The target for an effective laser therapy treatment is not any particular pathology itself, but rather stimulation of appropriate cell components that enhance the body’s natural repair mechanisms. These natural functions are not only extremely numerous, ranging from protein synthesis to enzyme secretion, from cell signaling to physical movement, but also highly cell-type dependent. Any attempt to directly target one of these specific enzymes is difficult and fundamentally unnecessary. If instead cellular metabolism, specifically the cell’s ability to use oxygen to create energy, can be stimulated, the functionality of all its natural processes will be enhanced. To do so, we have to introduce more oxygen, the principal fuel for aerobic organisms. The only way to get oxygen and nutrients to the cells for processing and waste products like lactic acid and carbon dioxide away from the cells is through the blood. Generating local circulation, both input and output of blood, is one of the primary mechanisms of laser therapy. Blood pressure determines the rate at which blood flows throughout the body. Obviously, it would help if the animal got up and ran around the office to increase its heart rate and blood flow, but for a lame dog, that’s not an option. When animals have conditions in the extremities, blood flow is poor so we need a way to make better use of the local flow. In the capillaries, blood flow is regulated through microscopic pressure and thermal gradients. It is not simply temperature elevation, but rather the creation of temperature differences that is of primary importance. Real-World Example Applying a hot pad will temporarily increase circulation, but only because that pad has a higher temperature relative to the body’s ambient temperature. After a few minutes, the body’s temperature will plateau (because it does not want to live at the hot pad’s temperature), and it will employ several mechanisms attempting to counteract the applied heat (Vogel J. Biosci. 2005, 30(4) 449-460 & 581-590). Applying a hot pad for 20 minutes then removing it for 20 minutes is a useful technique for boosting blood flow that takes advantage of temporal thermal gradients. The same effect is accomplished with ice packs. Heating or cooling through conduction is very slow. When the hot pad is removed, the body will take minutes to return to ambient temp, due to the amount of bulk tissue through which the heating/cooling has to propagate. Heating through radiation (i.e. laser therapy) is much quicker and more specific. Quick Physics Therapeutic laser moves at the speed of light, and contrary to popular lore, does not lose energy as it propagates. Though its direction may change, a photon of infrared radiation will travel at the speed of light until it is completely absorbed in one event. A beam of photons will “lose power” only in the sense that its constituent photons will continue to be absorbed until the number of photons (not the energy or speed of each) eventually diminishes. Water molecules in the cells absorb light energy in the therapeutic laser wavelength range. Water is a very simple molecule chemically, and when it absorbs a photon of infrared radiation, all of the energy gets converted to heat. The bonds that connect the hydrogens to the oxygen start to vibrate and all of that energy becomes heat. (Contrast with ionizing radiation such as ultraviolet and X-rays; these photons can break molecular bonds. Non-ionizing radiation does not have enough energy per photon to break bonds and the only effect is gentle heating.) The cell is made up of more than 80 percent water, so targeting water with radiation is the most efficient way to produce the temperature gradients that will initiate blood-flow. The water molecule is very small compared to the cell at large. After an absorption event, there is a local hot spot in the cell relative to the rest of the cell around it. This causes a local temperature gradient, which also creates a pressure gradient, along which blood will flow more readily. With more absorption events there are more temperature gradients, and local micro-circulation increases dramatically (Uozumi et al. Lasers Surg Med 2010, 42:566-576). From species to species, center mass to extremity, musculoskeletal to wound healing, laser therapy is a versatile modality in any veterinary practice. How is this any different from ultrasound or electrical stimulation? These modalities send either sound waves or electricity through the body in a very uniform manner. Only the smooth attenuation of the sound waves or interface reflections between different tissue types determines any heterogeneity of the deposited “dose.” Therapy lasers do the job better. Zooming out one level, random interference of coherent laser light will form what is called a “speckle” pattern that creates mini “hot and cold” spots within the laser beam. Cells, with water as the main thermal conductor, can dissipate heat very quickly, on the order of milliseconds. Pulsing a laser beam can allow these temperature gradients to form not only spatially (due to speckle) but also temporally, and on a time scale that corresponds with the natural thermal dissipation properties of the body. Enhancing local micro-circulation is the first step; not just input of blood, but through-put. This is one reason your laser-using colleagues have success treating both ends of the spectrum. In a condition like neuropathy, where the blood vessels are constricted, not enough blood gets to the nerve endings and pain results. But it also works on contusions and edema where there is already enough “dirty” blood present, full of toxins that need to be flushed away from the site. Circulation is certainly not the end of the road when it comes to how laser therapy benefits the body, but it is a necessary and important step toward biostimulation. For a more complete set of references or to learn more about how laser stimulates cellular metabolism after micro-circulation is increased and oxygen gets to the affected cells, contact the author directly. Bryan J. Stephens, Ph.D., is director of research and development for K-Laser USA. He is an expert in radiation’s interaction with biological matter, specifically in radiation dosimetry and photobiology. This Education Series article was underwritten by K-Laser USA of Franklin, Tenn.
