Non-invasive venous oximetry through venous blood volume modulation

For decades, the monitoring of mixed venous oxygen saturation has been done invasively using fibre-optic catheters. This procedure is not without risk as complications may arise from catheterization. This thesis describes an alternative and novel means of monitoring venous oxygen saturation. The technique outlined involves inducing regular modulations of the venous blood volume and the associated measurement of those modulations using an optical sensor. Just as pulse oximetry utilizes the natural arterial pulse to perform spectral analysis of the peripheral blood in order to estimate the arterial blood oxygen saturation, the new venous oximetry technique uses the artificially generated pulse to perform the task of measuring peripheral venous oxygen saturation. This thesis explores and investigates the feasibility of this new venous oximetry technique. A heuristic model was first developed to predict the effects of introducing an artificially generated pulsatile signal in the venous system. The effect on the underlying natural arterial pulsation was also examined. Experiments were then conducted to justify and interpret the model developed. Other experiments were also conducted to optimize the design of the artificial pulse-based venous oximeter, to explore the effects of prolonged modulation of the venous system and to establish evidence that the measurements made were indeed related to venous oxygen saturation. It is concluded that the new venous oximetry technique is indeed feasible and with further research and development would one day replace the current invasive method.