RBC

Photoplethysmography (PPG) is a low cost non-invasiveoptical technique that can be used to assess changes in tissueblood volume [6]. This method provides valuable informationrelated to the cardiovascular system. The tissue's region isilluminated using a light source and a photodetector recordsthe reflected light, which varies depending on the presenceand concentration of RBCs and their oxygenation levels.Depending on the oxygenation level of hemoglobin, RBCsabsorb light in different ways. When blood volume in themicrovascular bed increases, more light is absorbed due to thehigher concentration of RBCs. As a result, less light can reachthe detector. When blood volume decreases, less light isabsorbed, which causes the detected light intensity to increase.A measurement of the amount of light that is consistentlyabsorbed in response to variations in blood volume within thecirculatory system can yield the PPG signal