- Email: [email protected]
Therapeutic lasers
J
W %
.......................
Non-Reviewed This is the seventh in a conUnuing sedes of excerpts from the book Equine Sports Therapy, Published by Equine Veterinary Data., P.O. Box 1209, Wldomar, CA 92595, USA
THERAPEUTIC LASERS MimiPorter
The oldest form of therapy makes use of light, the light of the sun. Man's earliest medical history records note the use of sunlight to stimulate healing, and even today limited exposure to the sun's warmth and its rays is considered therapeutic. Recent research indicates that these effects may be due to a part of the light spectrum with which we are somewhat unfamiliar, invisible light, the ultraviolet and infrared wavelengths. The visible spectrum of red, orange, yellow, green, blue, indigo, and violet are familiar to us because we can see them in a rainbow or through a prism. Radiant energy from the sun will be bent into its various wavelengths when it is passed through a prism. Some of these wavelengths we perceive as colors. Each of the colors is a different wavelength of energy, from 390 nanometers for violet light to 770 nanometers for red light. Infrared radiation falls beyond 770 nm and ultraviolet falls below 390 nm. Lasers used for therapeutic purposes produce a light of 632 nanometers, which is within the visible red spectrum, producing a brilliant red light, and 904 nanometers which is invisible to the human eye. Wavelength is a term used to describe the distance between one peak and the next peak of a wave of electromagnetic energy. Light and sound are both forms of electromagnetic energy. This energy travels in wave formation. The number of peaks and valleys of the waves is termed its frequency or its cycles per second. Another term used to refer to frequency is Hertz. When quantifying sound waves we refer to its frequency or number of waves per second.
Volume 12, Number I, 1992
For example the human perceives sound between 16 hz to 18,000 hz. When we refer to large numbers of cycles per second it is more convenient to refer to the distance between the peaks of the waves, the wavelengths. Wavelengths are expressed in nanometers, one billionth of a meter. Our eyes perceive light between 393 nm to 759 rim. Lasers are not the first therapeutic tool to make use of light. Ultraviolet waves, found beyond the violet end of the spectrum, have been used in human medicine to treat certain diseases of the skin. At wavelengths of 150 to 390 nanometers, ultraviolet light waves are too short to be perceived by the human eye. Their existence was discovered in 1801, by Johann Ritter, who noted the changes they made on silver chloride. In the preceding year, Sir William Hershell had found radiations with wavelengths that were too long to be visible yet they caused an elevation in temperature registered by a thermometer. These heat producing waves were called infrared because they were beyond the red end of the spectrum. One type of low power laser produces a light in this spectral portion.
C h a r a c t e r i s t i c s of L a s e r Light
Laser is an acronym for "Light Amplification by Stimulated Emissions of Radiation". This indicates that the power of the light is greatly increased by emissions from certain substances contained in the laser apparatus. The concept of stimulated emissions was developed by Albert Einstein in 1917. His theory suggests that when the
49
:~iiiii i~i!ii : :::~%ii!:
Figure 1.
Drawing of Sir Isaac Newton separating the solar
spectrum into its visible components.
utilize 10 to 100 watts of average power and can cut through and coagulate tissue in what is called bloodless surgery. Perhaps the first laser beam seen popularly was in a James Bond movie. The villain Ooldfinger was using a red beam of light to cut through a sheet of steel to which James Bond was strapped. Lasers are now seen on the stage at rock concerts and in everyday life. They read prices at check out counters and are used to transmit voices in long distance phone conversations. Goldfinger's thin, red beam of laser light illustrated well the characteristics of laser that differentiate it from ordinary light. These factors are: non- divergence, coherence, and monoehromaticity. Non- divergence refers to the extreme parallelism of laser radiation. Laser radiation is emitted in a beam which is well focused with little spreading. By contrast, the sun's radiation or light from a light bulb is emitted in all directions. Light from a flashlight is somewhat non- divergent, although laser light is much more concentrated and the beam is much more narrow. Extremely small focal spots are possible, because of the parallelism of the beam, enabling a very high local density of radiation energy. Coherence is a term which indicates that all the waves are in phase and traveling in the same direction. In ordinary light there is much canceling out of energy production by waves that are not in phase because the wave frequencies vary. Energy in each wave is reinforced and the power of the radiation is amplified when the photons travel with a high degree of order and in a fixed phase relationship. Monochromaticity means all the light is of the same frequency or wavelength. It is all of the same color if it is
molecular arrangement of an atom is altered, fight of a particular frequency will be given off. This physical phenomena can be provoked by the arrival of another particle of light of the same frequency. Thereby, the stimulated emission of radiation occurs. A therapeutic laser is basically an apparatus to alter light to increase its speed and its energy so it will have WAVE LENGTH the power to penetrate skin. Therapeutic lasers have an output intensity of less than 100 milliwatts of average power. They are termed "cold" or "low power" lasers because they do not elevate tissue temperature. This output intensity is J Y comparable to that of a 60 W light bulb held a few inches from the skin. ComFREQUENCY mercial and industrial lasers, often called NUMBER OF CYCLES/SECOND "hot" lasers can be made powerful OR enough to evaporate any substance on HERTZ this planet. Their power output can be in the thousands and millions of watts. Surgical lasers Figure 2. Wave length is the distance between wave peaks. Hertz is the number of peaks and valleys of a wave of energy.
50
EQUINE VETERINARY SCIENCE
~
......~ ~ ~:~
light in the visible spectrum. Ordinary light is made up of many different wavelengths. Laser is one of the few light sources that produces one specific wavelength. Laser light possesses much more energy than a beam of ordinary light because all the light in a laser beam is the same wavelength, going the same direction in phase, and concentrated in a small area. Still, lasers used in therapeutic applications produce a very small amount of energy when compared to other types of lasers. The two types of low power lasers we commonly see in therapeutic use are the infrared gallium arsenide (GaAs) and the red beamed heliumneon (HeNe). Gallium arsenide crystals are a man made substance which emits light when stimulated. Light is amplified in a diode and the output is pulsed in the GaAs laser. Manufacturers often give the peak power of GaAs lasers as 2 watts. The average power can be as low as 0.2 milliwatts or as high as 40 milliwatts. The beam is emitted in pulses of extreme brevity, 200 nanoseconds. The beam of light emitted from a GaAs laser is invisible because the wavelength is 904 nanometers which falls outside the range of visible light. HeNe lasers amplify radiation by bouncing it back and forth between two parallel mirrors through a gas filled tube. When the gas resonates, the resulting light waves are in phase and of one color. It is finally transmitted through a flexible monofilament fiber optic system to the tip of the hand held wand. The average power is between 1 and 10 milliwatts. Using the pulsed mode decreases the average power to .5 mW. These lasers produce a red light with a wavelength of 632.8 nanometers. Penetration without divergence is thought to be .8 millimeters. Absorption of the refracted and dispersed beam is thought to continue to a depth of about 12 millimeters. Due to its longer wave length the GaAs laser can penetrate to 5-10 centimeters. Shorter wavelengthsbeeome more scattered as they pass through body tissues. Once the light is dispersed in the tissues the properties of coherence and columniation are lost.
\
Biological Effects The effects of laser are postulated in the biological field theory. This theory purports that a biological energy field exists around every cell and certain resonant frequencies exist
Volume 12, Number 1, 1992
......~ i : ~
"~ :~
~
J IlL
LASER LIGHT SOURCE
ORDINARY LIGHT SOURCE
Figure3. Divergence and non divergence of light. in the field. Larger structural levels, such as the organ and the organism exert influence on lower levels such as the cells. Resonant effects of low power lasers can restore the normal energetic status of the field when the resonant frequencies of cells are out of phase with the organ's frequency. That is, extemally applied energy influences specific cell functions. Researchers have explored the question of what lasers do and still many questions remain. Lasers are primarily used for their analgesic effects and for wound healing. The mechanism of influence on nerve conduction and on cell metabolism is as yet unclear but several published reports endeavor to identify the effects of laser application.
Pain Relief Laser is often used for pain relief. For this purpose, it is used with acupuncture techniques, pointing the beam at specific acupuncture points, trigger points, and nerves. This requires accuracy on the part of the therapist and knowledge of the location of these points. If the sites stimulated are not the correct points analgesia will not be achieved. Explaining how the laser affects pain is difficult and existing research throws only a little additional light on the question. Pain perception can be affected through interference in sensory nerve transmission. Studies using various techniques of cooling or heating have shown that prolonged cooling of a nerve will slow impulse transmission. Warming the tissues around a nerve will cause an increase in nerve transmission velocity. Two contrasting reports described the results of their
51
~i~~, ~ i ~
~ ~ ~:~
investigations into the effects of laser on nerve conduction velocity. One study utilized infrared laser radiation at doses of 20 seconds of application per square cm and 120 see of application per square cm over the radial nerve in man. The results showed no effect on the conduction rate of the nerve or on the temperature beneath the treatment area. Another report discussed the use of a HeNe laser over the radial nerve at 20 seconds of application per square cm. The results of this study indicate that sensory nerve conduction is significantly slower following HeNe laser radiation, resulting in the same affects as cooling the nerve. The placebo effect can confound the results of treatment sessions and even scientific studies when humans are used as subjects. With this in mind, a study was carried out using laboratory mice to compare laser analgesia with analgesia from acupuncture or morphine. Both GaAs and HeNe lasers were used but neither was found to produce an analgesic effect. Both the morphine and the acupuncture treatments produced marked delays in response time to a painful stimulus. Advocates of laser therapy claim that it is useful in eliminating areas of increased muscle spasm, called trigger points. A trigger point elicits pain when palpated and has lowered skin resistance to electricity compared to the surrounding skin. In an attempt to determine the effect of the HeNe laser on skin resistance overlying trigger points, favorable results were reported. Following a 15 second delivery of laser at a continuous output of .95 mW the resistance of skin overlying trigger points was seen to increase. An increase in skin resistance could indicate resolution of the tenderness and muscle spasm associated with the trigger point. The problem of chronic pain was addressed in a study using a 1 mW HeNe laser to treat subjects with pain lasting over six months. Laser was applied three times a week for ten weeks to specific sites over the radial, median, ulnar, and saphenous nerves in humans. The control subjects received radiation to sites near but not over these nerves. In this study the subjects who received laser over the nerves experienced pain relief after 4-8 treatments. After 12-30 treatments pain relief was more long lasting. The control subj~ts experienced no pain relief, a testimony to the precision with which laser must be applied to get results. The subjects who eventually became pain free demonstrated an increase in serotonin metabolism as mea-
52
ORDINARY
LIGHT
J
Figure 4. Coherence of light. LASER
LIGHT
suredby urinary excretion ofa serotonin metabolite. Serotonin is a nerve sensitizing substance coupled with endogenous opioids in providing pain relief. If its degradation can be measured and linked to relief from chronic pain perhaps this opens avenues for the study of laser initiated pain relief in the horse.
W o u n d Healing Open wounds can presem a problem to the horseman
because of the difficulty in keeping a bandage in place, the attraction of bacteria carrying flies, and the frequent inability of stitches to hold in an area subject to movement. Any tool or procedure which would aid in rapid wound closure would be a benefit. Low energy laser offers the possibility of being such atool as clinical observations indicate it promotes skin wound repair. Many scientific investigations have been devoted to determining how laser effects tissue repair. Although some studies have found no significance in wound closure rate following laser application others report DNA and RNA synthesis stimulation as well as improvement in the circulation within the wound. RNA and prot tin synthesis were measured in the mitoehondria of cells following HeNe radiation at an energy dose of 5 Joules/em 2. Both RNA activity and protein synthesis were observed to increase, giving rise to speculation as to how laser promotes wound healing in superficial skin wounds and decubitus ulcers. This study points to the evidence that mitochondria are the target of HeNe laser light. Mitochondria are thesource of energy in the cell and are involved
EQUINE VETERINARY SCIENCE
~ ~ ........... ~.................~~ ..~~ ........ ~:::~
in protein synthesis. An interesting study compared light from a HeNe laser with incoherent light of a similar wavelength. This study demonstrated that collagen production was increased significantly with the coherent laser light and was not affected by the incoherent light. The maximum effect was seen at 4 joules per square cm. According to this study, coherence is an important characteristic of laser light, perhaps more important than wavelength in terms of collagen stimulation. This concept is thought provoking, as there seems to be some difference in the response of tissue to the HeNe laser and to the GaAs lasers. The GaAs laser produces a more immediate response than the delayed one of the HeNe laser. This delay can be as long as 2 or 3 treatments. Also, tissue penetration of the GaAslaser is 5 cm, compared to that of the HeNe laser, which is 10-15 ram. These two lasers have different physical characteristics, the most obvious being a difference in wavelength of emission. Mester, perhaps the most often quoted laser researcher, reported that low energy laser radiation was seen to stimulate phagocytosis as well as epithelialregeneration. This occurred at doses of from 0.5 to 10 joules per cm 2 with the maximum increase in wound closure rate at a dose of I joule per cm 2. Contrasting with these findings, data collected from an experiment using swine as the subjects rather than mice, found no effects on wound closure rate with the use of the HeNe laser. Swine were used as subjects of this experiment because the dermal structure is similar to that of man. Unfortunately there are no studies published to date using horses as subjects. Clinical experience indicates that laser therapy promotes wound healing. The example shown in figures 4-7 shows how quickly a rather deep wound responded to laser therapy. Laser therapy began seven days after the accident and was applied twice per day, using a GaAs laser. Penicillin was the only other form of therapy and no sutures were used. The second photo was taken 15 days after treatment began. Substantial healing had taken place and the wound was closing. After 35 days the wound had dosed, the only evidence of it being a finger- width
Figure 5. A GaAs laser from the Respond Co., Madison, Ct. 1-800-722-1228. scar.
In a case where exuberant granulation tissue had prevented healing for over 5 months laser therapy following dchfidement reduced the wound size considerably. Treatment was administered with a GaAs laser for three months everyother day. Not only did this long standing wound close but the exuberant granulation was stopped and the wound closed with normal epithelium, as shown in figures 4-8. Other studies have measured the tensile strength of
Figure 6. HeNe laser from Dynatronic Corp., Salt Lake City, Utah.
Volume 12, Number 1, 1992
53
wounds stimulated by laser. Laser treated incisions had more strength against breaking than untreated incisions in both reports. Both low energy laser and ultraviolet light are used by human physical therapists to accelerate wound healing. One study found no advantage to the use of the HeNe laser when comparing the effectiveness of laser treated skin wounds to ultraviolet and to membrane occluded wounds. The skin wounds which were treated with a semipermeable plastic film appeared to respond the best. It should be noted that the laser treated wounds were treated once per day for 60 seconds. Perhapslonger treatment time could have created a more favorable effect. Most of the scientific reports make use of open wounds in their investigations of the effects of laser on tissue stimulation. A study using a closed wound, specifically a muscle bruise, looked at laser effects on wounds at depths beyond the reported direct penetration of laser energy. The severity of inflammation of the injured tissue was compared to the inflammation in noninjured tissue of the opposite limb in laser treated and nontreated conditions. After twelve days of HeNe laser application no difference was observed in the treated and nontreated tissue. This indicates that laser treatments to deep wounds may be ineffective. Although scientific studies are sometimes contradictory, clinical observations of laser treated wounds suggest a benefit. In my own experience, laser stimulates healing in non- responsive wounds. The amount of exuberant granulation is reduced and healing takes place at a noticeably faster rate than non- treated wounds.
Arthritis Arthritis is often listed among the health problems treatable by laser. A team of researchers recently used a neodymium glass laser with an emission wavelength of 1,060 nm. This laser is not generally available to equine therapists but the results of this investigation are interesting, none the less. The majority of the patients noted improvement in the joints of both hands, despite the fact that only one hand was actually lased. Tenderness, swelling, and heat in the joints improved in both hands,
54
Figure 7.
Wound on treatment day 1 and on day 15.
but more sio~nificantly in the lased hand. This indicates that the effects of laser stimulation could carry over to sites distant
from where the lasing occurs. It was speculated by the the authors that substances having distant effects, such as neurotransmitters, could be released by laser stimulation. By contrast a HeNe laser was applied to the joints of the hand of arthritic patients for 15 second irradiations four times per week. No benefit was observed from the regimen used in this experiment. This study points to the need for establishment of optimal dosage levels and treatment schedules. Clinical reports of laser use are often favorable, although the scientific literature presents both encouraging and dis-
Figure 8. Wound with exuberant granulation on day one of laser treatment and after three months of treatmenL
EQUINE VETERINARY SCIENCE
couraging evidence about the effectiveness of laser. This new therapeutic tool has been under scientific scrutiny for only a decade. Although the biological changes created by laser are yet to be completely understood, there is no doubt that the therapeutic laser is useful in shortening rehabilitation time in certain injury situations. Unfortunately, exaggerated claims have obscured the positive effects this modality can offer.
Techniques of Application Although laser is a relatively uncomplicated modality to use, attention to the techniques of application will make for a more successful treatment. The area to be treated should be clean, as with the use of any therapeutic modality. Remove any topical medications and clip the hair from the area to be treated. Debris around a wound could be debrided with a water pie or a whirlpool. The laser beam must be applied perpendicularly to the skin surface for the maximum penetration. The probe is held 1 or 2 millimeters from the skin when treating wounds and it is in contact with the skin when stimulating acupuncture points. Ninety seconds/cm a is recommended in physical therapy texts when treating open wounds, although dosages vary in the research literature. The recommendation for trigger and acupuncture points is 30 seconds per point. Adequate treatment of acupuncture points may require some patience on the part of the therapist and the horse as the entire wound surface is covered or all the appropriate points are stimulated. Giving the horse some hay to occupy his attention could make for a more efficient treatment session. Most laser equipment offers the user a choice of pulse modes. HeNe lasers usually offer a continuous mode for treating aeute pain and recent wounds. The pulsed mode is recommended for chronic conditions. GaAs lasers usually offer several pulse rate choices, labeled hertz levels. They are often designated by letters of the alphabet. Pulse rates and mode applications have not been conftrmed through research. The user's manual accompanying the unit will be the best guide for selecting the mode of treatment for each specific injury case. Hopefully, those who developed the
Volume 12, Number 1, 1992
Figure 9. Application of laser, guide arrived at their recommendations through extensive use and found the suggested settings to work best. The laser equipment itself must be kept clean. Keep the exit window of the applicator clean to avoid blocking laser emissions. Some lasers are equipped with an acupuncture point finder. This is actually an ohmmeterwhich detects areas of low electrical resistance compared to the surrounding skin. An audible signal is heard when the probe passes over such a spot, alerting the user to the location of the point. The therapist must hold a ground electrode against the horse's body to utilize this device. An informal survey of 5 different acupuncture point finders revealed a lack of repeatability in finding the points. Variables such as humidity in the air, sweaty or dry skin on the horse, or differences in the pressure with which the probe was pressed to the skin could affect the reliability of this tool. Advantages to the use of laser are that no gel or water are needed for conductivity and that laser treatment is completely painless. In fact, the patient feels nothing during treatment making it possible to treat nervous or fractious horses. There are few variables in application of laser. Generally application time and area of application are the only considerations. To obtain the desired biological response the power density or energy level applied to the tissues must be sufficient to surpass the threshold level but not exceed the tissue
55
destructive level. In other words, laser must be applied long enough to any given area to create an effect. Levels between 1 and 23 joules are thought to be optimum. Power output is measured in watts. Laser power output is in the milliwatt range or one thousandth of a watt. When a 1 mW laser beam is applied to a 1 cm2 area the power density is 1 milliwatt per square centimeter. A joule is equal to one watt of power applied for one second. Human tissue absorbs laser light quite readily and studies have shown that 99% of laser radiation is absorbed in the first 3- 4 millimeters of tissue in the skin. Infrared emis-sions in the ranges of 800 to 1,000 nanometers are able to pass through the skin with less absorption enabling them to get to deeper tissues. Laser energy absorption has been found to be color dependent and absorbed to a greater extent in dark or pigmented skin, although there are no published studies to date which measure the absorption of laser in equine skin. The effects of laser treatments are usually noted within the first three treatment sessions. A veterinarian should be consulted for re-evaluation if more than ten sessions produce no change in the condition. Presently lasers are considered by the FDA to be an investigational device. The operator must have an investigational device exemption from the Federal Food and Drug Administration when the laser is to be used on a human.
Contraindicstions
There are very few contraindications attached to the use of laser. Cold lasers with under 1 miUiwatt of average power are classified as a class I device. A class III b laser system must have output power of less than 500 milliwatts. These classifications indicate that they are considered a non-significant risk to humans unless held close to the cornea. Laser radiation should not strike the cornea of the eye. Although published research describing damage to the cornea utilized lasers of higher intensity than those avail-able to equine therapists, this is a reasonable precaution for low power lasers. Many laser manufacturers place a warning on their operating manuals advising the operator to avoid using certain drugs and the laser together. Such drugs as cortisone and furacin are light sensitive drugs and may be altered in their effects on tissue when exposed to light. This effect is undocumented in the scientific literature, but avoiding the interaction is a reasonable precauti.on. Iodine should be washed from a wound because it will block the transmission of laser light. Other reasonable, yet undocumented precautions include avoiding use on a pregnant female and use of a laser near a
56
cancerous lesion. Finally, although no apparent harm can result from proper laser use, it must be stated that laser can be misused if it is applied without a complete veterinary examination. Pain is nature's signal of an existing problem. The problem may grow and become untreatable or more difficult to treat successfully if this signal is ignored or covered up through pain reduction techniques. Optimal use of the laser is hampered by insufficient knowledge of the effectiveexposure conditions. It is also limited by our lack of knowledge of the effects laser light has on the cells and on physiological processes. Although the laser may prove to be an effective tool in certain applications, it should only be applied under veterinary guidance.
Conclusion
I would like to summarize some thoughts expressed to me by Mr. Donald E. Hudson, President of the Respond Company. Laser therapy has come a long way in the past five years. This is particularly true in Europe, where the majority of the scientific studies are conducted and 75% of all lasers, cold and hot, are sold. As one scans the scientific literature available it is difficult to get a clear picture of the mechanism of action since the available studies are inconsistent in their use of wavelength, power, and duration of treatment. New studies emerge continuously. Awareness of their results will help the user to develop skill in laser use so more consistent clinical results will be possible. Laser systems were introduced to the race track in the 70' s by salesmen selling the units. Exaggerated claims for the products elevated our expectations beyond what could be reasonably expected. Many of these units were under powered and lacked an adequate treatment guide. Many of these companies are out of business now. The companies that have endured produce a laser with more power, make reasonable claims for their machines, and include a treatment guide honed from field work over the years. The laser industry in America today has achieved a level of maturity and credibility in 1990. (To be continued)
EQUINE VETERINARY SCIENCE
W %
.......................
Non-Reviewed This is the seventh in a conUnuing sedes of excerpts from the book Equine Sports Therapy, Published by Equine Veterinary Data., P.O. Box 1209, Wldomar, CA 92595, USA
THERAPEUTIC LASERS MimiPorter
The oldest form of therapy makes use of light, the light of the sun. Man's earliest medical history records note the use of sunlight to stimulate healing, and even today limited exposure to the sun's warmth and its rays is considered therapeutic. Recent research indicates that these effects may be due to a part of the light spectrum with which we are somewhat unfamiliar, invisible light, the ultraviolet and infrared wavelengths. The visible spectrum of red, orange, yellow, green, blue, indigo, and violet are familiar to us because we can see them in a rainbow or through a prism. Radiant energy from the sun will be bent into its various wavelengths when it is passed through a prism. Some of these wavelengths we perceive as colors. Each of the colors is a different wavelength of energy, from 390 nanometers for violet light to 770 nanometers for red light. Infrared radiation falls beyond 770 nm and ultraviolet falls below 390 nm. Lasers used for therapeutic purposes produce a light of 632 nanometers, which is within the visible red spectrum, producing a brilliant red light, and 904 nanometers which is invisible to the human eye. Wavelength is a term used to describe the distance between one peak and the next peak of a wave of electromagnetic energy. Light and sound are both forms of electromagnetic energy. This energy travels in wave formation. The number of peaks and valleys of the waves is termed its frequency or its cycles per second. Another term used to refer to frequency is Hertz. When quantifying sound waves we refer to its frequency or number of waves per second.
Volume 12, Number I, 1992
For example the human perceives sound between 16 hz to 18,000 hz. When we refer to large numbers of cycles per second it is more convenient to refer to the distance between the peaks of the waves, the wavelengths. Wavelengths are expressed in nanometers, one billionth of a meter. Our eyes perceive light between 393 nm to 759 rim. Lasers are not the first therapeutic tool to make use of light. Ultraviolet waves, found beyond the violet end of the spectrum, have been used in human medicine to treat certain diseases of the skin. At wavelengths of 150 to 390 nanometers, ultraviolet light waves are too short to be perceived by the human eye. Their existence was discovered in 1801, by Johann Ritter, who noted the changes they made on silver chloride. In the preceding year, Sir William Hershell had found radiations with wavelengths that were too long to be visible yet they caused an elevation in temperature registered by a thermometer. These heat producing waves were called infrared because they were beyond the red end of the spectrum. One type of low power laser produces a light in this spectral portion.
C h a r a c t e r i s t i c s of L a s e r Light
Laser is an acronym for "Light Amplification by Stimulated Emissions of Radiation". This indicates that the power of the light is greatly increased by emissions from certain substances contained in the laser apparatus. The concept of stimulated emissions was developed by Albert Einstein in 1917. His theory suggests that when the
49
:~iiiii i~i!ii : :::~%ii!:
Figure 1.
Drawing of Sir Isaac Newton separating the solar
spectrum into its visible components.
utilize 10 to 100 watts of average power and can cut through and coagulate tissue in what is called bloodless surgery. Perhaps the first laser beam seen popularly was in a James Bond movie. The villain Ooldfinger was using a red beam of light to cut through a sheet of steel to which James Bond was strapped. Lasers are now seen on the stage at rock concerts and in everyday life. They read prices at check out counters and are used to transmit voices in long distance phone conversations. Goldfinger's thin, red beam of laser light illustrated well the characteristics of laser that differentiate it from ordinary light. These factors are: non- divergence, coherence, and monoehromaticity. Non- divergence refers to the extreme parallelism of laser radiation. Laser radiation is emitted in a beam which is well focused with little spreading. By contrast, the sun's radiation or light from a light bulb is emitted in all directions. Light from a flashlight is somewhat non- divergent, although laser light is much more concentrated and the beam is much more narrow. Extremely small focal spots are possible, because of the parallelism of the beam, enabling a very high local density of radiation energy. Coherence is a term which indicates that all the waves are in phase and traveling in the same direction. In ordinary light there is much canceling out of energy production by waves that are not in phase because the wave frequencies vary. Energy in each wave is reinforced and the power of the radiation is amplified when the photons travel with a high degree of order and in a fixed phase relationship. Monochromaticity means all the light is of the same frequency or wavelength. It is all of the same color if it is
molecular arrangement of an atom is altered, fight of a particular frequency will be given off. This physical phenomena can be provoked by the arrival of another particle of light of the same frequency. Thereby, the stimulated emission of radiation occurs. A therapeutic laser is basically an apparatus to alter light to increase its speed and its energy so it will have WAVE LENGTH the power to penetrate skin. Therapeutic lasers have an output intensity of less than 100 milliwatts of average power. They are termed "cold" or "low power" lasers because they do not elevate tissue temperature. This output intensity is J Y comparable to that of a 60 W light bulb held a few inches from the skin. ComFREQUENCY mercial and industrial lasers, often called NUMBER OF CYCLES/SECOND "hot" lasers can be made powerful OR enough to evaporate any substance on HERTZ this planet. Their power output can be in the thousands and millions of watts. Surgical lasers Figure 2. Wave length is the distance between wave peaks. Hertz is the number of peaks and valleys of a wave of energy.
50
EQUINE VETERINARY SCIENCE
~
......~ ~ ~:~
light in the visible spectrum. Ordinary light is made up of many different wavelengths. Laser is one of the few light sources that produces one specific wavelength. Laser light possesses much more energy than a beam of ordinary light because all the light in a laser beam is the same wavelength, going the same direction in phase, and concentrated in a small area. Still, lasers used in therapeutic applications produce a very small amount of energy when compared to other types of lasers. The two types of low power lasers we commonly see in therapeutic use are the infrared gallium arsenide (GaAs) and the red beamed heliumneon (HeNe). Gallium arsenide crystals are a man made substance which emits light when stimulated. Light is amplified in a diode and the output is pulsed in the GaAs laser. Manufacturers often give the peak power of GaAs lasers as 2 watts. The average power can be as low as 0.2 milliwatts or as high as 40 milliwatts. The beam is emitted in pulses of extreme brevity, 200 nanoseconds. The beam of light emitted from a GaAs laser is invisible because the wavelength is 904 nanometers which falls outside the range of visible light. HeNe lasers amplify radiation by bouncing it back and forth between two parallel mirrors through a gas filled tube. When the gas resonates, the resulting light waves are in phase and of one color. It is finally transmitted through a flexible monofilament fiber optic system to the tip of the hand held wand. The average power is between 1 and 10 milliwatts. Using the pulsed mode decreases the average power to .5 mW. These lasers produce a red light with a wavelength of 632.8 nanometers. Penetration without divergence is thought to be .8 millimeters. Absorption of the refracted and dispersed beam is thought to continue to a depth of about 12 millimeters. Due to its longer wave length the GaAs laser can penetrate to 5-10 centimeters. Shorter wavelengthsbeeome more scattered as they pass through body tissues. Once the light is dispersed in the tissues the properties of coherence and columniation are lost.
\
Biological Effects The effects of laser are postulated in the biological field theory. This theory purports that a biological energy field exists around every cell and certain resonant frequencies exist
Volume 12, Number 1, 1992
......~ i : ~
"~ :~
~
J IlL
LASER LIGHT SOURCE
ORDINARY LIGHT SOURCE
Figure3. Divergence and non divergence of light. in the field. Larger structural levels, such as the organ and the organism exert influence on lower levels such as the cells. Resonant effects of low power lasers can restore the normal energetic status of the field when the resonant frequencies of cells are out of phase with the organ's frequency. That is, extemally applied energy influences specific cell functions. Researchers have explored the question of what lasers do and still many questions remain. Lasers are primarily used for their analgesic effects and for wound healing. The mechanism of influence on nerve conduction and on cell metabolism is as yet unclear but several published reports endeavor to identify the effects of laser application.
Pain Relief Laser is often used for pain relief. For this purpose, it is used with acupuncture techniques, pointing the beam at specific acupuncture points, trigger points, and nerves. This requires accuracy on the part of the therapist and knowledge of the location of these points. If the sites stimulated are not the correct points analgesia will not be achieved. Explaining how the laser affects pain is difficult and existing research throws only a little additional light on the question. Pain perception can be affected through interference in sensory nerve transmission. Studies using various techniques of cooling or heating have shown that prolonged cooling of a nerve will slow impulse transmission. Warming the tissues around a nerve will cause an increase in nerve transmission velocity. Two contrasting reports described the results of their
51
~i~~, ~ i ~
~ ~ ~:~
investigations into the effects of laser on nerve conduction velocity. One study utilized infrared laser radiation at doses of 20 seconds of application per square cm and 120 see of application per square cm over the radial nerve in man. The results showed no effect on the conduction rate of the nerve or on the temperature beneath the treatment area. Another report discussed the use of a HeNe laser over the radial nerve at 20 seconds of application per square cm. The results of this study indicate that sensory nerve conduction is significantly slower following HeNe laser radiation, resulting in the same affects as cooling the nerve. The placebo effect can confound the results of treatment sessions and even scientific studies when humans are used as subjects. With this in mind, a study was carried out using laboratory mice to compare laser analgesia with analgesia from acupuncture or morphine. Both GaAs and HeNe lasers were used but neither was found to produce an analgesic effect. Both the morphine and the acupuncture treatments produced marked delays in response time to a painful stimulus. Advocates of laser therapy claim that it is useful in eliminating areas of increased muscle spasm, called trigger points. A trigger point elicits pain when palpated and has lowered skin resistance to electricity compared to the surrounding skin. In an attempt to determine the effect of the HeNe laser on skin resistance overlying trigger points, favorable results were reported. Following a 15 second delivery of laser at a continuous output of .95 mW the resistance of skin overlying trigger points was seen to increase. An increase in skin resistance could indicate resolution of the tenderness and muscle spasm associated with the trigger point. The problem of chronic pain was addressed in a study using a 1 mW HeNe laser to treat subjects with pain lasting over six months. Laser was applied three times a week for ten weeks to specific sites over the radial, median, ulnar, and saphenous nerves in humans. The control subjects received radiation to sites near but not over these nerves. In this study the subjects who received laser over the nerves experienced pain relief after 4-8 treatments. After 12-30 treatments pain relief was more long lasting. The control subj~ts experienced no pain relief, a testimony to the precision with which laser must be applied to get results. The subjects who eventually became pain free demonstrated an increase in serotonin metabolism as mea-
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ORDINARY
LIGHT
J
Figure 4. Coherence of light. LASER
LIGHT
suredby urinary excretion ofa serotonin metabolite. Serotonin is a nerve sensitizing substance coupled with endogenous opioids in providing pain relief. If its degradation can be measured and linked to relief from chronic pain perhaps this opens avenues for the study of laser initiated pain relief in the horse.
W o u n d Healing Open wounds can presem a problem to the horseman
because of the difficulty in keeping a bandage in place, the attraction of bacteria carrying flies, and the frequent inability of stitches to hold in an area subject to movement. Any tool or procedure which would aid in rapid wound closure would be a benefit. Low energy laser offers the possibility of being such atool as clinical observations indicate it promotes skin wound repair. Many scientific investigations have been devoted to determining how laser effects tissue repair. Although some studies have found no significance in wound closure rate following laser application others report DNA and RNA synthesis stimulation as well as improvement in the circulation within the wound. RNA and prot tin synthesis were measured in the mitoehondria of cells following HeNe radiation at an energy dose of 5 Joules/em 2. Both RNA activity and protein synthesis were observed to increase, giving rise to speculation as to how laser promotes wound healing in superficial skin wounds and decubitus ulcers. This study points to the evidence that mitochondria are the target of HeNe laser light. Mitochondria are thesource of energy in the cell and are involved
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~ ~ ........... ~.................~~ ..~~ ........ ~:::~
in protein synthesis. An interesting study compared light from a HeNe laser with incoherent light of a similar wavelength. This study demonstrated that collagen production was increased significantly with the coherent laser light and was not affected by the incoherent light. The maximum effect was seen at 4 joules per square cm. According to this study, coherence is an important characteristic of laser light, perhaps more important than wavelength in terms of collagen stimulation. This concept is thought provoking, as there seems to be some difference in the response of tissue to the HeNe laser and to the GaAs lasers. The GaAs laser produces a more immediate response than the delayed one of the HeNe laser. This delay can be as long as 2 or 3 treatments. Also, tissue penetration of the GaAslaser is 5 cm, compared to that of the HeNe laser, which is 10-15 ram. These two lasers have different physical characteristics, the most obvious being a difference in wavelength of emission. Mester, perhaps the most often quoted laser researcher, reported that low energy laser radiation was seen to stimulate phagocytosis as well as epithelialregeneration. This occurred at doses of from 0.5 to 10 joules per cm 2 with the maximum increase in wound closure rate at a dose of I joule per cm 2. Contrasting with these findings, data collected from an experiment using swine as the subjects rather than mice, found no effects on wound closure rate with the use of the HeNe laser. Swine were used as subjects of this experiment because the dermal structure is similar to that of man. Unfortunately there are no studies published to date using horses as subjects. Clinical experience indicates that laser therapy promotes wound healing. The example shown in figures 4-7 shows how quickly a rather deep wound responded to laser therapy. Laser therapy began seven days after the accident and was applied twice per day, using a GaAs laser. Penicillin was the only other form of therapy and no sutures were used. The second photo was taken 15 days after treatment began. Substantial healing had taken place and the wound was closing. After 35 days the wound had dosed, the only evidence of it being a finger- width
Figure 5. A GaAs laser from the Respond Co., Madison, Ct. 1-800-722-1228. scar.
In a case where exuberant granulation tissue had prevented healing for over 5 months laser therapy following dchfidement reduced the wound size considerably. Treatment was administered with a GaAs laser for three months everyother day. Not only did this long standing wound close but the exuberant granulation was stopped and the wound closed with normal epithelium, as shown in figures 4-8. Other studies have measured the tensile strength of
Figure 6. HeNe laser from Dynatronic Corp., Salt Lake City, Utah.
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wounds stimulated by laser. Laser treated incisions had more strength against breaking than untreated incisions in both reports. Both low energy laser and ultraviolet light are used by human physical therapists to accelerate wound healing. One study found no advantage to the use of the HeNe laser when comparing the effectiveness of laser treated skin wounds to ultraviolet and to membrane occluded wounds. The skin wounds which were treated with a semipermeable plastic film appeared to respond the best. It should be noted that the laser treated wounds were treated once per day for 60 seconds. Perhapslonger treatment time could have created a more favorable effect. Most of the scientific reports make use of open wounds in their investigations of the effects of laser on tissue stimulation. A study using a closed wound, specifically a muscle bruise, looked at laser effects on wounds at depths beyond the reported direct penetration of laser energy. The severity of inflammation of the injured tissue was compared to the inflammation in noninjured tissue of the opposite limb in laser treated and nontreated conditions. After twelve days of HeNe laser application no difference was observed in the treated and nontreated tissue. This indicates that laser treatments to deep wounds may be ineffective. Although scientific studies are sometimes contradictory, clinical observations of laser treated wounds suggest a benefit. In my own experience, laser stimulates healing in non- responsive wounds. The amount of exuberant granulation is reduced and healing takes place at a noticeably faster rate than non- treated wounds.
Arthritis Arthritis is often listed among the health problems treatable by laser. A team of researchers recently used a neodymium glass laser with an emission wavelength of 1,060 nm. This laser is not generally available to equine therapists but the results of this investigation are interesting, none the less. The majority of the patients noted improvement in the joints of both hands, despite the fact that only one hand was actually lased. Tenderness, swelling, and heat in the joints improved in both hands,
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Figure 7.
Wound on treatment day 1 and on day 15.
but more sio~nificantly in the lased hand. This indicates that the effects of laser stimulation could carry over to sites distant
from where the lasing occurs. It was speculated by the the authors that substances having distant effects, such as neurotransmitters, could be released by laser stimulation. By contrast a HeNe laser was applied to the joints of the hand of arthritic patients for 15 second irradiations four times per week. No benefit was observed from the regimen used in this experiment. This study points to the need for establishment of optimal dosage levels and treatment schedules. Clinical reports of laser use are often favorable, although the scientific literature presents both encouraging and dis-
Figure 8. Wound with exuberant granulation on day one of laser treatment and after three months of treatmenL
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couraging evidence about the effectiveness of laser. This new therapeutic tool has been under scientific scrutiny for only a decade. Although the biological changes created by laser are yet to be completely understood, there is no doubt that the therapeutic laser is useful in shortening rehabilitation time in certain injury situations. Unfortunately, exaggerated claims have obscured the positive effects this modality can offer.
Techniques of Application Although laser is a relatively uncomplicated modality to use, attention to the techniques of application will make for a more successful treatment. The area to be treated should be clean, as with the use of any therapeutic modality. Remove any topical medications and clip the hair from the area to be treated. Debris around a wound could be debrided with a water pie or a whirlpool. The laser beam must be applied perpendicularly to the skin surface for the maximum penetration. The probe is held 1 or 2 millimeters from the skin when treating wounds and it is in contact with the skin when stimulating acupuncture points. Ninety seconds/cm a is recommended in physical therapy texts when treating open wounds, although dosages vary in the research literature. The recommendation for trigger and acupuncture points is 30 seconds per point. Adequate treatment of acupuncture points may require some patience on the part of the therapist and the horse as the entire wound surface is covered or all the appropriate points are stimulated. Giving the horse some hay to occupy his attention could make for a more efficient treatment session. Most laser equipment offers the user a choice of pulse modes. HeNe lasers usually offer a continuous mode for treating aeute pain and recent wounds. The pulsed mode is recommended for chronic conditions. GaAs lasers usually offer several pulse rate choices, labeled hertz levels. They are often designated by letters of the alphabet. Pulse rates and mode applications have not been conftrmed through research. The user's manual accompanying the unit will be the best guide for selecting the mode of treatment for each specific injury case. Hopefully, those who developed the
Volume 12, Number 1, 1992
Figure 9. Application of laser, guide arrived at their recommendations through extensive use and found the suggested settings to work best. The laser equipment itself must be kept clean. Keep the exit window of the applicator clean to avoid blocking laser emissions. Some lasers are equipped with an acupuncture point finder. This is actually an ohmmeterwhich detects areas of low electrical resistance compared to the surrounding skin. An audible signal is heard when the probe passes over such a spot, alerting the user to the location of the point. The therapist must hold a ground electrode against the horse's body to utilize this device. An informal survey of 5 different acupuncture point finders revealed a lack of repeatability in finding the points. Variables such as humidity in the air, sweaty or dry skin on the horse, or differences in the pressure with which the probe was pressed to the skin could affect the reliability of this tool. Advantages to the use of laser are that no gel or water are needed for conductivity and that laser treatment is completely painless. In fact, the patient feels nothing during treatment making it possible to treat nervous or fractious horses. There are few variables in application of laser. Generally application time and area of application are the only considerations. To obtain the desired biological response the power density or energy level applied to the tissues must be sufficient to surpass the threshold level but not exceed the tissue
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destructive level. In other words, laser must be applied long enough to any given area to create an effect. Levels between 1 and 23 joules are thought to be optimum. Power output is measured in watts. Laser power output is in the milliwatt range or one thousandth of a watt. When a 1 mW laser beam is applied to a 1 cm2 area the power density is 1 milliwatt per square centimeter. A joule is equal to one watt of power applied for one second. Human tissue absorbs laser light quite readily and studies have shown that 99% of laser radiation is absorbed in the first 3- 4 millimeters of tissue in the skin. Infrared emis-sions in the ranges of 800 to 1,000 nanometers are able to pass through the skin with less absorption enabling them to get to deeper tissues. Laser energy absorption has been found to be color dependent and absorbed to a greater extent in dark or pigmented skin, although there are no published studies to date which measure the absorption of laser in equine skin. The effects of laser treatments are usually noted within the first three treatment sessions. A veterinarian should be consulted for re-evaluation if more than ten sessions produce no change in the condition. Presently lasers are considered by the FDA to be an investigational device. The operator must have an investigational device exemption from the Federal Food and Drug Administration when the laser is to be used on a human.
Contraindicstions
There are very few contraindications attached to the use of laser. Cold lasers with under 1 miUiwatt of average power are classified as a class I device. A class III b laser system must have output power of less than 500 milliwatts. These classifications indicate that they are considered a non-significant risk to humans unless held close to the cornea. Laser radiation should not strike the cornea of the eye. Although published research describing damage to the cornea utilized lasers of higher intensity than those avail-able to equine therapists, this is a reasonable precaution for low power lasers. Many laser manufacturers place a warning on their operating manuals advising the operator to avoid using certain drugs and the laser together. Such drugs as cortisone and furacin are light sensitive drugs and may be altered in their effects on tissue when exposed to light. This effect is undocumented in the scientific literature, but avoiding the interaction is a reasonable precauti.on. Iodine should be washed from a wound because it will block the transmission of laser light. Other reasonable, yet undocumented precautions include avoiding use on a pregnant female and use of a laser near a
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cancerous lesion. Finally, although no apparent harm can result from proper laser use, it must be stated that laser can be misused if it is applied without a complete veterinary examination. Pain is nature's signal of an existing problem. The problem may grow and become untreatable or more difficult to treat successfully if this signal is ignored or covered up through pain reduction techniques. Optimal use of the laser is hampered by insufficient knowledge of the effectiveexposure conditions. It is also limited by our lack of knowledge of the effects laser light has on the cells and on physiological processes. Although the laser may prove to be an effective tool in certain applications, it should only be applied under veterinary guidance.
Conclusion
I would like to summarize some thoughts expressed to me by Mr. Donald E. Hudson, President of the Respond Company. Laser therapy has come a long way in the past five years. This is particularly true in Europe, where the majority of the scientific studies are conducted and 75% of all lasers, cold and hot, are sold. As one scans the scientific literature available it is difficult to get a clear picture of the mechanism of action since the available studies are inconsistent in their use of wavelength, power, and duration of treatment. New studies emerge continuously. Awareness of their results will help the user to develop skill in laser use so more consistent clinical results will be possible. Laser systems were introduced to the race track in the 70' s by salesmen selling the units. Exaggerated claims for the products elevated our expectations beyond what could be reasonably expected. Many of these units were under powered and lacked an adequate treatment guide. Many of these companies are out of business now. The companies that have endured produce a laser with more power, make reasonable claims for their machines, and include a treatment guide honed from field work over the years. The laser industry in America today has achieved a level of maturity and credibility in 1990. (To be continued)
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