Mechanisms of action of laser radiation on biological tissues

Depending on character of interaction of laser light with biological tissues it is possible to distinguish three kinds of photobiological effects:

1) photodestructive influence at which thermal, hydrodynamical, photochemical effects of light cause destruction of tissues. This kind of laser interaction is used in laser surgery.

2) photophysical and photochemical influence, at which light absorbed by biotissues raises in them atoms and molecules, causes photochemical and photophysical reactions. This laser radiation is used as therapeutic.

3) unperturbed influence, when the biosubstance does not change the properties during interaction with light. These are such effects, as dispersion, reflection and penetration. This kind use for diagnostics (laser spectroscopy).

Photobiological effects depend upon parameters of laser radiation: wave length, intensity of a stream of light energy, time of influence for biotissues. In laser therapy light streams of low intensity is applied, no more than 100 mW/cm², that is comparable to intensity of radiation of the Sun on a surface of the Earth in clear day. Therefore it name low-intensity laser radiation (LILR).

Llight has photobiological activity in ultra-violet, visible and infra-red areas of a spectrum. Photophysical and photochemical reactions are a basis of photobiological processes arising under action of light.

Photophysical reactions occur at heating object to a various degree (within the limits of 0.1-0.3⁰ С) and distribution of heat to biotissues. The difference of temperature is more expressed on biological membranes that leads to outflow of ions Na + and K +, to disclosing of protein channels and increase of transport of molecules and ions.

Photochemical reactions occur at excitation of electrons in atoms of substance which absorbed light. It is expressed in the form of photoionization of substance on a molecular level, its restoration or photooxidation, photodissociation of molecules, their reorganization - photoisomeration.

Laser radiation is selectively absorbed by pigmentary substances containing in cells. The pigment melanin absorbs light most actively in violet area, porphyrin and its derivatives - in red area of a spectrum.

Absorption of laser energy occurs by various molecular formations which are not having specific pigments and photobiological targets too. Water absorbs visible light and a red part of a spectrum. It changes the structural organization of a water layer in membranes and changes function of channels of a membrane.

Own electromagnetic fields and free charges exist in biological structures of an organism which are redistributed under influence of laser radiation.

Primary chemical reactions are accompanied by occurrence of free radicals, start of processes of oxidation of biosubstrata. Low-intensity laser radiation stimulates metabolic activity of a cell, acts on processes of vital functions and regeneration (restoration), leads to increase quantity of DNA and RNA in kernels of cells of the person, renders antimutagen effect, makes active synthesis of DNA and accelerates regenerative processes in the cells, which have received radiation. It allows to use low-intensity laser radiation in oncology, on harmful manufactures, in military medicine.

Low-intensity laser radiation stimulates development of universal energy source ATP in mitochondrions.

Low-intensity laser radiation renders antioxidant effect. The parity of saturated and nonsaturated lipids changes at laser therapy, viscosity of lipidic components of membranes changes, a functional condition to a membrane changes too.

Secondary effects - a complex adaptable reactions. Low-intensity laser radiation removes disbalance in the central nervous system. The doze of laser radiation defines stimulating or oppressing effects, it gives possibility selectively to apply the laser to the weakened patients, in pediatrics, at chronic diseases.

At absorption by substance of quantum of light one of electron, being at the bottom power level, passes to the top power level and translates atom or a molecule in raised condition. Electron which has absorbed a photon, leaves substance at an external photoeffect. Tissues of an organism are semiconductors and dielectric. In such substances electron, has absorbed a photon, remains in substance and passes to higher power levels. It is an internal photoeffect. As a result of transition in the raised condition of a part of atoms or molecules of irradiated substance dielectric permeability of this substance changes (photodielectric effect).

Photoconductivity can be concentration, arising at change concentration of carriers of a charge, and mobile. Mobile photoconductivity arises at absorption of photons with low energy and is connected with transitions electrons within the limits of a zone of conductivity. At such transitions the number of carriers of charge does not change, but it changes their mobility. Formation of the electronic raised conditions leads to change of energy activity of cellular membranes, to conformation changes of liquid crystal structures.

Increase of energy activity of biological membranes leads to change of bioelectric processes, for increase in activity of transport of substances through a membrane. Under action of low-energy laser radiation the form of double lipidic layer of a cellular membrane changes. Influence by laser radiation on the damaged tissues leads to reduction of an endocellular hypostasis, that is connected with increase of a blood-groove in tissues, activation of transport of substance.

At absorption of light energy various physical processes arise, basic of which are external and internal photoeffects, electrolytic dissociation of molecules and various complexes.

Low-intensity laser radiation makes action on molecular and cellular level:

- Reduction of duration of phases of an inflammation;

- Reduction of hypostases and pressure of fabrics;

- Increase in absorption by fabrics of oxygen;

- Increase of speed of a blood-groove;

- Activation of transport substances through a vascular wall.

There are also clinical effects:

- Anti-inflammatory;

- Anesthetizing;

- Improvements of regional blood circulation;

- Bactericidal.

Список ИСПОЛЬЗОВАННОЙ литературы:

1. Под. Ред. Антонова В.Ф. Физика и биофизика, ГЭОТАР-Медиа, 2009

2. Орлов Р.С., Ноздрачев А.Д., Нормальная физиология, ГЭОТАР-Медиа, 2009

3. Под редакцией В.М. Покровского, Г.Ф. Коротько, М., «Физиология человека» «Медицина», 2001 г

4. Ремизов А.Н., Максина А.Г., Потапенко А.Я. Медицинская и биологическая физика, Дрофа, Москва, 2005.

5. В.О. Самойлов., «Медицинская биофизика», СПБ.: СпецЛит, 2004

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