Effects of tissue outside of arterial blood vessels in pulse oximetry: a model of two-dimensional pulsation.

We describe a new model of pulse oximetry that addresses the disagreement between theoretical calibration curves based on Beer-Lambert's Law and test results based on human test subjects. Sources of this discrepancy include variability among human subjects, experimental conditions and the effect of optical radiation propagating in tissue surrounding arteries. Unlike the conventional model, our model considers the change in the relative proportion of light that does or does not pass through blood in pulsating vessels in addition to the change in the path length of optical radiation through the blood. Theoretical calibration curves based on this model agree with human test results and help to explain the variability between in vitro and in vivo test conditions.