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
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 (bone conductor)?
30 dB
How does masking attempt to overcome cross hearing?
Introduction of a narrow band noise at an appropriate frequency in the non-test ear temporarily elevates the threshold of the non-test ear and allows us to obtain an accurate threshold of the test ear
What is rule 1 of masking?
Masking is needed at any frequency where the difference between the left and right non-masked air conduction thresholds is 40 dB or more when using supra- or circum- aural headphones or 55 dB or more using insert earphones
Explain why masking is needed in this example
-The non test ear is within normal range
-Anywhere where the difference in threshold between test ear and the non-test ear is greater than 40 dB cross-hearing may have occurred so the non-test ear has to be distracted through masking and the test ear re-tested
What are the two possible outcomes of masking?
-No change in threshold
-Threshold in the test ear changes once the non test ear is sufficiently distracted
-The threshold can only worsen, it will never get better
What is the ‘shadow curve’?
-The shadow curve reflects some hearing on the non-test ear
-It remains on the audiogram along with the true masked thresholds of the test ear
How is the masking level determined?
The masking level begins at the threshold of the non-test ear and increases by 10 dB until a plateau is established
What is the onward referral criteria for pure tone audiometry?
- Conductive hearing loss- 20 dB or greater average air-bone gap over three of the following frequencies: 500, 1000, 2000, 3000 or 4000 Hz
- Unilateral or asymmetrical sensorineural hearing loss- 20 dB or greater difference between the left and right bone conduction at two or more adjacent frequencies: 500, 1000, 2000, 4000 or 8000 Hz
- Evidence of deterioration of hearing compared with an audiogram taken in the last 24 months- has to be a deterioration of 15 dB or more in bone conduction thresholds at two or more frequencies: 500, 1000, 2000, 3000 or 4000 Hz
What is the second rule of masking?
Masking is needed at any frequency where the not-masked bone conduction threshold is better than the air conduction threshold of either ear by 10 dB or more
Describe the transducer placement for BC masking
-Both the bone transducer and the air conduction headphones used
-One of the headphones is placed on the better hearing ear and the other headphone is placed on the side of the patient’s head
-The bone conductor is placed on the patient’s poorer ear
Would we need to do masking in this example? What kind and according to which rule?
-On the left we have a mild to moderate hearing loss with normal bone conduction
-We suspect that the bone conduction reflects the right ear so we need to do bone conduction masking according to rule 2 (more than 10 dB difference between air and bone conduction)
Describe the hearing loss in this audiogram
Sensorineural hearing loss in the left ear, normal hearing in the right
Would we need to do masking in this example? What kind and according to which rule?
We need to do bone conduction masking according to rule 2 because there is a gap between bone and air conduction of more than 10 dB
Describe the hearing loss in this audiogram
Sloping mild to moderate sensorineural hearing loss on the right and moderate sensorineural hearing loss on the left
What happens if the bone conduction thresholds don’t change following masking?
-If the bone conduction threshold with masking is more than 10 dB worse than the not-masked bone conduction threshold then we can attribute the not-masked threshold to the other ear
-However if it is not more than 10 dB worse than the not-masked bone conduction it is possible that the not-masked bone conduction threshold was indeed from the test ear, and it may be necessary to test the bone conduction thresholds of the other ear with masking
Would we need to do masking in this example? What kind and according to which rule?
We can tell there is a conductive hearing loss on at least one ear but we can’t tell which ear it is from so we need to carry out bone conduction masking according to rule 2
Describe the hearing loss shown on this audiogram
Conductive hearing loss on the left, sensorineural hearing loss on the right
Describe the hearing loss shown on this audiogram
Bilateral conductive hearing loss
What is rule 3 of masking?
-Rule 1 has not been applied
-There is a 40 dB (headphones) or 55 dB (inserts) gap between the bone conduction threshold of one ear and the not-masked air conduction threshold of the other ear
Why is rule 3 necessary?
The air conduction frequencies that do not require masking under rule 1 may need to be masked if the bone conduction results show that the non-test ear has a conductive element
Would we need to do masking in this example? What kind and according to which rule?
Since the difference between the bone conduction and air conduction on the left ear is greater than 10 dB we would need to do bone conduction masking according to rule 2
Describe this audiogram. Is it complete?
-On the left we have a profound sensorineural hearing loss
-No rule 1 masking was needed because there was not a difference of 40 dB or more between the left and right air conduction
-However there is a big gap (40 dB or greater) between the not masked and masked bone conduction on the left side which means that doubt exists at the frequencies were bone conduction has not measured
-Therefore we apply masking to the right ear and test the left ear again at the frequencies that bone conduction was not done at (500 Hz and 8000 Hz)
What is overmasking?
When the masking sound is so loud that it is heard by the test ear
In what circumstances does cross masking/ overmasking occur?
-When there is a significant hearing loss in the non-test ear
-Conductive hearing loss in the test ear
What is peripheral masking?
-When the masking sound is heard by the test ear
-This is a cochlear phenomenon (peripheral auditory system)
-Slope is 1 dB per dB before the plateau- linear slope upwards is observed
What is central masking?
-The brain is unable to identify the tone in the presence of masking even if the tone and the noise are heard in opposite ears
-Masking is occurring centrally in the brain and not peripherally in the cochlea
-For every 10 dB increase in masking the apparent threshold is raised by 5 dB
-This is most common at high levels of masking and results in an inability to reach plateau
Describe the hearing loss presented on this audiogram. Is anything missing?
Normal hearing
Describe the hearing loss presented on this audiogram. Is anything missing?
Mild to moderate sensorineural sloping hearing loss bilaterally. Nothing is missing.
Describe the hearing loss presented on this audiogram. Is anything missing?
Moderate flat sensorineural hearing loss. Nothing missing.
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral severe to profound hearing loss. Bone conduction is missing so unknown type.
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral mild to severe steeply sloping hearing loss. Nothing is missing
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral reverse slope mild to moderate sensorineural hearing loss. Nothing missing.
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral mild hearing loss. Bone conduction missing so type unknown
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral moderate to profound hearing loss. Bone conduction missing so type unknown.
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral mild to profound steeply sloping hearing loss. Bone conduction missing so type unknown.
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral mild to moderate sensorineural hearing loss (cookie bite- often associated with congenital hearing loss).
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral mild to moderate reverse slope symmetrical sensorineural hearing loss. Nothing missing
Describe the hearing loss presented on this audiogram. Is anything missing?
Bilateral profound hearing loss (for some frequencies no response even at the maximum of the audiometer). Type unknown because bone conduction is missing
Describe the hearing loss presented on this audiogram. Is anything missing?
Hearing with normal limits on the left, mild to moderate hearing loss on the right. Bone conduction is missing so type unknown.
Describe the hearing loss presented on this audiogram. What would you do next?
-Hearing within normal limits on the right, moderate hearing loss on the left
-Carry out air conduction masking according to rule 1 for all frequencies except 250 Hz as gap between left and right is more than 40 dB
-Then carry out bone conduction and place the transducer on the right ear
Describe the hearing loss presented in this audiogram. What would you do next?
-Mild hearing loss on the right, mild to profound hearing loss on the left
-Need to carry out air conduction masking according to rule 1 for frequencies 2 kHz onwards since the difference between left and right ear is greater than 40 dB
-Can test intermediate frequencies at 1500 Hz and 700 Hz to define drop better
-Do bone conduction- transducer placed on the left ear
Describe the hearing loss presented on the audiogram. What would you do next?
-Profound hearing loss on the right, mild to moderate reverse slope hearing loss on the left
-Need to do air conduction masking according to rule 1 for frequencies of 1 kHz onawards as the gap between the left and right ear is greater than 40 dB
-Carry out bone conduction- place the transducer on the right ear
Describe the hearing loss presented on the audiogram. What would you do next?
-Normal hearing on the right, moderate hearing loss on the left
-Carry out air conduction masking according to rule 1 for all frequencies as the difference between the left and right is greater than 55 dB (insert earphones were used)
-Then carry out bone conduction by placing the transducer on the left ear
Describe the hearing loss presented on this audiogram. What would you do next?
-Mild hearing loss on the left, moderate to severe hearing loss on the right
-Carry out air conduction masking according to rule 1 for frequencies at 2 kHz onwards as the difference between the left and right ear is greater than 55 dB (insert earphones were used)
-Do bone conduction by placing the transducer on the right ear
Describe the hearing loss presented on this audiogram. What masking has been done so far?
-Normal hearing on the left, moderate to severe hearing loss on the right
-Air conduction masking has been carried out for frequencies of 500 Hz onwards
-The filled in circles are the shadow curve- not the true hearing thresholds
Describe the hearing loss presented on this audiogram. What masking has been carried out so far?
-Normal hearing on the right, moderate to severe hearing loss on the left
-Air conduction masking has been carried out for frequencies 1 kHz onwards and shadow curve present- thresholds changed
-Bone conduction has been carried out but we don’t know which ear it is applicable to so bone conduction masking needs to be done
Describe the hearing loss presented on this audiogram. What is missing?
-Normal hearing on the right, mild hearing loss on the left
-Bone conduction masking according to rule 2 is missing
Describe the hearing loss presented on the audiogram. Is anything missing?
-Mild sensorineural hearing loss on the left and moderate hearing loss on the right
-Missing masked bone conduction according to rule 2
Describe the hearing loss presented on the audiogram. What masking has been carried out so far? What would you do next?
-Hearing within normal limits on the right, mild to severe sloping hearing loss on the left
-So far masked air conduction according to rule 1 has been carried out
-Still need to carry out masked bone conduction according to rule 2
Describe the hearing loss presented on this audiogram. What masking has been carried out so far? What would you do next?
-Mild hearing loss on the right, moderate to severe hearing loss on the left
-No masking has been carried out so far
-Need to do air conduction masking at frequencies of 2 kHz, 4 and 8 kHz
-Then need to carry out bone conduction
Describe the hearing loss presented in this audiogram. What masking has been carried out so far? What would you do next?
-Moderate to severe sloping hearing loss on the right, mild hearing loss on the left
-No masking has been carried out so far
-Air conduction masking needs to be carried out according to rule 1 or 2, 4 and 8 kHz
-Then carry out bone conduction
Describe the hearing loss presented in this audiogram. Is anything missing?
-Bilateral moderate hearing loss with at least one ear having a conductive hearing loss
-Need to carry out masked bone conduction
Describe the hearing loss presented in this audiogram. What masking has been carried out so far? What would you do next?
-Mild hearing loss on the right, moderate hearing loss on the left
-Bone conduction masking has already been carried out
-Need to do bone conduction on the right and air conduction masking according to rule 3
Describe the hearing loss presented in this audiogram. What masking has already been carried out? What would you need to do next?
-Bilateral mild to moderate hearing loss
-Bone conduction masking according to rule 2 has already been carried out- the right ear has mixed hearing loss as the bone conduction is better than the air conduction but not within the normal range
-Need to carry out masked bone conduction on the left
Describe the hearing loss presented in this audiogram. What masking has been carried out so far? What would you need to do next?
-Mild hearing loss on the left, moderate to severe sloping hearing loss on the right
-Air conduction masking according to rule 1 has been carried out for frequencies of 4 and 8 kHz on the right
-Bone conduction masking according to rule 2 has also been carried out- mild conductive hearing loss on the right
-Need to do air conduction masking according to rule 3 for 1 and 2 kHz on the left as big difference between bone conduction of the right ear and the air conduction of the left
Describe the hearing loss presented on the audiogram. What masking has been carried out so far? What would you need to do next?
-Mild to moderate hearing loss on the left, severe hearing loss on the right
-Air conduction masking has been carried out according to rule 1 at 8 kHz for the right ear
-Bone conduction masking according to rule 2 has also been carried out on the right ear
-Need to do masking according to rule 3 for all frequencies for the left ear as there is a big gap between the bone conduction threshold of the left ear and the air conduction threshold of the right ear
Describe this audiogram. Which condition could be associated with it?
-Mild to moderate sensorineural sloping hearing loss bilaterally
-Characteristic of presbycusis if the patient is older
Describe this audiogram. Which condition could be associated with it?
-Mild to moderate bilateral conductive hearing loss
-Could be associated with an obstruction in the outer ear such as occluding wax
Describe this audiogram. Which condition could be associated with it?
-Mild to moderate bilateral mixed hearing loss
-2000 Hz Carhart notch in bone conduction characteristic sign of otosclerosis
Describe this audiogram. Which condition could be associated with it?
-Moderate bilateral hearing loss- most likely conductive
-Masked bone conduction unable to reach masking plateau- crossmasking
-This is indicative of a bilateral conductive hearing loss e.g. tympanic membrane perforation
Describe this audiogram. Which condition could be associated with it?
-Hearing within normal limits on the right
-Sloping moderate to severe hearing loss on the left
-Bone conduction abnormal- sensorineural hearing loss
-Could be a problem with the cochlea or the VIIIth nerve
Describe this audiogram. Which condition could be associated with it?
-Hearing within normal limits on the right
-Bone conduction normal for both ears
-Unilateral moderate conductive hearing loss on the left
-Caused by something like a unilateral glomus tumour
Describe this audiogram. Which condition could be associated with it?
-Sensorineural bilateral moderate hearing loss at 4 kHz (notch)
-Characteristic of noise-induced hearing loss
Describe this audiogram. Which condition could be associated with it?
-Normal bone conduction and hearing within normal limits on the right
-Mild to moderate conductive hearing loss on the left
-Could be caused by something like otitis media with effusion
Describe this audiogram. Which condition could be associated with it?
-Mild to moderate sensorineural sloping hearing loss on the right
-Moderate to severe mixed hearing loss on the left
-Indicative of presbycusis bilaterally with a conductive overlap on the left
Describe this audiogram. Which condition could be associated with it?
-Hearing within normal limits on the right
-Unilateral mild to severe sloping sensorineural hearing loss on the left
-Rule 1 and 2 of masking have been carried out
-Problem could be in the cochlea or further up the auditory pathway
Describe this audiogram.
Hearing within normal limits bilaterally
Describe this audiogram. Which condition could be associated with it?
-Mild to moderate reverse slope sensorineural hearing loss on the right
-Hearing within normal limits on the left
-Problem with the cochlea or further up the audiotory pathway
