Page 21 - Veterinary Laser Therapy in Small Animal Practice

Light is just the catalyst 7

the primary action of light (a wiggling electromagnetic that matter has, the molecules will vibrate along those
wave) when it is absorbed by (i.e. transfers all of its directions.
energy to) a slab of matter (a bunch of really light par-
ticles attached by very “boingy” springs) is the genera- 1.4.3 Physical chemistry
tion of heat. Things that move (or in this case vibrate)
cause – or in fact are defined as – heat. And I hate to But changing shape, when it comes to molecules, means
ruin the surprise, but that’s pretty much all infrared changing chemistry. Remember, if two molecules don’t
light does in the body: it creates little packets of heat fit, they don’t bond. And things that didn’t fit naturally
where it gets absorbed. can fit after being heated. In general, by changing the
I forgot to tell people who sell lasers to put their shape of one part of a molecule, even slightly and even
earmuffs on. Because they have been fighting against over a very short timescale, you can cause the molecule
the notion that healing comes from heating the tissue to shed parts of itself or grab onto new things. This is
for over a decade now. They fight against people who biochemistry at its very heart. Not a general rise in tem-
sell shock wave units or transcutaneous electrical perature across bulk tissue, but lots of microscopic heat
stimulation (TENS) or the skeptics who cling to the sources that change what is and isn’t bonded at a very
“nothing more than a heat pad” argument. And now small point in the body.
I’m saying it’s all about heat? You should probably So when you have long chains of enzymes that have
stop reading at this point if that’s all laser therapy is lots of parts in their synthesis or consumption pro-
about, right? cesses, small changes can have very big impact, in good
Not so fast. The key words here are “little” and ways and bad.
“where.” To give some perspective, let’s talk about the
scale of things. Take 1 joule of energy. That’s about 1.4.4 Shapeshifting examples
as much light as would hit your face in 12 seconds if
you were 20 meters away from a 100 watt light bulb. For a water molecule, that means the O-H bonds will
In those 12 seconds you would be hit with about bend and twist and stretch and contract. Since water is
16,000,000,000,000,000,000 pieces of light and not even in liquid form, and being that all the water molecules
notice a bit of warmth from it. So when each of those in a given area are vibrating to the same frequency of
pieces of light gets absorbed, a very very small amount light, these minor absorptions lead to more and more
of heat is transferred. That said, cells are very small resonance that propagates throughout its volume and
things. And molecules are even smaller. cascades into micro-pressure waves.
It turns out, then, that a small piece of light has a For a hemoglobin molecule, the absorption in the
pretty sizable effect on a small piece of matter like a iron core creates heat that propagates to its protein
water molecule. And as light shines, these little photons “claws,” changing their folded shape. This is the same
are getting absorbed at different rates at various depths shape that naturally holds on tight to oxygen molecules.
in the body. So what though? What happens when they A slightly deformed shape holds on a little less tightly
do get absorbed? to that oxygen molecule. The claw doesn’t naturally
hold on very well to a nitric oxide (NO) molecule. Even
1.4.2 Changing shape though N-O is pretty similar in shape to O-O, the body
is smarter than that and so NO–hemoglobin binding is
First, you have to understand that the main way chem- usually very weak. But add a little heat and the claw’s
istry works (i.e. the way that two molecules combine) shape might be a little more likely to bond.
is a very sensitive, physical lock-and-key mechanism. For cytochrome c oxidase, at one point in its cycle it
Things that fit together nicely (both spatially and elec- “accepts” an oxygen molecule, then transports it, then
trically) tend to bond together. If they don’t fit, they releases it to another enzyme. Add a little heat – in the
don’t bond. form of light absorption by that copper core – and the
Second, you have to understand what heat does to molecule may do this a little faster.
an object, any object no matter how small: it causes I’ve posed all this very hypothetically. After all,
that object to change shape. Remember, heat is just we can’t see these individual molecules change
energy in movement. So whatever degrees of freedom shape in the femtoseconds (10 −15 s) it takes for the

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