Forcecardiography: A Novel Technique to Measure Heart Mechanical Vibrations onto the Chest Wall

Abstract

This paper presents forcecardiography (FCG), a novel technique to measure local, cardiac-induced vibrations onto the chest wall. Since the 19th century, several techniques have been proposed to detect the mechanical vibrations caused by cardiovascular activity, the great part of which was abandoned due to the cumbersome instrumentation involved. The recent availability of unobtrusive sensors rejuvenated the research field with the most currently established technique being seismocardiography (SCG). SCG is performed by placing accelerometers onto the subject’s chest and provides information on major events of the cardiac cycle. The proposed FCG measures the cardiac-induced vibrations via force sensors placed onto the subject’s chest and provides signals with a richer informational content as compared to SCG. The two techniques were compared by analysing simultaneous recordings acquired by means of a force sensor, an accelerometer and an electrocardiograph (ECG). The force sensor and the accelerometer were rigidly fixed to each other and fastened onto the xiphoid process with a belt. The high-frequency (HF) components of FCG and SCG were highly comparable (r > 0.95) although lagged. The lag was estimated by cross-correlation and resulted in about tens of milliseconds. An additional, large, low-frequency (LF) component, associated with ventricular volume variations, was observed in FCG, while not being visible in SCG. The encouraging results of this feasibility study suggest that FCG is not only able to acquire similar information as SCG, but it also provides additional information on ventricular contraction. Further analyses are foreseen to confirm the advantages of FCG as a technique to improve the scope and significance of pervasive cardiac monitoring.

Respiration Monitoring via Forcecardiography Sensors

“…Figure 4a shows an excerpt of the raw FCG, ERB and ECG signals acquired. In the raw FCG signal, the typical FCG components related to the cardiac activity [90] appear as superimposed to a much larger and slower component, which is related to the respiration. Indeed, Figure 4b depicts the respiratory and the cardiac components extracted from the same FCG signal depicted in Figure 4a.…”

“…This circuit ensures linearity and minimizes sensor drift by keeping the voltage across the FSR at a constant value [91,93,94]. The FCG sensor was calibrated before In particular, considering that the FSR shows a linear response to the applied force in terms of electrical conductance, a conditioning circuit based on a transimpedance amplifier was used [90,91]. This circuit ensures linearity and minimizes sensor drift by keeping the voltage across the FSR at a constant value [91,93,94].…”

“…This circuit ensures linearity and minimizes sensor drift by keeping the voltage across the FSR at a constant value [91,93,94]. The FCG sensor was calibrated before measurements in order to obtain the transduction coefficient from voltage to force [90,91].…”

“…Very recently, some of the authors presented the novel forcecardiography (FCG) technique for the measurement of the chest wall vibrations induced by the mechanical activity of the beating heart [90]. This technique proved capable of acquiring, in addition to a seismocardiogram-like signal, a novel low-frequency component that seems to carry information on ventricular filling and emptying dynamics.…”

“…This study aims to demonstrate the suitability of the FCG sensor [90] for accurate, continuous and unobtrusive monitoring of respiration. Experimental tests were performed on seven healthy volunteers, who were asked to perform several respiration cycles while resting on a chair.…”