Ultra-high frequency and microwave currents. Physiotherapy

Influence of electromagnetic fields.

The organism of the person is subject to influence of electromagnetic fields (EMF). Living tissues test biological effects of EMF. EMF interacts only with such physical environments at which there are free or connected electric charges. In the environments containing charges of both types, EMF creates a current of conductivity, and a current of displacement which at the big frequency of a field becomes greater.

Interaction of magnetic and electric components of EMF with an organism leads to change of characteristics of biological system and strengthening of biological effects. It is necessary for considering at the resonant phenomena. In radiobiology all EMF are subdivided into two ranges: low (up to 10⁵ Hz) and high frequency (above 10⁵ Hz).

The body of the person in relation to low-frequency EMF possesses properties of a conductor. Under action of an external field the current of conductivity arises in tissues. As the basic representatives of free charges are ions. Length of electromagnetic waves (EMW) of low frequencies repeatedly surpasses the sizes of a human body, therefore such waves influence on whole organism. However this action on different tissues is not identical. Tissues differ on electric properties, and on sensitivity a current of conductivity. The most sensitive to the induced current of conductivity is nervous system. Current flows mainly on an intercellular liquid because its resistance is less than resistance of cellular membranes. The person and animals practically do not meet in an environment with such strong low-frequency EMF. Raising frequency of this field up to 200 Hz, it is possible to raise nerves and muscles, but sharp increase in a current is the biophysical mechanism of an electrotrauma.

In a basis of any mechanisms of medical action of high-frequency fluctuations is their primary action on the charged particles (electrons, atoms and molecules) of substances, from which tissues of an organism consist. In operation high-frequency fluctuations it is possible to divide two groups of effects - thermal effect and, so-called, specific effect. The thermal effect differs from the thermal effect received by other methods (hot-water bottles, an infra-red irradiation) by some advantages. Heating of tissues by currents and fields of high frequency occurs not due to transfer of heat brought to a surface of a body, and due to direct allocation of heat in the tissues located inside of a body and organs. It allows excluding heat-insulation action of a layer of a skin and hypodermic fatty tissue, and also thermotaxic action of system of blood circulation, which weakens transmission of heat to depth of a surface of a body. Unlike currents of low frequency currents of high frequency are capable to warm conductors and dielectrics. Currents of low frequency pass on all section of a conductor, and currents of high frequency basically pass in a thin superficial layer of a conductor. The current of low frequency force more than 50 mА is already dangerous to the person, currents of high frequency force 3-4 A are absolutely safe also any negative reactions in an organism of the person do not cause. It speaks that at passage through tissues of currents of low frequency the amplitude of fluctuation of ions can exceed breaking point of tissues. Painful sensations arise, a part of tissues collapse. At passage through tissues of currents of high frequency displacement of ions is small and currents of high frequency of unpleasant sensations do not cause.

Feature of thermal action of high-frequency fluctuations is that the quantity of heat allocated in organs and tissues of an organism, it depends upon parameters of fluctuations, basically frequencies, and from electric properties of tissues.

Selecting frequency of fluctuations, it is possible to provide allocation of heat in the certain tissues. Advantage of high-frequency methods is the opportunity easily to adjust power of the fluctuations acting on object, and, accordingly, intensity of thermal effect.

All methods of the treatment based on application of electromagnet fluctuations, differ by the way of influence on the patient and parameters of applied fluctuations: frequency, voltage, a power.

At darsonvalism a current with frequency 200-300 KHz at a voltage in some thousand volts is used. It is possible to take such current by means of an oscillatory contour with the automatic breaker. In this case there are electromagnetic fluctuations in the form of impulses.

At diathermy on the naked site of a body two lead plates connected with a therapeutic contour of the lamp generator are imposed. Between electrodes the high-frequency electric field arises, under which action in tissues of an organism a current with force 1,5-2 A and frequency 0,5-2 the MHz proceeds. At passage of a current in tissues of an organism the significant quantity of heat is allocated. If one of electrodes is made in rind of knife, then allocated energy can be used for welding of tissues (electrocoagulation) or their section which is not accompanied by a capillary bleeding.

At inductothermy the site of a body is located inside of coils of the solenoid connected to a therapeutic contour of the generator. The magnetic field of the solenoid induces in tissues currents with frequency of 10-15 MHz. It provides deeper warming up of tissues, than at diathermy.

At ultra high frequency (UHF) therapy the area of a body a subject treatment is located between two electrodes forming the condenser of a therapeutic contour. Between them the variable electric field frequency of 40 50 MHz arises (ultrahigh frequency). The electric field of such frequency influences current-carrying tissues and on tissues – dielectric, including bone substance, causing in them polarization. As a result of polarization dipole molecules of tissues come to oscillatory movement that is accompanied by formation of thermal energy and reception of medical effect.

The UHF-therapy, the most widespread electromedical method, represents influence on tissues of a body sick person of an electric field of ultrahigh frequency. The electric field is created by means of two

Fig. 1

a) diathermy, condenser electrodes connected by wires with generators of

б) inductothermy, UHF fluctuations. The part of a body of the sick person is

в) UHF-therapy. located

between electrodes

Distribution of heat between the superficial and deeply located tissues of a body of the sick person at UHF-therapy is more favorable, than at diathermy. Important advantage of UHF-therapy in comparison with diathermy is the opportunity to spend procedure with air-gaps between an electrode and a surface of a body. Presence of air-gaps allows reducing undesirable heating of superficial tissues. Area near electrodes in which density of power lines is maximal, settles down outside of a body of the patient.

Heating of tissues in electric field UHF is proportional to a square of intensity of a field. In a non-uniform field intensity is various and is characterized by concentration of power lines of a field. In absence of a body of the patient the field between electrodes is in regular intervals distributed in the center, to periphery power lines are bent. The area of a uniform field is more, than the attitude of distance between electrodes to their diameter is less. At an arrangement of the patient between electrodes of a line of a field go non-uniformly; they are bent in an average zone. Under electrodes the greatest intensity of a field is created. Therefore at absence of air-gap or small air-gap the greatest allocation of heat will be on a surface of a body and sharply decreases with depth. For maintenance of more uniform distribution of heat between the superficial and deeply located tissues about several centimeters are necessary to increase size of air-gaps. The most non-uniform part of a field near electrodes appears outside of a body and uniformity of influence on depth improves. For maintenance of effective heating tissues, the device for UHF-therapy should increase a voltage on electrodes as at increase in air-gaps the share of a voltage coming on them increases.

At possible to choose sizes of an electrode, size of a air-gaps, and also an inclination of an electrode in relation to a surface of a body, this can provide influence on the certain site of a body. Electrodes can be rigid and flexible. A flexible electrode and linings become stronger on a body elastic rubber bandage. Metal subjects in electric field UHF do not heat up, but near them, there is a concentration of power lines of a field thereof there can be local overheats and even burns. For this reason sitting or a bed for the patient at carrying out of procedures UHF-therapy should not have metal parts, the metal subjects which are being at the patient, should be removed, if they are located close to area of influence.

Extra care should be observed, if the patient has dental artificial limbs, and also the metal splinters which have remained in a body as a result of wounds, traumas. Crude clothes and its folds also can cause local overheats; therefore it is necessary to remove clothes before procedure, and a damp leather - to dry.

The thermal effect in tissues of an organism can be received by means of a high-frequency electric current (diathermy) or an electric field (UHF-therapy), at influence by a high-frequency magnetic field due to the phenomenon of an electromagnetic induction. The corresponding method refers to inductothermy. The magnetic field at inductothermy is created by means of the coil, flowed round by a high-frequency current.

At action of a variable magnetic field in tissues of an organism the electromotive power of an induction is directed, causing formation in them of so-called vortical currents. These currents create thermal effect. The method of inductothermy is based on it. The greatest formation of heat at inductothermy occurs in tissues to the big conductivity, in liquid environments (blood, a lymph), in a muscular tissues.

Contactless influence and allocation of heat in muscular and others tissues (rather with a layer of a leather and fatty tissues) is the important advantage of inductothermy. However, the certain restrictions are inherent for inductothermy. Allocation of heat in tissues to proportionally square of intensity of a magnetic field. The magnetic field is weakened at removal from coils of a spiral; the quantity of the allocated heat in tissues quickly decreases with depth. Burning in the limited site of a body testifies that coils of inductor in this place too close adjoin to a body owing to what the site with the raised intensity of a field and, hence, more intensive formation of heat is formed. In this case the air-gap between inductor and a body of the patient in a corresponding place should be increased.

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