As the volume of clinical evidence and anecdotal support swells, many chiropractors are now on the verge of adding a laser to their toolkit.
Vendors will often differentiate their products on the basis of the strength of their brand, the volume of supportive research, training and the unique features of their product. As helpful as this information may be, it does not clarify what specifications influence the therapeutic efficacy of a laser device; nor does it clarify what specifications are relevant for a particular type of practice.
This article provides information you won't easily find elsewhere; namely how to determine what kind of laser device you need and have the ability to compare products side-by-side on an objective basis. Laser therapy is extremely versatile, so let's confine the discussion to laser-only devices (rather than combined devices such as laser / electrotherapy) used in a "typical" chiropractic setting dealing with neuromusculoskeletal conditions.
There are many factors that influence your product choice. Let's consider the regulatory, therapeutic and nontherapeutic factors.
Regulatory Considerations
Check if the governing board in your state places restrictions on lasers in your practice. Some will require that the device be FDA cleared; others not. California recently introduced this requirement and it is foreseeable that other states will follow in time. A device that does not have medical device clearance is not necessarily less effective. Without FDA clearance, a vendor may not make claims of a medical nature and may only sell for research purposes. If a device is not FDA cleared, ensure that it complies with the FDA laser safety standards 21 CFR 1040.10 and 1040.11.
Therapeutic Factors – Laser Light Parameters
Aside from the dose and frequency of treatment, the only factors that determine therapeutic efficacy are the properties of the laser light emitted by the device. These are the wavelength in nanometers (nm), power in watts or milliwatts (W, mW) and the modulation (or pulsing) of the light.
Class 3 or Class 4? The "class" of a laser is a safety rating system developed by the FDA for laser devices. A higher number implies a greater risk of injury, and consequently determines the required safety measures that must be employed in its construction and use. Anything with a laser inside it is assigned to a class, even a laser printer. The class is determined by the maximum laser output power of the device and does not equate to therapeutic efficacy. Class 3 devices range from 1mW to 500mW. Class 4 devices emit more than 500mW. There is no upper limit on class 4.
Class 4 devices are unfairly criticized as being dangerous, with the suggestion that you can burn your patients. This is nothing more than a fear tactic spread in an attempt to gain competitive advantage. If used as directed, class 4 devices are no more dangerous than any other device in your practice. What is true is that there are more stringent safety requirements. Reflective surfaces, doorways and windows that can leak light are examples of factors that may limit where you can use such a device in your practice.
Vendors of high-power (class 4) therapeutic lasers will often state that more power is better, and that with more power, the same dose can be applied in shorter time. Industry consensus is that increased power is often advantageous in pain management, but this is not true for all conditions.1-2 Therefore, it is essential to be able to modify the output power of a class 4 device. Power control of class 3 devices is desirable for the same reasons, but not essential due to their lower maximum power.
Similar results can often be obtained with lower power levels at the expense of longer treatment time (or more treatments). Some claim that class 3 devices are too weak to produce results, but this view conflicts with favorable research findings over the past 30 years, most of which involved class 3 devices.
A treatment dose using laser is the total energy delivered to the tissue and is calculated as the product of average power and time. Some manufactures specify the peak power as well as the average power. Take care to ensure you are using the average power specification when comparing different devices. Superpulsed lasers are a notable exception, in that their penetration is around twice that of a continuous or pulsed device at the same power.3 So, for super- pulsed lasers, double the specified average output power for comparative purposes. As might be expected, device cost increases with output power.
Wavelength: Cells of various tissue types contain photoreceptors3 that convert light energy at specific wavelengths into signals that can stimulate biological processes.4-5 In addition, chromophores within cells cause them to absorb light at specific wavelengths, which is converted to heat. This heat is reradiated in the form of fluorescence and is also consumed in photobiochemical reactions.
Most laser therapy devices produce light in the red spectrum (typically 630-660nm) and/or near-infrared spectrum (800-1,000nm). Some newer devices use violet lasers (405nm), but other than their antibacterial properties, there is little scientific evidence of their therapeutic efficacy.
Infrared devices provide topical and deep heating that relieves pain, increases joint mobility and relaxes muscles. Local heating also increases circulation to stimulate healing. The absorption properties of various tissue types are well-known, and therefore it is simple to determine what wavelength will produce the greatest heating effect. However, you will be using the laser to treat patients, so the laser light will pass through skin, fat, muscle, vascular tissue, connective tissue and bone. As a result of the averaging effect of passing through various tissue types, laser wavelengths from 800-1,000nm produce similar results. Some devices include 830nm and 980nm lasers in order to improve coverage.
Whereas laser devices in the infrared range are available with power output of tens of watts, those in the red spectrum (630-660nm) only have an output power of tens of milliwatts. This does not mean they are thousands of times less effective than their infrared cousins. The modality of operation is totally different, and red lasers are best seen as a different kind of medical device. Similar technology, but a different tool.
These low-power red lasers do not deliver sufficient energy to elevate tissue temperature in order to stimulate heat-induced biological reactions. Instead, the light is consumed directly by biological process that stimulate cellular repair, growth and proliferation.6 Red laser light also appears to have a significant effect on nerve function, as observed by improved motor control and joint function. Although the mechanism is not yet fully understood, the clinical evidence prompted the FDA created a new medical device category of "NHN" for light therapy devices that are "non-thermal instrument with non-heating effect."
Modulation or Pulsing: Pulsing switches the light output on and off repetitively. The frequency or speed of pulsing can be very slow and observable, or much faster than the eye can detect. Devices that support pulsing typically cover the range of 1-10,000Hz (10,000 pulses per second). Clinical evidence has demonstrated that pulsing the laser light can improve outcomes over a continuous illumination, and that the particular frequency of pulsing also affects treatment outcomes.7-8
What is not yet known is why pulsing makes a difference and what particular frequencies are best for a particular condition or tissue type. Frequencies are often provided in courses and in literature for a range of treatments. Although these frequencies may have years of clinical use that supports their efficacy, there is still no guarantee that they are the best frequencies for those treatments.
As the science of laser therapy evolves, we can expect to gain more understanding of pulsing and how to make the best use of this capability. In order to be able to apply this knowledge as it unfolds, ensure that your laser has some flexibility to accommodate new pulse settings, either via the panel or through software updates.
Nontherapeutic Factors
Other factors such as portability, size and weight, corded or cordless operation, ease of use and cost factor into the buying decision. They matter to you, but not to the patient. Other than cost, these factors are influenced by the modalities used in your practice and to some extent by personal taste.
Size and weight are important considerations. It is not uncommon to use the laser with most treatments, so the associated occupational strain should be considered.
| Take-Home Considerations There are many areas of overlap, so the following statements are a guide, rather than a definitive position regarding therapeutic lasers:
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While portability might seem unnecessary for an office-bound practitioner, if you have multiple treatment rooms or a device that is shared, then one that requires an outlet can be an encumbrance. Portability usually carries a cost premium and thus needs to be weighed up against other factors. If you're looking at a portable unit, ensure that it can either be used while charging or has sufficient battery capacity to last for a typical day of use.
A cable between a base unit and treatment head that drags across your patient can be a distraction to them, and an encumbrance to you if you are moving around your patient during treatment. Bear in mind that cordless units can be heavier as a result of having everything in the treatment head.
Other than the initial purchase cost, be mindful of hidden costs. Many lasers are recommended for recalibration on an annual basis. For portable units, check the expected battery life and replacement cost, and if the unit needs to be returned to the manufacturer.
Laser diodes wear out like any other light source. Laser diodes typically have a life of more than 6,000 hours, although failure before that time due to non-ideal operating environment is possible. Laser diodes are also more susceptible to random failure than other semiconductors. For a device that may well be with you for 10 years, it is worth knowing what it costs to replace the laser diodes if they fail. In addition to factoring these costs into your budget, check if a loaner is available while yours is in for repair. You are likely to become quite dependent on your laser and will not want to be without it.
References
- Larkin KA, Martin JS, Zeanah EH, True JM, Braith RW, Borsa PA. Limb blood flow after class 4 laser therapy. Lasers in Surgery and Medicine, 2012;47:178-83.
- Karu TI, Pyatibrat LV, Ryabykh TP. Nonmonotonic behavior of the dose dependence of the radiation effect on cells in vitro exposed to pulsed laser radiation at lambda = 820 nm. Lasers in Surgery and Medicine, 1997;21:485-92.
- Enwemeka CS. Quantum biology of laser stimulation. Laser Therapy, 1999;11:47-52.
- Photoreceptor cell. Wikipedia: http://en.wikipedia.org/wiki/Photoreceptor_cell
- Welch AJ, van Gemert, MJC. Optical-Thermal Response of Laser-Irradiated Tissue, 2nd Edition. Springer Science + Business Media B.V., 2011.
- Hawkins D, Abrahamse H. Influence of broad-spectrum and infrared light in combination with laser irradiation on the proliferation of wounded skin fibroblasts. Photomedicine and Laser Surgery, 2007;25:159-69.
- Hasmi JT, Huang Y-Y, Sharma SK, Kurup DB, De Taboado L, Carroll JD, Hamblin MR. Effect of pulsing in low-level light therapy. Lasers in Surgery and Medicine, 2010;42:450-466.
- Oron A, Oron U, Streeter J, De Taboada L, Alexandrovich A, Trembovler V, Shohami E. Near infrared transcranial laser therapy applied at various modes to mice following traumatic brain injury significantly reduces long-term neurological deficits. Journal of Neurotrauma, 2012;29:401-7.
Andy Hewitson, the founder and chief technology officer of Avant Wellness Systems, a developer and manufacturer of therapeutic devices, received his BSc in engineering in from the University of Natal-Durban (South Africa). He applies his broad technical competencies to the research and development of new therapeutic laser technologies. You can reach him with questions and comments regarding this article at
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