Direct modulation of pulse oximetry probe light signals using a digital micromirror array for instrumental calibration of optical sensors

Pulse oximetry sensors are commonly calibrated during empirical volunteer studies, which includes the drawing of arterial blood samples and CO-oximetry as a reference. In contrast to other medical devices delivering physiological measurement values, there are no guidelines requiring regular metrological controls for pulse oximeters. The main reason for this is the lack of an adequate procedure for such controls, since volunteer studies are obviously not applicable for this purpose. This work presents an approach to this problem, based on the direct modulation of the pulse oximetry probe's light signals by a digital micromirror array. The probe's light was decomposed into its spectral components and the spectrum was imaged to the surface of the micromirror array. The amount of reflected light was controlled by the position of the micromirrors, thus allowing the spectral modulation of light signals. This spectral modulation was additionally varied over time to generate physiological photoplethysmographic signal forms. Finally the modulated light was re-emitted to the pulse oximetry probe. This study shows that the pulse oximeter accepted the artificially modulated light signals and displayed a heart beat rate accordingly to the generated signals. The pulse oximeter displayed SpO ₂ values, which could be altered by changing the modulation ratio of the red and the infrared spectral components.