## 1 Introduction  
Among the constituents that make up the atmosphere, oxygen (O2) and carbon dioxide (CO2) are essential for sustaining life and affect the environment, such as atmospheric temperature and the rise in sea levels [1]. The atmospheric concentrations of O2 and CO2 are undergoing rapid changes. In particular, CO2 concentrations maintained at an average of 300 ppm before the Industrial Revolution and increased to an average of 414 ppm in the 2020s due to factors such as the use of fossil fuels, deforestation, and industrialization [2]. Changes in atmospheric concentrations can lead to climate change, such as global warming, and can affect the survival of various living organisms. Aerobic organisms, especially humans, are highly dependent upon atmospheric concentrations of O2 and CO2. Through respiration, O2 is absorbed into the body, and CO2 is exhaled. Changes in blood O2 and CO2 concentrations are detected by the carotid and aortic bodies to maintain constant levels [3; 4; 5]. However, exposure to environments with insufficient O\({}_{2}\), such as high-altitude areas or environments with high CO\({}_{2}\) concentrations, can lead to hypoxia, blood acidification, and hypercapnia [6]. If this condition persists, the manifestation can develop, from mild symptoms such as headache and dizziness to more serious conditions such as coma [7]. Abnormal atmospheric concentrations are common indoors or in vehicles and can be mitigated through ventilation. However, proper atmospheric management is essential in enclosed spaces where ventilation is not possible [8; 9]. In particular, O\({}_{2}\) deficiency and carbon monoxide (CO) or CO\({}_{2}\) poisoning are serious hazards in confined spaces, such as coal mines, sewage worksites, and fire scenes [10; 11]. Excess CO or CO\({}_{2}\) binds to hemoglobin (Hb), disrupting O\({}_{2}\) exchange. Even with appropriate treatment, this condition can result in a loss of Hb function, with lasting effects [12; 13]. Diseases, symptoms, and poisoning caused by abnormal atmospheric O\({}_{2}\) concentrations can be treated with high-concentration O\({}_{2}\) therapy. In addition, high concentrations of CO\({}_{2}\) are used in cancer treatment and show positive effects when administered at appropriate concentrations for specific durations [14; 15]. High-concentration O\({}_{2}\) is also applied in various fields beyond medical treatment, such as oxygen cans used for athlete recovery and high-concentration oxygen rooms, which can improve cognitive function [16]. In particular, high-concentration oxygen rooms reflect changes in brain function according to O\({}_{2}\) levels, with studies reporting a correlation between O\({}_{2}\) concentration and brain function. For example, cognitive function improves with higher O\({}_{2}\) concentrations and declines with lower O\({}_{2}\) levels [17; 18]. The brain is more dependent on O\({}_{2}\) than other organs in the body. Despite accounting for only approximately 2% of human body weight, the brain consumes up to 20% of the body's O\({}_{2}\)[19]. This high dependence on O\({}_{2}\) is closely related to the importance of collateral vessels, such as the Circle of Willis (COW), a unique vascular structure in the brain [20]. The COW facilitates smooth blood flow through alternate routes, ensuring O\({}_{2}\) delivery to brain tissue, even when specific cerebral blood flow is compromised. This enables continuous metabolism and normal brain function [21]. However, when the COW cannot compensate for O\({}_{2}\) deficiency, brain function declines immediately. Severe hypoxia can result in cognitive impairment, brain damage, and even death [20]. Furthermore, in addition to O\({}_{2}\), CO\({}_{2}\) levels can also affect the brain. Most symptoms associated with high CO\({}_{2}\) concentrations occur due to an insufficient O\({}_{2}\) supply to the brain, which is highly reliant on O\({}_{2}\)[6]. This highlights the extreme sensitivity of the brain to O\({}_{2}\) and CO\({}_{2}\) concentrations compared with other organs.