Colored Light and Brain and Muscle Oxygenation

Abstract

Colored light is applied in medicine in the treatment of various diseases. The aim of this study was to investigate potential effects of exposure to blue and red light on brain and muscle blood volume ([tHb]) and tissue oxygenation (StO2) measured by noninvasive near-infrared spectrophotometry (NIRS). Ten healthy volunteers were included in a randomized crossover study. Blue light exposure leads to decreased oxygen consumption in the brain and the skeletal muscle. I ntr oductionLight of different colors (CL) is applied for various medical conditions to improve the physical, emotional or mental state of patients. Examples are the use of blue light in the treatment of the neonatal jaundice [1], a phenomenon due to the immature liver function of newborns, the application of red [2] and UV light in dermatology (physical level), and the use of bright white light to treat seasonal affective disorders [3] (emotional or mental level). It is known that blue light is strongly absorbed by the skin, suppresses melatonin production and is generally associated with coldness. In contrast, red light penetrates tissue relatively deeply and is associated with warmth. However, little is known about the effects of CL on hemodynamics and tissue oxygenation.We therefore investigated potential effects of blue and red light, being the two main colors used in medical treatments, on blood volume and tissue oxygenation in the brain and skeletal leg muscle using near-infrared spectrophotometry (NIRS). M ater ials and methodsTen healthy volunteers (5 male, 5 female; mean age 27, range 23-44 years) were measured during blue and red light exposure. Light was generated using thermal white light sources (60W, OSRAM Inc., Germany) and color filters (Lee Inc., Germany). During exposure phases the CL was projected onto a white wall. The subjects were seated in a comfortable chair facing the wall. Subjects were asked to keep their eyes open throughout the entire measurement. Otherwise the room was completely dark and instruments were shielded in order to avoid ambient light.All subjects were measured twice on different days, exposed to blue or red light in a randomized crossover protocol. The protocol consisted of 8 min baseline (darkness), 10 min CL (blue or red) exposure, followed by 16 min recovery (darkness). Blood volume, i.e. total hemoglobin concentration ([tHb] in µM) and tissue oxygen saturation (StO 2 in %) were measured with a Hamamatsu NIRO 300 instrument. One sensor was attached to the forehead and the other to the lateral calf muscle. Using a paired t-test the last 5 min of the baseline were compared to the first and last 5 min of the CL exposure, and to 3 periods of 5 min of the recovery. Blue and red exposures were compared by a linear mixed effects (LME) model (R statistical software).

Effects of Changes in Colored Light on Brain and Calf Muscle Blood Concentration and Oxygenation

“…Surprisingly, also, no significant difference between the blue and red light was observed. The latter may seem in contrast to the previous study [24], where highly significant differences between red and blue were detected. In this study, the changes are similar to those observed for red light in the previous study.…”

“…Again, for an easier understanding, we first summarize the findings of the previous publication [24]. In the leg, the THI significantly increased by 1.1 (blue) or 1.5 µM (red) continuously in the course of time and independently of the color, which was interpreted as reduced venous drainage, an accumulation of blood, and consequent venous pooling in the calf muscle during the measurement due to the sedentary position of the subjects.…”

“…To interpret the observed changes, they are best compared to the previous experiments, which focused on exposure to light of single colors without sequential color changes [24]. In this previous study in the brain, the THI remained constant, which corresponds to an unchanged cerebral blood volume and blood flow.…”

“…In a previous study, we investigated the effects of red and blue light severally [24]. Blue light exposure led to decreased oxygen consumption in the brain and the muscle, which may indicate a state of increased relaxation.…”

“…Blue light exposure led to decreased oxygen consumption in the brain and the muscle, which may indicate a state of increased relaxation. Blue and red light had significantly different effects on tissue oxygen saturation (StO 2 ), both in the brain and muscle [24].…”