Introduction to promoting wound healing with low energy laser treatment

Low energy lasers have been available for treating wounds for nearly three decades. But, while the basic science of their biologic effects has been known for quite sometime, their clinical evaluation is mired in controversy. This is so, mainly, due to studies lacking rigor, standardization and proper data documentation. As a result, no proper conclusions could be drawn from these studies. Recent studies conducted under more rigorous conditions have not been able to rid this controversy surrounding low energy laser treatment.

Effect of low energy lasers on cells

Earlier it was thought low energy lasers healed wounds by some kind of photochemical reaction and not through thermal damage. To throw more light on the subject, many animal studies were conducted to investigate the effect of low energy lasers on cell function and molecular changes. The early studies were conducted on experimentally induced wounds on various animal species and on human skin ulcers. These studies generated an abundance of data making this area one of the best investigated.

Early stage investigations suggested that low energy lasers aided wound healing. Further studies revealed that wound healing was mainly due to collagen formation. However there also emerged several different views about the mechanism of action. These included improved metabolic function of wound tissue, increased cell proliferation, increased tensile strength and improved proliferation phase of repair. Moreover, different studies on the effect of low energy lasers on the same kind of wounds showed different results. For instance, in one study venous ulcers showed significant improvement after low energy laser irradiation. In contrast low energy treatment by He: Ne lasers had no effect on the same ulcers.

In the light of these developments, it was suggested that further studies were needed before any definite conclusions could be drawn. It was also suggested that, beside the exposed dermal area, the systemic effect due to low energy laser treatment as related to the wound should also be studied.

Effect of low energy lasers on the immune system

In an earlier study on the effects of low energy irradiation on wound healing in humans, it was observed that the laser irradiation not only healed the irradiated ulcer but also similar lesions in other parts of the body. It was concluded that low energy laser irradiation might heal or improve the wound condition by eliciting some response from the immune system.

To study the effect of low energy treatment on the immune system, both humoral and cellular immunity were investigated. Patients irradiated by low energy He:Ne lasers showed changes in serum complement activity and in immunoglobin levels. When this immunosuppressive action of these lasers were studied in directly irradiated human lymphocytes, irradiation by argon laser at 488nm to 501nm wave length range was found more effective than the He:Ne laser.

Since lymphocytes are a well-known source of important factors of wound repair, it was believed that stimulation or inhibition of certain immune responses might play an important role in faster wound healing, after exposure to low energy lasers. An in vitro study showed that low energy lasers can interact with the immune system. It was speculated that the same process could occur in vivo in humans, irradiated by low energy lasers.

The role of macrophages, irradiated by low energy lasers, in speeding up wound healing by speeding up the proliferation phase of repair was also investigated. It was found that irradiation by 660nm, 820nm and 870nm wave lengths caused macrophages to release factors that triggered fibroblast proliferation above normal levels. In contrast, 880nm wavelength either suppressed release of these factors or triggered the release of factors which suppressed fibroblast production. According to the investigators, increased fibroblast production can speed up wound healing in the repair phase. So, some low energy laser wave lengths can serve as useful tools to stimulate or suppress fibroblast production.

Effect of low energy lasers on skin grafts

In a study, skin from inbred mice was allotransplanted on mice of a genetically different strain. Both the donor skin graft and the recipient graft beds on the backs of mice were exposed to low energy He:Ne laser. A similar group was given the immunosuppressant, antithymocite treatment. A combination therapy of laser and this immunosuppressant was also given. While the two groups given monotherapies, showed improved graft survival, in combined therapy, graft survival was further improved. The investigators inferred that combined therapy had an increased graft- protective effect on mouse skin grafts. Whether this benefit can be extended to humans has to be investigated. But it raises the possibility of successful skin grafts from foreign sources, when the patient’s own skin is found to be inadequate.