University of Toyama is a Japanese national university located in Toyama City and Takaoka City and established in 1949. It is comprised of 3 former national universities Toyama University, Toyama Medical and Pharmaceutical University, and Takaoka National College.
Modulight products: ML6600
Laser use: Studying pain treatment with photobiomodulation.
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Background
Photobiomodulation with low-level laser or light therapy is an effective treatment for pain. It has various effects, such as analgesic (pain-relieving) effects, anti-inflammatory effects, tissue regeneration promoting effects, and wound healing effects. Photobiomodulation can be used to relief both acute and chronic pain and has the advantage of being noninvasive and safe. Earlier studies have shown that photobiomodulation affects the activity of pain-transmitting nerves, even though the mechanisms are not fully understood. Because lasers are scattered and absorbed by biological tissues, the laser intensity reaching the nerves is expected to be lower than intensity at the tissue surface. The goal of this study is to elucidate better the pain relieving mechanisms of photobiomodulation.
Laser power investigation
To study how much laser power reaches the sciatic nerve, percutaneous laser irradiation with ML6600 was applied to the sciatic nerve of five in vivo test subjects. The laser light was guided to the skin with optical fiber and collimated using a lens. The irradiation parameters were: 808 nm wavelength, 0.79 cm2 illumination area, 1 Watt/cm2 power density, 3 min illumination time, 180 J/cm2 light dose. The laser parameters were controlled using the laser software. The laser power was measured at the sciatic nerve with an implanted photodiode sensor. The average power density at the sciatic nerve was 95.1 mW/cm2 compared to the 1,000 mW/cm2 at the skin surface, showing about 90% attenuation. The average distance from the skin surface to the sciatic nerve was 6.3 mm.
Studying mechanism of pain relief
The photobiomodulation mechanism for pain relief was studied by percutaneous laser irradiation of the sciatic nerve using ML6600 laser with same settings as before (808 nm, 0.79 cm2 area, 1 W/cm2). An electrode was advanced into the spinal dorsal horn (lamina II) neurons. Recordings were performed from superficial dorsal horn neurons at a depth of 20–150 µm from the surface. For mechanical stimulation, the skin was bent with thin von Frey filaments, and bending forces of 0.6, 8.0, and 26.0 g were applied. Results showed that laser irradiation did not inhibit firing evoked by 0.6 g and 8.0 g bending forces. However, a significant difference was observed between the pre-irradiation and 15 min post-irradiation at 26.0 g force.
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