ULTRASOUND

From Big Medical Encyclopedia

ULTRASOUND — elastic vibrations and waves, frequency to-rykh exceeds the upper bound of the range of acoustical frequencys heard by the person. The lower bound of ultrasonic frequency range is conditional since the threshold of acoustical perception of the person has considerable dispersion (see the Sound, Hearing, the Acoustic analyzer).

Depending on frequency At. has specific features of generation, reception, distribution and use.

Many animals perceive sounds of much more high frequencies, than the person. So, dogs are capable to hear sounds with a frequency up to 4,4-104 Hz, rats — to 7,2 * 104 Hz, bats — to

11,5-K)4 of Hz. The animals leading a nocturnalism or living in dark caves and also marine animals use At. for exchange of information and echolocation.

In the nature sources At. there can be earthquakes, eruptions of volcanoes, etc. Ultrasound arises during the operation of rocket engines, nek-ry types of machines and mechanisms.

In the technical purposes U. receive by means of special devices — ultrasonic converters (radiators At.). Depending on what energy they will transform, they are conditionally divided on mechanical and electric.

In mechanical converters a source At. mechanical flow energy of gas or liquid is. Such converters (air or liquid whistles and sirens) are rather simple on a design, however have the broad range and instability of frequencies that limits a possibility of their practical application. In electric converters as an energy source electric current is used, and operation of such converters is based on the magnetostrictive or piezoelectric phenomena.

Ability of bodies of iron, nickel, their alloys and nek-ry other materials to periodically change the sizes in variation magnetic field is the cornerstone of operation of magnetostrictive converters. Magnetostrictive radiators usually use for receiving ultrasound with frequencies up to 100 kHz. They found application in surgery, stomatology, pharmacy, etc.

Ability of the plates which are cut out definitely from quartz crystals, tourmaline, seignette salt, niobate of lithium, a piezoceramics and other materials to change the sizes under the influence of variation electric field (see is the cornerstone of work of piezoelectric radiators. Piezoelectric phenomena). Piezoelectric transducers use in medicine in devices for ultrasonic therapy, ultrasonic diagnosis, etc.

Action of ultrasound in biol. to Wednesday depends on frequency At., extents of its absorption, a form of the ultrasonic field and its intensity (i.e. the mean energy transferred by the ultrasonic wave in unit of time through unit of area located perpendicularly to the direction of distribution of a wave). Intensity At. in the International System of Units (SI) measure in W/sq.m. Average intensity At., radiated by a flat radiator (including medical), measure by means of so-called ultrasonic scales — the devices registering pressure, a cut the ultrasonic wave renders on an obstacle. Intensity At., the flat radiator radiated by different elements of a surface, it is not identical: over the center to an izl

of a chatel intensity At. exceeds average values by 2 — 4 times (theoretically by 4,3 times).

If intensity At. changes in time (pulse At.), it is characterized by average or maximum values in time. Average intensity of ultrasound (/with in) is connected with maximum (/m in) a ratio:

I = 1 —

page of century of m of Century. (Mr.)

where t — duration of an impulse, t — duration of an interval between impulses.

Rate of propagation At. in soft biol. fabrics (internals, muscles, etc.) changes ranging from 1450 to 1650 m/s, depending on the nature and concentration of substances in unit volume of fabric. Speed At. in a bone tissue about 3500 m/s. In medical practice results of measurement of speed At. in fabrics use for assessment of a condition of various fabrics, naira, extents of demineralization of a bone tissue.

Intensity At. decreases with increase in distance from a ystoch-nickname of radiation according to the equation:

7 - ah

I =/0 e i

where/0 and / — intensity At. in initial and remote from it on x a point, and — coefficient of attenuation, e — the basis of natural logarithms. The absorbtion coefficient depends on properties of that Wednesday, in a cut the ultrasonic wave, and external conditions extends (temperatures, pressure, frequencies At.). Than the high frequency of ultrasonic fluctuations, is stronger absorbed by that At. in this environment, in t. h, in biological fabrics. Thereof for impact on internals and fabrics in physical therapy use At. with a frequency of 800 — 900 kHz, and in dermatology frequency At. raise to 2,5 — 3 MHz.

Length of an ultrasonic wave of X is connected with the frequency of ultrasonic fluctuations (/) a ratio with = X f where with — rate of propagation At. in this environment. For At., used in therapy and diagnosis, I do not exceed 0,16 cm. Thanks to small wavelength At. it can be radiated in the form of the directed beam or be focused by means of special lenses.

During the focusing energy At. concentrates in the small volume of substance on nek-rum distance from a radiator: can be reached intensity At. up to the size about 104 — 105 W/cm2. Focused At. use for impact on separate nerve terminations, destructions of underlying structures of a brain or reversible suppression of separate functions (see. Stereotaxic neurosurgery), destruction of new growths in soft tissues, etc. Bases of use focused At are developed. for acoustical prosthetics.

At. renders on biol. systems combined effect — thermal, mechanical, chemical, electrophysical. Heat which is marked out in biol. to Wednesday at absorption of energy At., can lead to local temperature increase of fabrics, change of speeds of course of biochemical processes and even to thermal damages of fabrics. At intensity At. from cm '1 and the frequency of 1 MHz for 0,5 — 5 rumple about 1. (depending on conditions of heat exchange and properties of fabric) muscular tissue can heat up on 5 — 7 °.

Mechanical action At., connected with the oscillatory shift of particles of the environment in an ultrasonic wave (see Vibration), it is essential for obluchayemoi'i biol. systems at intensity of 1 — 2 W/cm2 and the frequency of 1 MHz. when ham of shift reaches a threshold of sensitivity mekhaporetsep t <>r ov (see).

In liquids, and also in biol. fabrics under the influence of continuous not focused At. formation of microbubbles — cavitation (see) can happen intensity of St. 0,3 W/cm2. In fabrics it is followed by formation of a number of chemical connections (e.g., hydrogen peroxide), free radicals (see Radicals free), etc., capable to react with macromolecules and macromolecular complexes, significantly changing their properties. As a result considerably permeability of cellular membranes increases.

Under action At. in fabrics there is a variable electric potential (so-called vibropotential) reaching at intensity At. about 1 W/cm2 of size, comparable with a potential of cellular membranes that can cause their depolarization (see) and change of permeability for nek-ry ions.

Efficiency of separate factors, from to-rykh develops ultrasonic influence, differently depends on parameters U. and conditions of radiation, but all of them are capable to influence a microenvironment of a cell, to change conditions of transportation of substances through its membrane.

Threshold intensity biol. actions At. its such intensity is, the cut is lower there is no change of permeability of cellular membranes and consequently, «are not started» regulatory and reparative process y in cells, directed to mitigation of consequences. caused by these changes. According to many researchers. this threshold makes 0,01 W/cm2.

In nek-rum an interval of higher intensivnost At. (0,01 — 0,1 W/cm2) at short-term influence (up to 10 — 15 min.) there are no visible changes in structure and functions of cells. It is caused by action of the compensatory processes caused by changes of permeability of cellular membranes directly during ultrasonic radiation. The upper bound of this interval of intensivnost is accepted as one more registered threshold biol. actions At. It on average corresponds to the lower bound of a therapeutic interval of intensivnost At. also lies within 0,05 — 0,1 W/cm2. In a certain interval itstens and in a nose those At., the exceeding 0,1 W.'sm2, observed biol. effects are reversible. The upper bound of this interval matches, as a rule, a threshold of cavitation or such parameters U., to-rye provide temperature increase of the environment to catastrophic for biol. object of values.

Physical. - chemical changes in biol. systems at ultrasonic influence of a lokalna. At the same time the response to ultrasonic influence has the general character. So, at action At. on one extremity changes in another are observed, local ultrasonic influences lead to increase of a tone of peripheral vessels, temperature increase of all organism, etc. An organism, being nonequilibrium dynamic system with many feed-backs and regulatory mechanisms, differently reacts to continuous and periodic (pulse) ultrasonic influence.

Thereof depending on the purpose of ultrasonic influence use At. this or that harak Terra. So, in physical therapy, generally apply continuous and pulse At. with a frequency within 0,8 — 3 MHz and intensity of 0,05 — 1 W/cm2. In the diagnostic purposes apply At. with

a frequency of 1 - 10 MHz in the continuous mode at intensity At., not exceeding 0,05 W! cm2, or in pulsed operation at intensity At., measured by tens and hundreds of W/cm2; at the same time average intensity At. in time does not exceed 0,01 W/cm2 that is reached by use short (10 ~ 6 sec.) impulses with a frequency of their following within 103 impulses of 1 sec. In ultrasonic surgery use tools, a cutting edge to-rykh continuously fluctuates with frequencies of 10 — 100 kHz and with an amplitude of 5 — 50 microns. Use also pulse and continuous focused At. with frequencies of 0,5 — 5 MHz and intensity in focal area from units to tens of thousands of W/cm2. Ultrasound with various parameters is used for processing of contaminated wounds, washing and sterilization of surgical instruments and materials, by definitions of mechanical resistance of membranes of erythrocytes, leukocytes, etc.

At. use also for a fonofo-cut, i.e. introduction to an organism of medicinal substances through the unimpaired skin (fonoforez differs from an electrophoresis in the fact that at a fonoforeza medicinal substances get in cells whereas at an electrophoresis they concentrate generally not in cells, and in intercellular space).

Professional harm during the work with the ultrasonic equipment. Working conditions and character of the irofvrednost influencing l and c about with l at 11 in and yu shch and x at l t r and z in at to about in y e installations, determine I many mi by factors, first of all frequency of v of fluctuations generated at l to a trazv of a kova.

Depending on the frequency characteristic At. the ultrasonic equipment is divided into two basic groups: 1) installations or devices, in to-rykh it is used low-frequency At. (frequency of fluctuations within 11 — 100 kHz), applied to active impact on substances and various technological processes (degreasing, cleaning, welding, the soldering, a tinning, machining, coagulation of aerosols, decontamination of liquids, crystallization of metals, cutting and connection biol. fabrics, sterilization of instruments, pharmaceuticals, hands, etc.); 2) installations, in to-rykh it is used high-frequency At. (frequency of fluctuations within 100 kHz — 1000 MHz), information applied to receiving, control, the analysis, processing and signaling in radio electronics (defectoscopy, viscometry, communication) and medicine (in diagnostic or to lay down. the purposes — sound vision, treatment of various diseases of a backbone, joints, a peripheral nervous system, in ophthalmology, dermatology, gynecology, etc.).

Idiosyncrasy of working conditions of operators of low-frequency ultrasonic installations is existence of the acoustic complex influencing them consisting of a high-frequency noise and low-frequency ultrasonic fluctuations. In addition to the general impact on an organism low-frequency At. renders local / action at contact with the processed details or devices, in to-rykh fluctuations are excited. The general level of sound pressure in the heard and ultrasonic frequency ranges in most cases fluctuates from 90 to 120 dB with a maximum of energy at a working frequency of installations 18 — 44 kHz. The range of the noise arising during the work of ultrasonic installations includes all sound, and also low-frequency ultrasonic frequency range. Intensity influencing hands At. during loading and unloading of details from ultrasonic bathtubs, at deduction of details and some other tekhnol. can reach operations — 7 W! szh2.

At service of the high-frequency ultrasonic equipment operators are affected At. with

a frequency within 0,5 — 5 MHz and intensity of 0.001 — 0,1 W/cm2 only at contact of a source At. with a body surface. From the technological processes based on use high-frequency At., the greatest distribution was gained by defectoscopy (see).

At systematic influence "At., intensity and time of influence to-rogo exceed marginal, functional changes from the central and peripheral nervous system, cardiovascular and endocrine systems can be observed, acoustical and ve with ti at l I r in N og about and N and l and z and that r about century.

Persons, the long time servicing the ultrasonic equipment complain of a headache, dizzinesses, the general weakness, bystry fatigue, frustration of a dream (sleeplessness at night and drowsiness in the afternoon), irritability, a memory impairment, hypersensitivity to sounds (hyperacusia), fear of bright light; complaints of dispeptic character are frequent.

By the end of change at workers bradycardia and hypotonia is noted, on an ECG reveal a bradisistoliya, disturbance of intra-atrial and vnut-rizheludochkovy conduction. In blood — a monocytosis, an eosinophilia, then passing into an eosinopenia. Quite often find decrease in a sugar content in blood, a hyperproteinemia, decrease in a vitamin saturation of blood. These symptoms have most often unstable character. When At. makes impact not only through air (it concerns low-frequency At.), but also a contact way (high-frequency At.), the specified symptomatology is expressed stronger.

At a wedge, a research it is diagnosed asthenic or astheno - a vegetative syndrome (see. Asthenic syndrome), diencephalic disturbances — a lose of weight, subfebrile condition, paroxysmal attacks like visceral crises, increase in mechanical excitability of muscles, an itch, etc. are sometimes observed (see. Hypothalamic syndrome). During the long work with ultrasonic defectoscopes at operators vegetovascular disturbances in the form of an angiodystonic syndrome (see Dystonia vascular), a vegetative polyneuritis (see), a vegeto-myofascitis of hands and vegetovascular dysfunction can develop (see. And ngiotro-fonevroza).

All-cerebral disturbances are, as a rule, combined with the phenomena of a vegetative polknevrit of hands (more rare than legs) different degree of manifestation (pastosity, a Crocq's disease, a hyperhidrosis, decrease in all types of sensitivity as short or long gloves).

Treatment symptomatic and fortifying. In the presence of early. sharply expressed manifestations of astenisation and vegetovascular shifts working capacity remains on condition of constant observation and out-patient treatment; the direction in a dispensary, sanatorium is reasonable. Transfer into the work which is not connected with influence At is in some cases recommended temporary (for 1 — 2 month). At development of the expressed permanent neurodynamic and neurocirculatory frustration, a hearing disorder and a vestibular mechanism, in addition to performing the corresponding treatment in out-patient or stationary conditions, the rational employment excluding influence of vibroakusti-chesky factors proiz is recommendedvodstvenny environment.

For prevention of an adverse effect At. on the persons servicing ultrasonic installations GOST 12.1.001-83 are developed («SSBT. Ultrasound. The general safety requirements»), «Sanitary standards and rules during the work on industrial ultrasonic installations», the limiting levels of sound pressure in high-frequency area of sounds and ultrasounds in workplaces, and also «Sanitary standards and rules during the work with the equipment creating ultrasound transferred in the contact way to hands working», according to the Crimea the maximum size of ultrasound in zones of contact of hands of the operator with working parts of devices and installations is limited to a limit 110 dB or 0,1 emi sm1 in frequency range from 0,1 to 10 MHz.

To improvement of working conditions of the persons which are affected At., first of all technical actions promote (creation of the automated ultrasonic equipment and installations with distance steering). Transition to the low-power equipment is of great importance that promotes decrease in intensity At. and noise in workplaces on 20 — 40 dB. When deceleration of power of the ultrasonic equipment contradicts interests of technology, it needs to be equipped with the soundproofing devices (casings, screens, etc.), to place in the soundproofed rooms or cabins with distance steering. Prevention of contact influence At. it is reached by switching off of supersonic generators during loading and unloading of details. During the loading of details it is necessary to use special devices (grids, clips, nippers with handles from sound-proof materials, etc.) «At design of ultrasonic installations it is reasonable to choose working frequencies, the most remote from the heard frequency range (it is not lower than 22 kHz).

When for the production reasons it is impossible sni-

to zit the level of noise and intensity At. to marginal values, obligatory use of individual protection equipment — antinoise (see), two-layer gloves is necessary (outside — rubber, internal — cotton).

The correct organization of a work-rest schedule of working is of great importance. In particular, it is recommended through everyone 11/2 — to arrange 2 hour of work 10 — 15-minute breaks, to-rye can be filled with other types of works which are not connected with impact of noise and At.

Operators of ultrasonic installations are subject obligatory preliminary (at employment) and to annual periodic medical examinations (see. Medical examination).

See also Ultrasonic diagnosis, Ultrasonic therapy. Bibliography: Gavrilov JT. River and Tsirulnikov E. M. The focused ultrasound in physiology and medicine, L., 1980, bibliogr.; Zhuravlev A. I. and Akopyan V. B. Ultrasonic luminescence, M., 1977, bibliogr.; M e l to at - A. S's mova., Lisichkina 3. Page and Pots S. I. Ultrazvuk, M., 1975, bibliogr.; Molchanov G. I. Ultrasound in pharmacy, M., 1980, bibliogr.; Sarvazyan A. P. The specific mechanisms of biological effect of a pulsed ultrasound connected with dynamics of biological systems in book: Molek. and cellular biophysics, under the editorship of G. M. Frank, page 107, M., 1977; H and r-kin A. A., Bogdanovich L. I. and At l and shch and to V. S. Ultrazvuk and reactivity of an organism, Minsk, 1977, bibliogr.; Elpiner I. E. Biophysics of ultrasound, M., 1973;

H a z-zard D. G. a. L i t z M. L. Biological effects and characterizations of ultrasound sources, L., 1979; Hussey M. Diagnostic ultrasound, An introduction to the interactions between ultrasound and biological tissues, Glasgow, 1975; N y-b about r g W. L. Physical mechanisms for biological effects of ultrasound, based on a series of lectures delivered, Rockville, 1978. V. B. Akopyan; G. A. Suvorov (gigabyte.).,

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