In the present study we evaluate the effects of laser irradiation on the area near the stellate ganglion on regional skin temperature and pain intensity in patients with postherpetic neuralgia. A double blind, crossover and placebo-controlled study was designed to deny the placebo effect of laser irradiation. Eight inpatients (male 6, female 2) receiving laser therapy for pain attenuation were enrolled in the study after institutional approval and informed consent. Each patient received three sessions of treatment on a separate day in a randomized fashion. Three minutes irradiation with a 150 mW laser (session 1), 3 minutes irradiation with a 60 mW laser (session 2), and 3 minutes placebo treatment without laser irradiation. Neither the patient nor the therapist was aware which session type was being applied until the end of the study. Regional skin temperature was evaluated by thermography of the forehead, and pain intensity was recorded using a visual analogue scale (VAS). Measurement were performed before treatment, immediately after (0 minutes) then 5, 10, 15, and 30 min after treatment. Regional skin temperature increased following both 150 mW and 60mW laser irradiation, whereas no changes were obtained by placebo treatment. VAS decreased following both 150 mW and 60 mW laser treatments, but no changes in VAS were obtained by placebo treatment. These changes in the temperature and VAS were further dependent on the energy density, i.e the dose. Results demonstrate that laser irradiation near the stellate ganglion produces effects similar to stellate ganglion block. Our results clearly indicate that they are not placebo effects but true effects of laser irradiation.

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The potential genetic toxicity of ultraviolet (UV) laser energy was examined using excimer lasers at wavelengths of 248 nm (UVC, krypton fluoride laser) and 308 nm (UVB, xenon chloride laser) with an incident energy per pulse of 1 mJ per unit area of 25 cm² (0.04 J/cm²). Dosage was controlled by the number of pulses delivered. The Ames screening test for potential carcinogenesis was applied to the specimens irradiated with both wavelengths, in addition to any induced chromosome aberrations in peripheral human lymphocytes. The Ames test and examination of irradiated chromosomes indicated that the 248 nm beam was capable of attacking DNA and had carcinogenic potential with genetic toxicity. The 308 nm beam on the other hand appeared to have no adverse effects on DNA and had no genetic toxicity potential at the parameters of the present study. It can therefore be concluded that cells have high wavelength specificity as far as the action potential of incident UV energy is concerned, which will have obvious implications on choice of laser wavelengths in the UV waveband.

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The purpose of the present in vitro study was to compare the effect of N₂ (5.4 J/cm²), HeNe (35.1 J/cm²) and GaAlAs (163.8 J/cm²) lasers on the microbes at doses in current clinical use. The suspensions of Escherichia coli NCTC 10418 with densities equivalent to 10⁸-10⁹ cells/ml and 5 x 10³ cells/ml were subjected to viable count study after irradiation with the above lasers. The N₂ laser revealed a distinct inactivating effect on bacteria at low cell densities and it was confirmed to be dose dependent for both Escherichia coli and Staphylococcus aureus. The N₂ laser did not show any obvious lethal effect over high density bacterial suspensions, possibly due to the poor penetration of the 337 nm beam owing to the high absorption in water associated with UV energy, but exhibited reduced growth in growth curve studies in comparison to the non-irradiated control. The various microorganisms including Escherchia coli, Staphylococcus aureus, Klebsiella aerogenes and Pseudomonas aeruginosa revealed similar reduction in growth on irradiation with N₂ laser. On the other hand, neither the HeNe nor GaAlAs diode lasers altered the growth and viability of E. coli at the varied cell densities.

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This study examined the effects of 830nm GaAlAs laser therapy on wound-healing processes in the rat skin to demonstrate possible diachronic alterations of cytokines, particularly interleukin-6 (IL-6), following laser irradiation, as IL-6 is one of the most typical, multifunctional cytokines and is moreover easy to detect. Two full-thickness incisional wounds (10 cm long) were made parallel to and 2 cm from the midline of the dorsum with a scalpel in 20 male Wistar rats. Immediately after incision the wounds were closed. The animals were separated into two groups of 10 animals each. Group A served as the unirradiated control group, and experimental group B received 20 seconds of LLLT along the right wound only with an 830 nm 60 mW GaAlAs diode laser, approximately 5 sec per point with the probe head 5 mm from the wound at the four points midway on each quarter of the wound giving a total dose per session of 24 J/cm². The left hand wound was unirradiated to test for possible systemic reactions. Laser therapy was repeated daily until the 7th postoperative day. Immediately before wounding and daily thereafter until the 8th postoperative day, 6 mm punch biopsies were obtained from skin between the line of the wound and the midline bilaterally on both groups. Biopsies were taken before laser irradiation on days 1 to 7. The specimens were examined histochemically for IL-6 and histologically to follow the morphological wound healing response. IL-6 was measured using a solid-phase ELISA kit employing the multiple antibody sandwich principle. Significant differences were demonstrated between group A (unirradiated control) and specimens from both the irradiated (B1) and unirradiated (B2) sides in group B with higher levels of IL-6 seen on postoperative days 2 (B1: p < 0.001; B2: p < 0.05); 4 (B1 and B2: P < 0.05); 6 (Bl: p < 0.05; B2: p < 0.01); and 8 (B1 and B2: p < 0.01). Histologically, a more controlled inflammatory response was seen in both B1 and B2 specimens compared to the unirradiated control group A, although B1 showed a speedier response than B2 specimens. A greater number of neutrophils appeared earlier and disappeared earlier in the subcutaneous tissues of group B animals, suggesting that both wounds in group B animals finished the inflammatory phase and were entering the proliferative phase of wound healing earlier than those in control group A. These data suggest that 830 nm diode LLLT at the parameters in the present study can increase the levels of IL-6 in healing tissue, and can induce an earlier proliferative phase of wound healing. The data also strongly suggest a systemic response to laser therapy which should be carefully considered in any trial using contralateral unirradiated controls in the same animal to prove or disprove the efficacy of laser therapy.

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The analgesic effects in the course of application of therapeutic lasers to affected tissue have been described in a number of works in the literature. Although a few scientific-based reports have appeared, those on laser-induced analgesia are mainly clinical works describing the effect of the therapy which, however, do not study the mechanism of the laser action. There are several different possible responses induced by non-invasive low level laser therapy (LLLT). The purpose of the present communication is to review the arrangement and characterization of these responses. By being aware of these effects, the laser therapist can acquire a physiological and morphological scheme making possible the appropriate choice of the site of application of LLLT, choice of the irradiation technique, and selection of appropriate doses.

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