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Objective tests of the auditory system

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

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Objective tests of the auditory system

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  1. Objective tests of the auditory system • Acoustic immittance measures • Static acoustic compliance • Tympanometry • Acoustic reflex • Otoacoustic emissions (OAE) • Transient-evoked OAE (TEOAE) • Distortion-product OAE (DPOAE) • Auditory evoked potentials • Electrocochleography (ECog) • Auditory brainstem response (ABR) • Auditory middle latency response (AMLR) • 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: • Loudspeaker to emit a pure tone • Microphone to pick up sound in ear canal • 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. • Clean ears • Tightly seal the external ear canal • Positive pressure is increased to +200 daPa using pressure pump. Measure equivalent volume. (c1) • Then decrease pressure till tympanic membrane is maximally compliant or till outer-ear pressure is at 0 daPa. (c2) • Static compliance = c2 – c1 • Normal values: 0.30 to 1.60 cm3

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

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

  6. Total Impedance (Z) Z = Impedance of a medium = Characteristic impedance [ R2 + (Xm – Xs)2 ]

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

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

  9. Types of tympanograms

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