Acoustic Impedance - Methods

2024 Author: Rachel Wainwright | [email protected]. Last modified: 2023-12-15 07:39

Impedance measurement

Acoustic impedance measurement is a set of diagnostic procedures that are performed to assess the condition of the middle ear, which is responsible for the transmission of sound air vibrations.

The anatomy of the ear is designed in such a way that the existing auditory reflex plays the role of a protective mechanism: under the influence of strong sound vibrations, the muscles of the tympanic cavity are strained, the chain of the auditory ossicles and the tympanic membrane is deformed, and there is resistance to sound vibrations that protects the sensitive hair cells. Impedance measurement makes it possible to check the degree of this resistance. Based on acoustic stimulation of the middle ear, impedance measurement allows to objectively assess the condition of the tympanic membrane, auditory tubes and ossicles, pressure in the middle ear, and find out if there are scars or fluid in the middle ear cavity.

In addition, ear impedance measurement makes it possible to record the contraction of the auditory muscles and assess the acoustic reflex threshold, incl. discomfort threshold, to differentiate diseases of the inner and middle ear: otitis media, tubo-otitis, otosclerosis, to confirm or deny the disease of the auditory nerve.

Impedance Methods

Ear impedance measurements include tympanometry and auditory reflex testing.

The impedance method - tympanometry means checking the mobility of the tympanic membrane under air pressure in the ear canal. Tympanometry is prescribed for adenoid diseases, pathologies of the eardrum and auditory tubes, diseases of the middle ear, hearing impairment, after otitis media.

An audiologist conducts tympanometry after examining the ears, removing sulfur masses (if necessary) and explaining the essence of the test to the patient. This procedure of impedance measurement takes place as follows: the doctor inserts a small rubber probe into the ear canal and turns on the device - an impedance meter, which, using a special pump, changes the pressure in the ear and makes the eardrum move. The pressure in the ear canal is measured using a small microphone connected to a probe inserted into the ear. The procedure is painless, the patient feels the same pressure in the ear as when climbing the mountains or during an air flight, and hears a squeak. During the acoustic test, do not chew, move or speak. Tympanometry lasts only 5-10 minutes, the audiologist receives the results instantly to analyze the patient's condition.

The second method of impedance measurement, the study of the auditory reflex, is based on the delivery of a loud sound stimulus to the ear. The sound is delivered directly into the ear canal, through an earpiece, earpiece or probe. The stimulus passes through the middle ear to the cochlea. From here, information about the intensity and frequency of sound is transmitted to the brain stem through the eighth nerve, where the sufficiency of the intensity of the sound stimulus for a reflex response is determined. With sufficient intensity, a two-way reflex response occurs: the impulse passes along the seventh nerve from both sides to the stapes muscles and causes them to contract. The sound stimulus for reflex research is 85 dB in one ear.

If there is no reflex response, the volume level is increased gradually by 10 dB until a reflex response occurs - the stapes muscles contract by 0.05 cm.

Acoustic impedance measurement is used not only for the diagnosis of ear diseases and hearing pathologies, but also for the selection of a hearing aid and for cochlear implantation. In these cases, the examination of the condition of the middle ear is combined with tonal audiometry. Ear impedance measurement is also used for control examination in the treatment of myasthenia gravis and facial paralysis.

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