overview of ABR and OAEs Flashcards
what is Electrophysiologic audiometry
-Electrophysiologic audiometry are measures that record and analyze the auditory systems physiologic responses
-They are objective in that they do not require the subject’s active participation, and are complementary to audiometry, which is subjective
what are different types of electrophysiological tested used in audiology
1)Immittance tests, which are:
-Tympanogram
-Middle ear acoustic reflexes and reflex decay
2)Otoacoustic emissions (OAEs)
3)Auditory evoked responses (AERs)
what does the neurons in the brain do for auditory evoked responses(AERs)
(how do they communicate?)
Neurons in the brain communicate via rapid electrical impulses that allow the brain to coordinate behavior, sensation, thoughts, and emotion
-were measuring those train of responses
how does the CNS contribute to AERs
it generates spontaneous and random neuroelectric activity at all times
The central nervous system, even in the absence of sensory stimulation, generates spontaneous and random neuroelectric activity
how do we record AERs?
-This activity can be recorded using scalp electrodes
-This activity forms the basis of the electroencephalogram (EEG)
What does it allow us to record?
-it allows us to record neural activity in response to a sensory stimulation, which can then be picked up by an EEG
-It also allows recording of neural activity in response to specific types of sensory stimulation, which can be extracted from the EEG
what exactly is Auditory evoked responses?
An auditory evoked potential (AEP) or response (AER) is an activity or response within the auditory system that is produced or stimulated (evoked) by sounds
what part of the ear is involved in AERs?
The activity may be in the :
Cochlea
Auditory nerve
Central auditory nervous system (CANS)
AERs are examples of what type of activity
-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, which, therefore, requires significant signal amplification and other mechanisms to read those responsesa
are auditory evoked responses and auditory potentials the same thing?
yes, it’s just a different name
in auditory evoked responses, what is the first area in the ear to get the response
the cochlea
do hair cells get a response in AERs ?
no, they don’t. the nerves do
how many sequential series are in ABRs
The ABR consists of a sequential series of 5-7 peaks (responses)
how long does the stimulus last in ABRs?
The response occurs for ~ 5 to 10 ms following stimulus onset
what peak do we focus on in clinical for ABR
In clinical practice the focus is on the following peaks :
I to V in general
I, III, and V in particular *****
what is are clinical application of ABR
-The ABR can provide a close estimate of hearing threshold for specific frequencies
-It can predict a conductive, sensory, or neural site-of-lesion
-It is a screening tool for retrocochlear pathologies
what is something SUPER important to remember in ABR
what are we measuring in ABRs?
were measuring NERVE RESPONSE not hair cells response
what will happen when the neurons aren’t in synchrony
you won’t be able to hear speech in noise because we hear with our brain and not with our ears
-ex ANSD
do audiograms reflect neural synchrony ?
NO because it focuses on OHC and ABRs functions are focusing on neural synchrony
why is ABR a screening tool and not a diagnostic tool?
it tells you something is wrong in general but not exactly what is wrong
what are the Anatomic generation sites of the ABR for wave 1,3, 5 and ?
-Wave 1
-Wave III
-Wave V
Blood supply:
Cochlea - labyrinthine artery, which is generally a branch of the anterior inferior cerebellar artery (AICA)
Brainstem - Vertebrobasilar artery
what are the normative peak latency values at 80 db nHL at wave 1
Wave I: 1.5 ms (mean)
(SD = + 0.25 ms)
what are the normative peak latency values at 80 db nHL at wave 2
Wave II: 2.6 ms (mean)
(SD = + 0.25 ms)
what are the normative peak latency values at 80 db nHL at wave 3
Wave III: 3.7 ms (mean)
(SD = + 0.25 ms)
what are the normative peak latency values at 80 db nHL at wave 4
Wave IV: 4.7 ms (mean)
(SD = + 0.5 ms)
what are the normative peak latency values at 80 db nHL at wave 5
Wave V: 5.5 ms (mean)
(SD = + 0.5 ms)
-this is the most important wave in terms of hearing levels and neural synchrony
where does wave 1 in ABR come from?
distal CN 8 in the cochlea
where does wave 3 in ABR come from?
cochlear nucleus, trapezoid body, superior olivary complex
where does wave 5 in ABR come from?
lateral lemniscus
what are are normative interwave or interpeak latency at 80dB nHL presentation level from wave 1-3
I - III IPL: 2.25 ms
(SD = + 0.5 ms)
what are are normative interwave or interpeak latency at 80dB nHL presentation level from wave 3-5?
III - V IPL: 2.0 ms
(SD = + 0.5 ms)
what are are normative interwave or interpeak latency at 80dB nHL presentation level from wave 1-5
I - V IPL: 4.0 ms
(SD = + 0.5 ms)
what does IPL mean?
inter-peak-latency
what does nHL mean?
normative hearing level
look at slide 10
try to memories
what is considered a good stimuli in an ABR?
between an ABR intensity and latency ?
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
in the relationship between ABR intensity and latency, what happens are intensity decreases??
-Wave 1 disappears first and with further intensity decrease (at ~ 55 to 65 dB nHL), all waves, except wave V, will disappear
-wave 1 disappears but that’s normal in humans, it happens in EVERY human but if intensity continues to decrease, every wave disappears except wave 5 and that’s not normal
-As intensity decreases the latency of the waves (wave V) increases *
-As intensity decreases the morphology of the ABR response deteriorates**IMPORTANT !!!!!
what is something to remember ABR intensity and intensity function
Actual hearing threshold is typically ~10 to 15 dB HL better than the ABR threshold
-look at slide 12
in normal bone conduction ABR, what does bone conduction ABR resemble?
BC ABR resembles AC responses seen with lower intensity air-conducted clicks because of poor mechanical characteristics of bone-conduction transducers
how does the bone conduction ABR resemble Air conduction response ?
-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
how does latency in wave 5 look like in normal bone conduction ABR?
Latency of wave V is slightly longer for BC clicks:
Adults = increase in wave V latency ~ 0.6 ms
Children = increase in wave V latency ~ 0.7 ms
how does dynamic range look like in normal bone conducted ABR?
-the dynamic range is different
-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
what are some ABR cautions?
1)The ABR is affected by neuromaturation
-we typically use ABRs on babies so we need different norms for them
2)A normal ABR, by itself, does not rule out all auditory abnormalities, for example low and high frequency hearing loss
3)Sedation is generally required for children between ~ 6 months and 4 years of age unless child in a natural sleep stage
what is affected in an ABR because of neuromaturation?
-A separate set of norms is required for newborns and babies
-The ABR begins to assume adult latencies by ~ age 2 and becomes “adult-like” by about age 3 years
-Interpretation should include consideration of chronological and developmental age
-baby should be sleeping
click ABRs are most sensitive in between what freq?
The click ABR is most sensitive between 2000 and 4000 Hz
- as a result, an abnormal ABR (ex delayed waveforms or no response) by itself doesn’t mean there is NO residual hearing
what do we see in ABRs with conductive HL?
-Absolute latencies are pushed out, but the relative interwave latencies were retained within normal limits
-Wave V was replicable at 70 dB nHL, but disappeared at 60 dB nHL
-Approximate hearing threshold would be 60 dB HL (70 dB nHL -10)
how does an ABR with sensorineural HL look like ?
-Prolonged wave 1: Wave 1 showing prolonged latency (~ 2 ms)
-Relatively normal Wave V: Wave V showing normal latency (~ 6 ms)
-Latency-intensity function shows a wave V not repeatable at 45 dB nHL – a higher hearing threshold
look at slide 17
how is stimulus rate affect ABR waveforms?
-ifthe stimulus is 20sec or below, it won’t affect the ABR
-if the stimulus is gets over 20 sec then the latency increaases and the ABR waveforms decrease in amplitude
-Stimulus rate (how fast the signal stimulus is delivered) up to 20/second is generally believed to have no effect on the ABR waveforms
-BUT higher rates can generally increase the latency of the ABR waveforms and decrease the amplitude
what happens when you increase the stimulus rate in ABR ?
Increasing stimulus rate up to 50-90/second typically will have little if any effect on a normal system important
how is increasing the stimulus rate help diagnois a neuropathology
Increasing stimulus rate, especially > 90/second, can be useful for diagnosing neuropathology such as vestibular schwannoma
Increasing rate with pathology can result in abnormal latency shifts or disappearance of later waveforms
look at slide 19 on pdf (on mine its 21)
look at slide 20 pdf (22 on mine)
look at slide 21 (23 on mine)
in ABR stimulus polarity and ANSD, are true ABRs reversed based on the stimulus polarity?
A true ABR response will not reverse based on stimulus polarity
But in ANSD, it will because its not a true ABR
what do responses look like in ABR and ANDS?
The response is actually an abnormally long ringing cochlear microphonic (CM) that reverse itself because it follows the stimulus exactly
how does refraction look like in ASND in ABRs?
Rarefacation = it’s a negative polarity, downward peaks
how doe condensation look like in ABR with ANSD?
Condensation = positive polarity, upward peaks
alternating polarity is the sum of what ?
Alternating polarity = sum of condensation and rarefaction
look at slide 23 (24 mine)
how will the polarity look like in ANSD
For ANSD, the response will reverse polarities based on the stimulus polarity, therefore, the following guidelines are put in place for performing a diagnostic ABR on an infant who failed the newborn hearing screening
what are steps you need to do when achild fails their newborn hearing screening
1)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
2)If the waveforms reverse – STOP – ANSD diagnosed!
3)If waveforms do not reverse, proceed to a threshold search by decreasing intensity and using any polarity
4)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
are management of the SNHL and ANSD the same ?
NO ! Management of SNHL and ANSD can be quite different
look at slide 25 (good notes 26)
will latency increase if intensity decreases IN ANSD ?
Latency will not increase with decreasing intensity
what are clinical applications of AERs?
-To establish functional integrity of the auditory tract within the peripheral and central auditory nervous system (CANS)
-Newborn infant hearing screening and threshold assessment
-To diagnose ANSD
-To 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
-To 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)
what are OAEs?
OAEs are sounds generated within the normal cochlea
how are OAES produced?
OAEs are produced either spontaneously or in response to acoustic stimulation
where are OAES measured ?
OHCS
OAEs are pre-neural [generated by sensory (OHCs) not neural cells or synapses]
what happens if OHCs are missing?
missing OHC means you hav emissing OAEs
Absence or damage of OHCs is associated with absence of OAEs further supporting the hypothesis that OAEs are generated by OHCs
what are OAEs vulnerable to ?
OAEs are vulnerable to noxious agents all of which can negatively affect the cochlea, for example
-ototoxic drugs
-intense noise
-hypoxia
where are OAEs present ?
OAEs are present when hearing sensitivity is normal
What db levels is needed for OAEs to be missing ?
OAEs are absent in frequency regions where cochlear hearing loss is > 30 to 40 dB HL
where are reliable OAEs obtained?
between ~500 to 8000 Hz
motility of the OHCs provides what?
Motility of OHCs provides the mechanical source of OAE energy
what is the percentage of normal ears having OAEs?
Prevalence of OAEs in normal ears is over 99%
Rare documented cases of absent OAEs in normal ears
-never 100%!!
what is something important to remember in OAEs?
Unlike the ABR, OAEs are present and robust in newborns and are not affected by neuromaturation effects
what are some limitations of OAEs?
peoplehave to sit quietly for a few mintues and it’s only a prediction of a hearing loss
-Patients must sit/sleep quietly for a couple of minutes to allow completion of testing
-OAEs allow only for prediction of a hearing loss
what are some predictions of hearing loss in OAES
-Absent OAE = anything from a mild to severe SNHL or middle ear disorder
-Present OAEs do not rule out a mild SNHL, auditory processing disorders, or CN VIII disorders
what is something important to remember in OAEs?
OAEs cannot determine severity of hearing loss, which makes them a great screening but a poor diagnostic tool
what are the 2 types of OAEs?
1)Spontaneous OAEs (SOAEs)
2)Transient evoked otoacoustic emissions (TEOAEs)
3)Distortion Product Otoacoustic Emissions (DPOAEs)
what is Spontaneous OAEs (SOAEs)?
-drawn out without external stimulation
-SOAEs measured by placing a sensitive miniature microphone in the ear canal
-No significant correlation between tinnitus and SOAEs
what is Transient evoked otoacoustic emissions (TEOAEs)??
Occur in response to brief acoustic stimulus (click or tone burst)
-TEOAES appear age-dependent
-Decreased amplitude as function of age with normal hearing
what are characteristics of OAEs?
-A healthy cochlea functions as a nonlinear system
-DPOAEs are a result of this nonlinear behavior
-DPOAEs can be generated from the cochlea by
-Simultaneously presented pure-tones of two appropriate frequencies (fi & f2) presented at two intensity levels (L1 & L2)
-2f1-f2 elicits the best DPOAEs in humans
what is something important to remember in Distortion Product Otoacoustic Emissions (DPOAEs)
2f1-f2 elicits the best DPOAEs in humans
can OAEs be measures with a middle ear pathology?
With middle ear pathology OAEs may not be measurable because they are not effectively transmitted through ME system to be measured in the ear canal – response attenuated by ME pathology
can you do OAEs with PE tubes?
it’s variable response but OAEs are not contraindicated
-just wait for the PE tube to come out but if not then don’t do OAEs
can you do OAEs with someone with negative ME pressure (type C tympanogram)
Variable response depending on severity of ME pathology
can you do OAEs with a collapse ear canal ?
Collapsed ear canals may interfere with obtaining OAEs
what should you do before doing OAES?
perform otoscopy and a tympanogram to assess ME function
what might reduce the amplitude of OAEs?
OAEs could be reduced in amplitude or obliterated due to PE tubes, -ve ME pressure, otitis media with effusion
what should you do once the middle ear is healthy again ?
Repeat OAEs after the middle ear is healthy again
why do we clinically use OAES?
-Newborn hearing screening
-Hereditary hearing loss
-Monitoring cochlear status
-Noise exposure
-Ototoxicity
-Difficult-to-test populations
-Young children, NOHL, unresponsive patients,
etc.
-Site-of-lesion testing
-To differentiate between cochlear and
retrocochlear pathology
-Diagnosis of auditory neuropathy spectrum
disorder (ANSD) (present OAES in ANSD)
-Confirmation of results of behavioral tests
