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Objective Tests of theAuditory System
SPA 4302
Summer A, 2004
Impedance (Z) vs. Admittance (Y)
Resistance(R)
Mass Reactance(Xm)
Stiffness Reactance(Xs)
Z = (R2 + Xt2)1/2
Conductance(G)
Mass Susceptance(Bm)
Stiffness Susceptance(Bs)
Y = (G2 + Bt2)1/2
Tympanogram:
• A plot of middle ear admittance as a function of ear canal pressure
• Pressure is swept from +200 to -200 or -400 dPa
• Should see peak at point where pressures are equal
Tympanogram types:
• A: peak between +100 and -200 dPa: normal
• C: peak beyond -200 dPa: neg pressure
• B: no peak flat tymp: effusion
• As: peak but shallow: stiff: otosclerosis
• Ad: peak off scale: floppy: dysarticulation
Tympanogram Types
Static Admittance
• A measure of the height of tympanogram peak
Adults 3-10 yrsA 0.30 to 1.70 0.25 to 1.05As < 0.30 < 0.2Ad >1.70 > 1.05
(All values are in ml of equivalent volume)
The Acoustic Reflex• Stapedius contraction measured as change
in compliance
• Reflex arc:– peripheral ear,
– VIIIth n.
– Cochlear nucleus
– Superior Olivary Complexes
– Medial Nuclei of VII
– VIIth nerves to both middle ears
R L
SOC
CN
8th
IE
ME
OE
SOC
CN
8th
IE
ME
OE
7th CN 7th CN
MN 7MN 7
Clinical Tests using Acoustic Reflexes:
• A.R. Threshold: how intense sound must be to elicit the reflex?
• A.R. Decay: Is the degree of a contraction maintained throughout a 10 second stimulus?
AR Threshold:
• to pure-tones, 0.5, 1, 2, 4 kHz
• = lowest level at which change in admittance can be read
• ipsilaterally or contralaterally
• should be between 65 and 90 dB SL.
Otoacoustic Emissions (OAE)
• Low-level sounds produced by the cochlea and recordable in the external ear canal.
• Spontaneous
• Click-evoked
• Distortion Product
• Stimulus Frequency
Recording OAEs
Spectrum of Sound in Ear Canal
OAE as Measure of Cochlear Health
Auditory Evoked PotentialsRecording: Comes From:
Electrocochleography Cochlea, VIIIth nerve
Auditory Brainstem Response VIIIth nerve & brainstem
Middle Latency Response Thalamus & auditory cortex
Auditory Late Response Auditory Cortices
P300 Hippocampus area
Auditory Brainstem Response
• Electrical response from neurons to sound
• Recorded by electrodes on scalp
• Coming from VIIIth nerve and brainstem
ABR MEASURES
Time (ms)
Am
plit
ude
(μV
)
Wave V Latency
I-V IPL
I-III III-V
I IIIII
IVV
Amp V
Conductive Loss: Curve shifted to higher levels by amount of
conductive loss
Severe Cochlear Losses