Page 27 - Veterinary Laser Therapy in Small Animal Practice

Blood and light 13

The exact same thing works in the opposite direction.
To see how this works in the tissues, where hemoglobin air, oxygen from the air gets absorbed into the
has all four oxygen molecules bound, look again at the blood, and that blood travels through the vessels
unique shape of the hemoglobin dissociation curve to a certain area. At this point, some of the blood
(Fig. 2.1). Fully oxygenated blood is on the top right of releases its oxygen to the tissue. Oxygen then
this curve (near 100% O saturation). As you lose one make its way from the outside to the inside of the
2
oxygen molecule (equivalent to 25% of a single hemo- cells and migrates to the mitochondria, where it
globin molecule’s capacity), you move left and down on is used as an electron acceptor in the respiratory
the curve toward 75% saturation. At that point, you can chain of enzymes whose final product is adenosine
see that the curve is a much more slippery slope, and triphosphate (ATP), the chemical currency
so the release of oxygen molecules two, three, and four the cells use to store and spend energy in their
(equivalent to moving to 50%, 25%, and 0% saturation) physiological reactions. Laser therapy can enhance
happens much more quickly. this process in three ways.
Why, you ask? Well this is chemistry, remember, and
chemistry is all about the shape of molecules. When • Enhancement #1: light therapy can increase
one of hemoglobin’s claws binds to an oxygen molecule the local circulation, either by causing mini
(or releases it), the shape of the rest of the molecule pressure gradients along the path, or promoting
changes in such a way that oxygen is more likely to be vasodilation via localized NO release (wherever
caught (or released) by the other claws. But what did the light is absorbed).
we just finish discussing in Chapter 1 about how light • Enhancement #2: light therapy can trigger
interacts with these complexes? Light absorption in hemoglobin dissociation, and therefore more
the iron core (heme group) of hemoglobin will cause a efficient release of oxygen from the blood to the
short-lived, tiny temperature change in the molecule. affected tissue.
But that’s all it takes. Not only does it take just a tiny • Enhancement #3: light therapy can stimulate the
bit of heat for a short time to trigger one of these claws mitochondria in the cells to make better use of
to change form slightly, but if you do that just once oxygen, producing more ATP and causing (either
(and force the first of the claws to release its oxygen), directly or indirectly) an increase of NO in the
a cascade of oxygen release will follow. This is a four- extracellular environment.
for-one efficient process that can be triggered by just a
little bit of light. The intervention of light does not fundamentally
change the natural process. Instead it enhances
the process at several steps along the way and in
Summary from a a variety of different ways. All roads lead to more
different perspective chemical energy for the cells, given the same input
of oxygen through the nose.
A quick summary is necessary here before we start Now you’ll read about all the wonderful
talking about the wider effects of laser. The goal of secondary and tertiary effects that come when
laser therapy is to enhance the natural processes the cells of the body have a heightened ability to
of the body and its cells. When we breathe in function.

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