ACOUSTIC INJURY (Greek akustikos — acoustical) — the specific damage of an acoustic organ caused by sounds of excessive force or duration. And. t. results more often from action on an auditory organ of noise (a noise injury) and is much more rare as a result of action of true tones. Distinguish acute and chronic A.T.
Etiology. The acute akusticheskayatravma arises at short-term action of sounds which intensity is close to a threshold of sensation of pain, or exceeds it. It can arise at action of periodic sounds (e.g., sirens) or powerful noise (e.g., jets of rockets and airplanes) and is observed as an epiphenomenon at a detonation injury. In the latter case preferential impact on an organism is exerted by change of barometric pressure (see. Barotrauma ).
Modern experimental data set limits of intensity of sounds which action can cause acute And. t. (fig.).
The chronic acoustic injury arises owing to long action on an auditory organ of noise of various intensity that takes place in some productions and military science.
Phenomena And. t. are most often noted at testers of jets, smiths, revolvershchik, punchers, weavers, drillers etc. From people of military professions the engineers and technicians servicing the aircraft equipment and also pilots, tankmen and gunners most often suffer from noise.
Expressiveness And. t. is defined by intensity of noise and its spectral structure, frequency and duration of action and depends on individual resistance of acoustical system to action of noise. Chronic And. t., as a rule, leads to development of so-called professional relative deafness (see).
Pathogeny and pathological anatomy. Acute And. t. arises at the intensity of sounds causing disturbance of a microstructure of elements of a middle and inner ear. V. F. Undrits, R. A. Zasosov (1933), N. I. Ivanov (1968) works confirm this situation. In a tympanic membrane and skin of a lateral wall of an attic vasodilatation and separate dot hemorrhages is found. In an inner ear the shift of cells of a kortiyev of body, their nabukhlost and a turbidity, hemorrhages etc. is noted.
Since 60th years by means of a submicroscopy, biochemical and histochemical methods it is found out that else before emergence of histologic disturbances at the cellular level there is a reorganization of protein and nucleinic metabolism, function of enzymes of tissue respiration changes. It is established that single action of pulse noise by intensity in 120 dB leads to increase in activity of enzyme of tissue respiration of cells of a kortiyev of body and nek-rum to increase in the content of RNA in them. Impact of noise of big intensity (135 — 160 dB) considerably lowers activity of respiratory enzyme and reduces the content of RNA, and is preferential in outside voloskovy cells of the lower and average curls. This phenomenon is estimated as a result of sharp increase in intracellular oxidizing processes, leading to bystry exhaustion of activity of respiratory enzyme and reduction of content of RNA at acute And. t.
At the noise levels exceeding 125 — 128 dB, sound energy appears already an irritant not only the acoustic analyzer, but also mechanioreceptors of a body of the person.
For emergence chronic A.T. major importance has repeated and long action of the sounds causing the constant tension of processes of intracellular metabolism in structures of the acoustic analyzer. Long action of sounds leads to acoustical exhaustion in the beginning, further causes the accruing degenerative changes in acoustical system and gradually progressing relative deafness.
For chronic And. t. the degeneration of cellular structures of all acoustic analyzer — the receptor device, nerve fibrils p the corresponding central formations of cortical and subcrustal structures of a brain is characteristic.
A picture of pathological changes at And. t. it is studied in the animal experiments made in laboratory and working conditions in detail. By experiments it is established that the acoustic injury caused by true tones is characterized not only by degenerative changes in the area of the main membrane corresponding to this tone, but also a degeneration of the cells located closer to the main curl of a snail where there are irritations of a kortiyev of body high-pitched sounds.
Chronic And. t. arises at action of sounds of any frequency characteristic, however most quickly develops at dominance of high-pitched sounds (more than 1000 Hz), especially with a frequency of 4000 Hz.
Clinical picture. At acute And. t. patients complain of pressure sense or ear pains. The Otoskopichesky picture at acute And. t. shows limited or diffuse redness of a tympanic membrane and skin of an outside acoustical tsrokhod. At audiometrip increase in thresholds of hearing of various expressiveness is noted.
At chronic And. t. victims feel a sonitus and complain of a hearing impairment. The Otoskopichesky picture happens or normal, or there is a vtyanutost of tympanic membranes.
In an initial stage chronic And. t. the hearing impairment characteristic of damage of the main curl of a snail appears the earliest symptom. In far come cases chronic And. t. the symptomatology of changes of hearing is typical for diffusion defeat, i.e. relative deafness on sounds of both high, and low frequency is noted.
Owing to functional interaction of afferent systems action of sound irritants at chronic And. t. causes not only change of function of the acoustic analyzer, but also a number of adverse responses from other systems of an organism. Changing a functional condition of c. the N of page, action of noise becomes the reason of vegetovascular dysfunction, asthenic and neurotic reactions and so forth.
The diagnosis is established according to the anamnesis, an otoskopiya and a research of hearing.
Treatment. At acute And. t. absolute rest is necessary for the acoustic analyzer, purpose of resorptional means (intravenously 40% solution of glucose, etc.) and toning (an aloe, an apilak, B1 vitamin, etc.). Also vitamins A, E which render positive effect on blood circulation p increase in oxidizing processes in an organism are recommended. In the expressed cases chronic And. t. treatment is ineffective since relative deafness is most often caused by irreversible degenerative changes of the acoustic analyzer. For reduction of unpleasant subjective feelings it is recommended to use drugs adenosine triphosphoric to - you, biogenic stimulators (FIBS), a complex of polyneuramins etc.
Prevention. Measures of collective protection are the most drastic remedy of prevention. Methods of decrease in intensity of noise of the source of noise and use of the means interfering distribution of noise by sound insulation, a sound absorption and sound reflection concern to them.
Rationing of noise levels and time of its action on production is important. «Sanitary standards on industrial facilities» (CH245-71) form a basis of rationing of action of noise in our country.
Norms for extremely transferable noise levels usually determine time of activity of the person in conditions where noise works incidentally, its level cannot be reduced, and methods of reduction of intensity of noise can worsen operation of units. However this type of rationing cannot be applied to the working operations demanding strictly certain time for performance. Norms of marginal noise levels are the most widespread.
Big distribution was gained also by various individual protection equipment — from the wadded ball inserted into outside acoustical pass, giving insignificant muting to the modern caps with a helmet reducing noise level at low frequencies to 20 dB (see. Protivoshuma ).
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E. M. Yuganov.