Temperature Dependence of Infrared Light Time Course Under Oxygenation and Deoxygenation of the Blood in Vitro

Abstract

Spectrometric hemoglobin saturation measurements are urgent now due to the need to monitor blood saturation in human beings’ serious state. Pulse oximeters typically used for these purposes have two or more wavelengths (in the red and infrared range). Under in vitro oxygenation of a blood sample, the intensity of red light (650 nm) scattered backward increases, reaching a plateau at high degrees of blood saturation with oxygen. Infrared (IR) light (λ≈808 nm), close to the isosbestic point 805 nm, often used as reference wavelength in oximeters, should not show any changes in the backscattered intensity or show a slight decrease during oxygenation and an increase during deoxygenation. We study temperature (19°C - 39 °C) dependence of the time course of IR signal in oxygenation and deoxygenation of donor's blood sample by the homemade oximeter. The setup allows us to measure light intensity (LED with two wavelengths - 650 and 808 nm) scattered back under continually stirring. When the red signal increases under oxygenation in the air atmosphere, we register a pronounced decrease in IR intensity (i.e., increase of absorbance). Our assessments show that the IR intensity minimum is achieved at approximately 50 % of hemoglobin saturation. The time from the start of oxygenation to the IR minimum and its depth increase with temperature increasing, which corresponds to a shift in the hemoglobin dissociation curve. Moreover, after such a decreasing of IR intensity, for temperature 19 - 32 °С, we observed the growth of IR intensity, and for 35 - 39 °С - signal flattening. We believe that these a pronounced changing of intensity is related to conformational changing of hemoglobin structure, the release of 2,3 bisphosphoglycerate, and membrane fluidity changing (crystallization) at low temperature.