Improved Detection of Ventricular Ejection Time for Impedance Cardiography

Impedance cardiography is a noninvasive technique for monitoring stroke volume (SV), based on sensing variation in the thoracic impedance due to blood flow. In this technique, first derivative of impedance (dz/dt) is used to calculate two parameters: ventricular ejection time and (-dz/dt)max. Respiration and motion artifacts cause base line drift in the sensed impedance waveform, and this results in errors in the estimation of the two parameters. Ensemble averaging of ICG signal suppresses motion artifacts but it introduces distortion in the signal. In this study, simultaneously acquired phonocardiogram (PCG) signal is used to estimate the time difference between the first and second heart sounds as a measure of ventricular ejection time. Since PCG signal is less influenced by respiratory and motion artifacts, it gives a relatively error free measurement.