Middle Ear Function Testing Flashcards
What are the underlying concepts of middle ear testing?*
What is multi-frequency tympanometry?*
What is wide-band tympanometry*
What is stapedial reflex testing and reflex decay testing?*
What is the purpose of tympanometry?
It allows us to measure the acoustic admittance of the middle ear - how easily sound energy is transferred through the middle ear system.
It has significant diagnostic use as it can inform us of any middle ear conditions that may be effecting the middle ear.
How is tympanometry preformed?
- A probe is inserted into the client’s ear. The probe includes:
- A microphone to measure the reflected sound
- A speaker to emit the 226 Hz tone
- A pump to vary the air pressure levels - A stimulus is played into the ear (continuous 226 Hz, wide-band clicks etc)
- The air pump varies the air pressure to be at, above and below atmospheric pressure. This will manipulate the tympanic membrane and ossicular chain to stiffen and relax.
- As the air pressure changes, the microphone measures a change in admittance
- When outer ear canal pressure and the middle ear pressure is equal there is the most admittance and least reflected sound
- When the middle ear and outer ear canal pressure is unequal there is less admittance and more sound pressure measured.
What are the main measurements given by tympanometry?
- Tympanometric shape
- Type A, Ad, As
- Type B
- Type C - Equivalent ear canal volume
- “Volume”
- Measured in ml, or cc - Peak-compensated static-acoustic admittance
- “Admittance” or “compliance”
- Measured in ml or mmho - Tympanometric gradient and width
- Measured in daPa
- Measures the sharpness of the tympanogram - Tympanometric peak pressure
- The pressure at which peak admittance occurs
- Measured in daPa
What is tympanometric compensation?
When performing tympanometry, we are wanting to measure the admittance of the middle ear.
However, because the probe of the tympanometer is in the middle of the outer ear canal, any admittance measurement will be from BOTH the outer ear canal and the middle ear.
Therefore, to find ONLY the admittance of the middle ear, the ear canal volume must be estimated and subtracted from the total admittance. This process is called tympanometric compensation.
The estimated ear canal volume is calculated at either extremes of positive or negative pressure. This is due to the assumption that at these pressures, the TM will be so stiff that any admittance measured can be attributed to the ear canal only.
Why is a 226 Hz tone used?
What are the different tympanometric shapes?
- Type A: Peak admittance and pressure WNL
- Type AD: Pressure WNL, Admittance high
- Type AS: Pressure WNL, admittance low
- Type B: No peak, admittance low
- Type C: peak admittance occurs at negative pressure
What different variables can effect the peak admittance?
- Whether or not the compensated ear canal volume was taken from the negative or positive extreme (value taken from extreme negative = static admittance is higher). This is due to tympanometric asymmetry.
- Pump speed (faster speed = higher static admittance)
- Direction of pressure change (positive to negative = lower pressure)
- repeated tests in close succession
What is the purpose of the Eustachian tube (ET)?
It regulates the pressure within the middle ear and therefore protecting the TM, ossicles and cochlear from damage that could occur from extreme changes in pressure.
It also acts to drain mucous
What are some limitations of using tympanic peak pressure?
- It is only an estimate, in reality is can grossly over-estimate the pressure of the middle ear (by 100% according to Katz).
- Important to use the cross-check principle to identify the presence of otitis media
In which cases may we see a type A tympanogram?
Type A tympanogram:
- Normal pressure, normal admittance
May be seen in:
- Normal functioning middle ear
- Otosclerosis
In which cases may we see a type Ad tympanogram?
Type Ad tympanogram:
- Normal pressure, high admittance
May be seen in:
- Flaccid ear drum (e.g., scarring, or recently healed perforation)
- Dis-articulation
In which cases may we see a type As tympanogram?
Type As tympanogram:
- Normal pressure, low admittance
May be seen in:
- Sclerotic eardrum
- Cholesteatoma
In which cases may we see a type B tympanogram?
Type B tympanogram
- No peak (need to interpret ear canal volume)
Normal ear canal volume:
- glue ear/otitis media
Large ear canal volume:
- Grommet
- Perforation
Small ear canal volume
- Blocked probe
- Ear wax obstruction
In which cases may we see a type C tympanogram?
Type C tympanogram:
- Negative pressure, normal admittance
May be seen in:
- Retraction
- Eustachian tube dysfunction
In which scenarios is 226 Hz tympanometry sufficient and in which should further testing be done?
226 Hz only:
- Adult, type A, no air-bone gap
- Adult, type B or C AND associated air-bone gap
Further testing (multi-frequency, wideband tymp)
- Adult, type A and air-bone gap (may be due to otosclerosis or ossicular disarticulation)
