What are the Methods of Heating the Tissues

 

Methods of Heating the Tissues

Physiological Effects of Muscles

The primary reactions to the temperature rise caused by heating the tissues using the techniques described in this section are:

(a) elevated levels of metabolic activity

(b) enhanced blood circulation;

(c) activation of tissues' or skin's neural receptors.

Influences on Tissue Alterations

These alterations in the tissues could result from distant, general, or local influences. Their magnitude will be determined by a number of variables, such as:

(a) the extent of the heated surface;

(b) the levels at which a particular radiation is absorbed

(c) the heating period's duration;

(d) the radiation's intensity;

(e) the application technique.

Accelerated metabolism

This supports the claim made by van't Hoff that an increase in temperature will accelerate any chemical change that is capable of doing so. As a result, heating tissues quickens their chemical "changes," or metabolism. The area of the surface tissues where the majority of heat is produced sees the most rise in metabolism. The increased metabolism leads to an increase in the need for food and oxygen as well as an increase in the production of waste products, such as metabolites.

An increase in the availability of blood

The cells produce more waste products as a result of their enhanced metabolism. Among them are metabolites, which cause dilatation of the capillary and arteriole walls by their action. Furthermore, the direct impact of heat on blood vessels results in vasodilatation, especially in the superficial tissue where the highest heating occurs. A reflex dilatation of the arterioles can also be brought on by stimulation of the superficial nerve terminals. Vasodilatation causes an increase in blood flow across the affected area, facilitating the removal of waste materials and the supply of essential nutrients and oxygen. Unlike erythema brought on by UV irradiation, superficial vasodilatation generates erythema of the skin, which manifests as soon as the affected area warms up and quickly goes away as the heat exposure stops. When exposed to infrared radiation on a regular basis, infrared erythema can take on a mottled appearance, and people who frequently sit near fires may notice an increase in pigmentation on their legs.

Heating's effects on nerves

There seems to be a noticeable sedative impact of heat. Further research is still needed to fully understand how heat affects nerve transmission. Heat has been used as a counterirritant, meaning that the application of heat may lessen pain perception. The possible explanation could potentially lie in the mechanism of endorphin activity.

Effects of heating indirectly

muscle mass As the increased blood supply guarantees the ideal conditions for muscle contraction, a rise in temperature causes muscles to relax and increases the effectiveness of muscular activity. overall increase in temperature. When there is widespread and persistent heating, the blood travels through the tissues that have experienced a rise in temperature, becoming heated and carrying the heat to other regions of the body. The hypothalamic heat-regulating center and the vasomotor center are both impacted, leading to a widespread dilatation of the superficial blood vessels.

Reduction in blood pressure

Peripheral resistance is lowered in the event of widespread vasodilatation, which lowers blood pressure. Heat causes the blood's viscosity to decrease, which also tends to lower blood pressure. Sweat gland activity is elevated Heat has an influence on sensory nerve endings, which causes the sweat glands in the exposed area to reflexively stimulate. Sweat gland activity is elevated throughout the body, and the heated blood travels throughout the body, affecting the centers responsible for regulating temperature. Waste product elimination is accelerated when widespread sweating takes place.

SHORT-WAVE DIATHERMY

Between 107 and 108 Hz is the frequency at which a short-wave diathermic current produces radio waves with a wavelength of between 30 and 3 m. Any application of current in this range is considered short-wave diathermy; however, the typical current used in medical settings has a frequency of 27120000 Hz (27.12 MHz), which produces radio waves with an 11 m wavelength. The machine circuit that generates this current is connected to the patient (resonator) circuit, which is utilized to treat the patient. As deep a kind of heat as any available to the physiotherapist is provided by short-wave diathermy, provided that an appropriate application technique is selected.

The circuitry of the machine

Since no mechanical device can be built that moves quickly enough to generate a high-frequency current, one way to create this kind of current is to discharge a condenser through an inductance with a low ohmic resistance. The fundamental oscillator circuit consists of an inductance and a condenser, and by choosing appropriate inductances and condensers, one can obtain currents of various frequencies. Small capacitance and inductance are used to produce a current of very high frequency, while bigger condensers and/or inductance are used to produce a current of lower frequency. The oscillator is integrated into a valve circuit to force the condenser to repeatedly charge and discharge in order to generate the high-frequency current.

The patient circuit

Inductors link the circuit to the machine circuit, causing electromagnetic induction to create a corresponding high-frequency current in the resonator circuit. The oscillator and resonator circuits must be in resonance with one another for this to occur, which necessitates that the product of capacitance and inductance for both circuits be the same. The electrodes and the patient's tissues create a capacitor when short-wave diathermy is delivered using the "condenser" field approach. The capacitance of this capacitor varies depending on the electrode size, distance, and material between them.

Adjusting Variable Condenser for Optimal Treatment

The placement of the cable electrode when it is utilized creates an inductance, whose value varies. As a result, the patient's circuit's capacitance or inductance are changed throughout each treatment, and a variable condenser is added to the patient circuit to make up for this. Following electrode placement, the variable condenser's capacitance is tuned until the oscillator circuit's capacitance multiplied by the resonator circuit's inductance is equal to that of the oscillator circuit. There is maximal power transfer to the patient circuit when the oscillator  

1. Equipment's indicator lights either illuminates or changes color.
2. By adjusting the knob that controls the variable capacitor in either direction, the maximum reading on an ammeter connected to the resonator circuit is reduced.
3. When the circuits are in resonance, a tube with a tiny quantity of neon gas within it that is positioned in the electric field between the electrodes or the ends of the cable will glow brightest.

Physiological effects of diathermy current

Motor or sensory nerves are not stimulated by a high-frequency current. Studying the muscle-stimulating currents in it was found that, with the exception of long-duration impulses, the effect on the neurons decreased with impulse duration, with 0.01 ms being the most commonly employed short duration. A high-frequency current is one whose frequency exceeds roughly 500 kHz. The duration of each impulse, which is one million per second, is 0.001 ms, which is more than what is needed for nerve activation. Thus, there is no pain or contraction of the muscles when such a current is run through the body. Chemical burns are not a risk because the current alternates evenly. As a result, currents with substantially higher intensities can be passed through the tissues than those with lower frequencies. The word "diathermy" refers to "through heating," and the current's intensity can be high enough to cause a direct heating impact on the tissues.

Techniques of use

An electromagnetic or electrostatic field is used to deliver electrical energy to the patient. Consequently, there are two application ways available: the inductothermy (cable) method and the condenser/capacitor field method.

Field technique of capacitors

The area that needs to be treated has electrodes put on both sides, separated from the skin by an insulating layer. The patient's tissues and the insulating substance separating them from the electrodes create the dielectric, with the electrodes functioning as the plates of a capacitor. A fast alternating electric field forms between the electrodes when the current is delivered because rapidly alternating charges are built up on them. The materials within the electric field are affected by it.

The electric field's effects

A conductor is a material that readily allows electrons to be separated from their atoms; when this kind of material is in an electric field that fluctuates, the electrons rapidly oscillate, creating a high-frequency current. Ions are found in substances called electrolytes, and when an electric field changes, the ions in an electrolyte have a tendency to flow first in one direction and then the other. Instead of the ions actually moving, the extremely high frequency of the short-wave diathermic current causes vibration. Dipoles, which are molecules made up of two oppositely charged ions, are also found in electrolytes.

Impact of Electric Fields on Tissues

The particle is electrically neutral overall, but it has a positive and a negative charge on one end. The dipoles swing around when the direction of the electric field changes, positioning each end as far away from the electrode that is carrying the same charge as possible. The body's tissue fluids are electrolytes, and when tissues with a significant amount of fluid are exposed to an electric field, ions vibrate and dipoles rotate within the tissues. Other tissues, like fat, are essentially insulators, and the electric field's impact on them results in molecular deformation. Joule's law states that all of these activities result in the production of heat and constitute electric currents. The main result of short-wave diathermy on the tissues is heat production; however, the distribution of this heat is different from other heat therapies. This is mainly dependent on how the electric field is distributed.

Changing the temperature of the tissues

The following ideas are based on the properties of electric lines of force and how they are distributed. The density of the electric field is normally highest near the electrodes because it tends to diffuse between them. Because the superficial tissues are located closer to the electrodes than the deep tissues, the superficial tissues often experience higher heating as a result of the increased field density. Since the body's tissues have a mean dielectric constant of roughly 80, they have a significant impact on the distribution of the electric field. Lines of force flow through materials with a high dielectric constant more readily than those with a low dielectric constant. The tendency for the lines of force to spread out significantly as they move through the body due to their ease of passage through the tissues makes it more likely that the superficial tissues will heat up more than the deep tissues. An exception arises when the part's cross-sectional area is smaller than the electrodes', so the force lines pass through the tissues instead of the surrounding atmosphere. The heating and field density are highest at the ankle, for instance, if one electrode is positioned on the sole of the foot and the other above the flexed knee.

Loss of heat

Heat is removed from the region being treated by the blood that flows through it. This is especially common in vascular regions, and the effect intensifies as the part's temperature rises due to the dilatation of the blood vessels. Because of this, all heat applications should be made gradually in order to permit vasodilatation and establish a constant rate of heat loss. Any obstruction that prevents blood from flowing through the area will prevent heat from being removed, which increases the risk of overheating. In addition, heat is lost through conduction to nearby tissues, radiation, and surface evaporation of perspiration, to a lesser degree. Heat generation is governed by the electric field's distribution and is often highest in surface tissues and low-impedance tissues when short-wave diathermy is applied using the condenser field approach. However, by positioning the electrodes appropriately, the tendency for the heating to be limited to specific locations can be reduced. Avoiding overheating the skin is essential to achieve deep heating since the warmth that results restricts the amount of current that can be tolerated. Most of the time, the goal is to create a field that is as even as possible over the deep and superficial tissues.

Size of electrodes

The electrodes should, in general, be somewhat larger than the structure being treated. An electromagnetic field has a tendency to expand. notably near the margins, causing the deep tissues to heat less than the surface tissues due to a reduced field density. The structure to be heated is in the more even core portion of the field; if the electrodes are big, the outer portion of the field where the spread is highest is purposefully not used. The electrodes should be as big as possible for treating the trunk, but they should be somewhat bigger than the limb's diameter for treating a limb. The dielectric constant of human tissues is higher than that of air. The size of both electrodes ought to be the same. Since their sizes vary, they create a capacitor with varying-sized plates, requiring varying amounts of current to charge them to the same potential. This causes an uneven burden on the device and could lead to tuning issues. In addition, as Fig. 4.8 illustrates, the charge may focus on the area of the bigger electrode that is across from the smaller electrode, negating the benefit of utilizing electrodes of varying sizes. The primary goal of doing this would be to produce varying temperatures beneath the two electrodes, which is more easily accomplished by modifying the distance.

The distance between electrodes

The material between the electrodes and the skin should have a low dielectric constant, with air being the most suitable, and the distance between the electrodes and the patient's tissues should be as wide as the machine's output permits. In a charged condenser, the lines of force propagate as they pass between the plates, especially if there is little space between the plates and a high dielectric constant material exists between them. The electric field spreads out very little when the distance between the electrodes is great, and it is also restricted when low dielectric constant spacing material is used. The density of the lines of force is highest near the electrodes since the field does, however, diffuse somewhat. The superficial tissues are heated more than the deep tissues, which have lower line-of-force density, when the electrode spacing is narrow. The superficial tissues are located in the concentrated area of the field near the electrodes.

Optimizing Electrode Spacing for Even Heating

There is less of a difference between the field density in the deep and superficial tissues when the electrode spacing is wide, and no tissues are located in the concentrated area of the field near the electrodes. Therefore, large spacing lessens the likelihood that the superficial tissues will heat up more than the deeper ones, especially if the substance used to create the space has a low dielectric constant. It does, however, place a significant burden on the machine's production. There is a bigger heating impact beneath the electrode that is positioned closer to the skin than under the one that is farther away. Compared to those under the closer electrode, the lines of force beneath the farther electrode have a longer distance to propagate before they reach the skin. As a result, they cover a larger surface area and have a lower density than the skin beneath the closer electrode. The guiding electrode on the distant surface is positioned farther from the skin than the active electrode for treating a structure that is closer to one surface of the body than the other, such as the hip joint. This lessens the chance that the patient would overheat beneath the guiding electrode, which could restrict the total current that can be tolerated.