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The present pilot study investigated the analgesic efficacy of light-emitting diode (LED). In view of a standardised and controlled pain reduction study design, this in vivo trial was conducted on experimentally induced delayed-onset muscle soreness (DOMS). Thirty-two eligible human volunteers were randomly assigned to either an experimental (n=16) or placebo group (n=16). Immediately following the induction of muscle soreness, perceived pain was measured by means of a visual analog scale (VAS), followed by a more objective mechanical pain threshold (MPT) measurement and finally an eccentric/concentric isokinetic peak torque (IPT) assessment. The experimental group was treated with infrared LED at one of both arms, the other arm served as control. Irradiation lasted 6 min at a continuous power output of 160 mW, resulting in an energy density of 3.2 J/cm(2). The subjects of the placebo group received sham irradiation at both sides. In post-treatment, a second daily assessment of MPT and VAS took place. The treatment and assessment procedure (MPT, VAS and IPT) was performed during 4 consecutive days. Statistical analysis (a general linear model followed by post hoc least significant difference) revealed no apparent significant analgesic effects of LED at the above-described light parameters and treatment procedure for none of the three outcome measures. However, as the means of all VAS and MPT variables disclose a general analgesic effect of LED irradiation in favour of the experimental group, precaution should be taken in view of any clinical decision on LED. Future research should therefore focus on the investigation of the mechanisms of LED action and on the exploration of the analgesic effects of LED in a larger randomised clinical trial and eventually in more clinical settings.

The introduction of light emitting diode (LED) devices as a novel treatment for pain relief in place of low-level laser warrants fundamental research on the effect of LED devices on one of the potential explanatory mechanisms: peripheral neurophysiology in vivo. A randomised controlled study was conducted by measuring antidromic nerve conduction on the peripheral sural nerve of healthy subjects (n=64). One baseline measurement and five post-irradiation recordings (2-min interval each) were performed of the nerve conduction velocity (NCV) and negative peak latency (NPL). Interventional set-up was identical for all subjects, but the experimental group (=32) received an irradiation (2 min at a continuous power output of 160 mW, resulting in a radiant exposure of 1.07 J/cm(2)) with an infrared LED device (BIO-DIO preprototype; MDB-Laser, Belgium), while the placebo group was treated by sham irradiation. Statistical analysis (general regression nodel for repeated measures) of NCV and NPL difference scores, revealed a significant interactive effect for both NCV (P=0.003) and NPL (P=0.006). Further post hoc LSD analysis showed a time-related statistical significant decreased NCV and an increased NPL in the experimental group and a statistical significant difference between placebo and experimental group at various points of time. Based on these results, it can be concluded that LED irradiation, applied to intact skin at the described irradiation parameters, produces an immediate and localized effect upon conduction characteristics in underlying nerves. Therefore, the outcome of this in vivo experiment yields a potential explanation for pain relief induced by LED.

The aim of this study was to investigate the effects of low intensity laser therapy (LILT) on the conduction characteristics of peripheral sensory nerve. Fifteen healthy subjects participated in this experiment. Six points on the sural nerve of the left leg were irradiated with an 830 nm GaAlAs laser with different parameters. All 15 subjects received at random one of the following treatments: an average power of 400 mW at a dose of 1.5 J per point (7.65 J/cm2) (treatment A); an average power of 140 mW and a dose of 1.0 J per point (5.1 J/cm2) (treatment B); an average power of 30 mW, 0.5 J per point (2.55 J/cm2) (treatment C) and to evaluate possible placebo effects in a fourth moment, no power was given (sham). The influence of skin temperature on conduction characteristics of peripheral nerve was taken into account by using correction factors for conductance velocity (1.47 m/s per °C) and negative peak latency (0.2 ms per °C) to a reference temperature of 32°C. One way analysis of variation with repeated measurements of the data collected within 15 min postirradiation showed a significant decrease in conduction velocity and increase in negative peak latency in treatment B. Those results could explain possible laser-mediated pain relief.

The purpose of this investigation was to examine the susceptibility ofPseudomonas aeruginosa to helium-neon (He-Ne) laser in order to gain an insight into the clinical implications for this type of low-level laser therapy (LLLT) in the treatment of infected wounds. Suspensions, in the presence and the absence of methylene blue (MB, 0.001% w/v), were exposed to the light from a 9 mW He-Ne laser for 5 and 50 min. Exposure of samples without MB did not affect the viability of this organism based on the lack of significant differences in the number of colony forming units (CFU) between irradiated and control samples. In the presence of MB, statistically significant mean reductions in CFU of 39.5% (22.6 J cm-2) and 58.2% (226 J cm-2) were found, and growth-free zones in irradiated confluent platings could be observed. Since no logarithmic reductions were achieved, the clinical implementation of He-Ne laser as a bactericidal agent seems to be of no relevance yet. Otherwise, no stimulation of bacterial growth was observed. Therefore, infection as a contraindication for LLLT should be excluded.