Noninvasive measurement of total hemoglobin and hemoglobin derivatives using multiwavelength pulse spectrophotometry -In vitro study with a mock circulatory system-

Total hemoglobin (tHb), carboxyhemoglobin (COHb), and methemoglobin (MetHb) are usually measured with a CO-oximeter. Noninvasive and continuous measurement of these blood components is expected to decrease the pain of a patient. Therefore, we developed an instrument to measure oxygen saturation (SpO ₂), tHb, COHb, and MetHb non-invasively. Multiwavelength LED (600, 625, 660, 760, 800, 940, and 1300 nm) and a combined detector (Si, InGaAs) were built into the instrument (Seven wavelengths transparent pulse spectrophotometer). We used the Waseda mock circulatory system, which can simulate blood circulation in tissues and generate a pulse wave mechanically, to estimate the instrument's performance. Furthermore we proposed new calculation formula including DC components of optical density (this method). Under conditions without any change of other components, the mean error ± standard deviation between this method and the CO-oximetry were SaO ₂=0.0±1.4%, tHb=0.0±0.0 g/dl, COHb=0.0±2.0%, and MetHb=0.0±0.3%. When the concentration of other components was changed, this method showed mean errors and standard deviations of SaO ₂=0.2±1.6%, tHb=0.0±0.4 g/dl, COHb=0.5±4.1%, and MetHb=0.0±0.3%.