Impedance audiometry test

Impedance audiometry test to identify hearing problems

An impedance analysis performed by an ENT doctor helps to identify possible problems with the auditory system, and in particular with the eardrum.

What is an impedance audiometry?

Auditory function tests can generally be divided into subjective and objective ones. Subjective examinations, for example the classic tonal and vocal audiometric examination, require the active collaboration of the person who, for example, has to raise the hand or press a button when they hear a sound sent through headphones inside a booth (tonal audiometry) or repeat a list of words sent both in headphones and without headphones (speech audiometry in headphones and in free field).

Objective exams do not require the active collaboration of the person being examined and are necessary both to complete the results of subjective examinations and to test the hearing of non-cooperating people (e.g. children under 4 years of age) and to obtain information precise on the functional state of the middle and inner ear and on the central acoustic pathways. Among the objective exams, impedance measurements, electrococleography, evoked potentials and acoustic otoemissions must be mentioned.

How is audiometry impedance test done?

Impedance audiometry is an objective, non-invasive diagnostic test that provides indications about

  • the motility of the tympanic membrane (tympanometry),
  • the presence or absence of endotympanic effusion (middle ear)
  • the presence or absence of stapedial reflexes, such as in case of otosclerosis.

The examination itself lasts about ten minutes and is carried out using a particular device called an impedance meter. It does not require any preparation procedure; a necessary condition is the integrity of the eardrum membrane, the absence of ear wax and the absence of secretions in the ear (for example purulent external otitis).

Impedance audiometry is usually performed after the specialist visit and audiometric examination at any public otolaryngology facility or private clinic. Once the doctor has established that the ear canal is free of secretions or earwax, he introduces a small probe, with a rubber terminal. The pressure delivered by the probe will determine a series of traces, visible on the impedance meter, which provide, in sequence, indications on the conditions of the eardrum and middle ear (tympanogram) and the presence or absence of stapedial reflexes.

Impedance test results and tympanogram

The impedance audiometry is used to assess the resistance that the middle ear structures (tympanic membrane and ossicular chain) oppose to the passage of mechanical vibratory energy (sound waves) from air to the liquids present in the cochlea. It therefore provides specific information on the functioning of the middle ear (eardrum-ossicular system).

It is a non-invasive, easy to perform examination designed to identify any hearing problems caused by middle ear pathologies (eg catarrhal otitis media, tympanosclerosis, otosclerosis, etc.). Generally impedance measurements are divided into tympanometry and study of the stapedial reflex. Tympanometry is performed by inserting a probe equipped with a soft rubber pad necessary for a perfect seal in the external auditory canal. A graph called tympanogram is obtained (visible as a bell-shaped curve) which is the exact value of the pressure existing in the middle ear. The graphic representation of the tympanometric curve allows the specialist to have useful information about the state of the middle ear. Generally the resulting curves are divided into:

  • type A tympanogram (bell curve, normal peaking at zero);
  • type B tympanogram (flat, sign of increased rigidity, index of endotympanic effusion as in the case of purulent otitis media);
  • type C tympanogram (curve with normal morphology with peak shifted to negative pressure values, typical of otitis media without effusion).

Curves of type D and E, rarer to see, are always an indication of middle ear pathology. Tympanometry also allows the exploration of the functionality of the Eustachian tube, while the study of the stapedial reflex is very useful in identifying some pathological phenomena that can affect the middle ear (eg. Otosclerosis).

Impedance audiometry in children

In children, the impedance test and, in particular, the tympanogram provide the specialist with basic information on the presence or absence of inflammation of the middle ear. Otitis media can be divided into catarrhal and purulent and may result in the presence of a more or less abundant mucous, serous or purulent exudate that partially or completely occupies the middle ear.

Less frequently during the summer months, otitis media have their highest incidence in the winter season in the middle of the flu period. Catarrhal otitis media can occur at any age, although it is more common in the pediatric range, so much so that about 80% of children have at least one episode of otitis media before school age.

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