Ultrasound therapy

Ultrasound therapy (UZT) is a physiotherapeutic method of influence using high-frequency mechanical vibrations of particles of the medium. Ultrasound is elastic mechanical vibrations of particles of the medium with a frequency higher than 16 kHz, i.e. lying beyond the hearing limit of the human ear.

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

In natural conditions, ultrasound occurs during earthquakes, volcanic eruptions, and during technological processes - the operation of machine tools, rocket engines, etc. For technical purposes, ultrasound is obtained using special emitters. Depending on the source of energy, they are divided into mechanical and electrical. In mechanical emitters, the source of ultrasound is the energy of a flow, gas, liquid (whistles, sirens). In electrical converters, ultrasound is obtained by applying electric current to bodies made of iron, nickel, and other materials. The piezoelectric effect is the basis of emitters made of quartz plates, barium titanite, tourmaline, and other materials that, under the influence of alternating electric current, change their dimensions and cause mechanical vibrations of the ultrasonic frequency medium.

Mechanism of action of ultrasound

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

Functions of ultrasound

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

Mechanical effects of ultrasound at the tissue level:

• acceleration of local blood circulation;
• acceleration of lymph flow;
• normalization of the processes of collagen and elastin formation (collagen and elastin fibers formed under the influence of ultrasonic vibrations have elasticity and strength increased by 2 or more times compared to non-sounded tissue);
• stimulation of the nervous system (reduction of compression of nociceptive nerve conductors in the area of impact).

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

• breaking of strong and weak intermolecular bonds;
• decrease in cytosol viscosity (thixotropy);
• the transition of ions and biologically active compounds into a free state,
• increasing the binding of biologically active substances,
• activation of non-specific immunoresistance mechanisms;
• activation of membrane enzymes (including activation of lysosomal enzymes of cells);
• depolymerization of hyaluronic acid (reduction and prevention of intertissue congestion);
• generation of acoustic microstreams;
• change in water structure;
• stimulation of cytoplasmic movement, mitochondrial rotation and cell nucleus vibration,
• increasing the permeability of the cell membrane.

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

2. When the intensity of ultrasound increases at the boundary of heterogeneous biological media, attenuating shear (transverse) waves are formed and a large amount of heat is released - the thermal function of ultrasound.

Due to the significant absorption of ultrasonic vibration energy in tissues containing molecules with large linear dimensions, the temperature increases 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 impedance - in collagen-rich superficial layers of the skin, fascia, scars, ligaments, synovial membranes, articular meniscus 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 volumetric blood flow in poorly vascularized tissues (by 2-3 times), increased metabolism, improved skin elasticity and decreased edema.

Approximately 80% of the heat is absorbed and carried away by the bloodstream, the remaining 20% is dissipated into nearby tissues. Patients feel a slight warming sensation during the procedure.

Thermal effects at the tissue and cellular level:

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

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

3. Physicochemical function. Biochemical function of ultrasound mainly comes from the reactive ability 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, enhance blood circulation, loosen connective tissue and increase its function, increase anti-inflammatory, resolving, analgesic and antispasmodic effects.

Catabolism is a process that reduces the viscosity and quantity of large molecules (so that the concentration of a medicinal substance, cosmetic product can be reduced) and accelerates their utilization. It is also noted that ultrasound has the following effects:

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