Development of a multi-parametric wearable device based on electrocardiography and photoplethysmography.

The focus on wearable, non-invasive and portable devices is increasing, following the research and development of new solutions to provide biomedical signals with high accuracy and precision. In particular, this work reports the design of a new device for home monitoring that combines electrocardiography (ECG) and Photoplethysmography (PPG) to obtain suitable parameters about the physiological state of humans. The knowledge about the physiological event that will be monitored is always the starting point to design a new biomedical device. The section ‘Physiological background’ reassumes the anatomy and physiology of cardiocirculatory and respiratory system, that works in synergy to allow the functional activity of the human body. The ECG signal mirrors the spreading of the contractile force of the heart cells through the body. It is generally collected as electrical signals that flow on the skin tissue. The PPG signal is an optical technique that produces a signal able to follow up the cardiac cycle of the heart. This technique has a high spread in the pulse oximeter, a medical device typically used to measure blood oxygen saturation. The developed prototype includes two sensors: a bioimpedance sensor and an optical sensor. The first one detects biopotential on the skin to obtain an ECG signal; the second is a multiwavelength sensor for PPG detection. Every sensor was tested on a developing board before producing the prototype of the device. The preliminary test on the device concerned concerns the functionality of the sensors and its communication protocol. The device collects raw data that are post analysed on MATLAB®. An algorithm filters the data and calculates the signal-to-noise ratio and the heart rate from the ECG recording of 6 healthy volunteers. The PPG results section includes the outcomes of a single green LED emitter tested on a healthy subject. In the prototype, the PPG sensor is substituted with a multiwavelength sensor that permits the estimation of some physiological parameters, like oxygen saturation. All the ECG recordings have a positive signal-to-noise ratio, and the waveform is confrontable with other certificate ECG devices. The green LED has a high sensitivity that looks promise for further application and improvement of this multiparametric device. In the future, this device could be implemented to be wear and used during daily activity and to follow up patients after their hospitalisation period.