10 - AR Basics Flashcards
What does AR stand for?
Middle Ear Acoustic Reflexes
What does MEMR stand for?
Middle Ear Muscle Acoustic Reflexes
What is an acoustic reflex?
A bilaterally reflexive contraction of the middle ear muscles
- activated by loud sound and tactile stimulation, movement
- In humans, it is the contraction of the stapedius muscle in each ear
The contraction of the stapedial muscle occurs when a sufficiently intense sound is presented to the ______ (eardrum/cochlea)
Cochlea
What does the contraction of the stapedial muscle do to the functioning of the auditory system?
- stiffens the ossicular chain
- changes compliance of the middle ear system
Admittance ______(decreases/increases) with stapedius muscle contraction
decreases
The Acoustic Middle Ear Muscle Reflex uses the auditory nerve as an ____(afferent/efferent) pathway and the facial nerve (CN VII) as an _______ (afferent/efferent) pathway
Auditory nerve: afferent
Facial nerve: efferent
What is the clinical value of measuring the AR?
- can help infer site of lesion (middle ear, cochlea, VIII nerve, brainstem, VIIth nerve)
- Not useful for “lesions” above lower auditory brainstem level
What does VCN stand for?
Ventral Cochlear Nucleus
- part of the AR arc
- stimulus travels from cochlea to CN VIII (auditory nerve) to the VCN
What does SOC stand for?
Superior Olivary Complex
- during the reflex arc, the stimulus travels from the VCN to the SOC both ipsilaterally and contra-laterally
What is the name of CN VIII?
Auditory nerve
What is the name of CN VII?
Facial nerve
What are the 2 types of AR tests typically used today?
Describe the basic procedure.
AR Threshold
AR Decay
- otoscopy and tympanometry performed first
- immittance equipment set up for AR measures
- probe in one ear (measures admittance change and delivers ipsilateral AR stimuli)
- earphone in opposite ear (delivers contra-lateral AR stimuli)
How is AR measured?
- measure conventional immittance
- activate AR with sound stimulus presented to one ear (Test Ear)
- stapedius muscle contraction increases stiffness of ME
- change in admittance measured by probe = AR
In AR Testing, the test ear is always the ear with the _____ (stimulus/probe)
Stimulus
Contralateral vs Ipsilateral refers to the ear with the probe placement. When measuring the LE contralateral AR, where is the probe? Where is the tone?
LE Contralateral:
Probe= Right Ear
Tone = Left Ear
When measuring ipsilateral AR, what 2 types of acoustic signals is the probe delivering?
226 Hz probe tone (to measure acoustic admittance)
High intensity test tones/noise (to induce AR)
Name 2 tips for accurate AR measures
- ensure ear is clear of debris
- create air-tight seal
- instruct patient to remain still
At what air pressure is the AR measured?
At the air pressure value where the compliance peak occurred (during tympanometric test)
What does it mean if the admittance is not affected after the loud tone is delivered in the test ear?
The reflex is absent
What is the lowest sound stimulus at which an admittance change can be detected above baseline noise?
The AR Threshold (> or = 0.02 cc or mmhos)
What is the AR amplitude?
The amount of admittance change induced by sound stimulus
What dB HL intensity level do we typically start our AR Threshold search at?
80 dB HL
What is the “lowest intensity at which an admittance change is replicated” known as?
The Acoustic Reflex Threshold (ART)
What frequencies do we test the AR at?
500, 1000 2000 (and 4000 Hz)
*4000 Hz often missing for NH individuals
