Abstract
Ballistocardiography is concerned with recording the movement of human body and deriving physically, physiologically, clinically pertinent information from the recording. The movement of the body on a table is exerted by the forces in the heart and aorta produced by the blood emitted from the heart. These forces are spatially distributed throughout the body corresponding to the phasses of cardiac cycle, and transformed into the motion of the table. Therefore, the human body as an oscillating system, i. e., mechanical characteristics of the body as well as those of the table should be first investigated in order to, make use of ballistocardiography.
The authors investigated the human body as an oscillating system by analyzing the : responses of the body to external forces, and simulated the combined system of body and table to a three-dimensional system with the the aid of an analog computer. It was assumed that the human body is rigid and possesses springs and dampers on its surface.
The experimental results indicate that the natural frequencies of the body in free-motion are 5 cps, and 5 cps and 10 cps and that the damping ratios are O. 1, 0.1 and 0. 17 in the left to right, head to foot and back to forward directions, respectively. The results of simulation suggest that the increase in the degrees of freedom of the table is desirable for better table-body characteristics.
