A miniature hybrid reflection type optical sensor for measurement of hemoglobin content and oxygen saturation of whole blood

A reflection-type hybrid optical sensor was designed for continuous measurement of both hemoglobin content ((Hb)) and oxygen saturation (OS) of whole blood. The sensor was based on a theoretical model using the photon diffusion theory. The prototype sensor consists of a light emitting diode (LED) and photodiode chips mounted on a single substrate and cased in a TO-5 can with its surface covered with clear epoxy resin. The effect of hematocrit variation was eliminated. It was test in goat, calf, and human whole blood over hematocrit range of 20-45%. The modified ratio method reduced the effect of hematocrit variation of hemoglobin OS measurement with improvement in standard deviation of errors from about 7.0 to 2.0%. The standard errors in the estimation of hemoglobin content ranged from 1.5 to 0.5 gm%. The oxygen contents of whole blood derived from the prototype sensor correlated well (r=0.997) with those analyzed using a hemoximeter. The prototype sensors have been used for continuous measurement of oxygen delivery to, and oxygen consumption by, peripheral tissues in artificial heart animals for a duration of 40 days, demonstrating satisfactory performance.