Midterm Flashcards
1
Q
What are AERs?
A
Electrical responses of the auditory system that occur in response to sound
electrical responses of the nervous system to externally presented stimuli
Takes about 1s post-stimulus presentation for an AER to happen
Represents brain waves generated in response to sound
2
Q
what generates AERs
A
Generated by the IE, auditory, and auditory brain regions
3
Q
what are AERs described by
A
Anatomical region (e.g., cochlea, bs, etc.)
Temporal relation to other stimuli → timing/latency after the stimulus
4
Q
AER/AEP are subjective responses
A
false
objective: do not need an individual’s subnective response to get
5
Q
what are AERs useful for
A
Evaluating hearing sensitivity - threshold ABR, ASSR
Evaluating CANS for pathology - neurodiagnostic ABR
Evaluation of the CANS including auditory processing - ALR, MLR, P300, MMN
Evaluation of children with language, cognitive, and other developmental disorders
Monitoring effectiveness of intervention, such as with CIs or HAs and auditory training, because of the plasticity of the CANS
6
Q
threshold ABR, ASSR
A
Evaluating hearing sensitivity
7
Q
neurodiagnostic ABR
A
Evaluating CANS for pathology
8
Q
Evaluation of the CANS including auditory processing
A
ALR, MLR, P300, MMN
9
Q
what type of PT might get neurodiagnostic study
A
asymmetric HL
abn reflexes
poor speech
unilateral tinnitus
Patients who are anesthetized and undergoing surgery that puts the auditory system at risk
Comatose patients with severe head injury who have central nervous system damage
10
Q
why might you perform a threshold abr
A
NBHS
adult/child that cannot do behavioral - developmental or cognitive delays
poor test agreement
Those with false or exaggerated hearing loss
11
Q
what are the types of potentials
A
evoked & non evoked
12
Q
Event-Related Potentials - ERP
A
evoked
13
Q
Non-Event Related Potentials
A
non-evoked
14
Q
what are evoked potentials
A
aka vent-Related Potentials - ERP
External stimulus is required
Conscious awareness is needed
Example tests → ECochG, ABR
Smaller than EEG & requires
Signal averaging & amplification
15
Q
what are non evoked potentials
A
Non-Event Related Potentials
Reflects ongoing brain activity in the absence of stimuli
External timulus is not required; spontaneous
No conscious awareness is needed
Recorded as EEG
16
Q
what is the ecochg
A
Used for the earliest response → components are generated in teh region of the IE (measures the cochlea & distal auditory N)
17
Q
components of ecochg
A
Cochlear Microphonic (CM) → ~1 ms latency
Summating Potential (SP)
Action Potential (AP) = ABR Wave I
18
Q
how are ecochgs measured
A
tymptrode - placed deep in ear canal (gold foil)
tiptrode - placed onto the eardrum (bead)
transtympanic - placed through the eardrum and onto the promontory
19
Q
what is the ABR
A
Measures the neural synchrony along the auditory pathway arizing mainly from the auditory regions in the BS
Represented by waves I-V
Wave I = AP of ECochG
Wave V → most robust & used for threshold estimation
20
Q
why do babies have poorer morphology in ABR
A
neuromaturation
21
Q
latency of abr
A
within 15ms
22
Q
Auditory Middle Latency Response (AMLR) contributors
A
Thalamus & primary auditory cortex (A1)
One primary peak & negative peaks w/ larger amps
23
Q
Auditory Late Responses (ALRs)
components
A
Reflects the conscious perception of sound
Requires awake state
Has primary and negative peaks
24
Q
how are AERs classified
A
by time epoch
stimulus type
electrode location
what structures in as generate the AEPs
25
what is an epoch
time window after which a stimulus occurs; length of time (ms) relative to a specific auditory eventj
26
why is the epoch essential
Too short - may miss and not see an entire response you are looking for
Too long - response may be to small and you miss it in teh bigger display; limits the details
*pick one with the best time frame for the potential of interes
27
epoch for ecocg
0 - 1.5 ms
28
abr epoch
1.5-12ms
29
MLR/AMLR epoch
12 - 50ms
30
ALR epoch
50-300ms
31
P300 epoch
>300ms
32
what are the stim types
exogenous
endogenous
33
what is exogenous and examples
earlier potentials; determined by physical characteristics of the stimulus
Do not have to hear the signal & responses are due to the presentation of the stimulus and organ itself
Good for sedation, coma, asleep, etc.
Elicited by external (environmental) stimul
ECochG, ABR, OAE, & some ASSR
34
what is endogenous and examples
determined by cognitive processes; later potentials
Must hear the signal; PT has to be awake and aware of the sound
Alert and attuned
Requires higher-level processing and awareness
P300 → appears when someone recognizes a sound & occurs after 250ms post-stimulus
35
what are the electrode locations
far field
near field
36
what is meant by far field locations
electrodes are at a distance from the generator
Causes a reduced response amplitude → Already has a low amplitude and movement away from the area doesn’t cause it to be much lower
All standard AERs
37
what is meant by near field electrodes
electrodes are near the generator
Amplitude is high when very close but even just a slight distance away it reduces a lot
Intracranial depth electrode studies
38
the further away you are from the generator site the better the response you will get
false
39
an electrode in the TM produces better responses and larget amplitudes than one on the ear lobe or in the ear canal
true
40
in clinic, always recorded far-field w/ electrodes on skull (extracranially) except for what exceptions
IOM → electrodes placed directly on 8 N
Transtympanic ECochG → recording electrode is placed on the promontory; CIs
41
what structures are in AS that generates AEPs
Receptor potentials → cochlear hair cells
ECochG
OAEs
Neurogenic → 8 N & BS
ABR, MLR
42
what are the Factors Affecting Recording & Measurement of AEPs
stimulus factors
acquisition factors
non-pathologic subject factors
waveform analysis
43
why are inserts recommended to use to measure AEPs
Prevent ear canal collapse
Increase IA
Attenuates more environmental noise
.9ms delay to separate stim artifact from the response onset making Wave I of ABR more visible
44
what are the stimulus factors looked at for AEPs
stim type
stim intensity
stim rate
stim polarity
(also interstim interval, stim duration and rise time)
45
what is the best stimulus type to use for early AEPs and why
best generated with brief stimuli w/ instantaneous onset and simultaneous responses form large number of neural units (synchronous neural discharge)
example would be electrical pusles (brief clicks or chirps)
the brief stimuli triggers the synchronous firing of the neural population in these areas that creates a robust and measurable signal
46
describe a click stimulus
BB bandwidth, rapid onset, used in ECochG & ABR, not frequency specific, large amps, & thresholds bw 2-4kHz
47
better neural synchrony worse frequency specificity; good for early AEPs
short duration stimuli
48
✅ better for neural synchrony, ❌ worse for frequency specificity
short duration stimuli
49
better frequency specificity and worse clear, synchronized responses
long duration stimuli
50
✅ better for frequency targeting, ❌ worse for producing clear, synchronized neural responses
long duration stimuli
51
Evoked responses directly depend on temporal synchronization of neuronal activity
true
52
what is the blackman ramp
reflects how long stim when turned on how long it plateaus before you turn it off
53
describe the changes in intensity and how it affects other measures
Intensity increases, latency decreases & amp increases = better morphology
More synchronized neural firing w/ higher intensity
Intensity decreases, latency increases & amp decreases = poor morphology
Fewer neurons firing with lower intensity
54
As many as ___ references can be used to describe intensity in AEP measurements
5
55
what is the unit for intensity
dB
56
what is meant by dB nHL
is it relative to normal behavioral hearing threshold level for a click stimulus
57
what is the stim rate
Rate (time per s) which the stimuli is presented
Affects latency & amplitude
No single correct rate or one appropriate for all test circumstances
58
what happens if you use a faster rate
shorter interstimulus levels & can increase latency and decrease amplitude
59
what happens if we use a slower rate
decreased latency & increased amp, better waveform for middle & lates, less stress on system, useful for neurdiagnostics
60
what is the rate used in ABRs
27.7/s
61
initial movement is away from ™ (stapes away from oval window = short latency and higher amp of early components of AEP)
rarefaction
62
initial movement is toward ™ (stapes into oval window = longer latency & larger Wave V amp)
condensation
63
short latency and higher amp of early components of AEP when this polarity is used
rarefaction
64
longer latency & larger Wave V amp when this polarity is used
condensation
65
stimulus pressure wavefront is alternated on successive trials bw the rare and cond
alternating
66
when is alternating used
Must use for EcogH to cancel out CM to see real response & for BC
Used to reduce stim artifact
67
what is the alternating polarity
Shows 1 waveform that is the sum of the 2 polarities
68
waht is the interstimulus interval
time bw each stimulus
69
what happens if ISI is too short
neural elements do not recover and miss or have weak waves
70
what happens if ISI is long enough
full neural recover and have clearer, stronger responses
1s/rate
71
ISI must allow for full neuron recovery otherwise responses will degrade
true
72
what is the ISI for transient stimuli (clicks)
1s/rate
example
20/s → 1000/20 = 50ms
10/s → 1000/10 = 100ms
81.1/s → 1000/81.1 = 12ms
73
why does ISI matter
refractory period
After each neural firing, a neuron enters a refractory (recovery) period
During this period neurons
May not fire at all or
Require more stimulation to fire
74
If ISI > refractory period
neurons fully recover = strong response
75
If ISI < refractory period
neurons have incomplete recovery = weak or a missed response
76
Fast-firing, small (brief time periods; <5-6ms) →
ABR, ECochG → short refractory period → think of ants 🐜
77
Slow-firing, large →
middle/late AEPs → long refractory period → think of sloths 🦥
78
what are the clinical implications to ISI
Choosing the wrong ISI rate can mimic signs of pathology
Increased latency & decreased amplitude
Always match stimulus parameters to the neural population you are testing to avoid false interpretations
79
better synchrony, worse frequency specificity; more abrupt onset
click
80
better frequency specificity, lower synchrony; longer duration & rise time
toneburst
81
what are the acquisition factors
electrode factors
amplifier
filters
82
what are the electrode factors
montage/placement
types
channel differences
electrode polarity
83
what are electrodes
sensing device detects bioelectrical activity & sends to pre-amp
84
what is the 10-20 montage
how the electrodes are set up on the patient
Cz – Top of head/vertex; non-inverting
Fz – Forehead (midline/high); non-inverting
Fpz - low forehead; often ground
A1 / A2 – Left (odd) / Right (even) aurus/earlobe or mastoid; both inverting
M1 / M2 – Left/right mastoid
M - Mastoid
T - Temporal
O - Occipital
P - Parietal
Odd - Left
Even - Right
Z - midline
85
Cz
Top of head/vertex; non-inverting
86
Fz
Forehead (midline/high); non-inverting
87
Fpz
low forehead; often ground
88
A1/A2
Left (odd) / Right (even) aurus/earlobe or mastoid; both inverting
89
M1 / M2
Left/right mastoid
90
M -
Mastoid
91
T
temporal
92
O
occipital
93
P
parietal
94
Odd
left
95
even
right
96
Z
midline/middle
97
non-inverting
(Active): Vertex (e.g., Cz or Fz)
98
inverting
(Reference): Earlobe or mastoid (e.g., A1, A2)
99
what is the ground electrode
Anywhere on the body (commonly Fpz)
100
what is a 1 channel set-up and when is this used
3-4 electrodes → basic ABR testing
Good for threshold estimation and more basic clinical needs or screenings; slower
Records 1 ear at a time & gives 1 waveform at a time (e.g., Cz-A1 or Cz-A2)
101
what is a 2-channel recording and when is it used
4+ electrodes → neurodiagnostic use (gets both ipsi & contra responses)
1 electrode at the vertex (point equidistant bw L & R ear canals in coronal plane & equidistant bw nasion & inion in the sagittal plane
Allows for simultaneous comparison of responses from each ear or brain hemisphere → helpful in diagnosing retro pathologies
Records both at same time or ipsi & contra, gives 2 waveforms (e.g., Cz-A1 & Cz-A2 together); faster
Used for neurodiagnostic testing, ANSD evals and more detailed; adv diagnostics & differentiating lesions
102
what is an inverting electrode
→ on earlobe or mastoid of the stimulus side (A1 or A2)
Polarity of the signal coming from this electrode IS inverted
Takes the AEP coming into the electrode and before signal processing happens it flips the whole thing 180 deg into the mirror image reference
The signal flipping causes phase cancellation and leaves us with the signal of interest
103
what is a non-inverting electrode
→ electrode located on Cz or midline forehead near Fz
Polarity of the signal coming from this electrode is NOT inverted
Takes AEP signal coming into the electrode, goes into pre-amp box and signal processing, is analyzed and stays the same → how it comes in is how it stays and there is no manipulation of the signal
104
what is the amplifier and why is it needed
device increasing the strength of an electrical or acoustical signal; taking something small and makes it larger
AEPs generated at cochlea or 8n are very small compared to EEG (1µV – a microvolt – a millionth of a volt) and the average amplitude for ABR wave V is 0.5µV
amps make them visible and measurable
105
what is the amplifier gain for echog and abr
have a large amplifier gain - ABR is amplified 100,000x
106
what is the amplifiers most important function
common mode rejection (CMR)
107
what is CMR
Removes noise that shows up the same at 2 electrodes
How it works: CMR allows the electrodes to pick up what is common to each electrode (noise) and cancel it out while retaining the evoked responses at the two electrode sites, because they are different
other way to explain it: It uses the inverted and non-inverted signals from the electrodes to cancel out the electrical activity we do not need to help see the evoked responses we are looking for. It does so by keeping the non-inverted signal, which stays the same as does when it comes into the system, and takes the inverted signal, which takes the signal that is the same between the electrodes, inverts it 180 degrees which cancels itself out. This leaves the signal we wish to see and removes the activity we do not need. The amplifier in the system allows for the amplitude of the signal we wish to see be increased and uses CMR to remove the activity that is the same to leave just the signal of interest to be amplified.
108
cancels out noise that is the same at both electrodes to keep the real signal
CMR
109
amp boosts small AER signals
gain
110
what is a filter
selectively removes part of something from the whole
Rejects electrical activity at certain frequencies & passes energy at others
111
Filter settings describes waht
the filter band that the physiological response is recorded from the electrodes
112
what is noise
any electrical activity detected by electrodes (PT-physiological or external/environmental - (lights, phones, computers, etc. 60Hz hum) and IS NOT AEP
113
Normal EEG frequency region
<30Hz
114
Neuromuscular noise
100-500Hz but can include those up to 5000Hz
115
high pass filter
Lets high frequencies through, blocks lows
Example: 100 Hz HPF = blocks below 100 Hz
116
3000 Hz LPF
blocks above 3000 Hz
117
100 Hz HPF
blocks below 100 Hz
118
low-pass filter
Lets low frequencies through, blocks highs
119
band pass filter
Allows frequencies within a range, blocks outside
120
what is the band pass filter used in ABR
100–3000 Hz
121
what is a band reject filter
Blocks a specific frequency range, lets others pass
Example: 60 Hz notch filter (used sparingly)
122
what are Non-Pathologic Subject factors
Subject factors are known to influence AEPs and has to be considered clinically during finding interpretations
age
body temp
state of arousal
medications
gender
123
how does AEP look when comparing infants and kids with adults
Infants & kids → longer latencies & smaller amps, immature auditory pathways (still myelinating)
Older adults → age related neural changes can show delayed responses
124
when does an ABR become adultlike
ABR becomes adult like around 2-3yrs+
125
how does the system maturate
Ecog, ABR and shorter latency responses mature at an earlier stage than longer latency (AMLR, ALR, P300)
Maturation proceeds from periphery to CANS in caudo-rostral direction within the CNS (most distal/lateral part to medial)
126
how does body temp affect AEP recording
Temp exceeding even 1 deg C from this value = consider as factor in AEP outcome
127
what is normal body temp
normothermia (37C or 98.6F) = no need to account for temp in AEP interpretation
128
those at risk for body temp changes in AEP that should be considered as a factor
infections (high temp), coma, under effects of alcohol or anesthesia (low temp)
129
what should be considered when analyzing the waveforms
latency
amplitude
morphology
reproducibility
130
AEP waveforms are in the time domain and a sequence of peaks (amplitude of greater voltage) and valleys (amplitude of lower voltage) occurring within a specific time period (analysis time or epoch)
true
131
what is latency
time of onset; time interval bw exact moment stimulus is presented and appearance of a change(peak/valley) in waveform
ms
for any waveform it depends on analysis criterion used to define each component
132
first step of analyzing the wave
Presence or absence of response → is there a detectable wave at all?
133
what is absolute latency
time of onset of the response; time between stimulus onset and peak of the waveform (when stimulus starts to when the peak arrives)
Most robust & reliable characteristic in clinical interpretation of ABRs
Provides mainstay of ABR interpretation - key component for repeatibility
134
what is the key component for repeatability
abs latency
135
what is the most robust and reliable characteristic for ABR interpretation
abs latency
136
what is interpeak lateny
time bw different wave peaks (I-III, III-V, I-V), used ot assess neural transmission times
137
what is amplitude
height of wave from baseline in microvolts, µV, indicates response strength
Described in microvolts usually
Measurement of voltage difference between peak of a wave to the following trough (valley) - technique used in ABR
138
what is interaural latency/amplitude difference or ratio
compares responses bw ears to assess asymmetry
139
what is morphology
pattern or overall shape and definition of the waveform; subjective analysis parameter
Clear peaks = good
blurry/poorly defined waves = abnormal
Even if latency & amp is normal, this can be poor
140
what is reproducibility
can you repeat the same waveform across multiple runs?
Confirms response is consistent and real
141
what is polarity
direction the wave moves (pos or neg) depending on
Electrode position
Stimulus polarity (rarefaction, condensation, alternating)
142
what is the acceptable inter-electrode impedance
<5000ohm/5kohms
143
what is the balanced inter-electrode impedance w/ diff bw electrodes
<2000ohm/2kohms
144
what are the objectives in the electrode placeent
consistent placement across subjects, anatomically correct, low inter-electrode impedance (<5000ohm/5kohms), balanced inter-electrode impedance w/ diff bw electrodes <2000ohm/2kohms, secure & consistent attachment through the assessment & minimal discomfort and no risk to PT
145
what is teh ABR
complex response to particular types of external stimuli that represent neural activity generated at several anatomical sites
test of neural synchrony
test that shows how well the hearing nerves and brainstem are working together. It measures how groups of nerve cells (from the ear up through the brainstem) all fire at the same time when they hear a sound
146
If the nerve signals are well-coordinated (synchronized) early in the pathway—starting from the ear—then they should stay coordinated as they move through the rest of the auditory system up to the brain
true
147
what is the normal waveform we should see of an ABR
5-7 vertex-positive peaks occurring in time period of 1.4 to 8ms after stimulus onset
148
describe wave I
Wave I - 1.5 (+/- 2 SD)
Distal VIIIth N
also the AP of the echog
149
describe wave II
Wave II
Proximal VIIIth N w/ some from Distal 8 N
150
describe wave III
Wave III - 3.5 (+/- 2 SD)
Neurons in cochlear nucleus (CN) and possibly fibers entering CN
151
describe wave IV
Unknown, 3rd order neurons in SOC most likely
152
describe wave V
5.5 (+/- 2 SD)
May be related to activity in lateral leminiscus and inferior colliculus
153
is it common to see all of the waves I-VII
Not uncommon to only see 1,3,5
Waves IV, V, VI, VII are complex and more than 1 anatomical structure contributes to each peak and more than one peak
154
what creates the waves/peaks
waves/peaks represent sums of neural activity from 1 or more souruces at various discrete points in time - neural generators create these points
155
what are the parameters used to inspect ABR waveforms
abs latency
Interwave latency intervals (IWI) or interpeak latencies (IPL)
Interaural latency differences
Latency-Intensity Function (LIF)
Stimulus Rate Changes
Waveform morphology & replicability
156
abs latency of ABRs
consistent across individuals; time of onset of the response; time between stimulus onset and peak of the waveform (when stimulus starts to when the peak arrives)
Most robust & reliable characteristic in clinical interpretation of ABRs
Provides mainstay of ABR interpretation - key component for repeatibility
Wave I - 1.5 (+/- 2 SD)
Wave III - 3.5 (+/- 2 SD)
Wave V - 5.5 (+/- 2 SD)
157
Interwave latency intervals (IWI) or interpeak latencies (IPL) of ABRs
time period bw peaks; distance between waves
Use latencies of earlier peaks in response as the reference; use each successive peak as reference rather than 0
Wave I - III: ≈ 2.0 msec
Wave III-V: ≈ 2.0 msec
Wave I-V: ≈ 4.0 msec
158
Wave I shows activity from early parts of the brain so the time between waves helps us to tell what
how well the signal is traveling through the BS to check the health of the AS and the brain
159
Interaural latency differences of ABR
ear to ear differences
Normal: latency of Wave V in each ear should be <.2-.4 difference
Relatively similar hearing
160
what is the Latency-Intensity Function (LIF)
Plots absolute latencies of Wave V as a function of intensity (stimulus level it is done at) to see if it is in the normative range & determine type of HL
X-axis = stimulus
Y-axis = Wave V latency
161
Distal VIIIth N contribution
wave I
162
Proximal VIIIth N w/ some from Distal 8 N
contribution
wave II
163
Neurons in cochlear nucleus (CN) and possibly fibers entering CN
wave III
164
Unknown, 3rd-order neurons in SOC most likely
wave IV
165
May be related to activity in lateral leminiscus and inferior colliculus
wave v
166
As stimulus intensity increases what happens to latency & amp
As stimulus intensity increases latencies decrease and amplitudes increase
167
As stimulus intensity decreases what happens to latency & amp
As stimulus intensity decreases latencies increase and amplitude decreases
168
Latency increase happens fast between intensities of 90-60 dB nHL & increases rapidly at lower intensities
false
slowly
169
what does a normal ILF look like
it is in the grey (normative range)
170
what does CHL ILF look like and why
characterized by prolonged absolute latencies of ALL waves due to intensity of the stimulus reaching the cochlea being decreased due to the conductive component
All absolute latencies are delated/shifted ot the right but interwaves are not affected
171
can you tell the difference bw CHL & retro based solely on ac ILF
no
need BC ABR or see the waveform and data
172
what does a cochlear HL ILF look like
Steeper than normal LIF with normal latencies at higher intensities and prolonged latencies at lower intensities
ABR can show normal at high intensities - need mutli intensity levels; this is because at high levels it looks normal but near threshold it steepents
173
what does a retrocochlear disorder ILF look like
Wave V latency prolongation (same as CHL)
In retrocochlear disorders, earlier peaks (I and/or III) may be within normal limits
174
describe how we can tell bw CHL or retro disorders with ILF
need to utilize audiometric data or BC abr to tell or look at interwave intervals
In CHL all waves (I, III, and V) will be offset by equal amounts.
In retrocochlear disorders, earlier peaks (I and/or III) may be within normal limits
175
If Wave V is shifted out, differentiate CHL from Retro by
Doing high-level and look for Waves 1 & 3
Retro - they will be normal
CHL - they will also be shifted out
Do BC ABR
Retro - BC aligns with air or Wave V abs
CHL - bone is normal & air is abn
176
earlier components are more affected by stimulus than later ones
false
less
177
Amp of Wave 5 stays consistent with rate increase but amplitude of earlier waves decreases
true
178
how does stimulus rate affect an ABR
earlier components less affected by stimulus than later ones
Increases IWI as a function of rate due to this - when sound is repeated faster the time bw the waves gets longer
Amp of Wave 5 stays consistent with rate increase but amplitude of earlier waves decreases
amp stays the same across rates but there are small latency changes as rate increases
179
higher intensities (75 dB nHL) =
well-defined peaks and presence of Waves I, III, & V
Those with significant peripheral HL = reduced amp in earlier peaks
180
what are the 3 principles to remember for stimulus
The shorter the duration the less frequency specific
As Intensity increases the latency of the response decreases and amplitude of response increases
As Intensity decreases the latency of the response increases and amplitude of response decreases
181
What are the parameters of an ABR and rank in order of reliability
#1 abs latency
rank of rest unsure but they are:
abs latency
Interwave latency intervals (IWI) or interpeak latencies (IPL)
Interaural latency differences
Latency-Intensity Function (LIF)
Stimulus Rate Changes
Waveform morphology & replicability
182
what is a rate study or neurologic abr
183
c80dB vs tb80dB
c80dB = large amp but not much frequency specificity
tb80dB = better to localize where it is coming from but small amp
184
what is the hallmark of what we look for in abrs
absolute latencies
wave 1 - 1.5, wave 3: 3.5, wave 5: 5.5
185
what happens if you have an open impedance
shows really high value (100 etc) or it wil say its open and recordings will have no sweeps
186
The Auditory Brainstem Response (ABR) has two main clinical applications:t
threshold search to establish hearing sensitivity and neurological assessment.
187
the ABR is a test of hearing
NOT
the information obtained can be very useful in estimating hearing sensitivity
188
faster stimulus rates causes
longer latencies and decreased amplitudes
189
slower rates causes
shorter latencies and increased amplitudes
190
<1.0 µV amp is indicative of what
retrocochlear losses
191
Neurodiagnostic purposes of an ABR includes
presence of occupying lesions (meningiomas, FN iomas, vestibular schwannomas, etc. and demyelinating conditions (25-39yr women for MS - uni vision and hearing complaints and run MRI with no tumors they run ABRs
192
what is a rate study or neurologic abr
Used to assess neural function with an emphasis on identifying intra-canicular tumors or neurological abnormalities such as MS
& ANSD
193
Why should you perform a neurological rate study ABR? What types of people would we do this type of ABR study on
Asymmetric HL that is not CHL
Elevated or absent ARTs or abnormal reflex decay (MEMR)
Poor word rec in quiet (relative to audio)
Unexplained dizziness/vertigo
Unilateral tinnitus
Progressive HL (cochlear or neural)
PI-PB Rollover on speech testing
Unknown SHL cause
Poor inter-test reliability (tests do not match)
Aid in diagnosis of demyelinating conditions (MS) or in ANSD
Might do them on those that cannot do imaging like pacemakers, shunts, artificial hips, plates in head, etc.
194
Parameters for Neurodiagnostic ABRs
Stimulus →100 µs click
majority of the energy falling between 2-4kHz range
High intensity - >/=80 dB nHL
Stimulus Polarity
Rarefaction or condensation
Rate
Start at 1–30 to get baseline (11.1 or 27.7)
If no responses then go to below 10/s
Then Slow rate to obtain baseline information initially (11.1 or 27.7/s), mid (57.7), fast (77.7)
1000 sweeps (or up to 2000 if SNR is not <10%)
Replicate each rate with 2 waves
Epoch
10 or 12 ms for adults & 15ms for kids
Filter bandwidth
100-3000Hz
Gain: 100,000
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The ABR is sensitive to neurological disorders of the VIIIth N and low- to mid-brainstem.
These disorders include
space-occupying lesions
diffuse lesions
functional (physiological) abnormalities.
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what can be done to enhance wave i appearnace
increasing the intensity of the stimulus
decreasing the presentation rate
comparing rarefaction and condensation clicks to distinguish cochlear potentials from neural responses
using a TM electrode in ECochG
using transtympanic ECochG
using a horizontal recording montage (A1 – A2)
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what does the abr not evaluate
integrity of CNS rostral/above BS
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what does a normal abr look like
Adults & kids >/=3yrs
Absolute:
Wave I: ~1.5 msec
Wave III: ~3.5msec
Wave V: ~5.5msec
Interpeak:
I-III: ~2msec
III-V: ~2msec
I-V: ~4msec
Should be repeatable w/ subsequent runs, good morphology, no prolongation w/ rate change
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what does an abnormal CHL neurologic abr look like
Absolute:
Wave I latency: typically >~2 msec (use LIF)
Wave III latency: typically >~4 msec (use LIF)
Wave V latency: typically >~6 msec (use LIF)
Interpeak:
I-III Interpeak latency ~2.0 msec
III-V Interpeak latency ~ 1.8 msec
I-V Interpeak latency ~ 3.8 msec
Waves I, III and V are all delayed equally AND interpeak latencies (I-III, III-V and I-V) remain at normal values
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what does an abnormal retro
neurologic abr look like
Absolute:
Wave I latency : normal or prolonged (use LIF)
Wave III latency: normal or delayed (use LIF)
Wave V latency: delayed (use LIF)
Interpeak:
I-III Interpeak latency prolonged = lower brainstem lesion if prolonged
III-V Interpeak latency prolonged = upper brainstem if prolonged with normal I-III
I-V Interpeak latency prolonged
Typically wave I at normal latency (though can be prolonged) but wave III or wave V or both are delayed. This results in prolonged I-III interpeak latency or III-V interpeak latency
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what is a cochlear microphonic
Stimulus dependent response - follows direction of the stimulus which is why we see mirrored image
Mirror image of the waveform present
Result of OHC excitation & inhibition
-20 or -10 latency = pre response generation (activity in the system we are using)
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Why should you perform a threshold ABR study?
Suspecting NOHL
Poor inter-test reliability on behavioral testing
Inability to test with conventional methods (newborn, handicapped, etc)
Amp fitting purposes for special populations (youngins, handicapped, dementia, etc.)
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test protocol for threshold ABR
Stimulus →tone burst or NB chirp
Stimulus rate: 33.3
Stimulus Polarity
Rarefaction
Alternating at HF and chirps
Protocol
Start at ABR protocol w/ click stim at 80dB nHL
Then perform at 500, 1000 and 4000 tonebursts (initially at 50-60 dB nHL)
Run 1000 sweeps (or up to 2000 if SNR is not <10%)
Replicate each rate with 2 waves
Epoch
10 or 12 ms for adults & 15ms for kids
Filter bandwidth
100-3000Hz
Gain: 100,000
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peak and interpeak prolongation is representative of
retro
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Steps for Threshold ABRs
1. First perform AC Click
75dB, 100 us pulse, rate of 27.7, 1000 sweepts w/ snr <10%
do one cond and one rare to look for ANSD
2. tonebursts next
do 500 at 75 and decrease in 20d until threhsold is met with one polarity
then 4, and 1 or 3
3. BC Clicks
Only done if click or the 500Hz toneburst responses are not present at expected normal levels
Also used if children have craniofacial abnormalities
Polarity
Alternating - used due to large electrical artifact emitted from bone oscillator
Everything else is the same as AC clicks
Bone oscillator rarely exceeds 45-55dB due to dynamic range of it
Rate 27.7
Epoch 10-12 ms
Filter bandwidth: 10-3000
Sweepts: 1000-2000 (<10% SNR)
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IA for kids
15-25dB
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IA for neonates:
25-35 dB (bones not fully fused)
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when do you not need to mask
If intensity of the testing is
210
when do you need to mask
if intensity of test is >IA of inserts
wave I is abnormal/absent
wave v latency is not normal for the intensity
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Wave I small, absent or slightly delayed
Interpeak latencies normal
Poor waveform morphology
Wave V can be delayed beyond normal
sensory hL
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sensory HL patterns
Wave I small, absent or slightly delayed
Interpeak latencies normal
Poor waveform morphology
Wave V can be delayed beyond normal
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Peak waveforms proportionally delayed
Normal (equal) interpeak latencies
CHL
214
chl patterns
Peak waveforms proportionally delayed
Normal (equal) interpeak latencies
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Wave I normal typically (can be prolonged)
Interpeak latencies of I-III or III-V or both delayed
Absence of wave III and/or wave V
Replication difficult or absent
neural/retro HL
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neural/retro HL patterns
Wave I normal typically (can be prolonged)
Interpeak latencies of I-III or III-V or both delayed
Absence of wave III and/or wave V
Replication difficult or absent
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using rarefaction & condensation polarity
OAEs are usually present but can disappear over time
ABR peaks are generally absent or abnormally delayed
Audiogram
Normal to profound
Rising LF configuration
Poor speech discrim even w/ normal audio
Normal CM in ECochG
Abnormal ART
Normal MRI bilaterally
ANSD
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ansd patterns
using rarefaction & condensation polarity
OAEs are usually present but can disappear over time
ABR peaks are generally absent or abnormally delayed
Audiogram
Normal to profound
Rising LF configuration
Poor speech discrim even w/ normal audio
Normal CM in ECochG
Abnormal ART
Normal MRI bilaterally
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what are chirps
narrowband??
maximizes synchronization, increases waveform amplitude and is easier to detect and interpret in the ABR with better morpholog
Latencies are earlier than in clicks
have larger amp & clearer to see
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phenomenon where a signal that is normally too weak to be detected by a sensor, can be boosted by adding white noise to the signal, which contains a wide spectrum of frequencies
stochastic resonance
221
what is a stacked abr
specialized version of the traditional ABR test designed to improve the detection of small acoustic tumors, particularly vestibular schwannomas (also known as acoustic neuromas), which might not show up clearly in standard ABR tests
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how did stacked abr become about
took click and broke it up into indiv components, added together and looked at the amplitude change
formed by first temporally aligning wave V of the derived-band ABRs, then summing the responses
Aligning the derived-band ABRs eliminates phase cancellation of lower frequency activity. Thus, the Stacked ABR amplitude
reflects activity from all frequency regions of the cochlea, not just the high frequencies.
Reduction of any neural activity
due to a tumor, even a small
tumor, will result in a reduction
of the Stacked ABR amplitude
