II. Immittance: Tympanometry and Acoustic Reflex Testing

What is admittance?

The ease with which sound energy flows through the middle ear.

What is impedance?

The resistance of the middle ear to sound energy flow.

What is immittance?

Describes how easily energy flows through the middle ear system.

What does the immittance probe tone loudspeaker do?

Presents a tone at 85 dB SPL and 226 Hz.

What does the immittance probe microphone do?

Measures residual sound in the ear canal.

What do the pressure pump and manometer do?

Change and measure air pressure.

What does a Type A tympanogram indicate?

Normal outer and middle ear function.

What are the characteristics of a Type A tympanogram?

Peak near ambient pressure, normal static admittance, and normal ear canal volume.

What does a Type AD tympanogram indicate?

Abnormally increased middle ear mobility.

What can cause a Type AD tympanogram?

Ossicular disruption or a flaccid tympanic membrane.

What does a Type AS tympanogram indicate?

Reduced middle ear mobility.

What can cause a Type AS tympanogram?

Ossicular fixation, middle ear inflammation or infection, or eardrum scarring.

What does a Type B tympanogram look like?

No clear peak.

What does a Type B tympanogram generally indicate?

Reduced compliance of the tympanic membrane.

What can a Type B tympanogram with high ECV indicate?

Possible eardrum perforation.

What can a Type B tympanogram with low or regular ECV indicate?

Possible otitis media.

What can a Type B tympanogram with very low ECV indicate?

The probe may be hitting the ear canal wall or the probe tube may be clogged.

What does a Type C tympanogram indicate?

A peak at negative pressure, below -150 daPa.

What can cause a Type C tympanogram?

Emerging or resolving otitis media with effusion (OME).

What is tympanometric peak pressure (TPP)?

The pressure at maximum admittance, measured in daPa.

What is the normal TPP range in the study guide?

-149 to +50 daPa.

What is peak compensated static admittance?

The maximum admittance, measured in mmho or ml.

What is the normal static admittance range?

0.25-1.7 mmho.

What is ear canal volume (ECV)?

The volume of the ear canal, measured in cc or ml.

What is the normal ECV range for children?

0.3-0.9 ml.

What is the normal ECV range for adults?

0.3-1.4 ml.

What happens to a tympanogram with negative middle ear pressure?

The peak shifts toward negative pressure.

What happens to admittance when fluid is in the middle ear?

Admittance decreases because the tympanic membrane has reduced mobility.

What happens to ECV with an eardrum perforation?

ECV becomes very large.

Why does normal middle ear pressure allow the greatest admittance?

Pressure on both sides of the tympanic membrane is equal.

What is the first step in the acoustic reflex pathway?

Sound enters the ear and travels through the middle ear to the cochlea.

Where does the auditory nerve carry the signal?

To the brainstem, including the cochlear nucleus.

Where does the signal travel after the cochlear nucleus?

Bilaterally to the superior olivary complex.

Which nerve carries the motor signal in the acoustic reflex?

The facial nerve.

Which muscle contracts during the acoustic reflex?

The stapedius muscle.

What happens when the stapedius muscle contracts?

It pulls on the stapes and stiffens the ossicular chain, reducing sound transmission to the cochlea.

What is the acoustic reflex?

The involuntary contraction of the stapedius and tensor tympani muscles in response to loud sounds.

What happens to admittance during the acoustic reflex?

Admittance decreases.

What happens to impedance during the acoustic reflex?

Impedance increases.

What is the protective function of the acoustic reflex?

It attenuates high-intensity sounds to help avoid potential hearing injury.

What is the perceptual function of the acoustic reflex?

It reduces interference from unimportant sounds and limits masking of high-frequency sounds by low-frequency sounds.

What is an ipsilateral reflex?

The stimulus ear and probe ear are the same.

What is a contralateral reflex?

The stimulus ear and probe ear are opposite.

What is right ipsilateral testing?

Right stimulus and right probe.

What is right contralateral testing?

Right stimulus and left probe.

What is left ipsilateral testing?

Left stimulus and left probe.

What is left contralateral testing?

Left stimulus and right probe.

What does the probe tone measure?

The response in the probe ear.

What does the stimulus tone do?

Activates the acoustic reflex.

What happens when the acoustic reflex is activated?

The middle ear system stiffens in both ears.

What does a right middle ear problem affect?

Measurements when the probe is in the right ear.

What happens with a right stimulus and left probe when the right ear has a conductive problem?

The reflex may occur, but the stimulus must be loud enough because of the conductive hearing loss.

What happens with a left stimulus and right probe when the right ear has a middle ear problem?

The right middle ear problem affects the measurement.

What happens with a right inner ear problem (unilateral SNHL)?

Whenever a tone enters the right ear, the acoustic reflex threshold is elevated or absent.

What reflex pattern can occur with a right nerve problem?

The same pattern as a right inner ear problem; reflexes are more likely absent or elevated.

What does a right efferent problem affect?

Measurements when the probe is in the right ear; both right ipsilateral and right contralateral measurements are affected.

What does a central brainstem problem affect?

The efferent crossed pathway, so contralateral reflex measurements are affected.

What does tympanometry measure?

How easily the middle ear moves in response to changes in air pressure.

Does tympanometry change air pressure?

Yes, it changes air pressure in the ear canal.

What does acoustic reflex testing measure?

The involuntary middle ear muscle contraction in response to a loud sound.

Does acoustic reflex testing vary air pressure?

No, it does not vary air pressure.

When are acoustic reflex measurements made?

At the peak pressure of the tympanogram.

What does acoustic reflex testing use in addition to the probe tone?

A stimulus tone.

What do tympanometry and acoustic reflex testing have in common?

Both use a 226 Hz probe tone and measure changes in sound in the external ear canal.