SRT (Stapedial Reflexes Threshold) Test
The Stapedial Reflexes Threshold (SRT) Test, also known as the Acoustic Reflex Threshold (ART) Test, measures the reflexive contraction of the stapedius muscle in the middle ear in response to loud sounds. This reflex is part of the body's natural protective mechanism against loud noises, and the test is used to evaluate the integrity of the auditory system, particularly the middle ear, cochlea, auditory nerve, and parts of the brainstem.
How the SRT/ART Test Works
Preparation:
The patient is seated in a quiet environment.
A probe is placed in the ear canal, similar to the setup for a tympanometry test.\
Procedure:
The probe emits a series of loud tones at varying frequencies (typically 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz).
The device measures the change in compliance (movement) of the eardrum, which occurs when the stapedius muscle contracts in response to the loud sound.
The threshold is determined by finding the lowest intensity level (measured in decibels, dB) at which the reflex occurs.
Bilateral Testing:
The test is performed on both ears, as reflexes can be recorded ipsilaterally (in the same ear as the sound) and contralaterally (in the opposite ear).
Results Interpretation
Normal Reflex Thresholds:
Typically, the acoustic reflex occurs at sound levels between 70 dB and 100 dB HL (hearing level).
Normal thresholds indicate that the middle ear, cochlea, auditory nerve, and brainstem pathways are functioning properly.
Elevated Reflex Thresholds:
Reflexes that occur at higher-than-normal levels (above 100 dB) may suggest:
Early sensorineural hearing loss.
Mild damage to the auditory pathway or facial nerve.
Absent Reflexes:
Reflexes that are absent even at high sound levels can indicate:
Significant sensorineural hearing loss.
Middle ear problems.
Damage to the auditory nerve or brainstem.
Facial nerve dysfunction, as it controls the stapedius muscle.
Importance of the SRT/ART Test
Diagnosing Hearing Loss:
The test helps differentiate between types of hearing loss, particularly conductive (middle ear) versus sensorineural (inner ear or nerve-related).
Assessing Auditory Pathway Integrity:
ART is used to evaluate the integrity of the auditory nerve and brainstem pathways, which is essential in diagnosing conditions like acoustic neuroma, multiple sclerosis, or Bell's palsy.
Monitoring Disease Progression:
The test can track changes in the auditory system over time, particularly in patients with progressive neurological conditions.
Cross-Checking with Other Audiometric Tests:
ART results are often used in conjunction with other tests like pure tone audiometry and tympanometry to provide a comprehensive assessment of a patient's hearing and middle ear function.
Non-Invasive and Quick: Like other audiometric tests, the ART test is painless, quick, and provides immediate results.
Sensitive Indicator: It can detect subtle changes in the auditory system that may not be evident in other tests.
The SRT/ART Test is a valuable diagnostic tool in audiology, providing insights into the functioning of the auditory system and helping to diagnose a range of hearing and neurological disorders.