2. Some important definitions
• It is a form of energy produced by a
vibrating object.
• A sound wave consists of compression &
rarefaction of molecules of the medium
(air, liquid or solid).
Sound
• It is the number of cycles per second (Hz)
• Pitch is a subjective sensation produce by
frequency of sound.
Frequency/Pitch
3. What hearing tests do
Hearing tests should answer 3 questions:
Is there a hearing loss?
If there is, how bad is it?
What kind of hearing loss does patient have?
Is it conductive?
Is it sensorineural?
Is it a mix of the two?
Is it bilateral or unilateral?
4. Conductive Hearing Loss
“Any disease process which interferes with the
conduction of sound from the outer ear to the cochlea”
Sensorineural Hearing Loss
It results from lesion of the cochlea (sensory type) or VIIIth
nerve & its central connections( neural type) .”
Mixed Hearing Loss
“A loss with both conductive and sensorineural component.”
6. Tuning Forks
• Tunning forks of 256,512,1024Hz are used because they fall
within speech frequency range.
• Fork of lower frequencies 128 produce sense of bone
vibration
• Fork of higher frequencies 2048 and 4096Hz have a shorter
decay time.
8. Rinne’s Test
First: Bone Conduction
Vibrating Tuning Fork held on Mastoid
process
Patient signals when sound ceases
Next: Air Conduction
Move the vibrating tuning fork over
the ear canal ,2cm from EAC, Parallel
to EAC.
Patient indicates when the sound
ceases
9. • Normal: Air Conduction is better than Bone Conduction
– Air conduction usually persists twice as long as bone
– Referred to as "positive test“
– NORMAL and SNHL
• Abnormal: Bone conduction better than air conduction
• Suggests Conductive Hearing Loss.
• Referred to as "negative test" .
• Indicate of minimum A-B gap of 15-20 db
10. False Negative Rinne :
It is seen in severe unilateral SNHL. Patient doesn’t preceive
any sound of tuning fork by AC but responds to BC testing.
This response to BC is, in reality, from the opposite ear
because of transcranial transmission of sound.
In such cases, correct diagnosis can be made by masking the
non- test ear with Barney’s noise box while testing for bone
conduction.
11. WeberTest
Tuning Fork placed at midline forehead /vertex
Normal: Sound radiates to both ears equally
Abnormal: Sound lateralizes to one ear
Conductive Hearing Loss – Lateralised to worse ear.
Sensorineural Hearing Loss- Lateralised to better ear.
12. Absolute Bone Conduction test
In ABC test, patient’s bone conduction is compared with that of
examiner ( presuming that the examiner has normal hearing)
External auditory meatus of both the patient & examiner should
be occluded( by pressing the tragus inwards), to prevent the
ambient noise entering through AC route
In sensorineural deafness, the patient hears a fork for shorter
duration
In conductive deafness, the patient and the examiner hear the
fork for the same duration of time
13. Schwabach Test
• It compares pt’s hearing sensitivity with that of an examiner (assuming
that he/she has a normal hearing)[but,meatus is not occluded]
1. Examiner places TF on patient’s mastoid
2. Patient asks examiner when he no longer hear tone.
3. Examiner places TF on his own mastoid.
Interpertation :
– If examiner hears longer, patient has a diminished schwabach which
is consistent with a sensorineural loss.
– If patient hears tone longer, patient has a prolonged schwabach
consistent with a conductive loss.
14. Bing Test
• A test for bone conduction.
• Examine the effect of occlusion of ear canal on hearing.
• Tuning fork is placed on the patient's mastoid, while the ear canal is
alternatively opened and closed by the examiner by depressing
tragus and the pt. is asked to state which position is louder
• When the ear canal is closed with normal hearing or SNHL, bone
conducted signals are heard more loudly (Occlusion Effect), a
"Positive Bing“
• Patient with CHL will not experience this sensation and the tone will
be the same when the ear canal is open and closed and the test will
be a "Negative Bing" because the ear already has a conductive
impairment
15. Gelle’s Test
It is also a test of bone conduction & examines the effect of increased
air pressure in ear canal on the hearing.
It is performed by placing a vibrating fork on the mastoid while
changes in air pressure in the ear canal are brought about by Siegle’s
speculum.
Normally, when air pressure is increased in the ear canal by Seigle’s
speculum, it pushes the TM & ossicles inwards, raises the intra
labyrinthine pressure & causes immobility of basilar membrane &
decreased hearing, but no change in hearing is observed when
ossicular chain is fixed or disconnected.
Positive in Normal persons & in SNHL.
Negative when ossicular chain is fixed or disconnected.
16. Test Normal Conductive Sensorineur
al
Rinne +
(AC > BC)
- +
Weber Not
Lateralised
Lateralize to
Poorer ear
Lateralize to
BETTER ear
ABC
Same as
examiner’s
Same as
examiner’s
Reduced
Bing + - +
Schwabach Equal Prolonged Diminished
Gelle’s + - +
17. Audiological test
• Indication for administering Audiological test to identify:
Cochlear Pathology
Retro Cochlear Pathology
Conductive Pathology
Functional Hearing Loss
17
24. • A single frequency sound.
Pure Tone
• Sound with more than one frequency.
• Human voice
Complex
Sound
• A complex sound has a fundamental
frequency i.e. the lowest frequency at
which a source vibrates. All frequencies
above that tone are called overtones
• It determines the quality/ timbre of sound
Overtones
25. Pure Tone Audiometry
-Audiometer is an electronic device which produces PURE TONES
,the intensity of which can be increased or decreased by 5dB steps
-Air conduction thresholds are measured from 125 to 8000 Hz
-Bone conduction thresholds from 250 to 4000 Hz
-This is charted on a graph called AUDIOGRAM
In 1879 Alexander Graham Bell Invented the audiometer
26. • The audiogram is a chart of hearing sensitivity with frequency
charted on the X- axis and intensity on the Y-axis.
Intensity is the level of sound power measured in decibels;
loudness is the perceptual correlate of intensity.
Audiogram
28. 1. Identify Best ear according to history
2. Start with AC on best ear
3. Start at 1000Hz at 60 dB or suprathreshold value and find
out if there is any response. Identify the hearing threshold.
4. Down by 10dB until no response
5. Then up by 5dB until reponse
6. Then again go down by 10 dB until response.
7. Up and down frequencies
8. Same for bone
9. It is to be done in a reasonably noiseless environment
Method
29. • The 1000-Hz re-test is done as a reliability check and is expected
to be within ±5 dB of the first 1000 Hz-threshold in that ear, and
the lower (better) of the two is considered the threshold.
• The semioctaves (750, 1500, 3000, and 6000 Hz) are tested
whenever there is a difference of ≥20 dB between two adjacent
frequencies (e.g., 3000 Hz is tested if the thresholds at 2000 and
4000 Hz differ by 20 dB or more).
30. Conceptual illustration of the “up-5 down-10” technique typically used in pure-tone
audiometry”conventional HUGHSON-WESTLAKE technique modified by CAHART and
JERGER”
31. --Degree of hearing loss is computed by using average of hearing
taken at 500 Hz, 1,000 Hz and 2,000 Hz.
--The average of these three frequencies is called the Pure Tone
Average and is the degree of hearing loss a person has expressed
in dB.
Pure Tone Average
32. • If B.C level <20 dB
• A-B gap is >=20 dB
• A.C threshold >30 Db
Conductive Hearing loss
33. • If B.C level >20 dB HL
• A-B gap is <=20 dB
• AC threshold >30 dB
• This type of hearing loss is secondary to cochlear abnormality
and/or abnormality of the auditory nerve or central auditory
pathways.
Sensorineural Hearing Loss (Deafness)
34. • If B.C level is >20 dB
• A. C. > 45 dB
• A-B gap >=20 dB
• This type of hearing loss has sensorineural and conductive
components.
Mixed Hearing loss (deafness)
35. BONE CONDUCTION TEST
• Bone conduction vibrator placed either over the mastoid bone or
over the forehead.
• Frontal placement is superior to the mastoid placement as
regards consistency of results, due to less variation of the amount
of tissue between the bone conduction vibrator & skull bone, &
lesser artifacts.
• As regards sensitivity, mastoid is more sensitive area & with the
usual bone conduction vibrators, thresholds on the mastoid are
about 10-15 dB better than those with the frontal placement.
36. Masking
“Presenting a constant noise to the non-test ear so that the non-
test ear is acoustically blocked and doesn’t participate in the
hearing test”
The purpose of masking is to prevent the non-test ear from
detecting the signal, so only the test ear can respond.
C/L masking should always be used during air condution tests for
A.C thershold difference b/w 2 ears >=45dB.
37. • For BC min. masking=B{t} + (Am – Bm)
• For AC min. masking= A{t} – 45+(Am - Bm)
• Maximum masking for both AC & BC =Bt + 45
• The aim is always to ensure that the intensity of masking
sound used is between overmasking & undermasking levels.
38. Sounds used for masking
• White noise: = broad band or wideband noise. It ideally contains
an equal amount of sound of all frequencies.
• Narrow band noise: this is more effective for masking & consists
of a narrow band of noise centered on the test tone frequency
with 100 to 200 Hz above & below that frequency. The band width
which will provide the maximum effective masking for a tone of a
particular frequency at minimum intensity is called as critical band
width for that particular frequency.
• Complex Noise
39. 1)Quantitative Information
• For U/L deafness the % of handicap for that ear is calculated by
the formula:
{[(a+b+c+d)/4] – 25}*1.5%
Where a,b,c,d are the air conduction hearing thresholds at 0.5,1,2 &
3 kHz respectively.
• Total hearing handicap for both ear:
[(5x+y)/6]%
Where x and y are percentage of handicap for better and worse ear
resp.
INTERPRATATION OF AUDIOGRAMS
41. The shaded areas show the range of speech sounds. This is called the "speech
banana"
This person can hear sounds even softer than the speech sounds.
But if he can't hear sounds in the area of the speech banana, he will have trouble
42. For Conductive lesions, it has
been found that pathologies
which increase stiffness ( like
otosclerosis) present a left
sloping audiogram (i.e., more
loss in the lower frequencies)
43. Pathologies which increase
mass (like secretory otitis
media) present a right
sloping audiogram ( more
loss in higher frequencies)
44.
45.
46.
47. A flat audiogram in
Sensorineural deafness
suggests an atrophy of stria
vascularis .
It is usually found in Strial
presbyacusis, salicylate
poisioning & other strial
lesions.
48. A stiffening of the basilar
membrane which impedes
normal vibration of the basilar
membrane usually presents a
descending audiogram.
A selective high frequency loss
with near normal hearing in a
low and middle frequencies is
usually produced by a lesion in
organ of corti.
The hair cells & the supporting
deiter’s cells are usually found
damaged in such cases (eg.,
sound trauma, ototoxic drugs
etc.)
49.
50. An ascending curve ( slopes to
left) is usually found in early
endolymphatic hydrops.
51.
52. • Damage to the sensorineural apparatus by certain diseases like
typhoid, meningitis, mumps etc. usually( but not always) present
characteristic patterns in the audiogram.
• In typhoid, usually a moderate to severe b/l SNHL is found.
• In meningitis the deafness is usually b/l & profound.
• In mumps, usually a u/l very severe or profound SNHL is
encountered.
53.
54. USES OF PURE TONE AUDIOGRAM
• To find Whether the subject has any definite hearing loss,
• Measure the threshold of hearing by air & bone conduction & thus
the degree & type (conductive, sensorineural,mixed) of hearing
loss.
• A record for future reference.
• Find degree of handicap for medicolegal purposes.
• For prescription of hearing aid.
• To predict speech reception threshold.
55. Limitations of pure tone audiometry
Audiograms are very often inaccurate (improper tech., test
condition, test instrument, examiner).
A subjective & Time- consuming test.
Doesn’t assess the main features of hearing e.g. frequency
discrimination, temporal resolution.
Doesn’t identify the site of pathology.
56. Speech audiometry
• SRT (speech reception threshold)
• Balanced two-syllable words (spondee words).e.g eardrum,
whitewash, toothbrush.
• Lowest hearing level in dB HL at which listener can repeat 50%
of words.
• Present groups of 6 spondee words first at a step 25 dB above
the pure tone threshold level & then at successively lower
intensities till a level is reached at which subject correctly
identifies 3 out of 6 spondee words presented.
57. • SRT is closely related to person’s pure tone hearing threshold
& the SRT is usually about 2 dB lesser than the pure tone
hearing thresholds at 500 & 1000 Hz.
• In neural lesions the SRT is much poorer than this pure tone
average( several decibels higher).
58. Speech audiometry (cont.)
• SDS (speech discrimination score)-it is the % of correctly
identified words when phonetically balanced one-syllable words
like as , can, age, your etc are presented to the subject.
• Intensity: SRT + 35 dB
• Percentage of words correctly repeated
• Normal: 90-100% but in neural lesions the SDS is considerably
low.
59. • Not a very reliable parameter to differentiate b/w cochlear &
neural types of sensorineural deafness.
• A better way of differentiating b/w above two is by graphically
plotting the performance- intensity function(PI-PB).
• Ascertain SDS at different intensity levels & plotting the % of
correctly identified words as a function of the intensity of
presentation of words correctly identified.
60.
61. • Roll over ratio=(Pbmax-Pbmin)/Pbmax
where Pbmax is the maximum score of correctly identified
words & Pbmin is the minimum score at maximum intensity.
• In cochlear lesions this rollover ratio is usually less than 0.40 &
in neural lesions it is more than 0.45.
• If speech audiometry is used for differentiation b/w the two
then rollover ratio or atleast the PI-PB curve should be used.
62. Bekesy Audiometry:
• Pt. controls level of intensity at various pure tone frequencies
• Continuous tone: tone on constantly (C)
• Interrupted(pulsed) tone: pulsed on and off (I)
• Adaptation should only occur for C, not I
63. Bekesy Results : Jerger classification
I: C and I overlap: normal or conductive
II: C below I at high freqs of HL: Cochlear
III: I follows loss, C drops to bottom: Retro- Cochlear
IV: C below I by 20-25 dB: Retrocochlear
V: I below C: False hearing loss
64. BEKESY AUDIOMETRY SUCCESS?
• Sensitivity = 42%
• Specificity = 95%
• It has now fallen out of favour of of most neurotologists as
other methods of ascertaining site of lesion are more
convenient & accurate.
65. TONE DECAY TEST
• For detection of the sensorineural hearing loss.
• Carried out on any pure tone audiometer & helps in diagnosing
neural lesions like acoustic neuroma quite accurately.
• A pathology in auditory nerve causes a rapid deterioration in
the threshold of hearing of a tone if that tone is presented
continuously
66. • Pathophysiology of tone decay: wedensky’s peripheral nerve
inhibition- if a short stretch of a nerve is partially narcotised &
then a series of impulses is presented to one end of the nerve &
electophysiological measurement is done at the other end , it
will be found that first few impulses will pass through the
narcotised section uninhibited, but the latter impulses will pass
successfully only if there is a sufficient time gap b/w the
repeated impulses.
67. Carhart’s method
STEPS:
1. Pure tone stimulus (4000Hz) presented 10 dB below
threshold & raised in 5 dB steps till the pt responds.
2. As pt responds, start the stop watch & tone is constantly
maintained.
3. Once pt fails to hear the tone, time in stop watch is noted. If
the tone is heard for 1 full minute terminate the test. If the
pt stops hearing before completion of 1 min then continue.
68. 4. Tone is raised by 5 dB without giving any time gap. Start stop
watch again repeat , the raising of intensity of tone by 5 dB is
continued till the pt can hear the sound for one full minute.
• Once tone has been raised by 30 dB above threshold & yet
the pt is unable to hear the tone for 1 full min, the test is not
continued .
69. • The result of this test is recorded as the difference in decibels
b/w the termination of the test(i.e the hearing level at which the
pt could hear the tone for 1 min) & the corresponding pure tone
threshold level for that particular frequency.
• If pt does not hear the tone for one full min even by increasing
sound level by 30 dB above hearing threshold, the result of tone
decay is recorded as strongly positive.
70. other methods for tone decay test:
• Green’s modified method
• Olsen Noffsinger method
• Rosenberg’s method
• Suprathreshold adaptation test- Jerger gave this test who
belived that abnormal tone decay first manifests not at
threshold level but with very high intensities of sound- much
above the threshold of hearing.
71. • Carhart’s method is little cumbersome & time consuming yet
is the more reliable method of predicting a retrocochlear
pathology.
72. RECRUITMENT
• Term coined by Fowler in 1937 & denotes an abnormally rapid
increase in loudness, noticed in certain types of SNHL.(a/w
cochlear pathology)
• As per a recent hypothesis recruitment is a normal phenomena
in high intensities of sound & that recruitment is present in all
ears when sounds of high intensity are used.
• Recruitment is not present in case of retrocochlear pathology
due to defective transmission in diseased auditory nerve.
73. • So presence of recruitment is not abnormal(in normal as well
as cochlear lesion)
• Absence of recruitment is abnormal & pathognomonic of a
retrocochlear lesion.
• Presence of recruitment in case of sensorineural deafness is
a/w a cochlear lesion.
74. Alternate Binaural Loudness Balance
(ABLB) test
• Uses specially designed audiometers which can alternately send
two tones of the same frequency in the two ears for same
duration.
1. Start with 500 or 1000 Hz at the air conduction hearing threshold .
2. Attenuator dial for worse ear is set at 20 dB SL & that for the
better ear at 0 dB SL.
3. Tone alternates b/w the two ears & the pt is asked to indicate in
which ear the sound appears louder.
75. If the tone in worse ear appears louder than that in better ear then
step 4 repeated. If opposite i.e louder in better ear then step 5 is
started.
4. Tone in better ear is raised by 5 dB.
5. Tone in better ear is lowered by 5 dB.
6. Pt is asked whether loudness is equal on both the ears. If equal
then this level of tone in the better ear is recorded as equal in
loudness to 20 dB SL in the worse ear.
76. • If not equal then step 4 or 5 are repeated accordingly. This
process is repeated till the loudness of the tone is equal in the
two ears .
• This process is repeated at steps of 10 dB increment for the
worse ear i.e at 30 dB SL, 40 dB SL….till the max of audiometer
of the audiometer is reached & the sound in the impaired ear
cannot be increased further.
77. • In this process deafer ear has been made the refernce ear &
the better ear has been made the variable ear because the
increase/decrease of sound intensity is done in the better ear
& the pt is asked to compare it with a fixed sound in the poor
ear.
• Plotting of results is done with poor ear data plotted from the
abscissa & the better ear results from the ordinate.
78. • Hearing level of the better ear & the hearing level of the
worse ear which are equal in loudness are connected by
straight lines.
• ABLB test is 100% sensitive in detecting complete recruitment
in cases of cochlear pathology.
79. Interpretation of test results
• Absence of recruitment
For equal loudness levels in the two ears the difference in the
hearing level will remain constant no matter what be the
intensity of the sound.
• Suggestive of retrocochlear pathology.
80. • Complete recruitment:
for equal loudness levels in the two
ears the difference in the hearing
level in between the better & worse
ear diminishes very rapidly with
increase in intensity & at a level this
difference becomes zero.
• Indicative of cochlear pathology.
81. • Partial recruitment:
difference in the hearing level
between the two ears for equal
loudness sensation, gradually
diminishes with increasing
intensities, but this difference
never becomes zero.
82. • Hyper-recruitment:
in some ears the loudness grows
so rapidly that a tone may be
louder in the worse ear than it is
in the better ear, at the same
hearing level.
83. • Derecruitment : when the growth in
loudness in the deafer ear is slower
than that in the better ear.
• For equal loudness between the two
ears the difference in the hearing level
between the better & the worse ear
will gradually increase with increase of
intensity.
• Derecruitment & absence of
recruitment in case of SNHL is
indicative of retrocochlear pathology.
84. SISI TEST
• Determines the capacity of a pt to detect a brief 1 dB increment
in a 20 dB suprathreshold tone( c/d the carrier tone)
• It usually tests for 1000 Hz & 4000 Hz only, but any frequency
above 250 Hz may be used.
• At interval of 5 sec a brief increase in the intensity of the carrier
tone occurs.
85. • The increase in the carrier tone takes 50 millisec to reach the
specified level, remains at that level for 200 millisec & then
returns to the 20 dB SL original carrier tone level in 50
millisec.
• 20 such 1 dB increments are presented to the ear & the pt is
asked to count how many of these 1 dB increments he could
correctly identify.
• Then multiplied by 5 gives the % SISI score.
86.
87. • Jerger categorisation is usually followed for differentiation
between cochlear & retrocochlear pathologies.
• SISI score from 70% to 100% indicate a cochlear lesion
especially if the test is done at frequencies of 1000 Hz &
above.
• If the test is done at 2000-4000 Hz scores of 80% to
100%(positive SISI) only are typical of cochlear lesions.
• Scores of 0% to 20 %(negative SISI) suggest a
retrocochlear pathology.
88. Limitation of SISI test:
• Requires active cooperation of the pt so not possible in some
difficult to test pts.
• Pts having severe deafness(>85 dB) cannot be tested as
most clinical audiometers have a max sound output of upto
100 dB.
• Very mild (<=35 dB) SNHL also may not show a high SISI
score even if the deafness is due to a cochlear leasion.
90. Compliance vs Impedance
• Compliance
Ease with which energy
flows through a system
• Impedance
Resistance to energy
flow through a system
91. Auditory Immittance
“The ease with which sound travels from one medium to
another, as from outer and middle ear into the cochlea”
92. Compliance
Pathologies with increased
compliance
• Ossicularchain
discontinuity
• Scarring of the tympanic
membrane
• Post-stapedectom year
• Very large tympanic
membrane(rare)
Pathologies with decreased
compliance
• Otoscelerosis
• Adhesive
orsecretoryotitismedia
• Tumors in the middle ear
likeglomusjugulare
• Ossicularfixations like
fixedmalleussyndrome
• Some cases
oftympanosclerosisor
thickening of the
tympanic membrane
Pathologies with normal
compliance
• ET obstruction only,
withoutsecretorychanges
in the middle ear.
• Some cases
ofotosclerosis.
93. Middle Ear Pressure
Negative middle ear
pressure
• Blocked Eustachian
tube.
• SecretoryOtitismedia.
Normal middle ear
pressure
• Stapedialotosclerosis.
• Ossicularchain
discontinuity.
• Scarring of TM.
• Fixation or adhesions
among theossicleslike
fixedmalleus.
Positive middle ear
pressure
• Early acuteotitsmedia.
94. Absence of any peak pressure
• Adhesiveotitismedia.
• Perforation of TM.
• Artifact(eg.
Blockedprobetip)
• Patentgrometin TM
• Externalearcanalcompletely
blocked bycerumen
95. Tympanometry
“The measurement of the change in impedance of the middle
ear at the plane of the tympanic membrane as a result of
changes in air pressure in the external auditory meatus”
In this way, the air pressure at which the ear functions most
effectively, i.e., transmit the highest amount of sound, can
also be determined. This particular pressure is the pressure of
the air inside the middle ear cavity & is referred to as the
Middle ear pressure.
96. • The middle ear acts as the impedence matching device
such that most of the sound energy coming from the air
is transmitted to the cochlear fluid.
• All ME pathologies alter this impedence matching
function & result in lesser sound energy being
transmitted to the cochlear fluid thus causing conductive
deafness.
97. • It is based on simple principle, i.e. when a sound strikes
tympanic membrane, some of the sound energy is absorbed
while the rest is reflected.
• A stiffer TM would reflect more of sound energy than a
compliant one.
• By changing the pressures in a sealed EAC & then measuring
the reflected sound energy, it is possible to find the compliance
or stiffness of the tympano-ossicular system & thus find the
healthy or diseased state of the middle ear.
98. • The pressure within the sealed cavity in the EAM can be
varied from +300 to -600 mm of water pressure.
• The purpose of varying the air pressure is to produce a
change in the stiffness of the TM, so that the amount of
sound energy that is being reflected back from the TM
can be measured in relation to the change of stiffness of
TM.
99. Instrumentation
• Major components
Probe tone oscillator and loudspeaker-
to deliver a tone of 220 hz
Monitor microphone- to pick up the
reflected sound through a microphone
Pressure pump and manometer- to bring
about changes in air pressure in the ear
canal from positive to normal & then
negative.
Ipsilateral reflex oscillator and loudspeaker
Probe tip
102. • Type As (Reduced compliance):
• otosclerosis,tympanosclerosis,
• malleus fixation
103. • Type C:maximum compliance
occurs with negative pressure
in excess of 100mm of H20
• auditory tube dysfunction
• Retracted TM
• Fluid in middle ear
104. • Type B (no compliance with
pressure change):
• TM perforation
• ME effusion (AOM)
• Patent grommet
• EAC block by cerumen
105. • Type Ad (Increased compliance):
• laxity of TM(Thinned TM)
• disruption of ossicular chain
106. Uses of Impedence AudiometryTest
• Objective test
• Differential diagnosis in case of conductive deafness
• Measurment of middle ear pressure and evaluation of
Eustachian tube function.
• To test the hearing in infant.
• Identification of the site of lesion in facial nerve
paralysis.
• Identifying Malingerers.
• Lesion of brainstem.
• To detect cochlear pathology.
• To detect VIIIth nerve lesion.
107. • Acoustic reflex:-
• It is based on the fact that a loud sound, 70-105 dB above the
threshold of hearing of a particular ear, causes bilateral
contraction of the stapedial muscles, which can be detected by
tympanometry.
• Tone can be delivered to one ear and the reflex picked from the
same or the contralateral ear.
108. • The reflex arc involved is:-
1. Ipsilateral : CN VIII → ventral cochlear nucleus → CN VII
nucleus → ipsilateral stapedius muscle.
2. Contralateral : CN VIII → ventral cochlear nucleus →
contralateral medial superior olivary nucleus → contralateral
CN VII nucleus → contralateral stapedius muscle.
109. The Middle Ear Muscles and the Acoustic
Reflex
• Tensor tympani muscle
• Stapedius muscle
110. • Loud sound reaches ear intra-aural muscles contract i.e
stapedius muscle pulls the stapes outward & upward, &
contraction of tensor tympani pulls the TM slightly inward
• Stiffens the ME conductive apparatus & changes the impedence
of the ME system.
111.
112. • The lowest sound intensity that is capable of eliciting a
contraction of the stapedius muscle is referred as the
acoustic reflex threshold.
• The normal range of acousic reflex threshold is between
70 dB SL to 105 dB SL( above the pure tone hearing
threshold).
113.
114. • Acoustic reflex present means no lesion in any of the
constituents of the reflex arc.
• Possible disorders on afferent side-
a) Disesase in I/L ME causing moderate to severe cinductive
deafness.
b) Lesion in I/L cochlea or 8th cranial nerve.
c) Lesion in cochlear nucleus or superior olivary complex.
115. • Possible disorders on the efferent side-
a) Lesion in facial nerve nucleus in braimstem
b) Facial nerve paralysis at a level proximal to the nerve to
stapedius like Ramsay Hunt Syndrome.
c) Disease of the stapedius muscle like myasthenia gravis
• # of stapedial crura is the only ME pathology which does not
abolish the reflex.
116. Interpretation of acoustic reflex
• Reflex is B/L.
• Ear having probe of the impedence audiometer is referred to as
the I/L ear & the ear having the audiometer headphone is
referred to as the C/L ear.
• If the acoustic reflex is present it is very unlikely that the ear has
any sort of ME disease except # of the stapedial crura.
117. • In cochlear lesions the acoustic reflexes will be present at
comparatively lesser sound intensity levels due to loudness
recruitment.
• In U/L moderate or severe conductive deafness the C/L as well as
I/L reflexes will be absent in the deaf ear as normal ME is a
prerequisite for the stapedial reflex to be present.
118. • In B/L conductive deafness, the acoustic reflexes will be absent
both on ipsi & contra stimulation bilaterally.
• In U/L severe SNHL the acostic reflex will be present in the deaf
ear only on C/L stimulation. I/L reflex in normal ear will
obviously be present. Thus presence of acoustic reflex in deaf
ear on C/L stimulation rules out the possibility of a conductive
or mixed deafness & indicates that the deafness is SNHL type.
119. • In B/L SNHL of severe degree the reflexes will be absent since
sufficient sound impulse will not reach the centre of the reflex arc.
• In case of B/L SNHL of moderate degree & cochlear in nature
then the reflex may be bilaterally present on both ipsi & C/L
stimulation. This is due to loudness recruitment.
• In central lesions i.e lesion in the brainstem, reflexes are present
on I/L stimulation only but absent on C/L stimulation.
120. Uses of Acoustic Reflex Test
1.To test the hearing in infants and young children:-It is an
objective method.
2. To find malingerers:- A person who feigns total deafness and
does not give any response on pure tone audiometry but shows a
positive stapedial reflex is a malingerer.
121. 3. Lesions of facial nerve :- Absence of stapedial reflex when
hearing is normal indicates lesion of the facial nerve, proximal
to the nerve to stapedius.
• The reflex can also be used to find prognosis of facial
paralysis as the appearance of reflex, after it was absent,
indicates return of function and a favourable prognosis.
4. Lesion of brain stem :-If ipsilateral reflex is present but the
contralateral reflex is absent, lesion is in the area of crossed
pathways in the brainstem.
122. 5. To detect cochlear pathology:- Presence of stapedial reflex at
lower intensities, e.g. 40 to 60 dB than the usual 70 dB indicates
recruitment and thus a cochlear type of hearing loss.
6. To detect VIIIth nerve lesion :- (stapedial reflex decay).
123. METZ RECRUITMENT TEST
• In presence of cochlear lesion the gap between the acoustic reflex
threshold & the pure tone audiometric hearing threshold
level(dynamic range) is considerably reduced.
• This is due to abnormally rapid growth of loudness that occurs in
loudness recruitment which is charactteristic of cochlear
pathology.
• Whenever this dynamic range is <60 dB then recruitment may
be suspected.
124. • Every decibel of cochlear hearing loss decreases the sensation
level of the reflex( i.e the acoustic reflex threshold) by the same
amt i.e by 1 dB thereby reducing the dynamic range.
• This continues till the dynamic range is approx 25 dB. If the
SNHL is so very severe that sufficient sound is not able to reach
the center of the reflex, then ,acoustic reflex will be absent &
Metz recruitment test will not be positive.
125. Acoustic Reflex Decay Test
• Calculated as the change in the intensity of the acousic
reflex during the first 10 sec of the contraction of the
stapedial muscle when a sustained sound stimulus is
presented to the ear.( done at 500 & 1000 Hz ).
• Sound stimulus is presented uninterruptedly at an intensity
of 10 dB above the acoustic reflex threshold for a particular
frequency for a duration of 10 sec.
126. • If the amplitude falls below 50% within 10 sec then it is
interpreted that there is abnormal decay of the acoustic
reflex which is indicative of neural or retrocochlear
pathology.
127. • If the acoustic reflex decay is above 50%,
• If the acoustic reflex threshold is higher than 85 dB above,
• If the acoustic reflexes are absent in an ear with no
conductive pathology but with moderate sensorineural
deafness,
• A BERA test for site of lesion should be essentially done
to rule out retrocochlear lesion.
