A portable electronic system for non-invasive real-time acquisition of multiple physiological signals

Abstract

In this work, we have designed and realised a portable and compact electronic system for the synchronous acquisition of multiple physiological signals. The system employs a Texas Instruments ADS1298 front-end with 24-bit resolution for data acquisition and supports up to 8 channels and 4 kHz sampling rate. The front-end communicates via SPI with a STM32 microcontroller which pre-processes the data and sends them through USB or Bluetooth to a suitable PC application. The system has been realized for the simultaneous acquisition of electrocardiographic (ECG) and photoplethysmographic (PPG) signals, but it can also be employed for acquiring other typologies of signals, e.g. breathing or electro-dermal activity, for a potential use in the automotive field to assess the driver’s health status in real-time or, in perspective, the stress level. PPG probes have also been realised, each one including dual wavelength LED (emitting at 735 and 850 nm), and a Silicon Photomultiplier (SiPM) detector (provided by STMicroelectronics) having high responsivity and gain [1]. The system integrates an I2C interface, 8-channel, 16-levels current LED driver for PPG probes and includes a Graphical User Interface (GUI) able, in real time, to (i) plot the signals, (ii) save the data, (iii) calculate and display main cardiovascular parameters (i.e., heart rate, breath rate, pulse arrival time, pulse transit time, pulse wave velocity). Both instantaneous or averaged values of heart rate are shown, also to display the time variation of the considered parameters and thus assess the so-called Heart Rate Variability [2]. Current version of the system is able to acquire up to 5 PPG waveforms and 3 ECG leads. Figure 1 shows a photo of the system, alongside with the PPG probes (on the right) and the standard ECG electrodes (on the left) which are used for signals acquisition. Figure 2 illustrates some screenshots of the developed GUI showing 2 ECG leads and 2 PPG waveforms. In detail, Fig. 2(a) depicts the windows displaying the waveforms, while, Fig. 2(b) exhibits the window dedicated to show in real-time the instantaneous and averaged values of the above-mentioned physiological parameters. Several measurement campaigns have been carried out on healthy volunteers of different ages to both test the correct functioning of the system, and also to compare the Pulse Arrival Time values computed between different body locations. In the future, by performing measurements on other typologies of subjects (e.g., hypertensive or diabetic patients), a statistical analysis of the collected data will be carried out, in order to evaluate the capability of using our system for distinguishing between different pathologies or for early disease detection, or even for assessing various stress levels. This activity was supported by Advancing Smart Optical Imaging and Sensing for Health (ASTONISH) Project (Grant no. 692470), funded by H2020-EU.2.1.1.7.-ECSEL programme.