Refresh Technology

IR Effect as the Light

INTRODUCTION TO ELECTROMAGNETIC RADIATION

Electromagnetic radiation is composed of electrical and magnetic fields that vary over time and are oriented perpendicular to each other (Fig. 15-1). Physical agents that deliver energy in the form of electromagnetic radiation include various forms of visible and invisible light and radiation in shortwave and microwave ranges. All living organisms are continuously exposed to electromagnetic radiation from natural sources, such as the magnetic field of the earth and ultraviolet (UV) radiation from the sun. We are also exposed to electromagnetic radiation from manufactured sources, such as light bulbs, domestic electrical appliances, computers, and power lines. This chapter serves as an introduction to the application of electromagnetic radiation in rehabilitation and provides specific information on the therapeutic application of lasers and other light therapy. The therapeutic use of electromagnetic radiation in UV, radiowave, and microwave ranges is covered in Chapters 10 and 16. Because infrared (IR) radiation produces superficial heating, the clinical application of IR lamps and other superficial heating agents is described in Chapter 8.

PHYSICAL PROPERTIES OF ELECTROMAGNETIC RADIATION

Electromagnetic radiation is categorized according to its frequency and wavelength, which are inversely proportional to each other (Fig. 15-2). Lower-frequency electromagnetic radiation, including extremely low-frequency (ELF) waves, shortwaves, microwaves, IR radiation, visible light, and UV, is nonionizing, cannot break molecular bonds or produce ions, and therefore can be used for therapeutic medical applications. Higher-frequency electromagnetic radiation, such as x-rays and gamma rays, is ionizing and can break molecular bonds to form ions.1,2 Ionizing radiation can also inhibit cell division and therefore is not used clinically, or it may be used in very small doses for imaging or in larger doses to destroy tissue. Approximate frequency ranges for the different types of electromagnetic radiation are shown in Fig. 15-3 and are provided in the sections concerning each type of radiation. Approximate ranges are given because reported values differ slightly among texts.3
The intensity of any type of electromagnetic radiation that reaches the patient from a radiation source is proportional to the energy output from the source, the inverse square of the distance of the source from the patient, and the cosine of the angle of incidence of the beam with the tissue. The intensity of energy reaching the body is greatest when energy output is high, the radiation source is close to the patient, and the beam is perpendicular to the surface of the skin.
As the distance from the skin, or the angle with the surface, increases, the intensity of radiation reaching the skin falls. Electromagnetic radiation can be applied to a patient to achieve a wide variety of clinical effects. The nature of these effects is determined primarily by the frequency and the wavelength range of the radiation4 and to some degree by the intensity of the radiation.
The frequencies of electromagnetic radiation used clinically can be in the IR, visible light, UV, shortwave, or microwave range. Far IR radiation, which is close to the microwave range, produces superficial heating and can be used for the same purposes as other superficial heating agents. It has the advantage over other superficial heating agents of not requiring direct contact with the body. UV radiation produces erythema and tanning of the skin and epidermal hyperplasia and is essential for vitamin D synthesis. It is used primarily for the treatment of psoriasis and other skin disorders. Shortwave and microwave energy can be used to heat deep tissues and, when applied at a low-average intensity using a pulsed signal, may decrease pain and edema and facilitate tissue healing by nonthermal mechanisms. Low-intensity lasers and other light sources in the visible and near-IR frequency ranges are generally used to promote tissue healing and to control pain and inflammation by nonthermal mechanisms.

PHYSIOLOGICAL EFFECTS OF ELECTROMAGNETIC RADIATION

When electromagnetic radiation is absorbed by tissues, it can affect them via thermal or nonthermal mechanisms. Because IR radiation and continuous shortwave and microwave diathermy delivered at sufficient intensity can increase tissue temperature, these agents are thought to affect tissues primarily by thermal mechanisms. IR lamps can be used to heat superficial tissues, whereas continuous shortwave and microwave diathermy heats deep and superficial tissues. The physiological and clinical effects of these thermal agents are generally the same as those of superficial heating agents (see Chapter 8), except that the tissues affected are different. UV radiation and low levels of pulsed diathermy or light do not increase tissue temperature and therefore are thought to affect tissues by nonthermal mechanisms. It has been proposed that these types of electromagnetic energy cause changes at the cellular level by altering cell membrane function and permeability and intracellular organelle function.6 Nonthermal electromagnetic agents may also promote binding of chemicals to the cell membrane to trigger complex sequences of cellular reactions. Because these agents are thought to promote the initial steps in cellular function, this mechanism of action could explain the wide variety of stimulatory cellular effects that have been observed in response to the application of nonthermal levels of electromagnetic energy. Electromagnetic energy may also affect tissues by causing proteins to undergo
conformational changes to promote active transport across cell membranes and to accelerate adenosine triphosphate (ATP) synthesis and use.7 Many researchers have invoked the Arndt-Schulz law to explain the effects of low, nonthermal levels of electromagnetic radiation. According to this law, a certain minimum stimulus is needed to initiate a biological process. In addition, although a slightly stronger stimulus may produce greater effects, beyond a certain level stronger stimuli will have a progressively less positive effect, and higher levels will become inhibitory. For example, a low level of mechanical stress during childhood promotes normal bone growth, whereas too little or too much stress can result in abnormal growth or fractures. Similarly, with some forms of electromagnetic radiation, such as diathermy or laser light, although too low a dose may not produce any effect, the optimal dose to achieve a desired physiological effect may be lower than that which produces heat. If excessive doses are used, they may cause tissue damage.

INTRODUCTION TO LASERS AND LIGHT

Light is electromagnetic energy in or close to the visible range of the electromagnetic spectrum. Most light is polychromatic, or made up of light of various wavelengths within a wide or narrow range. Laser (an acronym for light amplification by stimulated emission of radiation) light is also electromagnetic energy in or close to the visible range of the electromagnetic spectrum. Laser light differs from other forms of light in that it is monochromatic (made up of light that is only a single wavelength [Fig. 15-4]), coherent (i.e., in phase [Fig. 15-5]), and directional (Fig. 15-6).

PHYSICAL PROPERTIES OF LASERS AND LIGHT

Light is electromagnetic energy in or close to the visible range of the spectrum. Light from all sources except lasers comprises a range of wavelengths. Light that appears white is made up of a combination of light wave frequencies across the entire visible range of the spectrum. Sunlight includes visible light, as well as shorter wavelengths of light in the UV part of the spectrum and longer wavelengths of light in the IR part of the spectrum. Light that appears to the human eye to be one color but that is not from a laser includes light waves with a narrow range of wavelengths, with most of the light energy around a given wavelength. Lasers produce coherent light of a single wavelength only. Light sources used for therapy generally produce light in narrow ranges of the visible or near-visible part of the spectrum.

Light Sources

Light can be produced by emission from a gas-filled glass tube or a photodiode, with tubes being the older type of device. Spontaneously emitted mixed-wavelength light, such as light from a household light bulb, is generated by applying energy in the form of electricity to molecules of a contained gas. Electricity moves electrons in these molecules to a higher energy level, and as electrons spontaneously fall back down to their original level, they emit photons of light of various frequencies, depending on how far they fall (Fig. 15-7). The original clinical laser devices used vacuum tube technology similar to a tube fluorescent light bulb to produce monochromatic coherent laser light. With this type of laser, energy in the form of electricity is also applied to molecules of a contained gas. However, in this case, only certain gases can be used, and the gas is contained in a tube with mirrored ends. One end of the tube is fully mirrored, and the other end is semimirrored. Electricity applied to the gas causes electrons to jump up to a higher energy level. When these electrons fall, they produce photons that are reflected by the mirrored ends of the tube. As photons travel back and forth from one mirrored end of the tube to the other, each excited atom they encounter releases two identical photons. These two photons can then travel back and forth and encounter two more excited atoms, causing the release of a total of four identical photons. Eventually, many identical photons are traveling back and forth between the mirrored ends of the tube, stimulating the emission of yet more identical photons. When the number of identical photons is sufficient, this strong light, which is coherent and of a single frequency, escapes through the semimirrored end of the tube as monochromatic coherent directional laser light (Fig. 15-8). Today, therapeutic light sources generally use photodiodes instead of glass tubes (Fig. 15-9). Photodiodes are made up of two layers of semiconductor: one layer with P-type material, with more positive charges, and the other layer with N-type material, with more negative charges. When electrons fall from the N type to the P type, photons of various frequencies are emitted (Fig. 15-10). If the diode has mirrored ends, it can be engineered to produce monochromatic laser light. Photodiodes offer the advantage of being small, hardy, and relatively inexpensive. Photodiodes may be laser diodes, LEDs, or SLDs.
Laser diodes produce light that is monochromatic, coherent, and directional, providing high-intensity light in one area. LEDs produce low-intensity light that may appear to be one color but is not coherent or monochromatic. LED light is not directional and spreads widely.
LED therapeutic light applicators are generally arrays that include many (.30) LEDs, with each LED having low-output power. The low power of LEDs increases the application time required when they are used for treatment, but the large number of diodes and their divergence allow light energy to be delivered to a wide area. SLDs produce high-intensity, almost monochromatic light that is not coherent and that spreads a little, but less than the light produced by an LED (Fig. 15-11). Thus SLDs require shorter application times than LEDs and deliver energy to a wider area than do laser diodes. Many applicators include a few laser diodes, SLDs, and LEDs together in a cluster. Clusters usually consist of 10 to 20 diodes.

Wavelength

The wavelength of light most affects the depth to which the light penetrates and impacts the nature of the cellular effects of light.4 Light with wavelengths between 600 and 1300 nm, which is red or IR, has the optimal depth of penetration in human tissue and therefore is used most commonly for patient treatment.14,15 Light with a wavelength at the longer end and a frequency at the lower end of this range penetrates more deeply, whereas light with a shorter wavelength and a higher frequency penetrates less deeply.16,17
IR light penetrates 2 to 4 cm into soft tissue, whereas red light penetrates only a few millimeters, just through and below the skin. Light may also produce physiological effects beyond its depth of penetration because the energy may promote chemical reactions that mediate processes distant from the site of application.

Power and Power Density

Light intensity can be expressed in terms of power, measured in watts or milliwatts, or power density, measured in milliwatts per centimeter squared (mW/cm2). Power is the rate of energy flow, and power density is the amount of power per unit area. Laser and other light therapy applicators generally have a fixed power, although in some cases this can be reduced by pulsing the output. Evidence suggests that pulsed light may have effects that differ from those of continuous wave light, but further work is needed to define these effects for different disease conditions and pulse structures.18 Because high-intensity lasers have the potential to cause harm, lasers have been divided into four classes, according to their power ranges (Table 15-1). The power of most laser diodes used for therapy is between 5 and 500 mW; they are classified as class 3B.
When a laser or light therapy applicator includes a number of diodes, the power of the applicator is equal to the sum of the power of all its diodes, and the power density is equal to the total power divided by the total area. High-power density light applicators offer the advantage of taking less time to deliver a given amount of energy. It is not known whether the clinical effects are the same with longer applications of low-power light as with delivery of the same amount of energy in a shorter period of time using a high-power light source. More research has been done on the use of lower-power lasers rather than the newer higher-power lasers or SLDs, because they were available first. However, some studies have found that the effects of the laser are more pronounced with short-duration, high-power doses than with long-duration, low-power doses delivering the same total amount of energy.19

Energy and Energy Density

Energy is the power multiplied by the time of application and is measured in Joules: Energy (J) 5 Power (W) 3 Time (s) Energy density, also known as fluence, is the amount of power per unit area. Energy density is measured in Joules per centimeter squared (J/cm2). Energy density is the treatment dose measure preferred by most authors and researchers in this field. This measure takes into account the power, the treatment duration, and the area of application.
Most laser and light therapy devices allow for selection of energy or energy density. Energy (Joules) includes time (watts 3 seconds); therefore, the clinician, when using a laser light therapy device, generally does not need to select the treatment time (duration).

EFFECTS OF LASERS AND LIGHT

Low-intensity lasers and other forms of light have been studied and recommended for use in rehabilitation because evidence indicates that this form of electromagnetic energy may be biomodulating and may facilitate healing.20,21 The clinical effects of light are thought to be related to the direct effects of light energy—photons— on intracellular chromophores in many different types of cells.4,22,23 A chromophore is the light-absorbing part of a molecule that gives it color and that can be stimulated by light energy to undergo chemical reactions. To produce an effect, the photons of light must be absorbed by a target cell to promote a cascade of biochemical events that affect tissue function. Evidence suggests that light has a wide range of effects at cellular and subcellular levels, including stimulating ATP24 and RNA production, altering the synthesis of cytokines involved in inflammation, and initiating reactions at the cell membrane by affecting calcium channels25 and intercellular communication.26,27

PROMOTE ADENOSINE TRIPHOSPHATE PRODUCTION

The primary function of mitochondria, the power house of the cell, is to generate ATP, which then can be used as the energy source for all other cellular reactions. ATP generation is a multistep process that occurs on the inner mitochondrial membrane. Red laser (632.8 nm)28 and LED (670 nm)29 light have been shown to improve mitochondrial function and increase their production of ATP by up to 70%. It appears that light promotes this increase in ATP production by increasing cytochrome oxidase production and enhancing electron transfer by cytochromeC oxidase (Fig. 15-12).28,30-32 This effect may be partly mediated by cellular or mitochondrial calcium uptake.25,33 Increased ATP production promoted by laser and other forms of light is thought to be the primary contributor to many of the clinical benefits of laser and light therapy, particularly enhancement of tissue healing.24 In addition, increased ATP production may be why laser irradiation can reduce fatigue associated with electrically stimulated muscle contraction.34

PROMOTE COLLAGEN PRODUCTION

Laser and light therapy is also thought to enhance tissue healing by promoting collagen production, likely by stimulating production of mRNA that codes for procollagen. Red laser light has been shown to promote an increase in collagen synthesis34-37 and mRNA production,38 and to induce a more than threefold increase in procollagen production.37

MODULATE INFLAMMATION

Laser irradiation can modulate inflammation and is associated with increased levels of prostaglandin-F2a (PGF2a),39,40 interleukin-1a (IL-1a), and interleukin-8 (IL-8)41 and decreased levels of PGE2 38-40 and tumor necrosis factoralpha (TNF-a).42 The changes in prostaglandin balance likely result in increased blood flow. Stimulation of IL-1a and IL-8 release has been shown to induce keratinocyte migration and proliferation.41 Evidence also suggests that red (He-Ne) laser irradiation activates T and B lymphocytes,43 enhancing their ability to bind bacteria,44 and that laser light promotes degranulation of mast cells45,46 and synthesis and release of chemical mediators of fibroblast proliferation by macrophages.47,48 Laser and LED light in the red to IR wavelength range can also stimulate proliferation of various cells involved in tissue healing, including fibroblasts,49-51 keratinocytes,52 and endothelial cells.53

INHIBIT BACTERIAL GROWTH

Laser light can also inhibit bacterial growth. A study published in 1999 reported that red (632.8 or 670 nm) laser light had a dose-dependent bactericidal effect on photosensitized Staphylococcus aureus (S. aureus) and Pseudomonas aeruginosa (P. aeruginosa). 54 A more recent study examining the effects of different wavelengths of laser light on bacterial growth found that 630 nm laser irradiation at 1 to 20 J/cm2 was more effective than 660, 810, or 905 nm laser light in inhibiting the growth of P. aeruginosa, S. aureus, and Escherichia coli. 55 In addition, two more recent studies found that shorter-wavelength blue (405 nm or 405 nm combined with 470 nm) light had a dose-dependent bactericidal effect on S. aureus and P. aeruginosa when doses of 10 to 20 J/cm2 were used, reducing bacterial colonies by approximately 62% to 95%.56,57 However, one study found that certain doses and pulse frequencies of IR (810 nm) wavelength laser irradiation can enhance bacterial growth.58 Based on overall results of research on the effects of laser light on bacterial growth, it appears that light generally inhibits bacterial growth, and that wavelengths of 670 to 405 nm (visible red to blue) are most effective. It appears that only wavelengths that are longer but not shorter than this range have been studied for this effect.

PROMOTE VASODILATION

Some authors report that laser light can induce vasodilation, particularly of the microcirculation.21,59 This effect may be mediated by the release of preformed nitric oxide, which has been found to be enhanced by irradiation with red light.60 Such vasodilation could accelerate tissue healing by increasing the availability of oxygen and other nutrients, and by speeding the removal of waste products from the irradiated area.

ALTER NERVE CONDUCTION VELOCITY AND REGENERATION

Some studies have shown increased peripheral nerve conduction velocities, increased frequency of action potentials, decreased distal sensory latencies, accelerated nerve regeneration, and reduced nerve scarring in response to laser stimulation, all of which indicate increased activation of nervous tissue by laser light.38,61-68 This effect has appeared to be more pronounced with red laser light than with blue or IR.38 These positive effects occur in response to laser irradiation over the site of nerve compression and are enhanced by irradiation of corresponding spinal cord segments.69,70 In addition, laser irradiation has been found to induce axonal sprouting and outgrowth in cultured nerves71 and in in vitro brain cortex.72
As with other areas of laser and light research, conflicting findings are reported in the literature. Some studies have found that laser light irradiation results in decreased nerve conduction velocities and increased distal conduction latencies,73-75 indicating decreased activation of the nervous tissue; other studies report no change in nerve conduction in response to laser light irradiation.76-80 Given currently available data, further research is necessary to clarify the effects of lasers and light on nerve conduction, and to determine the specific parameters required to achieve these effects.

CLINICAL INDICATIONS FOR THE USE OF LASERS AND LIGHT

TISSUE HEALING: SOFT TISSUE AND BONE

A number of studies,9-12,25,81-94 review articles,95-98 and metaanalyses99-103 have been published concerning the use of low-level laser and light therapy to promote the healing of chronic and acute wounds in humans and animals. This area of research was based on Mester’s early findings that low-level laser irradiation appeared to accelerate wound healing.10 Although many studies supported the effectiveness of this intervention,9-12,25,82-89 a number of studies failed to show improved wound healing with laser light therapy.81,83,90-92 Therefore, various groups of authors have attempted to analyze the overall data through metaanalysis. Initial metaanalyses, published in 1999103 and 200099, of studies on the effects of low-level laser therapy (LLLT) on venous leg ulcer healing reported no evidence of any benefit associated with this specific application of laser therapy, although authors reported that one small study suggested that a combination of IR light and red He-Ne laser may have some benefit. Since that time, three additional metaanalyses—two published in 2004100,101 and another in 2009102—including between 23 and 34 studies have reported strong (Cohen’s d 5 11.81 to 12.22) positive effects of laser therapy on tissue repair. Laser therapy was associated with increased collagen synthesis, rate of wound healing and closure, tensile strength and tensile stress of healed tissue, and number of degranulated mast cells, as well as reduced wound healing times. Based on this extensive evidence, it appears that laser therapy can promote tissue repair. However, most published studies are of poor quality, lack adequate controls, and vary in or poorly report treatment parameters. The limited data available from clinical trials in humans continue to limit the strength with which laser and light therapy is recommended, and limit the development of clear guidelines for clinical application of lasers and light for the treatment of wounds in patients. Although most of the publications on tissue healing have focused on the effects of laser and light therapy on general soft tissue healing, as occurs with pressure ulcers or surgical incisions, some studies have examined the effects of laser or light therapy on the healing of specific types of tissue such as tendon,104-108 ligament,107 or bone.108-113 The few studies on tendon and ligament healing have consistently shown positive outcomes. However, studies on fracture healing have produced conflicting results; some have reported acceleration of fracture healing or physiological processes associated with fracture healing,108-110 whereas others have found no effect or even signs of delayed ossification after laser irradiation.111,112 A study that compared the effects of laser therapy with those of low-level ultrasound in promoting fracture healing found the two to be equally effective and the combination of both to be no more effective than either intervention alone.113 It is thought that low-level laser accelerates bone healing by increasing the rate of hematoma absorption, bone remodeling, blood vessel formation, and calcium deposition, and by stimulating macrophage, fibroblast, and chondrocyte activity90 and increasing osteoblast number, osteoid volume,113 and the amount of intracellular calcium in osteoblastic cells.114 Although the ideal treatment parameters for promoting tissue healing are uncertain, evidence at this time indicates that red or IR light with an energy density between 5 and 24 J/cm2 is most effective.101,115 Evidence suggests that a dose too high or too low may be ineffective, and a dose above 16 to 20 J/cm2 may even inhibit wound healing.116-118 Therefore, current recommendations are to use 4 to 16 J/cm2 for most wound healing applications, starting at the lower end of this range and progressing upward as tolerated. The addition of shorterwavelength light, in the blue to red range, may provide additional benefit in open areas infected or colonized by aerobic bacteria.

ARTHRITIS

A number of studies investigating the application of laser and light therapy for the management of pain and dysfunction associated with arthritis have been published. Some of these studies have found that laser therapy can benefit patients with arthritis, resulting in increased hand grip strength and flexibility and decreased pain and swelling in patients with rheumatoid arthritis (RA), decreased pain and increased grip strength in patients with osteoarthritis (OA) affecting the hands, and decreased pain and improved function in patients with cervical OA.95,119-123 However, some blinded, controlled studies using lasers for the treatment of RA124 and OA125,126 have reported that this intervention did not relieve pain nor did it improve function in the subjects studied. Metaanalyses and reviews of studies exploring the effects of laser therapy on pain, strength, stiffness, and function in patients with RA and OA have concluded that evidence is sufficient to recommend consideration of LLLT for short-term (up to 4 weeks) relief of pain and morning stiffness in RA, but that for OA, the results are conflicting, with only 5 out of 8 included studies reporting benefit.127-130 Different outcomes may result from different laser doses, different methods of application, or differences in the pathology of RA and OA. Improvements in arthritic conditions may be the result of reduced inflammation caused by changes in the activity of inflammatory
mediators,42,131 or reduced pain caused by changes in nerve conduction or activation. Given the variability of treatment parameters used in different studies, ideal treatment parameters are not clear. In general, shorter wavelengths, application to the nerve as well as to the joint, and longer durations of application may be more effective.

LYMPHEDEMA

A number of studies have examined the effects of LLLT on postmastectomy lymphedema.132-135 Based on findings of the first of these studies,132 the FDA authorized the use of one laser device (LTU-904, RianCorp, Richmond, South Australia) as part of a therapy regimen to treat postmastectomy lymphedema. This device has a 904 nm wavelength (i.e., in the IR range), a peak pulse power of 5 W, and a fixed average power of 5mW. In this study, laser treatment was applied at 1.5 J/cm2 (300 mJ/0.2㎠ spot to 17 spots, for a total of 5.1 J) to the area of the axilla 3 times per week for one or two cycles of 3 weeks each. Although no significant improvement was noted immediately after any of these treatments was provided, mean affected limb volume was significantly reduced 1 and 3 months after completion of two (although not one) treatment cycles. Approximately one-third of 37 actively treated subjects had a clinically significant (.200 mL) reduction in limb volume 2 to 3 months after receiving treatment with the laser. A second, smaller study,133 which included 8 subjects, found that those who completed 22 weeks of treatment with 890 nm IR laser at 1.5 J/cm2 to the arm and axilla had a greater reduction in limb circumference and generally less pain than placebo-treated patients. Another study found that laser therapy was associated with greater and longer-lasting reduction in limb volume, although similar pain, when compared with treatment with pneumatic compression.134 A 2011 study involving 17 subjects with postmastectomy lymphedema found that adding two treatment cycles of laser therapy produced significant additional benefits to conventional therapy, including reduced limb volume, reduced pain, and increased range of motion.135 A 2007 systematic review of common therapies for lymphedema concluded that, in general, more intensive, health professional–based therapies such as laser therapy, complex physical therapy, manual lymphatic drainage, and pneumatic compression are more effective than self-instigated approaches such as exercise, limb elevation, and compression garments.136 Based on these studies, it is suggested that laser treatment for lymphedema be provided at an energy density of around 1.5 J/cm2 to a total area of 3 cm2 3 times per week for a total of 3 weeks for 1 to 2 cycles.

NEUROLOGICAL CONDITIONS

Several studies have attempted to determine the impact of laser light irradiation on nerve conduction, regeneration, and function. The first FDA clearance for laser therapy was based on a 1995 study of IR laser (830 nm) therapy for approximately 100 General Motors employees with carpal tunnel syndrome.66 This randomized double-blind controlled study compared the effect of physical therapy combined with laser versus physical therapy alone for the treatment of carpal tunnel syndrome. Grip and pinch strength, radial deviation range of motion (ROM), median nerve motor conduction velocity across the wrist, and incidence of return to work were all significantly higher in the laser-treated group than in the control group. The treatment protocol was to apply 3 J (90mW for 33 seconds) during therapy for 5 weeks. A recent review of seven studies of laser or light therapy for the treatment of carpal tunnel syndrome found that two controlled studies and three openprotocol studies reported laser to be more effective than placebo, whereas two studies did not find such a benefit. The studies finding benefit applied higher-dose laser (>9 J or 32 J/cm2) than those not finding benefit (1.8 J or 6 J/cm2). Laser light treatment was applied to the area of the carpal tunnel or proximally up to the area of the nerve cell body at the neck. Laser therapy has also been investigated for the treatment of a number of other neurological conditions. Several studies have investigated the effects of laser and light therapy on diabetic peripheral neuropathy, and these trials are ongoing.137,138 Overall, researchers have found that IR light may help reduce the pain associated with this condition. IR139 and red140 laser irradiation has been found to be more effective than placebo in reducing the pain associated with postherpetic neuralgia, and preliminary studies have found improved functional outcome after stroke with application of IR laser therapy to the head within 24 hours of stroke onset.141 Studies in all of these areas are ongoing.

PAIN MANAGEMENT

Many studies have found that laser and light therapy may reduce the pain and disability associated with a wide variety of neuromusculoskeletal conditions other than arthritis and neuropathy,142 including lateral epicondylitis,143-145 chronic low back and neck pain,146-148 trigger points,149,150 and delayed-onset muscle soreness.151 The effects of laser light on pain may be mediated by its effects on inflammation,131 tissue healing, nerve conduction, or endorphin release or metabolism.152 Analgesic effects generally are most pronounced when laser or light is applied to the skin overlying the involved nerves or nerves innervating the area of the involved dermatome.144 Although some studies have not found a significant difference in subjective or objective treatment outcomes when comparing treatment with low-level laser with alternative sham treatments,153-155 two metaanalyses published in 2004 and 2010 on the effects of laser therapy on pain described an overall positive treatment effect (Cohen’s d 5 11.11 and 10.84, respectively) of laser light therapy on pain in humans.100,156

CONTRAINDICATIONS AND PRECAUTIONS FOR THE USE OF LASERS AND LIGHT

Various authors and manufacturers list different contraindications and precautions for the application of laser and light therapy. The following general recommendations represent a summary. However, the clinician should adhere to the recommendations provided with the specific unit(s) being used.

CONTRAINDICATIONS FOR THE USE OF LASERS AND LIGHT

CONTRAINDICATIONS for the Use of Lasers and Light

  • Direct irradiation of the eyes
  • Malignancy
  • Within 4 to 6 months after radiotherapy
  • Over hemorrhaging regions
  • Over the thyroid or other endocrine glands

Direct Irradiation of the Eyes

Because lasers can damage the eyes, all patients treated with lasers should wear goggles opaque to the wavelength of the light emitted from the laser being used throughout treatment.16 The clinician applying the laser should wear goggles that reduce the intensity of light from the wavelength produced by the specific device to a nonhazardous level. Goggles should be marked with the wavelength range they attenuate and their optical density within that band.
Clinicians should remember that the higher the optical density, the greater the attenuation of the light. Also, safety goggles suitable for one wavelength should not be assumed to be safe at any other wavelength. Particular care should be taken with IR lasers because the radiation they produce is not visible, but it can easily damage the retina. The laser beam should never be directed at the eyes, and one should never look directly along the axis of the laser light beam. This contraindication does not apply to nonlaser light sources, including SLDs and LEDs. Lasers can damage the eye, particularly the retina, because the light is directional and thus is very concentrated in one area. In contrast, other light sources are divergent and thus diffuse the light energy, so that concentrated light energy does not reach the eye.

Malignancy

Laser and light therapy has been shown to have a range of physiological and cellular effects, including increasing blood flow and cellular energy production. These effects may increase the growth rate or rate of metastasis of malignant tissue. Because a patient may not know that he or she has cancer or may be uncomfortable discussing this diagnosis directly, the therapist should first check the chart for a diagnosis of cancer.
Laser or light therapy should not be applied in the area of a known or possible malignancy.

Within 4 to 6 Months After Radiotherapy

It is recommended that lasers and light not be applied to areas that have recently been exposed to radiotherapy because radiotherapy increases tissue susceptibility to malignancy and burns.
recently had radiation therapy applied to an area, laser or light therapy should not be applied in that area.

Over Hemorrhaging Regions

Laser and light therapy is contraindicated in hemorrhaging regions because this intervention may cause vasodilation and thus may increase bleeding.

Over the Thyroid or Other Endocrine Glands

Studies have found that the application of LLLT to the area of the thyroid gland can alter thyroid hormone levels in animals.157 Therefore, irradiation of the area near the thyroid gland (the mid-anterior neck) should be avoided. LLLT may also result in changes in serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH),
adrenocorticotropic hormone (ACTH), prolactin, testosterone, cortisol, and aldosterone.

Low Back or Abdomen During Pregnancy

Because the effects of LLLT on fetal development and fertility are not known, it is recommended that this type of treatment not be applied to the abdomen or low back during pregnancy.
If the patient is or may be pregnant, laser light therapy should not be applied to the abdomen or low back.

Epiphyseal Plates in Children

The effect of laser light therapy on epiphyseal plate growth or closure is not known. However, because laser light therapy can affect cell growth, application over the epiphyseal plates before their closure is not recommended.

Impaired Sensation or Mentation

Caution is recommended when treating patients with impaired sensation or mentation because these patients may not be able to report discomfort during treatment. Although discomfort is rare during application of laser light therapy, the area of the applicator in contact with the patient’s skin can become warm and may burn the skin if applied for prolonged periods, or if malfunctioning.
Laser light therapy should not be applied to any area where thermal sensation is impaired. Laser light therapy should not be applied if the patient is unresponsive or confused.

Photophobia or Pretreatment With Photosensitizers

ertain authors recommend that laser and light therapy should not be applied to any patient who has abnormally high sensitivity to light, either intrinsically or as the result because increased skin sensitivity to light is generally limited to the UV range of the electromagnetic spectrum, only UV irradiation must be avoided in such patients. When wavelengths of light outside the UV range are being used in patients with photosensitivity, the clinician should check closely for any adverse effects and should stop treatment if they occur.
Treatment with laser or light therapy should be stopped if the patient shows any signs of burning.

ADVERSE EFFECTS OF LASERS AND LIGHT

Although most reports concerning the use of low-level laser or other light devices note no adverse effects in the treatment area from application of this physical agent,128,138 authors have described transient tingling, mild erythema, skin rash, or a burning sensation, as well as increased pain or numbness, in response to the application of low-level laser and light therapy.109,122,160-164 The primary hazards of laser irradiation are the adverse effects that can occur with irradiation of the eyes. Laser devices are classified on a scale from 1 to 4 according to their power and associated risk of adverse effects on unprotected skin and eyes (see Table 15-1). The low-level lasers used in clinical applications are generally class 3B, which means that although they are harmless to unprotected skin, they do pose a potential hazard to the eyes if viewed along the beam. Exposure of the eyes to laser light of this class can cause retinal damage as a result of the concentrated intensity of the light and the limited attenuation of the beam intensity by the outer structures of the eye. As noted previously, this hazard does not apply to nonlaser light sources (LED and SLD) where the light is divergent and therefore is not concentrated in one particular area.
The other potential hazard of laser or light therapy is burns. Although the mechanism of therapeutic action of laser and light therapy is not thermal, the diodes used to apply laser or other light therapy will get warm if they are on for a prolonged period. This is more likely to occur with lower-power LEDs that take a long time to deliver a therapeutic dose of energy, and where many diodes may be used together in an array (Fig. 15-13). For this reason, particular caution should be taken when applying laser or any other form of light therapy to patients with impaired sensation or mentation and to areas of fragile tissue such as open wounds.

PARAMETERS FOR THE USE OF LASERS AND LIGHT

Note that because laser and light therapy is an active area of research in which new information about the effects of different treatment parameters becomes available almost every day, recommendations for ideal parameters are evolving and change over time. The recommendations given here are based on this author’s interpretation of the current literature, which is likely to change as new discoveries are made about the effects of specific parameters of laser and light therapy.

Type of Diode

Much controversy in the literature and among experts surrounds the importance of selecting a specific type of diode for clinical application. Although it is clear that different diodes produce light of different degrees of wavelength range, coherence, and collimation, it is not clear whether these differences have a clinical impact, and very few studies have directly compared the effects of coherent (laser) with those of noncoherent (LED and SLD) light.162,163 A greater number of studies have explored the effects of laser light than have investigated the effects of light emitted by LEDs and SLDs, largely because laser applicators were available many years earlier, but studies have shown the beneficial effects of all three. What remains uncertain and controversial is whether the effects of coherent laser light can be assumed to also occur in response to noncoherent LED and SLD light, and whether one type of light is superior to another.49,166-168 LEDs provide the most diffuse light with the widest frequency range and are of low power individually. Because they output diffuse light, LEDs are most suitable for treating larger, more superficial areas. Applicators that use LEDs as the treatment light source generally contain many LEDs in an array (see Fig. 15-3) or cluster to provide more power for the entire applicator and to treat a larger area. The power of the applicator equals the sum of the power of each of its diodes. Some cluster applicators may include a small number of low-power LEDs in the visible wavelength range to serve as indicators of when the device is emitting, particularly when other higher-power SLDs or laser diodes emit only in the invisible IR range (Fig. 15-16). SLDs provide light that is less diffuse and of a narrower wavelength range than that provided by LEDs, and they emit higher power than LEDs (see Fig. 15-16). SLDs are suitable for treating superficial or moderately deep areas, depending on their wavelength. Laser diodes provide light of a single wavelength that is very concentrated (Fig. 15-17). Laser diodes are suitable for treating small areas and, for the same wavelength and power, will deliver the most light deepest to a focused area of tissue. Protective goggles should be worn by both the patient and the clinician when using any applicator that includes one or more laser diodes because this concentrated light can damage the eyes.

Wavelength

Laser light applicators output light in the visible or nearvisible wavelength range of the electromagnetic spectrum, that is, between 500 and 1100 nm. Most applicators include near-IR (<700 to 1100 nm) or red (<600 to 700 nm) light. IR, with its longer wavelength, penetrates more deeply than red light (Fig. 15-18) and therefore is most suitable for treating deeper tissues up to 30 to 40 mm deep. Red light is most suitable for treating more superficial tissues, at a depth of 5 to 10 mm, such as the skin and subcutaneous tissue. Applicators that output blue light have recently become available. They are most suitable for treating surface tissue such as skin or exposed soft tissue.

Power

Laser light applicator power is measured in milliwatts (1mW 5 1/1000th of a watt). Lasers are classified by international agreement as class 1 to class 4, according to their power and resulting effects (see Table 15-1). All lasers carry a label denoting their class (Fig. 15-19). Lasers used for therapy are generally power class 3B, with the power of any individual diode being more than 5mW and less than 500mW. A number of laser diodes may be combined in a single applicator to provide a total power greater than 500mW.

The laser classification system does not apply to LEDs and SLDs because these diodes do not produce light that is concentrated in a small area and that therefore can be damaging to the eye. The power of a single LED is generally in the range of 1 to 5mW but can be as high as 30 to 40mW. Numerous LEDs, often around 20 to 60, but up to 200 or more, are generally placed in a pad or array applicator to provide an applicator with increased total power. The power of each individual SLD is generally in the range of 5 to 35mW but may be as high as 90 mW or more. Several SLDs—generally about 3 to 10—are usually placed together in a cluster applicator to provide more total power. As discussed earlier in this chapter, lower-power light applicators require longer application times to deliver the same amount of energy as higher-power light applicators. Thus the applicator power should be selected to optimize the practicality of the treatment time.

Energy Density

In general, low-energy densities are thought to be stimulatory, whereas too high an energy density can be suppressive or damaging. Most recommend using lower doses for acute and superficial conditions and higher doses for chronic and deeper conditions, and that treatment be initiated at the lower end of the recommended range and increased in subsequent treatments if the prior treatment was well tolerated (see Table 15-2).

CHAPTER REVIEW

  1. Electromagnetic radiation is composed of electrical and magnetic fields that vary over time and are oriented perpendicular to each other.
  2. Different frequencies of electromagnetic radiation have different names, different properties, and different applications. Shortwave, microwave, infrared, visible light, and UV radiation all have clinical therapeutic applications.
  3. Laser light has the unique features of being monochromatic (one frequency), coherent, and directional; light produced by LEDs and SLDs has a range of frequencies, is noncoherent, and spreads. Low-intensity laser or noncoherent light may be used as physical agents in rehabilitation.
  4. Lasers and light affect cells via their interaction with intracellular chromophores. This interaction leads to a range of cellular effects, including increased ATP and RNA synthesis. These effects can promote tissue healing, reduce pain, and improve function in patients with a range of conditions, including arthritis, neuropathy, and lymphedema.
  5. Contraindications to the use of lasers include direct irradiation of the eyes, malignancy, within 4 to 6 months after radiotherapy, hemorrhaging regions, and application to the endocrine glands. Precautions include application to the low back or abdomen during pregnancy, epiphyseal plates in children, impaired sensation and mentation, photophobia or abnormally high sensitivity to light, and pretreatment with one or more photosensitizers. Clinicians should always read and follow the contraindications and precautions listed for a particular unit.
  6. When selecting a device, the clinician should first consider whether light therapy will be effective for the patient’s condition. After deciding on the type of diode (laser, LED, or SLD), the clinician should set the appropriate parameters, including wavelength, power, and energy density.

GLOSSARY

  • Band (frequency band) : A range within the electromagnetic spectrum defined by wavelength (e.g., the band for UVA radiation is 320 to 400 nm).
  • Chromophores : Light-absorbing parts of a molecule that give it color.
  • Cluster probe : Light therapy applicator with multiple diodes that may consist of any combination of laser diodes, LEDs, or SLDs. Use of multiple diodes allows coverage of a larger treatment area, takes advantage of the properties of different types of diodes, and may reduce treatment time.
  • Coherent : Light in which all waves are in phase with each other; lasers produce coherent light.
  • Diathermy : The application of shortwave or microwave electromagnetic energy to produce heat within tissues, particularly deep tissues.
  • Directional (collimated) : Light with parallel waves.
  • Divergent : Light that spreads; the opposite of collimated.
  • Electromagnetic radiation : Radiation composed of electrical and magnetic fields that vary over time and are oriented perpendicular to each other. This type of radiation does not need a medium to propagate.
  • Energy : The total amount of electromagnetic energy delivered over the entire treatment time. Energy is usually measured in Joules (J). Energy is equal to power multiplied by time. 1 J 5 1 W 3 1 sec Energy density: The total amount of electromagnetic energy delivered per unit area over the entire treatment time. Energy density is generally measured in Joules per centimeter squared (J/cm2). Most authors agree that this should be the standard dosage measure for laser light therapy.
  • Frequency : Number of waves per unit time, generally measured in hertz (Hz), which indicates waves per second.
  • Hot laser : Heats and destroys tissue directly in beam and is used for surgery. Also called high-intensity laser.
  • Ionizing radiation : Electromagnetic radiation that can penetrate cells and displace electrons from atoms or molecules to create ions. Ionizing radiation includes x-rays and gamma rays. Ionizing radiation can damage the internal structures of living cells.
  • Laser : Acronym for light amplification by stimulated emission of radiation. Laser light has the unique properties of being monochromatic, coherent, and directional.
  • Laser diode : Light source that uses semiconductor diode technology and optics to produce laser light.
  • Light-emitting diode (LED) : Semiconductor diode light source that produces relatively low-power light in a range of frequencies. LED light may appear to be one color (e.g., red) but will always have a range of wavelengths and will not be coherent or directional.
  • Low-level laser therapy (LLLT) : Application of laser light for therapeutic purposes. LLLT is also known as cold laser, low-intensity, low-power, or soft laser. LLLT generally uses laser light diodes that have less than 500mW power per diode. LLLT cluster probes may contain a number of diodes with a total combined power above 500mW.
  • Maser : Acronym for microwave amplification by stimulated emission of radiation.
  • Monochromatic : Light of single frequency, wavelength, and color. Laser light is monochromatic. Other light sources produce light with a range of wavelengths.
  • Photobiomodulation : Stimulatory or inhibitory effects on the body caused by light phototherapy; the therapeutic use of light.
  • Power : Rate of energy production, generally measured in milliwatts (mW) for laser light.
  • Power density (irradiance): The concentration of power per unit area, measured in watts per centimeter squared (W/cm2).
  • Speckling : Variability of light intensity that occurs when a coherent light illuminates a rough object.
  • Stimulated emission : Occurs when a photon hits an atom that is already excited (i.e., electrons are at a higher energy level than usual). The atom being hit releases a new photon that is identical to the incoming photon—the same color, going in the same direction.
  • Supraluminous diode (SLD) : Light source that uses semiconductor diode technology to produce high-power light in a narrow frequency range.
  • Ultraviolet (UV) radiation : Electromagnetic radiation with wavelength from ,290 nm to 400 nm, which lies between x-ray and visible light.
  • Wavelength : The length of a wave of light from peak to peak determines frequency and color. Longer wavelengths are associated with deeper penetration.

References

  1. Sears FW, Zemansky MW, Young HD: College physics, Reading, MA,1987, Addison-Wesley.
  2. Hitchcock RT, Patterson RM: Radio-frequency and ELF electromagnetic energies: a handbook for health professionals, New York, 1995,Van Nostrand Reinhold.
  3. Thomas CL: Taber’s cyclopedic medical dictionary, Philadelphia,1993, FA Davis.
  4. Hawkins D, Houreld N, Abrahamse H: Low level laser therapy(LLLT) as an effective therapeutic modality for delayed woundhealing, Ann NY Acad Sci 1056:486-493, 2005.
  5. Holick MF: The cutaneous photosynthesis of previtamin D: a unique photoendocrine system, Invest Dermatol 76:51-58, 1981.
  6. Adley WR: Physiological signalling across cell membranes and cooperative influences of extremely low frequency electromagnetic fields. In Frohlich H, ed: Biological coherence and response to external stimuli, Heidelberg, 1988, Springer-Verlag.
  7. Tsong TY: Deciphering the language of cells, TIBS 14:89-92,1989.
  8. Alster TS, Kauvar AN, Geronemus RG: Histology of high-energy pulsed CO2 laser resurfacing, Semin Cutan Med Surg 15:189-193,1996.
  9. Mester E, Spiry T. Szende B, et al: Effects of laser rays on wound healing, Am J Surg 122:532-535, 1971.
  10. Mester E, Ludany G, Sellyei M, et al: The stimulating effects of low power laser rays on biological systems, Laser Rev 1:3, 1968.
  11. Mester AF, Mester A: Wound healing, Laser Ther 1:7-15, 1989.
  12. Mester AF, Mester A: Clinical data of laser biostimulation in wound healing, Lasers Surg Med 7:78, 1987.
  13. Beckerman H, de Bie RA, Bouter LM, et al: The efficacy of laser therapy for musculoskeletal and skin disorders: a criteria-based meta-analysis of randomized clinical trials, Phys Ther 72:483-491,1992.
  14. Kolari PJ: Penetration of unfocused laser light into the skin, Arch Dermatol Res 277:342-344, 1985.
  15. King PR: Low level laser therapy—a review, Lasers Med Sci 4:141-150,1989.
  16. Goldman L, Michaelson SM, Rockwell RJ, et al: Optical radiation with particular reference to lasers. In Suess M, Benwell-Morrison D, ed: Nonionizing radiation protection, ed 2, European Series No. 25,Geneva, 1989, World Health Organization.
  17. Goldman L, Rockwell JR: Lasers in medicine, New York, 1971,Gordon & Breach.
  18. Hashmi JT, Huang YY, Sharma SK, et al: Effect of pulsing in low-level light therapy, Lasers Surg Med 42:450-466, 2010
  19. Trelles MA, Mayayo E, Miro L: The action of low reactive laser therapy on mast cells, Laser Ther 1:27-30, 1989.
  20. Oshiro T, Calderhead RG: Low level laser therapy: a practical introduction, Chichester, UK, 1988, Wiley.
  21. Basford JR: Low energy laser therapy: controversies and new research findings, Lasers Surg Med 9:1-5, 1989.
  22. Belkin M, Schwartz M: New biological phenomena associated with laser radiation, Health Phys 56:687-690, 1989.
  23. Karu T: Photobiology of low-power laser effects, Health Phys 56:691-704, 1989.
  24. Karu TI: Molecular mechanisms of the therapeutic effects of low intensity laser radiation, Lasers Life Sci 2:53-74, 1988.
  25. Smith KC: The photobiological basis of low level laser radiation therapy, Laser Ther 3:19-24, 1991.
  26. Baxter D: Low intensity laser therapy. In Kitchen S, Bazin S, eds:Clayton’s electrotherapy, ed 10, London, 1996, WB Saunders.
  27. Kitchen SS, Partridge CJ: A review of low level laser therapy,Physiotherapy 77:161-168, 1991.
  28. Passarella S, Casamassima E, Molinari S, et al: Increase of proton electrochemical potential and ATP synthesis in rat liver mitochondria irradiated in vitro by Helium-Neon laser, FEBS Lett 175:95-99, 1984.
  29. Eells JT, Henry MM, Summerfelt MTT, et al: Therapeutic photo biomodulation for methanol-induced retinal toxicity, PNAS 100:3439-3444, 2003.
  30. Eells JT, Wong-Riley MT, VerHoeve J, et al: Mitochondrial signal transduction in accelerated wound and retinal healing by near infrared light therapy, Mitochondrion 4:559-567, 2004.
  31. Winterle JS, Einarsdottir O: Photoreactions of cytochrome Coxidase,Photochem Photobiol 82:711-719, 2006.
  32. Silveira PC, Streck EL, Pinho RA: Evaluation of mitochondrial respiratory chain activity in wound healing by low-level laser therapy, Photochem Photobiol 86:279-282, 2006.
  33. Greco M, Vacca R, Moro L, et al: Helium-neon laser irradiation of hepatocytes can trigger increase of the mitochondrial membrane potential and can stimulate c-fos expression in a Ca(2+)-dependent manner, Lasers Surg Med 29:433-441, 2001.
  34. Lopes-Martins RA, Marcos RL, Leonardo PS, et al: Effect of low level laser (Ga-Al-As 655 nm) on skeletal muscle fatigue induced by electrical stimulation in rats, J Appl Physiol 101:283-288,2006.
  35. Carney SA, Lawrence JC, Ricketts CR: The effect of light from a ruby laser on the metabolism of skin tissue culture, Biochem Biophys Acta 148:525-530, 1967.
  36. Abergel RP, Meeker CA, Lam TS, et al: Control of connective tissue metabolism by lasers: recent developments and future prospects, J Am Acad Dermatol 11:1142-1150, 1984.
  37. Lam TS, Abergel RP, Castel JC, et al: Laser stimulation of collagen synthesis in human skin fibroblast cultures, Laser Life Sci 1:61-77,1986.
  38. Anders JJ, Geuna S, Rochkind S: Phototherapy promotes regeneration and functional recovery of injured peripheral nerve, Neurol Res 26:234-240, 2004.
  39. Mester E, Mester AF, Mester A: The biomedical effects of laser application, Lasers Surg Med 5:31-39, 1985.
  40. Bjordal JM, Lopes-Martins RA, Iversen VV: A randomised, placebo controlled trial of low level laser therapy for activated Achilles tendinitis with microdialysis measurement of peritendinous prostaglandin E2 concentrations, Br Sports Med 40:76-80; discussion 76-80, 2006.
  41. Yu HS, Chang KL, Yu CL, et al: Low-energy helium-neon laser irradiation stimulates interleukin-1 alpha and interleukin-8release from cultured human keratinocytes, Invest Dermatol 107:593-596, 1996.
  42. Aimbire F, Albertini R, Pacheco MT, et al: Low-level laser therapy induces dose-dependent reduction of TNFalpha levels in acute inflammation, Photomed Laser Surg 24:33-37, 2006.
  43. Kupin IV, Bykov VS, Ivanov AV, et al: Potentiating effects of laser radiation on some immunologic traits, Neoplasma 29:403-406,1982.
  44. Passarella S, Casamassima E, Quagliariello E, et al: Quantitative analysis of lymphocyte-Salmonella interaction and the effects of lymphocyte irradiation by He-Ne laser, Biochem Biophys Res Commun
    130:546-552, 1985.
  45. El Sayed SO, Dyson M: Effect of laser pulse repetition rate and pulse duration on mast cell number and degranulation, Lasers Surg Med 19:433-437, 1996.
  46. El Sayed SO, Dyson M: Comparison of the effect of multiwavelength light produced by a cluster of semiconductor diodes and of each individual diode on mast cell number and degranulation in intact and injured skin, Lasers Surg Med 10:559-568, 1990.
  47. Young S, Bolton P, Dyson M, et al: Macrophage responsiveness to light therapy, Lasers Surg Med 9:497-505, 1989.
  48. Rajaratnam S, Bolton P, Dyson M: Macrophage responsiveness to laser therapy with varying pulsing frequencies, Laser Ther 6: 107-111, 1994.
  49. Vinck EM, Cagnie BJ, Cornelissen MJ, et al: Increased fibroblast proliferation induced by light emitting diode and low power laser irradiation, Laser Med Sci 18:95-99, 2003.
  50. Pereira AN, Eduardo Cde P, Matson E, et al: Effect of low-power laser irradiation on cell growth and procollagen synthesis of cultured fibroblasts, Lasers Surg Med 31:263-267, 2002.
  51. Webb C, Dyson M, Lewis WHP: Stimulatory effect of 660 nm low level laser energy on hypertrophic scar-derived fibroblasts: possible mechanisms for increase in cell counts, Lasers Surg Med 22:294-301, 1998.
  52. Grossman N, Schneid N, Reuveni H, et al: 780 nm low power diode laser irradiation stimulates proliferation of keratinocyte cultures: involvement of reactive oxygen species, Lasers Surg Med 29:105-106, 2001.
  53. Schindl A, Merwald H, Schindl L, et al: Direct stimulatory effect of low-intensity 670 nm laser irradiation on human endothelial cell proliferation, Br J Dermatol 148:334-336, 2003.
  54. de Simone NA, Christiansen C, Dore D: Bactericidal effect of 0.95mW helium-neon and 5-mW indium-gallium-aluminum-phosphate laser irradiation at exposure times of 30, 60 and 120 seconds on photosensitized Staphylococcus aureus and Pseudomonas aeruginosa in vitro, Phys Ther 79:839-846, 1999.
  55. Nussbaum EL, Lilge L, Mazzuli T: Effects of 630-, 660., 810- and 905-nm laser irradiation delivering radiant exposure of 1-50 J/cm2 on three species of bacteria in vitro, J Clin Laser Med Surg 20:325-333, 2002.
  56. Guffey SJ, Wilborn J: Effect of combined 405-nm and 880-nm light on Staphylococcus aureus and Pseudomonas aeruginosa in vitro,Photomed Laser Surg 24:680-683, 2006.
  57. Guffey JS, Wilborn J: In vitro bactericidal effects of 405 nm and 470 nm blue light, Photomed Laser Surg 24:684-688, 2006.
  58. Nussbaum EL, Lilge L, Mazzulli T: Effects of 810 nm laser irradiation on in vitro growth of bacteria: comparison of continuous wave and frequency modulated light, Lasers Surg Med 31:343-351, 2002.
  59. Schindl A, Heinze G, Schindl M, et al: Systemic effects of low intensity laser irradiation on skin microcirculation in patients with diabetic microangiopathy, Microvasc Res 64:240-246, 2002.
  60. Lingard A, Hulten LM, Svensson L. et al: Irradiation at 634 nm releases nitric oxide from human monocytes, Laser Med Sci 22:30-36, 2007.
  61. Nissan M, Rochkind S, Razon N, et al: Ne-He laser irradiation delivered transcutaneously: its effects on the sciatic nerve of the rat, Lasers Surg Med 6:435-438, 1986,
  62. Schwartz M, Doron A, Erlich M, et al: Effects of low energy He-Ne laser irradiation on posttraumatic degeneration of adult rabbit optic nerve, Lasers Surg Med 7:51-55, 1987.
  63. Rochkind S, Nissan M, Lubar R, et al: The in-vivo nerve response to direct low energy laser irradiation, Acta Neurochir 94:74-77, 1988.
  64. Walker JB, Akhanjee LK: Laser induced somatosensory evoke potentials: evidence of photosensitivity in peripheral nerves,Res 344:281-285, 1985.
  65. Hamilton GF, Robinson TK, Ray RH: The effects of helium-neon laser upon regeneration of the crushed peroneal nerve, / Orthop Sports Phys Ther 15:209-214, 1992.
  66. Anderson TE, Good WT, Kerr HH, et al: Low level laser therapy in the treatment of carpal tunnel syndrome [Unpublished data), 1995, Microlight Corporation. www.laserhealthproducts.com/gmstudy.pdf.
    Accessed June 13, 2012
  67. Naeser MA: Photobiomodulation of pain in carpal tunnel syndrome: review of seven laser therapy studies, Photomed Laser Surg 24:101-110, 2006.
  68. Rochkind S, Nissan M, Barr-Nea L, et al: Response of peripheral nerve to He-Ne laser: experimental studies, Lasers Surg Med 7:441-443, 1987.
  69. Shamir MH, Rochkind S, Sandbank), et al: Double-blind randomized study evaluating regeneration of the rat transected sciatic nerve after suturing and postoperative low-power laser treatment,
    Reconstr Microsurg 17:133-137, 2001.
  70. Rochkind S, Nissan M, Alon M, et al: Effects of laser irradiation on the spinal cord for the regeneration of crushed peripheral nerve in rats, Lasers Surg Med 28:216-219, 2001.
  71. Wollman Y, Rochkind S, Simantov R: Low power laser irradiation enhances migration and neurite sprouting of cultured rat embryonal brain cells, Neurol Res 18:467-470, 1996.
  72. Wollman Y, Rochkind S: In vitro cellular processes sprouting in cortex microexplants of adult rat brains induced by low power laser irradiation, Neuro! Res 20:470-472, 1998.
  73. Snyder-Mackler L, Cork C: Effect of helium neon laser irradiation on peripheral sensory nerve latency, Phys Ther 68:223-225, 1988.
  74. Baxter D, Bell AJ, Allen JM, et al: Laser mediated increase in median nerve conduction velocities, Ir Med Sci 160:145-146, 1991.
  75. Vinck E, Coorevits P, Cagnie B, et al: Evidence of changes in sural nerve conduction mediated by light emitting diode irradiation,Lasers Med Sci 20:35-40, 2005.
  76. Basford JR, Daube JR, Hallman HO, et al: Does low intensity helium neon laser irradiation alter sensory nerve action potentials or distal latencies? Lasers Surg Med 10:35-39, 1990.
  77. Lundeberg T, Haker E, Thomas M: Effects of laser versus placebo in tennis elbow, Scand J Rehabil Med 19:135-138, 1987.
  78. Wu WH, Ponnudurai R, Katz J, et al: Failure to confirm report of light-evoked response of peripheral nerve to low power helium neon laser light stimulus, Brain Res 401:407-408, 1987.
  79. Jarvis D, Maclver MB, Tanelian DL: Electrophysiologic recording and thermodynamic modeling demonstrate that helium-neon laser irradiation does not affect peripheral A-delta or C-fiber noci centers. Pain 43:235-242. 1990
  80. Walsh D, Baxter G, Allen J: Lack of effect of pulsed low-intensity infrared (820 nm) laser irradiation on nerve conduction in the human superficial radial nerve, Laser Surg Med 26:485-490, 2000.
  81. Nussbaum EL, Biemann I, Mustard B: Comparison of ultrasound/ultraviolet-C and laser for treatment of pressure ulcers in patients with spinal cord injury, Phys Ther 74:812-823, 1994.
  82. Lyons RF, Abergel RP, White RA, et al: Biostimulation of wound healing in vivo by a helium-neon laser, Ann Plast Surg 18:47-50,1987.
  83. Surchinak JS, Alago ML, Bellamy RF, et al: Effects of low level energy lasers on the healing of full thickness skin defects, Laser SurgMed 2:267-274, 1983.
  84. Ma SY, Hou H: Effect of He-Ne laser irradiation on healing skin wounds in mice, Laser 7:146, 1981.
  85. Dyson M, Young S: Effect of laser therapy on wound contraction and cellularity in mice, Lasers Med Sci 1:125-130, 1986.
  86. Gogia PP, Hurt BS, Zirn TT: Wound management with whirlpool and infrared cold laser treatment: a clinical report, Phys Ther 68:1239-1242, 1988.
  87. Kahn J: Case reports: open wound management with the He-Ne cold laser, Orthop Sport Phys 6:203-204, 1984.
  88. Reddy GK, Stehno-Bittel D, Enwemeka CS: Laser photostimulation accelerates wound healing in diabetic rats, Wound Repair Regen 9:248-255, 2001.
  89. Schindl A, Schindl M, Schon H, et al: Low-intensity laser irradiation improves skin circulation in patients with diabetic microangiopathy,Diabetes Care 21:580-584, 1998.
  90. Cambier DC, Vanderstraeten GG, Mussen MJ, et al: Low power laser and healing of burns: a preliminary assay, Plast Reconstr Surg97:555-558, 1996.
  91. McCaughan JS Jr, Bethel BH, Johnson T, et al: Effect of low dose argon irradiation on rate of wound closure, Lasers Surg Med 5:607-614, 1985.
  92. Basford JR, Hallman HO, Sheffield SG, et al: Comparisons of cold quartz ultraviolet, low-energy laser, and occlusion in wound healing in a swine model, Arch Phys Med Rehabil 106:358-363, 1986.
  93. Oliveira FS, Pinfildi CE, Parizoto NA, et al: Effect of low level laser therapy (830 nm) with different therapy regimes on the process of tissue repair in partial lesion calcaneous tendon, Lasers Surg Med 41:271-276, 2009.
  94. Stergioulas A, Stergioula M, Aarskog R, et al: Effects of low-level laser therapy and eccentric exercises in the treatment of recreational athletes with chronic Achilles tendinopathy, Am J Sports Med 36:881-887, 2008.
  95. Walker JB, Akhanjee LK, Cooney MM, et al: Laser therapy for pain of rheumatoid arthritis, Clin) Pain 3:54-59, 1987.
  96. Matic M, Lazetic B, Poljacki C, et al: Low level laser irradiation and its effect on repair processes in the skin, Med Pregl 56:137-141,2003. (Croatian).
  97. Enwemeka CS: Laser biostimulation of healing wounds: specific effects and mechanisms of action, / Orthop Sports Phys Ther 9:333-338, 1988.
  98. Lucas C, Criens-Poublon LJ, Cockrell CT, et al: Wound healing in cell studies and animal model experiments by low level laser therapy: were clinical studies justified? A systematic review,
    Lasers Med Sci 17:110-134, 2002.
  99. Flemming K, Cullum N: Laser therapy for venous leg ulcers, Cochrane Database Syst Rev (2):CD001182, 2000.
  100. Enwemeka CS, Parker JC, Dowdy DS, et al: The efficacy of low power lasers in tissue repair and pain control: a meta-analysis study, Photomed Laser Surg 22:323-329, 2004.
  101. Woodruff LD, Bounkeo JM, Brannon WM, et al: The efficacy of laser therapy in wound repair: a meta-analysis of the literature,Photomed Laser Surg 22:241-247, 2004.
  102. Fulop AM, Dhimmer S, Deluca JR, et al: A meta-analysis of the efficacy of phototherapy in tissue repair, Photomed Laser Surg 27:695-702, 2009.
  103. Flemming KA, Cullum NA, Nelson EA: A systematic review of laser therapy for venous leg ulcers, Wound Care 8:111-114,1999.
  104. Reddy GK, Stehno-Bittel D, Enwemeka CS: Laser photostimula tion of collagen production in healing rabbit Achilles tendons, Laser Surg Med 22:281-287, 1998.
  105. Carrinho PM, Renno AC, Koeke P, et al: Comparative study using 685-nm and 830-nm lasers in the tissue repair of tenotomized tendons in the mouse, Photomed Laser Surg 24:754-758, 2006.
  106. Enwemeka CS, Cohen E, Duswalt EP, et al: The biomechanical effects of Ga-As laser photostimulation on tendon healing, Laser Ther 6:181-188, 1995.
  107. Bayat M, Delbari A, Elmaseyeh MA, et al: Low-level laser therapy improves early healing of medial collateral ligament injuries irrats, Photomed Laser Surg 23:556-560, 2005.
  108. Trelles MA, Mayayo E: Bone fracture consolidates faster with low-power laser, Lasers Surg Med 7:36-45, 1987.
  109. Chen JW, Zhou YC: Effect of low level carbon dioxide laser irradiation on biochemical metabolism of rabbit mandibular bone callus, Laser Ther 1:83-87, 1989.
  110. Tang XM, Chai BP: Effect of CO2 laser irradiation on experimental fracture healing: a transmission electron microscopy study, Lasers Surg Med 6:346-352, 1986.
  111. Niccoli-Filho W, Okamoto T: The effect of exposure to continu ous Nd:YAG laser radiation on the wound healing process after removal of the teeth (a histological study on rats), Stomatologiia 74:26-29, 1995.
  112. Kucerova H, Dostalova T, Himmlova L, et al: Low-level laser therapy after molar extraction, J Clin Laser Med Surg 18:309-315,2000.
  113. Lirani-Galvao AP, Jorgetti V, da Silva OL: Comparative study of how low-level laser therapy and low intensity pulsed ultrasound affect bone repair in rats, Photomed Laser Surg 24:735-740, 2006.
  114. Coombe AR, Ho CT, Darendeliler MA, et al: The effects of low level laser irradiation on osteoblastic cells, Clin Orthod Res 4:3-14, 2001.
  115. Hawkins DH, Abrahamse H: The role of laser fluence in cell viability, proliferation, and membrane integrity of wounded human skin fibroblasts following helium-neon laser irradiation, Lasers Surg Med 38:74-83, 2006.
  116. Hawkins D, Abrahamse H: Effect of multiple exposures of low-level laser therapy on the cellular responses of wounded human skin fibroblasts, Photomed Laser Surg 24:705-714, 2006.
  117. Houreld NN, Abrahamse H: Laser light influences cellular viability and proliferation in diabetic-wounded fibroblast cells in a dose and wavelength-dependent manner, Lasers Med Sci 23:11-18, 2008.
  118. Mendez TM, Pinheiro AL, Pacheco MT, et al: Dose and wavelength of laser light have influence on the repair of cutaneous wounds, J Clin Laser Med Surg 22:19-25, 2004.
  119. Goldman JA, Chiarpella J, Casey H, et al: Laser therapy of rheumatoid arthritis, Lasers Surg Med 1:93-101, 1980.
  120. Palmgren N, Jensen GF, Kaae K, et al: Low power laser therapy in rheumatoid arthritis, Lasers Med Sci 4:193-195, 1989.
  121. Asada K, Yutani Y, Shimazu A: Diode laser therapy for rheumatoid arthritis: a clinical evaluation of 102 joints treated with low level laser therapy, Laser Ther 1:147-151, 1989.
  122. Lonauer G: Controlled double blind study on the efficacy of He-Ne laser beams v He-Ne + infrared laser beams in therapy of activated OA of the finger joint, Lasers Surg Med 6:172, 1986.
  123. Ozdemis F, Birtane M, Kokino S: The clinical efficacy of low-power laser therapy on pain and function in cervical osteoarthritis, Clin Rheumatol 20:181-184, 2001.
  124. Meireles SM, Jones A, Jennings F, et al: Assessment of the effectiveness of low-level laser therapy on the hands of patients with rheumatoid arthritis: a randomized double-blind controlled trial, Clin Rheumatol 29:501-509, 2010.
  125. Basford JR, Sheffield CG, Mair SD, et al: Low energy helium neonlaser treatment of thumb osteoarthritis, Arch Phys Med Rehabil 68:794-797, 1987.
  126. McAuley R, Ysala R: Soft laser: a treatment for osteoarthritis of the knee? Arch Phys Med Rehabil 66:553-554, 1985.
  127. Brosseau L, Welch V, Wells G, et al: Low level laser therapy for osteoarthritis and rheumatoid arthritis: a metaanalysis, Rheumatol 27:1961-1969, 2000.
  128. Brosseau L, Welch V, Wells G, et al: Low level laser therapy (classes I, II and III) in the treatment of rheumatoid arthritis, Cochrane Database Syst Rev (2):CD002049, 2005.
  129. Brosseau L, Welch V, Wells G, et al: Low level laser therapy (class III) for the treatment of osteoarthritis, Cochrane Database Syst Rev (3):CD002046, 2006.
  130. Marks R, de Palma F: Clinical efficacy of low power laser therapy in osteoarthritis, Physiother Res Int 4:141-157, 1999.
  131. Ferreira DM, Zangaro RA, Villaverde AB, et al: Analgesic effect of He-Ne (632.8 nm) low-level laser therapy on acute inflammatory pain, Photomed Laser Surg 23:177-181, 2005.
  132. Carati CJ, Anderson SN, Gannon BJ, et al: Treatment of post mastectomy lymphedema with low-level laser therapy: a double blind, placebo controlled trial, Cancer 98:1114-1122, 2003.
  133. Kaviani A, Fateh M, Nooraie RY, et al: Low-level laser therapy in management of postmastectomy lymphedema, Lasers Med Sci 21:90-94, 2006.
  134. Kozanoglu E, Basaran S, Paydas S, et al: Efficacy of pneumatic compression and low-level laser therapy in the treatment of postmastectomy lymphoedema: a randomized controlled trial, Clin Rehabil 23:117-124, 2009.
  135. Dirican A, Andacoglu 0, Johnson R, et al: The short-term effects of low-level laser therapy in the management of breastcancer-related lymphedema, Support Care Cancer 19:685-690,2011.
  136. Moseley AL, Carati CJ, Piller NB: A systematic review of common conservative therapies for arm lymphoedema secondary to breast cancer treatment, Ann Oncol 18:639-646, 2007.
  137. Leonard DR, Farooqi MH, Myers S: Restoration of sensation, reduced pain, and improved balance in subjects with diabetic peripheral neuropathy: a double-blind, randomized, placebocontrolled study with monochromatic near-infrared treatment,Diabetes Care 27:168-172, 2004.
  138. Zinman LH, Ngo M, Ng ET, et al: Low-intensity laser therapy for painful symptom diabetic sensorimotor polyneuropathy: a controlled trial, Diabetes Care 27:921-924, 2004.
  139. Kemmotsu O, Sato K, Furumido H, et al: Efficacy of low reactive level laser therapy for pain attenuation of postherpetic neuralgia, Laser Ther 3:71-75, 1991.
  140. Iijima K, Shimoyama M, Shimoyama N, et al: Effect of repeated irradiation of low-power He-Ne laser in pain relief from posther petic neuralgia, Clin J Pain 5:271-274, 1989.
  141. Lampl Y, Zivin J, Fisher M, et al: Infrared laser therapy for ischemic stroke: a new treatment strategy, Stroke 38:1843-1849, 2007.
  142. Walker J: Relief from chronic pain by low power laser irradiation, Neurosci Lett 43:339-344, 1983.
  143. Haker E, Lundeberg T: Is low-energy laser treatment effective in lateral epicondylalgia? Pain Symptom Manage 6:241-246,1991.
  144. Vasseljen 0, Hoeg N, Kjelstad B, et al: Low level laser versus placebo in the treatment of tennis elbow, Scand J Rehabil Med24:37-42, 1992.
  145. Lam LK, Ceing GL: Effects of 904-nm low-level laser therapy in the management of lateral epicondylitis: a randomized controlled trial, Photomed Laser Surg 25:65-71, 2007.
  146. Gur A, Sarac AJ, Cevik R, et al: Efficacy of 904 nm gallium arsenide low level laser therapy in the management of chronic myofascial pain in the neck: a double-blind and randomize-controlled trial,
    Lasers Surg Med 35:229-235, 2004.
  147. Chow RT: The effect of 300 mW, 830 nm laser on chronic neck pain: a double-blind, randomized, placebo-controlled study,Pain 124:201-210, 2006.
  148. Basford JR, Sheffield CG, Harmsen WS: Laser therapy: a random ized, controlled trial of the effects of low-intensity Nd:YAG laser irradiation on musculoskeletal back pain, Arch Phys Med Rehabil 80:647-652, 1999.
  149. Snyder-Mackler L, Barry AJ, Perkins Al, et al: Effects of helium neon laser irradiation on skin resistance and pain in patients with trigger points in the neck or back, Phys Ther 69:336-341, 1989.
  150. Snyder-Mackler L, Bork C, Bourbon B, et al: Effect of helium neon laser on musculoskeletal trigger points, Phys Ther 66:1087-1090, 1986.
  151. Vinck E, Cagnie B, Coorevits P, et al: Pain reduction by infrared light-emitting diode irradiation: a pilot study on experimentally induced delayed-onset muscle soreness in humans, Lasers Med Sci 21:11-18, 2006.
  152. Laakso EL, Cabot PJ: Nociceptive scores and endorphin-containing cells reduced by low-level laser therapy (LLLT) in inflamed paws of Wistar rat, Photomed Laser Surg 23:32-35, 2005.
  153. Moore KC, Hira N, Kumar PS, et al: A double blind crossover trial of low level laser therapy in the treatment of post-herpetic neuralgia, Laser Ther (Pilot issue):7-9, 1989.
  154. Siebert W, Seichert N, Siebert B, et al: What is the efficacy of soft and mid lasers in therapy of tendinopathies? Arch Orthop Trauma Surg 106:358-363, 1987.
  155. Haker EH, Lundeberg TC: Lateral epicondylalgia: report of noneffective midlaser treatment, Arch Phys Med Rehabil 72:984-988, 1991
  156. Fulop AM, Dhimmer S, Deluca JR, et al: A meta-analysis of the efficacy of laser phototherapy on pain relief, Clin J Pain 26:729-736, 2010.
  157. Azevedo LH, Correaaranha AC, Stolf SF, et al: Evaluation of low intensity laser effects on the thyroid gland of male mice, Photomed Laser Surg 23:567-570, 2005.
  158. Moolenar H: Endolaser 476 therapy protocol, Delft, Netherlands, 1990, Enraf-Nonius Delft.
  159. Waylonis GW, Wilke S, O’Toole Do, et al: Chronic myofascial pain: management by low output helium-neon laser therapy,Arch Phys Med Rehabil 69:1017-1020, 1988.
  160. Chartered Society of Physiotherapy, Safety of Electrotherapy Equipment Working Group: Guidelines for the safe use of lasers in physiotherapy, London, 1991, Chartered Society of Physiotherapy.
  161. Moholkar R, Zukowski S, Turbill H, et al: The safety and efficacy of low level laser therapy in soft tissue injuries: a double-blind randomized study, Phys Ther 81:A49, 2001.
  162. Klebanov GI, Shuraeva NI, Chichuk TV, et al: A comparative study of the effects of laser and light-emitting diode irradiation on the wound healing and functional activity of wound exudate leukocytes, Biofizika 50:1137-1144, 2005.
  163. Osipov AN, Rudenko TG, Shekhter AB, et al: A comparison of the effects of laser and light-emitting diodes on superoxide dismutase activity and nitric oxide production in rat wound fluid, Biofizika 51:116-122, 2006.
  164. Blidall H, Hellesen C. Ditlevesen P. et al: Soft laser therapy of rheumatoid arthritis, Scand J Rheumatol 16:225-228, 1987.
  165. Lilge L, Tierney K, Nussbaum E: Low-level laser therapy for wound healing: feasibility of wound dressing transillumination J Clin Laser Med Surg 18:235-240, 2000.
  166. Pontinen PJ, Aaltokallio T, Kolari PJ: Comparative effects exposure to different light sources (He-Ne laser, InGaAl dios laser, a specific type of noncoherent LED) on skin blood flow to the head, Acupunct Electrother Res 21:105-118, 1996.
  167. Whelan HT, Buchmann EV, Dhokalia A, et al: Effect of NASA light-emitting diode irradiation on molecular changes for wound healing in diabetic mice, J Clin Laser Med Surg 21:67-742003.
  168. Vladimirov YA, Osipov AN, Klebanov GI: Photobiological principles of therapeutic applications of laser radiation, Biochmistry 69:81-90, 2004.

Effect of Heat
IR Effect as the Light
References

About Vibration (TDD)