Ultrasound therapy

Ultrasonic therapy (UZT) is a physiotherapeutic method of exposure, using high-frequency mechanical vibrations of particles of the medium. Ultrasound is the elastic mechanical vibrations of particles in a medium with a frequency above 16 kHz, that is, beyond the audibility of the human ear.

The human hearing aid perceives sound, mechanical vibrations, which do not exceed 16 kHz. Animals that lead a nocturnal life, living in caves, water, perceive sounds of higher frequencies (32 kHz and higher) for information exchange and echolocation.

In natural conditions, ultrasound occurs during an earthquake, volcanic eruptions, during technological processes - the work of machines, rocket engines, etc. For technical purposes, ultrasound is produced with the help of special radiators. Depending on the source of energy, they are divided into mechanical and electrical. In mechanical emitters, the source of ultrasound is the energy of the flow, gas, liquid (whistles, sirens, electric transducers, ultrasound is produced by the action of electric current on bodies of iron, nickel and other materials.) The piezoelectric effect is the basis of emitters made of quartz, barium titanite, tourmaline and other materials which under the influence of an alternating electric current change their dimensions and cause mechanical vibrations of the medium of ultrasonic frequency.

Mechanism of action of ultrasound

In physiotherapy, ultrasonic vibrations are used in the range 800-3000 kHz (0.8-3 MHz). In cosmetology, the frequency of ultrasonic vibrations for any device is fixed. Basically, the frequency is from 25-28 kHz to 3 MHz.

Ultrasound functions

1. Mechanical function (specific action of the ultrasonic wave). Elastic vibrations of the ultrasonic range due to the high gradient of sound pressure and significant shear stresses in biological tissues change the conductivity of the ion channels of membranes of different cells and cause microflows of metabolites in the cytosol and organoids (micromassage of tissues).

Mechanical effects of ultrasound at the tissue level:

• acceleration of local blood circulation;
• acceleration of lymph flow;
• normalization of the processes of formation of collagen and elastin (collagen and elastin fibers formed under the action of ultrasonic vibrations possess an elasticity and strength of 2 and more times higher than that of a non-sounded tissue);
• stimulation of the nervous system (reduction of compression of nociceptive nerve conductors in the area affected).

At the cellular level, the following processes occur under the action of ultrasonic waves:

• break strong and weak intermolecular bonds;
• decrease in the viscosity of the cytosol (thixotropy);
• the transition of ions and biologically active compounds into a free state,
• increasing the binding of biologically active substances,
• activation of mechanisms of nonspecific immunoresistance;
• activation of membrane enzymes (including activation of lysosomal cell enzymes);
• depolymerization of hyaluronic acid (reduction and prevention of interstitial stasis);
• generation of acoustic microflows;
• changing the structuredness of water;
• stimulation of cytoplasm, rotation of mitochondria and vibration of the cell nucleus,
• increasing the permeability of the cell membrane.

Accelerated by ultrasound, the movement of biological molecules in cells increases the likelihood of their participation in metabolic processes. The change in the functional properties of the mechanosensitive ion channels of the cytoskeleton of cells that occurs under the influence of ultrasonic vibrations increases the rate of metabolite transport and the enzymatic activity of lysosomal enzymes, stimulates reparative tissue regeneration.

2. With increasing ultrasound intensity, damped shear (transverse) waves form on the boundary of inhomogeneous biological media and a large amount of heat is generated-the thermal function of ultrasound.

Because of the significant absorption of the energy of ultrasonic oscillations in tissues containing molecules with large linear dimensions, the temperature rises by 1 ° C.

The greatest amount of heat is released not in the thickness of homogeneous tissues, but at the interfaces of tissues with different acoustic impedances in collagen-rich superficial layers of the skin, fasciae, scars, ligaments, synovial membranes, articular menisci and periosteum, which increases their elasticity and expands the range of physiological stresses (vibrothermolysis). Local expansion of the vessels of the microcirculatory bed leads to an increase in volume blood flow in weakly vascularized tissues (2-3 times), increased metabolism, improved skin elasticity and reduction of edema.

Approximately 80% of the heat is absorbed and carried away by the blood, the remaining 20% are scattered in nearby tissues. Patients feel a slight heat during the procedure.

Thermal effects at the tissue and cellular level:

• change in diffuse processes;
• change in the rate of biochemical reactions;
• the appearance of temperature gradients (up to 1 C);
• acceleration of microcirculation.

The ratio of the thermal and nonthermal components of the action of ultrasonic vibrations is determined by the intensity of the radiation or the regime (continuous or pulsed) of the action.

3. Physico-chemical function. The biochemical function of ultrasound mainly comes from the reactivity of anabolism and catabolism.

Anabolism is a process that centralizes identical and similar molecules. Small doses of ultrasound accelerate protein synthesis inside cells, restore injured, inflamed tissues, while therapeutic doses promote the synthesis of elastin and collagen fibers, increase blood circulation, loosen connective tissue and increase its function, increase anti-inflammatory, resolving, analgesic and antispastic effect.

Catabolism is a process that reduces the viscosity and number of large molecules (so that the concentration of drug substance, cosmetic agent can be reduced) and speeds up their utilization. It is also noted that ultrasound has the following effects:

• acts as a catalyst;
• accelerates the process of metabolism;
• changes the pH of tissues to alkali (facilitates inflammation in the skin after exposure to acid);
• promotes the formation of biologically active substances;
• promotes the binding of free radicals;
• decomposes drug molecules;
• bactericidal action (due to the penetration of ultrasonic waves and drugs into the bacterial environment).