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  • Title: Computer determination of systolic time intervals based on impedance cardiography.
    Author: Szilágyi N, Láng E, Balázs L.
    Journal: Int J Psychophysiol; 1992 Jul; 13(1):45-9. PubMed ID: 1522032.
    Abstract:
    A computerized system has been developed based on impedance cardiography for processing systolic time intervals (STI) in psychophysiological experiments. The conventional method of STI determination is based on transducing three signals: electrocardiogram, phonocardiogram and pulse tracing (carotid pulse). Because of its negligible pulse transmission time the first derivative impedance cardiogram (dZ/dt) is more reliable than other pulse signals. Since the sharply demarcated points of the dZ/dt waveform occur simultaneously with the cardiac events the dZ/dt makes phonocardiogram processing unnecessary. Computer algorithms for STI assessment are based on processing two signals: the ECG and dZ/dt. The pre-ejection period (PEP), the left ventricular ejection time (LVET) and electromechanical systole (QS2) are derived by recognizing the B and X points on the dZ/dt signal as the endpoints of PEP and LVET respectively. X point identification consists of two steps: (i) the estimation of the QS2 based on the regression relationship between QS2 and heart rate (HR) and (ii) a filtering procedure for exact localization of the X point. The B point is determined by calculating the curvature function of the dZ/dt and employing a clustering procedure. The accuracy and reliability of the software were tested by processing data from 40 subjects under stress condition (cold pressor and mental arithmetic).
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