3. OTOACOUSTIC EMISSIONS
• These are the low intensity sounds produced by the outer hair
cells of cochlea and recordable in the external ear canal.
• OAE is measured and documented as how much the OAE
generated is above the noise floor.
4. HISTORY
• Thomas Gold (1948) had postulated that a living human
ear must be having some biological mechanism by which it
can enhance the auditory energy after the auditory
stimulus enters the ear.
• David kemp (1977) first record the sound generated by the
biological activity of the normal human cochlea & invented
OAE.
5. • The sound emitted by the biological activity of the
normal cochlea (outer hair cells) which can be picked-
up, recorded & measured by placing a microphone in
the deep EAM is called as otoacoustic emissions
(OAEs).
Types-
1. Spontaneous OAEs.
2. Evoked OAES.
» Transient Evoked OAEs
6.
7. PRE-REQUISITES FOR GETTING OAEs
• Quiet environment (AC & fan switched off).
• Sedation for child.
• Unobstructed outer ear canal.
• Seal of the ear canal with the probe.
8. PRE-REQUISITES FOR GETTING OAEs
• Optimal positioning of the probe.
• Absence of middle ear pathology.
• Functioning cochlear outer hair cells.
• A quiescent patient: Excessive movement or vocalization
may preclude recording
9. NOISE FLOOR
• OAE are very faint sounds of 0-15dB, they are easily
masked by extraneous noise.
• These extraneous noises are generated from two sources:
1. The ambient environmental noise.
2. The biological noise of blood flow, respiration,
swallowing etc. generated within the subject’s body.
• These are generated at random while OAE is generated at
particular time after the presentation of stimulus.
Noise
floor
10. PROCEDURE
• Insert a probe with a soft flexible tip in the ear canal to
obtain a seal.
• The OAE recording set up basically consists of
– microphone
– A micro-sized loudspeaker
– A computerised averaging system
– An amplifier.
– A mechanism to record the sound graphically on a moving
strip of paper, or to indicate the presence of the emission by
some electronic device like as LED lamp.
11. • Two types of OAE machines
– Clinical machine that provides a waveform of OAE
– Handheld portable devices used for OAE screening
13. SPONTANEOUS OAEs
• Low intensity, continuous, very narrow band or pure tone
sounds produce by outer hair cells.
• SOAEs present- normal hearing at particular freq.
• Absent- normally in 50%.
14. CAUSE OF GENERATION OF SOAEs
• normal aberrations in the physical structure of the
organ of corti e.g., a fourth row of outer hair cells in
the cochlea is the probable cause of generation of
SOAEs.
15. FEATURES OF SOAES
• Avg. intensity: -3dB to 2.6dB (adults), 8.5dB (infants)
• Freq. : 1000- 2000Hz (adults), 3k-4k (infants)
• F>M
• Rt ear> Lt ear
16. CLINICAL IMPLICATIONS OF SOAEs
1. Detection of SOAE in an ear indicates that threshold is with in
normal limits in an around the frequency at which the SOAE
is generated.
2. Absence of SOAE doesn’t mean that there is some deafness.
17. LIMITATIONS OF SOAES
• Not detectable in all normal ears.
• When detectable, they are of variable intensities &
frequencies, hence cannot be used for cochlear function.
19. EVOKED OAEs
• OAEs that doesn’t occur spontaneously & has to be evoked
by presenting a sound stimulus to the ear.
• Can be produce by both clicks ( preferred) or tone pips.
• The character of the response is dependent upon the
character of the evoking stimulus.
20. EVOKED OAEs
• EOAEs reduce very rapidly as deafness increases & are
undetectable when the deafness is above 30-35 dB.
• Elicited by presenting clicks at intervals of 20 ms & the
response is obtained as a series of waves or oscillations
having a latency between 5-15 ms after the onset of
stimulus.
• 80db is standard stimulation intensity
22. TEOAEs
• Recorded in nearly all persons who have normal hearing.
• The basic idea on which TEOAEs work is that the OAE
response mirrors ( i.e., it is a replica) the spectral
properties of the evoking sound stimulus.
• The amplitude / intensity of OAE response will be lesser
than the intensity of the evoking sound stimulus. (Adult
30dB, infant 20dB)
23. Characteristics Of TEOAEs
1. Evoked by click stimuli as well as by tone bursts (i.e., pure
tone sounds).
– stimulus artifacts are more with tone bursts.
2. Stable & not variable as SOAEs.
3. The same sound stimulus will elicit the same response
provided hearing threshold remains same.
4. Elicited by sounds of 80-85dB.
24. 1. Louder sounds don’t elicit more robust response.
2. TEOAE amplitude saturates after about 70dB to 80dB
stimulus level, below that it increases in linear fashion.
3. Avg. loudness (amp./intensity) is about 20dB (neonates) &
just less than 10dB (adults) with sound stimulus of 80-85dB.
25. • TEOAE ( & SOAE) response that is elicited from an ear
after presenting a click sound is suppressed if a sound
is simultaneously presented in the other ear.
» Hypothesised to be due to some inhibitory effect
of central auditory nervous system on the
cochlear hair cells.
• This unique feature of OAEs being suppressed by
another sound has been used as a test for confirming a
newly discovered disease entity called Auditory
neuropathy.
26. CLINICAL USES
• Most commonly employed for neonatal hearing screening.
• Studies show that,
– Within 36hrs of birth- 75% chances of successful TEOAE
– At 108hrs- 95%
• in infants within 24hrs of birth TEOAE are evoked in about 93%
ears if 2-3 attempts are made & if ear is cleaned of any slimy
substance before test.
• Avg TEOAE response is 15dB at 24 hrs and 20 dB at 48-72hrs
27. DISTORTION PRODUCT OAE
• Obtained when pure tone is used as stimuli
• New sound obtained from cochlea by presenting two different
pure tone sounds of two diff. freq. is termed as DPOAE.
• Just like TEOAE, the DPOAE can be detected in nearly all normal
hearing ears & are quite stable.
28. CHARACTERISTICS OF
DPOAE
• By convention two sounds used for eliciting the DPOAE are :
• F2 primary- the freq. of puretone sound stimulus which is of
comparatively higher freq. than the f1
• F1 primary- the freq. of puretone sound which is of
comparatively lower freq. than the other puretone stimulus.
L1 : intensity level of the f1 primary.
• L2 : intensity level of the f2 primary.
29. • Most robust DPOAE response is obtained when the f2 :
f1 = 1.22 : 1.
» i.e., f2 should be f1 x 1.22 times.
• When the f2 to f1 ratio is 1.22, then the freq. of evoked
DPOAE is 2f1-f2.
• The average intensity of DPOAE response is of 5-
10dB or may be 15dB in some cases.
30. • Usually L1 65-70dB.
L250-55dB.
(But small changes are permissible)
Diff of 10-15dB
31. SPECTRUM OF SOUND IN EAR CANAL
Stimulus
Tones
Emission
Frequenc
y
Background
Noise
32. FACTORS AFFECTING DPOAE RECORDING
1. Ambient noise or any noise generated by the patient e.g., loud
breathing or snoring.
2. Ear canal wax.
3. TM perforation.
4. Middle ear disease.
» Hence, otoscopic examination is warrented if DPOAE is
absent.
(If any obstruction in EAM like wax or vernix caseosa is found, it
must be cleaned thoroughly & the test repeated).
33. CLINICAL IMPLICATIONS OF DPOAE
• If a test is done using 2 freq. f1 & f2 then the evoked DPOAE
of 2f1-f2 will represent the cochlear function of the f2
frequency (higher Hz/basal)region of cochlea .
• Tonotopic mapping by changing f1 and f2
• It can be Ascertained whether the hearing thersold is
normal at different frequencies and different zones of
cochlea can be tested for normal function.
• Structural and functional integrity assessment of Organ of
Corti
34. • DPOAE is absent in patients with SNHL loss greater than
40dB.
• Useful in screening infants for hearing loss.
• Early detection of cochlear damage due to ototoxicity &
noise trauma.
– In early ototoxicity / noise trauma, even when there is no
evidence of deafness on pure tone audiometry, absence
of DPOAE in the higher freq. e.g., at 4KHz is a sign of early
cochlear damage.
35. DPOAE IN NEONATAL HEARING SCREENING
• Infants & young children usually have higher DPOAE levels as
compared to adults.
• DPOAE is very useful in neonatal hearing screening.
• However, to identify hearing loss it is not the DPOAE amplitude
that is the best parameter, a much better parameter is the
difference between the DPOAE level & the noise floor.
36. • If the signal to noise ratio of the OAE is above 6dB in an
adequately quite room, it is accepted as a good enough
evidence of normal hearing.
37.
38. • If hearing loss > 40dB – 100% sensitive.
• 20-40dB- 90%
• Hearing loss is more accurate in the middle & high freq. as
compared to low freq.
39. DIFFERENCE B/W TEOAE & DPOAE
TEOAE
• More sensitive for low
frequency loss.
• Usually done using click
sounds.
• Gives less freq. specific
information.
• Gives us a gross overall
idea of entire cochlea.
DPOAE
• More sensitive for high
frequency loss.
• Usually done using different pure
tone sounds.
• Gives for freq. specific
information.
• The functional status of diff.
discrete portions of the cochlea
can be separately tested.
40. USES OF OTOACOUSTIC EMISSIONS
• As a Screening test for detection of hearing loss esp. in
neonates.
• To identify cochlear disorders like ototoxicity, noise trauma.
• To identify auditory nerve disorders like auditory neuropathy
& acoustic neuromas.
– Tests for functional (feigned) hearing loss.
41. DRAWBACKS OF OAE (TEOAE &
DPOAE)
• Doesn’t tell us hearing threshold.
• Doesn’t identify the extent of hearing impairment.
• Doesn’t identify the exact site of lesion in the auditory
pathway
(Absence of OAE indicates that there is probably a cochlear lesion
(but it could be a middle ear lesion also).
42. Don’t tell condition of the higher pathways from the auditory nerve
to auditory cortex.
Any middle ear defect which is capable of producing an air-bone gap
of just 30dB or above will make OAE undetectable. (hence, if OAE
absent, tympanometry should always be done to rule out middle ear
pathology)
43. BERA
Brain stem evoked response audiometry
Auditory brain stem response
ABR audiometry
BAER (Brainstem auditory evoked response audiometry).
44. HISTORY
• First described by Jewett and Williston in 1971, ABR audiometry
is the most common application auditory evoked responses.
• What is evoked potential
• Electrical potentials that occur in the group of neuron in
response to stimulation of a sense organ, which can be recorded
by surface electrodes is known as Evoked Potential
45. INTRODUCTION
• Auditory brainstem response (ABR) is a neurologic test of
auditory brainstem function in response to auditory (click)
stimuli.
• It’s a set of seven positive waves recorded during the first 10
miliseconds after a click stimuli. They are labeled as I - VII
46. PHYSIOLOGY
• Auditory brainstem response (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 mid brain generates
wave I to wave V.
47. PRINCIPLE OF BERA
• Passage of the impulse at different levels of auditory pathway,
generates electrical activity
• Monitored by surface electrode on the vertex of the scalp.
• On Graphic recording electrical activity presents a waveform
with discrete peaks.
• Depends on the functional and structural integrity of the
pathway.
48. NEUROPHYSIOLOGY OF BERA
• When a pure tone sound of a particular freq. is presented to the
cochlea, the sound wave enters the cochlea from the basal turn
& travels as a traveling wave through the cochlea & ultimately
reaches the specific portion of cochlea where that particular
freq. is processed & then gets converted into action potentials
in hair cells.
49. • The Aps passes through the synapses & enters the specific fibers
of the cochlear nerve & through the C.N. enters the brain as
electrical energy for further processing.
• In normal cochlea, there are functional filters c/a ‘Cochlear
Filters’ at the site of activation of the hair cells through which
the impulse passes before being converted into Aps.
50.
51. • Sound entering the ear to be converted into Aps. &
stimulate the cochlear nerve fibres has to undergo the
following processes each of which takes a certain amount
of time that is measurable in millisecs & differs from
person to person.
• Sound conduction time: from EAM to distal end of
cochlea.
• Cochlear Transport time: Sound passes through cochlea
as a travelling wave till all component freq. of sound reach
the specific region of cochlea where it is processed.
» High fq (basal turn)- less CTT , more energy.
52. • Cochlea Filter-build-up time : After the travelling wave
reaches the specific site of activation in the cochlea, it
negotiates its way through the cochlear filters, is processed
by the hair cells & is transformed into Aps.Time taken for
this is c/a CFBT.
» In cochlear lesions this filtering is defective c/a
broadening of cochlear filters & in this CFBT is reduced as
sound then passes through broadened filters more easily.
• Synaptic Delay : Time taken to pass through the synapse
b/w the inner hair cell of cochlea & the distal end of
cochlear nerve fiber.
• Neural conduction Time : Time taken from conduction
through C.N. to inferior colliculus.
» Produces various waves in BERA.
53. 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
16-07-2012 www.nayyarENT.com 53
54. • Now, click sound which has all freq. stimulates the entire
length of the cochlea but stimulation doesn’t occur at the
same time, the apical part being stimulated somewhat
later than basal part.
• As the basilar membrane is more taught & narrow at the
basal end & since velocity of traveling wave is much
higher at basal end, when the sound enters there is strong
neural synchrony at basal end (by high freq.)
55. •This strong synchronization & earlier activation of the basal turn
makes the neural activity generated from the basal turn a much
larger component of BERA response (esp. wave V) than apex.
•Hence, we measure in click-evoked BERA test primarily the
neural activity that is generated from the basal turn of the cochlea
which is stimulated by high freq.
56. PRINCIPLE OF BERA
The process of measuring the electrical activity in
the brain in response to a sound stimulus presented
to the ear is very complicated & cumbersome
process.
Because, some degree of random & spontaneous
electrical activity is continually occuring within the
brain.
A recording of this random electrical activity is c/a
EEG.
57. The electrical activity set up in the brain, in response
to a sound stimulus, gets mixes up with the random &
spontaneous electrical activity occuring within the
brain, & gets obscured
Process of measuring the electrical activity becomes
difficult due to the background potential generated
by the brain bcz electrical activity produced by sound
stimulus is not stronger than this random electrical
activity.
58. Scientists found that the sound evoked electrical activity
is time specific, & occurs at a fixed point of time after the
sound stimulation, whereas, the background potential is
not time specific & occurs at random.
Separation of the 2 activities by summation & averaging
with computerized technique.
59. 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)
60. MIDDLE LATENCY RESPONSE
• Wave peaks: N0(10ms), P0(10-15ms), Na (16-30ms) ,Pa(30-45ms)
and N3(50ms)
• Most consistent waves: Na, Pa
• Both Neurogenic & myogenic origin (originate from neck
muscles & can be partially lesend by relaxing pat.)
• Affected by sleep, anaesthesia( so not suitable for younge
childs).
• Origin: Proximal to the midbrain( thalamus , thalamocortical
tracts ,reticular formation in the brainstem ,medial geniculate
body ).
61. • Assess hearing level at low frequency range( 250-500 Hz).
• Important for fitting hearing aid and rehabilitating a deaf child.
• Elicited by tone pips of 10-20msecs duration at a stimulus rate of
2-40 per second .
• MLR is mainly useful for audiological purposes ,not for
neurological purpose because wave-peaks are not adequately
stable & there is considerable contamination of the recording by
myogenic components.
62. LATE LATENCY RESPONSE
• Recordable between 50-500ms.
• Originates in the cerebral cortex.
• Cortical Evoked Response Audiometry (CERA).
• 5 wave peaks: P1, N1, P2, N2 & P3
• Eliciated by tone pips of 1000-2000 Hz
• Rate: 1 stimulus every 2-3 secs.
63. • P300 Wave peak –appears at around 300msecs & is most imp LLR
wave-peak.
• It dependent upon cognitive and perceptive functions of the
brain.
• It related to cortical functions like short term memory ,auditory
information ,the mental concentration and intelligence .
• Important to neuropsychiatrist & neurotologists.
64. METHOD OF RECORDING BERA
• Elicited by click stimulus.
• Intensity: 50-60dB above avg. pure tone threshold.
• Location of electrodes:
» Active(Recording elecrode)- at vertex
» Reference- Mastoid or ear lobe of I/L ear.
» Ground- C/l mastoid.
• Air conditioned room.
• Good earthing Faraday cages (for electromagnetic
shielding).
65.
66. PRE-REQUISITES OF RECORDING BERA
• Position of patient.
• Relaxed.
• Sedation in infants & children.
» Triclofos sodium- 50mg/kg bdy wt.
» Promethazine HCL- 0.5mg/kg bdy wt.
• Prior PTA.
• Sound stimulus: Broad Band Clicks (100 microsecs duration)
67. ADVANTAGES OF BBC
• Synchronous stimulation of large no. of neurons.
• Elicit clear, sharp well- marked tracing and easily recognisable
peaks in the graph.
• Latency & amplitude measurement are easy and more
accurate .
• Lowest fq: 100-150Hz
• Highest fq: 3000-5000Hz
• Total recordings: 2000-4000
• Stimulus rate: 10-40 clicks/sec (11.1/sec)
68. PROCEDURE
• Subject lying supine with a pillow under his head.
• Room should be quite.
• Clean the scalp & apply electrode.
• Apply the ear phone (red for the right ear & blue for the left
ear)
• Select the ear in the stimulator & apply masking to the opposite
ear.
69. Contd..
• Stimulation rate : 11/sec.
• Find out the threshold of hearing.
• ABR should be done at around 80dB.
• Calculate the peak – interpeak latencies for the ABR waves.
70. 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.
71. Wave V
• Identified first.
• Most reliable & easily identifiable.
• Sharp negative deflection following the peak.
• Appears at 5.6-5.85 millisecs.
• Largest & most robust wave.
72. Wave IV
• Preceding wave V.
• Maybe superimposed on wave V.
• Distinct wave present in 50-60% subjects.
73. Wave III
• Upward peak between wave II & IV.
• Maybe bifid.
• May be fused with II.
• Preceding wave IV.
• Around the 3.8 msec.
• Amplitude: 0.2-0.25 microvolt.
75. Wave I
• Sharp peak beyond 1msec mark.
• Gives us an idea whether the stimulus has crossed over from
cochlea & distal end of auditory nerve.
• Importance of identification:
– Presence of wave I in the absence of others: lesion beyond
distal nerve end(cochlea).
– Delayed wave I( i.e., latency increased) but inter-peak latencies
I-III or I-V normal: conductive/cochlear pathology but as wave
crosses cochlea there is no subsequent obstruction, i.e., no
retro- cochlear pathology.
– Abolition of wave I: severe peripheral lesions(cochlear &
conductive pathology).
76.
77. 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.
78. 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.
• Inter-wave Latency: latency b/t waves I and V---4 msecs in
adult & 5 msecs in newborns.
– Any lesion b/w the cochlear nerve and brainstem ;
inter-wave latency will increase .
79. AMPLITUDE STUDIES
• Variable , so Studies are not very reliable.
• Used as supplementary evidence.
• Measured in microvolts.
• Known as Absolute amplitude of a wave.
• Relative Amplitude Ratio is commonly used(??) .
80. STUDY OF WAVE MORPHOLOGY
• Shape of the graph— provide some clinical information.
• Normal graph in adult : 5-7 peaks each separated by a time
interval of about one msecs.
• Graph in newborns : 3 peaks and waves II and IV are
inconspicuous .
81. • Pathological conditions like acoustic neuromas in which the
distance (i.e., time interval) b/w peaks I & III is increased.
• Of all the waves in the BERA, it has been found that wave V is the
most consistent & that is why wave V is used for studies of
latency & amplitude.
• Newborns has a larger wave I and much smaller wave V than in
adults .
82. NON CLINICAL FACTORS AFFECTING BERA
• Stimulus rate.
• Stimulus phase or polarity.
• Intensity of sound stimulus.
• Binaural/mono-aural stimulation.
• Filter characters of BERA machine.
• Nature of sound used.
• Sex/age of the patient.
83. STIMULUS RATE
• Recommended rate: 10-40/sec.(Normally 11.1 clicks/sec.)
• Rate >25/sec: increased latency & decreased amplitude. So
, its prudent to keep stimulus rate below 25/sec.
• Children: ~50/sec.( as, infants & children are often restless &
allow very little time to complete test).
• High stimulus rate: Multiple sclerosis (some changes are
found if only very high stimulus is used).
84.
85. STIMULUS PHASE OR POLARITY
• 2 types of phases: Condensation & rarefaction phase.
• When transducer moves outwards i.e., towards the eardrum c/a
condensation phase.
• When moves inwards i.e., in direction away from eardrum, c/a
rarefaction phase.
• Affects latency, amplitude, morphology of waves.
• Routine studies: rarefaction waves are used.
• Alternate phase: reduces the artifacts & also the sharpness of waves.
• However, the latency & amplitude of wave V is not much altered by
the change in phase of the sound stimulus.
86. INTENSITY OF SOUND STIMULUS
• 60 dB suprathreshold.
• Low intensity: increased absolute latency & decreased amplitude.
• First to disappear: wave I.
• Most stable: wave V.
87. BINAURAL/MONOAURAL STIMULATION
• In clinical studies only a monoaural stimulation is recommended
i.e., one ear at a time should be tested.
• Presenting the sound stimulus to both ears together ( binaural )
marginally increases the amplitude of wave III, IV, V but not of
wave I.
88. FILTER CHARACTRISTICS
• Recording of fixed range of frequencies.
• Low fq filter: 100-150 Hz.
• High fq filter: 3000-5000 Hz.
(i.e., any electrical activity above 3000/5000 & below 100 is being
filtered out ).
• Above or below fq. will lead to contamination by other electrical
noise.
89. 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
At 60 dB supra-threshold stimulus, stimulus rate @ 10-20
Hz, & a rarefaction stimulus polarity is used for recording
the BERA in a patient b/w 2-60 yr age.
91. 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.
92. IDENTIFICATION OF NATURE OF DEAFNESS
• By Analysis of latency-intensity function can ascertain conductive
, sensory or neural deafness.
• Latency of wave V is recorded for different sound stimuli of
different intensities.
• Plotted graphically.
• Conductive loss: upward & parallel shift.
• Sensory loss: shallow configuration.
• Neural: steep sloping graph.
93.
94. IDENTIFICATION OF RETROCOCHLEAR
PATHOLOGIES
• Most reliably identified.
• Parameters:
– Increased inter-aural latency difference of wave V.
– Increase inter-aural inter-wave/inter-peak latency
between wave I to V.
– Increase Inter-wave latency between wave I & III/V.
95. 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.
96. 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).
98. STACKED BERA
• Improvement of BERA.
• Increases the sensitivity & specificity of BERA for small tumours.
• Aligning 5 waves of derived band BERA & adding the amplitudes.
• Reduced in presence of tumours.
• Useful in patients with U/L SNHL with normal BERA.
99.
100. 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 interval with normal latency of wave
V indicate cochlear involvement (delayed wave 1st).
101. 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 retro-cochlear pathologies.
• Study of central auditory disorders.
• Study of maturity of nervous system in newborns.
• Objective identification of brain death.
• Assessing prognosis in comatose patients.
103. HIGH FREQUENCY DEAFNESS
• In this, wave V as well as other wave-peaks will be delayed (as
now BERA is generated from apical turn) & amplitude will be
lower even if the deafness is due to a cochlear lesion & not a
neural lesion.
• Ideally, peak-latency should increase & peak amplitude should
decrease only if there is a neural & not a cochlear lesion.
• Hence, high freq. purely cochlear deafness may present BERA
features that mimic a neural lesion.
• So, audiogram should be taken into account.
104. LOW FREQUENCY DEAFNESS
• In this BERA response will be produced from the basal turn i.e.,
high freq. portion, so, when there is low frequency deafness
only, the latency & amplitude of the BERA peaks will be normal
& not delayed as basal turn produce strong effect.
• So, if low freq. deafness is due to a neural pathology like a small
acoustic neuroma, the BERA wave peak latency may not be
delayed & the amplitude may not be as low as is expected in a
neural lesion.
• Hence, acoustic neuroma <1cm size are missed by BERA.
105. INTRA-CANALICULAR ACOUSTIC
NEUROMA
• Decrease latency and increase amplitude is observed.
• As, it induces a cochlear damage by compromising the cochlear
blood supply , the latency of wave V decreases because of
‘cochlear filter broadening’.
106.
107.
108.
109. USES OF INTRAOPERATIVE AUDITORY
BRAINSTEM RESPONSE
1. Monitoring cochlear function directed at hearing preservation:
• Cerebellopontine angle tumor resection .
• 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.
112. • Auditory evoked potential test .
• Used to objectively determination of frequency specific
hearing threshold .
113. • Overcomes the limitations of BERA:
– Ideal of hearing threshold for higher frequencies (2000-4000
Hz),Lower frequency hearing losses are undetectable by the
BERA.
– Insensitive for hearing loss above 75-80 dB. Beyond 80 dB
deafness, the BERA response is usually unrecordable.
• Importance in providing hearing aid
( frequency specificity and idea of the exact degree of
hearing loss even at high intensities are very important indices
to program digital hearing aids).
114. Modulation of sound
• Modulation of pure tone sound:
– Amplitude domain (alternate off & on)
– Frequency domain (warbling of tone)
• Amplitude modulation of 100% is used
• Frequency modulation of 20% is used
115. Modulation of pure tone sound stimulus
Narrows down the spectral splatter
Very restricted narrow area of the basilar membrane is
stimulated
116. Rate of Modulation
• Used for eliciting the neural response
– <20 per sec(20HZ) : response from cortical areas
– 20-50 per sec: subcortical areas( mid-brain and thalamus)
– >60 per sec: brain stem
• Response from brainstem---not affected by mental state of
the subject.
• Response from cortical and sub-cortical areas ---affected by
mental state.
117. • Elicit response in sedated infants by increasing the
modulation
• Carrier frequency(CF) : test frequency.
• Modulation frequency: no. of times CF is modulated.
118. Method of recording
• Pure tone sounds (500/1000/2000/4000Hz)
• Modulation: 90 times/sec
• Evoked neural response is-------- pre-amplified, filtered, sampled
& analyzed after averaging.
119. • 90 Hz component of evoked response is measured
( Frequency component of the elicited response that is measured
is always same of the modulation frequency )
• Brain is actually hearing the sound or not ------------determined
from consistency of response.
• Better ASSR threshold are obtained -----Individual presentation of
different frequencies
• Time taken: 45 mins
120. • Threshold of hearing that determine by PTA -----behavioral
threshold
• Determination of threshold:
– Click evoked BERA: >10 dB of behavioral threshold
– Tone evoked BERA: >20-30 dB
121. MEASUREMENT OF RESPONSE
• Discrepancy is more in the lower than higher frequencies .
• It more marked in normal hearing adult & children
• In hearing impaired subjects---discrepancy is –
<20 dB ----in higher frequencies
>20dB ----in mid frequencies
Discrepancy decreases--- if deafness & CF increases .
122. • Better correlation b/w behavioral threshold and ASSR threshold in
high frequency SNHL than low frequency .
• If hearing loss in low frequencies ---difference b/w both threshold
---30-40dB .
• If marked high frequency deafness ---difference b/w both
threshold --- <5dB .
123. BERA vs ASSR
Similarities
• Deliver an auditory stimulus.
• Stimulate the auditory system.
• Record bioelectric responses from the auditory system via
electrodes.
• Patient does not have to respond volitionally(objective).
124. DIFFERENCE
BERA
• stimulus: click or a tone
burst presented at a slower
rate;
• is dependent on a relatively
subjective analysis of
amplitude versus latency.
• response is measured in
microvolts.
ASSR
• amplitude or frequency
modulated sounds
presented rapidly.
• is dependent on a statistical
analysis of the probability
of a response, usually at a
95% confidence level.
• is measured in nanovolts .
125. • Hearing in Noise Test (HINT)
• What is the HINT test?
• The Hearing in Noise Test (HINT) measures a person’s ability to
hear speech in quiet and in noise.
• During the test, the patient uses both ears together (binaural
hearing) to repeat sentences.
• Binaural hearing ability is essential for communication in noisy
settings and for other aspects of functional hearing, such as
sound localization and recognition of environmental sounds.
126. • In this test, the patient is required to repeat sentences both in
a quiet environment and with competing noise being presented
from different directions.
• This test is primarily used for three populations.
• The first group is those patients with normal hearing or a very
mild hearing loss who report persistent difficulty understanding
conversation in background noise.
•This test provides some objective measure of how much difficulty
an individual is having compared to persons that have normal
hearing in quiet and in noise
127. •. The second group is peace officers who have hearing
impairment.
• They are required to have the HINT test because even minor
degrees of hearing impairment can make it increasingly difficult
for an officer to effectively carry out his/her duties.
• The third group is our hearing aid users who wish to assess
how different types of hearing aids benefit them in noisy
situations.
128. What is involved in taking this test?
• The HINT battery consists of four test conditions.
• For each test, speech is located directly in front of the subject
at 0° azimuth, and all sound sources are one meter from the
center of the subject’s head.
• For each of the four conditions, the subject is required to listen
to a sentence and repeat it..
129. The four test conditions are:
(1) sentences with no competing noise.
(2) sentences with competing noise presented directly in front of
the patient.
(3) noise presented at 90° to the right of the patient.
(4) noise presented at 90° to the left of the patient.
In all conditions, the competing noise is presented at a steady
loudness of 65dB(A).
The loudness of the sentences presented is varied throughout the
test, depending on whether the patient repeats it correctly or
not.
130. How is the HINT test scored?
• The tester scores each sentence repeated as either correct or
incorrect.
• All words in the sentence must be repeated correctly.
• At the end of the test, a signal-to-noise ratio (SNR) is generated
for each test condition.
• A signal-to-noise ratio equals how loud the sentences needed to
be turned up above the noise floor so that the patient could repeat
them correctly 50% of the time.
131. • The higher the SNR, the more difficulty the patient has hearing
in noise.
• The HINT test is scored as a “pass” or “fail” in each condition
and the cut-off criteria are based on the scores from a group of
more than 50 subjects with normal hearing.
• These scores were provided bu House Ear Institute who
developed the HINT test.
•Other than determining your SNR, the HINT test is useful for
finding suitable solutions for hearing loss.
