Automatic determination of cardiac output using an impedance plethysmography

A computer-based system which calculates stroke volume, heart rate and cardiac output automatically from the transthoracic impedance variation has been developed. A beat-by-beat determination was performed on several healthy subjects and patients with atrial fibrillation during spontaneous breathings at rest. The respiratory artifact appearing on the impedance cardiogram was canceled by (1) correcting the base line of dZ/dt for each cardiac cycle on the basis of assumption that the dZ/dt values at ECG-R waves would be invariable regardless of the respiratory phase when the respiratory movement ceases, and (2) averaging the signals for a number of cardiac cycles. Comparisons between the computed stroke volumes and those obtained from a manual calculation showed good agreement.