Impedance audiometry, also known as tympanometry, is a diagnostic test that measures the impedance or resistance to sound in the middle ear. It assesses the mobility and function of the eardrum (tympanic membrane) and the middle ear ossicles (bones) by measuring changes in air pressure within the ear canal.
During an impedance audiometry test, the individual sits comfortably while a small probe is inserted into the ear canal. The probe consists of a speaker and a microphone. The speaker generates a tone and changes the air pressure in the ear canal, while the microphone measures the sound that is reflected back.
The test measures two primary parameters:
Tympanometry: Tympanometry assesses the movement of the eardrum in response to changes in air pressure. The probe creates pressure variations in the ear canal while measuring the sound reflected back. This provides information about the compliance or stiffness of the eardrum and the mobility of the middle ear system.
The results of tympanometry are typically presented on a graph called a tympanogram. A tympanogram shows the compliance of the middle ear system at different air pressures. The shape of the tympanogram helps identify various middle ear conditions, such as normal middle ear function, eardrum perforation, fluid in the middle ear (effusion), or abnormal stiffness of the middle ear system.
Acoustic reflex testing: This part of impedance audiometry assesses the reflexive contraction of the middle ear muscles in response to loud sounds. When a loud sound is presented to the ear, the middle ear muscles contract, which can be detected by changes in the impedance of the ear.
Acoustic reflex testing helps identify the presence or absence of the acoustic reflex and its threshold, which can provide valuable information about the integrity of the auditory pathway.
Impedance audiometry is a valuable tool for diagnosing middle ear disorders such as:
- Otitis media: It helps determine the presence of fluid in the middle ear, which is common in ear infections.Eustachian tube dysfunction: It assesses the function of the Eustachian tube, which connects the middle ear to the back of the throat and helps equalize pressure.
- Tympanic membrane perforation: It detects abnormalities in the eardrum, such as perforations or scarring.
- Ossicular pathology: It can indicate problems with the middle ear bones, such as stiffness or dislocation.
Impedance audiometry is typically conducted by audiologists or trained healthcare professionals. It provides valuable information alongside other hearing tests, such as pure tone audiometry, to help diagnose and manage various middle ear conditions.
