Electrical impedance cardiogram in derivation of systolic time intervals.

The reliability and use of the differentiated electrical impedance cardiogram (dZ/dt) in calculating systolic time intervals were assessed in 185 subjects under varying conditions. In the first phase, simultaneous recording of carotid pulse, dZ/dt, electrocardiogram and phonocardiogram (PCG) was obtained in 50 normal volunteers under controlled conditions. In the second phase dZ/dt, electrocardiogram and phonocardiogram were obtained initially, and carotid pulses, electrocardiograms, and phonocardiograms were recorded immediately afterwards. Serial recordings were obtained in 35 subjects