The elimination of body resonance distortion from the direct-body ballistocardiogram.

T HE recorded ballistocardiogram is a distorted representation of cardiovascular forces.1, 2, 3 These forces, which are generated by the contracting heart and accelerated blood, are transformed in transmission to the surface of the body. The resultant body movement is determined by the amplitudes of the transmitted forces and the mechanical response of the body. It is the purpose of this paper to present a practical means of neutralizing the distorting effect of the body's resonance on the longitudinal ballistocardiogram of the supine subject lying on a rigid surface. The longitudinal motion of the supine body may be described mathematically, if it is assumed that the body behaves as a simple mechanical system. The normalized displacement and velocity amplitude responses of such a simplified body to sinusoidal forces are given in equations (1) and (2):4' 5, 6, 7