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Biphasic dose response in low level light therapy caused a bigger increase than 1 or 4 treatments per day measuring prolif- eration index in human HEP-2 and murine L-929 cell lines. They used a 670 nm light emitting diode device with an irradiance of 10 mW /cm2 and each single treatment was 5 J/cm2 and the course was stopped after 50 J/cm2 had been given (at 10, 5 or 2.5 days). Lopes-Martins showed a biphasic response to LLLT on the number of mononuclear cells that accumulate in pleural cavity after carrageenan injection. The results showed neutrophil influx mice treated with three different laser fluencies at 1, 2.5 & 5 J/cm2) with 2.5 having the greatest effect (Lopes-Martins et al. 2005). As stated in 3.2 above, Hashimoto reported on the laser treatment of the stellate ganglion to reduce pain in patients with post herpetic neu- ralgia of the facial type. The study compared the effects of 830-nm lasers delivering 60mW, 150mW and placebo, The greatest improvements were for the 150mW laser (Hashimoto et al. 1997). Again as stated in 3.2 above, there have been several systematic reviews and meta analyses of RCTs and these revealed some energy density dependant effects (Bjordal et al. 2003; Tumilty et al. 2009). 3.4. Beam measurement reporting errors One notable aspect of the dose rate (W/cm2) studies is the wide vari- ation of “optimal” irradiances in vitro studies as they range from 1-800 mW/cm2 in just the few papers referenced in this review. If the primary photo acceptor is cytochrome C oxidase as postulated here, then why would so many authors arrive at different conclusions for optimal param- eters in vitro, should it not be the same for all of them? Explanations may include, the slightly different wavelengths used or sensitivity due the redox state of mitochondia in the target cells (Tafur and Mills 2008), but we consider that the greater contributor may be laser beam measurement problems. It may be a surprise to non-physicists that diode laser beams are not inherently round, and even if circularizing lenses are used to correct this, then the beam intensity distribution is not homogeneous. Laser beams are brighter (higher irradiance) in the mid- dle and weaker towards the edge. Cells in the centre of a culture well will be exposed to considerably higher irradiances than those on the periph- ery. Because the edge of a laser beam is hard to define and find this could mean that irradiance calculations are significantly different between research centers. Agreement on beam measurement and reporting of intensity distribution is needed to reduce these inconsistencies. This is important not only for in vitro studies but also in vivo and clinical trials as reporting of irradiance is just as important though we accept that tissue scattering diffuses the beam probably making non-homogenous sources less critical to clinical effectiveness.PDF Image | BIPHASIC DOSE RESPONSE IN LOW LEVEL LIGHT THERAPY
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