Dynamic Comparison of Current Ballistocardiographic Methods

Abstract

Part I dealt with dynamic arrangements (Dock, Smith, Walter, Nickerson, Burger, v. Wittern) which could be treated approximately as single masses in the lower frequency range. It was shown that in addition to the cardiovascular forces sought, other undesired forces from the support were mixed in, seriously altering the record: especially for components in the important 4 to 8 cycles per second region. Second, emphasis was laid on the several meanings that could be assigned the displacement, velocity and acceleration (DVA) records, according to what dynamic aspect (motion, momentum or force) of the cardiovascular action they were referred. It was explained that all direct-body and stiff-bed ballistocardiographic records were "compound", as they could not be referred to any one of these dynamical quantities. In part II, we will discuss the platform methods in detail, showing how the platform mass comes into the record. The arguments for and limitations of the various platform methods are considered, including the "shin-platform" and the very light pendular platforms now being tried.