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Class IV Therapy Lasers Maximize Primary Biostimulative Effects

This new class of therapeutic lasers of laser therapy delivers higher-powered penetrating infrared energy to deeper target sites, as well as shortening treatment times for wide area applications.
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In this article, Drs. Phillip Harrington and Julian Vickers present the unique aspects of the Class IV therapeutic laser. This type of laser is fairly new on the therapeutic laser scene and has been creating a great deal of interest.

William J. Kneebone, CRNA, DC, CNC, DIHom

A rapidly growing number of progressive health care pro-viders are adding Class IV therapy lasers to their clinics. By maximizing the primary effects of the photon-target cell interaction, Class IV therapy lasers are able to produce impressive clinical results and do so in a shorter period of time. A busy office interested in providing a service that helps a variety of conditions, is cost-effective, and is being sought out by an increasing number of patients, should give a serious look at Class IV therapy lasers.

Background of Therapeutic Lasers

First theorized by Albert Einstein in 1916, and invented by Theodore Maiman in 1960, the laser has become one of the most beneficial medical inventions used in modern society. For the clinician, the most exciting use was first discovered by Hungarian physician Endre Mester, who performed experiments on cancerous tumor in rats. He found that although the laser didn’t kill tumor cells because it was underpowered for that purpose, it accelerated wound healing in the surgical sites of the experimental rats, as well as causing the shaved hair to regrow more quickly.

Therapy lasers have been used and researched extensively in Europe for more than 30 years. However, the United States Food and Drug Administration (FDA) only cleared a low level laser in 2002, and the first class IV therapy laser in 2003. Low Level Laser Therapy (LLLT) and it’s known effects have already been reviewed extensively in this journal. The most important clinical and therapeutic difference between Class IV Laser therapy and LLLT is that the Class IV is able to produce a primary biostimulative effect on deeper tissues than lower powered lasers— while also producing substantial secondary and tertiary effects. The FDA approved indications for use of Class IV laser include the following:

  • relief of muscle and joint aches, pain and stiffness;
  • relaxation of muscles and muscle spasms;
  • temporary increase in local blood circulation; and
  • relief of pain and stiffness associated with arthritis.1

Laser Classification

Lasers are classified by output power and are a hazard to the eye, with the potential for thermal injury being the primary mechanism. The Maximal Permissible Exposure, or MPE, is the level of laser radiation to which a person may be exposed without hazardous effects to the eye or skin. A system of hazard classification has been developed and is part of the ANSI Standard and State Regulations, however it is usually more convenient to establish safety controls based on the laser class than use of the exposure limits. In general, Class IIIa lasers have a power output of 1 to 5 milliwatts (1-5mW), Class IIIB lasers output power up to 500 mW, or 0.5 watts, and Class IV lasers include all of those with power output higher than 0.5 watts (500 mW).

The classification scheme makes no distinction between the Class IV therapy lasers, cosmetic and hair removal lasers, surgical lasers, and a military laser capable of shooting down a satellite. All of these are greater than 500 mW, and therefore all of them are Class IV. Lumping together every laser with power output greater than 500 mW is somewhat unfortunate, and has led to misunderstandings and discussions on several state physician licensing boards. One state chiropractic board first balked at the notion of its members using Class IV lasers, assuming that the intended usage was hair removal or a cosmetic procedure. However, after proper education and demonstration with a Class IV Therapy Laser, the board unanimously approved the use of such devices when used in a manner consistent with the scope of practice.

Class IV Therapy Laser Specifications

The most common Class IV therapy laser uses a Gallium-Aluminum-Arsenide (GaAlAs) semiconductor diode to produce infrared laser beams capable of deep penetration into tissue. The diodes may produce a continuous wave, or pulsation frequencies of 2-10,000 Hz with a 50% duty cycle. Typically, the laser diodes are housed in a control unit, and the infrared laser beams are carried by a fiber optic cable, through which coherence is maintained. The beam produced by a Class IV therapy laser is not collimated; it is allowed to naturally diffuse at a 10-12º angle. Beam sizes will range from 10 to 25 millimeters in diameter giving spot areas of 0.8 to 5cm2. Common power densities range from 0.4 to 3 W/cm2.

Wavelength is the main determinant of the laser’s depth of penetration into the tissue. Hemoglobin and melanin absorb photons at lower wavelengths and water absorbs those of higher wavelengths. There is an optical window around 790nm, where the laser photons are least absorbed by these three components and therefore penetrate the deepest. These deep penetrating infrared lasers are ideal for pain management therapy. Other factors affecting the depth of penetration are the technical design of the laser device and the treatment technique used.

Laser light attenuates the further from the surface it penetrates until it reaches a point at which the laser photon density is so low that no biological effect of the light can be measured. The biologically effective depth of an infrared therapy laser—for primary photon-tissue interactions—is conservatively stated as four centimeters. Secondary and tertiary photobiomodulation effects, as well as systemic effects, will be observed at a greater depth.

Primary, Secondary, and Tertiary Effects

The primary response is elicited when photons emitted by the laser reach the mitochondria and cell membranes of low lying cells such as fibroblasts where the energy is absorbed by chromophores and is converted to chemical kinetic energy within the cell. These primary effects are very predictable and are produced only by phototherapy. Chromophores absorb laser photons with wavelengths between 400 and 1100 nanometers, with those in the 790nm neighborhood being the deepest penetrating, as discussed earlier. Photons incident on tissue will reflect, absorb, transmit, or scatter. With a Class IV infrared laser, the scattered photons create an egg-shaped volume of treated tissue. The effective depth of penetration is roughly four centimeters, meaning that the primary interaction of photon with target cell will occur through that depth.

Secondary reactions lead to the amplification of the primary actions. A cascade of metabolic effects result in various physiological changes at the cellular level—such as changes in cell membrane permeability. Calcium is released from the mitochondria resulting in changes of intracellular calcium levels. This stimulates cell metabolism and the regulation of signaling pathways responsible for significant events required for wound repair such as cell migration, RNA and DNA synthesis, cell mitosis, protein secretion, and cell proliferation.

Last updated on: January 26, 2012
First published on: September 1, 2008