The objective of this space flight experiment is to correlate cardiovascular parameters with ballistocardiography parameters obtained through a novel analysis of 3 dimensions (3D) movements of the human body that are due to the mechanical action of the beating heart and the ejection of blood in the arteries. The aim is to better understand the cardiovascular changes following the fluid shift observed in microgravity from the analysis of the vecto-ballistocardiograms in humans.
Ballistocardiography (BCG) is a non-invasive technique for assessing the cardiac function from the body accelerations consecutive to the mechanical action of the heart. On Earth, it is based on the recording of horizontal 2D movements or accelerations of subjects in supine position at rest on a freely-moving platform. Thus the ventro-dorsal component is directed vertically and subject to gravity damping. However, symmetry considerations and blood ejection that is mainly directed along the feet-to-head direction lead to neglect it. While direct 3D-BCG is only feasible in sustained microgravity, only a very limited number of such recordings have been performed. From the analysis of 3D-BCG data recorded during the Spacelab-D2 mission, we showed that this ventro-dorsal component had the same magnitude as the other two, and that the 3D-BCG curve is likely linked to the asymmetry of the blood distribution in the arterial tree. This indicates that past assumptions were wrong. The analysis of 3D-BCG should provide outstanding new information on the mechanical aspects (contractility, stroke volume changes, blood shifts…) of the cardiovascular and autonomic adaptation in individual astronauts during long term space flights.
3D-BCG is recorded on free floating astronauts at rest, during asymmetric motor tasks and during imposed and controlled breathing protocols at different times of a space flight. Echocardiography, impedance cardiography and respiration are recorded simultaneously or consecutively to help understanding the physiological determinants of the 3D-BCG curve and interpret its possible changes during the flight. The analysis of heart rate variability helps assessing the possible contribution of autonomic adaptation. All protocols are based on non-invasive techniques and devices (with a single exception) already on-board the ISS.
Our proposal for the investigation of cardiorespiratory adaptation to microgravity is based on previous experiments performed in microgravity and on our participation in previous missions (Spacelab-D2; Euromir-95; Neurolab STS-90; odissea Soyuz-TMA-1; etc.). These experiments have shown that heart rate (HR) decreases in µG, shows an adaptation during the flight, increases on return to normal gravity and remains high still 15 days after return. These adaptation processes leads to changes that are likely the cause of orthostatic intolerance in the early days after the return from even a short (<15days) durations space-flight. Moreover adaptation to microgravity can lead also to muscular atrophy and consequently to cardiac atrophy which can lead to a decreased contractility. However these changes are still poorly understood and less documented for long-term (>15 days) adaptation.
A potential application of the study is the development of a wearable non-invasive monitoring system for astronauts, offering insight in both the electrical (ECG) and mechanical (BCG) cardiac function. The study is expected to confirm the correlations observed in the past as well as shed new light on the presently disregarded long-term cardiac mechanical adaptation to microgravity.
The output of this study could well be of high benefice for the cardiac monitoring, via non-invasive and non obtrusive techniques, of astronauts during long-term space flights as well as for the development of a ground based application.
The B3D project is run in collaboration with the following international teams:
- Kim Prisk, University of California San Diego, San Diego, USA
- Jens Tank, Medizinische Hochschule Hannover, Hannover, Germany
- Roman M. Baevsky, Institute of Biomedical Problems, Moscow, Russian Federation
- Enrico Caiani, Politecnico Di Milano, Milan, Italy
- Marco Di Rienzo, Fondazione Don Carlo Gnocchi Onlus, Milan, Italy