Transcript Current Technique in the Audiologic Evaluation of Infants

Current Technique in the Audiologic Evaluation
of Infants
Todd B. Sauter, M.A., CCC-A
Director of Audiology- UMass Memorial Medical Center
PhD Candidate – University of Massachusetts Amherst
Instructor – Dept. of Otolaryngology
University of Massachusetts Medical School
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Growing Repertoire of Tools at the
Disposal of Audiologist
•Auditory Brainstem Response (ABR)
•Auditory Steady-State Response (ASSR)
•Otoacoustic Emissions (OAE)
•Multiple Frequency Tympanometry
•Middle Ear Muscle Reflexes
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Questions about Infant Testing by
Audiologists (And Others)
• Which of these tests are most important?
• Which of these tests should come first?
• Do I have to do all these tests on every
child or just one test?
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Best Practices in Infant Testing
Evidence-Based
Clinically Efficient
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Overview of Tests
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What is an ABR?
• The Auditory
Brainstem Response
is the representation
of electrical activity
generated by the
eighth cranial nerve
and brainstem in
response to auditory
stimulation
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How is an ABR recorded?
• Electrodes are placed on the scalp and coupled
via leads to an amplifier and signal averager.
EEG activity from the scalp is recorded while
the ear(s) are stimulated via earphones with
brief clicks or tones.
• A series of waveforms unique to the auditory
neural structures is viewed after time-locking
the EEG recording to each auditory stimulus
and averaging several thousand recordings.
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Example Normal Hearing
18 Month-Old – 2000 Hz Tone-Burst
70 dBnHL
10 dBnHL
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Distortion Product Otoacoustic
Emissions (DPOAE)
Janet Stockard Sullivan 2003
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What does the presence or absence of
OAEs tell us?
• Presence = There is no significant conductive
loss (no need for bone conduction ABR) and
threshold sensitivity is better than ~35 dBHL
(except in cases of auditory
neuropathy/asynchrony)
• Absence = Possible conductive component
and/or sensorineural hearing loss ~35 dBHL or
greater
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Tympanometry
Janet Stockard Sullivan 2003
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What does Tympanometry tell us?
• If sound energy is being lost in the outer or middle ear
due to fluid, vernix, anatomical abnormalities, etc.
(conductive component to loss)
• Provides cross-check with bone conduction
• Had poor sensitivity in the past due to adult settings
being used in infant ears (different!).
• Now more appropriate equipment settings (1000 Hz
probe tone) and normative data for infants is available.
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Middle Ear Muscle Reflex
• Also known as acoustic reflex or stapedial reflex
• Measured using same equipment/probe as
tympanometry
• Looking for sharp reduction in middle ear admittance
in response to loud sound due to contraction of middle
ear muscles.
• Should not be present with conductive loss, severe or
profound sensorineural hearing loss, or auditory
neuropathy/asynchrony.
• Ideally is not used as a stand-alone test, but as a crosscheck against ABR, OAE, etc.
• Best elicited in infants using a 1000 Hz probe-tone and
broadband noise stimulus.
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What is Auditory Steady-State Response
(ASSR)?
• Similar to ABR, but EEG activity is
analyzed in frequency domain rather
than time domain.
• Stimulus is modulated pure tone
• If response, EEG activity will modulate
at same frequency as the stimulus
• Statistical computer algorithm
determines if response or no response
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Advantages of ASSR
– Can test up to limits of transducer (through
severe/profound range)
*** Artifactual results? (See Gorga 2004, Small and
Stapells 2004) from stimulus artifact or vestibular
system
– Has potential to be a faster test than ABR when
perfected
– Some equipment can test multiple frequencies and
both ears simultaneously
– Uses same basic set-up and equipment as ABR
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Limitations of ASSR
• Cannot analyze raw data, must trust pass/fail
criteria given by equipment for each run (can be
viewed as advantage)
• Extremely limited published clinical database
(improving)
• Bone conduction not yet perfected for clinical
use (Can’t determine conductive vs.
sensorineural with ASSR alone)
• Large threshold estimation range for normal
hearing and mild loss (20 db)
•High intensity steady state stimuli may cause
acoustic trauma
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What we still need to learn about
ASSR
• Conductive vs. Sensorineural loss
• Effects of auditory asynchrony,
retrocochlear disease, etc. on ASSR
• Sedation effects
• Are responses at very high levels (>100
dB) truly auditory or artifactual?
• Reliable bone conduction testing
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Gold-Standard: Tone-burst Auditory
Brainstem Response
Click ABR
OAE
ASSR
Tone-Burst ABR
High-Frequency
Tympanometry
Middle Ear
Muscle Reflex
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Myths about ABR in Infant Threshold
Assessment
1.
2.
3.
4.
It’s too slow
It isn’t accurate
It isn’t frequency-specific enough
It is difficult to interpret
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Myth #1: It’s too slow
• Slow stimulus rates (<20/sec) are not
necessary in most patients but are still
employed by many centers routinely.
• The click latency-intensity function is not
necessary in most patients and results in
too much valuable test time being spent
testing above threshold.
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Rate Effects Above Threshold
11.1/sec
Time for 4000 sweeps – 6 minutes
21.1/sec
Time for 4000 sweeps – 3 minutes
39.1/sec
Time for 4000 sweeps – 1 minute, 42 sec
55.9/sec
Time for 4000 sweeps – 1 minute, 10 sec
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Rate Effects Near Threshold
21.1/sec
39.1/sec
55.9/sec
- At low stimulus intensities or near threshold, the early ABR
waveforms are absent, while wave V amplitude stays relatively
consistent. The use of slow-stimulus rates, in most cases, gains
you nothing but longer test times. This is not true in cases of
neurological impairment or auditory asynchrony.
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Myth #2: It Isn’t Accurate
• A strict review of tone-burst ABR
literature with testing done under
appropriate parameters found threshold
accuracy of ± 5 dB (95 % Confidence Interval) for 5004000 Hz. (Stapells 2000)
• Poor accuracy is likely most often
associated with either poor technique or
attempts to interpret poor data
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Broadband Click ABR – Poorly Used
as Estimate of 2000-4000 Hz
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Broadband Click ABR – Poorly Used
as Estimate of 2000-4000 Hz
Stapells 1998
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Myth #3: It isn’t frequency specific enough
Stapells 1995
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Myth #4: It is Difficult to Interpret
50
30
20
- Poor Data
- Only Averaged ~ 1000 Sweeps
- Difficult to Interpret
- Waveforms marked Incorrectly
- Clean Data
- Averaged 4000+ Sweeps
- True Wave Vs are only significant
EEG deflection
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Most Common Mistakes in Infant
ABR (IMHO)
• Click stimulus used as estimate of 2-4 KHz
• Underaveraging of signal
• Lack of an consistent test sequence algorithm
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Sample Test Sequence
Present
Present
Air 2K
30 dB
DPOAE
Absent
Air .5, 1, 4 KHz
30 dB
Absent
Present
Bone 2K
30 dB
Absent
Present
Bone 2K
Thresh
Absent 60
Present
Air 2 KHz
Threshold
Absent 95
Air .5-4 KHz
Threshold
Present
< 80 dB
Air Click
Threshold
Present > 80 db or absent
Tymp/ Reflex
If Necessary
Bone Click
UMass Memorial Audiology
AER Decision Matrix
ASSR
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Testing Sequence for New Infants
•
Based on answering the most important questions
first while the child is asleep:
1. Is hearing normal at the most important speech
intelligibility frequency?
2. Both ears?
3. If hearing is not normal, is it a permanent loss?
4. How severe is it?
5. Other frequencies? (500-4000 Hz)
6. If profound loss, is there residual hearing?
7. Could it be Auditory Neuropathy/Asynchrony?
8. Will other tests support the diagnosis?
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Testing Sequence
1.
2.
3.
Is hearing normal at the most important speech
intelligibility frequency?
- Low intensity (30 dB) 2000 Hz air-conduction tone
burst ABR
Both ears?
- Get 2000 Hz on each ear before moving on
If hearing is not normal, is it a permanent loss?
- Get 2000 Hz bone-conduction information early in
the testing to determine if loss is conductive or
sensorineural in nature. Not necessary if DPOAEs
are present.
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Testing Sequence
4.
5.
How severe is it?
- Use aggressive bracketing technique - search in 30
dB intervals before using smaller (5/10 dB) steps to
mark threshold
Other frequencies?
- Use a logical sequence of frequencies to get the most
useful information first – 2000 Hz, then 500 Hz, then
4000, etc.
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Testing Sequence
6.
7.
If profound loss, is there residual hearing?
- If no tone-burst response, test click ABR at 90 dB
and ASSR up to 115 dB (never this high if DPOAE
present)
Could it be auditory neuropathy/asynchrony?
- Obtain 90 dB slow-rate click ABR at both
rarefaction and condensation polarities to look for
presence of cochlear microphonic (hair-cell response)
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Testing Sequence
8.
Will other tests support the diagnosis?
- If conductive hearing loss or auditory asynchrony is
suspected, cross-check with tympanometry and
middle-ear muscle reflexes.
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Questions?
[email protected]
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