The Influence of Low Intensity Infrared Laser Irradiation on Conduction Characteristics of Peripheral Nerve: A Randomised, Controlled, Double Blind Study on the Sural Nerve

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.