A comparison between ultralow-frequency ballistocardiograms and those secured by an improved high-frequency technique, with studies to explain remaining differences

Abstract

The advance in ballistocardiographic instrumentation which has been so rapid and so encouraging in recent years has been due primarily to the use of certain physical principles. On the assumption that well-known physical formulae could be properly applied to the vibration problems of the human body, a new viewpoint emerged. This included a well-based criticism of the high-frequency (HF) ballistocardiograph, ¹⁻² i.e., that the movement which took place between body and table was introducing an error, and that the vibration properties of this movement between body and table led to an undue magnification of certain components of the recorded forces, those delivered in resonance with the body's own vibration properties, and undue attenuation of others, those above the body's resonance frequency. It was proposed to avoid or minimize such errors by using another type of instrument, the ultralow-frequency (ULF) ballistocardiograph.³⁻⁶