Download Audiometric tests

Audiometric tests
Air conduction
• This test assesses sensitivity when the signal is
transmitted through the outer, middle, and
inner ear and then to the cortex. Testing may
be performed using headphones, insert
earphones.
Bone conduction
• This technique assesses sensitivity when the
signal is transmitted through the bones of the
skull to the cochlea and then through the
auditory pathways of the brain. This type of
testing bypasses the outer and middle ear.
Masking
Masking presents a constant noise to the nontest ear to prevent crossover from the test ear.
The purpose of masking is to prevent the nontest ear from detecting the signal , so only the
test ear can respond.
Pure tone
• A pure tone is a single frequency tone with no
harmonic content (no overtones). This
corresponds to a sine wave.
Pure tone
Pure tone
Pure tone audiometry
• An audiometer - electronic device which
produces pure tones, the intensity of which
can be increased or decreased in 5 db
PURE TONE AUDIOMETRY
Pure tone Audiometry
• In a sound proof room person is seated
comfortably.
• Ear phones are applied which are color coded.
(Red for right ear, Blue for left ear.)
• Masking sound is delivered to the non-test ear.
• Start with a frequency of 125Hz. & 0 dB.
• Gradually increase the dB. till person hears the
sound & respond.
• Mark the threshold intensity on the audiogram
paper.
Contd…
• Find the threshold of hearing from 125 Hz. to
8000Hz. & mark on the audiogram paper.
• Join the points to make air conduction
audiogram.
• Place the bone vibrator over the mastoid
process.
• Deliver the sound through the vibrator & find
out the threshold of hearing for different
frequencies of sound.
Contd…
• Use different sign to mark the bone conduction
audiogram.
• Select the other ear and repeat the whole
procedure.
Audiogram
• 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.
CHL
SNHL
Speech audiometry
• Speech reception threshold
Minimum intensity at which 50% of words are
correctly repeated
Spondee words (baseball, sunlight)
Intensity varied in 5db steps
Normal – within 10db of pure tone average
• Speech discrimination score
Measure of ability to understand speech
Phonetically balanced words ( pin, sin) at 30 –
40 db above SRT
Normal – 90 – 100%
Impedance audiometry
Acoustic reflex
Acoustic Reflex Pathways
• Ipsilateral
 Right ear
 Left ear
• Contralateral
 Probe right
 Probe left
Uses
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To test hearing in infants and small children
To find malingerers
To detect cochlear pathology
To detect facial n lesions
To detect lesions of brainstem
Special tests for hearing
• Recruitment
• Phenomenon of abnormal growth of loudness
• Seen in lesions of cochlea
Short increment sensitivity index
• A continous tone of 20 db above threshold is
presented and sustained for 2 minutes
• Every 5 seconds tone is increased by 1db and
20 such blips presented
• Cochlear deafness – 70 – 100 %
• Retrocochlear – 0 – 20 %
Tone decay test
• Measure of nerve fatigue
• Useful in retrocochlear hearing loss
• Normally a person can hear a tone continously
for 60 seconds. In nerve fatigue he stops
hearing earlier
• Tone of 4000hz 5db above hearing
thresholdfor 60 s
• Intensity is increased by 5db till it is heard for
60 s continously
• Result is expressed as number of db of decay
• >25 db – retrocochlear loss
Electrocochleography
• Measures electrical potentials in cochlea and
VIII n in response to auditory stimuli
• Response –
• Cochlear microphonics
• Summating potential
• Action potential
• Ratio – SP: AP <30%
• Increase in ratio – Meniere’s disease.
Auditory brainstem response (ABR)
• BERA/ BAER
• Auditory brainstem response (ABR) is a
neurologic test of auditory brainstem function
in response to auditory (click) stimuli.
• It is a set of seven positive waves recorded
during the first 10 seconds after a click stimuli.
They are labeled as I - VII
• 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
VIIwave V.
ORIGIN OF BAEP
Origin of each wave
Wave
Origin
I
Cochlear nerve
II
Dorsal & Ventral cochlear nucleus
III
Superior olivary complex
IV
Nucleus of lateral lemniscus
V
Inferior colliculus
VI
Medial geniculate body
VII
Auditory radiation(cortex
Intepretation
• Latency
• Amplitude
• Morphology
Uses
• As a screening procedure for infants
• To determine the threshold of hearing in
infants
• Diagnosis of retrocochlear pathology
• Diagnosis of brainstem pathology
• To monitor VIIIn intra operatively
Oto acoustic emissions
• Low intensity sounds produced by outer hair
cells of cochlea
• They are absent when outer hair cells of
cochlea are damaged
• OAE is normal in case of retrocochlear hearing
loss
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Types
Spontaneous
Evoked
Transient Otoacoustic Emissions (TOAEs)
Distortion Product Otoacoustic Emissions
(DPOAE)
Uses
• As a screening test in infants and to test
hearing in unco operative individuals
• To distinguish cochlear from retrocochlear
heaing loss
• Useful to diagnose auditory neuropathy
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