Low-Level Light Therapy
Chapter 19: PTA235: Modalities
Instructor Information
Dr. Nicole Patterson, PT
Light Energy
Definition: Light is a form of electromagnetic energy, which is the most abundant energy form in the universe.
Classifications of Light
Ultraviolet
Visible
Infrared
Therapeutic Lasers
Definition: Lasers generate a highly refined, focused, small-diameter, monochromatic light, meaning the light consists of the same color within visible, ultraviolet, or infrared ranges.
Acronym: Laser stands for Light Amplification by Stimulated Emission of Radiation.
Properties: Lasers generate highly organized light called photons, which induce physiological changes in tissues.
Low-Level Light Therapy (LLLT): Does not destroy tissue and is FDA approved for:
Carpal tunnel syndrome
Musculoskeletal shoulder and neck pain
A variety of clinical conditions
Laser Energy
Wavelength: Energy produced in wavelengths between 650-1200 nm.
Color Determination: The wavelength determines the color emitted by the laser.
Activation of Chromophores: Photons emitted during LLLT activate specific skin receptors, stimulating or inhibiting physiological events by activating chromophores like melanin and hemoglobin, which absorb specific wavelengths of light for effects beneath the skin surface.
Classes of Lasers: Classified from 1 to 4 (minimal to significant tissue changes):
Class 4: "Hot" lasers for surgical applications; not found in physical therapy.
Class 2: Commonly used in therapy to avoid pain and injury.
Other Light Types: Includes Super Luminous Diodes (SLD) and Light Emitting Diodes (LED) which can be combined with lasers.
Laser Characteristics
Main Features:
Monochromatic: All light is of the same wavelength (color).
Coherent: Waves are in phase with one another.
Collimated: Light remains tightly focused without diverging (e.g., laser pointer).
FDA Classification: Lasers categorized by power level (1-4). LLLT operates using Class 2 or Class 2A lasers with output not exceeding 1 mW. Class 2A and above must include a warning label: "Do not stare into beam."
Protective Measures: Class 3 and 4 lasers require both patients and clinicians to wear protective eyewear.
Laser Output Parameters
Thermal Effects: LLLT doesn’t cause significant thermal changes; it derives benefits from photochemical processes occurring beneath the surface.
Effects on Circulation: Increased circulation is observed, deemed the greatest benefit of LLLT.
Factors Affecting Tissue Reactions:
Output frequency/wavelength
Power density
Duration of treatment
Vascularity of target tissues
Skin factors: Melanin and hemoglobin content affect penetration depth.
Absorption of Photons
Direct Effect: Actual absorption of light.
Indirect Effect: Chemical changes caused by the interaction of absorbed photons and tissues; these effects penetrate deeper.
Wavelength Dependence: Longer wavelengths (800-1000 nm) penetrate deeper, while shorter wavelengths (600-700 nm) are more superficial.
Depth of Penetration: LLLT can penetrate up to 2 cm through indirect responses.
Specific Laser Types
Helium-Neon (HeNe) Lasers
Visible Light Range: Produces visible red light with a maximum output of 1 mW or less.
Penetration Depth: Can penetrate between 0.8-15 mm; indirect effects are deeper.
Clinical Availability: Limited due to expense.
Gallium Arsenide (GaAs) Laser
Penetration: Can penetrate tissue up to 2 cm.
Output: Delivers up to 2 mW, operating at a lower average power than HeNe lasers.
Gallium Aluminum Arsenide (GaAlAs) Laser
Output: Can have outputs up to 30 mW and uses multiple diodes for deeper penetration.
Power and Dosage
Dosage Definition: Amount of energy delivered to tissues, expressed in units of mW/cm².
Energy Output: Expressed in joules (J/cm²).
Calculation of Energy Density:
Formula:
LLLT Treatments: Dose-oriented per unit area, for example a treatment dosage of 5.0 J/cm² with an output of 1 mW over an area of 1 cm² would require 50 seconds.
Common Clinical Dosages: Range between 0.5-10.0 J/cm².
Effects on Injury Response Processes
Mechanism: Effects on tissue believed to arise due to photochemical or photomechanical effects.
First Law of Photobiology: Light must be absorbed by specific receptors to affect tissue.
Primary Photoreceptors in Human Tissue:
Hemoglobin: Major oxygen carrier and storer.
Cyclooxygenase (COX): An enzyme that promotes inflammation and pain; NSAIDs are used to inhibit COX activity.
Myoglobin: Another oxygen carrier and storer.
Flavoproteins: Enzymes affected by lasers.
Energy and Mitochondria: Lasers affect mitochondria, stimulating the production of ATP.
Energy from ATP alters molecular activity, stimulating the electron transport chain, increasing ATP production, reducing intracellular pH, and COX production.
Pain Modulation: It is theorized that LLLT restores normal properties of pain-producing tissues, such as muscle spasms, via increased ATP and enhanced enzyme activity.
Inflammation and Tissue Repair
LLLT Effects: Can produce anti-inflammatory responses, aiding in healing.
Effective Dosage: Anti-inflammatory and fibroblastic stimulation occurs most effectively at 2.5-5 J.
Fibroblastic production inhibition occurs at 7-14 J.
GaAs Laser: Promotes muscle healing in the active inflammatory phase.
HeNe Laser Application: Administered two days post-injury at 48-hour intervals shows better healing outcomes than placebo treatments.
Wound Healing
Applications: Lasers assist in healing superficial wounds, including:
Skin ulcerations
Surgical incisions
Burns
HeNe Lasers: Less effective at destroying bacteria when used in lower output.
Healing Mechanisms: Enhanced through increased phagocytic activity, ATP synthesis, accelerated cell metabolism, and free radical release.
Increased activity of fibroblasts, lymphocytes, and macrophages.
Improved blood and lymph circulation within the treatment area.
Promotes growth of granulation tissue and new capillary formation.
Increased collagen content leads to higher tensile strength of healing wounds without thermal effects, making LLLT suitable for acute injury.
Pain Reduction
Wide Application: Utilized for treating acute and chronic pain.
Mechanisms: May alter nerve conduction velocity or decrease muscle spasms.
Impact on Nerve Impulses: Reduces rate and velocity of sensory nerve impulses in inflamed nerves while decreasing prostaglandin production.
Latent Pain Reduction: A significant period exists after treatment before pain relief is observed.
HeNe Laser Efficacy: Proven to mitigate sensitivity to trigger points in patients with fibromyalgia.
GaAlAs Lasers Results: Demonstrated decreased pain and improved function following treatment over 10 days (5 days a week for 2 weeks) with a dosage of 2 J or 1 minute at each tender point.
Fracture Healing
Biophysical Effects: Similar healing effects observed in soft tissues are believed to enhance fracture healing and bone remodeling.
Observed Benefits: Include increased capillary formation, calcium deposition, callus formation, and reduction of hematoma.
Microcurrents Creation: Photons interacting with tissue may create microcurrents akin to those generated by ultrasonic bone growth stimulators.
Outcome on Callus: Results in denser callus formation but does not improve tensile strength.
Bony Fixation: May enhance bony fixation to titanium implants.
Current Studies: Limited and inconclusive, primarily focused on animal models.
Contraindications and Precautions
Contraindications
Over eyes
Cancerous areas
Pregnant patients
Precautions
Use with caution if the patient is on certain medications, such as:
Tetracycline
Oral contraceptives
Antidepressants (which can increase sensitivity to sunlight)
Caution when treating over tattoos, as pigments can cause uneven distribution of the laser light.
Anodyne Therapy
Definition: A form of light therapy that employs near-infrared light, also referred to as Monochromatic Infrared Photo-Thermal Energy or MIRE™.
Benefits:
Increases circulation
Decreases pain
Origination: Initially developed for treatment in diabetic neuropathy patients.
Significant Findings: Studies report a 1300-3200% increase in circulation after 20 minutes of treatment; an analysis of five studies with over 5000 subjects indicates a 67% decrease in pain.
Mechanism of Anodyne Therapy
Infrared Light Emission: Infrared light is emitted from diode pads.
Skin Interaction: Pads placed directly on skin; energy is absorbed by hemoglobin, leading to proliferation of nitric oxide.
Physiological Effects: Results in blood vessel dilation and improved blood flow while stimulating fibroblasts and osteoblasts.
Patient Experience: Initially reports pain reduction followed by improvements in functional capabilities, typically observed over 4 weeks with daily treatments (3 to 5 times a week).
Indications for Anodyne Therapy
Initially created for diabetic neuropathy, also indicated for conditions such as:
Wounds
Arthritis
Poor gait and balance
Loss of sensation
Chronic sprains and strains
Carpal tunnel syndrome
TMJ
Contraindications for Anodyne Therapy
Overactive malignancy
Areas over or near the womb in pregnant women
Areas over topical heating agents (e.g., BenGay, Icy Hot) due to their effect on light absorption.
Potential Side-Effects
Superficial burns
Hypoglycemia
Safe to use over metal implants, pins, and screws.
Compatible with patients who have pacemakers and defibrillators.
Anodyne Application Visualization
Various applications including TMJ, patients with external fixators, and diabetic neuropathy.
Typical Treatment Session Information
Duration: Anodyne treatment lasts approximately 20-40 minutes.
Frequency: Can be applied daily.
Resolution of Symptoms: Generally observed after about 30 days.
Home Units: Available for rental, to complement treatments with therapeutic exercises, range of motion improvement, stretching, strengthening, and balance and gait training.