Systolic Time Interval Estimation Using Continuous Wave Radar With On-Body Antennas

The estimation of systolic time intervals (STIs) is done using continuous wave (CW) radar at 2.45 GHz with an on-body antenna. Motivation: In the state of the art, typically bioimpedance, heart sounds and/or ultrasound are used to measure STIs. All three methods suffer from insufficient accuracy of STI estimation due to various reasons. CW radar is investigated for its ability to overcome the deficiencies in the state of the art. Methods: Ten healthy male subjects aged 25-45 were asked to lie down at a 30° incline. Recordings of 60 s were taken without breathing and with paced breathing. Heart sounds, electrocardiogram, respiration, and impedance cardiogram were measured simultaneously as reference. The radar antennas were placed at two positions on the chest. The antennas were placed directly on the body as well as with cotton textile in between. The beat to beat STIs have been determined from the reference signals as well as CW radar signals. Results: The results indicate that CW radar can be used to estimate STIs in ambulatory monitoring. Significance: The results pave way to a potentially more compact method of estimating STIs, which can be integrated into a wearable device.