Some observations on the relation of the high-frequency bed ballistocardiogram to that obtained from an aperiodic bed.

A previous analysis of the mechanical behavior of current ballistocardiographic systems allowed the prediction of certain relationships between records from the Starr high-frequency bed and those representing undistorted forces applied to the body by the cardiovascular "generator." The latter were obtained by recording the acceleration of an "aperiodic mercury bed" platform. A relationship between the form of these two types of records from 80 subjects was sought. In varying types of normal and abnormal records the predicted relationship between the two different kinds of ballistocardiograms was consistently observed. It is concluded that records from the high-frequency bed grossly reflect the slower forces applied to the body, but are distorted with respect to phase, amplitude and frequency content, this being due in part to the elastic properties of the dorsal surface of the body and in part to the weight and stiffness of the platform support.