Suppression of the respiration artefact and extraction of the cardiac component in the thoracic impedance recorded through defibrillation pads

Circulation detection by checking the carotid pulse in cardiac arrest patients during cardiopulmonary resuscitation (CPR) has been reported inaccurate. Thoracic impedance (TI) measured via the defibrillator pads has been recently proposed for the assessment of circulation during CPR. However, ventilation artefacts severely corrupt and spectrally overlap the cardiac component of the TI. This study proposes an adaptive scheme to suppress respiration artefacts and extract the circulation component from the TI recorded through the defibrillation pads. The database consisted of 12 records from hemodynamically stable volunteers including the TI and the ECG. Each record contained intervals without respiration and intervals with 5 respiration rates. R-R intervals detected in the ECG were used to estimate the instantaneous frequency of the cardiac component of the TI. An adaptive scheme was applied to estimate the amplitude and phase of the three-harmonic model of the cardiac component. The method was evaluated in terms of signal-to-noise ratio (SNR) improvement, and in terms of the normalized cross correlation coefficient of the circulation components obtained during respiration and in artefact-free intervals.