Forcecardiography: a novel technique to measure heart mechanical vibrations onto the chest wall

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Background and motivation

Electrocardiography (ECG) is undoubtedly the most used technique to analyse and monitor the heart and, indeed, it is currently used to diagnose many different cardiac pathologies. However, ECG only provides information about the electrical behaviour of the heart, so it cannot be used to analyse also the corresponding mechanical behaviour, thus limiting the scope of cardiac monitoring.

Since the second half of the XIX century, several different techniques have been proposed to gather information on cardiac mechanics. However, the cumbersome instrumentation involved, as well as the lack of reliable annotation standards, made them almost disappear from scientific research, in favour of more appealing techniques, such as  echocardiography. Thanks to the availability of modern, small and lightweight sensors, some of these techniques, i.e. Ballistocardiography (BCG) and Seismocardiography (SCG), came back in vogue as a mean for unobtrusive, long-term cardiac monitoring. SCG measures the mechanical vibrations induced by the beating heart via accelerometers placed on the chest wall, and provides information on different mechanical events of the cardiac cycle (e.g. opening and closure of heart valves, variations of blood flow, etc.).

 

Our research

In a very recent article, we presented a novel technique, the Forcecardiography (FCG), which measures the local, cardiac-induced, mechanical vibrations of the chest wall. FCG is performed via a custom force sensor, based on Force Sensitive Resistors (FSR), that we have already proposed for muscle contraction monitoring in a previous publication. This very small, lightweight, unobtrusive sensor, which does not require any electrical contact with the skin, is particularly suitable for continuous, long term patient monitoring.



We performed experimental tests by simultaneously acquiring FCG and SCG recordings from the same site on the chest wall. The signal provided by the FCG sensor, i.e. the forcecardiogram, showed a richer informational content as compared to SCG. Indeed, FCG turned out to be characterized by a large low-frequency component, which was not observed in SCG and seemed to be associated with ventricular volume variations, and by a small high-frequency component, which was very similar to SCG.
These preliminary, yet encouraging results, suggests that, in addition to the information provided by SCG, FCG could also acquire new information on ventricular contraction, thus paving the way for a more advanced, continuous, long term patient monitoring.

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