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

Abstract

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.

Bio-impedance signal decomposer: enhanced accuracy and reduced latency solution

“…The proposed improvements allowed to reduce the length of the FIR filters (Fig. 2) from 801 samples (in the previous version of the BISD [ [23][24][25][26][27]) to 401 samples. Thus the latency of the BISD is reduced from two to one second, taking into account that the whole BISD system sampling rate is 200 samples/s.…”

“…An adaptive bio-impedance signal decomposer, intended to solve the signals separation task and to overcome related difficulties, was proposed by the author in [ [23][24][25][26][27].…”

“…2. The module, which constructs the cardiac signal model by tracking its parameters synchronously with the estimated cardiac signal, is named signal-shape locked loop (SSLL), which is described in [25][26][27].…”

“…An amplitude estimator, which was used in the BISD before applying the proposed one, is described in [23][24][25][26][27]. In that correlation-based estimator, the input cardiac signal is multiplied by the in-phase reference signal, after that an absolute value of the result is passed through the IIR low-pass filter for smoothing the final amplitude estimate and then scaling it by a predefined constant factor.…”

An Adaptively Tunable Model of the Cardiac Signal for the Bio-Impedance Signal Decomposer (BISD)

“…The current paper proposes further development of the BISD, which is based on the previously developed method [3,4] and the system of the cardiac and respiratory BI signals separation, called the Bio-Impedance Signal Decomposer (BISD) [5].…”