Practical Applications of Low Level Laser Therapy
The North American Association of Laser Therapy (NAALT) adopted the term Phototherapy in 2003. This inclusive term is defined as: a therapeutic physical modality using photons (light energy) from the visible and infrared spectrum for tissue healing and pain reduction. Light photons can be produced by: low level lasers (therapeutic lasers), non-coherent narrow band light diodes, non-coherent broad band light diodes, polarized light, and photodynamic therapy.1 This article will be discussing therapeutic lasers as well as non-coherent narrow band and broad band light diodes.
Strictly speaking, a laser is a light amplifier if the radiation produced is within the visible range or a radiation amplifier if the radiation produced is in the infrared range. All lasers must have the following parts: an energy source (power supply), lasing or amplifying medium (solid, gas or liquid), and a resonating cavity (mirrors). The first working laser was presented to the public at a press conference in late 1960’s by Theodore Maiman.2He demonstrated a ruby laser. The potential for using lasers for surgery was soon explored and rapidly introduced into surgical suites in many countries throughout the world. A Hungarian physician named Endre Mester performed cancerous tumor treatment experiments on rats utilizing laser. He found that because it was underpowered for that purpose, the laser he was using didn’t kill tumor cells but, instead, accelerated wound healing in the surgical sites of the experimental rats.3 He is the grandfather of photobiomodulation since he was the first to observe the healing effects of low powered lasers. To date, there have been more than 2500 published studies worldwide involving low level laser therapy with approximately 120 double blind studies published.4
There are several extraordinary effects that have been observed with therapeutic lasers, and phototherapy in general, that make laser therapy unique among the various healing modalities available today. Photobiomodulation produces changes in oxidation/reduction status of the mitochondria which lead to dramatic increases in ATP synthesis. Activation of the sodium/potassium pump alters the cell membrane permeability to calcium5 (see Figure 1).
Phototherapy has been shown to effect cellular activity in the following ways:
- stimulates cell growth
- increases cell metabolism
- improves cell regeneration
- invokes an anti-inflammatory response
- promotes edema reduction
- reduces fibrous tissue formation
- stimulates nerve function
- reduces the production of substance P
- stimulates long term production of nitric oxide
- decreases the formation of bradikynin, histamine, and acetylcholine
- stimulates the production of endorphins6
These photo-biological responses are largely responsible for the pain relieving effects often observed in patients treated with phototherapy. There are three effects that commonly occur as a result of tissue exposure to light photons. They are:
Primary effects of photoreception are a result of the interaction of photons and cell mitochondria which capture, direct, and transduce photon energy to chemical energy used to regulate cellular activity.
Secondary effects occur in the same cell in which photons produced the primary effects and are induced by these primary effects. Secondary effects include cell proliferation, protein synthesis, degranulation, growth factor secretion, myofibroblast contraction and neurotransmitter modification—depending on the cell type and its sensitivity. Secondary effects can be initiated by other stimuli as well as light.
Tertiary effects are the indirect responses of distant cells to changes in other cells that have interacted directly with photons. They are the least predictable because they are dependent on both variable environmental factors and intercellular interactions. They are, however, the most clinically significant. Tertiary effects include all the systemic effects of phototherapy.7 Primary, secondary, and tertiary events summate to produce phototherapeutic activity.
The vast majority of therapeutic lasers are semiconductor lasers today. There are three diode types:
- Indium, Gallium-Aluminum-Phosphide (InGaAlP) laser
- Gallium-Aluminum Arsenide (GaAlAs) semiconductor laser
- Gallium-Arsenide (GaAs) semiconductor laser
Indium, Gallium-Aluminum-Phosphide (InGaAlP)
This is a visible red light laser diode that operates in the 630–700nm range. These lasers output light in a continuous manner. These lasers may also be pulsed by an electro-mechanical method (duty cycle). A duty cycle output means that the power is switched off for part of a second, and then switched back on. If it was off for ½ second and on for ½ second that would be referred to as a 50% duty cycle. This reduces the average power output by 50%. Red light lasers have the least amount of penetration of the three lasers with a range of 6–10mm. They effect the skin and superficial tissue.8
Gallium-Aluminum Arsenide (GaAlAs)
This is a near infrared laser, which means that the light emission is invisible to the naked eye. This laser operates in the 780-890nm range. This type of laser also has a continuous output of power and is often pulsed on a duty cycle as described above. This laser penetrates to 2–3 cm depth. These lasers are often utilized for medium to deep tissue structures such as muscles, tendons, and joints.9
This laser is unique in that it is always operated in superpulsed mode. Superpulsing means that the laser produces very short pulses of high peak power. These peak power spikes are usually in the 10–100 watt range but last for only 100–200 nanoseconds while maintaining a mean power output that is relatively low. This phenomenon is similar to what happens in a camera flash. Superpulsing allows for deep penetration into body tissues without causing the unwelcome tissue effects of continuous high power output such as heat production. Super pulsing allows for deeper penetration than a laser of the same wavelength that is not superpulsed but has the same average output power. Penetration is 3–5 cm or more. Superpulsing also allows for treatment times to be the shortest possible. These lasers are extremely well suited for medium and deep tissues such as tendons, ligaments and joints.10
Most phototherapy research has been historically laser centered. Several studies are now appearing in the literature utilizing light emitting diodes (LED’s) and infrared emitting diodes (IRED’s). LED/ IRED diodes have approximately 80% of the effect on tissues as lasers.6 The most commonly used light diodes for phototherapy are:
- Visible Red – 630nm, 640nm, 650nm, 660nm
- IRED – 830nm, 880nm, 950nm