A Brief Word on Reciprocity
Peter A. Jenkins, MBA
The 3rd Law of Photobiology (a.k.a. the Reciprocity Rule and the Bunsen-Roscoe Law) states that “the effects of irradiation will be independent of irradiance and exposure time as long as radiant exposure is maintained”, i.e. the differences in power and irradiation time don’t matter, it’s the dose that’s important.
However, while reciprocity may hold true in many areas of photochemistry (the field in which Bunsen and Roscoe worked in the 19th century), as far back as 1992 questions were raised as to whether the 3rd Law applied to laser therapy.
Since then, numerous papers have provided evidence to suggest that reciprocity does not hold true for laser therapy, except over very narrow ranges. As Schindl et al state, “responses of cells and tissues to electromagnetic radiation usually involve a sequence of interacting biological reactions making a linear dose-time relationship less likely”.
In short, the dose is actually of less importance in determining the outcome of laser therapy than the power/intensity of the laser and the irradiation time.
2 comments
Richard L Godine DVM
Dec 9, 2013
Could you post a few of the references that support the uniqueness of LPT with regard to the Reciprocity rule? Thank you.
ADMIN Peter A Jenkins
Dec 12, 2013
Of course! I should have added references in the first place.
Here are a few, in no particular order…
Lanzafame RJ, Stadler I, Kurtz AF, Connelly R, Peter TA Sr, Brondon P, et al (2007). Reciprocity of exposure time and irradiance on energy density during photoradiation on wound healing in a murine pressure ulcer model. Lasers Surg Med 39:534– 542 (Erratum in Lasers Surg Med 39:808)
Lubart R, Lavi R, Friedmann H, and Rochkind S. (2006). Photochemistry and photobiology of light
absorption by living cells. Photomed Laser Surg 24:179-85.
Schindl, B. Rosado-Schlosser, F. Trautinger: The reciprocity rule in photobiology - a review. (Sourced online < http://www.photobiology.com/reviews/bunsen/>)
Lopes, N.N., et al. (2009). Cyclooxygenase-2 and vascular en- dothelial growth factor expression in 5-fluorouracil-induced oral mucositis in hamsters: evaluation of two low-intensity laser protocols. Support. Care Cancer 17, 1409–1415.
Oron, U., et al. (2001). Attenuation of infarct size in rats and dogs after myocardial infarction by low-energy laser irradiation. Lasers Surg. Med. 28, 204–211.
Karu TI and Kolyakov SF. (2005). Exact action spectra for cellular responses relevant to phototherapy.
Photomed Laser Surg 23:355-61.
Ginsbach G. (1979). Laser induced stimulation of woundhealing in bad healing wounds. Proc Laser ’79 Opto Elektronics Conf Munich. IPC Science and Technology Press Guildford UK 5.
Nussbaum, E.L., Lilge,L ., and Mazzulli, T. (2003). “Effects of low-level laser therapy (LLLT) of 810 nm upon in vitro growth of bacteria: relevance of irradiance and radiant exposure” J Clin Laser Med Surg, 21(5), pp283-290