LASER is an acronym for Light Amplification by Stimulated Emissions of Radiation. It is a form of electromagnetic energy classified within the infrared and visible light portions of the spectrum. The laser produces a beam that is monochromatic and spatially coherent. There are two basic categories of lasers: high power lasers (hot lasers) and low power lasers (low level lasers). The early lasers in medicine were hot lasers and gained notoriety for their use in surgery because of the high energy photothermal and ablative effect they had on tissues, which made them effective tools for incision, coagulation of vessels and thermolysis. It wasn’t until the 1970s that research began to examine the physiological effects of low level laser. Low level laser or therapeutic laser basically is defined as laser using energy densities below the threshold where irreversible changes occur in the cells (below 500 megawatts). Low level laser is considered athermal and its effectiveness is the result of biostimulation causing chemical changes in the body. In 1967 Prof. Andre Mester in Hungary conducted an experiment to see if low level lasers would stimulate the growth of cancer cells. He not only found that the irradiated carcinomas were unaffected by laser stimulation, he also found that the hair on the shaved experimental animals grew back faster than on the control animals. This was the first indication of the biostimulation effect of low level lasers. Dr. Freidrich Plog of Canada in 1973 published results of his experiment in which he found that the use of laser was a viable alternative to the use of needles in acupuncture. Since then, laser research has accelerated with thousands of articles and studies and hundreds of RCTs. In the treatment of soft tissue injuries, the most significant advancement was in the field of semiconductor diode technology that led to the first gallium-arsenide laser diode in 1979.
Although surgical lasers can be defocused and arranged to give energy densities in the low level range, superluminous diodes (SLDs, also known as light therapy) can deliver the same power and wavelengths much more economically and more safely.
Light energy consists of photons or packets of electromagnetic energy. The number of photons and the photons’ wavelength will determine the energy delivered to the tissue being irradiated. This energy is either absorbed by tissues and cells or scattered within the body to eventually become absorbed. The light energy is absorbed by chromophores or photoacceptors. Tissues have optical properties and their light absorption ability is wavelength dependent. In animals and humans the most effective wavelengths are in the red and near infrared (NIR) light range (600 to 950 nanometres). Cells and tissues that are compromised as a result of ischemia, inflammation and edema appear to be more receptive to the photons compared to normal cells. These injured cells appear to have a lower threshold to the stimulation of laser light.
It has been suggested that the mechanism of low level laser is based on the absorption of photons by chromophores of the respiratory chain. The mitochondrial membrane has complex proteins (NADH dehydrogenase, succinate dehydrogenase, cytochrome c reductase, cytochrome c oxidase and ATP synthase), which are electron or proton transfer proteins helping to produce energy for many biological functions. Cytochrome c oxydase and nitric oxide synthase are particularly reactive to photon stimulation. The resultant increase in ATP molecules and nitric oxide enhances cellular metabolism, circulation and nerve function. Since many of the reactive proteins are enzymes, low level laser therapy helps in the treatment of neuromusculoskeletal conditions in three ways: (1) anti-inflammation, (2) pain reduction, (3) tissue healing. Richard Martin in Practical Pain Management, Nov/Dec 2003, outlines these very effectively.
- Stabilization of cellular membrane Ca++, Na+ and K+ concentrations.
- Production and synthesis of ATP is enhanced
- Vasodilation reduces ischemia and increases perfusion
- Acceleration of leukocytic activity
- Increased prostaglandin production
- Reduction in Interleukin 1
- Enhanced lymphocyte response
- Increased angiogenesis for both blood and lymphatic capillaries
- Temperature modulation
- Enhanced Superoxide Dismutase levels
- Decreased C reactive protein levels
- Increase in b-Endorphins
- Suppression of C fiber afferent excitation
- Increase Nitric oxide production
- Restoration of nerve cell action potential
- Axonal sprouting and nerve cell regeneration
- Decreased bradykinin levels
- Increased release of acetylcholine
- Normalization of Ca++, Na+ and K+ ions concentrations
- Enhanced leukocyte infiltration
- Increased macrophage activity
- Increased neovascularization
- Increased fibroblast proliferation
- Keratinocyte proliferation
- Early epithelialization
- Growth factor increases
- Enhanced cell proliferation and differentiation
- Greater healed wound tensile strength
Chiropractic and light therapy
Although researchers in the field of laser therapy have no doubt that lasers have come of age and are a viable adjunct in the management of neuromusculoskeletal conditions, there are still a lot of unanswered questions. As clinicians, chiropractors are concerned about the dosage, wavelength, treatment duration, depth of penetration, pulsed versus non-pulsed machines, high powered lasers versus superluminous diodes and how to fit these therapies into our existing treatment protocols. This is a rapidly expanding field and, as more research is undertaken, more of these questions will be answered.
Researchers have established that for our purposes wavelengths in the 600 to 950 nanometres range are most effective. Determining the right dosage has been likened to watering a lawn. Too little water and the lawn remains parched, while too much water creates a mud bath. Recent research has also ascertained that the physiological changes mentioned above are more likely to occur when the tissue treated can absorb approximately four to six joules of energy per square centimetre. Considering the dosage requirements, SLDs can deliver this in three minutes for more proximal tissues and, in the odd case when deeper tissues are being treated, treatment times can be extended.
Assessing the technology
This brings up the next question that clinicians need to ask themselves. What machine do I buy? Early laser machines were very expensive and this trend has continued putting them out of reach for many chiropractors. The development of SLDs has now made low level energy laser therapy affordable for everyone. Of course, the question for many is how can machines with such a disparity in price deliver the same benefits. Dr. Tina Karu, a top laser researcher from Finland, writes, “Coherent properties of laser light are not important when cellular monolayers, thin layers of cell suspension as well as thin layers of tissue surface, are irradiated. In these cases, the coherent and non-coherent light (i.e., both lasers and LED’s) with the same wavelength, intensity and dose provides the same biological response.” Another important feature of SLDs is their safety. Coherent light beams can cause retinal damage so safety goggles should be worn by the treating practitioner and the patient whereas non-coherent light from SLDs do not cause retinal damage.
Low level laser therapy has a bright spot in chiropractic’s future. When you look at this form of treatment, it fits right in with the basic philosophy of chiropractic. Light beams, like chiropractic, provide a natural non-invasive form of treatment that helps the homeostatic properties of the body heal itself.
It is now up to us to learn more about this effective form of treatment and hopefully conduct research and add to the existing body of knowledge.