A Compact Calibratable Pulse Oximeter Based on Color Filters: Towards a Quantitative Analysis of Measurement Uncertainty

Compact and low-cost opto-biomedical sensing systems today are ubiquitously available for measuring the oxygen saturation in blood. The oxygen saturation is derived by a complex, usually not well defined analytical process from the optical absorption of tissue at different wavelengths. The amount of information, which is originally contained in absorption measurements, is drastically reduced by this circumstance. However, the reliability of the analytical process as well as the influence of external parameters like blood pressures on the experimental uncertainty of such systems are widely unknown. Thus, to explore the experimental uncertainty quantitatively, original experimental data have to be used. In commercial systems, however, these data are usually not accessible. Therefore, test systems with full access to original absorption data are necessary. In this work, we develop and describe a test system consisting of color filters and a charge-coupled device (CCD) image sensor, which has substantial advantages in comparison to usually used systems based on multi-color light-emitting diodes (LEDs). Color filters with well-defined filter functions allow for a higher spectral resolution, and will finally guide the way to multi-spectral analysis of blood absorption measurements with reduced uncertainty.