrical responses of the __ to assess ___

cochlea; cochlear function

is ECoG used to assess the brainstem

NO even though it does collect the auditory nerve compound action potential

3 components of ECoG

1) cochlear microphonics

2) summating potential

3) auditory nerve compound action potential

cochlear microphonics

receptor potentials of cochlear hair cells

aka "stim artifact" b/c of LOW latency

ONLY ECoG

summating potential

receptor potentials of cochlear hair cells

ECoG & ABR

auditory nerve compound action potential

AP of CN VIII

EQUIVALENT to WI with BAEP --> WI = NI (negative 1 on the ECoG)

ECoG & ABR

BAEPs are used to assess __

auditory nerve and/or brainstem & possibly a higher subcortical structure to acoustic stimulation

does BAEP have a summating potential & auditory nerve compound action potential

YES

why does NI exceed WI in amp

b/c there is an electrode in the external auditory meatus

does ECoG use a cephalic electrode (CZ)

no --> A1-EAM1 vs BAEP that uses CZ-A1

why is ECoG used intraoperatively

to get a NI/WI response but it is MOSTLY a clinical modality

ECoG:

analysis time

channel

types of clicks

analysis time = 5 ms

channel = A1-EAM1 (ipsilateral earlobe to ipsilateral external auditory meatus/canal)

clicks = condensation or rarefaction

can you use alternating clicks in ECoG

NO b/c it will cancel out the cochlear microphonic --> it changes direction (up or down) with condensation & rarefaction clicks

how is Wave 1 differentiated from cochlear microphonic

based on click polarity

what does reversing polarity (switch from rarefaction to condensation or vice versa) do

change direction of cochlear microphonic but WI (NI) will stay pointed UP

what do BAEPs record

responses of the auditory nerve & brainstem to acoustic stimulation

do BAEPs assess the thalamus or auditory cortex

no b/c of short latency (how short the CN VIII is)

what are the most important BAEP waves per ACNS

I

III

V

since we ONLY monitor waves I, III, & V, the generators for waves ___ are grouped together

II & III

IV & V

wave I

distal auditory nerve (CN VIII)

neg polarity

wave II

proximal auditory nerve (CN VIII)

junction of pons & medulla

wave III

superior olivary complex (CONTRALATERAL side) --> AKA "cochlear nucleus"

from rostral medulla to mid-pons

pos polarity

wave IV

lateral lemniscus

pons to midbrain

wave V

inferior colliculus (CONTRALATERAL side) --> AKA "lateral lemniscus"

midbrain

pos polarity

waves IV & V are merged to form the?

IV-V complex --> better seen on the CONTRALATERAL side

do BAEPs have specific latencies

NO --> just expected/standard

absolute latency

expected latency of each waveform

interpeak latency

time between waveforms

effect tubing has on absolute or interpeak latencies

absolute latencies: adds 0.9-1 ms delay to ALL

interpeak latencies: NOT affected

interpeak latencies:

I-III

III-V

I-V

2 ms

2 ms

4 ms

absolute latencies:

I

III

V

1.5 ms

3.5 ms

5.5 ms

absolute latencies with tubing (+0.9 ms):

I

III

V

2.4 ms

4.4 ms

6.4 ms

what does dB SPL mean?

sound pressure level

dB SPL

physical measure of lowest sound intensity

what we consider to be 0 dB

what does dB pe SPL mean?

peak equivalent sounds pressure level

dB pe SPL

measurement unit by sound level meters

uses pressure to quantify sound intensity

compare peak-to-peak amplitude of the stimulus (click) with amp of a sine wave of a pure tone with known SPL

what is a click's pe SPL

SPL of a pure tone which matches the peak-to-peak amp of the click's acoustic waveform

pressure measured by a certain sound correlates to its amp on a tool using SPL

output of dB pe SPL equipment

standardized

what does dB HL or dB nHL mean?

decibels hearing level; NORMAL hearing level

dB HL/dB nHL

dB ABOVE the average hearing threshold of a group of normal young adults

determined for different frequencies since some people have difficulty hearing low or high sounds

what is the softest sound that can be heard by the average person with NORMAL hearing

0 dB HL

hearing level for individuals ABOVE average hearing

LOW

EX: -10 dB HL

normal hearing level

0-20 dB HL

what does dB SL mean?

sensation level

dB SL

dB ABOVE the subject's INDIVIDUAL hearing threshold in the ear tested

individual hearing theshold

stim intensity in db HL formula

individuals threshold (dB HL) + 60 db SL = stim intensity in dB HL

EX: If a patient is tested to hear a 2,000 Hz frequency at 12 dB HL, their BAEPs should be tested at: 12dB HL + 60db SL = 72dB HL

just focus on dB HL

what type of stimulation does BAEPs use

broad band clicks

broad band clicks frequency

2000-4000 Hz (2-4 KHz)

broad band clicks

wide range of frequencies; used for neurologic applications

examples of narrow-broad band clicks

tone bursts

tone pips

filtered clicks

single-cycle clicks

why AREN'T narrow broad band clicks used for BAEPs

they have a more restricted frequency spectrum (less range)

more suited for audiologic applications

clicks should be delivered one/two ears at a time?

one (monoaurally)

the non-stimulated (contralateral) ear should be masked with ___

white noise to eliminate bone crossover (bone-conducted responses)

can you use interleaving stimulation for ABRs

NO b/c it does NOT allow for contralateral masking

bone conducted crossover

when unilateral stimulation is performed without sufficient contralateral masking tone or simultaneous stimulation

failure to use white noise masking introduces __

false negatives

false negative

data does NOT change; pt wakes up with a deficit

do we want to use bilateral stimulation for ABRs

NO

what does the BAEP sound stim intensity at the tympanic membrane depend on

acoustic coupling between the sound stimulus generator & the ear

sound waves are transduced to mechanical movement/vibrations in the outer/inner/middle ear?

outer & middle

mechanical movement is transduced to electrical potentials via ___ at the hair cells in the inner ear

depolarization

how often should calibration of the stimulus delivery system (head phones or ear inserts) be repeated

every 6 mo

earplugs are connected to a ___

transducer

what does obstruction of the tubing system lead to

failure of sound transmission (EX: kinking)

what should ear plus be protected from

blood & fluid by waterproof tape

purpose of bone wax

secure earphone

DOESN'T completely protect the canal from fluid entry

purpose of otoscopic visualization

- used before placing ear plugs

- visualize excessive cerumen that could interfere with stimulation

cerumen

ear wax

an otoscope is used to examine:

external ear

auditory canal

tympanic membrane

BAEP duration (pulse width)

100 usec (0.1 msec) rectangular pulse (singular monophasic square wave)

BAEP stim rate/rep rate:

9C

11C

avoid anything divisible by 60 Hz ! !

9C: 8-10/sec

- ranges from 5-200/sec

- HIGHER than 10/sec = reduces WI, II, IV, VII amp

- HIGH rates (50-70/s) = FASTER identification of WV

11C: 5-12 sec - 30.1/sec

- OPTIMAL for WI, III, V = 5-12/sec

- HIGHER rates of 30/sec = FASTER acquisition of WI & V, but WIII is DEGRADED

WV disappears __ dB HL above/below threshold?

1 dB HL below

do you have to reset baselines if the stim rate is changed during the procedure

YES

stim intensity & white noise masking:

9C

11C

9C: 40-120 dB pe SPL

- white noise = 60 dB SPL

11C: 100 dB pe SPL or 60-70 dB HL

- white noise = 60 dB SPL or 30-35 dB HL

^ use HIGHER stim intensity if the pt has pre-existing hearing loss or fluid in middle ear

sound pressure levels measurements are used as a ___

reference level

0 dB =?

20 micopascals (Pa) = 0.0002 dyne2/cm2

types of stimulus polarities

1) rarefaction

2) condensation

3) alternating

rarefaction polarity

apply NEGATIVE pressure

pulls AWAY from tympanic membrane

best WI amp

condensation polarity

apply POSITIVE pressure

pushes TOWARD tympanic membrane

best WV amp

alternating polarity

NEG & POS pressure

BEST for IOM

cancel stim artifact & cochlear microphonic

can you use alternating polarity for ECochG

NO

stim polarity 9C

NO clear rational for preferring rarefaction over condensation clicks or vice versa

normative data needs to be collected using stim polarity or polarities to be used in clinical setting

summating responses is acceptable whenever NO differences exist

stim polarity 11C

alternating clicks

HIGH int = high stim artifact --> use alternating to reduce it

bandpass:

9C

11C

9C: 10-30 to 2,500-3,000 Hz

- raise LFF to 100-200 Hz if muscle artifact is present

11C: 100-150 to 2,500-3,000 Hz

- reduce HFF to 1,000 Hz for OR noise