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Tissue optics, electro-photonic sensors for diffuse multispectral photoplethysmography, associated signal processing to derive human physiological parameters and demonstration of clinical functionality.

In medicine knowledge about the blood circulation and respiratory function is crucial. Feeling the pulse and counting breaths is an art practiced for thousands of years. For just as long doctors have desired a way to simultaneously and objectively monitor multiple patients and being called upon only if needed. Medical photonic diagnosis started in 1937 when Hertzman built the first photoplethysmography (PPG) device, which was capable of measuring heart rate. But - as described by Hertzman - its PPG signal was “disturbed by changes in blood oxygenation”. A breakthrough occurred in 1974 when Aoyagi invented the pulse oximeter by exploiting this “disturbance” (caused by spectral absorption differences for Hb and HbO2) by measuring PPGs at two different wavelengths. Today pulse oximetry has become a standard vital monitoring parameter. By 1999 Masimo added extra tools like discrete saturation transform (DST) and Signal Extraction Technology (SET), also they added extra wavelengths to derive additional parameters like HbCO, MetHb, pulse index variability and oxygen reserve index. However advanced and useful presently marketed pulse-oximeters are, they have some limitations: • They need probes applied on heavily perfused areas like fingertip, earlobe, forehead, nose or toes. That can be quite cumbersome in daily life activities. Unobtrusive probes, e.g. integrated in a wrist watch or chest patch are more comfortable, but they make engineering harder because the signal is much weaker and more vulnerable to movement artifacts. • Current devices have a limited resolution (1%) and accuracy (must meet a root-mean-square difference of less than 4%). • Oxygen intake is realized through breathing, which has a slow pulsatile character, whereas the body uses oxygen in a constant fashion. This means that between breaths the oxygen diffusion force is decreasing. Traditional pulse oximeters, however cannot distinguish this small cyclic variation of arterial oxygenation, due to their limited resolution. Capturing this (and other) dynamic cardio-respiratory phenomena requires >10x times higher resolution. We intend to achieve this higher resolution to add extra diagnostic value to pulse oximetry. • When Hertzman wanted to study the arterial pulsation waveform via PPG in 1937 he was fully right that changes in oxygenation level influence PPG waveform morphology. We intend to measure at additional wavelengths to record both the truly mechanical pulse waveform and also the oxygenation level. • Oxygenation is the most dominant variable parameter in the bloodstream, but also other optical variables are present (HbCO, MetHb, Hematocrit/Hydration). • Present pulse oximeters suggest that SpO2 is a global parameter throughout the body, but it is not. The capillary vascular bed serves the oxygen exchange and looking into this micro circular exchange is the key to investigate early warnings of metabolic distress. This PhD will focus on tissue optics, design of electro-photonic sensors capable of capturing high signal to noise ratio diffuse photoplethysmography (PPG) as well as the derivation of physiological parameters within the human body. In particular, we will investigate possibilities for: Simultaneous measurements of arterial and capillary blood oxygenation, improvement of perfusion index, Carbon Monoxide hemoglobin, systemic and cephalic hydration. We will furthermore look into calibration aspects.

Date:1 Nov 2018 →  Today
Keywords:photonics, biomedical
Disciplines:Nanotechnology, Design theories and methods, Sensors, biosensors and smart sensors, Other electrical and electronic engineering
Project type:PhD project