Pulse currents in medicine. Use of pulse current. Action mechanism and effect

IN lately For diagnostic and therapeutic purposes, an intermittent direct current is used in the form of individual jigs (pulses) with pauses between them, the so-called pulse current.

Each impulse is characterized by a certain duration t and the subsequent pause of T 0, constituting together the period T.

Pulse currents are distinguished by:

• a) the form of impulses;
• b) the frequency of the recurrence of pulses per second (expressed in Hertz - Hz);
• c) the duration of each impulse (expressed in milliseconds - MSEK).

When electroplating, a slow increase in current, causing a gradual change in the concentration of ions in cells, in the conditions of adaptation of the tissue of leader, the non-timber irritation of the nerve endings. There is no contraction of the muscles; If the current includes and turn off quickly, the muscles cuts. This can be explained by some displacement of ions and the lag of diffusion processes in short-term current pulses. The degree of change in the concentration of ions is due to the power of the current and the duration of its impact.

Some forms of current pulses applied before different names. For example, intermittent galvanic currentwhich was obtained by incorporating a DC circuit of various kinds of interrupters (manual electro-breaker, a breaker metronometer, etc.). An ice-drying current was known with a number of breaks of 100 per second (with the ratio of the duration of the closure and the duration of the opening 1: 9), which caused the phenomenon of the electric circuit.

The pharadic current obtained from the induction coil, with the pulse frequency of 60-80 per second and the duration of the irrigation pulse of 1-2 ms are widely used. (Application of the pharadic current with therapeutic goal Wears title faradization.) Since the pharadical current is able to cause a long-term ("Tetanic" skeletal muscle ("Tetanic") reduction to the muscle fatigue and ultimately to its atrophy, for the electrostimulation of the muscles, they were offered to use periodic currents of current, the so-called rhythmic pharaduation, which causes alternately reduction and Muscle relaxation.

Currently, mainly apply next species Current pulses different in shape, duration and frequency.

1. Current with pulses rectangular shape. Duration of each pulse 0.1-1 MSEK at a frequency of 10-100 Hz. This type of current enhances the brake processes in the central nervous system and is used to obtain a condition similar to physiological sleep (Electroson).

The power supply apparatus is a pulse generator using an electron-parameter diagram. Electrodes are superimposed on the orphanage and maternity processes. This type of treatment with protective braking is used for some mental diseases, as well as in diseases associated with violation of the function of the corticisceral system ( ulcerative disease Stomach, hypertensive disease).

2. The tetanizing current is characterized by a triangular form of pulses. Duration of each pulse 1-1 1/2 ms, frequency of 100 Hz.

The source of this current form is the devices with electron-via schemes.

The Tetanizing Current causes a long reduction in transverse muscles, and it is used for electrogyamnascular - muscle exercise with the impaired function.

3. The exponential current (lark current) has a hollow rising curve), resembling the form of nerve action currents during its irritation. Pulse duration from 1.6 to 60 ms. The pulse frequency can be changed. Depending on the degree of damage, the muscles choose and the corresponding exponential current. To obtain a reduction rhythm - muscle relaxation uses the so-called modulator. The advantage of the exponential form of current is that it can cause motor reaction And more deeply affected muscles, when the Tetanizing current does not. This current form is used to stimulate muscles.

The source of pulse currents is the AFM device. It consists of a short-term pulse generator, pulse modulator and a modulating cascade transformer. In addition to the tetanizing and exponential forms of current, the apparatus can be used to treat continuous direct current (galvanization) and rhythmic galvanization.

The ACM apparatus is used for electrical stimulation (electrogymannascular) of muscles in violation of their contractile ability. Rhythmic electrostimulation improves blood supply and trophic of the neuromuscular apparatus, contributes to an increase in the volume and improvement of muscle performance, restoring the conductivity of nerve elements, favorably affects the regeneration of nerve fibers, thereby speeding up the restoration of the function of the affected muscle.

Electrostimulation is used in the lesions of the peripheral motor neuron (residual phenomena after transferred polio, neurutity of the facial nerve, traumatic neurites, secondary atrophies and paresis developed in connection with long-term inaction of muscles, functional paralymps). In order to enhance the function of smooth muscles, electrostimulation is shown, for example, in atony of the stomach, intestines, bladder.

Physical bases of low-frequency electrotherapy

Laboratory work №№ 14, 15

Literature

1. Remizov A.N. Medical and biological physics, "Higher School". M., 1987, ch. 15, 18, and 19.

2. Livent residents N.M. Course of physics, "Higher School". M., 1978, ch. 6, 27, 28.

3. Gubanov N.I., Uptbergenov A.A. Medical biophysics, "medicine". M., 1978, ch. nine.

4. Medizinische Physik (Physik Fur Mediziner, Pharmazeten und Biologen). SPRINGER - VERLAG WIEN NEW YORK. 1992.

Control questions

1. What is electric current? The conditions for its existence.

2. Ohmos law for the chain section. Ohm law for full chain.

3. What is the current density? How is it located?

4. What is the impulse, pulse current?

5. Name the main characteristics of the pulse, pulse current.

6. Give the definition alternating current. Write down the sinusoidal current equation.

7. Electrolite as an electric current conductor.

8. What does the conductivity of the electrolyte depend on?

9. What is electric container? What does it depend on?

10. What are the capacitive properties of biological tissues?

11. How do the capacitive properties of tissues on the passage of pulse current?

12. What is the impedance in the AC circuit?

13. What does the electrical conductivity of biological tissues depend on?

14. Equivalent electrical diagram of biological tissues (with explanations).

15. How does the capacitive resistance depend on the AC frequency?

16. Law of Joule-Lenza.

17. Can devices for low-frequency electrotherapy be used to warm the biological tissues (the answer to substantiate using the relevant laws).

Brief theory

An irritation of a certain character and force in the majority of organs and tissues causes the same reaction as natural excitement. In addition, this impact can be strictly dosed both by strength and time. It is widely used in physiology and medicine. In physiology when studying excitability various organs and fabrics, mostly nervous and muscle, in medicine - with insufficiency or violation of the natural function of certain organs and systems.

Using an irritant electric current to change functional state Cells, organs and tissues are called electrical stimulation.

The result of the AC action on a living biological tissue depends not only on its amplitude values, but also on the frequency, shape and duration of pulses. So at high frequencies (500 kHz and more), the electric current has mainly thermal effect, and at low and sound - annoying.

To discuss this issue, we must remember that biological tissue has a property of both the conductor and a dielectric. The irritant effect of the electric current is the movement of charged particles of tissue electrolytes (shifting and conductivity currents arise). At the same time, the movement of free ions located outside the cell is not limited. Free ions inside the cell medium can move only in the volume of limited plasma membrane. Displacement of related charges, under action electric fieldlimited by the size of an atom or molecule.

Experience shows that the constant current in the permissible limits of an irritant action on the body fabric does not have. Irritation occurs only when the current is changed, and the force of irritation depends on speed This change and its instantaneous values \u200b\u200b(the law of Dubois-Rimon).

And if the current is the charge passing through the cross section of the conductor per unit time,

this changing current can be represented by the expression:

Consequently, the irritating effect of electric current on biological tissue can be associated with an accelerated movement of infected particles under the action of an electric field.

In practice, electrical impulses are used for these purposes (short-term effect of current or voltage). (*) In this case, the impact is carried out both single and repeated pulses - pulsed current. It is experimentally established that at the time of the closure of the electrical circuit (permanent or impulse currents), the largest irritant effect occurs at a negative electrode (cathode), and the smallest - at a positive (anode). This is due to a decrease in cell excitability threshold. Therefore, with electrical stimulation by pulsed currents, the cathode is considered an active electrode.

(*) Electrical pulses are short-term changes in current or voltage cylinders.General form electric impulse Presented in Fig. 1a, rectangular pulse - in fig. 1b. The characteristics of the pulse are: 1-2 - front front, 2-3 - vertex, 3-4 - slice (rear front). In fig. 1a marked: TF - the duration of the front front of the pulse; TI - pulse duration; TSR - the rear edge duration. The ratio of changes in voltage or current to the time for which this change occurred

tF \u003d 0.8 Umax / TF or (3)

dU / DT \u003d (0.9UMAX - 0.1UMAX) /tSR \u003d 0.8 Umax /tSR,

called the steep edge of the pulse. As it is easy to see, the rate of increases (steepness) of the front front of the rectangular pulse (Fig. 1b) is maximal (in the ideal case, it is infinitely important).

Irritant Pulse is closely related to their characteristic. According to the law of Dubois Rimon, an irritating action of a single pulse depends on the rate of increasing its instantaneous values, i.e. from the steepness of its front edge. This dependence is associated with accommodation - The ability of excitation tissues to increase their excitation threshold (adapt) to the increasing force of an irritant factor. It is expressed in reduction The threshold of tangible current (I P) with an increase in the steepness of the front front of a single sufficiently long pulse. Thus, a current pulse should have the greatest irritant ability, the front front of which has maximum speed increment, i.e. The pulse of the rectangular shape, the smallest - linearly increasing current. In other words, the threshold current for the rectangular pulse is lower than for pulses of any other shape (Fig. 1b and Fig. 2).

U.

0.9Umax U, I.

0.1UMAX

1 TF 2 3 TSR 4 T TI T

a)tIb)

The minimum inclination angle () of a linear increase current current, which is still able to cause the excitation process, received the name of the critical angle of inclination or a minimum gradient. It reflects the speed of current change and is determined in units reobe / C. or ma / S..

The fact of the lack of irritation, with slowly increasing in the time of the action of the irritant, is due to the fact that in the membranes of cells of excitable tissues, the phospholipid formations are restructuring, leading to the appearance of sodium inactivation, i.e. closing sodium channels.

IP

1

Fig. 2. Current threshold force at different rates of increasing the front edge of the linear increases. The smallest threshold for the front edge of the rectangular pulse is a digit 1.

The process of sodium inactivation without preliminary sodium activation, aimed against the emergence of the excitation process, with slowly increasing the strength of the stimulus, was called "Accommodation".

The faster the accommodation occurs, the greater the angle () of the critical inclination (Fig. 2) and, on the contrary, at a slow reaction of cells - the angle () is small. Normally, the nervous fabric has the property of a quick accommodation, a relatively slow accommodation has a smooth muscles. It should be noted that the ability to accommodate in excitable tissues depends on their functional state. So in pathologically modified muscle tissue, the speed of sodium inactivation is reduced. For them, current pulses with the corresponding nature of the cell reaction are gradually increasing the front edge (the growth of the front edge may have a dependence that is different from linear, for example, exponential), will be more physiological during electrical stroitations.

Action on the tissue of rhythmically repeated impulses is called frequency irritation. It allows you to identify the ability of the tissue to produce an optimal reaction to the action of an irritant factor under certain limits of the frequency of its repetition. This ability is called N.E. Introduced lability or functional mobility. The determination of lability is carried out by observing the nature of the reaction at different frequency of irritating pulses.

When electrical stimulation, as therapeutic methodMore often used frequency irritation with pulses in the form of parcels various durability With pauses for recreation. However, so that the procedure does not harm and had good effectThe characteristics of the pulses are such as: amplitude, duration, frequency and shape must correspond to the state of the tissues. For example, for the affected muscles of the musculoskeletal system "Physiological" will be longer pulses with a gradually increasing front front and a much lower frequency than for healthy. The identification of this important conformity is carried out using electrodiagnostics. In electrodiagnosis, the nature of the tissue reaction on electrical irritation with various parameters (single pulses of different duration and shape, rhythmic irritation of various frequencies, etc.) is investigated. It is possible to simultaneously establish the cause and degree of their defeat. The parameters of pulses or pulse current giving an optimal reaction to irritation are then used to conduct therapeutic procedures.

To avoid chemical burn Electrostimulation is carried out with the help of electrodes superimposed on the body with a gasket moistened with isotonic solution (0.9% NaCl). In this case, the active electrode has a small area (point electrode), which allows you to focus the irritant effect of the current in small areas of the body, the irritation of which is most effectively in this case (Points in which nerve fibers are located close to the surface of the body, the point of occurrence of the nerve fiber in the muscle, etc.).

Pulsed current used during electrical stimulation

Electrostimulation (pacemaker, stimulation of the musculoskeletal system, etc.) in its direct purpose is one of the direction of use of pulsed currents. However, in modern electrotherapy, impulse currents are widely used in the treatment nerve diseases, diseases associated with metabolic disorders, during peripheral circulation disorders, pain syndromes etc. For these purposes other than those considered simple forms The pulses (Fig. 3) are used with a sinusoidal-pulse current of low frequency (sometimes called diadinamic) (Fig. 4), sinusoidally modulated audio frequency current and modulated ultrasonic frequency current.

In fig. 3 shows some pulse current graphs used in electrical stimulation of the central nervous system and muscles.

The sinusoidal-modulated current is a carrier - alternating or straightened audio current (4000 - 5000 Hz) or ultrasonic frequency modulated by amplitude frequency from 30 to 150Hz (Fig. 5).

To obtain a sinusoidal modulated sound frequency current, special devices like "amplipuls" are used.

The use of modulated high-frequency currents in the amplipuls apparatus is due to high resistance of live fabric (especially skin) low frequency currents. Due to the use of high-frequency current, it, with a minor resistance from the skin, deeply penetrates the tissue (capacitive properties). An irritating effect at the same time has its low-frequency modulating component. In amplipulse therapy devices there are four frequencies of amplitude modulation of carrier: 30, 50, 100 and 150Hz.

To reduce the adaptation phenomenon and thereby increasing the efficiency of the impact resort to automatic alternation of modulated oscillations with pauses, modulated and non-modulated oscillations, alternating 2 different modulating frequencies. When using a straightened current (see Fig. 5), the electrostimulating effect can be simultaneously accompanying therapeutic electrophoresis. In addition, the stepwise change in the device for modulation depth of carrier from 0 to\u003e 100% allows you to change the effect of exposure to biological tissue and thereby manage the treatment process.

In the "Spark" devices, the carrier has an ultrasound frequency (~ 110kHz and more), and the modulation is carried out by a low frequency current not sinusoidal shape (Fig. 10).

Despite the fact that the "Spark" apparatus uses a high-frequency carrier that this method can also be attributed to low-frequency electrotherapy, since the high frequency current flowing into the patient's circuit (~ 20 mk), cannot be called a noticeable thermal effect (see the Joule-Lenza law ).

Laboratory work number 14.