ObjectiveThe waveform of the first derivative of thoracic electrical bioimpedance was used to calculate systolic time intervals of the cardiac cycle, preejection period/left ventricular ejection time ratio, and diastolic time intervals, isovolumic relaxation period/filling time ratio.DesignProspective clinical study. Waveforms were examined from 913 normal and abnormal tracings from a thoracic electrical bioimpedance monitor. This monitor was coupled to a two-channel strip-chart recorder that identified preejection period/LV ejection time and isovolumic relaxation period/filling time in 86% of the tracings.SettingTwo university-affiliated hospitals and one community hospital.PatientsWe assessed 100 subjects (ranging in age from 17 to 93 yrs) under various conditions.Measurements and Main ResultsData from 15 normal subjects were used as a reference series to define normative values. Preejection period/left ventricular ejection time ratio was 0.35 ± 0.1 (SD) and was consistent with data from systolic time intervals derived from simultaneous study of the ECG recording, carotid artery tracing, and phonocardiography. The diastolic time ratio (isovolumic relaxation period/filling time) was 0.4 ± 0.2, in agreement with normal values derived by echocardiography and angiography.In a subgroup of 17 critically ill patients, a correlative study of simultaneously measured thoracic electrical bioimpedance, nuclear stethoscope, and radionuclide ventriculography was conducted. Systolic functions were compared by the ejection fraction derived by preejection period/left ventricular ejection time ratio displayed on the thoracic electrical bioimpedance monitor and by the radionuclide technique, and were found to be 57 ± 13.8% and 58 ± 8.6%, respectively (r2= .49; y = 4.06x + 0.94;p< .02; n = 17). Increased diastolic time ratios with normal or near-normal systolic time intervals were documented in nine (53%) of 17 critically ill patients with low systolic index.ConclusionBoth systolic and diastolic time intervals can be investigated noninvasively at the bedside by the thoracic electrical bioimpedance technique to provide a better understanding of left heart function.