1. Understanding and Interpreting Acoustic Reflexes
Jan Pollard
Chief Audiologist
Sonic

2. Tensor Tympani Muscle
Extends from wall of Eustachian tube and connects to manubrium of malleus

3. Tensor Tympani Reflex Innervated by Cranial V (trigeminal)
Part of startle response
Pulling eyebrow upward, puff of air into orbital area- but not to sound
Contraction draws malleus inward, tensing drum, stiffening ossicular chain, ossicular stiffening and canal volume change

4. Stadpedius Muscle
One end is connected near the facial nerve canal and the other connects to head of Stapes

5. Stapedial Reflex
Innervated by stapedial (motor) part of Cranial VII (facial) nerve
Tactile response to facial area around pinna (reflexogenic skin zone) or to sound (acoustic reflex)
Pulls stapes down and out of oval window, BILATERALLY
Stiffens ossicular chain but no canal volume change

6. The Model of the Acoustic Reflex Pathway
Information crosses over to the other side
ME Inner Ear Cranial VIII (vestibulocochlear nerve) cochlear nucleus (CN) superior olivary complex (SOC)
facial nerve (VII nerve) middle ear (Stapedius muscle)

7. Ipsi- and Contra-lateral Reflexes
Ipsi-lateral reflex
Sound is put into the ear that the reflexes are being measured in. Stronger than contra-lateral.
Contra-lateral reflex
Sound is put into the test ear and the reflex is measured form the other (non-test) ear.

8. Ipsi and Contra-lateral

9. Normal Reflex range

10. General Rules Normal reflex level is 85 dB (70 to 100 dB)
Ipsi-lateral thresholds occur at lower levels than contra-lateral reflexes (3- 5 dB)
Hearing loss <50 dBHL , there should be no effect on the reflex and the results should resemble a normal ear.
As the cochlear hearing threshold increases, the chances of an elevated or absent reflex increases
50-80 dB loss –elevated
>80 dB likely absent
Contra-lateral reflexes

11. 3 General Rules for Eliciting a Reflex

12. NUMBER 1
Ear with the probe assembly in it must not have any outer or middle ear pathology

13. Middle Ear Pathology Probe Ear Principle Stimulus Ear Principle
Usually ART absent when conductive component in probe ear even though stapedial muscle working
50% of ears have absent reflex with 5 dB Air/Bone gap
80% absent with 10 dB gap
Stimulus Ear Principle
The air/bone gap decreases the intensity of sound reaching the cochlea
Eg. 35 dB A/B gap = 115 dB threshold
45 dB = 130 dB

14. Any degree of air/bone gap or an abnormal tympanogram can result in no reflex being measured.
The gap can be as little as 5dB
Eg perforation no A/B gap but abnormal tymp so no reflex.

15. The stimulus ear must receive a tone that is loud enough
Number 2
The stimulus ear must receive a tone that is loud enough

16. Conductive losses
need to add that much to the tone to reach the cochlea at a level to elicit a reflex
Eg dB conductive loss and normal sn level
Expected level then = 115 dB (may be outside limit of machine so NR)
Negative ME pressure up to -240 daPa may elevate the reflex by about 10 dB, more negative than that can result in NR

17. Sensorineural Losses
SN loss - now related to recruitment, not just added on as in a conductive loss
For cochlear losses up to 70 dB HL it is expected that a reflex can be recorded.

19. NUMBER 3
The neural pathway must be adequate to activate the contraction of the stapedius reflex

20. VIIIth Nerve (8th ) involvement eg Acoustic Neuroma
Compromise of neural impulses that can illicit ipsi- and contra- reflexes, so usually absent reflexes on that side.
Can get reflexes sometimes between dB so need to look at 90th percentile figures (as long as no A/B gap)

21. VIIIth Nerve (8th ) involvement eg Acoustic Neuroma
Ipsi
Contra R L
Contra
Ipsi R L

22. VII th Nerve (7th ) involvement eg Bell’s Palsy
Ipsi
Contra R L
Contra
Ipsi R L

23. Low Brainstem Disorders
L ipsi Y, contra N R ipsi Y, contra N
Ipsi
Contra R L
Contra
Ipsi R L

24. Contralateral vs Ipsilateral Reflexes
Contralateral Reflexes
Advantages-
sensitive to disorders involving crossed reflexed pathway eg miss intra-axial brainstems lesions if just used ipsi
Contra less sensitive to artifacts than ipsi
More data for contra reflexes

25. Ipsilateral Reflexes Advantages- Sensitive to middle ear pathology
Each ear tested independently of each other, so not confounded by disorders in the other ear
Easier to do than contra for hard-to-assess children

26. Thank you