Chapter 13: Light Therapy PDF

Charles University Access Provided by: Therapeutic Modalities in Rehabilitation, 5e Chapter 13: Light Therapy Katie Homan; Nathan Newman OBJECTIVES Following...

Charles University Access Provided by: Therapeutic Modalities in Rehabilitation, 5e Chapter 13: Light Therapy Katie Homan; Nathan Newman OBJECTIVES Following completion of this chapter, student will be able to: Identify the different types of light therapy, specifically lasers and light emitting diodes (LEDs). Explain the physical principles used to produce laser light. Contrast the characteristics of the helium neon, gallium arsenide, and gallium aluminum arsenide low­power lasers. Analyze the therapeutic applications of lasers and LEDs in wound and soft­tissue healing as well as edema, inflammation, and pain reduction. Demonstrate the application techniques of low­power lasers and LEDs. Describe the classifications of lasers. Incorporate the safety considerations in the use of lasers. Be aware of the precautions and contraindications for low­power lasers. In recent years, there has been significant interest in light therapy as a clinical therapeutic intervention modality. This intervention provides the clinician with the potential of increasing cellular activity at any point during the healing cycle with few known contraindications. In this chapter, we will focus specifically on LASERS (light amplification by stimulated emissions of radiation) and LEDs (light emitting diodes). Einstein in 1916 was the first to postulate the theorems that conceptualized the development of lasers. The first work with amplified electromagnetic radiation dealt with microwave amplification of stimulated emission of radiation (MASER). In 1955, Townes and Schawlow showed that it was possible to produce stimulated emission of microwaves beyond the optical region of the electromagnetic spectrum. This work with stimulated emission soon extended into the optical region of the electromagnetic spectrum, resulting in the development of devices called optical masers. The first working optical maser was constructed in 1960 by Theodore Maiman when he developed the synthetic ruby laser. Other types of lasers were devised shortly afterward. It was not until 1965 that the term laser was substituted for optical masers.1 Lasers have been incorporated into numerous everyday applications that range from audio discs and supermarket scanning to communication and medical applications.2 LASER = Light Amplification by Stimulated Emission of Radiation Other light forms that can be used in the therapeutic setting include light emitting diodes and superluminous diodes (SLDs). Light emitting diodes are far newer technology that have some similarities to lasers in the light they produce. However, it is imperative that one understands these light forms are different from each other. Continued research needs to be completed to determine the physiological differences they can induced and their effectiveness in different medical conditions. This chapter deals principally with the application of low­level lasers and LEDs as they are used in the conservative management of medical conditions. PHYSICS OF LASERS A laser is a form Downloaded of electromagnetic 2023­10­31 energy 8:19 A Your that IP is has wavelengths and frequencies that fall within the infrared and visible light portions of the 195.113.14.2 Chapter electromagnetic Therapy,1Katie 13: Lightspectrum. Homan; Nathan Electromagnetic Newman light energy Page 1 / 47 is transmitted through space as waves that contain tiny “energy packets” called photons. ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Each photon contains a definite amount of energy, depending on its wavelength (color). Accessibility effectiveness in different medical conditions. This chapter deals principally with the application of low­level lasers and LEDs as they are used in the conservative management of medical conditions. Charles University Access Provided by: PHYSICS OF LASERS A laser is a form of electromagnetic energy that has wavelengths and frequencies that fall within the infrared and visible light portions of the electromagnetic spectrum.1 Electromagnetic light energy is transmitted through space as waves that contain tiny “energy packets” called photons. Each photon contains a definite amount of energy, depending on its wavelength (color). Three Properties of LASER: Coherence Monochromaticity Collimation A laser consists of a gain medium, which is a material (gas, liquid, solid) with specific optical properties contained inside an optical chamber (Figure 13–1). When an external power source is applied to the gain medium, photons are released, which are identical in phase, direction, and frequency. To contain them, and to generate more photons, mirrors are placed at both ends of the chamber. One mirror is totally reflective, whereas the other is semitransparent. The photons bounce back and forth reflecting between the mirrors, each time passing through the gain medium, thus amplifying the light and stimulating the emission of other photons. Eventually, so many photons are stimulated that the chamber cannot contain the energy. When a specific level of energy is attained, photons of a particular wavelength are ejected through the semitransparent mirror appearing as a beam of light.3,4 Thus, amplified light through stimulated emissions (LASER) is produced. Figure 13–1. A laser produces amplified light through stimulated emissions. The laser light is emitted in an organized manner rather than in a random pattern as from incandescent and fluorescent light sources. Three properties distinguish the laser: coherence, monochromaticity, and collimation.1 Coherence means all photons of light emitted from individual gas molecules are of the same wavelength and that the individual light waves are in phase with one another. Normal light, on the other hand, is composed of many wavelengths that superimpose their phases on one another. Monochromaticity refers to the specificity of light in a single, defined wavelength; if the specificity is in the visible light spectrum, it is of only one color. The laser is one of the few light sources that produces a specific wavelength. The laser beam is well collimated, that is, there is minimal divergence of the photons.5 That means the photons move in a parallel fashion, thus concentrating a beam of light (Figure 13–2). Figure 13–2. Depth of penetration with a GaAs laser. Direct penetration is up to 1 cm with a collimated laser beam. Stimulation causes indirect effects up to 5 cm. Downloaded 2023­10­31 8:19 A Your IP is 195.113.14.2 Chapter 13: Light Therapy, Katie Homan; Nathan Newman Page 2 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility concentrating a beam of light (Figure 13–2). Charles University Figure 13–2. Access Provided by: Depth of penetration with a GaAs laser. Direct penetration is up to 1 cm with a collimated laser beam. Stimulation causes indirect effects up to 5 cm. TYPES OF LASERS There are potentially thousands of different types of lasers, each with specific wavelengths and unique characteristics. Lasers are identified according to the nature of the gain medium placed between two reflecting surfaces. The gain mediums used to create lasers include the following categories: crystal and glass (solid­state), gas, semiconductor, liquid dye, and chemical. Lasers can be categorized as either high­ or low­power, depending on the intensity of energy they deliver. High­power lasers are also known as “hot” lasers because of the thermal responses they generate. These are used in the medical realms in numerous areas, including surgical cutting and coagulation, ophthalmologic, dermatologic, oncologic, and vascular specialties. The use of low­power, or most often called low­level lasers has gained popularity in a variety of different professional settings including dermatology, dentistry, chiropractic, and various health care settings to assist with the healing of wound and soft tissue injuries, control acute or chronic inflammation or edema, and for pain control. There has also been research investigating the effect of low­level lasers in the treatment of strokes, spinal cord injuries, brain injuries, and other nervous system impairments.40 In addition, new research has been investigating how low­level lasers applied prior to or post­activity can affect factors associated with muscular fatigue.41–47 Low­level lasers work by causing photochemical, rather than thermal effects. No tissue warming occurs. The exact distinction of the power output that delineates a low­ versus high­power laser varies. Low­level devices are considered any laser that does not generate an appreciable thermal response.7 Clinical Decision­Making Exercise 13–1 After watching a show on the use of lasers in surgery, a patient expresses genuine concern to the clinician that using a laser to treat a myofascial trigger point will cause skin burns. What should the clinician explain to the patient to allay his or her fears? Low­level laser Downloaded therapy8:19 2023­10­31 (LLLT) is theIPdominant A Your term in use today. Therapeutic laser, low­power laser, or low­energy laser are also used for laser is 195.113.14.2 Chapter therapy. 13: TheLight term Therapy, soft laser Katie Homan; Nathan was originally Newman used to differentiate therapeutic lasers from hard lasers, that is, surgical lasers. Several differentPage 3 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy designations then emerged, such as MID­laser (mid­infrared) and medical Policylaser. Notice Accessibility Biostimulating laser is another term, with the disadvantage that one can also give inhibiting doses.8 The term bioregulating laser has thus been proposed. Other suggested names are low­reactive­level laser, low­  After watching a show on the use of lasers in surgery, a patient expresses genuine concern to the clinician that using a laser to treat Charles University a myofascial Access Provided by: trigger point will cause skin burns. What should the clinician explain to the patient to allay his or her fears? Low­level laser therapy (LLLT) is the dominant term in use today. Therapeutic laser, low­power laser, or low­energy laser are also used for laser therapy. The term soft laser was originally used to differentiate therapeutic lasers from hard lasers, that is, surgical lasers. Several different designations then emerged, such as MID­laser (mid­infrared) and medical laser. Biostimulating laser is another term, with the disadvantage that one can also give inhibiting doses.8 The term bioregulating laser has thus been proposed. Other suggested names are low­reactive­level laser, low­ intensity­level laser, photobiostimulation laser, and photobiomodulation laser. Most commonly used lasers: Gallium aluminum arsenide (GaAlAs) Helium neon (HeNe) Gallium arsenide (GaAs) Low­level lasers, which have been studied and used in Canada and Europe for the last 50 years, have been investigated in the United States for the last three decades. The three most commonly used low­level lasers are the helium neon (HeNe), gallium arsenide (GaAs), and the gallium aluminum arsenide (GaAlAs). The characteristics of these three low­level lasers are summarized in Table 13–1. The HeNe was the earliest of the low­level lasers. A HeNe laser is a gas laser that delivers wavelength of 632.8 nm in the red portion of the visible light spectrum. The laser is delivered in a continuous wave and has a direct penetration of 2–5 mm and an indirect penetration of 10 mm. Table 13–1 Characteristics of Common Low­Level Lasers NAME HELIUM NEON GALLIUM ARSENIDE GALLIUM ALUMINUM ARSENIDE Abbreviation HeNe GaAs GaAlAs Type Gas Semiconductor Semiconductor diode Wavelength 632.8 nm 904 nm 650–980 nm* (800–830 nm most common) Typical Wave Form Continuous Superpulsed 1–1000 Hz Continuous Peak Power 3 mW 10–100 W >100 mW Depth of Penetration (Direct and Indirect) 2–10 mm 3–5 cm 2–3 cm Typical FDA Class Class IIIa Class IIIb Class IIIb *Varies based on aluminum content In the 1980s semiconductor lasers were developed. They produced radiation in both the red and infrared regions. A GaAs laser is a semiconductor laser and has a wavelength of 904 nm. They are naturally delivered in a superpulsed mode. This pulsed mode allows for these lasers to have higher peak powers (10–100 W), but maintain lower average powers due to the peak spikes occurring over a very short period of time (100–200 ns).48 This laser has a direct penetration of 1–2 cm and an indirect penetration up to 5 cm.9 The newest and most current lasers are diode lasers that use semiconductor crystals to emit radiation. The GaAlAs laser is the newest and currently the most commonly used laser (Figure 13–3). These lasers can vary in wavelengths with the wavelength depending on the aluminum content. In studies reviewed, wavelengths have ranged from 650 to 980 nm49,50 with most wavelengths occurring in the 800–830 nm range. Tissue penetration for this Downloaded 2023­10­31 8:19 A Your IP is 195.113.14.2 laser is approximately Chapter 2–3 cm. 13: Light Therapy, 48 This Katie laser naturally Homan; produces a continuous wave, but can be delivered in a selected pulse mode, similar to Page Nathan Newman ultrasound. 4 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility Figure 13–3. peak powers (10–100 W), but maintain lower average powers due to the peak spikes occurring over a very short period of time (100–200 ns).48 This Charles University laser has a direct penetration of 1–2 cm and an indirect penetration up to 5 cm.9 Access Provided by: The newest and most current lasers are diode lasers that use semiconductor crystals to emit radiation. The GaAlAs laser is the newest and currently the most commonly used laser (Figure 13–3). These lasers can vary in wavelengths with the wavelength depending on the aluminum content. In studies reviewed, wavelengths have ranged from 650 to 980 nm49,50 with most wavelengths occurring in the 800–830 nm range. Tissue penetration for this laser is approximately 2–3 cm.48 This laser naturally produces a continuous wave, but can be delivered in a selected pulse mode, similar to ultrasound. Figure 13–3. (a) Single diode GaAlAs laser device. (b) Multiple diode GaAlAs laser. (Courtesy DonJoy Global) Previous laser devices would only provide one laser beam, but today manufactures are making devices not only with multiple laser beams, but with different light sources including LEDs and SLDs. With these devices, occasionally different probes can be selected that offer different beam or cluster options (Figure 13–4). Therefore, it is possible to have a probe with a cluster that includes several laser, LED, and SLD beams at the same or different wavelengths or a combination of all of the light sources. A cluster is ideal for treating larger areas. Theoretically, a combination of different light sources with different physiological effects or the same light source with different wavelengths could potentially improve outcomes as different tissue depths could be affected. Additional research in this area needs to be completed. Figure 13–4. Single and multiple diode cluster probes. (Courtesy DonJoy Global) In addition, some available units have the ability to measure electrical impedance and deliver electrical point stimulation. The impedance detector allows hypersensitive or acupuncture points to be located. The point stimulator can be combined with a laser application when treating pain. The electrical stimulation is believed to provide spontaneous pain relief, whereas the laser provides more latent tissue responses.10 LASER TREATMENT TECHNIQUES The method of application of laser therapy is relatively simple, but certain principles should be discussed so the clinician can accurately determine the amount of laser energy delivered to the tissues. One should always refer to the specific device's user manual for specific instructions. Some units will have pre­set treatment options. For general application, typically only the treatment time, power, and the pulse mode vary. For research purposes, the investigator should measure the exact energy density emitted from the applicator before the treatments. The laser energy Downloaded is emitted8:19 2023­10­31 fromAa Your handheld IP is remote applicator. The HeNe lasers contain their components inside the unit and deliver the laser light to 195.113.14.2 Chapter 13: Light Therapy, Katie Homan; Nathan Newman Pagelasers the target area via a fiber­optic tube. The fiber­optic assembly is fragile and should not be crimped or twisted excessively. The GaAs and GaAlAs 5 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility house semiconductor elements in the tip of the applicator. The fiber­optics used with the HeNe and the elliptical shape of the semiconductor in the GaAs and GaAlAs lasers create beam divergence with the devices. This divergence causes the beam's energy to spread out over a given area so that as The method of application of laser therapy is relatively simple, but certain principles should be discussed so the clinician can accurately determine Charles the University amount of laser energy delivered to the tissues. One should always refer to the specific device's user manual for specific instructions.Access Some unitsby:will Provided have pre­set treatment options. For general application, typically only the treatment time, power, and the pulse mode vary. For research purposes, the investigator should measure the exact energy density emitted from the applicator before the treatments. The laser energy is emitted from a handheld remote applicator. The HeNe lasers contain their components inside the unit and deliver the laser light to the target area via a fiber­optic tube. The fiber­optic assembly is fragile and should not be crimped or twisted excessively. The GaAs and GaAlAs lasers house semiconductor elements in the tip of the applicator. The fiber­optics used with the HeNe and the elliptical shape of the semiconductor in the GaAs and GaAlAs lasers create beam divergence with the devices. This divergence causes the beam's energy to spread out over a given area so that as the distance from the source increases, the intensity of the beam lessens. Lasing Techniques Gridding Scanning Point stimulation Lasing Techniques To administer a laser treatment, the tip should be in light contact with the skin and directed perpendicularly to the target tissue while the laser is engaged for the designated time. Commonly, a treatment area is divided into a grid of square centimeters, with each square centimeter stimulated for the specified time. Lines and points should not be drawn on the patient's skin because this may absorb some of the light energy (Figure 13–5). It is not recommended to treat random spots in the desired treatment area and not the entire area. However, it is also not recommended to overlap treated spots. Ideally the entire desired treatment area should receive equal treatment and dosage.51 If open areas are to be treated, a sterilized clear plastic sheet can be placed over the wound to allow surface contact. Figure 13–5. Gridding techniques. An imaginary grid can be drawn over the area to be treated and each square centimeter of the injured area shout be lasered for the specified time. The laser should be in light contact with the skin. An alternative is a scanning technique in which there can be contact or no contact between the laser tip and the skin. This is used for larger treatment areas and the laser probe is scanned over the desired treatment area. This technique makes it challenging to ensure all portions of the treatment area get equal dosage. When the noncontact technique is used, the applicator tip should be held 5–10 mm from the wound or treatment area. Because beam divergence occurs, the amount of energy decreases as the distance from the target increases. The amount of energy lost becomes difficult to quantify accurately if the distance from the target is variable. Therefore, it is not recommended to treat at distances greater than 1 cm. When using a Downloaded 2023­10­31 laser tip of 1 mm 8:19 A ofYour with 90 degrees the red laser beam of the HeNe should fill an area the size of 1 cm2 (Figure 13–6). IP is 195.113.14.2 divergence, Chapter 13: Light Therapy, Katie Homan; Nathan Newman Page 6 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility Figure 13–6. Scanning technique. When skin contact cannot be maintained, the applicator should be held in the center of the square centimeter grid at a distance of  Charles An alternative is a scanning technique in which there can be contact or no contact between the laser tip and the skin. This is used for larger University treatment areas and the laser probe is scanned over the desired treatment area. This technique makes it challenging to ensure all portions of the treatment Access area Provided by: get equal dosage. When the noncontact technique is used, the applicator tip should be held 5–10 mm from the wound or treatment area. Because beam divergence occurs, the amount of energy decreases as the distance from the target increases. The amount of energy lost becomes difficult to quantify accurately if the distance from the target is variable. Therefore, it is not recommended to treat at distances greater than 1 cm. When using a laser tip of 1 mm with 90 degrees of divergence, the red laser beam of the HeNe should fill an area the size of 1 cm2 (Figure 13–6). Figure 13–6. Scanning technique. When skin contact cannot be maintained, the applicator should be held in the center of the square centimeter grid at a distance of less than 1 cm and should be at an angle of 90 degrees to the surface being treated. Although the infrared laser is invisible, the same consideration should be given when using the scanning technique. If the laser tip comes into contact with an open wound, the tip should be cleaned thoroughly with a small amount of an antiseptic to prevent cross­contamination. Finally, different points can be selected and treated when applying a laser treatment. This particular method can be used in a variety of ways including treating trigger points, acupuncture points, or predetermine points based on the injury that is being treated. Parameters The goal of LLLT is to supply light energy to the designated treatment area for a period of time. With this comes a wide range of parameters that can affect the treatment, which in turn can make determining the appropriate settings for a successful treatment challenging. The different parameters are detailed and described in Table 13–2. Table 13–2 Summary of Treatment Parameters PARAMETER How the Parameter is TYPICAL UNIT OF NOTES Calculated MEASUREMENT (ABBREVIATION) Wavelength Nanometers (nm) Plays a role in which molecules absorb the light and the depth of penetration. of laser Will determine the color of the light and if it is visible. Peak Power Power = Energy/Time Watts = Typically power is measured in mW (1000 mW = 1 W) Joules/seconds (W Downloaded 2023­10­31 8:19 A Your IP is 195.113.14.2 Chapter 13: Light Therapy, Katie Homan; Nathan Newman = J/s) Page 7 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility Average Average power = Peak Power × Watts = Watts × Only applicable with pulsed beam applications Power Pulse Width × Pulse Rate seconds × Hertz (W Parameters Charles University The goal of LLLT is to supply light energy to the designated treatment area for a period of time. With this comes a wide range of parameters that can Access Provided by: affect the treatment, which in turn can make determining the appropriate settings for a successful treatment challenging. The different parameters are detailed and described in Table 13–2. Table 13–2 Summary of Treatment Parameters PARAMETER How the Parameter is TYPICAL UNIT OF NOTES Calculated MEASUREMENT (ABBREVIATION) Wavelength Nanometers (nm) Plays a role in which molecules absorb the light and the depth of penetration. of laser Will determine the color of the light and if it is visible. Peak Power Power = Energy/Time Watts = Typically power is measured in mW (1000 mW = 1 W) Joules/seconds (W = J/s) Average Average power = Peak Power × Watts = Watts × Only applicable with pulsed beam applications Power Pulse Width × Pulse Rate seconds × Hertz (W = W × s × Hz) Pulse Rate Hertz (Hz) or Only applicable with pulsed beam applications or Pulse pulses/second Frequency Irradiance Irradiance = Power/Area Watts/cenimeter2 or Power (W/cm2) Density Energy Energy = Power × time Joules = Watts × It is important to note that in LLLT treatments, power and time are independent seconds (J = W × s) variables with no proven relationship. Five Joules due to a power of 5 W over 1 second and 5 Joules due to a power of 1 W over 5 seconds can be different and could possibly create a different physiological response.53 Energy Energy density = Energy/area Joules/centimeter2 The area is in reference to the area of the beam spot size. density or or Energy density = Power (J/cm2) Fluence density × Time or Energy density = Power × time/area Time of Seconds (s) Time spent giving the laser treatment. It is important to note how much time is exposure or spent per treatment point if applicable. Irradiation time Treatment Hour, days, weeks, It is important to note how often the treatment is applied as this could influence frequency etc. the final result. It is important when setting up or documenting a treatment you consider all the parameters. It is also important to note that many of the parameters are dependent on one or more variables and each other. One example of this is the impact of pulse modes drastically reducing the amount of energy emitted from the laser. For example, a 2 W GaAs laser is pulsed at 100 Hz: Average power=pulse rate×peak power×pulse width=100Hz×2W×(2×10−7s)=0.04mW Downloaded This contrasts2023­10­31 8:19output with the power A Your IP ismW of 0.4 195.113.14.2 at the 1000 Hz rate (Figure 13–7). Therefore, it can be seen that an adjustment of the pulse rate alters Chapter 13: Light Therapy, Katie Homan; Nathan Newman Page 8 / 47 the average power, which significantly affects the treatment time if a specified amount of energy is required. ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility It is important when setting up or documenting a treatment you consider all the parameters. It is also important to note that many of the parameters Charles University are dependent on one or more variables and each other. One example of this is the impact of pulse modes drastically reducing the amount of energy Access Provided by: emitted from the laser. For example, a 2 W GaAs laser is pulsed at 100 Hz: Average power=pulse rate×peak power×pulse width=100Hz×2W×(2×10−7s)=0.04mW This contrasts with the power output of 0.4 mW at the 1000 Hz rate (Figure 13–7). Therefore, it can be seen that an adjustment of the pulse rate alters the average power, which significantly affects the treatment time if a specified amount of energy is required. Clinical Decision­Making Exercise 13–2 A clinician is treating a postacute inversion ankle sprain with a HeNe laser. How can the clinician ensure that the amount of energy delivered to the injured area is relatively uniform? Figure 13–7. Continuous wave versus pulsed energies. The energy density or fluence of a laser is reported in the literature as joules per square centimeter (J/cm2). One joule is equal to 1 W × s. Therefore, energy density is dependent on (1) the output of the laser in mW, (2) the time of exposure in seconds, and (3) the beam surface area of the laser in cm2. The parameters should be accurately calculated to standardize treatments and to establish treatment guidelines for specific injuries. The intention is to deliver a specific number of J/cm2 or mJ/cm2. After setting the pulse rate, which determines the average power of the laser, the treatment time per cm2 can easily be calculated.11 TA=(E/Pav)×ATA=treatment time for a given areaE=mJ of energy percm2Pav=Average laser power in mWA=beam area incm2 For example: To deliver 1 J/cm2 with a 0.4 mW average­power GaAs laser with a 0.07 cm2 beam area: TA=(1J/cm2/0.0004W)×0.07cm2=175secondsor2.55minutes To deliver 50 mJ/cm2 with the same laser, it would only take 8.75 seconds of stimulation. Charts are available to assist the clinician in calculating the treatment times for a variety of pulse rates. It is broadly accepted that an inadequate irradiation time or irradiance (power density), which compose the energy density, will not create enough of a stimulatory effect to create a pathologic or biological response, but conversely too much irradiance or too long of an irradiation time can have an inhibitory effect or destructive outcome.40,49,51–53 This concept follows the Arndt­Schultz principle and can also be described as a biphasic dose response in which a stimulatory effect will only occur in a specific therapeutic window. As an example, Albertini and associates found that when using a 650 nm, GaAlAs laser, edema changes varied depending on the power setting, which affected the energy density. It was found that a setting of 1 J/cm2 (1 mW) and 2.5 J/cm2 (2.5 mW) reduced edema by 27% and 45.4%, respectively, but an energy density of 5 J/cm2 (5 mW) didn't produce any significant changes compared to the control group when all other variables were controlled (0.08 cm2, 80 seconds).49 The importance of the amount of energy applied to the tissue is well documented, but it is important to note that even though energy density is dependent on2023­10­31 Downloaded irradiance (power 8:19 Adensity) Your IPand irradiance time, no proven relationship exists between the latter variables when it comes to determining is 195.113.14.2 Chapter 13: Light if a particular Therapy, energy densityKatie Homan; will have Nathan a certain Newman biological Page 9 / are response. It is plausible that the irradiances or treatment times as independent variables 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility equally important parameters compared to the energy density as a whole in order for the desired response to occur.53 55 650 nm, GaAlAs laser, edema changes varied depending on the power setting, which affected the energy density. It was found that a setting of 1 J/cm2 Charles University (1 mW) and 2.5 J/cm2 (2.5 mW) reduced edema by 27% and 45.4%, respectively, but an energy density of 5 J/cm2 (5 mW) didn't produce any significant Access Provided by: changes compared to the control group when all other variables were controlled (0.08 cm2, 80 seconds).49 The importance of the amount of energy applied to the tissue is well documented, but it is important to note that even though energy density is dependent on irradiance (power density) and irradiance time, no proven relationship exists between the latter variables when it comes to determining if a particular energy density will have a certain biological response. It is plausible that the irradiances or treatment times as independent variables are equally important parameters compared to the energy density as a whole in order for the desired response to occur.53 Bolton55 found when using an 820 nm, pulsed GaAlAs laser to irradiate macrophages at the same energy density but different peak irradiances and times, different results were achieved when all of the other parameters were controlled. Specifically, greater fibroblast proliferation occurred when 800 mW/cm2 was applied for 3 seconds versus 400 mW/cm2 for 6 seconds even though the energy density (2.4 J/cm2) was the same. He also found greater cell proliferation occurred when 400 mW/cm2 was used for 18 seconds versus 800 mW/cm2 for 9 seconds even though again the energy density (7.2 J/cm2) was controlled. In both trials, the ineffective treatment also was shown to have no significant difference compared to the placebo laser treatment.55 In another study, Castano and associates also found that different parameters, despite having similarities, can create different biological responses.56 After inducing rats' knees with swelling, various laser parameters were tested and applied daily for 5 days. An irradiance of 5 mW/cm2 for 10 minutes was effective in reducing the swelling over the course of the testing period compared to an irradiance of 50 mW/cm2 for 1 minute that was not significantly effective despite having the same energy density (3 J/cm2). Conversely, they found 5 mW/cm2 irradiating for 100 minutes and 50 mW/cm2 irradiating for 10 minutes (both parameters eliciting 30 J/cm2) to be effective at reducing swelling over the course of the 5 days. There was not a statistically significant difference noted between these two groups. It is important to note that in this particular study the laser probe was held 10 cm from the treatment site, which is typically not recommended and could have affected the results. Nonetheless these studies indicate the importance of considering and reporting all variables involved with laser therapy.56 The frequency of treatment can also play a role in a tissue's physiological response. The accumulation of energy over time can have a positive or negative impact in the outcome, similar to any other parameter. The World Association for Laser Therapy (WALT) has published recommendations to help clinicians determine appropriate parameters for different pathologies. These recommendations were last updated in 2010. They recommend daily treatments for 2 weeks or laser treatments every other day for 3–4 weeks.57 Again, it is important to note that any change in any parameter (energy, power, irradiance time, beam spot size, wavelength, and frequency of treatment) could potentially change the outcome of the treatment.51 Further research investigating the relationship of the parameters and how they can impact treatment outcomes is needed. As previously indicated, effective physiological responses induced by LLLT have a therapeutic window. These dose dependencies have been seen when trying to induce anti­inflammatory effects,49,58,59 tissue or wound healing,60 or the promotion of cellular growth61 making determining effective parameters difficult. What makes things even more challenging is that it is possible that these therapeutic windows can vary for different patients, tissues, and parameters.62 Further adding to the complexity, it is plausible that different parameters are required for different phases of healing or treatment goals such as inflammation control, tissue repair, or pain control as some treatments might seek a stimulated response while others might want to induce an inhibitory effect. A positive LLLT response can be dependent on what particular phase of healing and the timing that the treatment occurs.65,66 Prior to the current WALT dosage recommendations, in 2001 Bjordal63 considered the target location of the laser treatment, parameters that were shown to create cellular changes in the laboratory trials, and the appropriate timing and frequency of a treatment based on laboratory trials when reviewing previous literature. Similarly, in 2003, Bjordal and associates69 considered multiple variables when creating suggested settings to determine the effectiveness of LLLT in chronic joint disorders. They considered the targeted tissue location and depth, energy loss estimations, appropriate anti­ inflammatory dosages, and the potential differences in absorption rates with different wavelengths, setting it apart from other studies and reviews. The authors tried to take all factors in consideration but cautioned that their dosages were hypothetical.69 Nonetheless, the concept of taking in account anatomical considerations, biological responses, and other parameters when determining appropriate LLLT dosages and parameters is important. To supplement their dosage recommendations, the World Association for Laser Therapy (WALT) also have recommendations for researchers on how to conduct meaningful research in the realm of LLLT.57 They have called for improved study designs including blinding, proper exclusion/inclusion criteria, randomization, and clearly stated parameters.57 Many researchers and authors have acknowledged there are many studies that use parameters outside the recommended range, have poor methodological protocols, or simply do not state all of the laser parameters making it Downloaded 2023­10­31 8:19 A Your IP is 195.113.14.2 challenging to compare studies and create conclusions.40,58,67,68 Chapter 13: Light Therapy, Katie Homan; Nathan Newman Page 10 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility Tumilty and associates67 investigated the effects of LLLT on tendinopathies and found twenty­five studies for their review. According to the authors, five of the twenty­five articles examined had a PEDro scale below six. More specifically seven of the twenty­five studies did not include patient blinding, important. Charles University To supplement their dosage recommendations, the World Association for Laser Therapy (WALT) also have recommendations for researchers onby: Access Provided how to conduct meaningful research in the realm of LLLT.57 They have called for improved study designs including blinding, proper exclusion/inclusion criteria, randomization, and clearly stated parameters.57 Many researchers and authors have acknowledged there are many studies that use parameters outside the recommended range, have poor methodological protocols, or simply do not state all of the laser parameters making it challenging to compare studies and create conclusions.40,58,67,68 Tumilty and associates67 investigated the effects of LLLT on tendinopathies and found twenty­five studies for their review. According to the authors, five of the twenty­five articles examined had a PEDro scale below six. More specifically seven of the twenty­five studies did not include patient blinding, in which the WALT guidelines recommend, and eleven of the studies reviewed were missing laser parameters, thus making comparisons between studies challenging. In addition, the authors concluded some studies used parameters outside of the recommended dosage guidelines. It is easy to see that LLLT dosage is very complex with a lot of different independent and dependent variables. There seems to be boundaries for the multiple different parameters in order for the treatments to be effective. However, despite the high magnitude of research studies that have tried to determine the appropriate parameters for effective treatments, there has not been one study that has been able to investigate all of the varying parameters synonymously. More human research needs to be completed to find the correct combination of parameters for different physiological responses, injury pathologies, and treatment goals. Clinical Decision­Making Exercise 13–3 The clinician is trying to calculate the dosage in J/cm2 of a GaAlAs laser treatment. What factors will need to be taken into account that collectively determines the correct dosage? Depth of Penetration Any energy applied to the body can be absorbed, reflected, transmitted, and refracted. Biologic effects result only from the absorption of energy, and as more energy is absorbed, less is available for the deeper and adjacent tissues. Typical wavelengths in light therapy range from 600 to 1000 nm in the current literature.52,53 What molecules absorb the light will be dependent on the wavelength of the light source.40 Typically superficial tissues will be treated by shorter wavelengths while deeper tissues will be treated by longer wavelengths.40,51 Wilson70 noted that the depth of light penetration has an inverse relationship to blood concentration. It has been specifically noted that below 600 nm the absorption by hemoglobin can play a large role in reducing the light penetration along with other factors in an animal population and in vivo.70,71 The 700–770 nm wavelength range is typically avoided due to limited biochemical activity.40 Water and fat content is thought to play a role in affecting light penetration at higher wavelengths.40,71 Exact penetration depths are difficult to determine as penetration abilities will vary not only in different species but also in different individuals and tissues.70 The current WALT guidelines indicate greater energy is needed for the GaAlAs lasers from 780–860 nm compared to the GaAs lasers at 904 nm. For all applications, the recommended energy for the lower wavelength range is doubled.57 Joensen and associates72 found that a superpulsed 904 nm, GaAs laser had better penetration abilities in rat skin compared to a continuous wave 810 nm, GaAlAs laser. However, they believe the difference in wavelength only accounts for a part of the penetration difference. They also believe a laser's penetration ability is dependent on if it is pulsed or continuous. For this particular study, not only did the lasers have different wavelengths and modes, but they also had different parameters with regard to peak power, power density, energy, and energy density. The authors noted how penetration differs due to these other parameters was not an area of investigation in their study.72 This is an area that has not been research thoroughly, indicating a need for further investigation, particularly in human applications. As indicated earlier in the chapter, absorption of HeNe laser energy occurs rapidly in the superficial structures, especially within the first 2–5 mm of soft tissue. The response that occurs from absorption is termed the direct effect. The indirect effect is a lessened response that occurs deeper in the tissues. The normal metabolic processes in the deeper tissues are catalyzed from the energy absorption in the superficial structures to produce the indirect effect. HeNe laser has an indirect effect on tissues up to 8–10 mm.11 The GaAlAs laser, which can vary in wavelength, but has a longer wavelength than HeNe lasers, is reported to penetrate 2–3 cm.48 The GaAs laser, which is naturally superpulsed and typically has a longer wavelength than HeNe and GaAlAs lasers, is directly absorbed in tissue at depths of 1–2 cm and has an indirect effect up to 5 cm (see Figure 13–2). Therefore, this laser has better potential for the treatment of deeper soft­tissue injuries, such as strains, Downloaded 2023­10­31128:19 A Your IP is 195.113.14.2 sprains, and contusions. Chapter 13: Light Therapy, Katie Homan; Nathan Newman Page 11 / 47 ©2023 McGraw Hill. All Rights Reserved. Terms of Use Privacy Policy Notice Accessibility The radius of the energy field expands as the nonabsorbed light is reflected, refracted, and transmitted to adjacent cells as the energy penetrates. The clinician should stimulate each square centimeter of a “grid,” although there will be an overlap of areas receiving indirect exposure. It is also important tissues. The normal metabolic processes in the deeper tissues are catalyzed from the energy absorption in the superficial structures to produce the Charles University indirect effect. HeNe laser has an indirect effect on tissues up to 8–10 mm.11 Access Provided by: The GaAlAs laser, which can vary in wavelength, but has a longer wavelength than HeNe lasers, is reported to penetrate 2–3 cm.48 The GaAs laser, which is naturally superpulsed and typically has a longer wavelength than HeNe and GaAlAs lasers, is directly absorbed in tissue at depths of 1–2 cm and has an indirect effect up to 5 cm (see Figure 13–2). Therefore, this laser has better potential for the treatment of deeper soft­tissue injuries, such as strains, sprains, and contusions.12 The radius of the energy field expands as the nonabsorbed light is reflected, refracted, and transmitted to adjacent cells as the energy penetrates. The clinician should stimulate each square centimeter of a “grid,” although there will be an overlap of areas receiving indirect exposure. It is also important to note that skin oils and pigmentation can affect laser penetration. CLINICAL APPLICATIONS FOR LASERS Because the production of lasers is relatively new, the biologic and physiological effects of this concentrated light energy are still being explored. The effects of low­level lasers are subtle, primarily occurring at a cellular level causing either stimulation or inhibition. Various in vitro and animal studies have attempted to elucidate the interaction of photons with the biologic structures. There are many different complex reactions, mechanisms, cellular components, and ions that are thought to play a role in the physiological outcomes due to photostimulation.73 It seems that the laser beam photons are absorbed by molecules and increase the energy level through the excitation of the electrons. This energy is absorbed by cytochrome c oxidase (CCO), a complex that is housed within the mitochondria and functions as the last enzyme in the respiratory chain 54,62,73,113 Albuquerque and associates62 found CCO expression increased after healthy rat anterior tibialis tendons were irradiated. They found at different wavelengths, different energies were more effective at various time points within 24 hours of irradiation. Crisan50 found that mitochondrial activity in human skin fibroblasts were significantly stimulated by pulsed 830 and 980 nm wavelengths compared to a control group 24, 48, and 72 hours after a treatment. It has been shown that laser irradiation can increase the production of adenosine triphosphate (ATP) within the mitochondria.74 Studies using a laser intervention have also documented an increase in cellular proliferation.75,76 It is thought that this reaction can be in part explained by the stimulated CCO in the mitochondria resulting in an increase of ATP along with other complex reactions allowing for cellular proliferation to occur. These possible physiological effects have led to thousands of studies examining the effectiveness of LLLT on wound and tissue healing, inflammatory conditions, chronic joint disorders, pain, and neurological disorders. Low­level lasers are best recognized for increasing the rate of wound and ulcer healing by enhancing cellular metabolism.13 Results from animal studies have varied as to the benefits on wound healing, perhaps owing to the fact that the types of lasers, dosages, and protocols used have been inconsistent. In humans, improvement of nonhealing wounds indicates promising possibilities for treatment with lasers. Wound Healing Applications The effectiveness of laser in wound healing was discussed in detail in Chapter 3. Early investigations of the effects of low­power laser on biologic tissues were limited to in vitro experimentation.6,16 Although it was known that high­power lasers could damage and vaporize tissues, little was known about the effect of small dosages on the viability and stability of cellular structures. It was found that low dosages (