Lecture 2 Flashcards
what are electrophysiologic audiometry
measures that record & analyze the as physiologic responses
another term for physiological responses
objective responses
what are types of electrophysiologic tests
immitance tests (tymps, reflexes & decay)
OAEs
auditory evoked responses (AERs)
what does in mean when we say the electrophysiologic tests are objective
they do not require the subject’s active participation, and are complementary to audiometry, which is subjective
is audiometry objective
no subjective
how do neurons in the brain communicate
rapid electrical impulses
what do the electral impulses allow the brain to do
coordinate behavior, sensation, thoughts, and emotion
what does the CNS do even in the absence of sensory stimulation
generates spontaneous and random neuroelectric activity
how can we record spontaneous and random neuroelectric activity
scalp electrodes
what happens to the brain once the sound goes in there?
auditory evoked responses
do neurons fire without stimulus
yes
what happens when there is a stimulus
neurons fire at a higher rate and amplitude
what forms the basis of electroencephalogram (EEG)
neuron firing spontaneously and random
are eeg good for us?
no
we have to look at tiny responses in the sea of large responses
we cannot remove eeg because that would mean the pt would be dead
what is a AEP
activity or response within the auditory system that is produced or stimulated (evoked) by sounds
where can the activity be
Cochlea
Auditory nerve
Central auditory nervous system (CANS)
AERs are an example of
neural activity in response to specific types of sensory stimulation, which are extracted from the EEG
The EEG response are huge while any other evoked response are relatively small. What does this mean
requires significant signal amplification and other mechanisms to read those responses
term physicians prefer for ABR
brainstem evoked auditory response
bear
What does the ABR consist of
sequential series of 5-7 peaks (responses)
The response occurs for ~ 5 to 10 ms following stimulus onset
clinically, focus is on what peaks
I-V in general
I, III, & V particular
what is latency
time frame signal is turned on and you see the response
time frame of the response of when you see the response occur
what is stimulus onset
signal turning on
what are the clinical applications of the ABR
can provide a close estimate of hearing threshold for specific frequencies
can predict a conductive, sensory, or neural site-of-lesion
screening tool for retrocochlear pathologies
The ABR is not a ________ but rather a measure of ________
test of hearing sensitivity but rather a measure of neural synchrony
why do we not focus on all peaks of I-V
if you see 1 and 3, 2 is assumed ot be there
if you see a 3 and 5, it is assumed 4 is there
4 can be right with 5 and that is not abnormal
why is ABR not a test of hearing sensitivity
because you are measuring nerve response, not sensory hair cell response
used as a test of hearing sensitivity in an indirect way because it tells how the system is hearing and a test of neural synchrony
what is neural synchrony
firing of all of the nerves
CN’s when they receive signal they fire, they do not fire randomly, they fire synchrony based on the signal they receive
low vs high frequency causes different neurons firing
synchronous firing and disruption causes clinically
speech understanding in general and more in speech in noise
why do they have difficulty hearing in noise?
they hear the noise with their ears but it doesn’t get to the brain so the brain cannot understand the information because the firing is
is the audio independent of neural dysynchrony
YES
audio can show anything, it is not a reflection of neural dysynchrony
audiogram tests
the integrity of the OHC & IHC
function of the ABR
neural synchrony
can you see hearing level on an ABR?
yes you can predict CHL, SNHL or neural site of lesio
why is ABR a screening tool & not a diagnostic tool
it tells you something is wrong but it doesn’t tell you where the issue is arising
would dr send baby for an abr with symtpoms of vestib schwanoma
no they will go to an mri because it is more definitive
what are the generation sites of the ABR for each wave
1: distal viii n in the cochlea
3: cochlear nucleus, trapezoid body, superior olivary complex
5: lateral leminiscus
what is the blood supply of the cochlea
labyrinthine artery
where does the labyrinthine artery branch from
generally AICA
anterior inferior cerebellar artery
what is the blood supply of the brainstem
vertebrobasilar artery
how does the brain work
in unison
why do we want to look at blood supply?
problem could be here instead of a vestib schwanoma when problems show up on an abr
how long does it take before the waveform appears
latency
Absolute peak values at _______ nHL presentation level
Absolute peak values at ~80 dB nHL presentation level
nHL vs HL
normalized hearing level -
what is nHL
taking group of normal hearing young adults and looking at where the thresholds come in
what is the latency value for wave I
1.5 ms (mean)
(SD = + 0.25 ms)
(sd = standard deviation)
wave II
2.6 ms (mean)
(SD = + 0.25 ms)
about _____ latency above wave I
wave III latency
3.7 ms (mean)
(SD = + 0.25 ms)
about 1 ms above wave II
wave IV latency
4.7 ms (mean)
(SD = + 0.5 ms)
above 6 ms latency
start to get suspicious
wave V latency
5.5 ms (mean)
(SD = + 0.5 ms
latency norms can also be referred to as
jewitt norms
Inter-peak values at _____nHL presentation level
~80 dB
interpeak I-III
I - III IPL: 2.25 ms
(SD = + 0.5 ms)
interpeak III-V
2.0 ms
(SD = + 0.5 ms)
IPL I-V
4.0 ms
(SD = + 0.5 ms)
what are the transducer for ABR stim
inserts
stim type for ABR stim parameters
Clicks, chirp, tone burst (short frequency specific signal), and speech stimuli (/ba/, /da/)
what are the polarity for ABR stim paramaters
Rarefaction (-ve signal polarity)
Condensation (+ve signal polarity)
Alternating (combined polarity)
rate parameters for abr stim
> 20/s, e.g., 21.1 or 27.3/s
90/s useful for neurodiagnosis
typically is 21.1 or 27.7
intensity abr stim parameters
Variable in dB nHL – 10 to 90 dB
what are clicks
broadband very short signals
2000-4000 Hz
what are tone bursts
longer in duration and similar to tones and are frequency specific
which stim type for abr is frequency specific
tone bursts
rarefaction polarity
negative ve signal
condensation
positive ve signal
rate that the click/tone burst is delivered
rate
alternating polarity
alt on the computer, computer will math add condensation and rarefaction and give a waveform, instead of doing each individually and adding them together
gives better morphology and clearer signal
what is polarity
how sound goes in and whether it is pos or neg that it touches the membrane of the headphone
what is neurodiagnosis
not looking for hearing estimation sensitivity looking for problems at retro level
usually vestib schwanoma
why are higher rates useful for neurodiagnosis
at this higher rate you are stressing the system and causes the abr to fall apart because the system is already stressed with the tumor
stay at 75-80 dB
An ABR response showing all waves in a normal listener is best elicited with a
click stimulus at a high intensity (~ 75 to 90 dB nHL
Level in decibels relative to the subjective click threshold level for subjects with normal hearing
nHL