2. Recording of the synchronous electrical
activity recorded by a far-field electrode
placed on the scalp in response to a sound
presented to the cochlea.
Changes produced by the passage of
electrical stimulus generated in the cochlea
through the neural pathway
2
3. HISTORY
First described by Jewett and Williston in
1971, ABR audiometry is the most
common application of auditory evoked
responses.
3
4. USES OF BERA
Detection & quantification of deafness in
difficult to test patients
Detection of the nature of deafness
Identification of the site of lesion in
retrocochlear pathologies
Study of central auditory disorders
Study of maturity of nervous system in
newborns
Objective identification of brain death
Assessing prognosis in comatose patients
4
5. USES OF INTRAOPERATIVE AUDITORY
BRAINSTEM RESPONSE
Monitoring cochlear function directed at hearing
preservation:
Cerebellopontine angle tumor resection (acoustic neuroma
surgery)
Vascular decompression of trigeminal neuralgia
Vestibular nerve section for the relief of vertigo
Exploration of the facial nerve for facial nerve
decompression
Endolymphatic sac decompression for Mèniére disease
Monitoring brainstem integrity:
Brainstem tumor resection
Brainstem aneurysm clipping or arteriovenous
malformation resection
5
6. PRINCIPLE OF BERA
Processing at different levels
Generates electrical activity
Monitored by surface electrode
Graphic recording presents a waveform
Depends on the functional integrity of the pathway
6
7. PRINCIPLE OF BERA
Process becomes difficult due to the
background potential generated by the brain
Separation of the 2 activities by summation &
averaging
Sound evoked electrical potential: time
specific
Electrical activity of brain: occurs randomly
7
9. PROCESSING OF THE SOUND
STIMULUS
‘Sound conduction time’
‘Cochlear transport time’
• Less for high fq sound
• High for low fq sound
Passage through cochlear filters
Cochlear filter –build-up time
• Broadening of cochlear filters
Synaptic delay
Neural conduction time
9
10. MECHANISM OF ACTIVATION IN BERA
Click sound presented to the ear
Earlier stimulation by the high fq sounds
The middle & apical parts don’t contribute
much to BERA response
Changes in high fq loss
Relation of intensity of sound stimulus to the
latency & amplitude of the waves
10
11. AUDITORY EVOKED POTENCIALS
Electrical activity in brain elicited by sound stimulus
Recorded upto 500 millisecs
3 responses are recorded:
• Short Latency Response (10ms) i.e BERA
• Middle Latency Response (10-50ms)
• Late Latency Response (50-500ms)
11
12. PRE-REQUISITES OF RECORDING
BERA
Elicited by click stimulus
50-60dB above avg. pure tone threshold
Location of electrodes: active, reference & ground
Air conditioned room
Good earthing Faraday cages
12
14. ADVANTAGES OF BBC
Synchronous stimulation of large no. of
neurons
Clear, sharp well- marked tracing
Very rapid onset & fall
Easy latency & amplitude measurement
Lowest fq: 100-150Hz
Highest fq: 3000-5000Hz
Total recordings: 2000-4000
Stimulus rate: 10-40 clickssec (11.1/sec)
14
15. RECORDING
Graph plotted with amplitude (in microvolts) on the ordinate &
time (in msec) on the abscissa
5-7 peakswaves within 8-10 millisecs
BERA waves: 5 prominent & 2 small
Numbered I-VII
15
16. SITE OF NEURAL GENERATOR
Wave Site of Neural Generator
I Cochlear nerve (distal end)
II Cochlear nerve ( proximal end)
III Cochlear nucleus
IV Superior Olivary Complex
V Lateral Leminiscus & Inferior
Colliculus
VI & VII Not definitely known
16
17. WAVE V WAVE IV
Identified first
Most reliable & easily
identifiable
Sharp negative
deflection following
the peak
Appears at 5.6-5.85
millisecs
Largest & most robust
wave
Preceding wave V
Maybe superimposed
on wave V
Distinct wave present
in 50-60% subjects
17
18. WAVE III WAVE II
Upward peak between
wave II & IV
Maybe bifid
Maybe fused with II
Preceding wave IV
Around the 3.8 msec
Amplitude: 0.2-0.25
microvolt
Immediately
preceding wave III
Latency: 2.8 msec
18
19. WAVE I
Sharp peak beyond 1msec mark
Importance of identification:
• Presence of wave I in the absence of others: lesion beyond distal
nerve end
• Delayed wave I: conductive/cochlear pathology
• Abolition of wave I: severe peripheral lesions
19
21. PARAMETERS STUDIED
Latency of the wave(s)- absolute, interwave, interaural
Amplitude of the wave(s)- absolute & relative (amplitude ratio)
Wave-form morphology
Latency-intensity functions of wave V
21
22. LATENCY STUDIES
Time interval between onset of stimulus &
peak of the wave
Measured in millisecs
Also known as Absolute Latency
Most important for clinical measurements
Latency of wave V depends on intensity of
sound stimulus
Interwave Latency
Interaural Latency
22
23. AMPLITUDE STUDIES
Variable
Studies are not very reliable
Used as supplementary evidence
Measured in microvolts
Known as Absolute amplitude of a wave
Relative Amplitude Ratio
23
24. STUDY OF WAVE MORPHOLOGY
Shape of the graph
Normal graph
Graph in newborns
Conditions altering the morphology of the graph:
• Acoustic neuroma
• Lesion in the auditory pathway
• Variation in rateintensity of stimulus
24
25. NON CLINICAL FACTORS AFFECTING
BERA
Stimulus rate
Stimulus phase or polarity
Intensity of sound stimulus
Binauralmonoaural stimulation
Filter characters of BERA machine
Nature of sound used
Sexage of the patient
25
26. STIMULUS RATE
No. of clicks presented to the ear/sec
Recommended rate: 10-40/sec
Normally used: 1.1 clicks/sec
Rate >25/sec: increased latency & decreased
amplitude
Children: >50/sec
High stimulus rate: Multiple sclerosis
26
27. STIMULUS PHASE OR POLARITY
Condensation & rarefaction phase
Affects latency, amplitude, morphology of
waves
Routine studies: rarefaction waves are used
Alternate phase: reduces the artifacts & also
the sharpness of waves
27
28. INTENSITY OF SOUND STIMULUS
60 dB suprathreshold
Low intensity: increased absolute latency &
decreased amplitude
First to disappear: wave I
Most stable: wave V
28
29. FILTER CHARACTRISTICS
Recording of fixed range of frequencies
Low fq filter: 100-150 Hz
High fq filter: 3000-5000 Hz
Frequencies of the recorded electrical
stimulus
29
30. NORMAL VALUES & CRITERIA FOR
ABNORMALITY
Parameter
measured
Normal value
(ms)
Criteria for
abnormality (ms)
I to III IPL 2 More than 2.4
III to V IPL 2 More than 2.4
I to V IPL 4 More than 4.4
Interaural
difference of
wave V
Less than 0.3 More than 0.3
Morphology of
wave V
Present Absent
30
32. ESTIMATION OF HEARING THRESHOLD
Useful in newborns, infants, difficult patients
Estimation of hearing threshold
Estimation of type & degree of hearing loss
Avg. pure tone threshold = 0.6 (BERA threshold)
Comparison of latency of wave V at different
intensity sounds
Frequency specific audiogram cannot be obtained
32
33. IDENTIFICATION OF NATURE
OF DEAFNESS
Analysis of latency-intensity function
Conductive, sensory or neural
Latency of wave V is recorded for different
intensities
Plotted graphically
Conductive loss: upward & parallel shift
Sensory loss: shallow configuration
Neural: steep sloping graph
33
34. IDENTIFICATION OF
RETROCOCHLEAR
PATHOLOGIES
Most reliably identified
Parameters:
• Increased interaural latency difference of wave V
• Increase interaural interwave/interpeak latenct
between wave I to V
• Interwave latency between wave I & III/V
34
35. DERIVED BAND STACKED BERA
Elicit response from several discrete regions
of cochlea
Composite picture of neural activity
Increases sensitivity of the test
Cochlea is divided into 5 segments &
response from each is noted
35
36. DERIVED BAND STACKED BERA
1st segment: sounds above 8000Hz (extreme
basal end)
2nd segment: 4000-8000Hz (basal end of
cochlea)
3rd segment: 2000-4000Hz (between basal &
mid-portion)
4th segment: 1000-2000Hz (mid portion of
cochlea)
5th segment: 500-1000Hz (apical part of
cochlea)
36
38. STACKED BERA
Improvement of derived band BERA
Increases the sensitivity & specificity of
BERA for small tumours
Aligning 5 wave Vs of derived band BERA &
adding the amplitudes
Reduced in presence of tumours
Useful in patients with U/L SNHL with normal
BERA
38
39. OTOACOUSTIC
EMISSONS
These are low intensity sounds produced by the cochlea as
the outer hair cells expand and contract
Sound produced by outer hair cells travels in a reverse
direction
Outer hair cell > perilymph > oval window > ossicles >
tympanic membrane > ear canal
39
40. TYPES OF OAE
Spontaneous otoacoustic emissions (SOAEs) - Sounds emitted
without an acoustic stimulus (ie, spontaneously)
Transient otoacoustic emissions (TOAEs) or transient evoked
otoacoustic emissions (TEOAEs) - Sounds emitted in response
to an acoustic stimuli of very short duration; usually clicks but
can be tone-bursts
Distortion product otoacoustic emissions (DPOAEs) - Sounds
emitted in response to 2 simultaneous tones of different
frequencies; often can be recorded in individuals with mild-to-
moderate hearing losses for whom TOAEs are absent.
Sustained-frequency otoacoustic emissions (SFOAEs) - Sounds
emitted in response to a continuous tone; not used clinically.
40
41. USES
To determine cochlear status, specifically hair cell function.
• Screens hearing in neonates and infants, comatosed and
disabled individuals.
• Partially estimate hearing sensitivity within a limited range
• Differentiate between the sensory and neural components of
sensorineural hearing loss
• Tests for functional hearing loss
41
42. HOW IS IT DONE?
Insert a probe with a soft flexible tip in the ear canal to obtain
a seal.
Multiple responses are averaged. All OAEs are analyzed
relative to the noise floor; therefore, reduction of physiologic
and acoustic ambient noise is critical for good recordings.
42
43. PREREQUISITES FOR
OAE
Unobstructed outer ear canal
Seal of the ear canal with the probe
Optimal positioning of the probe
Absence of middle ear pathology: Pressure equalization (PE)
tubes alone probably will not interfere with results. However,
if emissions are absent, results should be interpreted with
caution.
Functioning cochlear outer hair cells
A quiescent patient: Excessive movement or vocalization
may preclude recording.
Relatively quiet recording environment: A sound booth is not
required, but a noisy environment may preclude accurate
recording.
43
44. INTERPRETATION
The presence of SOAEs usually is considered a sign of
cochlear health, but the absence of SOAEs is not necessarily
a sign of abnormality.
The presence of a TOAE in a particular frequency band
suggests that cochlear sensitivity in that region is
approximately 20-40 dB HL or better.
44
