Noninvasive Measurement of Systolic Time Intervals in the Dog Through the Use of Bioelectric Impedance

Abstract

Systolic time intervals which include pre-ejection period (PEP), electromechanical systole (EMS), and left ventricular ejection time (LVET) were recorded from the ascending aortic pressure (AP) waveform, and these values were compared to simultaneously derived measurements from the impedance waveform. In 11 male hounds anesthetized with 25 mg/kg thiopental, the changes in impedance (delta Z) and the first derivation (dZ/dt) of the latter waveform were studied over a heart rate range of 149-208 beats/min. The onset of the AP and delta Z waveforms along with the ejection point (E point) of the dZ/dt waveform (point on dZ/dt waveform that occurs at the same point in time as the most rapid upstroke point of delta Z), occurred simultaneously. The dicrotic notch (termination of LVET) of the AP and delta Z waveforms and the major downward deflection of dZ/dt also occurred simultaneously. Derived from the above mentioned waveforms, PEP ranged from 0.045 to 0.090 s (r = 1.0 in each case), LVET ranged from 0.120 to 0.190 s (r = 0.998), and EMS ranged from 0.180 to 0.250 s (r = 0.998). These results indicate that noninvasive bioelectric impedance techniques may allow for accurate determination of systolic time intervals.