impedance audiometry part 1

IMPEDANCE AUDIOMETRYAditya Ghosh RoyPGT2MS ENT

IMPEDANCE AUDIOMETRY

•USE

• TESTTYMPANOMETRY

EUSTACHIAN TUBE FUNCTIONSTAPEDIAL

REFLEX

SOUND WAVE

SOUND WAVESOLID

RELECTED SOUND

WAVE

AIR

AIR

ABSORBED SOUND

SOUNDAIR

SOLIDREFLECTED SOUND

IMPEDANCE

STIFFNES

S

MASS

FRICTION

IMPEDANCE

AIR

COCHLEA

SOUNDMIDDLE EAR IMPEDANCE MATCHING

DEVICE

COCHLEA

EAC

TM

TYMPANOMETRY (DEF)

• CHANGE IN PRESSURE --- CHANGE IN TM STIFFNESS ---SOUND ENERGY REFLECTED BACK DEPENDS ON STIFFNESS OF TM OR PRESSURE CHANGE

PROBE TONE AMPLIFIER

MANOMETER

SOUND

TYMPANIC MEMBRANE

REFLECTED

SOUND

PRESSURE

• THEREFORE TYMPANOMETRY MAY BE DEFINED AS MEASUREMENT OF CHANGE IN IMPEDANCE OF MIDDLE EAR CAVITY AT THE TM PLANE IN RELATION TO CHANGE IN PRESSURE IN EAC.

• TYMPANOGRAM

Y or ORDINATEIMPEDANCE OR

STIFFNESS

X OR ABSCISSAAIR PRESSURE

• IMPEDANCE

• NONE OF THE PARAMETERS MEASURED INDIVIDUALLY

SO AS A RESULT ACOUSTIC ADMITTANCE IS MEASUREDADMITTANCE IS RECIPROCAL OF IMPEDANCE

STIFFNESSMASS

FRICTION

IMPEDANCEOPPOSITION TO FLOW OF

ENERGYACOUSTIC OHM

ADMITTANCEEASE TO FLOW OF ENERGY

ACOUSTIC MHO

• AUDIOMETERS STILL AUDIOMETERS DO NOT MEASURE ADMITTANCE DIRECTLY COMPLIANCE

LOW FREQUENCY PROBE TONE USED IMPEDANCE

EASE OF MOVEMENT OR SPRINGINESS OF MIDDLE EAR SYSTEM

IS ALSO RECIPROCAL OF STIFFNESS

• HENCE IF COMPLIANCE IS MEASURED USING LOW FREQUENCY TONE

• IMPEDANCE OF MIDDLE EAR SYSTEM

• MOST OF THE IMPEDANCE AUDIOMETERS MEASURE COMPLIANCE

IMPORTANT POINTS

• C1 – COMPLIANCE VALUE AT +200mm water

• C2 – COMPLIANCE VALUE AT (MAXIMUM)

• CX – STATIC COMPLIANCE (C2- C1=CX)

STATIC COMPLIANCE IS DEFINED AS COMPLIANCE OF AUDITORY CONDUCTIVE PATHWAY AT TM.

MIDDLE EAR PRESSURE

• PRESSURE AT WHICH COMPLIANCE VALUE IS MAXIMUM IS CALLED AS MIDDLE EAR PRESSURE IE PRESSURE OF AIR IN MIDDLE EAR CAVITY.

PHYSICAL VOLUME TEST VALUE

THE COMPLIANCE VALUE AT +200mM water IS THE VOLUME OF EAC .

TYMPANOMETRY

MEASUREMENT OF STATIC

COMPLIANCE

MEASUREMENT OF MIDDLE EAR PRESSURE

MEASUREMENT OF STATIC COMPLIANCE

• cc/ ml if COMPLIANCE• Millimho if SUSPECTANCE

• IF A 220 Hz PROBE– 1MILLIMHO OF SUSPECTANCE = 1 CC/ML OF COMPLIANCE

TYMPANOGRAM

ABSOLUTE

RELATIVE

COMPENSATED

• BASELINE IS COMPLIANCE AT +200

• SHADED AREA IS VOLUME OF EAC

• ALSO CALLED NON COMPENSATED TYPE

ABSOLUTE

• BASELINE IS 0 AT ORDINATE• BRACKET PORTION IS

COMPLIANCE

RELATIVE

• BASELINE IS 0 AT ORDINATE• BRACKET PORTION IS

COMPLIANCE• SHADED AREA BESIDE THE

TYMPANOGRAM IS VOLUME OF EAC

COMPENSATED

• NORMAL RANGE COMPLIANCE

• IMP POINT– CLINICAL CONDITION OF TM TO BE ALWAYS NOTED

• STUDY BY A.S. FELDMAN– HEALED TM INVALIDATES COMPLIANCE AS ONE OF THE TESTS OF TYMPANOMETRY

.35 TO 1.40 ML

>2.50mL

<.28 mL

AB

NO

RMAL

LY

HIG

H

ABNO

RMALL

Y LOW

LARGE TM

OSSICULAR DISCONTINUITY

SCARED/HEALED TM

POST STAPEDECTOMY EAR

OTITIS MEDIA WITH EFFUSION

OSSICULAR FIXATION

TYMPANOSCLEROSIS

OTOSCLEROSIS

TUMOUR OF MIDDLE EAR

MEASUREMENT OF MIDDLE EAR PRESSURE• EXPRESSED IN mm WATER / DEKA PASCAL

(daPa)

• 1mm WATER = 1.20 DEKA PASCAL

• RANGE = +50 TO -50 mm WATER

• MEP NEGATIVE WHEN P < -100 mm WATER

• PAED AGE GROUP-- +25 TO -100mm WATER

NORMAL MEP• SCARRED TM• OSICULLAR FIXATION• OSICULLAR DISCONTUINITY• STAPEDIAL OTOSCLEROSISNEGATIVE MEP• ET DYSFUNCTION• SECRETORY OTITIS

MEDIA/EFFUSION

ABSENCE OF PEAK• PERFORATED TM• ADHESIVE OTITIS MEDIA• ARTIFACT• PATENT GROMET IN TM• CERUMEN

POSITIVE MEP•EARLY ACUTE OTITIS MEDIA

IMP POINT--POSITIVE PRESSURE PEAK

• SWALLOWING• CHILD CRYING PHYSIOLOGICAL• VALSALVA• HOLD BREATH IN EXPIRATION

• IN EARLY AOM PUS FORMED IN MEC AND ET DYSFUNCTION

DECREASE VOLUME + INCREASE PRESSURE OF MEC

POSITIVE PRESSURE PEAK

TYPES AND SHAPES OF TYMPANOGRAMS

TYMPANOGRAMS

J. JERGER

A

B

A.S. FELDMAN

TYPE A

• SHARP MAXIMUM AT 0 mm WATER• NORMAL EAR AND SOME CASES OF

OTOSCLEROSIS

TYPE AD• NORMAL MIDDLE EAR PRESSURE WITH

HIGH COMPLIANCE• SEEN IN OSSICULAR CHAIN

DISCONTUINITY OR SCARRING OF TM• NOTCHED PEAK OR DOUBLE MAX AT 0

mm USUALLY SEEN WITH A HIGH FREQUENCY PROBE IN OSSICULAR DISCONTUINITY

TYPE AS

• NORMAL MIDDLE EAR PRESSURE WITH LOW COMPLIANCE

• OTOSCLEROSIS AND THICKENED TM

TYPE B

• FLAT TYMPANOGRAM• LITTLE OR NO COMPLIANCE AND NO SHARP PEAK• SEEN IN ADHESIVE OTITIS MEDIA, OTITIS MEDIA

WITH EFFUSION, PERFORATION OF TM

TYPE C

• NEGATIVE MIDDLE EAR PRESSURE WITH NORMAL COMPLIANCE

• ET DYSFUNCTION WITHOUT EFFUSION

TYPE CS

• NEGATIVE MIDDLE EAR PRESSURE WITH LOW COMPLIANCE• ET DYSFUNCTION WITH OTITIS MEDIA WITH EFFUSION

CLASSIFICATION BY A.S. FELDMAN

PEAK PRESSURE

TYPE OF CONFIGURATION

OF TYMPANOGRAM

COMPLIANCE OR AMPLITUDE

1.NORMAL TYMPANO GRAM• GOOD COMPLIANCE AND PEAK PRESSURE AT 0

mm WATER• CORRESPONDS TO JAGER TYPE A

2.NORMAL MIDDLE EAR PRESSURE WITH HIGH COMPLIANCE • IF 226HZ PROBE USED THEN EITHER OSSICULAR

CHAIN DISCONTUINITY OR SCARRING OF TM• BUT IF A 660 OR 800 HZ PROBE USED THEN A

NOTCHED PEAK OR DOUBLE MAX AT 0 mm USUALLY SEEN IN OSSICULAR DISCONTUINITY

3.NORMAL MIDDLE EAR PRESSURE WITH LOW COMPLIANCE• OTOSCLEROSIS OR OSSICULAR FIXATION AND

THICKENED TM

4. FLAT TYMPANOGRAM• LITTLE OR NO COMPLIANCE AND NO SHARP PEAK• SEEN IN ADHESIVE OTITIS MEDIA, OTITIS MEDIA

WITH EFFUSION, PERFORATION OF TM .• CORRESPONDS TO JAGER TYPE B.

5.NEGATIVE MIDDLE EAR PRESSURE WITH LOW COMPLIANCE• ET DYSFUNCTION WITH OTITIS MEDIA WITH

EFFUSION• CORRESPONDS TO JAGER TYPE CS

6. POSITIVE MIDDLE EAR PRESSURE NORMAL COMPLIANCE• RARELY SEEN• IN EARLY AOM

IN EARLY AOM PUS FORMED IN MEC AND ET DYSFUNCTION

DECREASE VOLUME + INCREASE PRESSURE OF MEC

POSITIVE PRESSURE PEAK

7.NEGATIVE MIDDLE EAR PRESSURE WITH NORMAL COMPLIANCE• ET DYSFUNCTION WITHOUT EFFUSION

TO SUMMARISE

TO BE CONT..