An optical sensor for the non-invasive measurement of the blood oxygen saturation of an artificial heart according to the variation of hematocrit

Abstract

Abstract This study describes a non-invasive optical sensor and sensor system used to measure the blood oxygen saturation of an artificial heart, in vitro . The reflection type optical sensor consists of an LED for the light source and a PIN photodiode for the light detector in a flat pack. The emission wavelengths of the LED are 665 and 805 nm. The blood oxygen saturation was measured using the reflectance ratio of 665 to 805 nm. The sensor system for measurement of the oxygen saturation has been breadboarded. Changes in the blood oxygen saturation were detected by the developed sensor system in real time. The experimental set-up was designed to be identical in effects and circumstances to a living body. The non-invasive measurement of oxygen saturation in vitro was carried out. Using a constant volume (30 cc) of blood and various volumes (0, 10, 20, 30 cc) of a physical saline solution, the hematocrit level of the blood was determined. When the change in oxygen saturation is compared at each wavelength, the variation at 665 nm is four times more than at 805 nm. At the 805 nm wavelength there was only a small change over the 100-60% range of oxygen saturation. The reflectance ratio decreased with reduction of the hematocrit level. As the oxygen saturation was varied from 100 to 60%, the reflectance ratio R 805/ R 665 over the whole hematocrit range changed linearly.