04 Objective Audiometry

Question 1

What is the expected outcome of BERA in a patient with sensorineural deafness?

Answer 1

No waves can be observed in the BERA measurement.

Question 2

How can averaging improve OAE and AEP measurements?

Answer 2

Averaging helps to enhance the signal by reducing the impact of noise.

Question 3

What are the characteristics of Transient Evoked OAE (TEOAE)?

Answer 3

TEOAE involves short interrupted sounds of different frequencies with click stimuli of 1 ms at approximately 85 dB applied to the external auditory canal.

Given the tonotopic properties of the basilar membrane, the different frequency sounds will take different lengths of time to arrive at their specific locations. This also means the (reflected) emmisions will return at different times (staggered). The emmisions will be longer than the stimuli (3-20 ms) with a 60 dB average lower amplitude.

Question 4

What is the expected result of normal TEOAEs?

Answer 4

Normal TEOAE responses show high reproducibility and a clear separation of the OAE signal from the noise signal.

Question 5

What is the BERA test procedure?

Answer 5

1. Patient should be calm/relaxed or sleeping.
2. Electrodes placed on the patients head and behind the ear.
3. Measurement time to determine the hearing threshold: 1-1.5 hours.

Question 6

What is the main challenge in measuring OAEs and AEPs?

Answer 6

The continuous battle between signal and noise requires careful management of testing conditions and signal processing.

Question 7

What does a ‘Pass’ or ‘Refer’ result mean in a newborn hearing screening using TEOAE?

Answer 7

‘Pass’ indicates no significant hearing loss is detected while ‘Refer’ means further tests are needed to verify if hearing loss is present.

Question 8

What are the latency classifications of AEP?

Answer 8

AEPs are classified into early (0-10 ms), middle (10-50 ms), and late (50-150 ms) responses.

Question 9

Why are TeOAEs clinically important?

Answer 9

They can be performed quickly (less than a minute per ear) and are non-invasive (good for babies, children, or adults that are unable or unwilling to do conventional hearing tests).

Question 10

What is the clinical significance of Distortion Product OAE (DPOAE)?

Answer 10

DPOAEs are generated from the interaction of two stimulus tones inside the cochlea which produces several new frequency components that can be measured.

DPOAEs indicate that the outer hair cells in the cochlea are working

distortion product = 2f1 – f2

Question 11

Which parts of the brainstem generate the electric responses in BERA?

Answer 11

• Auditory nerve (Waves I & II)
• Superior olivary complex (Wave III)
• Nucleus of lateral lemniscus (Wave IV)
• Inferior colliculus (Wave V)

Question 12

What happens in the BERA test when there is elevated hearing threshold?

Answer 12

The latency can be clinically used to differentiate between types of hearing loss: conductive, sensorineural, or retrocochlear.

Question 13

What does reproducibility in TeOAEs refer to?

Answer 13

It refers to how consistently the emission signal can be reproduced across multiple measurements under the SAME CONDITIONS.

Question 14

What is the relationship between the amplitude of AEP potentials and noise during testing?

Answer 14

The amplitude of the potentials is smaller than the amplitude of noise requiring signal processing strategies to isolate the AEP signal.

Question 15

What non-pathologic problems can cause the absence of OAEs?

Answer 15

Poor probe tip placement, debris in the outer ear canal, amniotic fluid in neonates, an uncooperative patient.

Question 16

What is the primary use of Acoustic Evoked Potentials (AEP) in audiometry?

Answer 16

AEP assesses specific areas of the brainstem, midbrain, and auditory cortices to evaluate the electrical responses of the central nervous system to acoustic stimuli.

Question 17

What is the significance of TEOAE in newborn hearing screening?

Answer 17

TEOAE is a quick non-invasive test to evaluate cochlear hearing in newborns and children who cannot cooperate with conventional tests.

Question 18

What can be observed in BERA for a normal ear?

Answer 18

To determine the threshold, the amplitude of the stimuli is reduced until all waves (especially wave V) disappear.

It can also be observed that the latency of the 5th wave (L-V) increases with decreased stimulation levels.

Question 19

What is the Nyquist-Shannon Sampling Theorem?

Answer 19

It establishes a sufficient condition for a sample rate that allows a discrete sequence of samples to capture all information from a continuous-time signal of finite bandwidth.

Sampling must occur at a rate that is AT LEAST TWICE the highest frequency component.

Question 20

What role do outer hair cells (OHC) play in the generation of OAEs?

Answer 20

OHC amplify sound which results in the stimulation of inner hair cells and the acoustic nerve, and the amplified sound is emitted backwards as otoacoustic emissions.

Question 21

What are the two main types of OAE?

Answer 21

Transient evoked OAE (TeOAE) and Distortion product OAE (DPOAE).

Question 22

What is Brainstem Evoked Response Audiometry (BERA)?

Answer 22

BERA is an objective method to assess the auditory pathway from the cochlea to the brainstem using acoustic stimulation to produce electrical responses.

Acoustic stimulation of the cochlea produces an evoked electrical response in the CNS which can be recorded with scalp electrodes.

The responses should have an unvarying time-delay. The integrity of th eanatomical structures can be identified by the time interval of the generated response

Acoustic stimulation of the cochlea produces an evoked electrical response in the CNS which can be recorded with scalp electrodes.

Question 23

What pathologic problems can cause the absence of OAEs?

Answer 23

• Outer ear: conditions like stenosis or perforation
• Middle ear: conditions such as otosclerosis
• Cochlear exposure to ototoxic medication or noise exposure (e.g. music).

Question 24

What is the significance of objective measurements in audiometry?

Answer 24

They are important because pure tone audiograms may not be feasible in children, especially newborns or in cases of reduced compliance.

Question 25

What indicates that there is likely a NORMAL TEOAE response?

Answer 25

If reproducibility is > 60% or a signal to noise ratio (SNR) > 6 dB. This would indicate that hearing loss is less than 30dB in the frequency range from 1 to 4 kHz.

Question 26

What factors affect the reproducibility of OAE measurements?

Answer 26

Factors include probe fit quality, ambient noise levels, and the health of the outer hair cells.

Question 27

What are Otoacoustic Emissions (OAE)?

Answer 27

OAEs are sounds that arise in the ear canal when the tympanum receives vibrations transmitted backwards through the middle ear from the cochlea.

Question 28

What are the two objective measurements to test hearing?

Answer 28

Otoacoustic Emissions (OAE) and Auditory Evoked Potential (AEP).

Question 29

What indicates that there is likely HEARING LOSS when measuring TEOAE?

Answer 29

If reproducibility is below 60 or the signal-to-noise ratio (SNR) is less than 6 dB it suggests hearing loss greater than 30 dB in the frequency range from 1 to 4 kHz.