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
what happens as the intensity decreases
Wave 1 disappears first and with further intensity decrease (at ~ 55 to 65 dB nHL), all waves, except wave V, will disappear
latency of the waves (wave V) increases
morphology of the ABR response deteriorates
is wave I disappearing with decrease in intensity normal
YES
with further decrease in intensity waves disappear but V is this normal
yes
why do the waves disappear?
I-III are tiny waves compared to wave V because the tech isnt available at the moment to keep amplifying without losing them
what is the relationship bw latency and intensity
intensity and latency relationship - waveforms disappear and latency will increase
a ____ in intensity causes a _____ in latency
decrease, increase
what are the 3 important relationships to understand with decrease in intensity
as intensity goes down, earlier waveforms disappear and v stays
as intensity goes down, latency goes up (only wave v)
as intensity goes down, morphonly starts to deteriorate
Actual hearing threshold is typically _____ dB HL better than the ABR threshold
~10 to 15
if wave V threshold is 20 what is the actual threshold?
5-10 dB
abr ____ threshold
overestimates
how do you determine wave V and not the other wave shows in 40
because as you decrease intensity the latency should increase and on 40 the other wave did not shift to the right
ABR threshold is determined at
lowest intensity that wave V can be recognized
BC ABR resembles AC responses seen with lower intensity air-conducted clicks because
poor mechanical characteristics of bone-conduction transducers
what can you note about bc abr
Morphology is poorer and rarely are five wave responses observed because bone-conducted output is limited
Wave V, however, is clearly visible, which is the one we need to assess
limitation of the bone oscillator
you cannot go above a certain dB level
Latency of wave V is slightly ___ for BC clicks
longer
what are the increase latency of wave v in BC clicks
Adults = increase in wave V latency ~ 0.6 ms
Children = increase in wave V latency ~ 0.7 ms
why is the dynamic range different in bc abr
With bone-conducted ABR, stimuli rarely exceed 55 dB nHL because you can’t deliver intensity greater than 55 to 60 dB HL via the bone oscillator
are limitations of bc in audio also seen in abr
yes but worse with abr
cna only go up to 55-60
why do we lose earlier waveforms in bc abr?
because we can only do low intensities and these low intensities causes those waves to disappear
would almost 7 ms be normal in bc abr
yes but in ac abr would be abnormal
what will you see in bc abr
poor morphology
loss of other waves regardless of normal/abnormal results
only see wave 5
what is neuromaturation
nervous system is not fully mature when the baby is born
if it was, they would start walking and hold their head and sit up, etc.
because it is looking at the neurons and pathways it will affect the testing
what does that mean for us testing children abr?
the norms we have are for adults so we hae to have baby norms
babies change week/week month/month, there is a chart of norms to reference
why are abr affected by neuromaturation
because we are testing abr for children primarily so because of this we have to understand how their system works
different than adults due to neuromaturation
how long until abr looks adult like?
2-3 yrs
when can you use adult abrs norms for children
around age 3
Interpretation should include consideration of chronological and developmental age
what does this mean
a child can be 3 mos old but was 6 mos premature, so the child chronologically is 3 mos old but biologically they are 6 weeks less
what are the abr cautions
abr is affected by neuromaturation
abr normal itself doesn’t rule out all auditory abnormalities (low & high freq HL)
sedatioin is usually required for children between 6 mos and 4 yrs old unless they can sleep
what is a corner audio
everything is no response and then 80-75 dB around 250-500Hz
where is a click abr the most sensitive
bw 2-4 kHz
what are the ideal situation for children with ABR
Sedation is generally required for children between ~ 6 months and 4 years of age unless child in a natural sleep stage
what do we see with CHL in an abr
if whole wave shifts, the time bw I-V is the normal latency just shifted ot the right so the entire waveform is pushed out
to confirm it is CHL, you would need BC to determine
why do they not sedate newborns for ABR anymore
respiratory depressant for sedation and the young babies would cause them to stop breathing which is why they do not do this on them anymore
Wave V was replicable at 70 dB nHL, but disappeared at 60 dB nHL
what is the level of the hl? threshold?
55-60 dB
Characteristic of SNHL ABR
wave 1 prolonged latency (around 2 ms)
relatively normal wave V normal latency
BC abr is normal
list what you would see in abr with CHL
absolute latency is increased
mechanical issue in the middle ear, need more intensity to get the same levels so things shift out
list what you would see in abr with SNHL
Wave 1: distal part of the 8th nerve
wave 1 may be absent or increased latency
may see all the wave latencies being higher too
BS dysfunction in abr
only wave 1 is in tact and is intact and as you increase intensity it is still present (normally should disappear)
most common type of spina bifida
myelomeningocele
chiari ii malformation
congenital malformation of brain
significant manifestations of chiari ii
include structural changes to the pons and 4th ventricle, and downward displacement of the medulla, 4th ventricle and cerebellum into the cervical spinal canal
as latency increases, intensity
decreases
what is stilulus rate
how fast the signal stim is delivered
stimulus rate has no effect on abr waveforms
up to 20/s
higher stim rates can ____ latency of ABR waveforms and ____ amp
increase, decrease
what can be useful in diagnosing neurpathology like vestib schwannoma
increasing stim rate especially >90/s
why does increase stim rate be useful for diagnosing neuropathology
because the nervous system is stressed beyond its functional capacity
Increasing rate with pathology can result in abnormal latency shifts or disappearance of later waveforms
Increasing stimulus rate up to 50-90/second typically will have
little if any effect on a normal system
waht can you see with increasing rate with pathology
esult in abnormal latency shifts or disappearance of later waveforms
what do latency/intensity studies do
determine sensitivity
what do rate studies do
neuropathology
what would a normal rate study look like
want to see wave v, everything repeatable and all waveforms are present because you are not increasing intensity so everything is in tact
what is the difference between nf 1 & 2
nf 2 transmission - dominant
vestib schwanomas
CNS tumors
nf1
cafe au leat spots
subcutaneous & cutaneous tumors (not CNS tumors
abr with a vestibular schwannoma
tumor side will show wave 1 but no other waves
terrible morphology
why do they not do surgery right away to remove it?
they sacrifice their hearing because they take away the 8th nerve
they usually leave them alone
what are cochlear microphonics
characteristic: follows the stimulus exactly so when you change polarity the CM reverses, will see wave reversal
cochlear potential
from the OHCs
important for ANSD
how to tell cm from a peak in abr
cm peaks will flip and abr always stays up
A true ABR response will not reverse based on stimulus polarity
true
A true ABR response in ANSD will reverse based on stimulus polarity
yes because it is not a true ABR
what is abr a test of?
the nerve is generating the response, measuring neurosynchrony of the 8th nerve
if there is dysynchrony, what is clinical manifestation of this
they have more difficulty hearing in noise but difficulty understanding in general
why do PT with ansd have difficulties
because 8th nerve is not firing synchronously and we hear at the brain, 8th nerve is the first piece that goes from the cochlea and taking the information up and if it is effected everything following will get the same message and by brain, brain doesn’t understand the information
rarefaction
- polarity
peak goes down
condensation
+ polarity
upward peaks
alternating polarity
sum of condensation & rarefaction
how can cm mimic an abr and going all the way out?
we know it is a cm because when we reverse polarity can reverse so it is no longer an abr
because of the pathology - cm tends to ring longer
how can you figure out if it is an cm or abr
waveform reversal
what will cm look like in alternating polairty
flat line because they cancel each other out
why do abr peaks stay up in rarefaction
because they are neural responses and that is what they do
protocol for any child abr if they fail nbhs
start at higher intensity level (75-80)
start with two polarities and if waveform that doesn’t reverse, you are not looking at ansd
if they do reverse, = ansd
*do not start with alternating
how do you look for ansd
you have to run both polarities first
the CM mimics an ABR
true
what are the guidelines for abr on infant who failed NBHS
Perform one run with either a rarefaction or condensation polarity followed by a second run of the other polarity at a 70 to 75 dB nHL intensity
If the waveforms reverse – STOP – ANSD diagnosed!
If waveforms do not reverse, proceed to a threshold search by decreasing intensity and using any polarity
Do NOT use an alternating polarity initially because the +ve and –ve responses will sum resulting in what appears as no response and an incorrect diagnosis of SNHL
is management of snhl and ansd similar
NO they can be very different
relationship between latency and intensity in abr
as intensity decreases, latency increases
two ways you can diagnose ansd with ABR
- whole waveform reversal (two polarities)
- latency and intensity (latency will not shift to the right with an intensity decrease)
Latency will not increase with decreasing intensity
ANSD
what are clinical apps of abr
establish functional integrity of the auditory tract within the peripheral and central auditory nervous system (CANS)
Newborn infant hearing screening and threshold assessment
diagnose ANSD
confirm results of behavioral tests & establish site of lesion
Intra-operative monitoring of CN VIII
Assessment of difficult-to-test and non-cooperative patients such as sleeping/unresponsive patients & very young children
assess children & adults with intellectual disability and psychological disorders (mid and late AERs)
Detection of nonorganic hearing loss (NOHL)
Assessment of developmental disorders such as ADHD and (C)APD (mid and late AERs)
Assessment of dementias (mid and late AERs)
te closer you are to the periphery, the____ the latency is
shorter
AERs
auditory evoked responses
OAEs are sounds generated within
normal cochlea
OAEs are produced either n
spontaneously or in response to acoustic stimulation
strongly implicated and widely accepted as generators of all types of OAEs
OHCs
associated with absence of OAEs further supporting the hypothesis that OAEs are generated by these
Absence or damage of OHCs
OAEs are vulnerable to
noxious agents all of which can negatively affect the cochlea
what could affect/damage the OHCs
ototoxic drugs
intense noise
hypoxia (usually babies)
give a brief description of what OAEs are
pre neural
present when hearing sensitivity is normal
absent in frequency regions where cochlear hearing loss is >/= 30-40 dB HL
reliable OAEs are abtained between
around 500-8000 Hz
provides the mechanical source of OAE energy
motility of OHCs
can OAEs be absent in normal ears
yes, but very rare
why are they not affected by neuromaturation?
because they are developed by month 5, when you do oaes it doesn’t matter if they are a newborn or not you will still see them due to fully development of them
when does abr start to look adult like and use their data
2-3 yrs old
what is a limitation of OAEs
PT must sit/sleep quietly for a few min to complete the test
only allow for prediction of HL
what could an absent oae predict
anything from mild to severe snhl or middle ear disorder
present OAEs do not rule out
mild snhl, auditory processing disorders, or cn viii disorders
why are OAEs great screening tools but not diagnostically
because they cannot determine the severity of HL
what are soaes
spontaneous oaes
elicited without external stim
how are soaes measured
place a sensitive miniature microphone in ear canal
is there a correlation bw tinnitus and soaes
NO
what are teoaes
transient evoked otoacoustic emissions
occurs in response to a brief acoust stim (click/tone burst)
age dependent
how are teoaes age dependent
decreased amp as fxn of age with normal hearing
waht are dpoaes
distortion product oaes
these are a result of the nonlinear behavior of a healthy cochlea fxning as a nonlinear system
how are dpoaes administered
simultaneously presenting pure tones of two appropriate frequencies (f1 & f2) presented at two intensity levels (L1 & L2)
what elicits the best DPOAEs response in humans
2*f1-f2
why are oaes not measurable with ME pathology
responses are attenuated by ME pathology because it is not effectively transmitted through the ME system to be measured in the ear canal
what would you expect to see in OAEs with PE tubes?
may see responses or may see nothing
cannot say they failed because you know they have a tube
what are ME paths that could affect OAEs
pe tubes
negative me pressure (C)
collapsed ear canals
should you repeat OAEs after ME is healhty again?
YES
what would you get in OAE of negative type c tymp
variable responses
can you meausre oae in type b
do not do oaes
due to fluid and will attenuate the stimulus so they cannot be measured
what are collapsed ear canals? who gets them?
kids (up to 2 years of age)
cartilage isn’t fully formed so it is not hard and it causes a problem when headphones are used because it will close the canal with the tragus
old people
as we grow older skin loses elasticity and the cartilage isn’t as firm so when you put the headphone on you collapse the canal with the headphone or you push the enlarged tragus into their canal
what should you do before performing oaes
otoscopy and tymps
clinical uses of oaes
NBHS
hereditary HL
monitor cochlear status (noise exposure/ototoxicity)
difficult to test populations (young kids, NOHL, unresponsive PTs etc.)
site of lesion testing (cochlear vs retro)
diagnosis of ANSD)
confirmation of results of behavioral tests
