Laser Inhibition versus Laser Stimulation (LI vs. LS)
It’s important to realize that photobiomodulation is multiphasic in its dose response, meaning that stimulation can become inhibition simply by transferring additional energy to the targeted tissues until tissue inhibition occurs - and with contunued dosing stimol. Most of the time we want to stimulate targeted tissues, such as when healing is our primary goal. There are other times when we would rather choose to inhibit tissue function, which is we work to reduce or inhibit metabolism in targeted areas that are causing pain, especially in nerve tissues. Pain will be better controlled and mitigated through the inhibition of targeted tissues - this represents the upper end of the multiphasic dose response in photomedicine, and there are times when this will be our primary goal. Experimental studies of non-ablative laser irradiation have been done on peripheral nerve morphology, physiology, and function to learn more about treatment parameters for pain relief. The findings were then evaluated with special reference to the neurophysiology of pain and implications for the analgesic effect of inhibitory laser therapy.
So… When does laser stimulation end and laser inhibition begin? Again, we have to rely on tissue variability factors, all else being equal.
Almost all Initial laser therapy studies were based on muscle tissues in a Petri dish, with extremely low levels of energy being administered. In this setting it is easy to understand why any therapeutic laser dose higher than 2J to 4J/cm2 will produce an inhibitory response and eventual tissue destruction, because the muscle tissues are completely vulnerable to any type of energy transmission no matter how low the dosage. The very same muscle tissues in a real-world situation will be highly protected by skin, subcutaneous, and other tissue layers. Figuring results based on primary tissue variability factors suggests that a much higher laser dosage will be required for stimulation and an even higher dosage required for inhibitory factors.
To what degree laser stimulation (LS) will occur and when it becomes laser inhibition (LI) is dependent again on tissue variability factors other treatment factors such as contact versus non-contact, continuous wave versus pulse mode, single wavelength versus multiple wavelengths, maximum laser output power, duration of treatment, and more.
It is the responsibility of each therapy laser practitioner to accurately diagnose each patient, and taking into account all variables, come up with optimal treatment protocols for individual patients. As stated before, the preset protocols found on all therapy laser programs are simply guidelines, or baseline figures determine for the most vulnerable of all patients.
HOW MUCH IS TOO MUCH?
Therapy lasers offer us many choices in the treatment of pain, amongst them has been treatments involving neuro-stimulatory effects and treatments involving neuroinhibitory effects. Researchers at NASA use a measurement of luminosity to define the amount of energy the sun can emit. Luminosity is recorded in Joules per second internationally. The sun's luminosity is about 3.8 x 1026 Joules continuously (that’s 10 with 26 zeros following). In other words, in one second the sun generates more energy than has been used in all of mankind’s history!
Discounting solar energy absorbed by the atmosphere, it is correct to say that during one hour of sunbathing every exposed square centimeter of the body will receive many hundreds of Joules per centimeters squared of solar energy (300Jcm2+) with 41% of the energy in the infrared range, 40% in the visible range, and the rest in UVA, UVB, and other more energetic waves.
Using solar radiation as an example, it is correct to assume that inhibitory dosages in laser therapy can reach 100Jcm2 or more without causing permanent tissue damage.