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acoustic immittance refers to either
- acoustic impedance (Za or Ohms) - tests resistance to the flow of energy
- acoustic admittance (Ya or mmhos) - tests ease of flow
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what does acoustic admittance test
- not hearing.
- it tells us how well the middle ear amplifies sound
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SPL and Middle Ear Status
- arrow to far right = fluid build up
- arrow middle = normal
- arrow to far left = absorbs energy / ossicle chain busted
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tympanograms
measure of change in SPL
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Three Immittance measures
- tympanograms
- static immittance
- ear canal volume
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two classification systems for tympanograms
- PAS System - pressure amplitude shape
- The Jerger System - 3 types A B C
- these test the ear drum
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Types of tympanograms
back of slide 8
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PAS pressure
- negative = E-Tube dysfunction (start of Otitis Media)
- WNL = within normal limits
- positive = AOM (rare) - ear drum about to rupture, people with this go to physicians
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PAS amplitude
- increased = flaccid (loose) - the peak it very high
- WNL = winthin normal limits
- reduced = stiff - the peak is very low
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PAS shape
- flat = fluid or perforation or ECV=0 - tympanogram is flat
- increased (notched) = healed perf. - area of the ear drum with 2 layers instead of 3, occurs after a rupture heals
- increased 'w' shape = disarticulation - break something, no ossicular chain
- bumpy = glomus tumor - gets bumps per min
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70 bumps/min means
- you are hearing the heart beat
- the tumor is hitting the ear drum
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12 bumps/min
- you are hearing the breathing
- opening to Eustachian tube is flopping
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Jerger classification chart
slide 12
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As means
- stiff
- pressure normal but shallower than normal
-
A means
- disarticulation
- very flaccid
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C means
normal but negative pressure
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Jerger charts
slide 13 - 17
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Static Immitance units
- Acoustic Impedance (Ohms)
- Acoustic Admittance (mmhos)
- Compliance (ml)
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static immittance usefullness
almost useless because normal and abnormal have too much overlap
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tympanometric width is used for
screening kids in schools
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ear canal volume
- expressed in ml
- if reduced = probe in cerumen or against wall of EAM, clean and do it again
- if increased = perforated (hole) tympanic membrane, open PE tube
- probe can tell the amount of volume between tip of probe and ear drum
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negative pressure on a tympanogram means
E-tube dysfunction
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three types of acoustic reflex tests
- presence or absencce of the reflex
- acoustic reflex threshold (ART) - as you raise sound, the muscle contracts at a higher magnum
- acoustic reflex decay - tumor testing
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presence/absense acoustic reflex tests 4 thing
- 2 ipsilateral
- 2 contralateral
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presence/absence flow charts
slide 31 - 33
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ART in normal people
- approximately 90 dB HL
- reduced SL's imply sensory loss in cochlea
- increased HL's imply Neural Loss - could be very serious (brain tumor)
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acoustic reflex decay charts
38 - 39
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