The Microvascular Response to Photobiomodulation in Healthy Subjects – The Role of Wavelength, Gender, and Age: A Randomized Controlled Clinical Study

Background: The microvascular flow is influenced by many factors, including age and gender. Photobiomodulation was previously shown to increase blood flow.

Objective: Characterizing the microvascular flow in response to irradiation with noncoherent RED and near-infrared (NIR) light emitting diodes (LEDs), and investigating the relationships between wavelength, age, and gender.

Materials and Methods: This was a randomized controlled clinical study (2080-15-SMC, NCT02527070) Twenty-one healthy non-smoking subjects without any known vascular pathologies were randomized to receive irradiation with either red LEDs (633 nm, 70 mW/cm²) or NIR LEDs (830 nm, 55 mW/cm²). Irradiation was applied for 5 minutes to the left wrist (ulnar and radial arteries). Laser Doppler flowmeter was used to quantify capillary blood flow, red blood cell (RBC) concentration, and RBC velocity. Continuous measurements were conducted before irradiation, during irradiation, and during 15 mins follow up. The relationships between wavelength (red/NIR), age (18-29/30-65), and gender (male/female) were investigated.

Results: During irradiation both red and NIR increased blood flow, RBC concentration, and velocity. This increase remained up to 15 minutes after irradiation. Tissue perfusion was not affected by gender. However, age groups responded differentially to wavelength with the younger age group having an increased response to Red, while the older age group to NIR.

Conclusions: Non-coherent light sources have immediate vasodilative effects that enhance downstream tissue perfusion. Further studies investigating the interaction between light sources and personal characteristics such as age, gender, smoking, and disease status may lead to optimal personalized light therapy.