Objective tests of the auditory systemObjective tests of the auditory system

1.1. Acoustic immittance measuresAcoustic immittance measures Static acoustic complianceStatic acoustic compliance TympanometryTympanometry Acoustic reflexAcoustic reflex

2.2. Otoacoustic emissions (OAE)Otoacoustic emissions (OAE) Transient-evoked OAE (TEOAE)Transient-evoked OAE (TEOAE) Distortion-product OAE (DPOAE)Distortion-product OAE (DPOAE)

3.3. Auditory evoked potentialsAuditory evoked potentials Electrocochleography (ECog)Electrocochleography (ECog) Auditory brainstem response (ABR)Auditory brainstem response (ABR) Auditory middle latency response (AMLR)Auditory middle latency response (AMLR) Auditory late response (ALR)Auditory late response (ALR)

Acoustic immittance measuresAcoustic immittance measures

Equipment: Equipment: Headset with Headset with probe on one side and probe on one side and acoustic reflex activator acoustic reflex activator on other side.on other side.

Probe with three tubes:Probe with three tubes:

1.1. Loudspeaker to emit a Loudspeaker to emit a pure tonepure tone

2.2. Microphone to pick up Microphone to pick up sound in ear canalsound in ear canal

3.3. Air pump to change Air pump to change pressure in the ear canalpressure in the ear canal

Static acoustic complianceStatic acoustic compliance

Mobility of the tympanic membrane in response to a given Mobility of the tympanic membrane in response to a given pressure in the external ear canal.pressure in the external ear canal.

Clean earsClean ears

Tightly seal the external ear canalTightly seal the external ear canal

Positive pressure is increased to +200 daPa using Positive pressure is increased to +200 daPa using pressure pump. Measure equivalent volume. (cpressure pump. Measure equivalent volume. (c11))

Then decrease pressure till tympanic membrane is Then decrease pressure till tympanic membrane is maximally compliant or till outer-ear pressure is at 0 maximally compliant or till outer-ear pressure is at 0 daPa. (cdaPa. (c22))

Static compliance = cStatic compliance = c2 2 – c– c11

Normal values: 0.30 to 1.60 cmNormal values: 0.30 to 1.60 cm33

ImpedanceImpedance

Opposition to vibrationOpposition to vibration

Two forms:Two forms:

Reactance (X)Reactance (X)

Resistance (R) Resistance (R)

Remains same across frequenciesRemains same across frequencies

Reactance (X)Reactance (X)

Two componentsTwo components

Due to mass (XDue to mass (Xmm))

Greatest at high frequencies Greatest at high frequencies

Due to stiffness (XDue to stiffness (Xss))

Greatest at low frequencies Greatest at low frequencies

Total Impedance (Z)Total Impedance (Z)

Z = Z =

Impedance of a medium = Characteristic Impedance of a medium = Characteristic impedanceimpedance

[ R2 + (Xm – Xs)2 ]

Impedance

0

20

40

60

80

100

120

100

400

700

1000

1300

1600

1900

2200

2500

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3100

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Frequency (Hz)

Imp

ed

en

ce

(Z

)

Stiffnessreactance Mass reactance

Resistance

TympanometryTympanometry

Measuring the compliance of the tympanic Measuring the compliance of the tympanic membrane as a function of the pressure in the membrane as a function of the pressure in the ear canal.ear canal.

Membrane vibrates most efficiently when the Membrane vibrates most efficiently when the pressure on both sides is equal.pressure on both sides is equal.

Aim: To determine the pressure at which the Aim: To determine the pressure at which the membrane is maximally compliant membrane is maximally compliant (peak (peak pressure)pressure), and the amount of , and the amount of compliancecompliance at at that point.that point.

AA: Peak around 0 daPa; anywhere between ±100 : Peak around 0 daPa; anywhere between ±100 daPa: normaldaPa: normal

CC: Peak beyond -100 dPa: neg pressure: Peak beyond -100 dPa: neg pressure

BB: No peak flat tymp: effusion: No peak flat tymp: effusion

AAss: Peak near 0 daPa but shallow: otosclerosis: Peak near 0 daPa but shallow: otosclerosis

AAdd: Very high peak: Dysarticulation: Very high peak: Dysarticulation

Types of tympanogramsTypes of tympanograms

Types of tympanogramsTypes of tympanograms