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.