LLLT / LED-LLLT / PBMT Therapy
Low Level Laser Therapy (LLLT), sometimes also called Red Light Therapy or Photobiomodulation therapy (PBMT) is a non-invasive therapeutic modality using the application of light. Usually an emitting source is a low power laser or light emitting diode (LED) in the power range of 1 mW to 12 W. It encompasses visible red light, which ranges from 630 to 660 nanometers (nm); and an infrared light, which is just outside the range of visible light for humans and ranges from 810nm to 850nm.
How it works?
Both laser and LED therapies rely on being able to deliver an adequate amount of energy to the target tissue in order to precipitate a photochemical process known as photobiomodulation (PBM). Photobiomodulation is a athermal and atraumatic process involving the transfer of energy from the absorbed photons directly to the absorbing cell or chromophore (organic molecule), causing photoactivation of the target cells (some kind of change in their associated activity). It starts with the cell but the outcome can be seen at various biological scales. Some processes that are impacted include, but are not limited to, the alleviation of pain or inflammation, immunomodulation, and promotion of wound healing and tissue regeneration. [1, 2, 4-5].
The difference between laser light and LED light
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Both sources of light use a diode technology and (when used and studied in therapeutic applications) are often built to emit similar wavelengths. Significant differences between the two do exist, however; including the power generated, the specificity of wavelength, and the physical characteristics of the beam generated from the diode [2].
Laser light is monochromatic (single wavelength ∼1nm wide), coherent (photons ”in-sync” with each other) and collimated (low beam divergence) (Fig1). While old-generation LEDs emitted non-monochromatic (in a small band of wavelengths about 20 nm wide), non-coherent and non-collimated light, the new-generation LEDs are able to produce quasi-monochromatic light (∼2-3nm wide) with much less divergence and much higher and more stable output powers. Additionally the new generation gives us the photon interference phenomenon - if LEDs are organized together in a planar array, overlapping beams impacts with each other which result in developing extremely high photon intensity (even exceeding a rated output power) (Fig. 2.)
Fig. 1 The difference between coherent and incoherent light
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(Image source: Abdulsalam, Abdulrazak & Qasmarrogy, Ghassan. (2021). Thermal effect on the optical signal of fiber optics networks. International Review of Applied Sciences and Engineering. 10.1556/1848.2021.00328.)
What does this mean for therapy?
Laser light is more selective (single wavelength to target specific structures) penetrates deeper and can deliver large amounts of energy to a small region over a short period of time. On the other hand LED light allows treatment of larger surfaces and (with the new generation LEDs) penetrates reasonably deep (with the greatest photon intensity actually beneath the surface of the target tissue) [3].
So is light-emitting diode phototherapy (LED-LLLT) really effective?
Provided an LED phototherapy system has the correct wavelength for the target cells, delivers an appropriate power density and an adequate energy density, then yes - it will be effective [4].
Will all types of LEDs work?
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Up until the end of the 1990's, phototherapy was strictly dominated by laser sources, because LEDs (although cheap and cheerful) were highly divergent with low and unstable output powers, and a wide waveband. With very few exceptions, old generation LEDs were incapable of producing useful clinical reactions in tissue. All this changed in 1998 with the development of the so-called ‘NASA LED’ which emits light with less divergence, much higher and more stable output powers, and quasi-monochromaticity (nearly all of the photons at the rated wavelength). Whats more this new-generation LEDs have additional feature - an effect of photon interference. When multiple LEDs are mounted close together in a planar array, beams (generated by different LEDs) interacts with each other. When the beams impacts with each other, they interfere which result in an extreme photon density (particularly with the physical forward- and backward-scattering properties of red and infra-red light) [6]. This means that the penetration depth and the deposited energy will be greater, in some cases exceeding the nominal output value of the array [Fig. 2]
Fig. 2 Comparison between single LED and LED array efficiency.
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(Image source: Calderhead RG. (2007): The photobiological basics behind light-emitting diode (LED) phototherapy. Laser Therapy, 16: 97–108)
The basics of photobiology
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The first law of photobiology (The Grottus-Draper Law), states that only energy which is absorbed in a target can produce a photochemical or photophysical reaction. In other words - light must be absorbed in order for photochemistry (or photophysics) to occur. However, there are many scenarios what can happen with this absorbed energy.
When a photon is absorbed by a molecule, the electrons of that molecule are raised to a higher energy state. This excited molecule must lose its extra energy, and it can do this either by re-emitting a photon of longer wavelength (as fluorescence or phosphorescence), or it can lose energy by giving off heat, or it can lose energy by undergoing photoactivation. In order to archive a photo therapeutic effect we need photoactivation to occur.
Why is the length of the light wave is important?
So what condition have to be fulfilled in order to induce a photo-physical or -chemical reaction? We need a wavelength appropriate to the target that will penetrate deeply enough with the high enough photon density. In photobiology this is determined by an Absorption Spectrum and Action Spectrum.
An Absorption Spectrum describes the probability that light of a given wavelength will be absorbed by the system of interest (a cell, a tissue, a molecule etc.). Each chemical compound has a different absorption spectrum, because of its unique electronic structure, therefore the different wavelengths will be absorbed to different degrees. In another words - an Absorption Spectrum of the biological system informs about the probability that light of a given wavelength will be absorbed, and therefore the possibility of producing a photobiological effect.
An Action Spectrum gives information about relative effectiveness of different wavelengths of light causing a particular biological response. [8]
LED systems delivering 633 nm visible red light and 830 nm near infra-red light at high-enough photon densities, have been reported as having significant effects on their target tissues and at good range of depths. Literature-based summary of the phototherapeutic wavelength-specific actions in raising action potential of specific cells is presented in Table 1.
Table 1. Summary of the wavelength specific reactions significance
within the specific cells.
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(Image Source: Calderhead RG. (2007): The photobiological basics behind
light-emitting diode (LED) phototherapy. Laser Therapy, 16: 97–108)
Five of six cell groups mentioned in Table 1 are associated with wound healing. Mast cells, neutrophils and macrophages are associated with the inflammatory stage of wound healing. Fibroblasts - with proliferative stage and fibr-myo (transformational cells) with remodeling stage. Keratinocytes can be found in epidermis and when photoactivated are an extremely important source of cytokines which can be involved in either pro- and anti-inflammatory reactions. [6]
From the various wavelengths reported, two are notable for their photobiomodulation properties: 633 nm red light and 830 nm near infra-red (IR) light.
What is happening within the cell?
Now, when we have chosen wavelengths (red and infrared) let's concentrate on what is actually happening on the cellular level. Well, it turned out, that depending on the used waveband, absorption mechanisms within the cell are different.
A photochemical reaction is induced by absorbed photons of visible red light. It is usually initiated in mitochondria, acting directly and mostly on cytochrome-c oxidase - the end terminal enzyme in the cellular mitochondrial respiratory chain mainly responsible for inducing adenosine triphosphate (ATP) synthesis, the fuel of the cell [9].
On the other hand, infrared photons are mainly involved in photophysical reactions which occurs in the cell membrane, changing rotational and vibrational characteristics of membrane cells. This affects membrane transport mechanisms (through Na++/Ca++ and Na++/K++ pumps) and changes in chemical balance, finally resulting in secondary chemical cascade which gives similar output as visible light photons [7].
Visible red light has been reported to have profound effects on fibroblasts, inducing fibroplasia (the development of fibrous tissue) with increased number of active mitochondria and moderate effect on mast cell degranulation and macrophage activation. Near IR has a profound effects on inflammatory stage of wound healing cells [11-13]
Both visible and near IR wavelengths photomodulate the mechanism of epidermal keratinocites.
Both visible and near IR wavelengths are well-associated with increased local blood flow post-irradiation. It is important as it not only increases the flow of nutrients and oxygen into targeted area, but also provides a gradient between areas of low and high oxygen tension creating a “highway” for the wound-healing cells into the target area [10].
In practical terms, low level light therapy promotes tissue regeneration as well as reduces inflammation and pain.
The use of PMBT for equines
Therapeutical lasers have been utilized in equine industry for almost 40 years. New information is being discovered weekly providing a greater insight into broader clinical and regenerative medical applications of PBMT therapy.
Conditions suitable for PBMT treatment are listed below, with some (far from all) appropriate references:
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Nerve compression / bruising [32]
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Wound healing (including open and post-surgical wounds) [16, 21]
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Tendon and ligament injuries [22]
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Post-operative myofasciitis [31]
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Oedema [27]
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Pain reduction (of all origins, including pain management in laminitis horses, neuropathic pain) [18, 19, 25]
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Muscle injuries, muscle fatigue, muscle recovery [20, 30]
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Inflammation [24]
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Relief of trigger points [23, 26]
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Rehabilitation therapy [23]
Contraindications:
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The eye
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Pregnancy
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Grow plates
Addition information:
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Treatment times should be closely monitored as over treating inhibits rather than enhance tissue activity [14].
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Clipping and cleaning the area to be irradiated prior to treatment with PMBT would increase the penetration depth [17].
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PMBT will not penetrate the hoof wall, however it can be administer to coronary band and all of the descending neuromuscular supply to the foot.
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PMBT can be successfully applied to acupuncture points, affecting neural response in similar manner to needle acupuncture.​
Side effects
Side effects are minimal, specially compared to the benefits received with PMBT, but it is important to know what to expect:
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In the treatment of any type of chronic pain there may be a pain reaction the following day after treatment. This is because the condition is made “acute” when the healing process starts. The pain is of a short-term nature and a positive sign. [28, 29]
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When treating equine patients with extreme tiredness, the effect of total exhaustion may be observed for 1-2 days after application of PMBT. This is due to a fact that longstanding pain is eased [29]
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Sometimes discomfort and pain disappear rapidly after PMBT treatment. At this stage it is important that the affected tissue will not be overloaded and is given a proper time to recover, as a false picture of health may emerge.
REFERENCES
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