Lecture 12 Flashcards
What are some advantages of physiological assessments?
Don’t require active cooperation or cognitive ability
Are not affected by patient attention or motivation
Are objective
Are reliable and repeatable
Can help narrow down site of lesion
Can be fast
What do acoustic immittance measures do?
What are they affected by most?
Set of objective measures of middle ear function
Based on how energy flows through the OF and ME
Determined by the acoustic and mechanical properties of the OE and ME
Affected by mass and stiffness of TM, ossicles, stapes footplate in cochlea
What are mass and stiffness of the ear related to?
Air pressure in ME relative to outside the ear - ET function
Ability of the TM to move optimally:
- Fluid in the ME, status of the TM (normal, perforated, tense, floppy, retracted)
- Status of the ossicles (normal to malformed; too stiffly or too loosely connected)
Pressure of cochlear fluid on the stapes (entire chain may become stiff)
When measuring acoustic immittance with an immittance meter or ME analyzer, what 3 components does the probe unit have?
- Mini loudspeaker to produce a probe tone
- Microphone to measure the SPL of the reflected energy
- Air pressure pump to change the pressure in the canal
What does the probe do in acoustic immittance?
Sends a signal (226Hz), seeing how much is bouncing back - how much its’ making through into middle ear system
Reflex - measuring bounce back too, seeing if that changes - stapedius muscle, how much is reflected back
Changing pressure in ear canal
Measuring reflected back on TM
In the acoustic reflex, what does the middle ear do, the stapedius muscle, and the muscle contraction?
What is the role of the probe?
Middle ear muscle contraction which is elicited by fairly loud sounds
Primary muscle involved is the stapedius muscle - attached to the neck of the stapes
The muscle contraction pulls on the ossicular chain, therefore momentarily decreases the ME admittance
Measured with probe - where muscle is pulling, if it increases impedance of ME system - why you see decrease able to move a certain amount, decreases then reflects less sound back
What are otoacoustic emissions?
Low intensity sounds generated by action of the OHC, measurable as they emanate into the outer ear canal.
Where do the emitted sounds come from in the OAE?
Nonlinear systems: add spectral components not in original input
Movement of OHC’s cause distortions in the BM and lead to sound production
How common are spontaneous OAE’s?
Present in about half of normal-hearing ears
What two tests can elicit OAE’s?
Click train - transient evoked, showing response of entire BM. (BBN - use tones for frequency responses)
2 tones close in f - distortion product, showing response at 2f1-f2 (results in a third tone). This is close to f2.
- two tones introduced, it creates reaction on 3rd spot on BM - which is a shorter, more readable sound that can be measured. Can change which frequencies are put in to see different areas of BM and OHC
What information do OAE add?
Knowing whether or not something is conductive
Differentiate between cochlear/retrocochlear
Adds more to diagnostic picture
Knowing something without doing anything more - that loss isn’t more than 30dB
Frequencies below 1000Hz - noise more with low frequency - noise obscures measure more
What are DPOAE’s present and absent in?
What frequencies are hard to assess?
Present in: Normal ears, ears with cochlear hearing loss up to about 30dBHL (TEOAE’s) or 50dBHL (DPOAE’s)
Absent in: ears with cochlear loss > above-noted levels, ears with conductive loss
Frequencies below 1kHz are hard to assess
What is an important thing for the client to do while doing a DPOAE?
Quiet subject - responses are very small amplitude and not visible in noise
What can TEOAE tell us?
About hearing loss, lack of hearing loss it if works, don’t get it, can’t tell if it’s conductive, noise…
What is seen on a graph of a DPOAE?
Trace will follow shape of someone’s loss - look at hearing frequencies of loss for individual
Want response above noise (anything obscuring response); if in noise, can’t tell if its’ OHC problem…
What things do you have to consider for these types of tests?
Useful for infant evaluation
Useful for adult evaluation
Provide site of lesion information
Measure hearing - give binary continuum, person can hear better or worse than a certain dB level
What are auditory evoked potentials?
What are things you have to consider with these tests?
Changes in neural activity in response to a sound stimulus - i.e., a change in electrical activity of the brainstem and brain
Exist from the VIII nerve up to the cortex
Are small voltage; many responses must be added together to see a response come out of the brain’s background electrical activity
Put signal in over and over many times, machine looks for responses - noise pretty random, end up reducing it…response should get bigger.
What are some indicators on the graph of an AEP?
Higher is more cortical, how brain is attending to different sounds based on what it looks like.
Need to look at wave 1, 3, 5
ABR: if the auditory brainstem is getting the sound; tells threshold and diagnostic info if it’s working the way its supposed to
What is an auditory brainstem response?
Is an auditory evoked potential
Neural activity occurs in the adult brainstem 2-10 (sound to cochlea and nerve) msec after auditory stimulation, in a systematic pattern, or morphology
The ABR reflects activity from the VIII to the IC
Tells a lot if the 8th nerve is working
Why would you want to know the 8th nerve is working? From an ABR…
Ruling out that there is something going on along the auditory nerve - if it is cochlear/retrocochlear - if there is an acoustic neuroma/schwannoma
If getting a response, you know sound is going through to the auditory nerve - you know that peripheral auditory system is at least travelling through.
Can be used for threshold searches - at what level you get ABR - adults or children - not getting subjective results - maybe too young, want level of hearing loss.
What is the procedure of an ABR?
Put electrodes on mastoid, vertex, earphones. Present 2000 stimuli, add them together
Noise ideally gets reduced, response should increase
Average the electrical responses from the electrodes on the subject’s head
Replicate responses at least twice, to make sure the tune presence of a response - if wave looks the same
What do you look for in an ABR graph?
Look at wave 5. Look at latency time it occurred for each ear and compare LE and RE. (how long it takes to get from 1-5)
See the largest and most robust peak at about 6msec, wave V.
What normative data exist for the ABR?
Absolute latency of all waves (V the most important) Interpeak intervals (I-V the most important) Interaural latency differences (ILD5) Maturational changes
What happens if there is a large time delay from I-V in an ABR?
If time is long, there is something holding it up…something between 1-5 can tell you where acoustic neuroma is
What are two uses of the ABR?
Threshold ABR, looking for softest sound to produce a readable wave V - tone pipe or click stimulus, to estimate hearing ability
Neurological ABR, comparing wave V latency to normative data - high intensity click stimulus, look for neural pathology, high sensitivity to VIII tumours
What happens in a threshold ABR for infants?
Present at 2000; click stimulus for screening; tone pip stimuli to approximate audiogram
Takes a few mx to get to its point - beyond that time, can’t measure response at 5ms point. Needs to be shorter than what you expect to see at response.
Spectral integrity changed when this short - frequency specific. Turning on/off quickly
What happens in neurological ABR?
Typically for adults (asymmetrical hearing loss)
High-intensity click stimulus
Look at 1-5 response latency (time it takes)
Lots of info pulled from this test
When should the latency be for wave V?
When are middle and long latency?
6msec
8-50 msec post-stimulus
What is slow cortical testing?
Conducted ‘blind’ by an audiologist with no prior knowledge of client’s behavioural thresholds
Looking at N1 P2 complex
Want to know if pure tone results are valid
Person reads or does quiet activity for each test
They just hear beeps
What must occur for all audiometric tests?
All tests results in the battery must relate to each others in ways that reflect anatomy and physiology of the auditory system
How do various conditions affect the AR threshold?
Normal threshold 70-100dBHL
CHL causes an elevation of the AR threshold by the amount of air-bone gap
Cochlear HL below about 60dBHL does not affect the AR threshold
Cochlear HL of about 60dBHL starts to raise the AR threshold
Retrocochlear HL tends to have a great effect on the AR
Stimulus ear with CHL - has to be loud enough to elicit reflex - sometimes limit of equipment, can be NR
Ipsilateral ear - CHL - won’t see reflex, won’t be able to measure
How do various conditions affect the AR threshold?
All those effects refer to the stimulus ear
But if the probe ear has a CHL - i.e., a middle ear condition of any type
Then the probe ear’s TM cannot be moved by the reflex - the reflex arc cannot be completed
A middle ear condition in probe ear will wipe out the reflex
The system is very sensitive to the state of the mechanics of the probe ear
