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Diagnostic Audiology > Acoustic reflexes > Flashcards

Acoustic reflexes Flashcards

Acoustic reflex threshold testing and acoustic reflex decay

1
Q

What is an acoustic reflex?

A

The acoustic reflex is caused by the contraction of the stapedius muscle and the subsequent change in the stiffness of the ossicular chain

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2
Q

What is the role of the stapedius muscle?

A

The stapedius muscle holds the stapes in place in the ossicular chain

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3
Q

When does the acoustic reflex happen?

A

When a very loud sound is presented to the ear

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4
Q

Describe the sequence of events of the acoustic reflex following the presentation of a loud sound

A
  1. Loud sound is presented to the ear
  2. The cochlea picks up the sound and sends activity to the cochlear nucleus
  3. The cochlear nucleus passes the information to the superior olivary complex and you become aware of the sound
  4. At the same time it branches off to the facial nerve nucleus and a signal is sent through the VIIth nerve to the stapedius muscle which will contract
  5. Positioning of the ossicular chain and transmission of sound through the middle ear becomes different
  6. The cochlear nucleus also sends a signal to the superior olivary complex on the other side of the head which activates the acoustic reflex in the other ear
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5
Q

What is the stapedius muscle innervated by?

A

The cochlear nucleus VIIth nerve (facial nerve)

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6
Q

What is the role of the stapedius muscle once innervated?

A

To pull the stapes in the posterior direction (backwards)

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7
Q

Describe the acoustic reflex pathway starting from stapedius muscle innervation

A
  1. VII nerve innervates the stapedius muscle
  2. Cross over between the two sides- information coming from the right ear will cross over and cause a change in the contralateral ear
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8
Q

Describe the left and right ipsilateral pathways

A

-The sound is played in either the left or right ear and the response is measured in the same ear
-The change in admittance is measured with the same probe used to present the sound

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9
Q

Describe the left and right contralateral pathways

A

-The sound is played in one ear and measured in the other ear
-Cross over in the brain occurs
-Probe in both the right and left ear in order to play the sound and measure the response
-E.g. the sound presented in the left ear and the response is measured in the right ear

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10
Q

What test should always be carried out prior to acoustic reflex testing?

A

Tympanometry

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11
Q

What should be the relationship between the pressure in the ear canal and the inner ear cavity for us to measure acoustic reflexes?

A

Acoustic reflexes should be measured at the point where the pressures are the same

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12
Q

What happens to the peak of the tympanogram during the contraction of the stapedius muscle?

A

It gets pulled down as it becomes less easy for the probe done to pass through the middle ear system

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13
Q

Why do reflexes go in a negative direction?

A

As the stapedius muscle gets pulled it becomes less easy for the sound to go into the middle ear

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14
Q

What is the meaning of the acoustic reflex threshold?

A

The lowest intensity where we can detect a threshold using detection criterion

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15
Q

What are the four measurements we obtain from acoustic reflex testing?

A

-Right and left ipsilateral
-Right and left contralateral

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16
Q

Describe what kind of hearing loss would be associated with these acoustic reflex results

A

-Normal hearing or a mild to moderate sensorineural hearing loss
-The activity is going to the cochlear nucleus for a quiet sound is lower but not fo a loud sound
-This kind of hearing loss does not affect the acoustic reflex so they appear normal

17
Q

Describe what kind of hearing loss would be associated with these acoustic reflex results

A

-Sensorineural hearing loss greater than 50 dB on the right side, left ear normal
-The activity going to the cochlear nucleus is decreased
-Acoustic reflex pathway will only be activated if the intensity is raised

18
Q

Describe what kind of hearing loss would be associated with these acoustic reflex results

A

-Conductive hearing loss on the right, normal hearing on the left
-Sound is not reaching the cochlea with the same intensity
-Cannot make the activator loud enough to create activity in the cochlear nucleus
-If we activate from the left and try to measure a contralateral reflex the compliance would be so low that even though the muscle might be contracting, we cannot measure a change

19
Q

What are the three sites along the acoustic reflex pathway that a neurological lesion may impact?

A
  1. VIIth nerve: prevents the ipsilateral and contralateral reflex from being measured on the affected side ipsilaterally and the unaffected side contralaterally but can be measured on the affected side contralaterally and the unaffected side ipsilaterally
  2. VIIIth nerve: The reflex cannot be measured on the affected side either ipsilaterally or contralaterally but can be measured on the unaffected side both ipsilaterally and contralaterally
  3. Intra-axial (prevents cross-over between the two halves of the brain)- can do the ipsilateral measurement in both ears but no contralateral measurements
20
Q

What is a retrocochlear pathology? How does it affect acoustic reflexes?

A

-Retrocochlear pathology refers to an acoustic schwannoma
-Affects the activity within the cochlear nucleus
-Causes the threshold to be raised or absent ipsilaterally and contralaterally on the affected ear

21
Q

What is the acoustic reflex decay?

A

-Indicates a retrocochlear pathology
-Carried out by inserting the probe into the ear, finding the acoustic reflex threshold and measuring a reflex with an activator 10 dB above the threshold
-Activate for 10 seconds
-The decay is the difference in deflection at the beginning and the end of the 10 seconds of activation
-When the decay is more than 50% that is an indication of the retrocochlear pathology

22
Q

What is another function of the acoustic reflex other than protecting against very loud external sounds?

A

-When you speak you are presenting loud sounds to your own hearing
-By having the acoustic reflex contracting while you speak, you reduce the lowest frequencies and increase the middle frequencies
-This allows you to still hear the sounds going on around you while you speak

23
Q

How are acoustic reflexes carried out?

A
  1. Ear is pressurised at peak pressure found in tympanometry
  2. Start the sound presentation at 70 dB and work up in 5 dB increments
  3. Look for change in admittance greater than 0.02ml (criteria)
  4. Once this is achieved, increase the volume once more to observe growth and ensure the previous result was not an artefact
24
Q

Where is the acoustic reflex in this result?

A

90 dB (change in admittance of 0.04ml)

25
Q

Where is the acoustic reflex observed here?

A

80 dB (change in 0.02ml)

26
Q

Where is the acoustic reflex observed here?

A

100 dB

27
Q

What are screening reflexes?

A

One measurement which can test 4 frequencies for acoustic reflexes very quickly- however cannot see growth of the threshold

28
Q

Based on these acoustic reflex results, what condition could the patient be suffering from?

A

Right cochlear pathology

29
Q

Based on these acoustic reflex results, what condition could the patient be suffering from?

A

Left middle ear pathology

30
Q

Based on these acoustic reflex results, what condition could the patient be suffering from?

A

Left retrocochlear pathology

31
Q

Based on these acoustic reflex results, what condition could the patient be suffering from?

A

Right facial (VII) nerve pathology

32
Q

Based on these acoustic reflex results, what condition could the patient be suffering from?

A

Intra-axial pathology

33
Q

What would the acoustic reflex results be for a bilateral tympanic membrane perforation?

A
34
Q

What would the acoustic reflex results be for a problem in the left cochlea or left VIIIth nerve?

A
35
Q

What would the acoustic reflex results be for a glomus tumour in the left ear?

A
36
Q

What would the acoustic reflex results be for noise induced hearing loss?

A
37
Q

What would the acoustic reflex results be for otitis media with effusion?

A
38
Q

What would the acoustic reflex results be for sensorineural hearing loss in the right ear?

A

Diagnostic Audiology (12 decks)

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