Page 115 - Veterinary Laser Therapy in Small Animal Practice

CHAPTER 8

Different flavors (frequencies) for different tissues

The real question is not whether machines think but perform. Narrow down some useful effect whose
whether men do. amplitude can be measured, and then, for a given cell
— B.F. Skinner line, “turn one of the knobs at a time” and record the
differences. Karu (and others) did this first with the
You are clinicians, so it is overtly intuitive to you that dose “knob,” showing lots of peaks and valleys in the
2
there are some fundamental differences between bone, response curves from 0.0007 J/cm all the way up to 50
2 [203]
muscle, connective tissue (tendons/ligaments), dermis, J/cm . We talked about this study back in section
and the other tissue types in the body. It should be 6.5 when we discussed the differences between in vitro
equally obvious, then, that you probably need differ- and in vivo experiments and how people often mistak-
ent “flavors” of light to optimally target each of these. enly apply the Ardnt–Schultz law and assume that “too
Unfortunately, only a minute percentage of the research large a dose is harmful.”
literature covers these differences. Instead, research is Her team went one better and repeated this same
focused on either uncovering new physiological ben- experiment with a different cell line and saw even more
efits in the laboratory or quantifying known benefits in different behavior, uncovering the idea that different
the clinical setting. For ease of research and to increase cell types react differently to changing parameters. [268]
sample size, both of these sectors tend to focus their Then she went even further, and started turning differ-
efforts on a single parameter-set, so that they are using ent “knobs.” This time it was pulse frequency vs. the
the same power, dose, wavelength, frequency, treat- continuous wave (CW) lasers she had been using.
ment time, etc. Undoubtedly they’ve referenced some For a given cell line, they varied the pulse frequency
previously successful study to decide which single and noted the change in behavior of the measured
parameter-set to use. But this leaves the real-world cli- effect (they used chemiluminescence in one study, cell
nician a little wanting … adhesion in another, and more). And we are not talking
about small percentage point differences. They noticed
8.1 Evidence that tissue type matters effects that differed by FACTORS OF TWO depend-
ing on the pulse frequency of light used. Further down
Those that have truly studied laser to the core have the rabbit hole, they trialed this for several cell lines
noticed a distinct variation in effect as the parameters (mouse, human, etc.) and each time noticed differences
are modified. First (and most famous) to make this in behavior based on pulse frequency used. [269]
observation was Tiina Karu, who (as you may be able to This really let the cat out of the bag, from a clini-
tell from the numerous references to her work through- cal standpoint. We spent entire chapters in this book
out this book) has done the most significant work in showing that dose is ALWAYS going to vary within
this industry (and as a fellow physicist, the “godmother” a given treatment volume depending on the type of
of laser therapy wins my favor). anatomy, amount of scatter and absorption, and treat-
At its heart, this is a fairly easy experiment to ment technique. So the best we can do is make some

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