Functional Near-Infrared Spectroscopy Analysis of Cerebral Physiological Changes in Response to Atmospheric Gas Concentrations

Compared with other organs in the body, the human brain is extremely sensitive to changes in O2 and CO2 levels. This study applied functional near-infrared spectroscopy (fNIRS) to analyze the changes in cerebral oxygen saturation (COS) and hemoglobin (Hb) concentrations in response to various atmospheric gas concentrations and investigate their effects on brain function. Twenty-nine adults were exposed to four gas conditions, namely atmospheric concentration (C1), high O2 concentration (C2), high CO2 concentration (C3), and high O2 and CO2 concentrations (C4). Changes in COS and Hb concentrations were measured using fNIRS, whereas heart rate (HR) and percutaneous oxygen saturation (SpO2) were measured using a patient monitor. COS, oxy-Hb (HbO), and total-Hb (HbT) increased progressively from C1 to C4, whereas deoxy-Hb (HbR) exhibited a decreasing trend. Moreover, the COS and Hb concentrations were more strongly influenced by high CO2 levels than by high O2 levels. High O2 concentrations increased the blood O2 saturation, whereas high CO2 concentrations increased blood flow as a physiological response, enhancing O2 delivery to the brain. Additionally, HR and SpO2 increased at high CO2 concentrations. However, at high O2 concentrations providing a sufficient O2 supply, SpO2 increased while HR decreased. Therefore, adjusting the concentrations of CO2 and O2 may improve cerebral blood flow and change brain function, supporting cerebrovascular health and preventing related diseases.