ABR DRSHHASHEMI 1 2 Auditory Assessment Subjective tests Pure Tone Audiometry Speech Audiometry Objective tests Acoustic Immittance Auditory Brainstem Responses ABR Electrocochleography ID: 217676
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AUDITORY BRAINSTEM RESPONSE (ABR)
DR.S.H.HASHEMI
1Slide2
2Auditory Assessment
Subjective tests:
Pure Tone
Audiometry
Speech
Audiometry
Objective tests:
Acoustic
Immittance
Auditory Brainstem Responses (ABR)
Electrocochleography
(
ECochG
)
Otoacoustic
Emissions (OAE)
Auditory Steady-State Response (ASSR)Slide3
What is an auditory evoked potential ?
Electrical activity of the auditory system that occurs in response to an acoustic stimulus, which can be recorded by
surface electrodes.
3Slide4
Short latency response (
< 10 ms )
Middle latency response ( 10-100 ms )
Long latency response (
> 100 ms
)
4Slide5
Introduction
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.
Jewett &
williston ( 1971)
BSER (Brainstem Evoked Response)
BAER (Brainstem Auditory Evoked
Responce
)
BAEP (Brainstem Auditory Evoked potential)
5
ABR assesses the
integrity
of the
peripheral auditory system
and
auditory brainstem pathway.Slide6
Introduction . . .
It’s a set of seven
positive waves recorded during the first
10
msec
after a click stimuli. They are labeled as I – VII.
Waves labeled with
Roman
numerals
6Slide7
PHYSIOLOGY
ABR typically uses a click stimulus that generates a response from the hair cells of the cochlea, the signal travels along the
auditory pathway from the cochlear nuclear complex to the inferior
colliculus
in midbrain generates wave I to wave V.
7Slide8
Origin of each wave
Wave
Origin
I
Distal cochlear nerve
II
Proximal cochlear nerve
III
Cochlear nucleus
IV
Superior
olivary
complex
V
Lateral
lemniscus
VI
Inferior
colliculus
VII
Medial
geniculate
body
8Slide9
9
I
II
III
IV
V
VI
VIISlide10
10
Auditory cortex
Inferior colliculi
Medial geniculate bodies
VII
VISlide11
11Slide12
12Slide13
Electrode placement
Cz (at vertex) (recording electrode)Ipsilateral ear lobule or mastoid process (reference electrode)
Contra lateral ear lobule (act as a ground)
13Slide14
14Slide15
Normal values
ABR should be done at around 80dB
1000Hz – 4000Hz
Latencies are the key measure
Peaks I, III, and
V
most useful
Calculate the peak –
interpeak latencies for the ABR waves
Find out the
interpeak
latencies of
I–III
,
III–V
,
I–V
Disorders will produce delays
Wave
Latency
I
1.5 m.sec
II
2.5 m.sec
III
3.5 m.sec
IV
4.5 m.sec
V
5.5 m.sec
VI
6.5 m.sec15Slide16
LatencyAmplitude
Morphology
Interpretation
16Slide17
Interpretation . . .
Wave I : delayed or absent may indicate
cochlear lesion.
Wave
V
: delayed or absent may indicate
upper brainstem lesion.
I – III
inter-peak latency: prolongation may indicate lower brainstem lesion.
III – V
inter-peak latency: prolongation may indicate
upper
brainstem lesion.
I – V
inter-peak latency: prolongation may indicate
whole
brainstem lesion
. 17Slide18
Applications
Auditory threshold testing
Identifying the hearing loss
Differential diagnosis
Classification of type of deafness (conductive or
sensorineural
)
Neonatal hearing screening
Identification of
retrochoclear
pathology
Neurosurgical
interoperative
monitoring
18Slide19
Disadvantages
Not normally possible for awake children
SkillTime consuming
Not frequency specificity
Not sensitive to hearing loss
< 1000 Hz
or
> 4000 Hz
Cannot provide information about entire audiogram
ABR recorded just at
90dB
( cannot differentiate between
sever
and
profound
hearing loss )
19Slide20
Factors affecting the ABR
Factors that not affecting
AwakeSleep
Sleep stages
Level of arousal
Degree of attention paid to the eliciting stimulus
Factors that affecting
Age
Gender
Females
have slightly shorter wave
III
and
V
latencies than males.
Pharmacological agents
No affect
→
sedatives, general anesthetics, neuromuscular blocking agents Affect
→ phenytoin,
lidocaine
,
alcohol
Body temperature
↓ Body temperature → ↑ latencies
20Slide21
Limitation
ABR assesses the integrity of the
peripheral auditory system
and
auditory brainstem pathway
, before sound is received by the cortex.
ABR will
not be sensitive
to lesions above the midbrain level.
[Example:
Central deafness
(bilateral temporal lobe lesions),sever to profound pure tone hearing loss but ABR is normal ]
21
ABR is generated
subcortically
, it
does not
truly measure hearing. Slide22
Auditory threshold testing
Click : 1000 Hz – 4000 Hz
Beginning at a
80dB
and continuing down to lower levels until wave
V
is
no larger seen ( 20 dB)
.It is good practice to obtain two waveform at each stimulus level.
In normals
and
conductive HL
click threshold will be
~10-20 dB
higher than the best audiometric threshold.
In
Sensory HL
click threshold will be
~ 5 dB
higher than the best audiometric threshold.Because maximum output for click is limited to ~ 90-100 dB
one will not be able to differentiate between sever
and
profound losses.
The most common cause of
absence
of ABR waves is
sever to profound hearing loss
.
22Slide23
23Slide24
Latency-intensity function ( LIF )
24Slide25
25
The
relation
between LIF and hearing loss is quite
complex
(due to the myriad of possible audiometric contours). Slide26
Normal 26Slide27
Normal27Slide28
Identifying the hearing loss28Slide29
Conductive HL
Latency-intensity function ( LIF ) slope
→ NL
The latency of wave
V
at each intensity → prolonged
Shifted to the
right
29Slide30
Conductive HL30Slide31
Sensory hearing loss
Wave V latencies show NO or
LESS prolongation compared with conductive HL.
LIF lies close to normal curve
31Slide32
Sloping sensory hearing loss
Slope of the LIF is typically steeper than normal.
The region of the cochlea
where the response is initiated (
high-frequency fibers
in the
basal region
are stimulated and longer when
lower frequency fibers toward the apical region are stimulated ).32Slide33
Low frequency sensory (cochlear) hearing loss with normal ABR
33Slide34
Sever high frequency sensory (cochlear)hearing loss with normal ABR
34Slide35
Mild-to-moderate, high frequency sensory (cochlear) hearing loss with normal ABR
35Slide36
Mild-to-moderate , high frequency neural (retrochochlear) hearing loss
36Slide37
Severe-to-profound hearing loss with absent ABR
37Slide38
Neonatal hearing screening
Several clinical trials have shown ABR testing as an effective screening tool in the evaluation of hearing in newborns.
sensitivity of 100%
and
specificity of 96-98%
Can be recorded as early as
28wks
gestational age.
38Slide39
Neonatal hearing screening . . .
Wave I amplitude
is larger
than in adults
(Recording electrode is closer to the cochlea due to the smaller head size of infants.)
The
latencies
of the ABR waveform components are
longer than adults
(Decreased throughout the maturation of the cochlea and brainstem.)
Should correct by
18-24 months
of age.
39Slide40
Intraoperative monitoring
IN SURGERY :
ABR is useful in the prevention of
neurotologic
dysfunction and the preservation of postoperative hearing loss.
For many patients with
tumors of CN VIII
or
the cerebellopontine
angle, hearing may be diminished or completely lost postoperatively, even when the auditory nerve has been preserved anatomically.
40Slide41
Identification of retrochoclear pathology
ABR is considered an effective
screening tool in the evaluation of suspected
retrocochlear
pathology such as an
acoustic
neuroma
or vestibular schwannoma.
41Slide42
42Slide43
43Slide44
44Slide45
Acoustic neuroma
45Slide46
Likely abnormal in:
Multiple Sclerosis and other demyelinating
processes
Hyperbilirubinemia
at levels requiring exchange transfusion
46