1.1 Introduction In this chapter, the first phase of the project is explained. First, a brief description of the working principle of the SpO2 sensor and its resulting PPG signal, second the features extracted and their significant meaning and finally the classification process. 1.2 The SpO2 sensorThe hemoglobinis the protein in the blood responsible for transporting oxygen to the bodyorgans, when it is carrying 4 oxygen molecules (completely saturated) it iscalled oxyhemoglobin (HbO2) otherwise it is called reducedhemoglobin or non-oxygenated hemoglobin (RHb).
The oxygen saturation measuredby the SpO2 sensor shows the amount of oxygen that is being carriedby the hemoglobin. The SpO2 sensor is a non-invasive method thatmeasures in addition to the oxygen saturation, the heart rate, and aphotoplethysmogram waveform by being placed on the finger of the individual. 1.2.1 Working PrincipleThe SpO2 sensorcontains 2 light sources (LEDs); they emit red and infrared signals with 660nmand 940nm respectively since the absorption trait of the hemoglobin differswith respect to its synthetic binding and the wavelength of the light sent.
Thenon-oxygenated hemoglobin absorbs red light (660nm) whereas the oxygenatedhemoglobin absorbs infrared light (940nm). These signals pass through the bloodvessels in the finger where only the unabsorbed ones reach the photodetector onthe opposing side of the sensor; these signals are then sent back to themonitor for processing where the oxygen saturation is calculated and displayed.Figure ?3.1: SpO2 working principle 1.2.
2 Photoplethysmographic SignalWhen theinfrared and red light passes through the finger, they are not only absorbed bythe blood vessels, but they are absorbed, scattered and reflected by othertissues, bones, skin, and arterial and venous blood. This leads to a photoplethysmogramwaveform having both AC and DC components as shown in the figure below (figure 3.2);since the arterial blood is pulsatile and acquire AC components it can beextracted from the non-pulsatile blood and other tissues that acquire DCcomponents. The resulting signal (shown in figure 3.
3) has a unique form thatdiffers between individuals which made it a good cause to be used as a biometrictechnique after extracting its features.