ASLP 3040: Immittance Testing, Acoustic Reflexes & OAEs

What does the term 'immittance' combine?

Impedance and admittance.

What is impedance?

The extent to which the system resists the flow of energy.

What is admittance?

The ease with which energy flows through a system.

How are impedance and admittance related?

They are reciprocal terms; if one is high, the other is low.

What is the primary function of immittance testing in audiological assessment?

To detect middle ear disorders. Is useful in differentiating cochlear from retrocochlear disorders

Immittance bridge

Signal generator #1: loudspeaker for probe tone

Microphone: measures sound pressure reflected eardrum

Pressure pump/manometer: varies air pressure in ear canal

Signal generator #2: loudspeaker for ipsilateral or contralateral signal

What is tympanometry?

Measurement of acoustic admittance of the middle ear as a function of air pressure variations.

Peak Pressure

(daPa) measured by varying the pressure in the ear canal using the manometer. Determines the point at which the pressure in the ear canal is equal to the pressure in the middle ear. Normal atmospheric pressure is 0daPa

What does static admittance describe?

The height of the tympanogram is measured at the plane of the eardrum. Measured in millimhos (mmho) and is interpreted based on normative data.

What does a Type A tympanogram indicate?

Normal middle ear function.

What does a Type As tympanogram suggest?

A stiff middle ear system.

What does a Type Ad tympanogram indicate?

A flaccid middle ear system.

What does a Type B tympanogram suggest?

Flat. No mobility of the middle ear system, possibly due to fluid or blockage.

What does a Type C tympanogram indicate?

Negative pressure buildup in the middle ear system.

What is the significance of ear canal volume measurements?

They can detect small perforations of the tympanic membrane.

What is an acoustic reflex?

An involuntary response of the stapedius muscle to sound.

What is the acoustic reflex threshold (ART)?

The lowest intensity level at which the acoustic reflex can be elicited.

What is acoustic reflex decay testing?

Present a tone contralaterally for 10 seconds at a level that is 10 dB above the reflex threshold at that frequency.

The test is looking for a continuous reduction in amplitude that does not change during the 10s presentation

What is positive decay in Acoustic reflex decay testing?

Positive decay is when a reduction in amplitude of more than 50% is noted during presentation

Positive decay indicates a retrocochlear disorder

How will a cochlear disorder look on a tympanogram, static immittance, and reflex threshold?

Normal tympanogram (peak pressure)

Normal static immittance

Normal reflex thresholds (up to a 50 dB HL loss)

How will a retrocochlear disorder look on a tympanogram, static immittance, and reflex threshold?

Normal tympanogram (peak pressure)

Normal static immittance

Absent or elevated reflex thresholds

Positive reflex decay

How will a conductive hearing loss look on a tympanogram, static immittance, and reflex threshold?

•Abnormal (flat) tympanogram

•Abnormal static immittance (no peak)

•Absent or elevated reflex thresholds

How will a sensorineural hearing loss look on a tympanogram, static immittance, and reflex threshold?

•Normal tympanogram

•Normal static immittance

•Normal reflex thresholds (up to ~50 dB HL hearing loss)

What are otoacoustic emissions (OAEs)?

Sounds generated in the cochlea that can be measured in the ear canal. Only generated by the outer hair cells.

What types of OAEs are there?

Spontaneous OAEs and evoked OAEs (TEOAEs and DPOAEs).

What is the significance of a signal-to-noise ratio (SNR) in OAEs?

OAEs are present if the SNR is greater than or equal to +6 dB SPL.

Spontaneous OAEs

Sounds generated by the cochlea and recorded in the ear canal without the introduction of a stimulus

Recorded with a sensitive low-noise microphone housed in a probe that is placed in the ear canal

Often absent in ears with normal hearing (50/50), so not clinically useful

Evoked OAEs

Sounds generated by the cochlea in response to the presentation of a stimulus

Can be consistently recorded in patients with normal hearing, so a clinically useful tool

Transient Evoked Otoacoustic Emissions (TEOAEs)

Elicited with a brief stimulus, such as a click

Somewhat frequency-specific up to 4000 Hz

Typically quicker to run

Distortion Product Otoacoustic Emissions (DPOAEs)

Two different tones presented to the ear simultaneously

Cochlear response (OAE) is a third tone - the "distortion product" of the two stimuli

Frequency-specific up to 12000 Hz

What is the clinical application of OAEs in newborn hearing screening?

They provide an indicator of normal or abnormal cochlear function.

What is the role of OAEs in pediatric assessment?

To help identify children with normal hearing and confirm behavioral test results.

What is the clinical significance of present OAEs in conjunction with demonstrated severe hearing loss?

It indicates a mismatch in behavioral and objective results.

What can affect the OAE response?

Compromised outer and/or middle ear function.

What does the presence of OAEs indicate about outer hair cells?

They are healthy when OAEs are present.