Pulse oximetry: theoretical and experimental models.
In the paper a pulse oximetry model is developed using an approach which combines both theoretical and empirical modelling. The optical properties of whole blood are measured as a function of cuvette depth by transmission spectrophotometry using red (660 nm) and infra-red (950 nm) light-emitting diodes as light sources. Twersky's theoretical model gives the best fit to the experimental data. A simple theoretical model which takes into account the nonlinear relationship between optical density and cuvette depth is then used to obtain an expression for the R:IR ratio, which relates the measurement of transmission at the two wavelengths. The R:IR ratio is found to be more or less independent of cuvette depth (SD = 0.14 at 100 per cent SaO2). To validate the predictions of the theoretical model, the results of a previous experiment in which the relationship between SaO2 and the R:IR ratio was recorded using a flexible cuvette are used. The experimental values are found to lie within one standard deviation from the theoretical curve relating SaO2 and the R:IR ratio. It is argued that a reasonably accurate model for pulse oximetry which is based on whole blood and not haemoglobin solutions has been developed.
de Kock
J P
JP
Department of Engineering Science, Oxford University, UK.
Tarassenko
L
L
D006801:Humans; D008433:Mathematics; D008955:Models, Cardiovascular; D055095:Optics and Photonics; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood; D011673:Pulsatile Flow
D010100:Oxygen