Pulsed Magnetic Field Therapy - How Does It Work?An extract taken from a lecture delivered on 28th January, 1995
by Dr. D. C. LAYCOCK Ph.D. (Med. Eng.); MBES; MIPEM*;
B.Ed. (Hons)(Phys. Sciences); CGLI (Ind. Electronics);
Consultant Clinical Engineer, Westville Associates and Consultants (UK).
All living cells within the body possess potentials between the inner and outer membrane of the cell, which, under normal healthy circumstances, are fixed. Different cells, e.g. Muscle cells and Nerve cells, have different potentials of about -70 milli-Volts respectively. When cells are damaged, these potentials change such that the balance across the membrane changes, causing the attraction of positive sodium ions into the cell and negative trace elements and proteins out of the cell. The net result is that liquid is attracted into the interstitial area and swelling or oedema ensues. The application of pulsed magnetic fields has, through research findings, been shown to help the body to restore normal potentials at an accelerated rate, thus aiding the healing of most wounds and reducing swelling faster. The most effective frequencies found by researchers so far, are very low frequency pulses of a 50Hz base. These, if gradually increased to 25 pulses per second for time periods of 600 seconds (10 minutes), condition the damaged tissue to aid the natural healing process.
Pain reduction is another area in which pulsed electromagnetic therapy has been shown to be very effective. Pain signals are transmitted along nerve cells to pre-synaptic terminals. At these terminals, channels in the cell alter due to a movement of ions. The membrane potential changes, causing the release of a chemical transmitter from a synaptic vesicle contained within the membrane. The pain signal is chemically transferred across the synaptic gap to chemical receptors on the post synaptic nerve cell. This all happens in about one 2000th of a second, as the synaptic gap is only 20 to 50 nanometres wide (1 nanometre = 1/1000,000,000 of a metre). As the pain signal, in chemical form, approaches the post synaptic cell, the membrane changes and the signal is transferred. If we look at the voltages across the synaptic membrane then, under no pain conditions, the level is about -70 milli-Volts. When the pain signal approaches, the membrane potential increases to approximately +30 milli-Volts, allowing a sodium flow. This in turn triggers the synaptic vesicle to release the chemical transmitter and so transfer the pain signal across the synaptic gap or cleft. After the transmission, the voltage reduces back to its normal quiescent level until the next pain signal arrives.
The application of pulsed magnetism to painful sites causes the membrane to be lowered to a hyper-polarisation level of about -90 milli-Volts. When a pain signal is detected, the voltage must now be raised to a relatively higher level in order to fire the synaptic vesicles.
Since the average change of potential required to reach the trigger voltage of nearly +30 milli-Volts is +100 milli-Volts, the required change is too great and only +10 milli-Volts is attained. This voltage is generally too low to cause the synaptic vesicle to release the chemical transmitter and hence the pain signal is blocked. The most effective frequencies that have been observed from research in order to cause the above changes to membrane potentials, are a base frequency of 200Hz and pulse rate settings of between 5 and 25Hz.
*Member of the Institute of Physics and Engineering in Medicine.
Veterinary Application of Pulsed Magnetic Field Therapyby Dr. D. C. Laycock Ph.D. (Med. Eng.); MIPEM*; B.Ed. (Hons)(Phys. Sciences); MBES:
CGLI (Ind. Electronics); Consultant Clinical Engineer, Westville Associates and Consultants (UK)
and M. Laycock: B.A. (Sciences); P.G.C.E.; Research Co-ordinator
Research into Pulsed Magnetic Field Therapy
Although the therapeutic use of pulsed magnetic fields has long been in existence, understanding of its mode of action has been poorly understood. As early as 1940, Nagelshmidt proposed that its action was at the cellular level and this has now been supported by research. It has been shown that damaged cells have a reduced negative charge, with subsequent effect on the flow of ions. This causes a build-up of fluid and prevents the normal cellular metabolism from taking place. Research by Bauer and more recently by Sansaverino (1980), confirmed that pulsed electromagnetic fields can restore the ionic balance and return the cell to its normal functions.
Initially, pulsed magnetic fields were applied mainly to fractures, where it was shown that they could bring about a reduction in the time needed for resolution of the fractures. It has been shown that under the influence of a pulsed magnetic field, osteoblasts are attracted to treatment sites, where small eddy currents are then induced into trace elements of ferro-magnetic material within the bone. Also, work by Madronero has shown that calcium salts are purified, hence bone crystals become stronger. More recently, research by Bassett has been investigating the wider applications of pulsed magnetic fields in the area of orthopaedics.
Bassett also foresaw the extension of pulsed magnetic field therapy to other areas of medicine. This has now taken place, with an increase in scientific research and clinical trials in the UK, and throughout Europe, Russia and the USA.
The range of applications has covered :-
Treatment of vascular disorders (Steinberg 1964)
Reduction of inflammation and oedema (Golden et al 1980)
Enhancement of the rate of healing in skin grafts (Golden et al 1981)
Reduction of pain (Warnke 1983)
Treatment of neuropathy (Lau)
Nerve regeneration (Hayne)
Reduction in symptoms of Multiple Sclerosis (Guseo 1987)
Research into these and other areas have shown good rates of success, with no detrimental side effects. For optimum results, low-frequency sustained pulsed magnetic fields should be applied, with specific problems responding best to specific frequencies. For example, pain can be blocked using a base frequency of 200Hz as this brings about hyperpolarisation of nerve cells and inhibits transmission of pain signals. For wound healing, a base frequency of 50Hz is most effective, with a pulse rate of 17.5Hz.
The role of Pulsed Magnetic Field therapy in veterinary practice
Initially, pulsed magnetic field therapy was used primarily in treating horses for resolution of back and leg injuries. This was followed by widespread use with greyhounds, since these incur frequent sprains, ligament injuries and fractures, all of which respond well to pulsed magnetic field therapy. It is now used with other animals for similar injuries and has also been used to improve metabolism. The range of animals treated is wide - from elephants to buzzards! Pulsed magnetic field therapy has been found to be particularly effective in treating leg and wing fractures of small birds, as they often are difficult to splint and, in the worst cases, difficult to pin because of splintering of small bones. These injuries show a good response given daily treatment with pulsed magnetic field therapy.
The use of a 200Hz base frequency as a pain block also has been beneficial in facilitating the examination of an injured animal. Practitioners have found that an initial 10 minute treatment reduces an animal's distress, so that it will then tolerate further handling in order to apply treatment or to enable the manipulation of an injury.
German shepherd dogs are noted for suffering symptoms which resemble those of Multiple Sclerosis. In the UK, some success has been achieved by treating these symptoms with pulsed magnetic field therapy. There is also evidence from research that nerve regeneration has been achieved under the influence of pulsed magnetic fields.
Once a diagnosis has been made and the desired therapeutic frequency determined, pulsed magnetic field therapy is simple to apply and can safely be administered by the owner. This means that treatment can be given more than once a day on a regular basis between visits to the surgery - thus speeding up the rate of healing and reducing demands on the time of the practitioner. In the UK, trained animal therapists operate under the direction of veterinary surgeons to provide pulsed magnetic field therapy as part of a physiotherapy programme for animals. Students come from all over the world to a training centre to be taught the methods and how to use the equipment to optimum effect.
Equipment
There is a range of equipment available. The larger units have a blanket applicator on which the animal can lie during treatment. These also are particularly useful for treating back injuries in large animals. There are also strap-on applicator pads available. The desired frequency range and treatment time is selected on the control panel of the unit. Current research shows that long treatment sessions are not essential, as maximum therapeutic effect is generally achieved in a 10 minute session. Naturally the duration over which treatment is required is dependent on the severity of the injury. Fractures require longer treatment.
The latest equipment now coming onto the market is a smaller, battery operated unit which is particularly useful for small animals or where a small area is to be targeted for treatment, such as the legs and wings of birds. These units have a dual advantage. Firstly, the operator can easily transport the equipment, allowing prompt treatment anywhere at any time and removing the need to take the animal to the surgery. Secondly, this type of unit can be left with the owner on a hire basis to allow regular support treatment to be given between visits.
*Member of the Institute of Physics and Engineering in Medicine
HOW CAN PULSED MAGNETIC FIELD THERAPY ASSIST IN THE HEALING OF BONES AND LIGAMENTS?by Dr. D. C. Laycock Ph.D. (Med. Eng.); MBES; MIPEM*; B.Ed. (Hons)(Phys. Sciences);
CGLI (Ind. Electronics); Consultant Clinical Engineer, Westville Associates and Consultants (UK).
Bone is essentially calcium structure which contains trace elements. One particular element recently identified is Alpha Quartz. This is the same type of material which is used in computers and digital or electronic watches. When this material is compressed, it develops a voltage across its two compressive faces, a phenomenon known as the piezo-electric effect. The old crystal pickups on record players used this effect to generate electrical sound signals. Gas appliances and some cigar lighters also utilise the same effect to generate a spark for ignition.
In bone, areas of stress generate small electric charges which are greater than those of less stressed areas, so that polarised bone-laying cells (osteoblasts) are believed to be attracted to these areas and begin to build up extra bone material to counter the stress.
With bone injuries, bleeding occurs to form a haematoma in which capillaries quickly form, transporting enriched blood to the injury site.
Pulsed Magnetic Field therapy of a base frequency of 50Hz, pulsed at above 12Hz, causes vaso and capillary dilation, so helping to speed up the process of callus formation. Within the bone itself, pulsed electro-magnetism causes the induction of small eddy currents in the trace elements, which in turn purify and strengthen the crystal structures. These have the same effect as the stress-induced voltages caused by the alpha quartz and as such, attract bone cells to the area under treatment. This can, therefore, accelerate the bone healing process to allow earlier mobilisation and eventual full union. Ligaments and tendons are affected in similar ways to solid bone by pulsed electromagnetic therapy, since they are uncalcified bone structures in themselves.
*Member of the Institute of Physics and Engineering in Medicine
Neural RegenerationDr D.C.Laycock PhD, MIPEM
The severance of nerves in all living beings occurs frequently. Every deep cut severing capillaries will usually also sever some nerve fibers. It is apparent that as the normal process of healing the wound takes place, the injured nerve fiber also heals; otherwise all areas of injury would probably end up numb permanently. The amount of healing that takes place and the method by which it is caused to happen may be due to several factors. Becker’s theories of Perinueral currents along the glial cells offer a possible insight into the process.
When an injury takes place along a nerve fiber, the ‘circuit’ for Perinueral current flow is broken. A small current flows from the proximal severed fiber to its distal counterpart. The research carried out by Becker suggests that this current of injury has two possible effects. These are:
a) Repair is initiated in the damaged glial cell.
b) The small current flowing across the injury site stimulates
Nerve regeneration takes the form of a tube of glial cells slowly growing across the injury site to meet up with its distal segment. This is followed by the nerve fiber (axon) regenerating within the tube. The method of targeting with small nerve injuries to the correct distal segment may be due to chemo tactic processes, that is, chemical signals given out the distal site will cause regenerative growth to a very specific point reconnecting the nerve and establishing its original function.
Regeneration of more complex bundles of nerves servicing motor functions and from dermal regions would have greater problems in their regeneration process. This is because of location of the nerves, i.e. within the central nervous system or in the peripheral system. Neural repair to severances in either the whole or part of the spinal chord rarely re-establishes normal function because of the many fibers bundled together and also the type of glial cell surrounding them. Within the central nervous system each nerve fiber is surrounded by myelin formed from Oligodenrocyte cells. These cells have up to sixteen ‘arms’ which each wrap around nerve fibers. Damage to just one cell, therefore, affects many fibers. Research studying severed spinal chords has shown some evidence of re-growth of the nerves but where the fracture has been successfully bridged, these have been shown to be relatively few in number and also random in their attachments.
The peripheral nervous system is less complicated since each glial cell is single celled. These are called Swann cells and are known to recover from injury. With the total severance of major peripheral nerve bundles some repair and regeneration may take place but it is debatable whether full function would ever be regained.
The question as to whether any aid to the repair and regeneration of nerve injuries can take place depends on the type of therapy being used. The normal process would take place unless multiple injuries or disease have affected the area. Speeding up the process may be aided by pulsating magnetic fields. This may induce extra current flow into the Perinueral current flow and increase the current of injury. Also, damaged Swann/Oligodenrocyte cells may be helped in the normal process of repair as with any cells by assistance to cationic/anionic flows through their membranes. There has been some research into the use of PMF to aid regeneration, such as that by Sisken (1990) and Walker (1993) and this has generated interest in further trials using pulsed magnetic therapy.
A possible treatment regime for nerve injuries would be pulsed magnetic therapy set at specific frequencies. Research has suggested that neurons respond more to pulsating frequencies of 200Hz and above. This causes hyper-polarization at the synapse and is more to do with the inhibition of chemical transmissions across the synaptic gap. However, where there is neural injury applying the 200Hz may have a number of effects.
These are:
a) Possible greater induction along the glial cells than induced by 50Hz. This may aid the establishment of currents of injury to sufficiently high levels to initiate glial cell regeneration.
b)Supply the proximal and distal segments of the injured axons with the required nutrients to sustain them, thereby preventing the possibility of a permanent injury.
c) Another benefit may be the reduction of pain from receptors in close proximity to the site.
Pulse frequencies applied with the 200Hz would have to be determined by effect as they may differ for the type and size of injury. One possible method would be to use a constant setting in the initial stages, which may be reduced to 5Hz once healing is established.
A Theory of Electromagnetic Interactions with Bone and Connective TissueDr. D.C.Laycock, PhD, MIPEM
The use of magnetic fields to aid the healing of long bone fractures have long been practiced with good results, particularly so when applied to non unions. The method of interaction of the field with the bone has never been well explained, however work by Becker has brought some explanation with regards to the action of piezo- electric charges and the way they are processed within bone structures. These present an osteoblast attracting or regeneration charge in areas of injury or stress. This article is intended to go further and identify possible interactions of dynamic magnetic fields in both healing of fractures and attracting bone cells to areas under treatment.
Becker identified and established the existence of perineural currents, which flow through myelin cytosol in a conventional type of electric current fashion. Each segment of the myelin sheath is in contact with the each other at the ‘Nodes of Ranvier’. Micro apertures between them allow a flow of charge carriers along their length. This is different to nerve impulses which are due to a wave type sodium inflow / chlorine outflow along the fibers. The brain is the source of negatively charged particles, which form the basis of such currents. A continuous loop of efferent and afferent nerves normally completes the circuit back to the brain. An injury to soft tissue or bone exposes the nerve endings in such a way that minute currents then flow across the injury site from damaged efferent to afferent nerves. Such currents are termed ‘currents of injury’. These in themselves are sufficient to trigger healing at the site. In long bones, the marrow produces DNA bearing, immature blood cells. The minute injury current triggers a process of dedifferentiation of these blood cells, which transform to become bone. Under normal conditions, therefore, the healing of fractures takes the form of regeneration as opposed to repair.
Non-union fractures may be ones that have damage to the nerve endings at some distance away from the actual fracture site. This could occur through additional stress fractures, disease or infection. The distances between the exposed nerve endings of the afferent nerves to the efferent may be too great to allow a sufficiently large enough ‘current of injury’ to flow. Hence the regeneration process does not occur. It also possible that delayed union may be caused by the need for neural repair and re-growth to be well established towards the fracture site before currents of injury are sufficient to trigger the bone regeneration process.
An American Orthopaedic surgeon, Dr Gus Sarmiento, suggested that fractures are aided in their healing process by slight movements at the injury site. Such movements are believed to encourage blood flow to stimulate the formation of callus. Now it may be speculated that the compressive action between the fracture segments could induce small currents in the bone. Such currents are termed piezo electric. This is a phenomenon that occurs when crystal structures are forcibly compressed or extended. A voltage appears across the face of the crystal structure during the dynamic phases of both compression and extension. The polarity, therefore, may present a negative aspect, adding to the current of injury during compression but then counter it with an opposite, positive one during its extension back to normal. Therefore the voltages would effectively cancel each other out. Becker’s work suggested that bone material has properties such that they filter out the positive voltage so that only the compressive, negative ones are left. These will, therefore, only ever add to the current of injury. This may be sufficient to speed up initial regeneration of the bone. This would be in keeping with Woolff’s Law, which states that bone growth is increased in areas of stress.
The voltage filter mentioned above is due to the bonding together of two crystalline forms making up bone structures. Within these crystal structures are different types of ‘free’ charge carriers. Anyone familiar with solid states electronics would know these as ‘N’ (negative) and ‘P’ (positive) type charges in semiconductors. Osteones comprising collagen and apatite are bonded together by copper ions. The junction between the two brings together the ‘P’ type collagen tightly to the ‘N’ type apatite. When in contact, some of the positive ‘P’ carriers cross into the apatite and vice versa. A ‘PN’ junction is formed which has the properties of allowing current to flow one way only, that is, ‘N’ electrons can only flow one way and the ‘P’ charges the other. This occurs only if the biased nature of any piezo electric voltage is correctly orientated. The opposite voltage is effectively cut off, as current cannot flow in the opposite direction.
This phenomenon would not only apply to injuries but also to where bone is stressed. Osteoblasts, formed from osteo-progenitor cells at the periosteum, are attracted directly to the area producing piezo-electric activity through the haversian canals. Where voltages do not exist or are dormant, osteoclast action removes bone material and hence problems of osteoporosis and osteo-malacia may occur. Where movement is not possible for any reason, pulsating magnetic fields may provide an alternative method of causing the minute voltages similar to the natural piezo-electric ones. To understand how this can happen one has to take a look in simple terms at the production of magnetic fields. The whole subject of magnetism is extensive and a deep study is beyond the scope of this article, however, there are some readily understandable concepts. Magnetic fields are produced when charged particles such as electrons or ions are moving uniformly in a straight line, i.e. through a conducting wire or crystalline structure. Conversely if a magnetic field is moved through a wire or crystal structure, then the charged particles in that structure are caused to move at right angles to the movement and in a direction dependant on whether the field is increasing or collapsing. Static fields have no effect. This phenomenon is termed ‘electromagnetic induction’. The main requirement is that there is some dynamic interaction, i.e. relative movement between the field and target tissue.
With bone, the collagen/apatite ‘PN’ junction will allow ‘N’ electrons to move in one direction across the junction and ‘P’ charges in the other. When a dynamic magnetic field is applied to the structure, the N and P charges cross the junction. This causes a charge to appear biased in one way when the field is moved in one direction due to the free movement of charges across the junction, but effectively filtered when the movement of the field is in the opposite direction. This induced charge therefore mimics the charge caused by natural piezo-electric activity within the bone and may attract osteoblasts to the target area. The same process would occur with non-union fractures. The electro- magnetically induced micro currents would only aid the currents of injury. This may possibly raise the current to the threshold required to trigger regeneration and eventual union of the fracture.
This article presented a possible explanation for the effectiveness of pulsed magnetic therapy to mimic that which would naturally occur in the bone. Robert O Becker MD has carried much of the background work out over many years. Works on animals here in the UK have confirmed the efficacy of pulsating magnetic fields both with bone and soft tissue injuries, as well as demonstrating the beneficial effect on nervous systems in both the reduction of pain and psychological conditions.
"LASERS vs SUPER luminescent LIGHT emitting DIODES" - A question of choice!by M. Laycock BA (Sciences); PGCE; Research Co-ordinator
and Dr. D. C . Laycock Ph.D. (Med. Eng.); MIPEM*; B.Ed. (Hons)(Physical Sciences);
MBES; CGLI (Ind. Electronics);
Consultant Clinical Engineer, Westville Associates and Consultants (UK).
Keywords: LASER; SLD; coherent light; collimated light; energy densities;
Photo-Biological Reactions
Although the basic principle of laser devices was developed at the turn of the century, rapid development in laser technology did not occur until the 1960's. In 1961, work began to assess the potential surgical applications of lasers, with the first successful surgical use being in the field of ophthalmology. The CO2 laser developed to overcome the early problems of high power machines became popular in the early 1970's, remaining the prime system in neurosurgery, dermatology and plastic surgery. Research into the development of and use of low energy lasers was begun almost a decade later by Professor Endre Mester in Budapest and simultaneously by Dr. Friedrich Plog in Canada. Since then, extensive research has been carried out in Russia and Eastern Europe, leading to the acceptance and clinical use of low intensity laser therapy. Later in the 1980's, reports began to be produced in Western Europe on the clinical use of low power lasers. Many of these reports tend to based on semi-conductor lasers and superluminous diodes.
Debate has arisen among many therapists regarding the use of semi-conductor lasers and superluminous diodes, referred to hereafter as SLD's, rather than true lasers. We need to answer a number of questions. Do they have different properties? Do they have different biological effects? Are there different safety parameters? Can they be used to treat the same conditions?
Looking first at some basic properties, both true lasers and SLD's produce monochromatic light, however, the true laser beam is also collimated. This means that it produces beams that are close to parallel. The small spot size produced by the beam is still maintained if the head is held away from the treatment area. The beams from SLD's have a greater level of divergence. In terms of beam size, the true laser has a smaller spot size of around 3mm² and SLD's are in the region of 20mm² . Whilst it would seem from these figures that the true laser has the advantage, its higher collimation means that the risk of eye damage is significantly greater with a true laser if the beam is accidentally viewed during treatment.
It is a common belief that the more powerful a piece of equipment, the better it is. At face value, the true laser has more power (between 30 and 200mW) than the SLD (power approx. 10mW). Higher average powers are believed to be best for musculoskeletal problems, lower powers for wound healing. However, it is the power density (brilliance) that is more important. This can be calculated using the formula:-
Using this, it can be calculated that the true laser has a greater power density (800 - 4000W/cm² ) than the SLD, where the power density is, on average, 50 - 75mW/cm² . Again, other facts need to be taken into consideration. For example, changing the pulse rate changes the number of fixed pulses in a specific time period. At 5Hz there are 5 pulses per second. At 5KHz there are 5000 pulses per second. As the rate increases, the radiant power output also increases, since each pulse contains a fixed number of photons. A pulsed SLD can therefore have as great a power as a simple true laser. Cluster units are also becoming common and for these it is essential to look at the sum of the individual effects. According to Baxter et al (1991), cluster units using SLD's have shown no obvious difference in effect from true lasers.
Another property that can be considered is coherence. With the true laser, the photons and waves are in phase, whilst SLD's produce incoherent light. However, it has been shown that the temporal coherence of a laser beam is mostly lost by the time the beam has passed through the first 1mm of tissue and that the property of coherence is of no significance at cellular level. Research by both Karu (1987) and Young et al (1989) has shown that coherence is not of importance when considering photo-biological reactions.
A more important aspect of comparing the two methods is that of laser-tissue interaction. High power and energy densities of the true laser can bring about strong thermal effects that are able to produce thermal coagulation and vapourisation. This lends them to surgical use. In contrast, the low power therapy is to a greater extent athermic. Although some thermal interactions do occur, the main interaction is photochemical, so that SLD's are an ideal clinical tool.
A major clinical application of the therapeutic laser is that of wound healing, since open wounds require lower energy densities. Considerable research has been carried out recently to find out why this irradiation stimulates the regenerative process. Firstly, the stages underlying the healing process were determined. Different aspects of the process were addressed by different groups. It has been shown that irradiation produces an increase in cell proliferation, essential for new growth to repair the wound.
Early work in this area was carried out by Hardy et al (1967) and has been continued at Guy's Hospital, London 1989. Collagen plays an important role in wound healing and it has been shown that irradiation by SLD's, (in this case GaAlA's), stimulates the production of collagen by fibroblasts (Lam et al 1986). In the same area, an increase in the proliferation of fibroblasts can be produced by the use of infra-red, as this stimulates protein metabolism (Toco et al 1985).
Synthesis of ATP (Adenosine Triphosphate) is also involved in the healing process. It has been shown that laser therapy can enhance ATP synthesis by stimulation of the respiratory/electron transport chain (Karn 1988). Furthermore, Inouie et al (1989), have shown that chronic wounds respond better after treatment with this therapy because it suppresses the immune reaction. As the immune response is involved in persistent chronic wounds, the healing process is accelerated.
This makes low energy laser therapy of use across a broad spectrum of applications. For the physiotherapist, it is an ideal treatment for ulcers. This includes trophic, varicose and diabetic ulcers as well as pressure sores (decubitus ulcers). Soft tissue injuries such as muscle tears and tendinopathies also have a good response, so that the treatment also is useful in sports medicine. In hospital use, post-operative wounds and burns also respond well to the treatment, at the same time giving a notable reduction in scarring. For the dental practice, laser therapy has been shown to reduce bleeding. It can also be of value in the treatment of cold sores and herpetic gingival stomatitis. In the case of alternative medicine laser acupuncture has been shown to be effective, as it is of benefit over metal needles when treating nervous patients or children. It also reduces the risk of the spread of HIV.
Veterinary practices also can gain from applying this form of laser therapy. In addition to soft tissue injuries and wound healing, it can be used to supplement treatment of respiratory tract infection if applied to the neck and underside of the throat. It has been used on horses to enhance the rate and texture of foot growth by irradiating the coronary band.
Although the application of low energy laser therapy has been shown to be a significant advantage when managing the treatment of wounds, research is now emerging to show the potential of this being applied to other areas. Infra-red diodes have been used to irradiate joints damaged by osteoarthritis and good results have been obtained (Trelles et al 1990). Pain relief has been effected in the treatment of tennis elbow using gallium arsenide emitters (Terashima et al 1990). There is also potential for low energy emitters to be used to alter the neurochemistry of both the central and the peripheral nervous system (Amemiya et al 1990).
While there are differences between true lasers and SLD's, it is clear that both produce physiological changes. SLD's are capable of doing the same job as many true lasers, with lowered risk of eye damage and at considerably lower cost. The important thing for the therapist to consider is the condition to be treated, the depth of penetration required and, taking power output etc. into account, to carefully calculate the optimum treatment duration.
by Dr. D. C. LAYCOCK Ph.D. (Med. Eng.); MBES; MIPEM*;
B.Ed. (Hons)(Phys. Sciences); CGLI (Ind. Electronics);
Consultant Clinical Engineer, Westville Associates and Consultants (UK).
All living cells within the body possess potentials between the inner and outer membrane of the cell, which, under normal healthy circumstances, are fixed. Different cells, e.g. Muscle cells and Nerve cells, have different potentials of about -70 milli-Volts respectively. When cells are damaged, these potentials change such that the balance across the membrane changes, causing the attraction of positive sodium ions into the cell and negative trace elements and proteins out of the cell. The net result is that liquid is attracted into the interstitial area and swelling or oedema ensues. The application of pulsed magnetic fields has, through research findings, been shown to help the body to restore normal potentials at an accelerated rate, thus aiding the healing of most wounds and reducing swelling faster. The most effective frequencies found by researchers so far, are very low frequency pulses of a 50Hz base. These, if gradually increased to 25 pulses per second for time periods of 600 seconds (10 minutes), condition the damaged tissue to aid the natural healing process.
Pain reduction is another area in which pulsed electromagnetic therapy has been shown to be very effective. Pain signals are transmitted along nerve cells to pre-synaptic terminals. At these terminals, channels in the cell alter due to a movement of ions. The membrane potential changes, causing the release of a chemical transmitter from a synaptic vesicle contained within the membrane. The pain signal is chemically transferred across the synaptic gap to chemical receptors on the post synaptic nerve cell. This all happens in about one 2000th of a second, as the synaptic gap is only 20 to 50 nanometres wide (1 nanometre = 1/1000,000,000 of a metre). As the pain signal, in chemical form, approaches the post synaptic cell, the membrane changes and the signal is transferred. If we look at the voltages across the synaptic membrane then, under no pain conditions, the level is about -70 milli-Volts. When the pain signal approaches, the membrane potential increases to approximately +30 milli-Volts, allowing a sodium flow. This in turn triggers the synaptic vesicle to release the chemical transmitter and so transfer the pain signal across the synaptic gap or cleft. After the transmission, the voltage reduces back to its normal quiescent level until the next pain signal arrives.
The application of pulsed magnetism to painful sites causes the membrane to be lowered to a hyper-polarisation level of about -90 milli-Volts. When a pain signal is detected, the voltage must now be raised to a relatively higher level in order to fire the synaptic vesicles.
Since the average change of potential required to reach the trigger voltage of nearly +30 milli-Volts is +100 milli-Volts, the required change is too great and only +10 milli-Volts is attained. This voltage is generally too low to cause the synaptic vesicle to release the chemical transmitter and hence the pain signal is blocked. The most effective frequencies that have been observed from research in order to cause the above changes to membrane potentials, are a base frequency of 200Hz and pulse rate settings of between 5 and 25Hz.
*Member of the Institute of Physics and Engineering in Medicine.
Veterinary Application of Pulsed Magnetic Field Therapyby Dr. D. C. Laycock Ph.D. (Med. Eng.); MIPEM*; B.Ed. (Hons)(Phys. Sciences); MBES:
CGLI (Ind. Electronics); Consultant Clinical Engineer, Westville Associates and Consultants (UK)
and M. Laycock: B.A. (Sciences); P.G.C.E.; Research Co-ordinator
Research into Pulsed Magnetic Field Therapy
Although the therapeutic use of pulsed magnetic fields has long been in existence, understanding of its mode of action has been poorly understood. As early as 1940, Nagelshmidt proposed that its action was at the cellular level and this has now been supported by research. It has been shown that damaged cells have a reduced negative charge, with subsequent effect on the flow of ions. This causes a build-up of fluid and prevents the normal cellular metabolism from taking place. Research by Bauer and more recently by Sansaverino (1980), confirmed that pulsed electromagnetic fields can restore the ionic balance and return the cell to its normal functions.
Initially, pulsed magnetic fields were applied mainly to fractures, where it was shown that they could bring about a reduction in the time needed for resolution of the fractures. It has been shown that under the influence of a pulsed magnetic field, osteoblasts are attracted to treatment sites, where small eddy currents are then induced into trace elements of ferro-magnetic material within the bone. Also, work by Madronero has shown that calcium salts are purified, hence bone crystals become stronger. More recently, research by Bassett has been investigating the wider applications of pulsed magnetic fields in the area of orthopaedics.
Bassett also foresaw the extension of pulsed magnetic field therapy to other areas of medicine. This has now taken place, with an increase in scientific research and clinical trials in the UK, and throughout Europe, Russia and the USA.
The range of applications has covered :-
Treatment of vascular disorders (Steinberg 1964)
Reduction of inflammation and oedema (Golden et al 1980)
Enhancement of the rate of healing in skin grafts (Golden et al 1981)
Reduction of pain (Warnke 1983)
Treatment of neuropathy (Lau)
Nerve regeneration (Hayne)
Reduction in symptoms of Multiple Sclerosis (Guseo 1987)
Research into these and other areas have shown good rates of success, with no detrimental side effects. For optimum results, low-frequency sustained pulsed magnetic fields should be applied, with specific problems responding best to specific frequencies. For example, pain can be blocked using a base frequency of 200Hz as this brings about hyperpolarisation of nerve cells and inhibits transmission of pain signals. For wound healing, a base frequency of 50Hz is most effective, with a pulse rate of 17.5Hz.
The role of Pulsed Magnetic Field therapy in veterinary practice
Initially, pulsed magnetic field therapy was used primarily in treating horses for resolution of back and leg injuries. This was followed by widespread use with greyhounds, since these incur frequent sprains, ligament injuries and fractures, all of which respond well to pulsed magnetic field therapy. It is now used with other animals for similar injuries and has also been used to improve metabolism. The range of animals treated is wide - from elephants to buzzards! Pulsed magnetic field therapy has been found to be particularly effective in treating leg and wing fractures of small birds, as they often are difficult to splint and, in the worst cases, difficult to pin because of splintering of small bones. These injuries show a good response given daily treatment with pulsed magnetic field therapy.
The use of a 200Hz base frequency as a pain block also has been beneficial in facilitating the examination of an injured animal. Practitioners have found that an initial 10 minute treatment reduces an animal's distress, so that it will then tolerate further handling in order to apply treatment or to enable the manipulation of an injury.
German shepherd dogs are noted for suffering symptoms which resemble those of Multiple Sclerosis. In the UK, some success has been achieved by treating these symptoms with pulsed magnetic field therapy. There is also evidence from research that nerve regeneration has been achieved under the influence of pulsed magnetic fields.
Once a diagnosis has been made and the desired therapeutic frequency determined, pulsed magnetic field therapy is simple to apply and can safely be administered by the owner. This means that treatment can be given more than once a day on a regular basis between visits to the surgery - thus speeding up the rate of healing and reducing demands on the time of the practitioner. In the UK, trained animal therapists operate under the direction of veterinary surgeons to provide pulsed magnetic field therapy as part of a physiotherapy programme for animals. Students come from all over the world to a training centre to be taught the methods and how to use the equipment to optimum effect.
Equipment
There is a range of equipment available. The larger units have a blanket applicator on which the animal can lie during treatment. These also are particularly useful for treating back injuries in large animals. There are also strap-on applicator pads available. The desired frequency range and treatment time is selected on the control panel of the unit. Current research shows that long treatment sessions are not essential, as maximum therapeutic effect is generally achieved in a 10 minute session. Naturally the duration over which treatment is required is dependent on the severity of the injury. Fractures require longer treatment.
The latest equipment now coming onto the market is a smaller, battery operated unit which is particularly useful for small animals or where a small area is to be targeted for treatment, such as the legs and wings of birds. These units have a dual advantage. Firstly, the operator can easily transport the equipment, allowing prompt treatment anywhere at any time and removing the need to take the animal to the surgery. Secondly, this type of unit can be left with the owner on a hire basis to allow regular support treatment to be given between visits.
*Member of the Institute of Physics and Engineering in Medicine
HOW CAN PULSED MAGNETIC FIELD THERAPY ASSIST IN THE HEALING OF BONES AND LIGAMENTS?by Dr. D. C. Laycock Ph.D. (Med. Eng.); MBES; MIPEM*; B.Ed. (Hons)(Phys. Sciences);
CGLI (Ind. Electronics); Consultant Clinical Engineer, Westville Associates and Consultants (UK).
Bone is essentially calcium structure which contains trace elements. One particular element recently identified is Alpha Quartz. This is the same type of material which is used in computers and digital or electronic watches. When this material is compressed, it develops a voltage across its two compressive faces, a phenomenon known as the piezo-electric effect. The old crystal pickups on record players used this effect to generate electrical sound signals. Gas appliances and some cigar lighters also utilise the same effect to generate a spark for ignition.
In bone, areas of stress generate small electric charges which are greater than those of less stressed areas, so that polarised bone-laying cells (osteoblasts) are believed to be attracted to these areas and begin to build up extra bone material to counter the stress.
With bone injuries, bleeding occurs to form a haematoma in which capillaries quickly form, transporting enriched blood to the injury site.
Pulsed Magnetic Field therapy of a base frequency of 50Hz, pulsed at above 12Hz, causes vaso and capillary dilation, so helping to speed up the process of callus formation. Within the bone itself, pulsed electro-magnetism causes the induction of small eddy currents in the trace elements, which in turn purify and strengthen the crystal structures. These have the same effect as the stress-induced voltages caused by the alpha quartz and as such, attract bone cells to the area under treatment. This can, therefore, accelerate the bone healing process to allow earlier mobilisation and eventual full union. Ligaments and tendons are affected in similar ways to solid bone by pulsed electromagnetic therapy, since they are uncalcified bone structures in themselves.
*Member of the Institute of Physics and Engineering in Medicine
Neural RegenerationDr D.C.Laycock PhD, MIPEM
The severance of nerves in all living beings occurs frequently. Every deep cut severing capillaries will usually also sever some nerve fibers. It is apparent that as the normal process of healing the wound takes place, the injured nerve fiber also heals; otherwise all areas of injury would probably end up numb permanently. The amount of healing that takes place and the method by which it is caused to happen may be due to several factors. Becker’s theories of Perinueral currents along the glial cells offer a possible insight into the process.
When an injury takes place along a nerve fiber, the ‘circuit’ for Perinueral current flow is broken. A small current flows from the proximal severed fiber to its distal counterpart. The research carried out by Becker suggests that this current of injury has two possible effects. These are:
a) Repair is initiated in the damaged glial cell.
b) The small current flowing across the injury site stimulates
Nerve regeneration takes the form of a tube of glial cells slowly growing across the injury site to meet up with its distal segment. This is followed by the nerve fiber (axon) regenerating within the tube. The method of targeting with small nerve injuries to the correct distal segment may be due to chemo tactic processes, that is, chemical signals given out the distal site will cause regenerative growth to a very specific point reconnecting the nerve and establishing its original function.
Regeneration of more complex bundles of nerves servicing motor functions and from dermal regions would have greater problems in their regeneration process. This is because of location of the nerves, i.e. within the central nervous system or in the peripheral system. Neural repair to severances in either the whole or part of the spinal chord rarely re-establishes normal function because of the many fibers bundled together and also the type of glial cell surrounding them. Within the central nervous system each nerve fiber is surrounded by myelin formed from Oligodenrocyte cells. These cells have up to sixteen ‘arms’ which each wrap around nerve fibers. Damage to just one cell, therefore, affects many fibers. Research studying severed spinal chords has shown some evidence of re-growth of the nerves but where the fracture has been successfully bridged, these have been shown to be relatively few in number and also random in their attachments.
The peripheral nervous system is less complicated since each glial cell is single celled. These are called Swann cells and are known to recover from injury. With the total severance of major peripheral nerve bundles some repair and regeneration may take place but it is debatable whether full function would ever be regained.
The question as to whether any aid to the repair and regeneration of nerve injuries can take place depends on the type of therapy being used. The normal process would take place unless multiple injuries or disease have affected the area. Speeding up the process may be aided by pulsating magnetic fields. This may induce extra current flow into the Perinueral current flow and increase the current of injury. Also, damaged Swann/Oligodenrocyte cells may be helped in the normal process of repair as with any cells by assistance to cationic/anionic flows through their membranes. There has been some research into the use of PMF to aid regeneration, such as that by Sisken (1990) and Walker (1993) and this has generated interest in further trials using pulsed magnetic therapy.
A possible treatment regime for nerve injuries would be pulsed magnetic therapy set at specific frequencies. Research has suggested that neurons respond more to pulsating frequencies of 200Hz and above. This causes hyper-polarization at the synapse and is more to do with the inhibition of chemical transmissions across the synaptic gap. However, where there is neural injury applying the 200Hz may have a number of effects.
These are:
a) Possible greater induction along the glial cells than induced by 50Hz. This may aid the establishment of currents of injury to sufficiently high levels to initiate glial cell regeneration.
b)Supply the proximal and distal segments of the injured axons with the required nutrients to sustain them, thereby preventing the possibility of a permanent injury.
c) Another benefit may be the reduction of pain from receptors in close proximity to the site.
Pulse frequencies applied with the 200Hz would have to be determined by effect as they may differ for the type and size of injury. One possible method would be to use a constant setting in the initial stages, which may be reduced to 5Hz once healing is established.
A Theory of Electromagnetic Interactions with Bone and Connective TissueDr. D.C.Laycock, PhD, MIPEM
The use of magnetic fields to aid the healing of long bone fractures have long been practiced with good results, particularly so when applied to non unions. The method of interaction of the field with the bone has never been well explained, however work by Becker has brought some explanation with regards to the action of piezo- electric charges and the way they are processed within bone structures. These present an osteoblast attracting or regeneration charge in areas of injury or stress. This article is intended to go further and identify possible interactions of dynamic magnetic fields in both healing of fractures and attracting bone cells to areas under treatment.
Becker identified and established the existence of perineural currents, which flow through myelin cytosol in a conventional type of electric current fashion. Each segment of the myelin sheath is in contact with the each other at the ‘Nodes of Ranvier’. Micro apertures between them allow a flow of charge carriers along their length. This is different to nerve impulses which are due to a wave type sodium inflow / chlorine outflow along the fibers. The brain is the source of negatively charged particles, which form the basis of such currents. A continuous loop of efferent and afferent nerves normally completes the circuit back to the brain. An injury to soft tissue or bone exposes the nerve endings in such a way that minute currents then flow across the injury site from damaged efferent to afferent nerves. Such currents are termed ‘currents of injury’. These in themselves are sufficient to trigger healing at the site. In long bones, the marrow produces DNA bearing, immature blood cells. The minute injury current triggers a process of dedifferentiation of these blood cells, which transform to become bone. Under normal conditions, therefore, the healing of fractures takes the form of regeneration as opposed to repair.
Non-union fractures may be ones that have damage to the nerve endings at some distance away from the actual fracture site. This could occur through additional stress fractures, disease or infection. The distances between the exposed nerve endings of the afferent nerves to the efferent may be too great to allow a sufficiently large enough ‘current of injury’ to flow. Hence the regeneration process does not occur. It also possible that delayed union may be caused by the need for neural repair and re-growth to be well established towards the fracture site before currents of injury are sufficient to trigger the bone regeneration process.
An American Orthopaedic surgeon, Dr Gus Sarmiento, suggested that fractures are aided in their healing process by slight movements at the injury site. Such movements are believed to encourage blood flow to stimulate the formation of callus. Now it may be speculated that the compressive action between the fracture segments could induce small currents in the bone. Such currents are termed piezo electric. This is a phenomenon that occurs when crystal structures are forcibly compressed or extended. A voltage appears across the face of the crystal structure during the dynamic phases of both compression and extension. The polarity, therefore, may present a negative aspect, adding to the current of injury during compression but then counter it with an opposite, positive one during its extension back to normal. Therefore the voltages would effectively cancel each other out. Becker’s work suggested that bone material has properties such that they filter out the positive voltage so that only the compressive, negative ones are left. These will, therefore, only ever add to the current of injury. This may be sufficient to speed up initial regeneration of the bone. This would be in keeping with Woolff’s Law, which states that bone growth is increased in areas of stress.
The voltage filter mentioned above is due to the bonding together of two crystalline forms making up bone structures. Within these crystal structures are different types of ‘free’ charge carriers. Anyone familiar with solid states electronics would know these as ‘N’ (negative) and ‘P’ (positive) type charges in semiconductors. Osteones comprising collagen and apatite are bonded together by copper ions. The junction between the two brings together the ‘P’ type collagen tightly to the ‘N’ type apatite. When in contact, some of the positive ‘P’ carriers cross into the apatite and vice versa. A ‘PN’ junction is formed which has the properties of allowing current to flow one way only, that is, ‘N’ electrons can only flow one way and the ‘P’ charges the other. This occurs only if the biased nature of any piezo electric voltage is correctly orientated. The opposite voltage is effectively cut off, as current cannot flow in the opposite direction.
This phenomenon would not only apply to injuries but also to where bone is stressed. Osteoblasts, formed from osteo-progenitor cells at the periosteum, are attracted directly to the area producing piezo-electric activity through the haversian canals. Where voltages do not exist or are dormant, osteoclast action removes bone material and hence problems of osteoporosis and osteo-malacia may occur. Where movement is not possible for any reason, pulsating magnetic fields may provide an alternative method of causing the minute voltages similar to the natural piezo-electric ones. To understand how this can happen one has to take a look in simple terms at the production of magnetic fields. The whole subject of magnetism is extensive and a deep study is beyond the scope of this article, however, there are some readily understandable concepts. Magnetic fields are produced when charged particles such as electrons or ions are moving uniformly in a straight line, i.e. through a conducting wire or crystalline structure. Conversely if a magnetic field is moved through a wire or crystal structure, then the charged particles in that structure are caused to move at right angles to the movement and in a direction dependant on whether the field is increasing or collapsing. Static fields have no effect. This phenomenon is termed ‘electromagnetic induction’. The main requirement is that there is some dynamic interaction, i.e. relative movement between the field and target tissue.
With bone, the collagen/apatite ‘PN’ junction will allow ‘N’ electrons to move in one direction across the junction and ‘P’ charges in the other. When a dynamic magnetic field is applied to the structure, the N and P charges cross the junction. This causes a charge to appear biased in one way when the field is moved in one direction due to the free movement of charges across the junction, but effectively filtered when the movement of the field is in the opposite direction. This induced charge therefore mimics the charge caused by natural piezo-electric activity within the bone and may attract osteoblasts to the target area. The same process would occur with non-union fractures. The electro- magnetically induced micro currents would only aid the currents of injury. This may possibly raise the current to the threshold required to trigger regeneration and eventual union of the fracture.
This article presented a possible explanation for the effectiveness of pulsed magnetic therapy to mimic that which would naturally occur in the bone. Robert O Becker MD has carried much of the background work out over many years. Works on animals here in the UK have confirmed the efficacy of pulsating magnetic fields both with bone and soft tissue injuries, as well as demonstrating the beneficial effect on nervous systems in both the reduction of pain and psychological conditions.
"LASERS vs SUPER luminescent LIGHT emitting DIODES" - A question of choice!by M. Laycock BA (Sciences); PGCE; Research Co-ordinator
and Dr. D. C . Laycock Ph.D. (Med. Eng.); MIPEM*; B.Ed. (Hons)(Physical Sciences);
MBES; CGLI (Ind. Electronics);
Consultant Clinical Engineer, Westville Associates and Consultants (UK).
Keywords: LASER; SLD; coherent light; collimated light; energy densities;
Photo-Biological Reactions
Although the basic principle of laser devices was developed at the turn of the century, rapid development in laser technology did not occur until the 1960's. In 1961, work began to assess the potential surgical applications of lasers, with the first successful surgical use being in the field of ophthalmology. The CO2 laser developed to overcome the early problems of high power machines became popular in the early 1970's, remaining the prime system in neurosurgery, dermatology and plastic surgery. Research into the development of and use of low energy lasers was begun almost a decade later by Professor Endre Mester in Budapest and simultaneously by Dr. Friedrich Plog in Canada. Since then, extensive research has been carried out in Russia and Eastern Europe, leading to the acceptance and clinical use of low intensity laser therapy. Later in the 1980's, reports began to be produced in Western Europe on the clinical use of low power lasers. Many of these reports tend to based on semi-conductor lasers and superluminous diodes.
Debate has arisen among many therapists regarding the use of semi-conductor lasers and superluminous diodes, referred to hereafter as SLD's, rather than true lasers. We need to answer a number of questions. Do they have different properties? Do they have different biological effects? Are there different safety parameters? Can they be used to treat the same conditions?
Looking first at some basic properties, both true lasers and SLD's produce monochromatic light, however, the true laser beam is also collimated. This means that it produces beams that are close to parallel. The small spot size produced by the beam is still maintained if the head is held away from the treatment area. The beams from SLD's have a greater level of divergence. In terms of beam size, the true laser has a smaller spot size of around 3mm² and SLD's are in the region of 20mm² . Whilst it would seem from these figures that the true laser has the advantage, its higher collimation means that the risk of eye damage is significantly greater with a true laser if the beam is accidentally viewed during treatment.
It is a common belief that the more powerful a piece of equipment, the better it is. At face value, the true laser has more power (between 30 and 200mW) than the SLD (power approx. 10mW). Higher average powers are believed to be best for musculoskeletal problems, lower powers for wound healing. However, it is the power density (brilliance) that is more important. This can be calculated using the formula:-
Using this, it can be calculated that the true laser has a greater power density (800 - 4000W/cm² ) than the SLD, where the power density is, on average, 50 - 75mW/cm² . Again, other facts need to be taken into consideration. For example, changing the pulse rate changes the number of fixed pulses in a specific time period. At 5Hz there are 5 pulses per second. At 5KHz there are 5000 pulses per second. As the rate increases, the radiant power output also increases, since each pulse contains a fixed number of photons. A pulsed SLD can therefore have as great a power as a simple true laser. Cluster units are also becoming common and for these it is essential to look at the sum of the individual effects. According to Baxter et al (1991), cluster units using SLD's have shown no obvious difference in effect from true lasers.
Another property that can be considered is coherence. With the true laser, the photons and waves are in phase, whilst SLD's produce incoherent light. However, it has been shown that the temporal coherence of a laser beam is mostly lost by the time the beam has passed through the first 1mm of tissue and that the property of coherence is of no significance at cellular level. Research by both Karu (1987) and Young et al (1989) has shown that coherence is not of importance when considering photo-biological reactions.
A more important aspect of comparing the two methods is that of laser-tissue interaction. High power and energy densities of the true laser can bring about strong thermal effects that are able to produce thermal coagulation and vapourisation. This lends them to surgical use. In contrast, the low power therapy is to a greater extent athermic. Although some thermal interactions do occur, the main interaction is photochemical, so that SLD's are an ideal clinical tool.
A major clinical application of the therapeutic laser is that of wound healing, since open wounds require lower energy densities. Considerable research has been carried out recently to find out why this irradiation stimulates the regenerative process. Firstly, the stages underlying the healing process were determined. Different aspects of the process were addressed by different groups. It has been shown that irradiation produces an increase in cell proliferation, essential for new growth to repair the wound.
Early work in this area was carried out by Hardy et al (1967) and has been continued at Guy's Hospital, London 1989. Collagen plays an important role in wound healing and it has been shown that irradiation by SLD's, (in this case GaAlA's), stimulates the production of collagen by fibroblasts (Lam et al 1986). In the same area, an increase in the proliferation of fibroblasts can be produced by the use of infra-red, as this stimulates protein metabolism (Toco et al 1985).
Synthesis of ATP (Adenosine Triphosphate) is also involved in the healing process. It has been shown that laser therapy can enhance ATP synthesis by stimulation of the respiratory/electron transport chain (Karn 1988). Furthermore, Inouie et al (1989), have shown that chronic wounds respond better after treatment with this therapy because it suppresses the immune reaction. As the immune response is involved in persistent chronic wounds, the healing process is accelerated.
This makes low energy laser therapy of use across a broad spectrum of applications. For the physiotherapist, it is an ideal treatment for ulcers. This includes trophic, varicose and diabetic ulcers as well as pressure sores (decubitus ulcers). Soft tissue injuries such as muscle tears and tendinopathies also have a good response, so that the treatment also is useful in sports medicine. In hospital use, post-operative wounds and burns also respond well to the treatment, at the same time giving a notable reduction in scarring. For the dental practice, laser therapy has been shown to reduce bleeding. It can also be of value in the treatment of cold sores and herpetic gingival stomatitis. In the case of alternative medicine laser acupuncture has been shown to be effective, as it is of benefit over metal needles when treating nervous patients or children. It also reduces the risk of the spread of HIV.
Veterinary practices also can gain from applying this form of laser therapy. In addition to soft tissue injuries and wound healing, it can be used to supplement treatment of respiratory tract infection if applied to the neck and underside of the throat. It has been used on horses to enhance the rate and texture of foot growth by irradiating the coronary band.
Although the application of low energy laser therapy has been shown to be a significant advantage when managing the treatment of wounds, research is now emerging to show the potential of this being applied to other areas. Infra-red diodes have been used to irradiate joints damaged by osteoarthritis and good results have been obtained (Trelles et al 1990). Pain relief has been effected in the treatment of tennis elbow using gallium arsenide emitters (Terashima et al 1990). There is also potential for low energy emitters to be used to alter the neurochemistry of both the central and the peripheral nervous system (Amemiya et al 1990).
While there are differences between true lasers and SLD's, it is clear that both produce physiological changes. SLD's are capable of doing the same job as many true lasers, with lowered risk of eye damage and at considerably lower cost. The important thing for the therapist to consider is the condition to be treated, the depth of penetration required and, taking power output etc. into account, to carefully calculate the optimum treatment duration.