1. Objective tests of the auditory system 1. Acoustic immittance measures Static acoustic compliance Static acoustic compliance Tympanometry Tympanometry Acoustic reflex Acoustic reflex 2. Otoacoustic emissions (OAE) Transient-evoked OAE (TEOAE) Transient-evoked OAE (TEOAE) Distortion-product OAE (DPOAE) Distortion-product OAE (DPOAE) 3. Auditory 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)

2. Acoustic immittance measures Equipment: Headset with probe on one side and acoustic reflex activator on other side. Probe with three tubes: 1. Loudspeaker to emit a pure tone 2. Microphone to pick up sound in ear canal 3. Air pump to change pressure in the ear canal

3. Static acoustic compliance Mobility of the tympanic membrane in response to a given pressure in the external ear canal. Mobility of the tympanic membrane in response to a given pressure in the external ear canal. Clean ears Clean ears Tightly seal the external ear canal Tightly seal the external ear canal Positive pressure is increased to +200 daPa using pressure pump. Measure equivalent volume. (c 1 ) Positive pressure is increased to +200 daPa using pressure pump. Measure equivalent volume. (c 1 ) Then decrease pressure till tympanic membrane is maximally compliant or till outer-ear pressure is at 0 daPa. (c 2 ) Then decrease pressure till tympanic membrane is maximally compliant or till outer-ear pressure is at 0 daPa. (c 2 ) Static compliance = c 2 – c 1 Static compliance = c 2 – c 1 Normal values: 0.30 to 1.60 cm 3 Normal values: 0.30 to 1.60 cm 3

4. Impedance Opposition to vibration Opposition to vibration Two forms: Two forms: Reactance (X) Reactance (X) Resistance (R) Resistance (R) Remains same across frequencies Remains same across frequencies

5. Reactance (X) Two components Two components Due to mass (X m ) Due to mass (X m ) Greatest at high frequencies Greatest at high frequencies Due to stiffness (X s ) Due to stiffness (X s ) Greatest at low frequencies Greatest at low frequencies

6. Total Impedance (Z) Z = Z = Impedance of a medium = Characteristic impedance Impedance of a medium = Characteristic impedance [ R 2 + (Xm – Xs) 2 ]

8. Tympanometry Measuring the compliance of the tympanic membrane as a function of the pressure in the ear canal. Measuring the compliance of the tympanic membrane as a function of the pressure in the ear canal. Membrane vibrates most efficiently when the pressure on both sides is equal. Membrane vibrates most efficiently when the pressure on both sides is equal. Aim: To determine the pressure at which the membrane is maximally compliant (peak pressure), and the amount of compliance at that point. Aim: To determine the pressure at which the membrane is maximally compliant (peak pressure), and the amount of compliance at that point.

9. A: Peak around 0 daPa; anywhere between ±100 daPa: normal C: Peak beyond -100 dPa: neg pressure B: No peak flat tymp: effusion A s : Peak near 0 daPa but shallow: otosclerosis A d : Very high peak: Dysarticulation Types of tympanograms