Development of techniques for measurement of left ventricular ejection time

This study aimed to develop different measurement techniques for measurement of left ventricular ejection time (L VET) measurement from echocardiography, thoracic impedance cardiography (ICG) and peripheral photoplethysmography (PPG). Healthy subjects volunteered for this preliminary investigation. For each subject, cardiac aortic valve movement and aortic blood flow were examined by Mmode and Doppler echocardiography simultaneously with ICG and peripheral PPG pulses for 15 s. Using all the measureable beats from each subject, the beat-by-beat measurement variability (SD of LEVT) and the mean value of L VET were compared between techniques. The L VET measured from Doppler imaging had the smallest mean of beat-by-beat SD across all subjects (9 ms), which was better than that from M-mode echocardiography and PPG (both were 11 ms). ICG had the largest mean beat-by-beat SD (22 ms). The mean L VET across all subjects from the M-mode echo cardiography was 328 ms, which was longer than that from Doppler imaging (309 ms) (P < 0.001). Mean LVETs from ICG (364 ms) and PPG (348 ms) were both significantly longer those from images (P < 0.05). In conclusion, with simultaneously recorded cardiac images and physiological signals, it has been quantitatively demonstrated that the ICG and PPG not only gave longer L VET measurements, but also had larger measurement variability than the M-mode and Doppler images.