Wavelet Based Cancellation of Respiratory Artifacts in Impedance Cardiography

Impedance cardiography is a noninvasive technique for monitoring stroke volume, based on sensing variation in the thoracic impedance, z(t), due to blood flow. In this technique, first derivative of impedance, dzjdt, is used to calculate two parameters: ventricular ejection time and (-dzjdt)max. Respiration and motion artifacts cause base line drift in the sensed impedance waveform, particularly during exercise, and this drift results in errors in the estimation of the two parameters. Ensemble averaging of dz/dt signal suppresses respiratory and motion artifacts but it introduces distortion in the signal. In this study, a wavelet based denoising method is used to cancel corrupting respiratory artifacts from the dz/dt and z(t) signals in order to make a reliable estimate of cardiac output.