Reference Values of Regional Oxygen Saturation (rSO\({}_{2}\)) Determined by Near-Infrared Spectroscopy (NIRS) for 18 Selected Regions of Interest (ROIs) in Young and Elderly Healthy Volunteers  
[PERSON]  
1 Department of Functional Diagnostics and Physical Medicine, Pomeranian Medical University in Szczecin, Zdnierska 54, 71-210 Szczecin, Poland; [PERSON][PERSON]  
1 Department of Functional Diagnostics and Physical Medicine, Pomeranian Medical University in Szczecin, Zdnierska 54, 71-210 Szczecin, Poland; [PERSON][PERSON]  
1 Department of Functional Diagnostics and Physical Medicine, Pomeranian Medical University in Szczecin, Zdnierska 54, 71-210 Szczecin, Poland; [PERSON]  
2 Student Research at the Department of Functional Diagnostics and Physical Medicine, Pomeranian Medical University, Zdnierska 54, 71-210 Szczecin, Poland; [PERSON]
vascular bed (small arteries, arterioles, capillaries, venules and small veins) and the heme group of myoglobin (Mb) in the muscle fibers [3]. Differences in the oxygen-dependent absorption spectra of iron and/or copper centers in these molecules enable measurement of relative changes in the amounts of oxidized copper and oxidized forms of heme present in muscles [4; 5]. In NIRS, based on the absorption of near-infrared light by hemoglobin, as the absorption properties of hemoglobin change with its oxygenation status, measuring the transmitted/reflected light from tissue provides information on the oxygenation state of tissue [6]. The oxygen delivery (DO\({}_{2}\)) to the tissues depends on the cardiac output (CO) and on the arterial O\({}_{2}\) content (CaO\({}_{2}\)). CaO\({}_{2}\) describes the concentration of oxygen in arterial blood and represents the sum of oxygen bound to hemoglobin and oxygen dissolved in plasma, thus it is dependent on the hemoglobin (Hgb) concentration, the O\({}_{2}\) saturation (SaO\({}_{2}\)) and the partial pressure of O\({}_{2}\) (PaO\({}_{2}\)) [7]. This means that NIRS signals are the result of the weighted average of oxygen saturations of the heme group of hemoglobin (Hb) in the vascular bed (small arteries, arterioles, capillaries, venules and small veins) and the heme group of myoglobin (Mb) in the muscle fibers. The NIRS method provides the ability to monitor the patient's condition in real time and, above all, allows for the assessment and monitoring of tissue oxygenation and hemodynamics of tissue in vivo. Two different basic variables, tissue oxygen saturation (SPO\({}_{2}\)) [8; 9] and regional oxygen saturation (rSO\({}_{2}\)), can be extracted, depending on the device used [10; 11]. Regional oxygen saturation (rSO\({}_{2}\)) is a measure of Oxy-Hb in a volume of tissue, expressed as a percentage of oxygenated hemoglobin to total hemoglobin (HbO\({}_{2}\)/Hb) [12]. The rSO\({}_{2}\) value is believed to reflect the perfusion and metabolism of the tissue being assessed, assessing the balance of local tissue oxygen supply and demand. Tissue microcirculation includes arteries, veins and capillaries, which means that rSO\({}_{2}\) represents a \"weighted average\" of these structures, with approximately 75-85% of the signal coming from the venous vessels [13; 14; 15]. The first conducted research allowed for the determination of penetration depth at approximately 1/3 of the emitter-detector distance [16]. It was further assumed that when setting the detector-source system at a distance of 3 cm, the area of maximum sensitivity would be located at 1.5 cm deep below the skin layer [17]. The NIRS method has been widely adopted over the past two decades for research and is now increasingly being deployed for clinical use. It has been widely used in assessment of cerebral oxygenation in neonates [18; 19] and adult patients [18]. NIRS is also becoming a widely used research instrument in the field of cognitive neuroscience [19].