Low Level Laser Therapy (LLLT): What it is, how it is applied and an overview of the research.
Summary
TLDRThis lecture covers the principles and applications of low-level laser therapy (LLLT), an electro-therapeutic modality that uses lasers to relieve pain and stimulate cell function. The lecture explains how lasers work, emphasizing key properties such as monochromaticity, coherence, and collimation. It also describes how factors like wavelength, power, and fluence influence tissue interaction. Despite its growing use in treating musculoskeletal conditions, evidence for LLLT’s effectiveness remains inconsistent, with conflicting research results across various conditions, including tendinopathy, neck pain, and low back pain. Ongoing research aims to clarify its therapeutic potential.
Takeaways
- 🔬 Lasers produce light through stimulated emission of radiation, and are characterized by coherent, monochromatic light with minimal divergence.
- 💡 Low-level laser therapy (LLLT) is used in physiotherapy to relieve pain and enhance cell function, though its mechanisms and effectiveness are still under research.
- 📜 LLLT is theorized to follow the Grotthus-Draper law, where light must be absorbed to trigger photochemical reactions, potentially boosting ATP production through enzymes like cytochrome C oxidase.
- ⚡ The unique properties of lasers include monochromaticity (same wavelength), coherence (synchronized photons), and collimation (nearly parallel beams).
- 📏 Various factors influence laser interactions with tissues, including wavelength, power, pulse rate, and spot size, all of which affect penetration and energy absorption.
- 📊 LLLT parameters such as energy density, power output, and pulse rate are adjustable, and machines used in therapy typically operate in the 600-1000 nm wavelength range for deeper tissue penetration.
- 🧪 Evidence on the effectiveness of LLLT is mixed, with studies on conditions like tendinopathy and low back pain showing inconsistent results.
- 🧠 Placebo effects may play a role in LLLT’s perceived benefits, emphasizing the need for high-quality randomized controlled trials in research.
- 📝 Systematic reviews on LLLT for conditions such as rheumatoid arthritis, osteoarthritis, and frozen shoulder show conflicting results, often due to study bias or varying methodologies.
- 🧑⚕️ LLLT treatment protocols differ by condition, with recommendations such as 8 joules per square centimeter for Achilles tendinopathy, though treatment effectiveness can vary significantly.
Q & A
What is a laser and how does it function?
-A laser is a device that amplifies light through stimulated emission of radiation to produce a coherent, monochromatic beam. It consists of an energy source, a resonant chamber, and an active medium. Electrons in the active medium are excited and emit photons when they return to their ground state. These photons reflect between mirrors in the chamber and exit as a focused beam directed at a target tissue.
What are the unique properties of laser light compared to conventional light?
-Laser light has three unique properties: monochromaticity (all photons have the same wavelength), coherence (photons are synchronized in time and space), and collimation (laser beams are nearly parallel and can be focused to a small area with little divergence).
How does low-level laser therapy (LLLT) theoretically work?
-LLLT works on the principle of the Grotthus Draper law, which states that light must be absorbed by a chemical substance for a photochemical reaction to occur. LLLT is believed to stimulate cellular processes like oxidative phosphorylation and the production of ATP by affecting enzymes such as cytochrome C oxidase in mitochondria.
What are some of the factors that influence how a laser interacts with tissue?
-Several factors influence laser-tissue interaction: the wavelength of the laser, the power and power density, pulse duration, spot size, fluence (energy density), properties of the target tissue, and the duration of exposure. Longer wavelengths penetrate deeper into tissues, and energy density affects the intensity of the treatment.
How is energy density calculated in laser therapy?
-Energy density (fluence) is calculated by dividing the total energy (in joules) by the area of application (in square centimeters). The energy itself is determined by multiplying the power (in watts) by the treatment time.
What is the role of pulse duration in low-level laser therapy?
-Pulse duration (or pulse rate) is crucial for determining how the laser energy is delivered. For more acute and superficial injuries, lower pulse rates are used, while chronic conditions typically require higher pulse rates. The pulse duration is related to the thermal relaxation time, which is the time it takes for tissue to return to its baseline temperature after being heated.
What evidence exists for the effectiveness of low-level laser therapy?
-The evidence for LLLT's effectiveness is mixed and often of variable quality. Some studies show benefits for conditions like tendinopathy and low back pain, while others find no significant effects. Systematic reviews often highlight inconsistencies and methodological flaws in existing research.
What are some of the common applications of low-level laser therapy?
-LLLT is commonly applied to treat musculoskeletal conditions, such as tendinopathies, low back pain, neck pain, and frozen shoulder. However, the efficacy of treatment varies depending on the condition and the parameters used in the therapy.
How do the wavelength and spot size affect tissue penetration in laser therapy?
-Wavelength determines the depth of tissue penetration; longer wavelengths penetrate more deeply. Spot size also affects energy delivery, with larger spot sizes leading to less scattering and deeper penetration compared to smaller spot sizes.
What are the primary challenges in conducting research on low-level laser therapy?
-Challenges in LLLT research include variability in treatment protocols (wavelength, power, duration), difficulty controlling for the placebo effect, and the lack of high-quality randomized control trials. Many studies also suffer from low quality, small sample sizes, and inconsistent results.
Outlines
🔬 Understanding Laser Devices and Their Mechanisms
This paragraph explains the fundamental workings of lasers, focusing on their use in both medical and therapeutic settings. It introduces the concept of low-level laser therapy (LLLT), describing how lasers stimulate chemical reactions within cells. The theory behind LLLT is based on the Grotthus Draper law of photochemistry, which states that light must be absorbed by a substance to cause a reaction. The paragraph also discusses how LLLT may influence processes such as ATP production and mitochondrial function to benefit tissue healing, though ongoing research is still determining its full therapeutic potential.
💡 Production, Properties, and Application of Lasers
The second paragraph delves deeper into how lasers function, focusing on the components like the resonant chamber, active medium, and mirrors that generate laser beams. It outlines the properties of lasers—monochromaticity, coherence, and collimation—that make them unique compared to conventional light sources. It also discusses how laser beams interact with tissue, explaining the factors such as wavelength, power, and fluence that influence their effectiveness and tissue penetration. The paragraph concludes with an overview of how pulse duration and spot size impact the thermal effects of laser energy on tissues.
🔍 Parameters and Application of Low-Level Laser Therapy
This paragraph discusses the practical aspects of applying low-level laser therapy (LLLT), including the importance of various parameters like energy density, power, and spot size. It explains how energy is delivered to tissue, with smaller spot sizes leading to greater scattering, and highlights the importance of energy density and power for determining treatment effectiveness. The paragraph also walks through an example calculation for determining treatment time for Achilles tendinopathy using laser therapy, explaining how to adjust pulse rates for acute versus chronic injuries.
📊 Evidence and Research on Low-Level Laser Therapy
The fourth paragraph focuses on the research surrounding low-level laser therapy (LLLT), noting that evidence for its effectiveness is mixed and often inconclusive. It presents findings from systematic reviews and clinical trials that have investigated LLLT for conditions like tendinopathy, low back pain, and rheumatoid arthritis. The paragraph points out that while some studies suggest benefits, many others show no significant effect or are deemed to be of low quality due to biases and inconsistent methodologies. The paragraph concludes by acknowledging the ongoing debate about LLLT’s efficacy and the need for more rigorous research.
🧪 Summary of Research on Low-Level Laser Therapy
This paragraph continues the discussion on the evidence supporting low-level laser therapy, summarizing the results of various systematic reviews and studies. It highlights inconsistent and conflicting results across research, especially in studies of neck pain, rheumatoid arthritis, osteoarthritis, and frozen shoulder. The paragraph stresses that many of the studies suffer from a high risk of bias and low-quality evidence, although some positive results have been observed. It ends by reiterating the need for better-quality research to clarify the true effectiveness of LLLT in clinical settings.
Mindmap
Keywords
💡Low-Level Laser Therapy (LLLT)
💡Grotthus-Draper Law
💡Chromophores
💡Monochromaticity
💡Coherence
💡Collimation
💡Fluence
💡Pulse Duration
💡Thermal Relaxation Time
💡Clinical Evidence
Highlights
Lasers rely on stimulated emission of radiation to produce coherent wavelengths in the ultraviolet, visible, or infrared spectrum.
High-power lasers are used in laser medicine to cut or destroy tissue, while low-power lasers are used in physiotherapy for pain relief and enhancing cell function through phototherapy.
Low-level laser therapy is based on the Grotthus Draper law, which states that light must be absorbed by a chemical substance for a photochemical reaction to occur.
The theory suggests that low-level laser therapy can impact chemical reactions like oxidative phosphorylation, potentially increasing ATP production and respiratory enzymes such as cytochrome C oxidase.
Lasers have unique properties such as monochromaticity, coherence, and collimation, which differentiate them from other electromagnetic radiation forms.
Monochromaticity means all photons in the laser beam are of the same wavelength, while coherence refers to the synchronization of photons in time and space.
Collimation ensures that laser beams are nearly parallel, allowing the energy to be focused on a small area without substantial divergence.
The interaction of laser energy with tissues depends on variables like wavelength, power, spot size, energy density, and tissue exposure duration.
Longer laser wavelengths penetrate tissue more deeply, and the pulse duration is tied to the thermal relaxation time of the target tissue.
The spot size affects energy delivery, with smaller spot sizes causing more scattering, while larger ones enable deeper penetration.
Power density, measured in watts per square centimeter, affects how quickly tissue heats, determining whether the effect is coagulation or vaporization.
For low-level laser therapy, the optimal energy density is generally below 35 joules per square centimeter, depending on the condition treated.
Inconsistent research evidence regarding the effectiveness of low-level laser therapy, particularly in conditions like tendinopathy and low back pain, suggests mixed results.
Placebo effects and variable parameters across studies complicate the evaluation of laser therapy's clinical effectiveness.
Systematic reviews and meta-analyses show conflicting outcomes, with studies on conditions like tendinopathy, back pain, and rheumatoid arthritis offering inconclusive evidence.
Research continues, and while some low-quality trials suggest potential benefits, high-quality randomized control trials are rare, making definitive conclusions challenging.
Transcripts
Lasers are devices that rely upon the stimulated emission of radiation to produce a single,
coherent wavelength within the ultraviolet, visible or infrared portion of the electromagnetic
spectrum. Whereas high power lasers are used in laser medicine to cut or destroy tissue,
physiotherapists use low power lasers to relieve pain and stimulate or enhance
cell function through phototherapy (or so the theory goes). Briefly,
low-level laser therapy is theorised to work on the basis of the first law in photochemistry:
the Grotthus Draper law, which states that light must be absorbed by a chemical substance
in order for a photochemical reaction to take place. The generally accepted theory is that
low-level laser therapy can impact chemical reactions (like oxidative phosphorylation)
and therefore the production of ATP or chemical substances like the respiratory enzyme
cytochrome C oxidase (which is involved in the electron transport chain in mitochondria),
for therapeutic benefit. Research is ongoing about these therapeutic mechanisms but its
effects appear to be limited to a specified set of wavelengths and parameters. In this lecture,
we will review the basic principles of low-level laser therapy: how it is produced,
applied and its evidence for treating a number of different musculoskeletal conditions.
Lasers are devices that rely upon the stimulated emission of radiation to produce a beam of light.
The word 'laser' is an acronym for 'Light Amplification by Stimulated Emission of
Radiation'. Lasers are comprised of an energy source, a resonant chamber
and an active medium. Let's start with the resonant chamber, which contains the active
laser medium and several reflective mirrors. When they are in an unexcited state the electrons of
the atoms in the active medium orbit their nucleus at their lowest energy level or 'ground state',
and these orbits are closer to the nucleus. But when an external energy source is applied to
the resonant chamber, this excites the electrons in the active medium and moves them to a higher
orbit. As the electrons return from the excited state back to the ground state,
they spontaneously emit photons of energy in the form of electromagnetic radiation.
These photons reflect back and forth between the mirrors of the resonant chamber,
some of which reflect all of the photons and others which reflect only some of them, and then
they ultimately exit the device where they are directed to a target tissue. These target tissues
contain 'chromophores' or biomolecules which are capable of being excited by the incoming photons.
The way lasers are produced means that they have some unique properties,
when compared to other forms of electromagnetic radiation, and these include monochromaticity,
coherence and collimation. 'Monochromatic' means that all the photons in a laser beam
are of the same wavelength. 'Coherence' refers to the synchronisation of a laser beam in time
and space where the photons of the beam are in phase and coherent. By comparison the photons
in conventional light travel randomly. 'Collimation' means that the elements of
the laser beam are nearly parallel because there is little divergence. Laser beams can be focused
to a small area. Again, this property differs from conventional light (which diverges substantially).
When laser energy strikes the tissue surface that energy can be absorbed, reflected, transmitted
elsewhere or scattered. The kind of interaction that happens depends upon a number of variables,
including the active medium (which determines the wavelength of the laser), the power, the power
density of the laser, its pulse duration, the spot size used, the fluence (or energy density)
of the laser, the properties of the target tissue and the duration of tissue exposure.
The wavelength of the laser beam determines the degree of tissue penetration, the amount
of energy that is absorbed and the amount that is scattered. Basically, longer wavelengths
penetrate more deeply. The pulse duration, also known as the pulse frequency or pulse rate, is
determined from the thermal relaxation time of the target chromophore. The thermal relaxation time
is the time needed for the tissue temperature to return to its baseline temperature after heating.
For example, if a tissue is heated for a period less than or equal to its thermal relaxation time,
the accumulated heat is confined to the target object whereas if a target is heated for longer
than its thermal relaxation time, conduction leads to heating of surrounding structures.
The spot size is the diameter of the beam emitted from the laser as it strikes the tissue surface.
Energy entering the target tissue is attenuated more rapidly with the small spot size compared
with the larger spot size because scattering is greater with a small spot size. The spot size is
usually determined by the equipment you are using. For example, the spot sizes of the equipment we
will be using in our practical classes ranges from 0.13 to 0.28 centimetres-squared. Next, the amount
of energy that is delivered. Energy is measured in joules and 'fluence' (or energy density)
is energy divided by the application area, so its units are in joules per square centimetre.
When it comes to medical lasers, the destruction of large tissues or structures requires high
fluence due to the amount of tissue that needs to be heated to achieve thermal coagulation.
But for low-level laser therapy, the fluence is generally below 35 joules per square centimetre.
'Power' describes the rate of energy delivery and is measured in joules per second or 'watts'. Power
density-the power transmitted per unit area of cross section of a laser beam (which is measured
in watts per square centimetre)-is inversely proportional to the square of the diameter of
the spot size. In other words, energy applied over a small surface area means higher power densities
compared with the same amount of energy applied over a larger surface area.
Lower power density produces slow heating that coagulates tissue,
while high power density heats tissue quickly and can vaporise tissue.
So they are the various parameters, but how is low-level laser therapy actually applied? Well,
a lot comes down to the type of machine that you have. For example, I had mentioned before how the
wavelength of the laser (and therefore the depth of penetration) is determined by the active laser
medium of the machine. So for this parameter, the machines that we have here are capable of
producing lasers with wavelengths of between 600-1000 nanometers, which is associated with
the depth of penetration below the level of the dermis into the underlying subcutaneous tissue.
Their spot sizes range from 0.1-0.3 centimetres-squared, and their power outputs are
between 65 and 200 milliwatts. So really, the only parameters we're going to have any control over
are the pulse rate and the treatment time. When calculating the desired energy density, the World
Association of Laser Therapy have guidelines for a variety of different conditions. So for instance,
they recommend delivery of an energy density of 8 joules per centimetre squared for treating
achilles tendinopathy. As I said before, energy density is the energy divided by the spot size,
and energy is equal to power multiplied by time. So we have the target energy density (8 joules
per square centimetre), we have the power of the machine (let's say 0.2 watts), and we have the
spot size (which is 0.25 centimetres-squared). So the last remaining unknown-treatment time-is
the energy density, multiplied by the spot size, divided by the power, or '8' multiplied by '0.125'
divided by '0.2', which gives us a 5-second treatment time. For the area we are treating,
the last parameter-the pulse duration-can be controlled on the machine.
Generally, for more acute and superficial injuries low pulse rates are used, while higher pulse
rates are preferred for chronic conditions. Taking the example of achilles tendinopathy,
which would be considered a chronic condition, a pulse duration of 5 kilohertz might be used.
Treatment might be performed daily for 2 weeks, or every other day for 3-4 weeks. Contraindications
according to the North American Association for Laser Therapy are presented on screen.
But does laser are actually work, what's the evidence? Like other electrophysical modalities,
the evidence for the effectiveness of laser is conflicting, of variable quality and depends on
the population being studied. The World Association of Laser Therapy (or WALT)
recently published recommendations for the design and conduct of clinical studies of low-level laser
therapy, but currently available evidence rarely follows all of these recommendations. You see,
performing research on electrophysical modalities is complicated because patients expectations
probably have an important role in the benefit that comes from a treatment, so the placebo effect
is often at play. That's why high quality, randomised control trials where the patients
and therapists are blinded to group allocation are so important in this field, but they are rare.
Convincing evidence for the efficacy of low-level laser therapy in patients with tendinopathy is
lacking; a systematic review and meta-analysis of controlled clinical trials reported inconsistent
results with 12 studies showing some benefit while 13 reported inconclusive results or no effect.
The authors noted that, like much of the research investigating other electrophysical modalities,
studies varied in quality and in the doses or parameters used.
A 2005 systematic review of studies of low-level laser therapy for patients with lateral epicondyle
tendinopathy concluded that there was no clinically significant effect, either in
the short- or long-term compared with placebo. And several controlled trials in which patients were
randomly assigned to treatment with low-level laser therapy or placebo laser reported that
active laser treatment did not improve outcomes beyond those achieved with eccentric exercise.
For patients with low back pain, results again are largely inconsistent.
For example, four trials found laser therapy to be superior to sham therapy for pain relief and
improvement in function up to one year following treatment. However,
two other trials failed to show a benefit of laser therapy when used either alone or with exercise.
Findings from a 2008 Cochrane review found that the evidence was inconclusive for the
use of low-level laser therapy in the treatment of non-specific low back pain,
with the authors noting that protocols varied widely with lots of different treatment doses,
durations and wavelengths used. And these findings were echoed in two other systematic
reviews published in 2010 and 2015. And there's lots of other research which has been done in
other patient populations. I can't go into too much detail (because it would take too long),
but I'll give you a brief summary of some of the better systematic reviews,
one review concluded that low-level laser therapy may be useful in the treatment of
both acute and chronic neck pain, but then another more recent review with meta-analysis
concluded that the benefits were insignificant and that the evidence had a high risk of bias,
which is just another way of saying the available studies were low in quality.
A Cochrane review published in 2005 found that low-level laser therapy may be useful for
short-term pain relief in patients with rheumatoid arthritis, but again the studies that were
included were deemed to be at a high risk of bias. For osteoarthritis, another Cochrane review found
results to be conflicting, making it difficult to draw any conclusions. And another Cochrane
review published in 2014 investigating a range of electrotherapeutic modalities for frozen shoulder
found that there might be some benefit for laser, but this was based on one, low-quality
trial. And I could go on, but the findings are largely the same: inconsistent and conflicting
with lots of low quality, heterogeneous studies, but new evidence may emerge to change this. So
that concludes this lecture on low-level laser therapy. To recap, I started by outlining what
lasers are and how low-level laser therapy is used as an electro-therapeutic modality.
I outlined the theory of how it might work and the various treatment parameters.
I finished by discussing some of the research investigating its clinical effectiveness.
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