Is low-power pulsed laser ineffective in neural growth?
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LETTER TO THE EDITOR MICROSURGERY 29:251 2009 IS LOW-POWER PULSED LASER INEFFECTIVE IN NEURAL GROWTH? Dear Editor, The article by Chen et al. ‘‘Effect of low-power pulsed laser on peripheral nerve regeneration in rats’’ in Microsurgery 25:83–89, 2005 indicates that pulsed laser irradiation does not provide any positive effects on neural growth. This well-designed and carefully reported article is, however, flawed for several reasons. The authors have used a 904-nm GaAs laser. This type of laser is always pulsed with very high peak powers, but with rather low average powers. Several articles by Rochkind et al. are referred to, unfortunately not 1 below. In this review arti- cle Rochkind writes: The continuation of this work with different wavelengths showed that green 540 nm is more effective than 632 nm. The i.r. pulsed laser 904 nm has no stimulating effect in our experimental model. Compar- ing 632 nm wavelength with 660 nm, 830 nm, 880 nm and 950 nm confirmed that single 632 nm laser irradia- tion on the injured nerve maintains the action potential at a high level on the first operative day. It is interesting to note that all continuous wave- lengths indicated here had some positive effect, whereas 904 nm did not, although even a higher continuous wave- length of 950 nm did show positive effects. It is quite feasible that the negative effect of the 904 nm laser was not wavelength specific, but rather due to its superpulsed character. It was reported already in 1984 by Abergel that GaAs requires much lower dosages than continuous lasers for stimulation of collagen. 2 Lasers can not only stimulate; doses above of the ‘‘therapeutic window’’ will have an inhibitory effect. 3 For pain treatment this is a valuable quality, for stimulation not. None of the researchers in the articles referred to have used 904-nm GaAs and it cannot be taken for granted that continuous and superpulsed lasers have the same biological effect. Therefore, the conclusion of Chen et al. is correct and valuable considering the lack of effect obtained in their experiment but incorrect in comparing their experiment with previous experiments using other wavelengths and modes. Not only are the effects of superpulsed and continu- ous lasers different but also there are also two types of ‘‘pulsing’’—the superpulsing and the ‘‘chopped’’ wave, where each pulse is part of a continuous emission. It can be hypothesized that the lack of effect reported by Chen et al. is an example of bio-inhibition. REFERENCES 1. Rochkind S, Ouaknine GE. New trend in neuroscience: Low-power laser effect on peripheral and central nervous system (basic science, preclinical and clinical studies). Neurol Res 1992;14:2–11. 2. Abergel P, Meeker CA, Lam T, Dwyer RM, Lesavoy MA, Uitto J. Control of connective tissue metabolism by lasers: Recent developments and future prospects. J Am Acad Dermatol 1984;11:1142–1150. 3. Chow RT, David MA, Armati PJ. 830 nm laser irradiation induces varicosity formation, reduces mitochondrial membrane potential and blocks fast axonal flow in small and medium diameter rat dorsal root ganglion neurons: Implications for the analgesic effects of 830 nm laser. J Peripher Nerv Syst 2007;12:28–39. JAN TUNE ´ R, D.D.S.* Swedish Laser Medical Society Grangesberg, Sweden *Correspondence to: Jan Tune ´ r, D.D.S, Spjutvagen 9, 77232 Grangesberg, Sweden. E-mail: [email protected] Received 7 November 2008; Accepted 18 November 2008 Published online 9 February 2009 in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/micr.20616 V V C 2009 Wiley-Liss, Inc.
Transcript of Is low-power pulsed laser ineffective in neural growth?
LETTER TO THE EDITOR
MICROSURGERY 29:251 2009
IS LOW-POWER PULSED LASER INEFFECTIVEIN NEURAL GROWTH?
Dear Editor,
The article by Chen et al. ‘‘Effect of low-power
pulsed laser on peripheral nerve regeneration in rats’’ in
Microsurgery 25:83–89, 2005 indicates that pulsed laser
irradiation does not provide any positive effects on neural
growth. This well-designed and carefully reported article
is, however, flawed for several reasons. The authors have
used a 904-nm GaAs laser. This type of laser is always
pulsed with very high peak powers, but with rather low
average powers. Several articles by Rochkind et al. are
referred to, unfortunately not1 below. In this review arti-
cle Rochkind writes: The continuation of this work withdifferent wavelengths showed that green 540 nm is moreeffective than 632 nm. The i.r. pulsed laser 904 nm hasno stimulating effect in our experimental model. Compar-ing 632 nm wavelength with 660 nm, 830 nm, 880 nmand 950 nm confirmed that single 632 nm laser irradia-tion on the injured nerve maintains the action potentialat a high level on the first operative day.
It is interesting to note that all continuous wave-
lengths indicated here had some positive effect, whereas
904 nm did not, although even a higher continuous wave-
length of 950 nm did show positive effects. It is quite
feasible that the negative effect of the 904 nm laser was
not wavelength specific, but rather due to its superpulsed
character. It was reported already in 1984 by Abergel
that GaAs requires much lower dosages than continuous
lasers for stimulation of collagen.2 Lasers can not only
stimulate; doses above of the ‘‘therapeutic window’’ will
have an inhibitory effect.3 For pain treatment this is a
valuable quality, for stimulation not.
None of the researchers in the articles referred to have
used 904-nm GaAs and it cannot be taken for granted that
continuous and superpulsed lasers have the same biological
effect. Therefore, the conclusion of Chen et al. is correct
and valuable considering the lack of effect obtained in their
experiment but incorrect in comparing their experiment
with previous experiments using other wavelengths and
modes. Not only are the effects of superpulsed and continu-
ous lasers different but also there are also two types of
‘‘pulsing’’—the superpulsing and the ‘‘chopped’’ wave,
where each pulse is part of a continuous emission.
It can be hypothesized that the lack of effect reported
by Chen et al. is an example of bio-inhibition.
REFERENCES
1. Rochkind S, Ouaknine GE. New trend in neuroscience: Low-powerlaser effect on peripheral and central nervous system (basic science,preclinical and clinical studies). Neurol Res 1992;14:2–11.
2. Abergel P, Meeker CA, Lam T, Dwyer RM, Lesavoy MA, Uitto J.Control of connective tissue metabolism by lasers: Recent developmentsand future prospects. J Am Acad Dermatol 1984;11:1142–1150.
3. Chow RT, David MA, Armati PJ. 830 nm laser irradiation inducesvaricosity formation, reduces mitochondrial membrane potential andblocks fast axonal flow in small and medium diameter rat dorsal rootganglion neurons: Implications for the analgesic effects of 830 nmlaser. J Peripher Nerv Syst 2007;12:28–39.
JAN TUNER, D.D.S.*
Swedish Laser Medical Society
Grangesberg, Sweden
*Correspondence to: Jan Tuner, D.D.S, Spjutvagen 9, 77232 Grangesberg,Sweden. E-mail: [email protected]
Received 7 November 2008; Accepted 18 November 2008
Published online 9 February 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/micr.20616
VVC 2009 Wiley-Liss, Inc.
