Otoacoustic emissions and brainstem evoked response potentials Objective hearing evaluation

1. OAE AND BERA

2. Otoacoustic emissions
• Otoacoustic Emissions are the sound that result from
energy generated in cochlea
Propagated through middle ear
Transmitted through External Auditory cannal;
Captured by a microphone in External Auditory cannal

3. Hypothesis of OAE generation
• A healthy, living cochlea demonstrates nonlinear behavior
and refined frequency specificity at low stimulus levels,
similar to the characteristics demonstrated by individual
hair cells and auditory nerve fibers
• Cochlear amplifier are biological mechanisms that
enhances vibration of basellar at peak of travelling wave
particularly at low stimulus levels
• Outer haircells main contributers
• Reduced auditory sensitivity, broader tuning, and
abnormal response growth when OHCs are damaged or
missing

4. OAE and Outer Hair Cells
• Preneural phenomenon
• Present even if 8th CN severed
• OAE evoked during low stimulus are vulnerable to agents
like
Acoustic trauma
Hypoxia
Ototoxic medication

5. Measurement of OAE
• Sensitive miniature microphone fits in Ear cannal
• Microphone housed in a small probe that coupled to ear a
foam or rubber tip
• Output to be amplified
Noise has to be reduced –
Procedure in sound treated room
Fan or sound producing instrument switched off
Child test done during asleep, Adult avoid movements
and talk
Probe has to be secured tightly

6. • OAE divided into Spontaneous and evoked OAE
• Evoked OAE divided into
• Stimulus frequency OAE
• Transcient OAE
• Distortion OAE

7. Spontaneous OAE
• SOAEs are measured in the absence of external stimulation
• SOAEs appear as puretone-like signals coming from the ear.

8. • + ve in 50% of healthy indivudals
• Considered as a screening test rather than a diagnostic
test
• If SNHL present more than 30dB SOAE not positive
• More in females

9. Stimulus frequency OAE
• Occur at same frequency and at same time when a pure
tone is introduced into ear
• Microphone records Puretone used for evoking and
SFOAE
• SFOAE has to be filtered
• Common filtering method – Evoking frequency with
SFOAE measured. Suppressive tone given – Vector
subtraction of tone alone and tone presented with
suppressor tone

10. • Not used routinely in clinical practice
• SFOAE equally efficient in finding hearing loss in 1k and
2k and superior to other EOAE at .5k

11. Transient evoked OAE
• As their name suggests, TEOAEs are measured following
the presentation of a transient or brief stimulus.
• Also called COAE or Click Evoked OAE
• A click or toneburst is presented to the ear, and the
response occurs following a brief time delay.
• TEOAE checked in different frequencies
• Best to detect hearing loss in 2k and 4k

12. • A click or toneburst is presented to the ear, and the
response occurs following a brief time delay.
• Measurement of TEOAEs is accomplished using time
synchronous averaging
• Even with averaging Noise : TEOAE ratio is high
• The energy from the stimulus may also persist in the ear
canal long enough to obscure the onset of the TEOAE
response

14. BASIC CHARACTERISTICS OF TEOAESAND THE EFFECTS OF
STIMULUSAND RECORDING PARAMETERS
• Frequency dispersion – higher frequency appears
first then lower frequency
• Or higher frequency have lesser latency period

15. Distortion-Product Otoacoustic
Emissions
• Distortion-product OAEs (DPOAEs) are measured
simultaneously with the presentation of two puretone
stimuli, called “primaries”, to the ear.
• The frequencies of the primaries are conventionally
designated as “f1” and “f2” (f1 < f2) and the corresponding
levels of the primaries as “L1” and “L2.”
• OAE output are mathematically related to frequencies
• f2–f1, 2f1–f2, 3f1–2f2, 2f2–f1

17. Characterstics of DPOAE
• The frequency separation of the two primaries, generally
described as the f2/f1 ratio, influences the DPOAE level
that will be measured

18. BRAIN STEM EVOKED
RESPONSE AUDIOMETRY

19. Auditory pathway

20. • BERA is an objective way of eliciting brain stem
potentials in response to audiological click stimuli.
These waves are recorded by electrodes placed over
the scalp.
• This investigation was first described by Jewett and
Williston in 1971.
• Never a substitute for other audiological tests

21. • The stimulus either in the form of click or tone pip is
transmitted to the ear via a transducer placed in the
insert ear phone or head phone.
• The wave froms of impulses generated at the level of
brain stem are recorded by the placement of
electrodes over the scalp.

22. • The standard electrode configuration for BERA
involves placing a electrode over the vertex of the
head, and ear lobe or mastoid prominence. One
more earthing electrode is placed over the forehead.
This earthing electrode is important for proper
functioning of preamplifier.
•

24. • Wave I appeared to be generated by the more distal
aspect of cochlear nerve and
• Wave II by the more proximal aspect of the auditory nerve
• Wave III in humans is a CN-generated response
• Wave IV is likely generated primarily by the superior
olivary complex
• Wave V of the ABR is likely generated for the most part by
fibers of the lateral lemniscus as they enter into the area
of the inferior colliculus

26. Interpretation
• Wave I : small amplitude, delayed or absent may indicate
cochlear lesion
• Wave V : small amplitude, 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. Shortening of wave the interval with normal
latency of wave V indicate cochlear involvement.

28. PATTERNS OFABR FINDINGS IN VESTIBULAR
SCHWANNOMA
• Absolute Latency Delay
• An absolute latency delay for Wave V is likely vestibular
schwannoma to be considered
• Absolute latency delay is also seen in cochlear,
retocochlear or conductive hearing loss

29. • other measures of the ABR as well as patient history can
become important and helpful.
• When Wave V latency measurements are greater than 6.1 ms
in response to a click stimulus presented at a moderately high
intensity level, the possibility of an eighth nerve tumor should
be considered

30. • Interwave Latency Delay
• Because of the fact that most eighth nerve tumors grow
between the generator sites of Waves I and III, the I–III
interwave interval (IWI) is likely to be extended in these
cases
• In many clinics and laboratories a I–III IWI extending
beyond 2.4 ms is considered abnormal

31. • Many times 1 and 3 waves wont be present
• If present 85% IWI delay present
• The I–V IWI may also be used in the detection of
vestibular schwannoma
• Absence of wave 2 causes suspicion. Suspected case of
acoustic neuromas where 2nd were is patent rule out
involvement of cochlear nerve

33. • Interear Latency Comparisons
• An interear latency comparison, or interaural latency
difference (ILD), using Wave V measurements obtained
from the left and right ears can be diagnostically relevant,
especially when used alongside interwave latency
measurements.
• Wave V is the only wave of the ABR that is present in
each ear conform. So wave 5 is taken for measurement

34. • Should be aware that a asymmetrical hearing loss
produce abnormal ABR.
• Correction factors like 0.1ms for 10Db used at 4KHz
greater than 50dB
• Change in 0.3 to 0.4 ms is diagnostic

35. Amplitude Comparison of Waves
Wave 5: wave 1 amplitude ratio is considered as a reliable
source
The test should be repeated atleast once with no difference
in amplitude more than 20%
5:1 ratio is less than .75 is indicative of vestibular
schwanommas
Incase of wave 4 and 5 complex the peak of complex is
considered

36. • Waveform Morphology and Absence of Waves
• Absence of wave is another indicator of VS
• Wave 3 is most commonly absent wave
• Presence of wave to rule out cochlear involvement of VS
• Wave 1 present others absent conforms a retro cochlear
involvement
• Loss of early waves is suspecious of VS not a reliable
indicator

38. • Repetition Rate Shifts
• Controversial
• This measure involves the comparison of the latency of
Wave V at low and high rates of presentation such as 11
clicks per second to 81 clicks per second.
• If there is a greater than expected latency increase or a
disappearance of Wave V during the high rep rate
recording, then the interpretation is for possible eighth
nerve pathology.

39. • Laterality
• Small tumours will produce ipsilateral ABR affected
• When tumour is large contralatral ABR wave 3 to 5
affected due to compression of tumour

40. ABR AND BRAINSTEM
INVOLVEMENT
• Absolute Latency Delay
• Wave 1 or 2 not useful
• Delay in wave 3 or 4 or 5 without a delay in 1 or 2
indicates a brainstem involvement in adjacent areas

41. • Interwave Latency Delay
• 3-5 waves or 1-5 waves delay can be due to brainstem
involvement
• 1-3 delay may be due to cochlear nerve involvement or
caudal brain stem
• If the I–III IWI is extended but Wave II present indicates
brainstem involvement only
• 3-5 indicates brainstem involvement
• 1-5 latency delay is present subcomponents has to be
checked

43. • Interear Latency Comparisons
• Not reliable as majority of brainstem lesions are bilateral

44. • Amplitude Comparison of Waves
• Neurologists have generally supported the use of the V–I
amplitude ratio as a diagnostic criteria for brainstem
involvement
• When these conditions are met then the V–I amplitude
ratio, though not highly sensitive, is highly specific if a
ratio of less than 0.75 is used

45. • Waveform Morphology and Absence of Waves
• Brainstem involvement often results in a highly
dependable index for brainstem abnormality when Waves
I and III are present and the IV–V complex or Wave V is
absent
• When Wave III is absent and Wave V is present, one
should look at the I–V IWI. If this interval is normal, then it
is likely that the response is normal.
• The absence of all waves can also occur in individuals
with brainstem involvement with severe periphral hearing
loss

46. • Contralateral Effects
• Large mass lesions on one side, such as an acoustic
neuroma, can compress and cause ABR brainstem
finding on the opposite side when stimulating that ear
• The ear opposite the large lesion, if the hearing is
reasonably good, will show normal Waves I and III and an
abnormal III–V interval or compromised V or IV–V
complex
• This kind of information can be clinically useful when
there may be no ABR response or no hearing on the
involved side

47. • Repetition Rate Shifts
• Some reports indicate that when rep rate functions are
abnormal other ABR indices are also abnormal,
• Not much reliable in brainstem pathology