Decrease in hearing

Description:

Hearing disorder — full (deafness) or partial (relative deafness) decline in the ability to find and understand sounds. Any organism capable to perceive a sound can have a hearing disorder. Sound waves differ on the frequency and amplitude. Loss of ability to find some (or all) frequencies or inability to distinguish sounds with a low amplitude, is called a hearing disorder.

Is caused by a wide range of biological and ecological factors. Diseases of an inner ear and an acoustical nerve, an inflammation of a middle ear or some infectious diseases — meningitis, flu, etc. can be the reasons; sometimes — an injury or long impact of strong noise and vibrations.

The person has a hearing disorder making impossible perception of the speech, is called deafness, and easier degrees of a hearing disorder complicating perception of the speech — relative deafness (neurosensory, conductive or the mixed character). Besides, deafness happens inborn or acquired.

Symptoms of Decrease in hearing:

When structures of an outside or middle ear cease to transmit correctly a sound signal to an inner ear, conductive decrease in hearing becomes result. Usually such type of relative deafness is reversible and can be corrected by surgery or other methods. Ear infections, injury of an ear, for example perforation of a tympanic membrane, and also cerumen impaction are the reasons. Ear infections quite often occur at children therefore it is regularly very important to parents to check hearing and to know relative deafness signs.

The neurosensory hearing disorder happens because of an anesthesia of spiral body of a snail of an inner ear or disturbances in work of acoustical nerves. Such disturbances can result in relative deafness of all degrees — from easy to heavy — and even to full deafness.

The most part of a neurosensory hearing loss is caused by anomalies of voloskovy cells in kortiyevy body of a snail in people. Sometimes the neurosensory hearing loss caused by disturbances in the VIII cranial nerve (eighth cranial nerve) or in the departments of a brain which are responsible for hearing meets. In extremely exceptional cases of this kind of a hearing disorder only the acoustical centers of a brain (the central hearing disorder) suffer. In this case the person hears normally, but quality of a sound so bad that he is not able to sort the human speech.

Anomalies of voloskovy cells can be inborn or acquired during lifetime by an individual. It can be both genetic anomalies, and injuries from intensive noise and defeat owing to infectious diseases.

Neurosensory (sensonevralny) relative deafness arises when the inner ear ceases to process a sound normally. It is caused by various reasons, however the most widespread is defeat of voloskovy cells of a snail because of a loud sound and/or age processes. When voloskovy cells are insensitive, sounds are not transmitted normally on an acoustical nerve of a brain. The Sensonevralny hearing loss occupies 90% of all cases of relative deafness.

In spite of the fact that sensonevralny relative deafness is irreversible, it is possible to avoid bigger harm, using ear caps at a loud sound or listening to music at a smaller loudness.

Reasons of Decrease in hearing:

The hearing disorder is caused by various biological and ecological factors. Usually vulnerable part of a body is the ear.
Long-term impact of noise. The people living about the airports or brisk highways are exposed to continuous sound radiation by intensity 65 — 75 dB. If in such conditions of people it is forced to spend much time on the street or to be at home with open windows, then gradually at it hearing easing can develop. There are certain standards according to which tolerance level of noise and risk for human health is established. In particular, the USEPA organization (United States Environmental Protection Agency — Agency on environment protection of the United States of America) establishes a threshold in 70 dB at the round-the-clock radiation as acceptable for health (EPA, 1974).

    * The hearing disorder from long-term impact of noise usually acts on frequencies about 4000 Hz.
    * The noise level, the less safe time of stay under its radiation is louder. Usually this time decreases twice by each additional 3 dB. Sometimes for convenience use not 3, but 5 dB.
    * The portable losing devices, such as iPod (which loudness can reach 115 dB), can cause a severe hearing disorder.


Genetic disorders of hearing. There is not syndromal (isolated) and syndromal hearing disorder.

Not syndromal hearing disorder - the relative deafness which is not accompanied with other symptoms which would be descended. Happens in 70% сучаев hereditary deafness.

The syndromal hearing disorder is the genetically caused decrease in hearing in combination with other signs or diseases of other bodies and systems. Happens in 30% сучаев hereditary deafness. More than 400 various syndromes in which one of signs is deafness are described.
The most known of them:

Syndrome of Pendreda-tugoukhost in combination with an enlargement of the thyroid gland

Usher's syndrome - the combined hearing disorder and sight.

Syndrome of Vaardenburga - a hearing disorder and pigmentation.
Jervell and Lange-Nielsen syndrome - a combination of deafness and arrhythmia of heart to increase in an interval of QT.


On a mode of inheritance of a hearing disorder it is possible to divide into the following forms:

  1. Autosomal and recessive (78%)
  2. Autosomal and dominant (20%)
  3. H-linked (1%)
  4. Mitochondrial (1%)

Now more than 100 genes in which mutations lead to a hearing disorder are known. Mutations, certain, specific to it, are characteristic of each population. At the same time mutations in a gene коннексин 26 (GJB2) are the reason of one third of cases of genetically caused hearing disorder. The mutation 35delG most often occurs among Caucasian race. About 2% of Russians - carriers of this mutation.

Treatment of Decrease in hearing:

    * purpose of medicamentous means;
    * use of special surdologichesky and logopedic techniques;
    * development of hearing and speech;
    * recommendations of the psychoneurologist;
    * hearing aid.