The hearing impedance

We may not know all the details of the mechanism of hearing, but it is important to know that an important phenomenon occurs at the eardrum and ossicles. Hearing impedance will tell us more
Description and details

The hearing impedance is a review that assesses the overall transmission of the hearing. This exam will primarily assess the level of resistance of the eardrum with the sounds perceived and atmospheric pressure.

The impedance is necessary in case of otitis, or in case of hearing impairment.

Mechanism tympanoossicular impedance

The eardrum

The eardrum is a flexible membrane that separates the middle ear from the outer ear.

Flexibility or rigidity of the eardrum depends on:

The pressure at the middle ear pressure that must be balanced with that of the (outer ear) external environment

The permeability of the Eustachian tube: this is an important factor in the balance of pressure between the middle ear and the outer ear obtaining

The operation of bones: the eardrum is accollé the bones. The vibration of the bones in a sound stimulation also generates a resistance movement of the eardrum.

An alteration in these factors could interfere impedance of the eardrum.

The acoustic reflex

The acoustic reflex is a control system for the transmission of sound waves. The bracket has two muscles whose contraction provides a protective role:

A selection of sound waves of high intensity, which helps reduce the intensity of sound waves transmitted at the inner ear

A selection of very high frequency sounds, we speak of the masking effect. The bass tend to hide the treble to reduce the frequency of sound waves transmitted into the inner ear

An adaptation of the auditory system to avoid ear fatigue

The acoustic reflex is under the influence of some factors:

Age (reflex is less bright in the elderly)

The duration and frequency of the sound stimulus

Thus, by varying flexibility / rigidity, tympanic-ossicle system helps regulate the speed, frequency and amplitude of the sound waves before transmitting at the inner ear.

Techniques and results

The patient is examined in a sitting position. The doctor places a speculum in the ear to be examined, which are introduced from three small flexible probes.

- Probe to change the air pressure at the eardrum,

- A probe emits sound waves at high intensity to cause stiffness at the eardrum and ossicles

- A probe collects the sounds and movements back at the eardrum.

This system is connected to a pressure gauge also displays the responses of the eardrum following various pressures generated in the external auditory canal. The result is in the form of a curve.

There are two main factors to consider:

Tympanometry studying the change in stiffness and strength tympanoossicular system when the pressure variation. In this technique, the pressure is gradually increased. Changing the elasticity and mobility of the eardrum has resulted in a curve that can be interpreted by the physician. Depending on the shape of the graph (tympanogram), the doctor may have information about a violation of the tympanic cavity, impaired the function of the eustachian tube and the presence of fluid in the middle ear.

The acoustic reflex study the reflex contraction of the muscles of the bracket on the issue of a loud noise. This technique basically allows to study the mobility of the bracket facing intense auditory stimulation. The acoustic reflex is a normal reflex phenomenon which corresponds to the reaction of the ossicles at a high frequency sound. When this reflex is diminished or absent, it is the sign of a breach of bones (otosclerosis, for example). When this reflex is even for low-intensity sounds, presumably irritation auditory sensory pathways of the inner ear by a tumor.