Development of a clinical Pulse Wave Velocity estimation system using innovative graphene pressure sensors

Cardiovascular disease (CVD) is the leading cause of mortality in the world, with about 17.9 million deaths per year corresponding to 32% of total annual deaths. Early diagnosis and treatment of CVD can drastically reduce the chance of premature mortality and guarantee a normal life to the patients. Among the several predictive parameters, arterial stiffness has been proven to be an effective marker for evaluating the cardiovascular risk and it is strongly related with the Pulse Wave Velocity (PWV). Pulse Wave Velocity (PWV) represents the propagation speed of the pressure wave inside the arteries, and it is usually evaluated between the carotid and the femoral sites. In particular, it is calculated as the ratio between the two sites distance and the time elapses for running that length. Nowadays, the PWV estimation is performed using instruments based primarily on applanation tonometry, but the high cost has severely limited their use in clinical environment. For this reason, the aim of this thesis is the development of a low-cost, non-invasive device for PWV estimation. The sensitive elements used for this study are graphene-based pressure sensors created in partnership with the Nanochemistry research group, at “Institut de Science et d’Ingénierie Supramolécularies” of the University of Strasburg. They are characterized by a high sensibility and a short time response, which make them a good solution for this application. In fact, if placed on the skin in proximity of an artery, they can detect the smallest pressure variations caused by the artery displacement (pulse wave). The first part of the thesis has been focused on the design and implementation of a specific read-out electronics able to detect and amplify the signals acquired. The conditioning circuit has then been integrated in a system, run by a Pyboard D-series, in order to collect and send the pulses directly to a laptop. In addition, with the purpose of creating an easy to use and intuitive software a dedicated Graphical User Interface (GUI) has been realized and implemented in Python. Besides the real-time waves display, it allows the user to interact with the device and to adjust the settings of the system depending on the signal characteristics. Since the sensors provided by the University of Strasburg are extremely experimental and prototypal, they were characterized through mechanical tests to define their sensibility and mechanical behaviour. These tests have been carried out at DIMEAS (Departement of Mechanical and Aereospace Engineering) at the Polytechnic of Turin. Finally, thanks to the collaboration with “A.O.U. Città della Salute e della Scienza di Torino”, the system was validated on 5 patients in clinical environment. Data obtained by the developed system have been compared with the ones given by Sphygmocor, the golden standard for PWV estimation, and ATHOS, an innovative and validated device developed by “Politecnico di Torino”.