impedance (z) vs. admittance (y) resistance(r) mass reactance(xm) stiffness reactance(xs) z = (r 2 +...

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