Three dimensional Ballistocardiogram and Seismocardiogram: what do they have in common?

3D-body accelerations, i.e. Ballistocardiograms (BCG) and Seismocardiograms (SCG), ECG and Impedance-cardiograms (ICG) were recorded on healthy volunteers participating to the European Space Agency (ESA) 59th parabolic flight campaign. In the present paper we document the similarities and differences that can be seen in the seismo- and ballisto-cardiogram signals in different positions (standing and supine) under normal gravity condition as well as during the weightlessness phases (0G) of a parabolic flight. Our results demonstrate that SCG and BCG both present a similar three dimensional (3D) nature, with components of the BCG having lower frequency content than the SCG. The recordings performed in the 0G environment are the one with the smoothest shape and largest maximum magnitude of the Force vector. The differences seen between SCG and BCG stress further the importance for the need of using different nomenclature for the identification of peaks in both signals.

Cardiovascular changes in parabolic flights assessed by ballistocardiography.

This paper presents a comparison of the cardiovascular changes observed in microgravity as compared to ground based measurements. The ballistocardiogram (BCG), the electrocardiogram (ECG) and the transthoracic impedance cardiogram (ICG) were recorded on five healthy subjects during the 57th-European Space Agency (ESA) parabolic flight campaign. BCG is analyzed though its most characteristic wave, the IJ wave complex that can be identified along the longitudinal component of BCG and which has been demonstrated to be linked to cardiac ejection. The timings between the contraction of the heart and the ejection of blood in the aorta are analyzed via the time delay between the R-wave of the ECG and the I and J-waves of BCG (RI and RJ intervals respectively). Our results show that the IJ complex presents a larger amplitude in weightlessness and suggest that stroke volume (SV) increases in microgravity. We assume that ballistocardiography is an efficient method to assess the ventricular performance.

Timing and source of the maximum of the transthoracic impedance cardiogram (dZ/dt) in relation to the H-I-J complex of the longitudinal ballistocardiogram under gravity and microgravity conditions.

The transthoracic impedance cardiogram (ICG) and the acceleration ballistocardiogram (BCG) measured close to the center of mass of the human body are generated by changes of blood distribution. The transthoracic ICG is an integrated signal covering the whole thorax and spatial resolution is poor. Comparison between both signals can be used to elucidate the source of the ICG signal. We recorded the ECG, ICG, and BCG simultaneously in healthy subjects under resting and microgravity conditions during parabolic flights. The time interval between the R-peak of the ECG and the maximum of the ICG (R-dZ/dtmax) and the time interval between the R-peak of the ECG and the I-peak in the BCG (R-I) differed significantly (p<0.0001). The I-peak in the BCG always occurred earlier during systole than dZ/dtmax. The delay of dZ/dtmax ranged between 23 and 28 ms at rest and was lowest under microgravity conditions (12 ± 4 ms, p<0.02). Our results suggest that both signals have different sources. Combination of modern imaging techniques with classical non invasive approaches to detect changes of blood distribution may provide new insights into the complex interaction between blood flow and mechanocardiographic signals like the BCG.