Systolic time interval estimation at the sternum using continuous wave radar with body-contact antennas

Cardiovascular vital signs are measured using continuous wave (CW) radar at 2.45GHz with a body-contact antenna. Using a previously collected database of thirty second recordings at paced breathing conditions, CW radar signals were measured together with heart sounds, electrocardiogram (ECG), respiration and impedance cardiogram (ICG) were as reference signals. Using arbitrarily chosen features from the radar signal, the systolic time intervals (STI)s from radar are compared with those from the ICG. The correlation coefficients between the STIs of radar and ICG were 0.72, 0.66 and 0.81 for the pre-ejection period, left ventricular ejection time and electromechanical systole respectively. The p-value was below 0.0001 for all coefficients, indicating a significant correlation. The results indicate that the radar signals capture cardiomechanical signals, which have great potential to be used for STI estimation in ambulatory conditions.