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MLS Master Class - Veterinary Imaging
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Celtic SMR
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Introduction to laser therapy

Carl Gorman BVSc MRCVS

Key words : Laser, therapeutic, healing, chromophores, analgesia

 

The word laser was first published in a paper in 1959.  It is an acronym for:

                                                      'Light Amplification by Stimulated Emission of Radiation'

The essential feature of lasers is that they emit light at a single frequency, allowing  the properties of that light frequency to be used for a variety of purposes.  Depending on the frequency, lasers can be a light source, cut materials (including biological tissue), carry information or impart energy.  They are widely used in all aspects of our lives today from bar code scanners to fibre optic communications, or from DVD drives to industrial cutting applications.

In order to produce a laser, energy (which may be an electrical charge or a light source) is applied to again medium. The gain medium is material with properties which allow it to amplify light bystimulated emission. Thus a light passed through the gain medium becomes amplified, and depending on the medium involved that light will be of one specific wavelength.  Gain mediums may be a gas, liquid or solid.  It needs to be pure to ensure that only one frequency is produced.

Commonly the amplification process occurs in a chamber containing the gain medium.  The chamber has a 100% reflective mirror at one end and a partially (e.g. 99%) reflective mirror at the other.  Light bounces back and forth between the mirrors, becoming amplified as it passes through the energised medium.  A proportion of light passes through the partially reflective mirror at one end and emerges as the laser beam.  (Fig 1).

LA1F1

Fig 1 A simple diagram of the components of a laser

The beneficial effects of laser therapy have been recognised and explored in human medicine since the 1970s.  Initially lasers were used as a cutting source, before the therapeutic benefits were explored.  CO2 lasers are an example of cutting lasers, emitting light at the 10,600 nm wavelength.  Therapeutic lasers emit light at lower wavelengths.  The MLS laser, for example, utilises two wavelengths: 905nm and 808nm.

Any laser with a wavelength above 500nm and producing power in excess of 500mW (0.5 watts)  is categorised as a Class IV laser, with the potential to damage eyes or tissue, and precautions must be taken.  Laser safety will be covered in detail in a later module.

Therapeutic lasers have a number of benefits which can be summarised as:

  • Reduction in pain
  • Reduction in inflammation
  • Accelerated healing time

These effects are brought about by the laser stimulating cells and tissues and inducing a large number of processes.  Unlike normal light, which contains many different wavelengths, the majority of which are reflected by the epidermis, infra red laser wavelengths pass through the skin to reach deeper tissues.  The light energy then brings about chemical, thermal and biomechanical effects.  (Fig 2).

LA1F2

Fig 2 Effects of laser therapy

Fig 3 Chemical Effects Of Laser Therapy

Fig 3 Chemical effects of laser therapy

The biological effects of a therapeutic laser at cell and tissue level are as follows.

Cellular effects:

  • Increased ATP synthesis
  • Increased synthesis of ATP binding proteins, making ATP more accessible for anabolic and metabolic processes
  • Increased RNA production
  • Increased cell proliferation
  • Induction of cellular differentiation processes
  • Release of growth factors (e.g. fibroblast growth factor) and other active substances
  • Increased production of extra cellular matrix molecules by fibroblasts and chrondrocytes
  • Increased protein PP1 and phosphatise activity, enhancing restoration of the cell basal state and modulating glycogen metabolism and muscular contraction/relaxation processes
  • Increased levels of MyoD proteins, α-enolase and PP1, which regulate myogenesis and mediate reconstruction of damaged muscle fibres
  • Increased levels of the anti-inflammatory protein NLRP 10 which acts via negative feedback to the production of pro-inflammatory interleukins

Fig 4 Thermal Effects Of Laser Therapy

Fig 4 Thermal effects of laser therapy

Tissue effects:

  • Modulation of the inflammatory processes
  • Extracellular matrix remodelling
  • Induction of myogenesis, and of damaged muscle fibre regeneration
  • Modulation of the production of muscular  structural proteins, such as actin and tropomyosin, critical for the mechanism of muscle contraction
  • Increased Galectin-3 and HNRNP K proteins, which can induce angiogenesis and regeneration of nerve fibres, promoting neuronal function and lymphatic and vascular regeneration
  • Endothelial function stimulation
  • Decreased oedema resorption time
  • Prevention of exuberant scar tissue formation and hyperkeratotic reactions

FIg 5 Biomechanical Effects Of Laser Therapy

Fig 5 Biochemical effects of laser therapy 

As a result of the above effects, and others, we can see in patients the actual benefits from laser therapy.  These include:

1)      Analgesic effects

  • Reduction of inflammation
  • Reduction of oedema
  • Reduction of muscle spasm
  • Wash out of pain inducing substances
  • Increased endorphin synthesis
  • Regulation of pain sensory conduction

2)      Anti-inflammatory and anti-oedema effects

  • Vasodilation and alteration of the permeability of  lymphatic vessels and capillaries
  • Wash out of pro-inflammatory mediators
  • Inhibition of production of inflammatory mediators

 3)      Biostimulating effects

  • Increased availability of nutrients, oxygen and growth factors due to vasodilation
  • Activation of cellular functions
  • Restoration and regulation of the cellular energy metabolism
  • Stimulation of cell proliferation and differentiation
  • Encouragement of repair to damaged muscle fibres and nerve endings
  • Stimulation of matrix protein synthesis and organisation
  • Control of the formation and organisation of scar tissue

These effects of therapeutic lasers mean that they can be use to help treat a variety of painful inflammatory conditions, as well as helping to enhance healing of wounds and musculoskeletal injuries.

The MLS system delivers two wavelengths of laser energy.

Fig 6 MLS Laser

Fig 6 MLS Laser

The 905nm wavelength is delivered in a pulsed fashion.  The frequency of the pulse is adjustable, and ranges from 1 to 2000 Hz (pulses per second).  This frequency and delivery produces theanalgesic effects of the laser.

The 808nm wavelength is delivered at the same time in a continuous pattern.  This mode particularly enhances the anti-inflammatory and anti-oedema effects of the laser.

There is a wide variety of conditions which might be suitable for laser therapy.  In essence any painful or inflammatory condition could potentially benefit.

Conditions suitable for treatment include:

  • Osteoarthritis
  • Intervertebral disc disease
  • Back pain due to muscle strain etc.
  • Acute and chronic tendon lesions
  • Sprains and strains
  • Fractures
  • Otitis externa
  • Stomatitis
  • Infected wounds
  • Surgical wounds
  • Slow healing wounds
  • Lick granulomas
  • Contusions

However, this is not an exhaustive list, and more applications will be discovered in practice.