Objective Diagnostic Techniques Flashcards
Why do you perform objective diagnostic techniques?
- They provide information to accurately estimate hearing thresholds in difficult to test subjects e.g. babies in the NHSP.
- They can be used to differentiate between the types of hearing loss e.g. conductive or cochlear due to lesions on the auditory nerve.
What is tympanometry?
This measures middle ear pressure and middle ear compliance that help diagnose middle ear pathologies such as glue ear, otosclerosis or hyper-flaccid drum.
What is a tympanogram?
These are the results from a tympanometry measure, presented in a graph. The results are plotted of pressure against middle ear compliance showing a peak at the maximum compliance.
Does a tympanogram estimate someone’s hearing threshold?
No, it doesn’t give hearing threshold information, it provides information on middle ear pathologies.
What are the 3 tubes connected to the tympanometer probe?
- A pump to vary the pressure from positive to negative.
- A loudspeaker to deliver the sound stimulus into the ear.
- A microphone to measure the amount of sound that is reflected back from the ear drum.
What does type As mean on a tympanogram?
This line represents the middle ear pathology otosclerosis, the overgrowth of the spongy bone around the stapes footplate. This increases the middle ear system’s stiffness so low compliance.
What does type A mean on a tympanogram?
Type A is within the normal range and means there is normal hearing function in the middle ear.
What does type Ad on a tympanogram mean?
This indicates a hyper-flaccid ear drum so a very high level of middle ear compliance. This insinuates a moderate conductive hearing loss or ossicular discontinuity because the peak of compliance is above the normal region.
What does type B on a tympanogram mean?
This type indicates glue ear or otitis media with effusion (OME). Because the person’s eustachian tube has been blocked for an extended period of time, their ear drum is heavily pulled inwards. The middle ear cavity is filled with so much fluid that it cannot move so there is very low compliance which explains the flat line on the tympanogram.
What does type C mean on a tympanogram?
Type C is where the peak has shifted to the negative pressure and implies eustachian tube dysfunction. The middle ear cavity already has a negative pressure from the eustachian tube dysfunction so when the tympanometer changes to negative pressure, this is when there is a peak of middle ear compliance as this is when the middle ear cavity and ear canal have equal pressure, on the negative side.
What does OAE stand for?
Otoacoustic Emissions
What are otoacoustic emissions?
OAEs are sounds generated by the cochlear (specifically the OHCs) in response to auditory stimuli. These sounds from the cochlea travel back to the middle ear and into the ear canal where they can be measured with a mini microphone.
What do OAEs aim to measure?
They want to measure an individual’s cochlear health and OHCs function. OAEs disappear if the cochlear has been damaged so if there are no OAEs, this indicates a sensory hearing loss.
How do OAEs work?
A probe containing a mini loudspeaker and microphone is placed into the ear canal. Then 260 broadband clicks are presented using a range of frequencies where the response is picked up by the cochlear and amplified by the microphone. The 260 clicks are averaged by a computer which gives the otoacoustic emissions results.
What do OAEs results tell you?
If there are OAE responses for frequencies between 500-5000H, this tells us the person’s hearing is better than 30dB. However, OAEs don’t tell us specific hearing thresholds, they only tell us if a baby’s hearing is better or worse than 30dB for example.
It is still a useful tool in the hearing screen process because if an individual has absent OAEs, they are sent for further investigation.
What does ABR stand for?
Auditory Brainstem Response
What is an Auditory Brainstem Response?
This is a way to measure the electrical activity along the auditory pathway in the first 10ms following a sound stimulus. The response of the 5 wave forms represents electrical activity from the auditory nerve action potential (wave I) to the inferior colliculus nerve (wave V).
What number of decibels needs to be used to generate a typical ABR?
90dB.
What is the ABR procedure?
Electrodes or sensors are placed behind the left and right ear love and the midline of someone’s head and up to 1024 broadband clicks are presented as the sound stimulus. The electrodes pick up the neural response which is amplified, filtered and then averaged by a computer.
How do you use an ABR to measure hearing threshold?
The stimulus intensity is decreased (reduction of decibels) and the test is repeated until no trace of waveform V is seen. The threshold is taken from the lowest stimulus level where wave V was apparent. For normal hearing, the threshold is traced down to 0dB.
What is the cross check principle?
The cross check principle is the idea that we take the results from our behavioural hearing tests and marry them with our objective hearing tests to form an overall auditory diagnosis.
The cross check principle isn’t used for every child but for the babies who fail the newborn screening programme.
What is screening?
Screening is a national programme to identify hearing loss as early as possible. It consists of two tests to identify any hearing loss levels for newborn babies.
What is the purpose of the NHS Newborn Hearing Screening Programme? (NHSP)
- You want to find the children who have a level of hearing loss to refer for further investigation so the screening process needs to be sensitive to this and specific so you aren’t referring children who don’t have issues with their hearing when they don’t need further investigation.
- Early identification contributes to early intervention which will give better outcomes for the child.
- Gives children a better chance of developing speech and language skills plus able to engage in social and emotional interactions.
- Gives them more accurate diagnoses, including the causality, type and degree of loss.
- Informs parental guidance and professional planning.
What are the 2 screening protocols used in this programme?
The automated OAE is usually carried out within 1-2 days of the baby being born. If they fail the AOAE, another 1-2 days later this test is repeated. If they fail it again, they will then have an automated ABR test.
