SPO2 principle

T?he principle of the SpO2 probe is as follows: The ratio of blood reflection at wavelengths near 660nm and 900nm (ρ660/900) most sensitively reflects changes in oxygen saturation, and clinical oximeters generally use this ratio as the variable. In the optical transmission path, besides arterial blood hemoglobin absorbing light, other tissues (such as skin, soft tissue, venous blood, and capillary blood) also absorb light. When incident light passes through a finger or earlobe, it is absorbed simultaneously by pulsatile blood and other tissues, but the absorbed light intensities differ. The light intensity absorbed by pulsatile arterial blood (AC) changes with arterial pressure waves, while the light intensity absorbed by other tissues (DC) remains constant regardless of pulsation or time. Thus, the light absorption ratio R at the two wavelengths can be calculated: R=(AC660/DC660)/(AC940/DC940). R is negatively correlated with SpO2, and based on the R value, the corresponding SpO2 value can be obtained from a standard curve.?