Evaluation of the proper level of specific absorption rate of human blood for 532 nm laser in blood low-level laser therapy

Low-level laser has been used for a variety of clinical applications as a practical non-medicinal treatment, due to its ability to modulate blood rheology and improve biostimulation. This article research aim was to evaluate the proper level of specific absorption rate (SAR) of human blood during low-level laser treatment. Measurements were conducted on human blood in vitro, at different laser powers (wavelength 532 nm at powers of 50, 60, 70 and 80 mW) and exposure duration. Dielectric parameters were observed as a function of frequency from 40 Hz–30 MHz by utilizing an Agilent 4294A impedance analyzer at average room temperature of 25 °C. The SAR increased steadily with increasing frequency until it attained saturation peak, and thereafter exhibited a decrease trend. The SAR values range from 0.173–1.417 W kg⁻¹ for blood irradiated using laser power of 50 mW and range from 0.178–0.754 W kg⁻¹ for 60 mW. These values of SAR within 5–10 min of radiation present better stimulation results. Using laser powers of 70 and 80 mW for irradiations, the SAR values within the range from 0.003–0.791 W kg⁻¹ and 0.130–0.491 W kg⁻¹, respectively, were computed. The SAR values here portend high risk associated to blood than its stimulation mechanism because the blood already attained a plateau and became saturated. This causes imbalance within the blood molecules resulting in a decrease in SAR as the frequency increases. This is due to a phase lag that develops between the electric field and induced dipole alignment creating a significant drop in the SAR of blood. The rate of inhibition increases rather than stimulation since the thermal radiation becomes exceedingly high resulting in crenation and hemolyzation of the blood. Therefore, we recommend using a laser at an output of power 50 mW for 5–10 min to reach the maximum capacity of SAR for more absorption and optimal stimulation. (paper)