In Vitro Measurement of Blood Oxygenation Based on Near-Infrared Diffuse Optical Spectroscopy

Based on near-infrared spectroscopy（NIRS） and modified Beer-Lambert law（MBLL）, a new method for measuring oxygen content in vitro blood was proposed, at the same time, a blood oxygen saturation real-time monitoring system was developed to realize continuous monitoring of blood oxygen parameters during cardiopulmonary bypass. NIRS computes the absorption and scattering coefficients of tissues by using the difference in the absorption rates of the two wavelengths of near-infrared light by deoxyhemoglobin and oxygenated hemoglobin. Beer-Lambert law is a mathematical expression that characterizes the relationship between light intensity attenuation and photon transmission path. Combining the two can estimate the absorption coefficient of hemoglobin. Different from the traditional measurement method, the transmission measurement method proposed in this paper can obtain multi-parameter optical signal by alternating the probe of double wavelength（660–904 nm） light source. The signal was uploaded to the acquisition interface（LabVIEW） in real time and processed by logarithm, a linear model of blood absorption coefficient, oxygenation and optical signals was developed using an innovative blood oxygen algorithm. In order to verify the feasibility of the research scheme, the experiments of liquid phantom and in vitro blood solution were carried out, and the volume of Ink Drop（phantom experiment） and yeast（blood solution experiment） were taken as variables, by adjusting the concentration of solution to change the change amplitude of optical density, it was proved that both of them had a good linear relationship with optical density（DO）（r2＞0. 95, p＜0. 01）). The novel oximetry method and real-time oximetry monitoring system proposed in this study are suitable for oximetry of isolated blood, with accurate and reliable data, good repeatability and stability.