1
Q
Electrocochleography (ECochG)
Auditory Brainstem Response (ABR)
Middle Latency Response (MLR)
P300
Auditory Steady-State Response (ASSR)
Otoacoustic Emissions (OAE) - Don’t worry about we get a whole separate class for this
Which are more common in the clinic?
A
ECochG
ABR
ASSR
2
Q
Sound arrived at the?
A
Round window
3
Q
When sound arrives at the round window it?
A
Vibrates the fluids of the inner ear & BM
Creates a traveling wave
4
Q
BM is organized?
High frequencies peak at the?
Low frequencies peak at the?
A
Tonotopically
Base
Apex
5
Q
BM moves in response to?
A
Sound - causes ionic channels to open or close
6
Q
Vibration of the BM results in _____ or _____ of the stereocilia at the _____ of each hair cell
A
bending or shearing
Top
Causes ionic channels to open or close
*the brain can only interpret electrical signals
7
Q
Hair cells are different in?
A
morphology, innervation, and function
8
Q
OHC?
A
Three rows of OHC - separated by supported cells
efferent pathway - bringing sounds up from the cochlea
9
Q
IHC?
A
One row of IHC - predominantly for haring
Sensory receptors 95% of auditory nerve fibers of the brain arise from IHC
10
Q
IHC are part of the _____ pathway - away, brain to the ear
A
afferent - travels to the brain from the ear
11
Q
Nerve endings exit the _____ to form?
A
Cochlea - cranial nerve eight (vestibulo-cochlear nerve or CNVIII)
12
Q
CNVIII synapses at the ______, and then information travels to the higher structures in the brainstem
A
brainstem
Sound is processed in the auditory cortex in Heschl’s gyrus in the temporal lobe
13
Q
_____ auditory pathways form a complex network of cell types, oranizations, and interconnections
A
Subcortical
14
Q
_____ is maintained in the auditory cortex
A
tonotopicity
15
Q
Neural redundancy is evident in?
A
CANS processes information in overlapping ways
16
Q
CANS =
A
Central Auditory Nervous System
Cochlea → brainstem → thalamus → auditory cortex
Cochlea → cochlear Nucleus (brainstem, pitch, loudness, timing) → Superior olivary complex (localization, this is where sound is compared from both left and right ears) → Lateral Lemniscus (pons, more like fibers, ascending pathway, bringing sound from lower structures up) → Inferior Colliculus (midbrain, processing, relaying sound, detecting changes in sound like rhythm) → Medial Geniculate body (thalamus, brings signals to AC) → Auditory cortex (sound becomes meaningful)
17
Q
What are AEPs? or EV?
A
Involves the process of stimulating (evoking) responses/potentials from the auditory system
18
Q
AEPs is an _____ signal elicited as a result of auditory stimulation
A
electrical
sounds are presneted & brain waves ( electrical potential) are generated
Waves are analyzed, and this is what we are interpreting (our test results)
Brain waves in response to all kinds of sounds
They are analyzed against norms, and their responses are all called time-locked
19
Q
Responses are ______
A
time-locked - generally very quick
20
Q
Stimulation that elicits a series of electric signals (potentials) within the ear and nervous system can be used to?
A
Assess hearing
Intraoperative monitoring
Neurophysiologic research
The patient does not need to actively participate - objective test resting, but awake
21
Q
we use ____ to record neural activity, specifically focused on the auditory system
A
technology
22
Q
Why is this important?
A
Early detection & diagnosis of auditory dysfunction
Hearing screening and threshold estimation
Leads to effective intervention for hearing loss and other auditory disorders
Site-of-lesion testing
Retrocochlear disorders
Intraoperative monitoring
Patients who are undergoing surgery - so if a patient has a risk of losing their hearing, they run evoked potentials while they are under anesthesia to monitor their hearing
Vestibular
Contributes to the diagnosis of pathology (i.e. Meniere’s)
EchoG is what is used to test for Meniere’s
Useful for difficult-to-test populations Infants Difficult to test children or adults
Patients with cognitive impairment, patients with false/exaggerated HL
23
Q
What are the different classes of AEPS
A
Early
- Electrocochleography - cochlea
-ABR - responses come from regions of the brain
24
Q
Late
A
P300
ALR
Latency is the response after the stimulus has occurred
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Middle
AMLR
Latency is the response after the stimulus has occurred
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Far-field recordings - what we typically see
recordings are made far from where the response is generated
Ex. surface electrodes on the forehead
Most recordings are usually far-field recordings
Information is conveyed from the auditory structures through body tissue, fluids, bone, and skin
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Near-field recordings
Recordings are made close to where the response is generated
Recording electrodes are often placed on or very close to the neural generator
Generally invasive - used more in surgical cases
Sensitivity of electrode placement
Millisecond (ms) - One thousandth of a second
Microvold (μV) - one thousandth of a millivolt
One millionth of a volt
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AEP measures changed over time
*Remember, these are very quick responses
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1. Amplify
2. Signal Averaging
1.
a. Amplifiers (bio-amplifiers) make the signals large enough to see
2.
a. Synchronization of stimulus onset and response
b. Several responses are recorded and averaged to minimize noise
30
Noise is referred to as?
anything that is not a response of interest:
Non-auditory brain activity
Actual noise - like lights, talking, typing, clock ticking
Electrical interference - cellphones, lights, outlets
Patient movement, they need to stay still, which will lead to a better waveform
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Latency is measured in? on the ____ axis and the _____ at which the response ____
Measured in ms
Horizontal X-axis
The time at which the response peaks
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Amplitude is measured in? on the __ axis and intensity level affects the _____ of the response
Measured in microvolts
Vertical Y-axis
Intensity level affects the amplitude of the response
Measured the distance between peaks and dips
*Waves 1-5 are usually the most important
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Most AEPs are elicited by breif acoustic transient sounds presented via a?
transducer such as
Headphones
Insert phones - usually preferred, reduce ambient noise, reduce IA, more sanitary
Bone oscillator
In some cases, we even use the loudspeaker
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Inserts are preferred why?
1.
2.
1. Reduce ambient noise, prevent collapsed canals, and infection control
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What are subject variables?
Age
Gender
Body temperature
State of arousal - awake, asleep - eye blinks will create a lot of artifacts in recordings
Drugs/medication
Muscular artifact is the patient restless
Hearing status - depending on their statis, this might limit us from testing *their hearing cannot be too severe
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What are stimulus variables?
for ____ and _____ NOT ___
Most common for ABR and ehochG, NOT used for ASSR
Clicks - short
Tone bursts - short
*Creates simultaneous firing of multiple neurons of the auditory nerve
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Click
Most commonly used for ABR
Broad-spectrum stimulus because they are not frequency specific - Encompasses a wide range of frequencies, and all regions of the cochlea are activated
Well-suited for generating synchronous firing of neurons
Brief (also known as transient sounds ~ .1ms)
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Tone Burst - better for adults or children
Brief
Modified Pure tone
Standard of care for ABR in Infants and young children - Because they are frequency specific
Frequency specific - 500, 1000, 2000, 4000 Hz
Can be used to define the degree and configuration of hearing loss - It can be important for early intervention, and no patient participation to figure out the threshold estimation
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Chirps
Newer stimuli
sounds similar to tone burst
Provides a larger ABR amplitude - low + high frequency stimuli, and low-frequencies are presented before high
More confident identification of wave (ABR)
Reduced test time
40
Duration refers to?
a.
b.
a. The length of the acoustic stimulus from beginning to end
b. The sum of the rise time, plateau time, and fall time
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Intensity
a.
b.
c.
a.How loud is the stimulus
b. Amplitude increases with increasing intensity
C. Latency decreases with increasing intensity
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Rate of stimulus
a.
b.
a. The frequency at which the stimuli are presented
b. Slow vs Fast
i. Slow is better morphology, getting a better picture of what you are trying to obtain, activating areas like the mid-brain thalamus, and auditory cortex
ii. Faster rate, you may get delayed responses, cochlear CNVIII, lower brain stem
43
Number of stimuli (sweeps # times presented)
a.
b.
c.
a.More stimuli, more time to average response
b. better chances of a good result
c. sometimes with EChoG, they will tell you to get 400-800 sweeps, but ABR will be 2000
44
Three types of polarity?
Rarefaction - negative
Condensation - positive
Alternating
1. switching between the first two
2. can help eliminate the response we are not interested in
45
Clinical applications?
1.
2.
3.
4.
1. Diagnosis/assessment/monitoring of menieres disease - used to help diagnose it
2. Enhancement of ABR Wave 1 and V total that we are concerned about
3. Monitor cochlear and 8th nerve function during surgical procedures
e.g. cochlear implantation to monitor pre and post implantation
-Also possibly during surgery for semicircular canal dehiscence
4. Contribute to the diagnosis of auditory neuropathy
46
All time locked
Latency is ______ ms recorded within a ___ms window
use a ________ signal 90-100 dB
Generators: _____ and _____ nerve
.2-4.0 ms - 10ms
high-intensity
Cochlear & 8th nerve
Dependent on the integrity of hair cells, you need to have a good hearing, or you may not be able to get a recording, or you can't repeat, or even its not that clear to mark
47
Components?
CM - while important, it is typically not marked for clinical purposes; however, we are not gonna see that for the diagnosis of Meneres disease
SP - always gonna mark before AP
AP - always gonna mark between 1-2ms for the purpose of this class
-also wave 1 - same thing
The base is simply there so you can find your other peaks and have somewhere to start - the baseline is gonna be right around the 0ms mark, its gonna be the first thing we see
47
Endolymphatic Hydrops:
swelling of the membranous labyrinth because of increased production or decreased absorption of endolymph
47
CM
1st direct measurement of hair cell function
AC (alternating current) - electrical potential - believed to originate mainly from the sum of extracellular components arising from IHCs and OHCs
Believed that OHCs contribute more to CM more than IHCs generation
Instantaneous response - no delay
-Also known as the presynaptic response
47
SP - 2nd
Arises from the hair cells of the cochlea
-OHC & IHC - >50% from IHCs
DC - direct current potentials
Can be evoked by transient stimuli
Clicks (most common) or tone bursts
Usually appears as a bump or a ledge on the beginning of the slope of the action potential (AP) or as a distinct wave peak
*patients with meners disease will have an enlarged SP
48
AP 3rd - also known as compound action potential (CAP)
Post-synaptic response
Generated from fibers in the distal/cochlear end of CNVIII
Larger amplitude than SP
Latency (where we expect to see) of AP can be seen arounf 1.5 ms
AP= wave 1 of ABR
48
Morphology
overall shape and calrity of a waveform
48
How well can the components of the ECochG be identified?
Good morphology
-clear baseline
-Distinct peaks/troughs
Poor morphology
-Smeared/Noisy
-Components are hard to identify
In menieres for reference to what were talking about the sp increases in size and the CAP decreases in size as the disorder/pathology progresses
SP/AP ratio
49
ECochG Generators
CM - OHC
SP - OHC IHC >50%
AP - afferent fibers in the distal part of CNVIII
50
TT - transtympanic
1.
2.
3.
1.Invasive
2.Elctrode inserted through TM
3. Promontory wall of the cochlea
50
Waht are some advantages and disadvantages of TT electrodes
Advantages:
-Larger amplitudes - probably the largest of all the types
-Fewer signal averages - computer runs fewer sweeps = more stable response
-Helps with preimplantation with cochlear implants
-Stable Response
-Quicker
Disadvantages:
-Need MD supervision
-Anesthesia
-Patient Discomfort
50
ET - Extratympanic - can use clinically
Electrode placed directly on the TM
Invasive but lessish
Better responses, but the amplitudes wont be as large
51
TipTrode is?
Least invasive of the three - most common in the clinical setting - covered in conductive gold foil
An electrode is placed on the skin of the ear canal - scrub the ear canal
51
ET- Tymptrode advantages and disadvantages
Advantages:
-No need for MD
-No anesthesia
-Little to no patient discomfort
Disadvantages:
-Smaller SNR
-Smaller amplitude
-More signals are needed to average
-Longer test time
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54
TipTrode advantages and disadvantages
Advantages:
-Good conduction for electrical impulses
-Can do alone - No MD
-Easy
Disadvantages:
-Very small amplitudes
- Artifact
Longer test time - 30-40 min
54
What are the three primary electrodes?
TT, ET, TipTrode
54
Ground/common electrode is ________ _______
Vertex _______ ______
Between eyebrows
High forehead
54
Low end filters _ kHz
High end filters _ kHz
5 & 8
*canceling out high and low frequency noise that may interfere with our recordings
54
What stimuli is preferred?
Clicks over tone bursts
54
Subject variables
Gender -
Age -
AP will be larger for females
AP will be smaller with increased age
54
Rate
7.1 sec - slower / faster if needed
If using a faster rate we may not see SP
Using a high rate, our AP may go away and we will not see it
54
Repetitions (sweeps)
TT ?
ET ?
100-200
1,000-1,500
54
Why don't we want the CM
Can be mistaken for an artifact
Its not the clinical marker we want
It is too sensitive to the stimulus
It can interfere with interpreting AP and SP
54
Describe SSCD
Semicircular Canal Dehiscence
In normal ears, sound travels through the oval/round windows
Because it is a third window disorder, the dehiscence shunts fluid and pressure, changing cochlear mechanics
Thinning of the bony structure of the semicircular canals
SP/AP ratio may be elevated - the ECochG cannot be used alone, and the best way to confirm this is ith a CT scan, where they can actually see the thinning
ECochG cannot be used alone to aid in SSCD diagnosis
54
Why is polarity important?
Influence the cochlear response and affect what our waveform looks like
54
Condensation - its gonna go up first
Positive Polarity
The signal starts in the upward/positive position
The diaphragm of the speaker pushes sound towards the ear canal, producing a positive pressure wave at the TM.
This makes the BM move downward
54
WAVESSSS
The first five waves (I, II, III, IV, V) are the most important
Wave V is the most robust & important of the five waves
Will have the larger amplitude of the 5 and has a very strong role in diagnostics and threshold seeking/estimation, but also looking for retrocochlear lesions
54
What are characteristics of auditory neuropathy?
Variable hearing thresholds
Present OAEs
Absent ABR
Absent Acoustic Reflexes
CM present and may have normal CM
No ABR present
54
When would you want to record the CM?
ANSD - auditory neropathy spectrum disorder
Absent AP (Wave 1)
54
Alternating - Combo
This alternates between condensation and rarefaction polarities with each presentation of a stimuli
Alternating between positive and negative, and alternating with each stimulus present
The alternating polarity is the preferred choice for recording ECochG
54
Rarefaction - important for ABR
Negative Polarity
The signal starts in the downward/negative direction
The diaphragm of the speaker pulls away from the ear canal, producing a negative pressure wave
Makes the BM move upward
54
Why is an alternating polarity preferred?
Reduces artifact
Improves clarity of SP & AP
Prevents CM from obscuring wave forms
Cancels the CM and it is the only one that mimics/moves
54
What is the normative value range?
.16-.31
54
SP and AP ratio greater than .40 is suggestive of?
Endolymphatic hydrops or Meniere’s Disease
Even third window disorders (semicircular canal dishicence)
54
What are characteristics of menieres disease
Low frequency rising HL
Fluctuating HL
Multiple episodes of vertigo
Aural fullness
Tinnitus
Excessive endolymph in the cochlea - cochlear hydrops has no vertigo
54
An enlarged SP/AP ratio is indicative of pathology
60-65% of patients with Meniere’s Disease have increased SP/AP amplitude
54
How to know the SP amplitdue is enlarged?
> than 40%
Because if increase endolymphatic volume and pressure
SP is sensitive to changes in the Organ of Corti, in particular
54
Interpeak Latency
Distance in time between the waves - how much time passes
54
What is an ABR?
Measurement of neuroelectrical potentials that occur within the CANS in response to auditory stimuli and are recorded from electrodes on the scalp
An acoustic stimulus that has turned into an electrical stimulus in the brain
Not a hearing test
A test of neural synchrony - make predictions, but it is not a true test of hearing and never replace a comprehensive evaluation, but sometimes we will use this instead of that battery
54
What is Intraoperative Monitoring
The presence if AP may indicate that hearing was preserved during a procedure specifically for repairing a dehiscence
Shunting of the endolymphatic sac - reduction in the ratio when the shunt was open can be suggestive of a successful outcome
Cochlear implantation - recordings can be obtained before, during, and after electrode insertion - to see how much of the auditory nerve (hearing) we are preserving
54
Limitations of ECochG?
Does not provide information on the auditory system beyond the eighth nerve
Not a test of hearing, only an evaluation of the auditory periphery
Subject variability
Dependent on having good hearing - difficult to obtain if HL is greater than 40 dB
Although it is the standard for MD testing, there are - limited reliable norms, Lack of standards, Prone to clinician bias
54
ABR is _______- and uses what recordings?
non-invasive - most popular in electrophysiology
Far-field recording
1. to find the threshold
a. It's a threshold estimation, so we are getting an idea of where they may be
b.This is really useful for pediatric or infants in particular - if there is a loss or not
c. If they cannot participate in a standard behavioral test, they will use this
2. Otoneurological (SOL)
a. Or neuro diagnostic, and this is for sight of lesion testing
b. Use it as a screening or in conjunction with a test to determine if there is a retrocochlear pathology in our patients
3. screening
54
latency for ABR is ?
2-12 ms - usually a little earlier than 2 and can go to 15ms
54
Where is the recording site for ABR
Generators are ?
Vertex to earlobe or mastoid
Easier to prep mastoid
8th nerve and brainstem nuclei
54
Clicks
Neurodiagnostic purposes
not frequency specific
activating a larger range
54
Tone Bursts
Are better suited for finding hearing threshold - these are frequency specific, so you can get a better range
54
Response?
Five waves - always marked at the peaks
54
Generators:
Wave 1 -
Wave 2
Wave 3
Wave 4
Wave 5
Distal portion of the eighth nerve
Proximal end of the eighth nerve
Cochlear nuclei SOC
SOC and acending auditory fibers - LL
LL and IC - stops here
54
Absolute Latency
Where the wave peak falls
54
Latency Intensity Function
Relationship between ABR latency and Intensity
54
V-I Amplitude Ratio
Will determine if something is off or abnomal - more sight of lesion testing
54
Reproducibility
Goes hand in hand with morphology - can I do it again - is it clear the second time, nor all messed up
54
Wave 1 : __ms
Wave 3 : __ms
Wave 5 : __ms
1.5ms
3.5ms
5.5ms
*Gender difference is really for adults - about .2 milliseconds quicker in females than males
54
Peak latencies
The time after the onset at which a given peak occurs
Latencies are unaffected by the position of recording electrodes
Latencies are affected by the amount of residual noise
55
Wave morphology
How clear, how good does that tracing look, are they all present
55
Absolute Latency
Time in ms from stimulus onset to wave peak
I, III, V - most important for diagnostic purposes, because they are usually the easiest to see II and IV are harder to see, and you get a wave 4 and 5 complex in which they morph together
Presence of I, III & V at slow rates
Normal values: general rule, every clinic has its own set of rules, and all come with a plus or minus .2 milliseconds
55
Interpeak Latency
Time in milliseconds from the positive peak of one wave to the positive peak of another wave
Important for how long the stimulus will take to get from one part of the brainstem to the other
*Remember how each single wave of the ABR comes from a different part of the brainstem, and we need to know how long the signal is taking to get there
If there were a mass, it would affect the wave and interpeak latency, being delayed because it is taking longer for the sound to get there
The intervals between:
I-V
I-III
III-V
If there is a mass, you'll see a delay in the waves 1-3 affecting the upper pons, 1-5 affecting the total time between the something and the brainstem
Electrophysiology
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