Centracchio, Jessica (2023) Cardio-respiratory monitoring via Forcecardiography. [Tesi di dottorato]

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Abstract

To date, Seismocardiography (SCG) is the most widespread technique for cardio-mechanical monitoring. SCG measures infrasonic cardiac-induced mechanical vibrations via accelerometers placed on the chest. The SCG signal is mainly used to locate important cardiac cycle events, thus allowing the estimation of cardiac time intervals of clinical relevance. Very recently, a novel, non-invasive technique, namely Forcecardiography (FCG), has been introduced to record the weak forces induced onto the chest wall by the mechanical activity of the beating heart via broadband force sensors. FCG sensors proved capable of capturing signals with much richer information content as compared to SCG. Indeed, the FCG signal consists of two infrasonic components, namely low-frequency FCG (LF-FCG) and high-frequency FCG (HF-FCG), and a sonic component corresponding to the heart sounds. In this thesis, a deeper investigation on the information content of FCG signals was carried out, and the performance of FCG was assessed against reference techniques. To this aim, FCG and SCG signals were acquired simultaneously on a cohort of healthy subjects, along with Electrocardiography recordings. Results of the experimental tests showed that the HF-FCG shares a very high similarity with the SCG signal and provides very accurate localization of aortic valve opening and closure events and estimates of inter-beat interval, pre-ejection period and left ventricular ejection time. The LF-FCG reflects heart walls motion, thus potentially carrying information on ventricular volume variations. This low-frequency component is generally not visible in SCG recordings. In this thesis, a specifical numerical procedure was proposed to recover this information from SCG. However, despite its high similarity with the LF-FCG, this low-frequency SCG component has not very high consistency within the cardiac cycle, thus leading to inaccuracies in inter-beat intervals estimation. In addition to the cardiac components, a large, very low-frequency component related to respiration, referred to as the Forcerespirogram (FRG), was observed in FCG signals. The FRG captures the forces impressed onto the chest wall by the expansions and releases of the ribcage during the breathing acts. For this reason, FCG signals were acquired simultaneously with reference respiration signals. The FRG signals achieved high accuracy and precision in respiratory acts detection and inter-breath intervals measurement. In addition, cardio-respiratory interactions have been shown to cause amplitude modulations of the LF-FCG and HF-FCG components, as well as changes in various parameters of heartbeat morphology. Finally, FCG sensors were used to monitor finger pulse waves. In conclusion, FCG stands as a very promising cardio-respiratory monitoring technique.

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