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Objective Tests of the Auditory System

Objective Tests of the Auditory System. SPA 4302 Summer A, 2004. 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. Impedance (Z) vs. Admittance (Y). Tympanogram:.

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Objective Tests of the Auditory System

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  1. Objective Tests of theAuditory System SPA 4302 Summer A, 2004

  2. 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 Impedance (Z) vs.Admittance (Y)

  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 • As: peak but shallow: stiff: otosclerosis • Ad: 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. L R MN 7 SOC CN 8th IE ME OE SOC CN 8th IE ME OE MN 7 7th CN 7th CN

  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

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

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

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

  19. Severe Cochlear Losses

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