Audiometry

Question 1

What is pure tone audiometry?

Answer 1

Most common method used to assess hearing loss, determines it’s type and severity

Question 2

Describe how audiometry is performed?

Answer 2

Sounds are played at a range of frequencies (from 250-8,000). Initial the sound is played above threshold and this is decreased in 10db increments until the sound can no longer be heard. This then plots the point on the graph at which the frequency can no longer be heard.

Question 3

How are bone and air conduction assessed with pure tone audiometry?

Answer 3

Air conduction is assessed using headphones

Bone conduction is assessed through a transducer placed over the mastoid process

Question 4

What are the axis of a pure-tone audiometry graph?

Answer 4

X Axis- Frequency of sounds

Y Axis- Decibel hearing level (dBHL)

Question 5

What must the test environment be like for pure tone audiometry?

Answer 5

Background noise must be kept to a minimum, it is therefore often done in sound proof rooms

Question 6

What does the patient do during a pure tone audiometry test?

Answer 6

Listens to the sound and presses the button when they hear the sound, if they don’t press the button it indicated that they have not heard the sound.

Question 7

Which patients might pure-tone audiometry not be suitable for?

Answer 7

Patients with cognitive deficits as the patient has an active role and must press the button when they hear the sound. If they don’t understand this the test can’t be done.

Question 8

What can be a cause of false negatives in a pure tone audiometry test? What false impression does this give?

Answer 8

Patient fails to indicate that they have heard the sound, e.g. didn’t understand instruction or cognitive deficits. Gives the impression that hearing is much worse than it actually is.

Question 9

What can be a cause of false positives in a pure tone audiogram? What impression does this give?

Answer 9

Patient clicks the button for sounds they haven’t heard or haven’t been played. Could suggest that hearing is better than it really is.

Question 10

What is normal range dBHL?

Answer 10

-10 to 20 (this is a deviation from the norma). It is shown by a horizontal line on the graph.

In this range a person can understand speech in a normal environment and there is no amplification needed. Below this there is deficit in hearing and amplification may be required.

Question 11

What is suggested if the line for bone conduction is greater than the line for air conduction?

Answer 11

This suggests there is conductive hearing loss

Question 12

What are the findings for Rinne’s and Webbers and pure tone audiometry for conductive hearing loss?

Answer 12

Webbers localises to the affected side

Rinne’s Bone conduction is louder than air conduction.

Pure tone audiometry- bone conduction line is above the air conduction line.

Question 13

What are the findings for Rinnes and Webbers and Pure tone Audiometry for sensorineural hearing loss?

Answer 13

Rinne’s- Air conduction is greater than bone conduction (this is also a normal sign as bone conducts better than air)

Webber’s sound localises to the contralateral ear.

Pure tone audiometry- both air and bone conduction decline towards higher frequencies

Question 14

What are the findings for conductive hearing loss on pure tone audiometry?

Answer 14

Bone conduction is normal

Air conduction is reduced

For conductive hearing loss air conduction must be at least 10db less than bone conduction. This is called the air-bone gap.

Question 15

What must the difference be between bone conduction and air conduction in conductive hearing loss? What is this difference called?

Answer 15

At least 10db- air conduction should be atleast 10db less than bone conduction

This is called the AB gap.

Question 16

What are some causes of conductive deafness?

Answer 16

Obstruction of auditory canal- wax, foreign body, tumour, auditory exostosis

Tympanic membrane issues- perforation, sclerosis

Ossicle dysfunction- otosclerosis, trauma, erosion following infection

Question 17

What are the findings for sensorineural hearing loss on pure-tone audiometry?

Answer 17

Deficits in both air and bone conduction are seen and decreases are seen at higher frequencies.

Question 18

What are some causes of sensorineural hearing loss?

Answer 18

Labyrinthitis
Trauma
Acoustic neuroma- sudden onset unilateral sensorineural hearing loss.
Presbycusis- normal sensorineural hearing loss that occurs with age (most common cause of hearing loss)
Drugs
Systemic disease- DM, Hypothyroidism, Autoimmune disease, MS

Question 19

What is the purpose of impedance audiograms?

Answer 19

Impedance audiograms allow the conduction of the tympanic membrane and ossicles to be assessed. Therefore allows for assessment of middle ear status.

Question 20

When are impedance audio-grams indicated?

Answer 20

Impedance audiograms are indicated when there is conductive hearing loss

Question 21

How are impedance audiograms carried out?

Answer 21

A probe is inserted into the ear which alters the pressure. Pressure is changed from negative, to neutral to positive. The probe emits a tone at a steady intensity and a microphone listens for the tone that bounces back. A compliant tympanic membrane causes less sound to bounce back most, if compliance reduces less sound bounces back.

Question 22

When is the tympanic membrane most compliant?

Answer 22

The tympanic membrane is most compliant when the pressures either side of it are equal

Question 23

How can impedance audiometry/tympanometry be used to estimate pressures in the middle ear?

Answer 23

The tympanic membrane is most compliant when the pressures either side of it are equal. When it’s at its most compliant the tympanic membrane reflects the least amount of sound.

Question 24

Why is less sound bounces back there is increased compliance of the conduction system but more when there is reduced compliance?

Answer 24

The sound energy is converted into kinetic energy when there is conduction, and therefore compliance is at its greatest.

When there is reduced compliance there is reduced conversion to kinetic energy and the sound bounces back- it is picked up by the microphone on the probe.

Question 25

What is indicated by the least amount of sound bouncing back to the probe for impedeence audiometry?

Answer 25

This is when the tympanic membrane is at it’s most compliant

Question 26

What does a normal impedance audiogram look like?

Answer 26

Compliance is at it’s greatest when there is ambient pressure (as the eustachian tube equalises pressure in the middle ear). This is called a type A tympanogram

Question 27

What does a type B tympanogram indicate?

Answer 27

Restricted tympanic membrane mobility- there is little or no point of maximum motility- typical of a stiff middle ear as occurs with otitis media.

(The graph consistently has reduced motility)

Question 28

What does a type C tympanogram indicate?

Answer 28

Significant negative pressures in the middle ear (as greatest conduction are seen in seen at lower pressures). Can occur with sinusitis or URTI, resolving otitis media.

Question 29

What does a type As tympanogram indicate?

Answer 29

There is a reduced peak height but it is when the pressure is 0. This occurs with sclerosis of the tympanic membrane or otosclerosis.

Question 30

What does a type Ad tympanogram indicate?

Answer 30

Normal middle ear pressures but hypermobility- the peak is higher than normal but occurs at 0 pressure. This can occur with a flaccid tympanic membrane- may be due to diastriculation of the ossicles.