PHYSICAL ASPECTS OF INFLUENCE OF LOW-LEVEL LASER RADIATION ON TISSUES

In a modern medicine, especially in Russia and in a number of other Eastern European countries, different physiotherapeutic methods of treatment and prevention of diseases are widely used. These methods cover application of various natural or artificially created physical healing factors and forces of mechanical, thermal or electromagnetic nature. In the past 15-20 years special area among them was occupied by low-level laser radiation (LLLR) due to such specific characteristics as monochromatic and high spectral density of radiation power, coherence, what has a result in a small divergence of light ray, possibility of simple focusing (defocusing) and transporting of radiation by optic lenses and mirrors, possibility of transmitting of light energy through optic fiber, transparency of upper skin layers and mucous membranes of man’s and animal’s organs for LLLR and so on. Such features of electromagnetic radiation in the optic waveband after the invention of lasers (later - of light diodes (LEDS) especially superluminescent ones with close technical characteristics) could not be not noticed, and in a period of 1980-2000 besides a laser surgery the intensive evolution of low-level laser therapy (LLLT) had started in Russian medicine, especially in physiotherapy.

     At the same time, in serious literature, especially in developed European countries, USA, Japan, etc. as well as in the national classical scientific periodic literature biophysical mechanisms and real clinical effects of LLLT are still a subject of disputes. Even today one may surely speak of at least 4-5 existing mechanisms of LLLT: thermal (heating of tissue), photodynamic (activation of singlet oxygen), photochemical (direct photo-destruction of organic molecules), placebo effect and so on. Thus, the question is opened yet. The healing effect of LLLT is far not always reproducible or guaranteed. In medical publications one can often find reports of absence of the healing effect after LLLT as well as can find an information about a negative effect of LLLT for patient’s organism. One of the reasons of such situation with LLLT, in our opinion, is an insufficient application of objective methods for direct and quantitative visualization of therapeutic effect during LLLT procedure on a local and system's levels (blood microcirculation system, cell metabolism and oxygenic status of patient’s cells and tissues, etc.) as well as on a total organism's level (control of basic parameters of homeostasis, diurnal biorhythms, etc.). Majority of works showing the positive LLLT effect were implemented on cell's structures in "grass-house" conditions - in a laboratory, or represented results of clinical doctor’s observations with the use of trivial common scheme: “It was observed before” -> “LLLT course has been applied” -> “it is observed now”, what is too little for explanation of mechanisms of LLLR action and has a little scientific meaning without a method of  double blind control study (in opposite case it’s easy to prove all what is desired). Historically LLLT appeared as extension of traditional techniques of light-healing in physiotherapy, having a thousand-year history and traces back to teachings of Hippocrates, Galen and Avicenna (sun-light baths). On the eve of the XX-XXI centuries LLLT is trying to include into itself some bright characteristics of a modern time: terminology of quantum physics (LLLT is often called as quantum therapy since light is not just an electromagnetic wave, but also is a flux of energy quanta), terminology of radiation biology (concepts of radiation dose, summary dose, radiation loading), modern influence of Eastern philosophy and Eastern medical and philosophical doctrine (laser acupuncture, laser correction using biological activated points, using body's meridians), etc. But everything of these, to our point of view, in LLLT goes lubberly and just brings a confusion into a problem of initial mechanisms in LLLT and its practical use. Take just speculations on dosage determination in LLLT! Recommended values of  power density and energetic exposition ("dose") in different manuals on LLLT vary in hundred times and more (correspondingly from 0,5 to 200 mW/cm2  and from 0,1 up to 120 J/cm2)". Besides that the dose term (a key item in LLLT application!) in different publications has different physical and technical meaning and is varied from surface power density (W/cm2) to volume energy density (J/cm3). Note: the dose in a modern physics, engineering, radiobiology, medicine (excluding pharmacology) and a medical physics (if one wants to use this notation correctly) is the energy of any type of radiation, coming to mass unit of exposed medium (J/kg). All other parameters used by doctors as a slang "dose" have different names, different physical units and different physical meaning. And this confusion in terminology often brings to confusion in a problem of LLLT action mechanisms. If a doctor speaks of LLLT mechanisms, resulting in microcirculation growth, pain syndrome remission, homeostasis normalization etc., then he speaks of derived effects, caused by organism response to LLLT irradiation, not of the mechanisms of the laser light action itself. Physical mechanisms (excluding the placebo "mechanism") are hidden deeper, if they exist at all, in a photo-physics and a photo-chemistry processes of interaction of laser light radiation and matter. According to the First Law of photo-chemistry (Grotgus-Dreyper’s law), for example, only the absorbed light causes a photo-chemical reaction. I.e. primary process in LLLT is absorption of the photon by matter. What a molecule or a set of molecules absorb energy and which way they spend it (heating, dissociation of molecules, singlet oxygen activation etc.), how this chain of photo-physical and photo-chemical processes brings to the integral healing effect and to response in organism – what are the problems of direct (initial) mechanisms of LLLT. Development of specialized physical and technical equipment and devices to register the mentioned effects, organism's reactions and for accurate dosimetry in LLLT as well as next medical and biological scientific investigations with the use of these devices, new techniques of joint medical and physical studies may only give finally possibility to find out a presence or absence of the LLLT effect itself, mechanisms of its initiation, more optimal parameters for its accomplishment, etc.

     Attempt to create devices for objective control of dynamics of blood microcirculation in a zone of irradiation during LLLT procedures was one of such attempts from the beginning of 1990th in MONIKI. Various technologies of photoplethismography, pulsoximetry, reflectance tissues oximetry, laser Doppler flowmetry, optical infrared thermometry etc., and also combined application of them were tested. Year from a year devices were improved, their sensitivity raised, new areas of their application opened (functional diagnostics, for example), however with their help till today's time we cannot register objectively, with authentic and reproducible results any dynamics of blood microcirculation at LLLT without heating. In June 2011 at 25-years anniversary conference of the State Scientific Centre (SSC) of "Laser medicine" this material has been reported in the form of the oral report and has caused enough fierce dispute. Our articles with results of these researches you can read here and here.

 
 
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