Towards a hemodynamic model to characterize inaccuracies in finger pulse oximetry

Abstract

A pulse oximeter monitors a patient's functional arterial oxygen saturation (SpO2) by illuminating vascularized tissue. However, the optical signals measured, called photoplethysmograms (PPGs), are easily distorted by motion, leading to inaccurate SpO2 readings. Motion artifacts in PPGs are partly attributed to hemodynamic variations, though the exact mechanism is not understood. This paper introduces a model-based approach to improve insight in the effects of hemodynamic variations on SpO2. To make a first step towards an improved understanding of hemodynamic variations, a hemodynamic fingertip PPG model has been developed, including hydrostatic pressures. Measurements on a healthy male subject show that the PPG model can explain changes in PPG baseline and pulsatility in a limited range of arterial and venous pressures. The measurements moreover indicate that modeling of blood flow regulations is required to explain transients in PPGs and inaccurate SpO2 readings in more situations