Pure Tone Audiometry Flashcards
Equipment, recommended procedures, recording and interpreting results, masking for bone and air conduction, limitations
What is pure tone audiometry (PTA)?
A behavioural, subjective hearing assessment method
-Patients press a button when they can hear a sound
-Used to identify hearing threshold levels at different frequencies
-Measuring the quietest sound someone can hear at each frequency
What is PTA used for?
To determine the degree, type and configuration of hearing loss
What are the PTA test results plotted on?
An audiogram
What two things need to be carried out before PTA?
Thorough clinical history and otoscopy
What frequencies of sound does PTA test?
250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz
What types of transducers can be used to present the pure tone stimuli?
-Headphones (over the ear or insert0
-Bone conductor
What is air conduction?
-The conduction of sound waves to the organ of hearing in the inner ear through the air
-Carried out first in PTA
Name the three types of air conduction transducers
- Supra-aural headphones
- Circum-aural headphones
- Insert earphones
What are supra-aural headphones?
-Commonly used
-Rest on the ear but do not fully enclose it
What are circum-aural headphones?
-Surround and cover the entire ear
-Good at sound isolation
What are insert earphones?
-Disposable foam tip is attached to direct sound to the ear canal
-May not be suitable for ears with infection or obstruction
-If a patient has excessive wax the insert earphones could push the wax further in
What is bone conduction?
-Conduction of sound to the inner ear through the bones of the skull
-Occurs as sound waves vibrate the skull
-Cochlea is embedded into the mastoid bone
-Bone conduction audiometry is carried out at specified frequencies after air conduction audiometry
What is a bone conductor?
-Bone conduction oscillator placed on the mastoid bone behind the pinna
-Directly stimulates the inner ear and bypasses the outer and middle ear
What is considered normal hearing?
20 dB HL or better (lower)
What is considered mild hearing loss?
21-40 dB HL
What is considered moderate hearing loss?
41-70 dB HL
What is considered severe hearing loss?
71-95 dB HL
What is considered profound hearing loss?
In excess of 95 dB HL
What are key elements of PTA?
- Calibration- stage A checks carried out to ensure there are no issues with the equipment which may impact accurate testing
- Instructions- PTA is a subjective test so the patient must be given precise instructions
- Frequencies are tested in a specific order (test-retest reliability)
- The duration of each pure tone presentation should vary between 1-3 seconds to avoid false positive responses
- 10 down 5 up method used to find hearing threshold at each frequency
What is the hearing threshold?
The lowest level at which responses occur in at least half of a series of ascending trials with a minimum of two responses required at that level
Describe this PTA result
-The results for air and bone conduction are similar
-Therefore we can conclude that this is a sensorineural hearing loss
Describe this PTA result
-The air conduction and bone conduction values are separated by more than 10 dB HL
-Conductive hearing loss in at least one ear since the bone conduction is in the normal range
Why is it not possible for bone conduction to be worse than air conduction?
Air conduction tests the entire auditory system but the bone conduction only tests the inner ear function
What are the limitations of PTA?
- Relationship between PTA thresholds and speech in noise perception- PTA does not reflect the real world and poorly predicts people’s speech in noise abilities
- Bone conduction at 3 and 4 kHz is not typically done- can miss asymmetrical sensorineural hearing loss, identifying collapsing external auditory meatus, identifying a Carhart notch at 2 kHz and providing information for hearing aid fittings with a conductive loss
- Vibrotactile responses with bone conduction can occur as low as 25 dB at 250 Hz and can also occur at frequencies 500 Hz and above especially at high hearing levels
- Placement of bone conductor on the poorer ear- we assume that the inter-aural attenuation of the bone conductor is 0 dB but it could be up to 15 dB at 4 kHz, it may also be uncomfortable for the patient to have the bone conductor on one side for bone conduction and masking
- Limitations of the speech banana
- Test-retest variability
What is the purpose of audiometer calibration?
To ensure the audiometer is functioning correctly
How many calibration stages are there?
3- stage A, stage B and stage C
What are stage A checks? How often are they carried out?
-Stage A checks are carried out every day before the patient testing begins
-Carried out by or with someone with normal hearing thresholds as you need to listen to the audiometer’s production of very low level sounds
-Make sure the audiometer is producing tones at low and high sound levels with no distortion and that all equipment such as the transducers and response button are working properly
What are stage B checks? How often are they carried out?
-Stage B checks are carried out every 3 months and not less than every 12 months
-Performed by an external company
-Measure and compare frequencies of test signals, sound pressure levels in an acoustic coupler or artificial ear from earphones, vibratory force levels on a mechanical coupler from bone vibrators, levels of masking noise, attenuator steps over a significant part of the range, harmonic distortion
What are stage C checks? How often are they carried out?
-Only required if a serious fault is identified or if the equipment is not performing to specification
-Usually performed by an external company
-Assess all things included in stage B checks plus rise and fall times of test tones, interrupter effectiveness, cross-talk between transducers and channels, masking noise spectra, distortion of speech and other external input systems
What is a programmable ventriculo-peritoneal (PVP) shunt? How does it affect audiological testing?
-PVP shunts are inserted into the ventricle of the brain surgically to drain excess cerebrospinal fluid
-They have a magnetically adjustable valve often near or on the mastoid bone which can be externally activated and change the person’s intracranial pressure which could be life threatening
-A lot of audiological equipment emits an external magnetic field and must therefore be kept at least 5cm away from the PVP shunt
How does the PVP shunt affect PTA?
-Ear inserts can be used but a cautious approach is recommended
-Bone conduction can only be performed on the ear contralateral to the PVP shunt
-If a transducer ends up being placed too close to the shunt inform the patient there is a possibility the shunt settings may have been affected and common symptoms of PVP shunt malfunction (vomiting with little or no nausea, constant headache, vision problems, irritability, fatigue, loss of balance, swelling and redness along the shunt path)
What is cross hearing?
-Cross hearing refers to circumstances where the sound being presented to one ear is not actually detected by the intended (test) ear
-When the volume has to be turned up very high, it is possible that when testing the worse ear the better (non-test) ear is actually detecting the sound as it leaks out of the headphones
Is cross hearing more of a problem with air or bone conduction?
-During air conduction testing the non-test ear is typically covered so the air conduction pathway is minimised
-Cross hearing during air conduction is primarily a bone conduction mechanism (the headphones are acting as a bone conductor)
What is interaural attenuation?
The amount of sound which is reduced or attenuated when crossing from one ear to the other
What does interaural attenuation depend on?
- Subject variability (thickness of the skull- how much is needed to rattle it)
- Type of transducer
- Frequency of the pure tone
Why does the type of transducer matter for interaural attenuation?
It takes less intensity to “rattle the skull” with the supra-aural and circum-aural headphones compared to the insert earphones because of where the speaker is housed and the surface area of the headphone
What is the interaural attenuation for supra-aural headphones?
-40 dB
-This means that if the threshold of one ear is 0 dB HL, we would be worried about cross-hearing at sound presentations of 40 dB HL on the other ear
What is the interaural attenuation for insert earphones?
-55 dB
-This means that when the threshold of the non-test ear is 0 dB HL, we would be worried about cross-hearing when presenting sound in the test ear at 55 dB or louder
What is masking?
-The technique of isolating the test ear to distract it so that the results obtained are the true thresholds of the test ear
What are the definitions for non-test ear and test ear in terms of masking?
Non-test ear: The ear to be masked
Test ear: The ear to be presented by presentation of pure tones
If the threshold of the left ear is 0 dB HL, at what level of sound presentation on the right would we become worried about cross hearing (supra-aural headphones)?
40 dB
If the threshold of the left ear is 50 dB HL, at what level of sound presentation on the right would we become worried about cross hearing (supra-aural headphones)?
90 dB
If the threshold of the left ear is 0 dB HL, at what level of sound presentation on the right would we become worried about cross hearing (insert earphones)?
55 dB
If the threshold of the left ear is 30 dB HL, at what level of sound presentation on the right would we become worried about cross hearing (insert earphones)?
85 dB
What is the interaural attenuation for bone conduction?
-0 dB
-Crossing over of the stimulus may always occur no matter where on the skull you place the bone conductor
-Even if the patient has profound hearing loss on one ear and normal hearing on the other you will get a normal result because the skull is fused together and the sound automatically goes to your better-hearing cochlea