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.

Estimating the center of mass of a free-floating body in microgravity.

This paper addresses the issue of estimating the position of the center of mass (CoM) of a free-floating object of unknown mass distribution in microgravity using a stereoscopic imaging system. The method presented here is applied to an object of known mass distribution for validation purposes. In the context of a study of 3-dimensional ballistocardiography in microgravity, and the elaboration of a physical model of the cardiovascular adaptation to weightlessness, the hypothesis that the fluid shift towards the head of astronauts induces a significant shift of their CoM needs to be tested. The experiments were conducted during the 57th parabolic flight campaign of the European Space Agency (ESA). At the beginning of the microgravity phase, the object was given an initial translational and rotational velocity. A 3D point cloud corresponding to the object was then generated, to which a motion-based method inspired by rigid body physics was applied. Through simulations, the effects of the centroid-to-CoM distance and the number of frames of the sequence are investigated. In experimental conditions, considering the important residual accelerations of the airplane during the microgravity phases, CoM estimation errors (16 to 76 mm) were consistent with simulations. Overall, our results suggest that the method has a good potential for its later generalization to a free-floating human body in a weightless environment.

3D-ballistocardiography in microgravity: comparison with ground based recordings.

3D-Ballistocardiograms ECG and Impedancecardiograms (ICG) were recorded on 5 healthy volunteers participating to the European Space Agency (ESA) 57(th) parabolic flights campaigns. Comparisons are made between the baseline recordings performed on the ground and the recordings made during the microgravity phases of a parabolic flight. The spatial curves of the displacement, velocity and acceleration vectors, instead of their individual components are used to compute the magnitude of the force vector, kinetic energy and work during the cardiac cycle. Our hypothesis is that the 3D-BCG provides parameters correlated with the timings of ejection (PEP, LVET). Although our subject population is limited (N=5), this is the first study of BCG to be performed with N>1. Our results suggest that microgravity decrease the complexity of the 3D displacement curve and that peaks in curvature are consistently present in microgravity and on the ground. However they do not seem to be perfectly related to the classical cardiac ejection timings from ICG.

Three dimensional ballisto- and seismo-cardiography: HIJ wave amplitudes are poorly correlated to maximal systolic force vector.

Ballistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to the ESA 55(th) and DLR 19(th) parabolic flights campaigns. In this paper we demonstrate further the usefulness of recording and analyzing ballistocardiograms (BCG) in three dimensions. The spatial curves of the displacement, velocity and acceleration vectors are analyzed instead of their individual 2-D components. The maximum magnitude of the force vector is shown to be poorly correlated to the HI and IJ wave amplitude traditionally computed on the longitudinal (feet-to-head) component of acceleration (uni-dimensional BCG). We also suggest that kinetic energy and work are useful parameters to consider for a physiological interpretation of the 3D-BCG. The technique presented is invariant from the axis of representation and provides important novel physiological information. We stress further the need of 3D recordings and analysis techniques for Ballisto- and Seismo-cardiography.

Comparison between EEMD, wavelet and FIR denoising: influence on event detection in impedance cardiography.

During thoracic impedance signal acquisition, noise is inherently introduced and hence, denoising is required to allow for accurate event detection. This paper investigates the effectiveness of Ensemble Emperical Mode Decomposition to filter random noise. The performance of the EEMD method is compared with an optimal FIR filter and wavelet denoising. The IMF selection for signal reconstruction in the EEMD denoising method is optimized using a sequential search. Denoising performance was evaluated by the SNR and the accuracy in event detection after filtering. When all criteria are taken into account, wavelet seems to outperform both EEMD and FIR denoising.

Three-dimensional ballistocardiography in microgravity: a review of past research.

This paper gives a short review of research on ballistocardiography in microgravity and indicates the benefits from this research for the use of BCG as a terrestrial cardiac monitoring system. In the past, 3-D methods required large devices to decouple the subject from the terrestrial environment and hence, BCG on Earth is usually limited to unidirectional recordings of the motion in the head-to-foot direction. However, microgravity provides a suspension-free environment where accelerations can be measured in all directions without the influence of gravity. Microgravity research indicated that along with the acceleration in the head-to-foot direction, the accelerations in the lateral and dorso-ventral direction are important in understanding the physiological forces during a cardiac cycle. Further, lung volume has a large influence on the transmission of cardiac forces to the surface of the body. To date, only the three separate components of the acceleration vector have been analyzed in 3-D BCG studies. Using the true acceleration and displacement vector (orientation and magnitude), rather than the three separate components, may permit more accurate cardiac event detection.

Three dimensional ballistocardiography: methodology and results from microgravity and dry immersion.

Balistocardiography was recorded in 3-D on a free floating astronaut in space as well as on healthy volunteers participating to a dry immersion study in a terrestrial laboratory. We demonstrate a new technique suitable for the analysis of 3-D BCG. The spatial curve of the displacement vector is analyzed instead of the three components of acceleration. The technique presented is invariant from the axis of representation and provides important novel physiological information.

A new model for utricular function testing using a sinusoidal translation profile during unilateral centrifugation.

The utricle plays an important role in orientation with respect to gravity. The unilateral centrifugation test allows a side-by-side investigation of both utricles. During this test, the subject is rotated about an earth-vertical axis at high rotation speeds (e.g. 400°/s) and translated along an interaural axis to consecutively align the axis of rotation with the left and the right utricle. A simple sinusoidal translation profile (0.013 Hz; amplitude = 4 cm) was chosen. The combined rotation and translation induces ocular counter rolling (OCR), which is measured using 3-D video-oculography. This OCR is the sum of the reflexes generated by both the semicircular canals and the utricles. In this paper, we present a new physiological model that decomposes this total OCR into a canal and a utricular contribution, modelled by a second-order transfer function and a combination of 2 sine functions, respectively. This model yields parameters such as canal gain, cupular and adaptation time constants and a velocity storage component for the canals. Utricular gain, bias, phase and the asymmetry between the left and the right utricle are characteristic parameters generated by the model for the utricles. The model is presented along with the results of 10 healthy subjects and 2 patients with a unilateral vestibular loss due to acoustic neuroma surgery to illustrate the effectiveness of the model.