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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
Mass and Stiffness Reactance
0
0.2
0.4
0.6
0.8
1
1.2
100 500 1000 4000
Frequency
Rea
ctan
ce
Xm
XsRes
onan
t F
req
.
Mass and Stiffness Susceptance
0
0.2
0.4
0.6
0.8
1
1.2
100 500 1000 4000
Frequency
Susc
epta
nce Bs
BmRes
onan
t F
req
.
RESISTANCE AT THE EARDRUM
0100200300400500600700800900
1000
0.01 0.1 1 10 100
Frequency (kHz)
R (
Oh
ms)
Reactance at the Eardrum
-4000-3500-3000-2500-2000-1500-1000
-5000
5001000
0.01 0.1 1 10
Frequency (kHz)
X (
Ohm
s)
Reactance
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
• 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
Gradient = hp/ht
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
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
0
1
2
3
4
5
6
-300 -200 -100 0 100 200
Air Pressure (daPa)
Adm
itta
nce
(mm
hos)
PerfEffClog
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.
“The Boxes”
Probe (Measured) Ear/
Condition
Right Left
Contralateral Right ear Reflex
Stimulated Contralaterally
Left ear Reflex Stimulated Contralaterally
Ipsilateral Right ear Reflex Stimulated Ipsilaterally
Left ear Reflex Stimulated Ipsilaterally
Vertical
Right Left
Contralateral Present Absent
Ipsilateral Present Absent
7th Nerve
Diagonal
Right Left
Contralateral Present Absent
Ipsilateral Absent Present
8th Nerve
Horizontal
Right Left
Contralateral Absent Absent
Ipsilateral Present Present
Brainstem
Inverted L
Right Left
Contralateral Absent Absent
Ipsilateral Present Absent
Conductive/8th Impinging on 7th
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