DIAGNOSTICS: Acoustic Reflex Threshold (ART)

What is anatomically happening with an acoustic reflex?

-A loud sound enters the auditory system

-The CNVII is stimulated, causing the stapedius muscle to contract

-This pulls the stapes muscle away from the oval window and causes the ossicles to stiffen

-Admittance into the middle ear decreases and impedance increases

What are you measuring with an ART?

-The change in compliance when the stapedius muscle contracts due to the presentation of a stimulus tone

-Impedance (dB SPL)

What are you graphing with an ART?

-the decrease in admittance (mmho or mL)

What is the acoustic reflex threshold?

-the lowest intensity level of the reflex eliciting tone in dB HL that produces a repeatable admittance change of at least 0.02 mmhos (or 0.02 ml)

What is the purpose of the acoustic reflex?

-To attenuate loud sounds

-Protection

What is the reflex arc?

-The contralateral pathway of an ART

When a loud sound enters the auditory system, which stapedius muscle contracts?

-BOTH

Why would you measure ART's?

-If you suspect retrocohlear pathology

-If you suspect non-organic hearing loss

Can you make a diagnosis solely on ART results?

-NO

-Other tests are needed for confirmation

Which ear determines if you can ELICIT the reflex?

-The stimulus ear

In what situations would you NOT be able to elicit an acoustic reflex?

-Conductive hearing loss: does not mean the reflex does not exist, just cannot elicit or measure it

-Sensorineural hearing loss greater than 50 dB

What ear determines if you can MEASURE the reflex?

-The probe ear

Why should you ALWAYS do tympanometry BEFORE ART's?

-If there is a middle ear dysfunction, you will not be able to elicit or measure the ART

-TPP from tympanometry is used to determine the pressure level for ART's because this is where the system is most compliant

What dB reference level should you be reporting ART's in?

-dB SL

What is considered a normal dB SL range for ART's?

-70 to 90 dB SL

When is reduced ART dB SL levels found?

-Patients with sensorineural hearing loss due to loudness recruitment

What is the ART pathway?

-Middle ear-->cochlea-->CNVIII-->Cochlear nucleus-->SOC-->FMN-->CNVII

What is the cutoff dB HL for a patient with sensorineural hearing loss to have an ART response?

-Between 50-55 dB HL

-If hearing is <50-55 dB HL, ART's can be present at a REDUCED sensation level (due to loudness recruitment)

When is the range in dB HL for a patient with sensorineural hearing loss to typically have absent ART responses?

-50 to 80 dB HL

When, in dB HL, would you expect there to be absent ART responses?

-80 dB HL and above

What is the only type of hearing loss that effects BOTH reflex arcs?

-Conductive