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Audiology
part i
Dr Humra
Shamim
Evolution of audiology
• Prior to World War II, hearing-care services were provided by
physicians and commercial hearing a...
Some of the earliest tests of hearing probably consisted merely
of producing sounds of some kind-
• such as clapping the h...
CLINICAL TESTS OF HEARING
1.FINGER FRICTION TEST
• It is a rough but quick method of screening and consists of rubbing
or ...
4.TUNING FORK TESTS
• The three tuning forks generally used
include : 256 Hz, 512 Hz, 1024 Hz.
• Most common being 512 Hz ...
PREREQUISITES FOR AN IDEAL TUNING FORK:
• It should be made of a good alloy
• It should vibrate at the specified frequency...
Advantages of tuning fork tests
1. Easy to perform
2. Can even be performed at bed side
3. Will give a rough estimate of t...
The following tests can be performed using a tuning fork:
1. Weber test
2. Rinne test
3. Absolute Bone Conduction test
4. ...
METHODOLOGY OF USING TUNING FORK
• The tuning fork must be struck against a firm surface (rubber pad / elbow
of the examin...
Bone conduction:
• Cochlea gets stimulated in 3 ways
when bone is stimulated
• The three normal routes of bone
conduction ...
• In the presence of a conductive
defect, the osseous route A is the
only route for sound vibrations to
reach the inner ea...
OUTER EAR COMPONENT OF BONE
CONDUCTION
• The outer ear bone conduction component arises from vibration of
the bony and esp...
MIDDLE EAR COMPONENT OF BONE
CONDUCTION
• The middle ear component of bone conduction is the inertial lag of the
ossicles ...
INNER EAR COMPONENT OF BONE
CONDUCTION
• Inner ear bone conduction has been described as resulting from alternate
compress...
• Transmission routes for air conduction, right ear example
(narrow arrows) and bone conduction, right mastoid
example (bo...
RINNES TEST
• In this test air conduction of the ear
is compared with its bone
conduction. A vibrating tuning fork is
plac...
• False Negative Rinne It is seen in severe unilateral sensorineural hearing
loss. Patient does not perceive any sound of ...
• A prediction of air-bone gap can be made if tuning forks of 256, 512 and
1024 Hz are used.
 Rinne test equal or negativ...
Rinnes Test
• Pts. with normal hearing and SNHL will hear the tone louder at the ear
(Because AC is a more efficient means...
• The 256-Hz Rinne tuning fork test
will detect a conductive deafness
above 30 dB in 90 %of patients.
Between 20 and 30 dB...
Weber test
• In this test, bone conduction of
both the ars are compared with
one another
• A vibrating tuning fork is plac...
• It is a very sensitive test and even a 5db difference in two ears is indicated
by this test
• The Weber tuning fork test...
• Normally, it is heard equally in both ears. It is lateralized to the worse ear
in conductive deafness and to the better ...
Absolute bone conduction (ABC) test.
• Bone conduction is a measure of cochlear function.
• In ABC test, patient’s bone co...
Schwabach’s test
• Here bone conduction of patient is compared with that of the normal
hearing person (examiner) but meatu...
Bing test
• It is a test of bone conduction and examines the effect of occlusion of ear
canal on the hearing. A vibrating ...
Gelle’s test
• It is also a test of bone conduction and examines the effect of increased
air pressure in ear canal on the ...
Tuning fork tests &their interpretation
Test Normal Conductive
deafness
Sensorineural
deafness
Rinne AC>BC(RINNE
POSITIVE)...
STENGER’S TEST
• This test is performed to identify feigned hearing loss and malingering.
• This test is based on the audi...
CHIMANI-MOOS TEST
• This is actually a modification of Weber test. When the vibrating fork is
placed on the vertex, the pa...
PURE TONE AUDIOMETRY:Definition
• MEASURING RELATIVE HEARING THRESHOLD USING PURE TONES IS
CALLED PURE TONE AUDIOMETRY.
• ...
• Sound is generated when an object vibrates in elastic medium.
• No of sound waves set up in air by vibrating object in o...
WHY PURETONE THRESHOLDS?
• The auditory system is organized tonotopically(i.e., a frequency-to-
place mapping) from the co...
CALIBERATION
• The human ear does not perceive
sound equally well at all frequencies.
The ear is most sensitive to sound i...
• The audiometer is calibrated to correct for these differences in threshold
sensitivity at various frequencies
• Conseque...
Aims
• To find out any hearing loss or not.
• Degree of hearing dysfunction.
• Conductive or SNHL.
• If SNHL then cochlear...
COMPONENTS OF A PURETONE AUDIOMETER
• Oscillator : The role of the oscillator in a Puretone audiometer is to generate
elec...
The basic design of a pure tone audiometer
Typical face of a pure-tone audiometer
• A) On-off power switch. (B) Output
selector switch. Selects right ear, left ear,
...
• Proper positioning
during pure-tone
audiometry carried out
with a single sound-
treated room for (A)
examiner, (B)
audio...
TECHNIQUE OF MEASUREMENT
• Some audiologists assess the threshold of air conduction by going from an
inaudible to an audib...
Symbols used in audiometry
• Blue line for left ear
• Red line for right ear
• Continuous line for air conduction
• Broken...
Instructions to the patient:
• The patient is instructed to raise the index finger if the sound
is heard. The patient shou...
Technique of recording air conduction threshold
• Most commonly used is Conventional Hughson & Westlake
technique (modifie...
HUGHSON & WESTLAKE TECHNIQUE
• Complete history and examination
• Better ear tested first.
• 1000 Hz 2000 4000 8000 10,000...
EXAMPLES OF DIAGNOSES
Normal-hearing Sensitivity
• Owing to calibration, air
conduction thresholds will be
near 0 dB HL,bo...
• CHL with Air–Bone Gaps
• Sensorineural hearing loss. The
audiogram show no A-B gap.
• MHL with Air–Bone Gaps of Outer
or Middle Ear Origin
• Noise induced hearing loss.
• The audiogram in NIHL shows a
typical notch, at 4 kHz, both for
air and bone conduction (F...
• Ménière’s disease.
• Hearing loss is sensorineural and
more in lower frequencies—the
rising curve. As the disease
progre...
• Otosclerosis
• Pure tone audiometry shows loss
of air conduction, more for lower
frequencies.
• Bone conduction is norma...
Uses of Pure Tone Audiogram
• It is a measure of threshold of hearing by air and bone conduction and
thus the degree and t...
MASKING
• A major objective of the basic audiologic evaluation is assessment of
auditory function of each ear.
• Although ...
• Whenever it is suspected that the nontest ear is responsive during
evaluation of the test ear, a masking stimulus must b...
• Cross hearing occurs when a stimulus presented to the test ear “crosses
over” and is perceived in the nontest ear. There...
• IA refers to the “reduction of energy between ears.” Generally, it
represents the amount of separation or the degree of ...
• Interaural attenuation (IA) is
calculated as the difference
between the hearing level (HL) of
the signal at the test ear...
• Expected unmasked puretone air-
and bone-conduction thresholds
in an individual with normal
hearing in the left ear and ...
IMPEDANCE AUDIOMETRY
It is an objective test, widely used in clinical practice and is particularly useful
in children. It ...
• The equipment consists of a probe which snugly fits into the external
auditory canal and has three channels:
• (i) to de...
• Type A: Normal tympanogram.
1. Type As: Compliance is lower at or near ambient air pressure. Seen in
fixation of ossicle...
• (B)Acoustic reflex. It is based on the fact that a loud sound, 70–100 dB
above the threshold of hearing of a particular ...
CLINICAL USES
To test the hearing in infants and young children.
To find malingerers. A person who feigns total deafness a...
REFERENCES
• HANDBOOK OF CLINICAL AUDIOLOGY, 7th edition, JACK KATZ.
• Cummings Otolaryngology HEAD AND NECK SURGERY
• Cli...
•Thank
you
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Audiometry

  1. 1. Audiology part i Dr Humra Shamim
  2. 2. Evolution of audiology • Prior to World War II, hearing-care services were provided by physicians and commercial hearing aid dealers. • Because the use of hearing protection was not common until the latter part of the war, many service personnel suffered the effects of high-level noise exposure from modern weaponry. • It was the influx of these service personnel reentering civilian life that created the impetus for the professions of otology (the medical specialty concerned with diseases of the ear) and speech pathology (now referred to as speech-language pathology) to work together to form aural rehabilitation centers.
  3. 3. Some of the earliest tests of hearing probably consisted merely of producing sounds of some kind- • such as clapping the hands or • making vocal sounds • the ticking of a watch • the clicking of two coins These tests provided little information of either quantitative or a qualitative nature.
  4. 4. CLINICAL TESTS OF HEARING 1.FINGER FRICTION TEST • It is a rough but quick method of screening and consists of rubbing or snapping the thumb and a finger close to patient’s ear 2. WATCH TEST • A clicking watch is brought close to the ear and the distance at which it is heard is measured. 3.SPEECH (VOICE) TESTS • The patient stands with his test ear towards the examiner at a distance of 6 m. Eyes are shielded to prevent lip reading and the non test ear is blocked by intermittent pressure on the tragus by an assistant. The examiner uses spondee words walks towards the patient. The distance at which conversational voice and the whispered voice are heard is measured. • Disadvantage :lack of standardization in intensity and pitch of voice used for testing and the ambient noise of the testing place.
  5. 5. 4.TUNING FORK TESTS • The three tuning forks generally used include : 256 Hz, 512 Hz, 1024 Hz. • Most common being 512 Hz because –  It is present in the mid speech frequency range  Overtones are minimal  Sound is more auditory than tactile in nature  Tone decay is optimal.
  6. 6. PREREQUISITES FOR AN IDEAL TUNING FORK: • It should be made of a good alloy • It should vibrate at the specified frequency • It should be capable of maintaining the vibration for one full minute • It should not produce any overtones
  7. 7. Advantages of tuning fork tests 1. Easy to perform 2. Can even be performed at bed side 3. Will give a rough estimate of the patient’s hearing acuity
  8. 8. The following tests can be performed using a tuning fork: 1. Weber test 2. Rinne test 3. Absolute Bone Conduction test 4. Schwabachs test 5. Bing test 6. Stenger’s test 7. Gelle test 8. Chimani-Moos test
  9. 9. METHODOLOGY OF USING TUNING FORK • The tuning fork must be struck against a firm surface (rubber pad / elbow of the examiner). The fork should be struck at the junction of upper 1/3 and lower 2/3 of the fork. It is this area of the fork which is capable of maximum vibration. • Vibrating fork should be held parallel to the acoustic axis of the ear being tested.
  10. 10. Bone conduction: • Cochlea gets stimulated in 3 ways when bone is stimulated • The three normal routes of bone conduction of sound vibrations to the inner ear:  route A: via the skull bone;  route B: via the ossicular chain;  route C: via the external auditory canal. • In a normal ear, when the skull is vibrated by bone-conduction, it not only vibrates the cochlea via route A, but it also vibrates the tympanic membrane and ossicular chain (route B) and the air in the external auditory canal (route C).
  11. 11. • In the presence of a conductive defect, the osseous route A is the only route for sound vibrations to reach the inner ear. When there is a middle ear conductive defect, routes B and C are materially diminished in magnitude
  12. 12. OUTER EAR COMPONENT OF BONE CONDUCTION • The outer ear bone conduction component arises from vibration of the bony and especially the cartilaginous walls of the outer ear canal that, in turn, causes sound waves to radiate into the outer ear canal .These sound waves propagate through the middle ear and finally to the inner ear. • The outer ear component may play little role in the normal unoccluded ear canal, but its role is magnified by the occlusion effect .Normally the outer ear canal acts as a high-pass filter that is, high-frequency energy is passed into the middle ear whereas low- frequency energy escapes through the ear canal opening. Outer ear canal occlusion traps this low-frequency energy and thereby enhances bone conduction hearing up to 20 dB in the lower audiometric test frequencies.
  13. 13. MIDDLE EAR COMPONENT OF BONE CONDUCTION • The middle ear component of bone conduction is the inertial lag of the ossicles . Middle ear ossicles are not directly attached to the skull, but are instead suspended by ligaments and tendons and attached at either end to the elastic tympanic and oval window membranes. The ossicles are free to move out of phase with skull vibrations and will do so because of inertia, much as coffee would lag and spill from a cup moved precipitously. • Middle ear ossicles vibrate relative to the skull in a like manner as during air conduction hearing, and thus energy is propagated into the inner ear. The middle ear component occurs mainly at and above 1,500 Hz and is especially significant near 2,000 Hz, the approximate resonant frequency of the middle ear
  14. 14. INNER EAR COMPONENT OF BONE CONDUCTION • Inner ear bone conduction has been described as resulting from alternate compressions and expansions or distortions of the bony cochlear capsule. In turn, cochlear fluids are displaced and basilar membrane-traveling waves are initiated. • One factor making cochlear fluid displacement possible is the out-of- phase and disproportionate yielding of the round and oval cochlear windows, which creates alternating spaces for fluid displacement. Cochlear fluid movement, in turn, displaces the basilar membrane and initiates traveling waves.
  15. 15. • Transmission routes for air conduction, right ear example (narrow arrows) and bone conduction, right mastoid example (bold arrows). Note: Higher intensity air-conducted signals can activatethe bone conduction transmission route.
  16. 16. RINNES TEST • In this test air conduction of the ear is compared with its bone conduction. A vibrating tuning fork is placed on the patient’s mastoid and when he stops hearing it is brought beside the meatus. If he still hears, AC is more than BC. • Alternatively, the patient is asked to compare the loudness of sound heard through air and bone conduction. • Rinne test is called positive when AC is longer or louder than BC. It is seen in normal persons or those having sensorineural deafness. • A negative Rinne (BC > AC) is seen in conductive deafness. A negative Rinne indicates a minimum air-bone gap of 15–20 dB.
  17. 17. • False Negative Rinne It is seen in severe unilateral sensorineural hearing loss. Patient does not perceive any sound of tuning fork by air conduction but responds to bone conduction testing. • This response to bone conduction 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 Barany's noise box while testing for bone conduction.
  18. 18. • A prediction of air-bone gap can be made if tuning forks of 256, 512 and 1024 Hz are used.  Rinne test equal or negative for 256 Hz but positive for 512 Hz indicates air-bone gap of 20-30 dB.  Rinne test negative for 256 and 512 Hz but positive for 1024 Hz indicates air-bone gap of 30-45 dB.  Rinne negative for all three tuning forks, indicates air-bone gap of 45-60 dB . Remember that a negative Rinne for 256, 512 and 1024 hz indicates a minimum AB gap of 15, 30, 45 dB respectively
  19. 19. Rinnes Test • Pts. with normal hearing and SNHL will hear the tone louder at the ear (Because AC is a more efficient means of sound transmission to the IE than BC) than behind the ear (Positive Rinne) • Pts. with CHL (more than mild) or MHL will hear the tone louder with the stem of the fork behind the ear because their BC hearing is better than their AC hearing (Negative Rinne)
  20. 20. • The 256-Hz Rinne tuning fork test will detect a conductive deafness above 30 dB in 90 %of patients. Between 20 and 30 dB, the sensitivity will fall to 70 % and between 10 and 20 dB will be less than 50% • The specificity of the test is high above 30 db conductive deafness, but falls as the air–bone gap narrows.
  21. 21. Weber test • In this test, bone conduction of both the ars are compared with one another • A vibrating tuning fork is placed in the middle of the forehead or the vertex or chin or upper incisor teeth and the patient is asked in which ear the sound is heard. • Normally, it is heard equally in both ears.
  22. 22. • It is a very sensitive test and even a 5db difference in two ears is indicated by this test • The Weber tuning fork test is only applicable if a patient has asymmetrical hearing as might be assesed by a preformed clinical test • In conductive deafness the sound is lateralised to poor ear because ambient noise does not disturb the diseased ear as much as the normal ear
  23. 23. • Normally, it is heard equally in both ears. It is lateralized to the worse ear in conductive deafness and to the better ear in sensorineural deafness. • In weber test, sound travels directly to the cochlea via bone. • Lateralization of sound in weber test with a tuning fork of 512 Hz implies a conductive loss of 15–25 dB in ipsilateral ear or a sensorineural loss in the contralateral ear.
  24. 24. Absolute bone conduction (ABC) test. • Bone conduction is a measure of cochlear function. • In ABC test, patient’s bone conduction is compared with that of the examiner (presuming that the examiner has normal hearing). • External auditory meatus of both the patient and examiner should be occluded (by pressing the tragus inwards)to prevent ambient noise entering through AC route. In conductive deafness, the patient and the examiner hear the fork for the same duration of time. In sensorineural deafness, the patient hears the fork for a shorter duration.
  25. 25. Schwabach’s test • Here bone conduction of patient is compared with that of the normal hearing person (examiner) but meatus is not occluded. It has the same significance as absolute bone conduction test. • Schwabach is reduced in sensorineural deafness and lengthened in conductive deafness
  26. 26. Bing test • It is a test of bone conduction and examines the effect of occlusion of ear canal on the hearing. A vibrating tuning fork is placed on the mastoid while the examiner alternately closes and opens the ear canal by pressing on the tragus inwards. • A normal person or one with sensorineural hearing loss hears louder when ear canal is occluded and softer when the canal is open (Bing positive). A patient with conductive hearing loss will appreciate no change (Bing negative).
  27. 27. Gelle’s test • It is also a test of bone conduction and examines the effect of increased air pressure in ear canal on the hearing. Normally, when air pressure is increased in the ear canal by Siegel’s speculum, it pushes the tympanic membrane and ossicles inwards, raises the intralabyrinthine pressure and causes immobility of basilar membrane and decreased hearing, but no change in hearing is observed when ossicular chain is fixed or disconnected. • Gelle’s test is performed by placing a vibrating fork on the mastoid while changes in air pressure in the ear canal are brought about by Siegel’s speculum. • Gelle’s test is positive in normal persons and in those with sensorineural hearing loss. It is negative when ossicular chain is fixed or disconnected. It was a popular test to find out stapes fixation in otosclerosis but has now been superceded by tympanometry
  28. 28. Tuning fork tests &their interpretation Test Normal Conductive deafness Sensorineural deafness Rinne AC>BC(RINNE POSITIVE) BC>AC AC>BC Weber Not lateralized Lateralized to poorer ear Lateralized to better ear ABC Same as examiner’s Same as examiner’s Reduced Schwabach Equal Lengthened Shortened
  29. 29. STENGER’S TEST • This test is performed to identify feigned hearing loss and malingering. • This test is based on the auditory phenomenon known as “Stenger’s principle”. This principle states that when two similar sounds are presented to both ears only the louder of the two would be heard. Patients usually are not aware of this phenomenon. • When two similar tuning forks of same frequencies are made to vibrate and held simultaneously in the acoustic axis of both ears only the louder fork will be heard. Loudness of vibrating fork can be adjusted by adjusting the distance of the fork from the external canal. Usually the vibrating fork is held closer to the allegedly deaf ear of the patient. The patient will not acknowledge hearing in that ear. According to Stenger’s principle he should be able to hear the louder fork. If the hearing loss in worse ear is genuine, patient will respond to the signal presented to the better ear. This is known as negative Stenger’s test. Feigning patient will not acknowledge hearing when louder sound is presented to the worse ear. This is known as positive Stenger’s test
  30. 30. CHIMANI-MOOS TEST • This is actually a modification of Weber test. When the vibrating fork is placed on the vertex, the patient indicates that he hears it in the good ear and not in the deaf ear. The meatus of the good ear is then occluded. • A genuine deaf patient will still be able to lateralize the sound to the good ear, where as a malingerer will deny hearing the sound at all.
  31. 31. PURE TONE AUDIOMETRY:Definition • MEASURING RELATIVE HEARING THRESHOLD USING PURE TONES IS CALLED PURE TONE AUDIOMETRY. • Hearing threshold is typically defined as the lowest (softest) sound level needed for a person to detect a signal approximately 50% of the time • The instrument used in the measurement of auditory threshold is known as the audiometer. • Patients hearing threshold is measured in comparison to ideal fixed normal hearing level (0 dB) and thus is relative hearing threshold measurement. • PTA requires a subjective response from subject.
  32. 32. • Sound is generated when an object vibrates in elastic medium. • No of sound waves set up in air by vibrating object in one second is known as frequency measured in Hz. • Object vibrating in single fixed frequency is called Sine wave. • Sound sensation produced by this sine wave is called Pure tone.
  33. 33. WHY PURETONE THRESHOLDS? • The auditory system is organized tonotopically(i.e., a frequency-to- place mapping) from the cochlea to the cortex. The tonotopic organization of the cochlea is a result of the frequency tuning of the basilar membrane with high frequencies represented at the basal end and low frequencies at the apical end. Damage to sensory cells of the cochlea at a specific place along the basilar membrane can result in a loss of hearing that corresponds to the frequencies coded by that place. • For this reason, Pure tone threshold tests provide details that would otherwise remain unknown if a broadband stimulus such as speech were used.
  34. 34. CALIBERATION • The human ear does not perceive sound equally well at all frequencies. The ear is most sensitive to sound in the intermediate region from 1000 to 4000 Hz and is less sensitive at both the higher and lower frequencies. In normal ears more sound pressure is needed to elicit a threshold response at 250 Hz than at 2000 Hz. • Hearing sensitivity is defined as the threshold of audibility of pure-tone signals, graphed in sound pressure level (SPL) across a frequency range that encompasses most of human hearing. This curve representing hearing sensitivity is often referred to as the minimum audibility curve.
  35. 35. • The audiometer is calibrated to correct for these differences in threshold sensitivity at various frequencies • Consequently, when the hearing level dial is set at zero for a given frequency, the signal is automatically presented at the normal threshold sound pressure level required for the average young adult to hear that particular frequency
  36. 36. Aims • To find out any hearing loss or not. • Degree of hearing dysfunction. • Conductive or SNHL. • If SNHL then cochlear or retrocochlear. • To decide on the appropriate rehabilitation device which can be used to minimise the hearing disability.
  37. 37. COMPONENTS OF A PURETONE AUDIOMETER • Oscillator : The role of the oscillator in a Puretone audiometer is to generate electronically standardized frequencies within +/- 3% of their nominal value. The frequencies generated are 125,250, 500,750, 1000, 1500, 2000, 3000, 4000, 6000 and 8000 Hz. • Interrupter switch : The tones presented to the patient should be switched on and off. This feature is important because a continuous tone undergoes decay during a period of time. • Equalisation circuit : because the threshold of human hearing is not uniform • Output power amplifier • Hearing level attenuator: The attenuator can be varied in steps of 5 dB. The basic reference point is marked as 'O'. This indicates -5 to -10 dB hearing threshold levels. • Outpur transducers: Is of three different types. 1. Ear phones 2. Bone vibrator 3. Loud speaker (free field audiometry(pediatric patients)
  38. 38. The basic design of a pure tone audiometer
  39. 39. Typical face of a pure-tone audiometer • A) On-off power switch. (B) Output selector switch. Selects right ear, left ear, or bone conduction. Masking delivered to nontest earphone for air conduction and to left earphone for bone conduction. (C) Frequency selector dial. Air conduction and ,Bone conduction(D) Hearing-level dial. Air-conduction range: –10 to 110 dB HL (500 to 6000 Hz), –10 to 90 dB HL (250 and 8000 Hz), and –10 to 80 dB HL(125 Hz). Bone-conduction range: –10 to 50 dB HL (250 Hz), –10 to 70 dB HL (500 Hz), and –10 to 80 dB HL (750 to 4000 Hz). (E) Tone-presentation bar. Introduces tone with prescribed rise and fall time and no audibles ound from the switch. (F) Masking-level dial. Controls intensity of masking noise in the nontest ear
  40. 40. • Proper positioning during pure-tone audiometry carried out with a single sound- treated room for (A) examiner, (B) audiometer, and (C) patient
  41. 41. TECHNIQUE OF MEASUREMENT • Some audiologists assess the threshold of air conduction by going from an inaudible to an audible stimulus intensity. This method is known as ascending method of estimation of threshold of hearing, while others assess the threshold of air condution by going from an audible to an inaudible stimulus intensity. This is known as descending method of threshold estimation.
  42. 42. Symbols used in audiometry • Blue line for left ear • Red line for right ear • Continuous line for air conduction • Broken line for bone conduction
  43. 43. Instructions to the patient: • The patient is instructed to raise the index finger if the sound is heard. The patient should respond even if the sound is faintly heard. • Improper placement of head phones will cause threshold variations of even 15 – 20 dB. • Before placing the ear phones on the patient, the patient's ear should be examined for the presence of wax.
  44. 44. Technique of recording air conduction threshold • Most commonly used is Conventional Hughson & Westlake technique (modified by carhart and jerger).
  45. 45. HUGHSON & WESTLAKE TECHNIQUE • Complete history and examination • Better ear tested first. • 1000 Hz 2000 4000 8000 10,000 1000 500 250 Hz • If difference between these octaves is >20dB then half octaves i.e. 750, 3000, 6000 Hz tested. • Start with arbitrary supra threshold level. (Descending method) • "Up 5-down 10" method of threshold estimation: • The starting intensity of the test tone is reduced in 10 dB steps following each positive response, until a hearing threshold level is reached at which the subject fails to respond. Then, the tone is raised by 5 dB, if the subject hears this increment, the tone is reduced by 10 dB; if the tone is not heard then it is raised by another 5 dB increment. This 5 dB increment is always used if the preceding tone is not heard, and a 10 dB decrement is always used when the sound is heard.
  46. 46. EXAMPLES OF DIAGNOSES Normal-hearing Sensitivity • Owing to calibration, air conduction thresholds will be near 0 dB HL,bone conduction thresholds will be near 0 dB HL and be similar to air conduction thresholds (+_10DB).
  47. 47. • CHL with Air–Bone Gaps
  48. 48. • Sensorineural hearing loss. The audiogram show no A-B gap.
  49. 49. • MHL with Air–Bone Gaps of Outer or Middle Ear Origin
  50. 50. • Noise induced hearing loss. • The audiogram in NIHL shows a typical notch, at 4 kHz, both for air and bone conduction (Figure ). It is usually symmetrical on bothsides.
  51. 51. • Ménière’s disease. • Hearing loss is sensorineural and more in lower frequencies—the rising curve. As the disease progresses, middle and higher frequencies get involved and audiogram becomes flat or falling type (B & C)
  52. 52. • Otosclerosis • Pure tone audiometry shows loss of air conduction, more for lower frequencies. • Bone conduction is normal. In some cases, there is a dip in bone conduction curve. • It is different at different frequencies but maximum at 2000 Hz and is called Carhart’s notch (5 dB at 500 Hz, 10 dB at 1000 Hz, 15 dB at 2000 Hz and 5 dB at 4000 Hz) (Figure ). Carhart’s notch disappears after successful stapedectomy
  53. 53. Uses of Pure Tone Audiogram • It is a measure of threshold of hearing by air and bone conduction and thus the degree and type of hearing loss. • A record can be kept for future reference. • Audiogram is essential for prescription of hearing aid. • Helps to find degree of handicap for medicolegal purposes. • Helps to predict speech reception threshold.
  54. 54. MASKING • A major objective of the basic audiologic evaluation is assessment of auditory function of each ear. • Although a puretone or speech stimulus is being presented through a transducer to the test ear, the nontest ear can contribute partially or totally to the observed response.
  55. 55. • Whenever it is suspected that the nontest ear is responsive during evaluation of the test ear, a masking stimulus must be applied to the nontest ear to eliminate its participation
  56. 56. • Cross hearing occurs when a stimulus presented to the test ear “crosses over” and is perceived in the nontest ear. There are two parallel pathways by which sound presented through an earphone (i.e., an air-conduction transducer) can reach the nontest ear. Specifically, there are both bone- conduction and air-conduction pathways between an air-conduction signal presented at the test ear and the sound reaching the nontest ear cochlea. • Cross hearing is the result of limited interaural attenuation(IA).
  57. 57. • IA refers to the “reduction of energy between ears.” Generally, it represents the amount of separation or the degree of isolation between ears during testing. Specifically, it is the decibel difference between the hearing level (HL) of the signal at the test ear and the HL reaching the nontest ear: IA = dBHLTestEar – dBHLNontestEar
  58. 58. • Interaural attenuation (IA) is calculated as the difference between the hearing level (HL) of the signal at the test ear and the HL reaching the nontest ear cochlea. A puretone signal of 90 dB HL is being presented to the test ear through traditional supra- aural earphones. • Example A: If IA is 40 dB, then 50 dB HL is reaching the nontest ear cochlea. • Example B: If IA is 80 dB, then 10 dB HL is reaching the nontest ear cochlea
  59. 59. • Expected unmasked puretone air- and bone-conduction thresholds in an individual with normal hearing in the left ear and a profound sensory/neural hearing loss in the right ear. Without the use of appropriate contralateral masking, a shadow curve will result in the right ear. • Unmasked air-conduction thresholds in the right ear will shadow the bone-conduction thresholds in the better (i.e., left) ear by the amount of interaural attenuation.
  60. 60. IMPEDANCE AUDIOMETRY It is an objective test, widely used in clinical practice and is particularly useful in children. It consists of: • (a) Tympanometry • (b) Acoustic reflex measurements (a) Tympanometry. It is based on a simple principle, i.e.when a sound strikes tympanic membrane, some of the sound energy is absorbed while the rest is reflected. A stiffer tympanic membrane would reflect more of sound energy than a compliant one. By changing the pressures in a sealed external auditory canal and then measuring the reflected sound energy, it is possible to find the compliance or stiffness of the tympano-ossicular system and thus find the healthy or diseased status of the middle ear.
  61. 61. • The equipment consists of a probe which snugly fits into the external auditory canal and has three channels: • (i) to deliver a tone of 220 Hz, • (ii) to pick up the reflected sound through a microphone and • (iii) to bring about changes in air pressure in the ear canal from positive to normal and then negative . By charting the compliance of tympano-ossicular system against various pressure changes, different types of graphs called tympanograms are obtained which are diagnostic of certain middle ear pathologies.
  62. 62. • Type A: Normal tympanogram. 1. Type As: Compliance is lower at or near ambient air pressure. Seen in fixation of ossicles, e.g. otosclerosis or malleus fixation. 2. Type Ad: High compliance at or near ambient pressure. Seen in ossicular discontinuity or thin and lax tympanic membrane. • Type B :A flat or dome-shaped graph. No change in compliance with pressure changes. Otitis media with effusion, space-occupying lesions of the tympanic cavity, and tympanic membrane perforations • Type C: Maximum compliance occurs with negative pressure in excess of 100 mm H2O. Seen in retracted tympanic membrane and may show some fluid in middle ear. • Type D curve: which shows a notch in the pressure peak, is often seen with scarred eardrums or with normal, hypermobile eardrums.
  63. 63. • (B)Acoustic reflex. It is based on the fact that a loud sound, 70–100 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.
  64. 64. CLINICAL USES To test the hearing in infants and young children. 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. To detect cochlear pathology. Presence of stapedial reflex at lower intensities, e.g. 40– 60 dB than the usual 70 dB indicates recruitment and thus a cochlear type of hearing loss To detect VIIIth nerve lesion. If a sustained tone of 500 or 1000 Hz, delivered 10 dB above acoustic reflex threshold, for a period of 10 s, brings the reflex amplitude to 50%, it shows abnormal adaptation and is indicative of VIIIth nerve lesion (stapedial reflex decay). 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. Lesion of brainstem. If ipsilateral reflex is present but the contralateral reflex is absent, lesion is in the area of crossed pathways in the brainstem.
  65. 65. REFERENCES • HANDBOOK OF CLINICAL AUDIOLOGY, 7th edition, JACK KATZ. • Cummings Otolaryngology HEAD AND NECK SURGERY • Clinical Audiology An Introduction SECOND EDITION, Brad A. Stach • Scott brown 7th edition.
  66. 66. •Thank you
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