Photobiomodulation

Photobiomodulation, also known as low level laser therapy (LLLT), cold laser therapy,  and laser biostimulation, is an emerging medical and veterinary technique in which exposure to low-level laser light can stimulate or inhibit cellular function leading to beneficial clinical effects. The technique is also known by the more ambiguous terms phototherapy and laser therapy, which may also be used to describe other medical techniques. The "best" combination of wavelength, intensity, duration and treatment interval is complex and sometimes controversial with different diseases, injuries and dysfunctions needing different treatment parameters and techniques. These are still being explored and increasingly published by the academic community. USA National Institute for Health database.

History
Credit for the development of laser theory is generally given to Albert Einstein. In his theory "Zur Quantum Theories der Strahlung", published in 1916, he first used the name stimulated emission.

The word LASER is an accronym for Light Amplification by Stimulated Emission of Radiation.

In 1967 a few years after the first working laser was invented, Endre Mester in Semmelweis University Budapest, Hungary wanted to find out if laser light could cause cancer. He took some mice, shaved the hair off their backs, divided them into two groups and gave a laser treatment with a low-powered ruby laser to one group. They did not get cancer and to his surprise the shaved hair grew back more quickly on the treated group than the untreated group. That was how "laser biostimulation" was discovered.

Clinical applications
Clinical applications include treating soft tissue injuries and chronic pain, wound healing and nerve regeneration, and possibly even resolving viral and bacterial infections. One clinical application showing great promise is the treatment of inflammation, where the anti-inflammatory effect of location-and-dose-specific laser irradiation produces similar outcomes as NSAIDs, but without the potentially harmful side-effects.

The best documented laser type is the HeNe laser (Helium-neon, visible red light, 632.8 nm, continuous or chopped, usually non-polarized but with very high degree of coherence). The HeNe-laser is a gas laser, powered with high voltage and hence usually voluminous and expensive per milliwatt. Available on the market in Europe since 1975.

As an alternative one could choose an InGaAlP-laser diode laser (Indium gallium aluminum phosphide laser, visible red light, semiconductor laser type, and usually just named Indium laser) with wavelength 635 to 700 nm. The most common wavelength is 650 nm. The Indium lasers are cheaper per milliwatt than the HeNe-laser. Their light is polarized but less coherent light. Available since 1990. Both HeNe and Indium lasers seem to be best on problems in skin and mucosa (superficial).

The second best documented laser type is the GaAs-laser (invisible infrared, 904 nm, semiconductor type, always super-pulsed with very high peak power, often polarized but less coherent). Available on the European market since 1985. This laser is best suited for deep lying problems such as back, shoulders, spine and other joints, fibromyalgia, whiplash injury, lymph edema, trismus etc.

For the GaAs-lasers there is one extra factor to be aware of. Traditionally these lasers have low output at low pulse frequencies and high at high frequencies. Often the average output power is more or less proportional to the frequency set. This means that if the average output is 10 mW at 10,000 Hz, it is 1 mW at 1000 Hz and 0.1 mW at 100 Hz etc. Such a laser is more or less useless on all frequency settings except 10,000 Hz.

However, there are GaAs-laser (904 nm) instruments available where the output average power is independent on the frequency. This is very valuable as the dose given then simply is proportional to the treatment time. Such lasers are pulse train modulated.

The most commonly sold laser type today is found within a group of lasers - the so called GaAlAs-lasers. In this group there are lasers from about 750 nm and up to 980 nm. Originally the wavelength was 820 or 830 nm, invisible, infrared. Today there are two main types, the 808 nm one, usually produced in Europe and recently also in the USA and the 890 nm one, usually produced in Russia. The reason why so many lasers of this type are offered today is that they are the producers’ favorite; they are cheap (per mW) and easy to drive electrically. They can be made with powers up to hundreds of watts, e.g. for surgery and hair removal and in laser therapy they are usually emitting 100 mW and upwards. The light is invisible and always polarized. It is either continuous or chopped. These lasers are often suggested for the treatment of tendonitis and tinnitus.

Apart from this, also strong (surgical/esthetic lasers, such as CO2-, Ruby-, Nd:YAG-, Ho:YAG and some other types) can be used as therapeutic tools. Just set lower power.

For deep lying problems the GaAs laser is penetrating best (because of its high peak power) and for problems in skin and mucosa the HeNe laser is the most effective one (due to the high degree of coherency). The 808 or 890 nm lasers are more all-round types and often battery powered. There are single- or multi probes. For a multi probe, all the lasers should have the same wavelength (same laser type).

Conclusion: Red laser light for skin and mucosa problems, super pulsed types (GaAs) or stronger variants of continuous infrared types (GaAlAs) for deep problems.

Mechanism
Certain wavelengths of light at certain intensities (delivered by laser, LED or another monochromatic source) will aid tissue regeneration, resolve inflammation, relieve pain and boost the immune system. The exact mechanism is still being explored and debated but it is agreed that the mechanism is photochemical rather than heat-related. Observed biological and physiological effects include changes in cell membrane permeability, up-regulation and down-regulation of adenosine triphosphate and nitric oxide.

Contentious areas are: "the best" wavelength, dose, dose-rate effects, beam penetration, the role of coherence and pulses (peak power and repetition rates). Laser average power is typically in the range of 1-500 mW; some high peak power, short pulse width devices are in the range of 1-100 W with typically 200 ns pulse widths. The average beam irradiance then is typically 10 mW/cm2 - 5 W/cm2. The wavelength is typically in the range 600-1000 nm but some research has been done and products are available outside this range.

Safety
There appear to be no safety concerns in its application for therapy in people or animals, but the operator and patient should wear appropriate protection for the eyes (dense filter spectacles) in case of accidental or reflected exposure, and the laser beam should never be directed at the eyes.