The main purpose of impedance audiometry is to check the status of the tympanic membrane and middle ear. It checks how well the vibrations get transmitted from the tympanic membrane (eardrum) further into the ear. The tympanic membrane is a thin layer of tissue in the human ear. It receives sound vibrations from the atmospheric (outside) air and transmits them to the tiny bones in the tympanic (middle ear) cavity.
The secondary purpose of this test is to evaluate acoustic reflex. The acoustic reflex (also known as the stapedius reflex) is an involuntary contraction of the stapedius muscle in response to loud sound stimuli. The reflex is often used to evaluate facial nerve functioning.
Which are the tests covered under impedance audiometry?
Impedance audiometry comprises several tests. The main tests include:
Which diseases need impedance audiometry for their diagnosis?
Impedance audiometry test is used for assessing the patency of the middle ear. This study helps in the diagnosis of:
- Otitis media (infectious fluids of the middle ear)
- Perforation (hole/rupture) of the tympanic membrane
- Middle ear effusion (accumulation of fluid in the middle ear)
- Glue ear (collection of thick and sticky fluid in the ear)
- Eustachian tube dysfunction (inflammation of the eustachian tube making it unable to close or open)
- Otosclerosis (abnormal remodeling of the stapedius)
- Fracture of ear bones
- Facial palsy
- Hearing loss
Who is not fit for the test?
The test is not recommended for babies aged less than 7 months because it can damage their ear canal.
How is the impedance audiometry performed?
Impedance audiometry is completely painless and noninvasive. The operator inserts the probe tube into the ear. The entire arrangement is such that the entry of air in your ear remains completely blocked throughout the test.
Tympanometry measures the pressure in the middle ear while the operator changes the pressure in the ear canal.
Stapedius reflex test is used to measure the sound tolerability of your ear. Your ear is exposed to middle and high-frequency stimulus sounds (500, 1000, 2000, and 4000 Hz). The test will check whether the contraction of the stapedius muscle is present at a particular frequency of sound.
Eustachian tube patency or functioning test checks for how much the eustachian tube is open. The operator will ask you to swallow several times or yawn to check if the eustachian tube can clear the pressure. Several types of this test exist. Some of the types help evaluate the efficacy of treatments to improve Eustachian tube dysfunction.
The result of the impedance audiometry is a graph known as a tympanogram. The tympanogram shows values of the intensity of acoustic reflex on the frequencies 0.5, 1, 2, and 4 kHz.