Design of a real time optical sensor for continuous blood cell separation

For continuous measurement and display of oxygen saturation and RBC content in blood during cell separation a reflection type optical sensor is designed based on the theoretical model using the photon diffusion theory. The prototype sensor consists of two arrays of light emitting diodes, red and infrared, and photodiodes. The emission wavelength of LEDs are 660 nm and 800 nm. The 800 rim which is in the infrared region is very close to isobestic value for blood. The prototype sensor is mounted on the blood cell separator equipped with an antitwister mechanism. Each LED emits a specific wavelength of light through the blood chamber to the photodiode. Since oxygen saturated blood absorbs differing amounts of light at each wavelength as compared to unsaturated blood, the amount of light absorbed by the blood in each pulse can be used to calculate the oxygenated hemoglobin to total hemoglobin. The conventional reflection type dual wavelength method is modified adding the constants C1 and C2 as (R660 + C1)/(R800 + C2), where R660 and R800 are the reflectances at 660 and 800 nrn, and C1 and C2 depend upon the sensor geometry and the blood physiological characteristics. These constants are calculated using blood physiology, hematocrit variations, the sensor model and the cell separator model. Changes in the constants are corrected by a microprocessor for online sensor adjustments. The oxygen saturation and RBC content are displayed on the LED displays and are updated once a second. The sensor position on the blood chamber is indicated visibly by a LED array. The audio alert indicates the lower RBC content. The scattering of light at the boundary of red blood cells and white blood cells is sensed to control the electromechanical valve and the sampler. This valve and the sampler are used to collect the samples for further blood analysis. The microprocessor is used for controlling the system, storage of the signal level and comparison of signal ratios. The long-term aim is to design a reliable, intelligent, real time, online sensor system for blood cell separation devices