Besides Photothermal Effects, Low-Level CO2 Laser Irradiation Can Potentiate Skin Microcirculation Through Photobiomodulation Mechanisms

Background: Improvement of microcirculation is one of the important mechanisms of low-level laser therapy (LLLT) to treat some diseases such as wound healing. Most previous studies have been carried out with multiple lasers other than the 10,600-nm CO2 laser. Recently, the CO2 laser has been used not only as a tool for excision of soft tissues but also for therapeutic applications. Objective: To study whether low-level CO2 laser irradiation can influence microcirculation and further explore the underlying mechanisms. Methods: Seventy-milliwatt (70-mW) CO2 lasers irradiated the forearms of 12 participants and skin blood perfusion (SkBP) was measured with a laser speckle imager. The thermal effect of irradiation was evaluated by measuring the irradiated skin in vivo and the exposed cell suspensions in vitro. Extracellular adenosine triphosphate (eATP) of the human mast cell line (HMC-1) is assessed by luciferin-luciferase assay to explore the potential mechanisms. Results: Irradiation caused dose-dependent increase in SkBP. At a medium dose of 262 J/cm(2), SkBP reached its maximum value at 195.8% +/- 18.6% of the baseline (n = 12, p < 0.01). Such laser irradiation had a mild thermal effect, heating local skin temperature (SkT) by 6.1 degrees C +/- 0.3 degrees C (n = 10) and warming cell suspensions by 4.5 degrees C +/- 0.8 degrees C (n = 6). Irradiation dose-dependently lowered eATP levels of HMC-1 cells in vitro. At a medium dose of 262 J/cm(2), eATP levels declined to the minimum at 74.8% +/- 5.5% of the baseline (n = 12, p < 0.01). This downregulation effect could be significantly inhibited by 100-mu M ARL67156, a nonspecific ecto-ATPase inhibitor. On the contrary, heating itself slightly raised the level of eATP. Conclusions: Low-level CO2 laser irradiation can improve microcirculation. Besides the thermal effect, regulation of extravascular eATP by the photobiomodulation mechanism may be involved. This implies that CO2 lasers might be used in LLLT.