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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. Impedance (Z) vs. Admittance (Y). Mass and Stiffness Reactance. Resonant Freq . Mass and Stiffness Susceptance.

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Impedance (Z) vs. Admittance (Y)

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  1. 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)

  2. Mass and Stiffness Reactance Resonant Freq.

  3. Mass and Stiffness Susceptance Resonant Freq.

  4. RESISTANCE AT THE EARDRUM

  5. Reactance at the Eardrum

  6. 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

  7. Static Admittance • 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

  8. Gradient = hp/ht

  9. 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

  10. Tympanogram Types

  11. Physical Volume Test • Measure of volume of air enclosed under probe Adults 3-10 yrs. Intact TM: 0.9 to 2.0 0.3 to 0.9 TM Perf/Tube: > 2.0 >1.0 Blockage: small volume

  12. 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

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

  14. 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?

  15. 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.

  16. “The Boxes”

  17. Vertical 7th Nerve

  18. Diagonal 8th Nerve

  19. Horizontal Brainstem

  20. Inverted L Conductive/8th Impinging on 7th

  21. Eustachian Tube Function Test: • To see how well the Eustachian tube can resolve the pressure differences introduced with the bridge. • Note tympanogram peak pressure • introduce pressure into canal • Have patient swallow water • recheck tympanogram peak pressure

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