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The acronym laser stands for light amplification by stimulated emission of radiation. Lasers are electromagnetic wave amplifiers which can produce pencil-like beams of electromagnetic waves with special properties. The earliest medical lasers, developed in the 1960s and 1970s, were relatively high powered and utilized the concentration of energy in a tiny, pencil-like beam for tissue destruction and coagulation. [Robertson et al., 2006]
Low level laser therapy (LLLT) takes place at low radiation intensities and is used clinically for a wide range of conditions as it considered as a non-invasive, painless modality with low Incidence of adverse effects. It has been used to provide pain relief from the symptoms of chronic arthritis, tendonitis, carpal tunnel syndrome, fibromyalgia, knee injuries, shoulder pain, and symptoms relating to nerve injuries (sharp pain, paraesthesia). [Bjordal et al., 2006a]
Applications also include wound repair, leg ulcers in diabetic patients and peripheral nerve injury. As LLLT has an antiodematous, analgetic and anti-inflammatory effects belong to the most commonly recommended physiotherapeutic methods used for pain modulation. [Elwakil et la., 2007]
Although a research report was published in the late 1970s on the effects of laser phototherapy on the regeneration of traumatically injured peripheral nerves [Rochkind, 1978], it is only since the late 1980s that scientific interest was grown in this therapeutic approach for neural rehabilitation, leading to the publication of a number of studies that have shown positive effects of Laser therapy on peripheral nerve regeneration [Gigo-Benato et al., 2005 and Rochkind, 2009].
Studies have suggested that infrared laser therapy could also be beneficial for the treatment of injured peripheral nerves and spinal cord injury [Oron et al., 2007]. In addition, Laser has an effect on neural structures that are damaged by compression or inflammation, and this significantly improves nerve recovery [Konstantinovic et al., 2010a].
In peripheral nerve injury, laser therapy has an immediate protective effect, maintains functional activity of the injured nerve for a long period of time, decreases degeneration in corresponding motor neurons of the spinal cord and significantly increases axonal growth and myelinization. It has been suggested that phototherapy may enhance recovery of neurons from injury by altering mithochondrial oxidative metabolism [Gigo-Benato et al., 2005] A study in patients with incomplete long-term peripheral nerve injury, 780-nm laser irradiation can progressively improve peripheral nerve function, which leads to significant functional recovery. [Rochkind et la., 2007]
In spite of many applications in humans, the biomodulative effect of low level laser therapy has still not been completely understood. The spectrum of visible to infrared light can cause stimulation as well as inhibition of various organisms [Schaffer et al., 1997]. Photobiomodulation involves increased adenosine triphosphate (ATP) formation after energy absorption inside the mitochondria [Oron et al., 2007].
High Intensity Laser Therapy (HILT) was introduces to the field of physical therapy is relatively recent and this technology is in constant evolution and approved by FDA in 2004. High power pulsed Nd:YAG laser work with high peak powers that induce a non invasive regenerative therapy with a non-painful and non-invasive therapeutic system which able to reach and stimulate organs that are difficult to reach for classical lasers, such as the large and/or deep joints [Zati and Valent 2006]
Now the use of pulsed Nd:YAG Laser has been spreading in the therapy of pain with excellent results [Pires et al., 2008]. Studies exist which describe the anti-inflammatory, anti-oedemigenic and antalgic effects of Nd:YAG Laser, thus justifying its use in the therapy of pain [Viliani et al., 2009 and Saggini et al., 2009].
The laser effectiveness depends on factors such as wavelength, site, duration, and dose of LLLT treatment as well as depth of target tissue. Research into the dose response profile of laser therapy suggests that different wavelengths have specific penetration abilities through human skin. [Enwemeka, 2001 and Nussbaum and Van 2007] As, clinical effects could vary with depth of target tissue. There is a lack of knowledge to the effect of HILT on the radiculopathy as no studies - to our knowledge- have been conducted possible effects of HILT on patients with cervical pain with radiculopathy.
The aim of the present study was to compare the possible effect of HILT and LLLT on Electropgysiological changes in patients with cervical pain with radiculopathy.
Laser units were manufactured by Enraf Nonius. Laser unit has the following specifications: WL: 905 nm with frequency of 5000 Hz, beam area of 1 cm2, peak power 25mW.
First, choose the proper position of the laser probe by allocating point of application. The laser probe was contact during application and held perpendicularly over transforaminal points. [Konstantinovic et al., 2010b] the probe held for 120 seconds for each point with energy density 2 J/ point. After moving to all points, the process was repeated with total energy denisty 4 J/ point.
The apparatus provided the following options: (Nd:YAG), with pulsed emission (1064 nm), Very high peak powers (1-3 KW), Elevated energy content (150 - 350 mJ), High levels of fluence (energy density) ( 810-1780 mJ/cm2), Brief duration (120-150 ÂÂµs), Low frequency (10-40 Hz), Duty Cycle of about 0.1%. In spot treatment the frequency must be low (12-17 Hz) and conducted for a few seconds (5-7s). The equipment calculate the number of pulses , energy received to each point and the total energy delivered to the patient during the treatment session. [Zati and Valent ., 2006]
After allocating the points, laser hand piece was held for a maximum of 7 seconds for each point until all points being covered. Treatment of point occurred in steps in order to gradually increase the energy density and decrease frequency for each point . In the first step energy density 360 mJ/cm2 and frequency of 17 Hz were used. In second step the energy density gradually increased to 510 mJ/ cm2 and a frequency of 15 and last step with 610 mJ/ cm2 and 12 Hz. [Zati and Valent ., 2006]
Explanation to the effect of low level laser
Laser alters the cellular functions by altering intercellular communication in a manner that is dependent on the characteristics of the light itself (eg, wavelength, coherence). Laser light affects the mitochondrial respiratory chain by by increasing the activity of certain enzymes such as cytochrome oxidase and adenosine triphosphatase [Bashardoust et al., 2010]. It also increases DNA synthesis, collagen and pro-collagen production, and may increase the cell proliferation or alter locomotory characteristics of cells [Koutna et al., 2003].
The pain reduction effect of LILT is known to be due to its effect on pain sensation in the sensorial nerve endings. Moreover, it has been reported to have an increasing effect on ÎÂ²-endorphine stimulation. [Marks et al., 1999] LILT also widens the arterial and capillary vessels, reduction in swelling caused by inflammation , stimulates electrolyte interchange in the cell protoplasm, increases oxygen consumption and enhances nucleic acid and protein synthesis. [Tam, 1999]
One of the mechanisms for pain relief is the reduction of inflammation and swelling. Laser acupuncture is also used for the treatment of musculoskeletal pain. The application of laser to specific acupuncture points stimulates the release of endorphins and enkephalins which are natural pain-relieving chemicals.( Zalewska-Kaszubska and Obzejta 2004 & Giuliani, 2004) Also, it was reported that LLLT radiation significantly increases microcirculation, activates angiogenesis, stimulates immunological processes and nerve regeneration. [Taradaj, 2001 and Lampl et al., 2007]
laser therapy can modulate acute inflammation by causing a reduction in the levels of pro-inflammatory cytokines such as interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), and also an increase in the levels of anti-inflammatory growth factors and cytokines such as basic fibroblast growth factor, platelet-derived growth factor, transforming growth factor-beta (TGF-beta). [Picavet et al., 2003, Webb et al., 2003 and Fejer et al., 2006]
LLLT has the ability to modulate inflammatory processes and relieve acute pain conditions triggered by lesions in soft tissues [Bjordal et al., 2006b, Aimbire et al., 2006]. This activity may occur through the decrease in nerve conduction, release of endogenous opioids, increase in angiogenesis and, consequently, increase in local microcirculation. It may also have inhibitory effects on the release of prostaglandins, cytokine levels and cyclooxygenase (Cox)2 and it may accelerate cell proliferation, collagen synthesis and tissue repair. [Bjordal et al., 2006b and Lim et al., 2007]
LLLT may have a direct effect on nerve structures, which could increase the speed of recovery of the conductive block or inhibit A-d and C fiber transmission [Chow et al., 2007].
Number of studies investigated the effect of LLLT on acute low back pain and radiculopathy secondary to herniated lumbar disc and the result showed significant reduction in pain intensity and related disability, improved neurological status, local movements and quality of life after LLLT. Konstantinovic et al. 2010a and JoviciÄâ€¡ et al., 2012]. Also, There were significant reductions in size of the herniated mass on magnetic resonance imaging after the treatment. [Unlu et al. 2008]. While other study reported no differences between laser and placebo laser treatment on pain and functional capacity in patients with acute and chronic LBP caused by disc herniation. [Ay et al. 2010]
In humans, many studies investigated the effects of LLLT on Nerve Conduction Velocity (NCV) in healthy volunteers over the radial, median or sural nerves. [Bartlett et al., 1999 and Baxter and Basford 2008] Some of these studies reported the ability of laser stimulation to evoke action potentials in peripheral nerves. The principal laser-mediated effect was slowing of NCV, increase in conduction latency. Whilst other study reported a decreased in motor and sensory distal latencies in the treated limbs of the laser-treated subjects as compared to control groups.[Basford et al., 1993] Other studies failed to find any effect of laser on action potentials as compared to control group. [Walsh et al., 2000]
Chow et al ., 2011, in a systemic review study, summarize the possible effects of laser irradiation on peripheral mammalian nerves. The result show the pulsed or continuous wave visible and continuous wave infrared (IR) slowed conduction velocity (CV) and/or reduced the amplitude of compound action potentials (CAPs) In 13 of 18 human studies.[ Chow et al ., 2011]
In animal, LLLT was applied transcutaneously to points on the hind limbs of rats overlying the course of the sciatic nerve. LLLT significantly decreased SSEP amplitudes and increased latency after 20 min. CMAP proximal amplitudes and hip/ankle (H/A) ratios decreased at 10 and 20 min with increases in proximal latencies approaching significance. The 808-nm LLLT decreased SSEP amplitudes and increased latencies at 10 and 20 min. [Yan et al., 2011]
For many years high powered and highly focused lasers have been used to cut and separate tissue in many surgical techniques. More recently, therapeutic and biostimulating properties of high power laser were discovered.
Effect of HILT
HILT induces photo-thermal and photomechanical effects by means of pulsed laser emission characterized by a particular shape of pulse. It is believed that laser radiation stimulates several metabolic processes, including cell proliferation and cell differentiation, synthesis of collagen and other proteins, immunomodulation. [Zati and Valent, 2006]
The application of high power lasers in physiotherapy is quite recent. It is due to the development of instruments which allow the control of photothermal and photomechanical processes to obtain therapeutic effects without tissue damage. In particular, pulsed Nd: YAG laser has proved his efficacy in the treatment of many different musculoskeletal diseases and it is believed to have anti-inflammatory, anti-edema, analgesic and also reparative effects. The interaction between tissue and laser radiation alters the mechanics of cell micro-environment, thus acting on the cells as a mechanical stress [Monici et al., 2008].
Some preliminary studies indicated that HILT could be more effective than LLLT in pain control, due to its more intense and deeper effects and found that HILT seems to be more effective than LLLT, due to its higher intensity and to the depth reached by the laser ray. [[Zati and Valent, 2006, Conte et al., 2009 and Gleiser et al., 2009]