NEW METHODS FOR WHOLE BLOOD OXIMETRY

New techniques for determining the hematocrit (Hct) and oxygen saturation (So2) o f whole blood from backscattered light measurements are described. First, theoret-ical and experimental results are presented which show that the empirical linear rela-tionship between Sot and the infrared-red backscattered light intensity ratio on which previous instruments have been based is an inadequate description primarily because it does not account for the strong effects o f Hct and transducer geometry. Then it is shown that the ratio o f backscattered intensities f rom two appropriately positioned infrared sources can be plotted against he infrared-red intensity ratio to produce a family o f calibration curves from which So2 and Hct can be independently deter-mined. Finally, a practical implementation f an oximetry system which employs a microelectronic catheter-tip optical sensor and a microprocessor-based ignal processor is proposed. Keywords--Oximetry, Oxygen saturation, Blood gas measurement, Optical scattering