Otoacoustic Emissions (OAE)and Auditory Brainstem Response (ABR)

Sounds given off by the inner ear (outer hair cells) when responding to a sound. The vibration produces a very quiet sound that echoes back into the middle ear. This sound is the OAE that is measured.

What are otoacoustic emissions?

False

True or false: There are no hair cells in the inner ear that respond to sound by vibrating.

spontaneous - produced without a stimulus

Evoked - produced by a stimulus

2 classes of OAEs

Transient Evoked (TEOAE)

Stimulus Frequency (SFOAE)

Distortion Product (DPOAE)

3 types of evoked

Spontaneous OAES

Occur in 50% of the population, more often in females. Difficult to measure, and little clinical significance. Faint, low-intensity sounds produced by the inner ear (cochlea) that’s generated by the natural, active motility of outer hair cells (no external stimulation)

Stimulus frequency OAE

Low-level acoustic signals produced by the cochlea's outer hair cells in response to a continuous, single-freq "probe" tone. Most difficult to measure and little research. Present pure tone in ear canal and examine the sound in the ear canal

Transient evoked OAE

First measured, present a click stimulus and record sound level in the ear canal with a microphone. Maximum displacement of basilar membrane in basal region. This is an amplitude measure over time.

click

Brief sound with wide spread energy over many frequencies

Highly sensitive to injury of outer hair cells (OHCs). If high-frequency (HF) cochlear hair cells are damaged, the echo will be absent in that region because HF sounds are processed at the base, and only echoes from the healthy apical (low-frequency) region will be detected

What is the clinical application of TEOAE?

Distortion product OAE

Most widely used in clinical application. Identifies function of outer hair cells. THIS IS NOT A MEASURE OF HEARING THRESHOLD, but can correlate to hearing outside of the normal range! Stimulus: Presentation of 2 pure tones F1 and F2 with F2 being higher frequency than F1.

Distortion occurs when tones emerge in the response or output of the system. The most prominent one that emerges from the auditory system is the equivalent of 2F1- F2.

What causes the distortion in DPOAE? What is the most prominent one?

Universal newborn hearing screening, Assessment of young infants, Monitoring the function of the cochlea

What are the clinical uses of DPOAE

Auditory Brainstem Response

Clinical auditory electrophysiology involves recording the gross electrical potentials representing the activity of hundreds or thousands of individual hair cells or nerve fibers. The electrical potentials are usually recorded from remote locations on the surface of the head and require amplification and computer averaging of at least several hundred stimulus presentations to be visible.

Electrode on test ear, grounding electrode on opposite ear, Inserts in both (test ear)

Patient relaxed (asleep is preferred) can be sedated

1000-2000 clicks at rate of 33.1/sec

Begin at 70dBnHL(normative HL)

Decrease to find threshold- where Wave V is no longer identifiable

Describe the procedure for auditory brainstem response testing

- Very robust and can be recorded reliably and easily

- Sensitive to dysfunction occurring from the auditory periphery to the upper brainstem of the auditory CNS

- Useful in assisting with detection of neurologic problems along a large portion of the auditory CNS

- Can be used to estimate hearing loss

- Can be used to screen hearing of newborns and to estimate hearing thresholds in patients who are difficult to test

- Is the most definitive test to evaluate retrocochlear function.

What are the benefits of ABR?

• Waves I & II: Auditory Nerve (cranial nerve VIII)

• Wave III: Superior Olivary Complex

• Wave IV: Lateral Lemniscus

• Wave V: Inferior Colliculus

• Wave VI and VII: Undetermined

Identify each wave with the brain location.

• Estimate auditory sensitivity

• Newborn hearing screening

• Neurodiagnosis

• Intraoperative monitoring

Clinical Uses of ABR