Lecture 2 Flashcards
What is admittance measuring?
the total absorbency
What two components make up admittance?
Conductance (G)
Susceptance (B)
Conductance = ____
Friction
Susceptance = ____
Stiffness and mass
daPa = ____
Pressure
mmho = ____
Admittance (Y)
How did the oldest tympanometer work?
- There was no built-in pump (instead they would manipulate the pressure in the room)
- A thermometer would measure the pressure in the room
mmho converted to to ml is called ____
Equivalent volume
What do you see with a TM perf on a tymp?
A large volume because you are measuring the volume of the OE and ME
How do you check tubes?
Do tymps. A normal tymp means the tube is blocked and a flat tymp means the tube is open and working correctly
Explain sound in a small, hard walled cavity
- A small cavity has low admittance (this means sound will be louder in a small space)
- The sound will want to be louder, but has to be turned down to maintain constant SPL
Explain sound in a large, hard walled cavity
- A large cavity has high admittance (this means more sound is being absorbed, it is quieter)
- The sound will want to be quieter, so it has to be turned up to maintain constant SPL
Why did Otto Metz choose a LF probe tone?
Because HF tones were often distorted
Only a ____ tone can be used to estimate the ear canal volume.
low frequency
Why can a HF tone not estimate the ear canal volume?
- High frequency sound is processed by mass characteristics of the ME (letting the sound through)
- At low frequencies, the ME is dominated by stiffness (impeding low frequencies)
So why is a 226Hz probe tone used?
Because at 226Hz, the mmho value and the equivalent volume value align.
What is the difference between using a 226Hz probe tone vs. a 1000Hz probe tone?
- At 226Hz, any mmho value can be converted into Vea
- At 100Hz, the numbers do not align
Acoustic admittance of a 1 cubic cm/1 ml cavity is equal to 1 mmho at ____
226 Hz
What pressure and Hz is the estimate of the EAC taken at?
226Hz at +200daPa
Why does the probe tone have to be LF?
because HF tones have high admittance
How do we know this tymp is measured at 226Hz?
Because Vea is measured (which is equal to mmho at 226Hz)
What does it mean if Vea is not present on the tymp?
We dont know (all we know is that it isnt 226Hz because if it was, Vea would be present)
What is equal at 226Hz?
mmho and Vea (ml is a measure of volume which is equal to mmho at 226Hz)
What is the immittance test battery?
- Tympanometry
- MFC tympanometry (multi frequency multi component)
- Acoustic reflex testing
- Acoustic reflex decay testing
- Admittance over time (AOT)
- AOT for patulous eustachian tube (PET)
What is the acoustic immittance instrument for tympanometry?
Tympanometer
What does a tympanometer measure?
Measured change in admittance (Y) in response to pressure changes applied to the ear canal space
How is the tympanometer working?
- The speaker puts out a probe tone
- The microphone monitors it to maintain a constant SPL
- The pump pumps air in and out of the OE
- If we pump a bunch of air into the ME, the TM will balloon inward and the stiffness increases
- Slowly the air is removed from the OE, and the TM becomes less stiff (sound is quieter; going through ME)
Whatever is being absorbed by the ME is being ____
replaced
What does the peak of the tymp mean?
This is where the TM can vibrate most freely
What is happening when there is an increase of pressure into the OE?
Increase in pressure causes increasing stiffness and the ME can’t absorb sound. This causes the sound to maintain in the OE (the sound is louder and to maintain SPL, voltage goes down)
What are the 6 steps to measure tympanometry?
- place test probe in EAC and achieve airtight seal
- activate pump so pressure reaches +200daPa
- collect estimate of canal volume
- start recording
- adjust pump so that pressure steadily decreases into the negative pressure range
- continue until at least -200 or until peak is achieved (-300 to -400daPa limit)
What is an MFC tymp used for?
Helpful for determining ossicular disorders
B tymps = dark
G tymps = faded
What are the 7 steps to measure MFC tympanometry?
- determine probe tone frequency
- usual protocol is B/G tympanometry
- place test probe in ear canal and achieve airtight seal
- activate pump so that pressure reached +200daPa
- start recording
- adjust pump so that pressure steadily decreases into the negative pressure range
- continue until at least -300 or until peak(s) is/are achieved
What is acoustic reflex testing measuring?
Change in acoustic admittance (Y) in response to an activating acoustic stimulus (stim tone)
What are we NOT doing in AR testing?
There is no pressure change
When testing AR, we are measuring a very ____ admittance change of about ____.
small, 0.02mmho
Explain this AR test
- probe tone: 226Hz (ml value)
- stim tone: 1000Hz
- the probe and stim tone are both being presented in the right ear (I = ipsi)
What are the 6 steps of testing AR?
- complete tympanogram
- set pressure to the point of the highest admittance value (peak) of the tymp
- AR option will measure very small admittance changes
- 0.02ml/mmho will be a positive response
- activate stim tone, either ipsi or contra
- measure admittance changes in response to stim tone
Where does the TM move the easiest?
At the peak of the tymp (most compliant)
AR shows a ____ in admittance
decrease (the stapedius muscle stiffens the ME which causes admittance to go down)
Explain this AR test
- probe tone: 226Hz (ml)
- stim tone: 1000Hz
- probe is in the left and stim is in the right (contra)
What is another name for the admittance over time (AOT) test?
Ambient pressure tympanometry
What is AOT measuring?
A measure of the ME compliance/admittance over an extended period of time
What is NOT happening in AOT measuring?
There is no change of pressure or stim tones, only the probe tone is presented.
What is the frequency of the probe tone for AOT?
687Hz (more sensitive to events that are happening in the ME)
What are the 4 steps of an AOT test?
- set AR instrument for reflex decay or other long time window setting
- turn stim down or off; set to contra but do not put contra stim-phone in ear if possible
- run test presentation
- a stable ear should show a flat tracing across the whole time
What is this AOT showing?
Pulsatile tinnitus (if it was normal, the line would be flat, but it is synchronis to the individuals pulse)
What is this AOT showing?
PET (can see this when the person stops breathing)
Why can cerumen cause a flat tymp?
Wax is blocking the ME; just another solid wall (no matter the pressure changes, the admittance won’t change)
Why is daPa used for tymps?
It is the unit of pressure (pumping air in and out)
Why is there a peak on the tymp?
- The ME admittance is changing to maintain constant SPL
- The peak refers to where the pressure in the OE and ME are equivalent
If the peak is negative, what does this suggest?
It would mean there is negative pressure in the ME (because the peak is where the OE and ME are equal)
What is missing on this tymp?
The air in between the ME and the probe (in the space of the EAC)
Does this show total ME function?
No. We are mostly measuring the TM and the air trapped in there, not the ossicles/past the TM. This is a test of ME immittance not total ME function.
Explain compensated vs. uncompensated tymps
Uncompensated
- shows the volume of the OE and ME
Compensated
- subtracts the OE and just shows the volume of the ME (static admittance)
Where is the volume estimate of an EAC taken from on this tymp?
Take the volume estimate at 226Hz at +200daPa = 2.5ml
What are the main components of a tympanogram?
- static admittance/compliance (peak TM)
- the height of the tymp (ME admittance only; compensated tymp)
- ear canal volume (equivalent estimat)
- peak pressure
- morphology (shape, width, gradient)
- compensated vs. uncompensated
Explain static admittance
Right tymp
- the lower the height of the tymp, the stiffer the TM is
Left tymp
- the taller the height of the tymp, the more compliant (hypercompliant in this example)
What is the range of compliance?
0.2-2.0
What does it mean if you get a 3.0ml volume and a normal tymp?
If its a big guy, you wouldn’t expect there to be a hole even though it’s outside of the normal range, because the shape is type A and you wouldn’t see a pressure change with a perforation.
