Development and evaluation of venous oximetry

Photoplethysmography, a technique to measure by optical means volume changes, has been known and applied for many years. One of its most popular applications is pulse oximetry, a non-invasive method to measure oxygen content in arterial blood. It is based on the principle of arterial blood volume changes due to heart contractions, known as systoles. Systolic pulsations appear on the arterial vascular system, while blood flow in veins does not normally present pulsations, especially at remote parts of the peripheral vascular system, such as the fingers. Therefore, pulse oximetry is only applicable to arteries as their pulsations allow for separation of the pulsatile components from the rest of the absorbing components. A novel non-invasive technique permits the measurement of venous oxygen saturation by introducing a series of pulsations in the veins thus allowing the separation of venous signal components for calculation of venous oxygen saturation. This thesis presents a theoretical model describing the mechanical coupling of arteries and veins and its effects in the accuracy of oxygen saturation measurement. [Continues.]