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CSD9510 > 9 - Acoustic Immitance > Flashcards

9 - Acoustic Immitance Flashcards

1
Q

Acoustic immittance allows us to ____(directly/indirectly) measure biomechanical properties of the Middle Ear (ME)

A

Indirectly

Physical properties, such as TM mobility, may be directly observed through pneumatic otoscopy

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2
Q

Name 2 of the 3 acoustic immittance measures

A 
Tympanometry
ME Acoustic (Muscle) reflex testing
Eustachian tube tests
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3
Q

Which 3 components contribute to ME vibration?

A

Compliance or springiness (stiffness)
Mass
Resistance (friction)

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4
Q

What frequency does a conventional acoustic immitance probe use?

A

226 Hz

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5
Q

On an acoustic immitance meter, which two devices are attached to it, and what do they measure?

A

Probe - admittance

Earphone - acoustic reflex

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6
Q

Name two things to remember when inserting the probe for tympanometry

A
  • insert the probe into the ear so that it forms a seal with the EAM
  • probe tip should face the TM, not the canal wall
  • path to the TM should be clear (otoscopy first)
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7
Q

Name 2 things should you include in your instructions to the patient before tympanometry?

A
  • remain very quiet and still

- explain that they will experience pressure changes and hear some loud sounds

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8
Q

True or False: You should immediately stop the tympanometry test if your patient complains of discomfort or dizziness

A

True

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9
Q

What does conventional admittance measure?

A

The acoustic admittance for a low frequency probe tone (220 or 226 Hz), and how it varies as air pressure in the ear canal is varied

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10
Q

What does 0 daPa of air pressure represent?

A

Atmospheric pressure

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11
Q

Sound flows best when the TM/ME has ____ (good/bad) mobility

A

good

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12
Q

When is the acoustic admittance value the highest?

A

When the TM/ME is most compliant

- sound flows best at atmospheric pressure when the TM/ME mobility is normal

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13
Q

What position is the TM in when the external ear canal pressure = middle ear pressure?

A

Normal position at point of maximum mobility

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14
Q

During tympanometry, when is the admittance for low frequency sound the lowest?

A

When the TM/ME is stiff at extreme external canal pressures (+ and -)
- forms a closed hard wall cavity and the 226 Hz probe tone is reflected back

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15
Q

Describe how the tympanogram is recorded

A
  1. Sweep pressure in ear canal
  2. Measure proportion of 226 Hz probe signal admitted to middle ear
  • acoustic admittance (mmho) is plotted on the y-axis and ear canal pressure (from ~-300 to +200 daPa) is plotted on the x-axis
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16
Q

What does the peak on a tympanogram indicate?

A

The point at which maximum acoustic energy passes into the middle ear (minimal reflection)

17
Q

As pressure in the ear canal varies from the peak, what happens to the TM and middle ear?

A

They gradually stiffen, causing a decrease in acoustic admittance, and an increase in the reflection of acoustic energy back into the ear canal

18
Q

The baseline admittance in hard-walled ear canal cavity is measured at what pressure during tympanometry (i.e. what is your starting pressure)?

A

+200 daPa

19
Q

What are two types of tympanometers?

A

Full diagnostic assessment equipment

Screening equipment

20
Q

What are two ways you can store your tympanogram results?

A

Print them

Export to computer for permanent storage

21
Q

What are the 3 tubes/holes for on the tympanometer probe?

A
  • Air pressure pump (+/- mm H2O) and manometer (pressure meter)
  • Speaker (226 Hz tone generator)
  • Microphone (recorder)
22
Q

How is acoustic admittance measured?

A
  1. Receiver/speaker delivers 226 Hz tone into hard-walled EAM (+200 daPa)
  2. Speaker & Circuit: set reference level of 226 Hz probe (85 dB SPL)
  3. Microphone & Circuit: monitor the 226 Hz probe sound level within the EAM as pressure sweeps (tracks probe tone dB SPL changes away from 85 dB SPL reference, circuitry converts dB SPL deviations into equivalent acoustic admittance Ya (mmhos))
23
Q

Why do we use a 226 Hz probe tone during Immitance Tests?

A

Because, under standard atmospheric conditions, the acoustic admittance of a 1 cc cavity is equal to 1 mmho at 226 Hz

  • this simplifies calibration
  • low frequency sound is sensitive to the “compliant” springiness component of the middle ear admittance
24
Q

As volume increases, admittance _____ (decreases/increases)

A

Ya in mmhos increases

25
Q

As volume increases, the 226 Hz probe tone SPL ______ (decreases/increases)

A

Decreases

26
Q

How are calibration cavities used to account for differences in patient EAM volumes?

A
  • we use the calibration cavity to find the voltage needed for a dB SPL reference for our 226 Hz tone (provides voltage equal to Ya = 1 mmhos = 1 cc)
  • for patients with EAM’s larger than 1 cc, admittance at +200 daPa will show more voltage needed to achieve 85 dB SPL and this difference is used to calculate increase in admittance relative to 1 cc cavity
  • for patients with EAM’s smaller than 1 cc, it will show that less voltage is needed to set the probe tone to 85 dB SPL
27
Q

What is tympanometry used for?

A
  • it is an electronic and acoustic measurement technique to assess middle ear status
  • can also be used to assess outer and middle ear function when combined with otoscopy
  • it is objective, fast, and highly accurate
28
Q

What does qualitative tympanometry refer to?

A

Using the shape of the tympanogram to determine normality
e.g. Type A = normal
Type As = low static admittance (low peak)
Type Ad = high static admittance (high peak)
Type B = no peak
Type C = negative peak pressure (peak is left of 0)

29
Q

Name 2 quantitative tympanometry measures

A
  1. TPP: Tympanogram peak pressure
  2. TW: Tympanogram width or gradient
  3. Peak Ytm: Peak (compensated) static acoustic admittance
  4. Equivalent ear canal volume
30
Q

What does TPP refer to?

A

The pressure at the tympanogram peak (e.g. 0 daPa = normal, vs -200 daPa)

31
Q

How is TW measured?

A

TW (tympanometric width) is the distance measured between the 2 points at 50% of static acoustic admittance
- measured in daPa of pressure

32
Q

How is the Tympanometric gradient measured?

A

Gradient = hp/ht
where hp = the height ( in mmhos) at 50% of static acoustic admittance
and ht = the height from base to peak (in mmhos) of the tympanogram

CSD9510 (17 decks)

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