Innovative Oxygen Saturation Detection

The aim of the project is to examine the capability of the sensor VD6281 to evaluate the Peripheral Oxygen Saturation and the Heart Rate, in real-time and non-invasively. Nowadays, the SpO2 evaluations are mostly employed by transmission pulse oximeter, photoplethysmography application that works with the red and the IR LEDs. Each LEDs emit a light beam that it passes through the irradiated tissues, interacts with these and is partly absorbed. The residual transmitted rays are collected by a photodiode, opposite to the light beams direction. In this way, the PPG signal is obtain and it allows to estimate the Peripheral Oxygen Saturation. The measurements are essentials in the clinical environment to trace oxygen losses, in cases of severe cardiorespiratory diseases or to verify the anaesthetic efficacy. Specifically, commercial pulse oximeter are hand-held devices or probes applied to the finger, ear or forehead, utilized generally in the operating room and during the patients hospitalization. These devices have all the CE marking and are FDA approved. Most recent pulse oximeter develop system able to remotely send the SpO2 values to tablet or smartphones, in real-time. In this way, the clinicians can immediately recognize dangerous situation. Another important advancement could be incorporate the SpO2 estimation in wearable devices (e.g. smartwatch), as sleep monitoring parameter or to continuously monitor the blood oxygen concentration, during high altitude excursion. The data, indeed, is the only one not yet detected by wearable sensors, due to the not reliability of the estimated SpO2 values. It is correlated to the motion influence on the parameter and to the transmission probes typology, difficult to incorporate on this type of devices. The present work wants to determine the possibility to obtain a reflective pulse oximeter, easily to incorporate in a smartwatch, using the sensor VD6281. Precisely, this work is a preliminary study to understand if the measuring of the SpO2 with this new type of photodiode is trustworthy. The here employed pulse oximeter is composed by the VD6281 photodiode and the white led LM231A, provided by STMicroelectronics. The innovation of this work is the utilization of one LED only to estimate the SpO2, simplifying the hardware and the software necessary to design a typical pulse oximeter. The VD6281 is an ambient light sensor, which accurately distinguishes the visible spectrum (RGB), the infrared and the UV wavelengths. In this manner, it can perceive wavelengths from 350 to 1050 nm. The white led covers the wavelengths of interest for the calculation of the SpO2. The photodiode is characterized by 6 channels (red, green, blue, IR, UV and clear), these can be tracked contemporary. To maximize both the capabilities of the sensor and the absorbing properties of the tissues, the chosen wavelengths are the green and the red. Thus, the white LED can be used because it cover only the visible spectrum. The issues encountered in the work will be analysed and discussed throughout this report. The algorithm has been developed to estimate the value of the SpO2 and the HR in real-time. As a conclusive step in this work, the Rainbow PO has been tested by the comparison with the Onyx device, i.e. transmittance finger pulse oximeter which uses red and infrared wavelengths.