Signal-Shape Locked Loop (SSLL) as an Adaptive Separator of Cardiac and Respiratory Components of Bio-Impedance Signal

The paper presents an on-line signal processing system for adaptive separation of two infra-low frequency signals: cardiac and respiratory bio-impedance (BI) signals, which are the time varying components of the total BI signal. The separation process of such signals as cardiac and respiratory BI components, is not a trivial filtering due to overlapping of spectra and non stationarity of these signals, and moreover, due to the infra-low frequency range. Therefore, advanced signal processing concepts and methods are needed to achieve the goal. The Signal-Shape Locked Loop (SSLL) concept was introduced to solve the task. Using this concept, it is possible to separate two (or more) independent signal components from the total input signal. Technical solution of the system is intended for applications in portable and implantable cardiac devices.