Overview of ABR and OAE Flashcards
Are electrophysiologic tests objective or subjective?
Objective, does not require patient response
What are some electrophysiologic tests used in audiology?
Immittance tests (tymps, reflexes, reflex decay)
OAEs
AERs (ABR)
Can someone fake electrophysiologic audiometry?
No
What are auditory evoked responses (AER)?
Neurons in the brain communicate via rapid electrical impulses that allow the brain to coordinate behavior, sensation, thoughts, and emotion
The CNS, even in the absence of sensory stimulation, generated spontaneous and random neuroelectric activity
Can be recorded using scalp electrodes
What do these spontaneous brain activities form the basis of?
Electroencephalogram (EEG)
Can we also record responses (using EEG) to certain neural activity in response to sensory stimuli?
Yes, this includes hearing
Where is AEP or AER activity?
Cochlea
Auditory nerve
CANS
Are EEG responses huge?
Yes
Do we need to extract evoked responses from the general EEG responses?
Yes
Requires significant amplification and other mechanisms
What does an ABR consist of?
A sequential series of 5-7 peaks (responses)
What are we looking at for ABRs?
The latency of the response from onset of the stimulus
In clinical practice, what peaks of the ABR do we focus on?
I to V in general
I, III, V in particular
Why do we not care about waves II and IV?
Because they are assumed to be there if the others are there
Can an ABR provide a close estimate of hearing thresholds for specific frequencies?
Yes
Is ABR a test of hearing sensitivity?
No, just an estimate
Rather, it is looking at neural synchrony
Can ABRs predict a conductive, sensory, or neural site of lesions?
Yes
Why it is used for newborn hearing screening
Is an ABR used as a screening tool for retrocochlear pathologies?
Yes
Tells you something is wrong, but doesn’t tell you specifics
What area is wave I associated with?
Distal 8th nerve in the cochlea
What area is wave III associated with?
Cochlear nucleus, trapezoid body, and superior olivary complex
What area is wave V associated with?
Lateral limniscus
What is the blood supply to the cochlea?
Labyrinthine artery (branch of AICA)
What is the blood supply of the brainstem?
Vertebrobasilar artery
What is the normative peak latency for wave I at 80 dB nHL?
1.5 ms
What is the normative peak latency for wave II?
2.6 ms
What is the normative peak latency for wave III?
3.7 ms
What is the normative peak latency for wave IV?
4.7 ms
What is the normative peak latency for wave V?
5.5 ms
What is the standard deviation for latency values for waves I, II, and III?
0.25 ms
What is the standard deviation for the latency values for waves IV and V?
0.5 ms
What is the interpeak value for I - III?
2.25 ms
What is the interpeak value for III - V?
2.0 ms
What is the interpeak value for I - V?
4.0 ms
What transducers are used for ABR?
Inserts
What types of stimulus are used for ABR?
Clicks
Chirp
Tone burst (short frequency specific signal)
Speech stimuli (/ba/, /da/)
What are the polarities of ABR?
Rarefaction (negative)
Condensation (positive)
Alternating (combined polarity)
What is alternating polarity?
Computer will run rarefaction and condensation itself and add the information together
What is the rate of the ABR stimulus presentation?
> 20/s
Odd numbers like 21.1 or 27.3
Why is there an odd number of presentations for ABR?
Reduces artifact
What rate of ABR is used for neurodiagnosis?
> 90/s
What intensity is used for ABR?
It is variable depending on what you’re looking for
could be from 10 to 90 dB
What type of stimulus gives the best ABR responses in a normal hearing listener?
Clicks at about 75 to 90 dB nHL
What does nHL mean?
Normal hearing level
Levels in dB relative to the subjective click threshold level for subjects with normal hearing
As intensity of the ABR decreases, what occurs in the wave?
As intensity decreases, all waves disappear except for V
Wave I disappears first
The latency of the wave (V) increases
The morphology of the wave will change (become less clear)
Is an ABR threshold accurate to an actual hearing threshold?
An actual hearing threshold is typically 10 to 15 dB better than the ABR threshold
How is an ABR threshold determined?
At the lowest intensity that wave V can be recognized
What do BC ABRs look like?
They look like lower intensity AC ABR with clicks
Morphology poorer
Wave V visible, but no others
Why do BC ABRs look like that?
Because bone-conduction output is limited
Is the latency the same for BC ABR?
No, it is slightly longer than AC ABR
Adult latency increases by 0.6 ms
Children latency increases by 0.7 ms
Is the dynamic range different for BC ABR than AC ABR?
Yes
You rarely exceed 55 dB nHL because you can’t deliver intensity greater than 55 to 60 dB HL via a bone oscillator
Is an ABR affected by neuromaturation?
Yes
What does neuromaturation mean?
The maturity of the nervous system
Not mature when we are born
Is there separate norms for newborns and babies?
Yes
And they are constantly changing with the age of the child
There is a chart to reference
When does the ABR of a child begin to assume adult latencies?
By age 2
When does a child’s ABR become adult like?
By age 3
In your interpretation of an ABR, should you consider the chronological and developmental age?
Yes
Their developmental age may be different based on prematurity
Can an ABR rule out all auditory abnormalities?
No
What frequency range are click ABRs most sensitive?
2000 to 4000 Hz
Due to the optimal frequency range of a click ABR being 2000 to 4000 Hz, is an abnormal ABR mean no residual hearing?
No
Is sedation generally used for children between 6 months and 4 years of age?
Yes
Unless the child is naturally asleep
ABRs required no movement
ABR characteristics of CHL
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)
Brainstem dysfunction ABR
Only wave 1, no later waves seen
Probably a retrocochlear pathology
ABR characteristics of SNHL
Prolonged wave I
Relatively normal wave V (normal latency)
Does a stimulus rate up to 20/sec believed to have an effect on the ABR waveforms?
No
When it is higher than this, it puts stress on the system
What do higher rates of ABR produce?
Increased latency and decrease in amplitude
What is the goal of a rate study?
Diagnosis neuropathology
Vestibular schwannoma
What do they typically increase the rate to for a rate study?
> 90/sec
What will increasing the stimulus rate to 50-90/sec do to the ABR?
Typically have little effect
What does an ABR with a vestibular schwannoma look like?
Wave I is diminished and absent waves III and V
How does a tumor effect the rate of an ABR?
Increase in wave V latency with increasing rate
Increasing rate shows poorer morphology
Does a cochlear microphonic reverse?
Yes, when you reverse the polarity
Do people with ANSD have true ABRs?
No, they typically have abnormally long CM that look like ABRs
How do you tell the different between a CM that is long and looks like an ABR and a true ABR?
Change the polarity
True ABRs won’t reverse, but CMs will
Alternating will be a flat line for CM (cancel each other out)
Do CMs follow the stimulus exactly?
Yes
What are the guidelines for a diagnostic ABR that are performed on an infant who failed their NBHS?
Perform one run of either rarefaction or condensation followed by the other at 70-75 dB nHL
If the waves reverse, it’s ANSD and stop
Proceed with threshold search by decreasing intensity and using any polarity
Why should you not use an alternating polarity initially?
Because if they have ANSD, the positive and negative responses will sun resulting in what appears as a no response and an incorrect diagnosis of SNHL
Is the management of ANSD and SNHL different?
Yes
Why it is so important to distinguish the two
What does an alternating ABR of a person with ANSD looks like?
Flat line
The two CM cancel each other out
Can we diagnose ANSD?
Yes
Falls within our realm
Besides the CM, what are other indications of ANSD?
No latency increase with decreasing intensity
Poor morphology
What are the two ways to diagnose ANSD?
Reverse polarity (due to ABR being a CM) and no latency with decreasing intensity of stimulus
What are the clinical applications of AERs?
To establish functional integrity of the auditory tract within the peripheral and central nervous system
NBHS and threshold assessment
Diagnose ANSD
To confirm results of behavioral tests and establish site of lesion
Intra-operative monitoring
Assessment of difficult to test and non-cooperative patients
To assess children and adults with intellectual disability and psychological disorders (mid to late AERs)
Detection of nonorganic HL
Assessment of developmental disorders (ADHD and CAPD) (mid to late AERs)
Assessment of dementias (mid to late AERs)
What are OAEs?
Sounds generated within the normal cochlea
Produced either spontaneously or in response to acoustic stimulation
OHCs generate all types of OAEs
How does the absence or damage of OHCs affect the OAEs?
Result in absence of OAEs
Supporting the idea that they are generated by OHCs
Are OAEs vulnerable to noxious agents?
Yes
What are some things that can affect OHCs and, therefore, OAEs?
Ototoxic drugs
Intense noise
Hypoxia
Are OAEs preneural?
Yes
Are OAEs present when hearing sensitivity is normal?
Yes
What level of hearing loss would OAEs be absent?
At or greater than 30 to 40 dB HL
What frequency regions are robust OAEs obtained?
500 to 8000 Hz
Are OAEs present at birth?
Yes
The cochlea is fully developed at 5 months gestation
Limitations of OAEs
Patients much sit/sleep quietly for a couple of minutes
OAEs allow only for a prediction of HL
What does an absent OAE mean?
Anything from mild to severe SNHL or ME disorder
What does present OAEs mean?
Does not rule out mild SNHL, auditory processing disorders, or CN VIII disorders
Can OAEs determine severity of hearing loss?
No
Great screening tool, not diagnostic
What are spontaneous OAEs?
Elicited without external stimulation
Measured by placing a a sensitive mic in the ear canal
Is there a correlation between tinnitus and SOAEs?
No
What are transient OAEs?
Occur in response to brief acoustic stimuli (click or tone burst)
Appear to be age-dependent
Why are TOAEs age dependent?
Decreased amplitude as a function of age with normal hearing
Robust as a newborn
As integrity of hair cells decrease, so do OAEs
What are distortion product OAEs?
A healthy cochlea functions as a nonlinear system
Result of nonlinear behavior
Generated by the cochlea by presenting pure tones of two frequencies at two intensity levels
What elicits the best DPOAEs in humans?
2F1-F2
Should DPOAEs be above the noise floor?
Yes
Can you get OAEs on someone with a ME pathology?
May not be able to if they are not effectively transmitted through the ME system
Response attenuated by ME pathology
Can PE tubes affect OAEs?
Variable responses
OAEs are not contraindicated
Can someone with negative ME pressure (type C tymps) do OAEs?
Yes
Variable responses depending on the severity
Can collapsed ear canals affect OAEs?
Yes
Use inserts instead to fix this
Most common in babies and older adults
Prior to performing OAEs, what should be done?
Otoscopy and tymps to assess ME function
What should be done if the ME is not healthy and OAEs cannot be performed?
Wait until it is healthy again
Or repeat after healthy
What are the clinical uses of OAEs?
NBHS
Hereditary hearing loss
Monitoring cochlear status (noise exposure, ototoxicity)
Difficult to test populations
Site of lesion testing (cochlear vs retrocochlear)
Diagnosis of ANSD (present OAEs in ANSD) - needs to be done with ABR
Confirmation of results of behavioral tests
