impedance z vs admittance y n.
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Impedance (Z) vs. Admittance (Y)

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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
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)
tympanogram
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
static admittance
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

tympanogram types
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
physical volume test
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

the acoustic reflex
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
slide14

L

R

MN 7

SOC

CN

8th

IE

ME

OE

SOC

CN

8th

IE

ME

OE

MN 7

7th CN

7th CN

clinical tests using acoustic reflexes
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
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.
vertical
Vertical

7th Nerve

diagonal
Diagonal

8th Nerve

horizontal
Horizontal

Brainstem

inverted l
Inverted L

Conductive/8th Impinging on 7th

eustachian tube function test
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