Page 67 - Veterinary Laser Therapy in Small Animal Practice

Light’s path to all these places in the body 53

Spectrum of solar irradiance
ASTM G173-03 Reference Spectra
(Power density at each wavelength)
0.18

0.16

0.14
2 nm -1 )
(mW cm - 0.11

Spectral irradiance 0.07
0.09

0.05 ASTM G173-03 Reference Spectra

0.02

0
250 400 550 700 850 1000 1150 1300 1450 1600 1750 1900 2050 2200 2350 2500 Figure 6.9 Solar
{ { NIR by National Renewable
{ {
Ultraviolet Wavelength nm irradiance data recorded
Visible Infrared Energy Laboratory. [195]

We may not speed up more tissue growth by treating do a very first-order thermodynamic calculation to see

every 12 hours instead of every 24 hours, but if you if higher doses even have a chance at biostimulation
have an acute inflammation and the animal is before creating thermal damage.

staying overnight at the hospital, why Imagine we are testing the viability of 100 J/cm of
2
not benefit from the extra anti- 980 nm radiation on a monolayer of cells in a Petri dish

inflammatory effect? I do think you are with (as standard radiobiology protocols suggest) irra-

likely to see a difference in short-term diation in nutrient-rich growth medium to simulate in

inflammation at least, but the truth is that there are vivo pH and temperature. I won’t go into the back-of-

no clinical studies comparing these two treatment the-envelope calculations, [196] but suffice it to say that

regimes. this amount of energy deposited in the serum would
inevitably raise the temperature of the cellular environ-
ment well above the viability threshold.
6.8 Power density and patient comfort It is well known that bulk tissue can undergo irrevers-
ible tissue damage when raised above 40°C, never mind
On the high limit of the dose range, another limitation in a monolayer of cells with only two degrees of freedom
presents itself: one of thermal accumulation. Whatever to dissipate heat. In fact, this thermal accumulation is
energy of radiation is absorbed in the monolayer of often taken advantage of, and clinical hyperthermia is
cells and the serum environment is converted to heat, an increasingly popular technique in oncology. It turns

and in a Petri dish, thermal diffusivity is extremely low. out, using 980 nm light, that the threshold of thermal
2
Dose is defined as energy density and so the higher the damage to cell culture would be around 30 J/cm , even

dose, the more energy is absorbed, and thus the higher though we know that light can have a beneficial effect

the thermal accumulation. To get a real idea of what on the body at these doses.
contribution this has to the cellular environment, let’s Remember, this effect is simply an artifact of in vitro

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