Page 49 - Veterinary Laser Therapy in Small Animal Practice

Tissue healing 35

with a 150 mW power device. They had calculated a 6% 5.6 Treating contaminated and
penetration of the power to the level of the spine for the infected tissues
wavelength used. So patients with intervertebral disk
disease (IVDD) may also benefit from LT, shortening The clinical outcome of a tissue infection depends on
the post-recovery period and as part of conservative two types of factors: those that affect microbial survival/
management if indicated, but of course we would need proliferation/toxin production and those that affect the
higher power to improve penetration to that level in host’s immune response. We have already talked about
our patients and to cover a broader area in a clinically how LT can improve immune functionality. In vitro and
reasonable time. in vivo, LT increases polymorphonuclear cell activity,
Laser has shown promising results in stroke, by which is translated as an increase in phagocytic capac-
improving cerebral blood flow and neurogenesis and ity, reactive oxygen species (ROS) production, and a
decreasing apoptosis after experimental hypoxia of better ability to kill microorganisms. [49–52] Bacterial
the central nervous system (CNS). [172] Another mech- challenge increases oxygen consumption by phagocytes
anism of action is the increase in cerebral adenosine over 50 times, and oxygen supplementation has been
triphosphate (ATP) stores induced by laser, especially proven to decrease the risk of surgical site infection in
by pulsed radiation, which seems to be more effective humans. [177]
than continuous wave radiation to treat the CNS. [173] So LT can enhance the patient’s own responses,
Transcranial infrared laser therapy improved clinical increasing the ability to heal and fight infection by
(behavioral) rating scores after experimental strokes modulating the leukocyte response, but could it also
in rabbit and rat models – only if laser treatment was affect microbial survival? And if the answer is yes,
initiated up to 6 h post-embolization in the rabbit does LT promote microbial growth or inhibit it? Does
model, [174] but at 24 h post-stroke in the rats. [175] You it depend on the parameters of irradiation? Does it
can read some more about studies of LT for neurologi- depend on the microbial species, since Gram-positive
cal problems in Chapter 8. and Gram-negative bacteria have different morphology
So, in conclusion, there is quite some evidence that and bacterial wall structures?
LT can improve nerve healing and survival in both Some reports describe a decrease in the number of
central and peripheral nervous tissue, but it is no sur- pathogenic bacteria – but wait, this is not exactly the
prise that reviews of this effect on nerve healing and same as saying LT is antimicrobial, which by defini-
recovery again point out how “despite the potential tion (American Society of Microbiology) would imply
benefit of the use of lasers on nerve repair, further killing of at least three logs (99.9%) of a planktonic
double-blind controlled clinical trials should be con- microbial population, and it does not mean it will steri-
ducted in order to standardize protocols for clinical lize a wound. However, decreasing bacterial burden is
application.” [176] an important benefit when we are using LT to help in
the healing/analgesia of a wound. We may think we

If you had asked a neurologist 20 years ago, “do injured nerves regenerate?” the answer would have been a
resounding “no.” But not anymore. Regardless of how you may have to redefine the word “regenerate,” where there
was no signal between two CNS cells, we can now repair the chain in such a way as to get that signal back. And not
just on the periphery. There is some ground-breaking work being done on laser therapy of the brain
that merits some serious attention. And though I will echo María’s last quote here, cautioning against
the jump to any major conclusions, I will also bring up the example of fire. If we had waited to use fire
until we understood the ins and outs of combustion, we would literally still be in the Stone Age. As
much as it pains me to say this, the world was pioneered not by physicists, but by engineers: people
who care less about how/why it works, and more THAT it works. Once we convince ourselves that it is safe to treat
a particular condition, we should push toward treating it. It is our responsibility to continually go back and
understand the “why,” but to wait for the detailed mechanisms to be uncovered is to deny potential benefit to your
patients.

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