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Objective Tests of the Auditory System SPA 4302 Summer A, 2004.

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Presentation on theme: "Objective Tests of the Auditory System SPA 4302 Summer A, 2004."— Presentation transcript:

1 Objective Tests of the Auditory System SPA 4302 Summer A, 2004

2 Impedance (Z) vs. Admittance (Y) Resistance(R) Mass Reactance(Xm) Stiffness Reactance(Xs) Z = (R 2 + X t 2 ) 1/2 Conductance(G) Mass Susceptance(Bm) Stiffness Susceptance(Bs) Y = (G 2 + B t 2 ) 1/2

3 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

4 Tympanogram types: A: peak between +100 and -200 dPa: normal C: peak beyond -200 dPa: neg pressure B: no peak flat tymp: effusion A s : peak but shallow: stiff: otosclerosis A d : peak off scale: floppy: dysarticulation

5 Tympanogram Types

6 Static Admittance A measure of the height of tympanogram peak Adults 3-10 yrs A 0.30 to 1.70 0.25 to 1.05 As < 0.30 < 0.2 Ad >1.70 > 1.05 (All values are in ml of equivalent volume)

7 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

8 R L SOC CN 8 th IE ME OE SOC CN 8 th IE ME OE 7 th CN MN 7

9 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?

10 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.

11 Otoacoustic Emissions (OAE) Low-level sounds produced by the cochlea and recordable in the external ear canal. Spontaneous Click-evoked Distortion Product Stimulus Frequency

12 Recording OAEs

13 Spectrum of Sound in Ear Canal

14 OAE as Measure of Cochlear Health

15 Auditory Evoked Potentials Recording:Comes From: ElectrocochleographyCochlea, VIIIth nerve Auditory Brainstem ResponseVIIIth nerve & brainstem Middle Latency ResponseThalamus & auditory cortex Auditory Late ResponseAuditory Cortices P300Hippocampus area

16 Auditory Brainstem Response Electrical response from neurons to sound Recorded by electrodes on scalp Coming from VIIIth nerve and brainstem

17 ABR MEASURES Time (ms) Amplitude (μV) Wave V Latency I-V IPL I-III III-V I II III IV V Amp V

18 Conductive Loss: Curve shifted to higher levels by amount of conductive loss

19 Severe Cochlear Losses

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