Page 20 - Veterinary Laser Therapy in Small Animal Practice

6 Veterinary Laser Therapy in Small Animal Practice

are greenhouses green then? Probably because that’s proteins. Combined, they can quite literally “hold”
more aesthetically pleasing to the eye. But in principle, molecular oxygen (four molecules of O ). It is this iron
2
a green-tinted glass would act like a filter of green light, core that absorbs light very well, mostly because iron is
allowing through a greater proportion of what is left a very heavy element compared to the organic chemis-
(white light minus the green), which would therefore try (mostly carbon and oxygen) around it, and so it acts
be a more efficient illuminator of the chlorophyll. as a nice contrast agent, especially in the near-infrared
Well, the same holds with melanin. Darker skin con- close to its peak of absorption at 905 nm.
tains more melanin, which absorbs visible light more Lastly, an enzyme called cytochrome c oxidase
strongly, and also, as it turns out, near-infrared light. located on the membrane of the mitochondria inside
This is no accident. We have evolved skin to protect us your cells absorbs near-infrared light. Much like hemo-
from the sun’s light. Again, it is no accident that the globin, this enzyme absorbs principally because of its
majority of the sun’s light is in the visible and near- relatively heavy core of copper. Also like hemoglobin,
infrared range. In fact, only about 6% of the sun’s light this enzyme “carries” molecular oxygen, but this time
is in the ultraviolet (UV) range. The reason we care so within the cell as it works through the respiratory chain
much about this is that UV is ionizing light, meaning in the process that produces adenosine triphosphate
that with a single photon it can break a chemical bond (ATP), which the body uses as chemical energy.
and cause cellular damage, or worse, a genetic mutation. More on what happens next – next, but by and large,
That is worse because if one of your cells dies, you have that’s it. Nothing much else in the body absorbs enough
10,000,000,000,000 more to back it up. If one of your light, at least the colors of light that can get inside the
cells mutates, however, that can lead to a whole mess of body, strongly enough to do anything meaningful
altered cells that multiply faster than normal cells and chemically. That makes things simpler to understand,
spread through the bloodstream to other places where actually. The other keywords you’ll hear throughout the
they multiply further. This is called cancer. book, things that clearly have a positive healing effect
But back to the infrared. We’ve evolved with on individual cells and bulk tissue and were triggered by
melanin to protect us from sunlight, but that protec- light, must have gotten their power from some process
tion wanes as you creep from the visible to the infra- that these four targets started when they absorbed the
red, and by the time you get to about 900 nm and light. So, what are some of those things?
greater, absorption by melanin disappears and the skin
is virtually invisible. So, for the shorter wavelengths, As a veterinarian, I would like to say that there are
melanin acts like a barrier to light passing through the some cells and molecules that ARE susceptible to
body, but as wavelength increases, its effect becomes light that doesn’t otherwise penetrate well into the
negligible. body. For example, we know that
Absorbers #1 (water) and #2 (melanin) absorb best vitamin D synthesis depends on UV
on opposite sides of the spectrum: water on the longer light incident on the skin. Some
wavelengths (> 950 nm) and melanin on the shorter chemical compounds such as bilirubin
wavelengths (< 750 nm). This creates a valley in the can lead to photosensitization. And of course, the
spectrum where the body is most transparent. Light in cells in our retina transform light into electrical
this region can make it past the skin without burning a impulses. But like he said, most of the effects in the
hole and into the body without “searing the meat.” For cells come from these principal interactions.
that reason, we call it the “therapeutic window.”
Regardless of what other absorbers we talk about
next, their action outside this window is pretty much 1.4 Absorption leads to …
pointless, because even if their absorption led to the
growth of magic pixie dust in your cells, you really 1.4.1 Heat
couldn’t get enough light there to initiate the magic.
Fortunately for us, targets #3 and #4 do in fact absorb Heat is defined as the energy contained in a set of
well in this window. moving particles. So if anyone asks you how hot a
Hemoglobin is at the heart of red blood cells. It is single particle is, you yell at them. Heat is collective
comprised of an iron core and four “claws” of folded motion. Why would it be hard to believe, then, that

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