29 terms

Acoustic Reflexes & Reflex Decay

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Anatomy of Acoustic Reflex
-ME

-Cochlea

-Cochlear Nucleus (decussates)

-Superior Olivary Complex

-Motor Nucleus of the CN VII

-Muscles in the ME
Acoustic Reflex: Purpose
-Determines how well the acoustic pathways (ipsilateral and contralateral) are functioning.

-Measures how well the muscles in the middle ear (stapedius and tensor tympani) respond to loud sounds

-Helps determine the site of lesion (conductive, cochlear, or retrocochlear)
Acoustic Reflex: Ipsi Screening Procedure
1. Place the probe tip in the test ear.

2. Test 1000, 2000, and 4000 Hz

3. Present stimulus at 80 dB HL and go up in 5 dB HL steps (100 dB HL = max limits of immittance bridge) until you see a deflection of 0.02 ml or greater.

4. If there is a deflection of 0.02 or great the reflex is PRESENT

5. If there is not a deflection of at least 0.02 ml the reflex is ABSENT
Acoustic Reflex: Ispi Finding Threshold
1. Place the probe tip in the test ear.

2. Test 1000, 2000, and 4000 Hz

3. Present stimulus at 80 dB HL (100 dB HL = max limits of immittance bridge)

4. Use method similar to Hughson-Westlake
-If reflex is present, decrease by 10 dB HL
-If the reflex is absent, increase by 5 dB HL

5. Once you determine the threshold record results on the immittance form.
Acoustic Reflexes: Contralateral Procedure
1. Place the probe in the test ear and the stimulus in the non-test ear.

2. Test 500, 1000, and 2000 Hz

3. Present stimulus at 80 dB HL (100 dB HL = max limits of immittance bridge)

4. Use method similar to Hughson-Westlake
-If reflex is present, decrease by 10 dB HL
-If the reflex is absent, increase by 5 dB HL

5. Once you determine the threshold record results on the immittance form.

6. Plot thresholds onto the audiogram
Peak Pressure
We have to perform at peak pressure from the tympanogram
Introduce Stimulus
-Typically pure-tones, but can be noise

-If the sound is loud enough, the sound bouncing back will tell us the room is smaller.

-We are looking for 0.02 ml
Threshold of 0.02 ml
-Look for the lowest level we get a .02 ml shift

-We want a flat line, then .02 ml shift

-We need to get a twice

-Start at 80 dB, go up to 90 dB if there was no reflex (similar to the Hughson-Westlake method)

-We need the line to go down and back up
Ipsilateral
-Stimulus and probe on same side

-We typically do not test 500 Hz b/c of standing waves
Contralateral
-Stimulus and probe on opposite sides

-Test: 500, 1000, and 2000 Hz
Diagnostic Testing Pathways
-Right Contralateral: stimulus in right ear; probe in left ear (Left Crossed)

-Left Contralateral: stimulus in left ear; probe in right ear (Right Crossed)

-Right Ipsilateral: stimulus and probe in right ear (Right Uncrossed)

-Left Ipsilateral: stimulus and probe in left ear (Left Uncrossed)
Interpretation: Sensation Levels

Normal
-65 - 95 dB SL

-Normal hearing

-Mild Conductive loss
Interpretation: Sensation Levels

Reduced
≤ 60 dB SL

-Cochlear

-Suggests a sensory loss, specifically a problem related to the cochlea
Interpretation: Sensation Levels

Elevated
> 95 dB SL

-Conductive loss

-Retrocochlear loss

-Suggests a neural loss, specifically a problem with the VIII CN or beyond
Interpretation: Sensation Levels

Absent
-No response at the limits of the immittance bridge

-Conductive loss

-Sensorineural loss

-Suggests loss is sensory, neural, or both
Jerger Pattern
patterns suggest problem in the ear with the absent/elevated ipsilateral reflex
Normal Jerger Pattern
normal
Vertical Jerger Pattern
1. Mild middle ear disorder

2. 8th nerve disorder
Diagonal Jerger Pattern
1. 8th nerve disorder

2. Severe cochlear loss
Inverted-L Jerger Pattern
1. Unilateral middle ear disorder

2. Intra-axial brain stem disorder eccentric to one side

3. Combined 7th and 8th nerve disorder
Horizontal Jerger Pattern
1. Disorder of the intra-axial brain stem pathways
Uni-box Jerger Pattern
1. Extra-axial and/or intra-axial brain stem disorder
Reflex Decay
-You can tax the system just like WRS, but instead of making it louder we make it LONGER

-Figure out where their threshold was, then go in 10 dB above threshold at > .02 ml
Reflex Decay: Purpose
-Measures the amount of time, in seconds, it takes for the acoustic reflex to decay by half.

-Measures how the muscles in the middle ear respond to a constant and loud stimulus.
Reflex Decay: Procedure
1. Present stimulus at 1000 Hz at 10 dB SL above the contralateral threshold.

2. Measure the number of seconds it takes for the reflex to decrease in amplitude by half.

3. Record results on immittance form.
Reflex Decay: Interpretation

Normal
≥ 10 secs
Reflex Decay: Interpretation

Cochlear
7-9 secs
Reflex Decay: Interpretation

Retrocochlear
≤ 3 secs
Reflex Decay: Interpretation

Soft Sign of Retrocochlear
4-6 secs
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