Audiometry Flashcards
What is pure tone audiometry?
Most common method used to assess hearing loss, determines it’s type and severity
Describe how audiometry is performed?
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.
How are bone and air conduction assessed with pure tone audiometry?
Air conduction is assessed using headphones
Bone conduction is assessed through a transducer placed over the mastoid process
What are the axis of a pure-tone audiometry graph?
X Axis- Frequency of sounds
Y Axis- Decibel hearing level (dBHL)
What must the test environment be like for pure tone audiometry?
Background noise must be kept to a minimum, it is therefore often done in sound proof rooms
What does the patient do during a pure tone audiometry test?
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.
Which patients might pure-tone audiometry not be suitable for?
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.
What can be a cause of false negatives in a pure tone audiometry test? What false impression does this give?
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.
What can be a cause of false positives in a pure tone audiogram? What impression does this give?
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.
What is normal range dBHL?
-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.
What is suggested if the line for bone conduction is greater than the line for air conduction?
This suggests there is conductive hearing loss
What are the findings for Rinne’s and Webbers and pure tone audiometry for conductive hearing loss?
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.
What are the findings for Rinnes and Webbers and Pure tone Audiometry for sensorineural hearing loss?
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
What are the findings for conductive hearing loss on pure tone audiometry?
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.
What must the difference be between bone conduction and air conduction in conductive hearing loss? What is this difference called?
At least 10db- air conduction should be atleast 10db less than bone conduction
This is called the AB gap.
What are some causes of conductive deafness?
Obstruction of auditory canal- wax, foreign body, tumour, auditory exostosis
Tympanic membrane issues- perforation, sclerosis
Ossicle dysfunction- otosclerosis, trauma, erosion following infection
What are the findings for sensorineural hearing loss on pure-tone audiometry?
Deficits in both air and bone conduction are seen and decreases are seen at higher frequencies.
What are some causes of sensorineural hearing loss?
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
What is the purpose of impedance audiograms?
Impedance audiograms allow the conduction of the tympanic membrane and ossicles to be assessed. Therefore allows for assessment of middle ear status.
When are impedance audio-grams indicated?
Impedance audiograms are indicated when there is conductive hearing loss
How are impedance audiograms carried out?
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.
When is the tympanic membrane most compliant?
The tympanic membrane is most compliant when the pressures either side of it are equal
How can impedance audiometry/tympanometry be used to estimate pressures in the middle ear?
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.
Why is less sound bounces back there is increased compliance of the conduction system but more when there is reduced compliance?
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.
