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CMSD5280 Audition ll > Middle Ear > Flashcards

Middle Ear Flashcards

1
Q

What evokes the acoustic reflex?

A

Evoked by loud sound (>=80 dB pure tone; >=65 dB noise, SPL)

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2
Q

What is the role of the Acoustic Reflex?

A

To improve our perception of sounds by
1. protect cochlear from intense noise
2. Reduce masking from low-frequencies
3. Reduce hearing of own vocalization
4. prevent roll over of speech perception at high sound level

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3
Q

What causes a delay in the acoustic reflex?

A

Delay in neural circuit as well as Musclesc (20- 100ms)

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4
Q

Explain the relationship between binaural and unilaterality:

A

Binaural response to unilateral stimulation

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5
Q

What occurs to muscles in acoustic reflex at the time of vocalization?

A

When vocalizing, muscle contracts in advance (50-70 ms in chicken)

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6
Q

What else can evoke an acoustic reflex except for loud sounds?

A

Contraction of ME muscles can also be evoked by irritation of face, ear canal, etc. (Stronger for tensor tympani muscle)

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7
Q

What are the two types of Acoustic Reflex Measurements?

A

Direct and Indirect measurements

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8
Q

What is the Direct measurement of Acoustic reflex? (2)

A

Electromyogram
Direct observation through perforated TM

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9
Q

What is the indirect measurement of Acoustic reflex? (3)

A
  • Measure deflection of eardrum
  • Measure air pressure in sealed ear canal
  • Measurement of ME impedance: AR changes ME impedance. This is an important diagnosis tool!!
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10
Q

In impedance, how do mass and stiffness influence frequency? (2)

A

XC = k/(2.pi.f) Stiffness decreases with frequency
XM = 2.pi.fm Mass increases with frequency

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11
Q

Explain what happens in the concept of admittance vs Impedance:

A

Y=1/XC =2f/k = 2fV/(c2) = kV
Z inverse XC=1/kV): Z for air in V with solid wall (R is ignored).
Admittance is proportional related to volume

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12
Q

It was shown that Impedance is inversely related to

A

Impedance is inversely related to Volume
Z inverse 1/V: smaller the V, larger the Z

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13
Q

What is the relationship between impedance and volume?

A

Acoustic impedance can be expressed as volume: smaller the volume, larger the impedance

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14
Q

If we say the impedance of a middle ear (ME) is 2cc:

A

It means the impedance of this ME equals to the impedance of 2cc of air at standard condition (a 2cc cell with solid wall)

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15
Q

What is Electroacoustic impedance test?

A

A microphone picks up sound pressure level in the ear canal which is influenced by ME impedance and volume of the cavity

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16
Q

What is Equivalent Volume?

A

The amount air volume in a solid cavity that will have the same impedance as the tested auditory system

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17
Q

What are the standard conditions of Equivalent Volume? (3)

A

Standard air pressure at sea level (1Pa)
Defined temperature (20 Celsius)
Cell with solid wall

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18
Q

What is the comparison between Ve and real ear volume?

A

Real V has soft end and therefore smaller impedance as compared with the cell of the same size but surrounded by solid wall. Therefore, a solid cell must have a larger volume to have equal impedance as that of the real ear. Therefore, Ve is larger than V in real ear.

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19
Q

How does the volume change in the external ear tell the impedance of middle ear (ME)?

A

Eardrum is acoustically transparent.
The middle ear impedance change will change the stiffness of the eardrum thus changing the Ve of the external ear

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20
Q

What is the principle of an impedance bridge?

A

To match the impedance until sound level detected by mic is minimal

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21
Q

If stiffness is increased when AR is activated, Ve will be ?

A

Decreased

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22
Q

What will happen to Ve if MD is full of water?

A

Decreased

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23
Q

What will happen to Ve if there is a large perforation on eardrum?

A

Increased equivalent volume (1 to 5.5 mL) suggests a perforation

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24
Q

What will happen to Ve if the bone chain is disconnected?

A

Increased

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25
Q

How does changing air pressure allows detecting of middle ear pressure?

A

The OE pressure that results in the smallest impedance is the pressure of ME.

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26
Q

What is Acoustic Reflex measurement in summary?

A
  • We measure the AR by measuring the impedance change
  • AR is due to ME contraction
  • AR is evoked by loud sound
27
Q

Why do we change the air pressure of the OE in AR measurement?

A

Changing air pressure allows detecting of middle ear pressure

28
Q

What are the two sounds in AR measurement?

A

(1) continuous tone (low f) for impedance measuring,

(2) loud sound for impedance change (could be low and high in frequency)

29
Q

What are the ME elements to admittance? (3)

A

Mass, Stiffness and Resistance

30
Q

In the ME, the element of MASS to admittance comes from: (4)

A

Pars flaccida of TM
Ossicle chain
Perilymph in the cochlea
When ET open

31
Q

In the ME, the element of STIFFNESS to admittance comes from: (4)

A

Ligaments
Muscle tendons
TM
Air enclosed in ear canal (during test) and middle ear

32
Q

In the ME, the element of STIFFNESS to admittance comes from:

A

Bone joints and other; Cochlear mechanical structure

33
Q

What Stimulation parameters that cause practice issue of AR? (6)
Signal Spectrum:
Signal Presentation laterality comparison:
Duration:
Intensity growth?
AR can be initiated by?
Other Factors:

A

.

34
Q

What are the two effects of the Frequency on AR?

A
  1. Noise is better than puretone (lower threshold): suggests that bandwidth matters.
  2. Cross-band summation
    When band is > CB, AR threshold decrease
    Integration across different CBs.
35
Q

How does the Cross-band summation work in AR? (2)

A

Separate two tones by frequency. Test AR threshold until it decreases significantly

When the separation is in CB, no change in AR threshold; when it is over CB, threshold drops down. Turning point tells CB.

36
Q

What is the intensity effect on AR? (2)

A
  • AR magnitude increases with intensity above threshold
  • Appears as:
    Increase in impedance
    Decrease in latency
37
Q

In AR examination, what are the effectiveness findings of laterality? (2)

A
  • Bilateral > ipsilateral > contralateral
  • However, contralateral AR is often requested due to the ability to exam the whole circuit for AR
38
Q

How do we define AR threshold?

A

0.03 cm3 or intensity to elicit at 10% of the maximal AR response (85 dB HL)

39
Q

What is the effect of sounds on latency in AR? (2)

A

Latency change with intensity from 150 ms to 25-30 ms

Higher the intensity shorter the latency

40
Q

What are the two sources of AR latency?

A

Neural circuit delay
Delay of ME muscle

41
Q

Which of the two sources, neural circuit delay and muscular delay is larger in AR?

A

Muscular delay

42
Q

What are the effects of Stimulus Duration on the response of AR?

A

The longer duration of signals produce stronger response

43
Q

What are the effects of signal duration on the AR?

A

AR threshold decrease with signal duration: larger time range for the temporal summation (up to 500 ms)

44
Q

What conclusion can we make from Frequency to temporal summation in acoustic reflex?

A

The higher the frequency,higher the temporal summation in AR across frequency: more summation for high frequency

dB difference between 250 ms and 10 ms signals to produce the same AR

45
Q

In AR adaptation, for 500 Hz long duration tone signals:

A

AR goes down after 10 seconds

46
Q

What are the AR impact ME conduction?

A

Increases impedance by increasing stiffness

Attenuation at low frequency: A system with higher stiffness has high natural F because it does not respond well to low F signal

47
Q

How can we explain the results from this finding related to oscillation in AR to low F signals? (2) PROOF 1

A
  1. Loud sound initiates AR
  2. AR reduces low-frequency sound into the cochlea
  3. AR is reduced
  4. Then more sound gets into cochlea—AR increases again
    Repeated 1-4: oscillation
48
Q

What is the effect of Bell Pasly in AR? PROOF 2

A
  • Recording AR in the healthy ear, AR by stimulation ipsilateral (normal, solid line) versus contralateral ear (bell palsy, dashed line)
  • Left Panel: low-frequency signal showing larger impact.
  • Right panel: higher frequency signal showing less impact.
49
Q

What is the third proof of AR bias to low-frequencies?

A

TTS induced by low-frequency noise

Solid line: a subject with no AR
Dashed line: normal control

50
Q

What is the effect of increased stiffness in ME to AR?

A
  • Increased stiffness attenuates sound transmission at low frequencies (< 1000 Hz).
  • This is thought to provide some protection against noise exposure.
51
Q

What are other factors that can cause ME muscle contractions?

A

Swallowing, yawning, tickling on face, etc
vocalization

52
Q

What is the Intensity-control theory in AR?

A
  • Reduces high level sound. Therefore provides protection
  • Currently, this protection against noise is not considered as the main role of AR
53
Q

What is the Perceptual theory of AR? (4)

A

Improve hearing by:
- Protection from intense noise
- Reducing low-f masking
- Distinguish between own vocalization and external signal
- Prevent roll-over

54
Q

What is Roll-Over in AR?

A

Reduction of speech recognition scores that occurs at intensities above the level where PB max is obtained.

55
Q

What are the potential sources of artifacts in AR measurements? (5)

A
56
Q

What is Extra tympanic manometry?

A

One of the indirect methods involves monitoring air pressure changes in the external ear because of eardrum movement.

57
Q

Explain the abnormal reflex decay:

A

When there is more than 50% decay in AR in the low frequencies in the Contralateral ear. Explains Retrocochlear pathology or Bell’s palsy

58
Q

What is the impact the AR on ME Conduction? (2)

A

The AR Increases impedance by increasing stiffness

It attenuates low Frequencies (Higher stiffness affects low frequencies)

59
Q

How can we explain the results from an AR cycle in these graphs?

A

There is a cycle of AR by from:

  1. AR evoked by loud sounds,
  2. then AR causes increased stiffness so reduces low-frequency sound into the cochlea
  3. AR reduces
  4. More sound gets into cochlea, so AR is increases again

Repeat

60
Q

What can we see from this graph?

A

We can see high sound levels are more attenuated at low frequencies because of increased stiffness (<1000 Hz)

This is thought to provide some protection against noise exposure.

61
Q

ME muscle contractions could be evoked by: (3)

A
  • Swallowing, yawning, tickling on face, etc
  • vocalization
  • Loud Sounds
62
Q

What can we see from this graph?

A

There is an attenuation in CM from AR attenuation which we can see from a decrease in CM magnitude

63
Q

What is the effect of Bell’s palsy on speech dis?

A

Increased rollover in subjects with Bell’s palsy

64
Q

What could affect your results of AR? (5)

A

Previous ME diseases
Sequential variability
Test operation (skill of tester)
Age
Medications

CMSD5280 Audition ll (19 decks)

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