The use of a two channel Doppler radar sensor for the characterization of heart motion phases

Abstract

This paper investigates a two-channel Doppler radar sensor that can provide information on the direction of movement. The radar sensor has the advantage of non-invasive, contactless measurements, compared to ultrasound. From theoretical considerations and a working model, we deduce a criterion for extracting points of no movement in a heart cycle. We propose to use this criterion to characterize the heart motion phases, beyond looking at signal morphology only. In contrast to the ECG, this technique provides easy and comfortable access to information about the mechanical activity of the heart.

Blood Pressure Estimation Using Pulse Transit Time From Bioimpedance and Continuous Wave Radar

“…This challenge has been stated in Thijs and Muehlsteff's investigations [31], although they worked with the I and Q signals instead calculating the arc tangent of Q/I [57]. It is known that the heart size, position within the thorax and orientation will vary with each individual.…”

“…The dominating source of phase modulations has been proven to be the motion at the surface of the body [27]. When the radar antennas have been placed in contact with the body, the radar phase modulations have been hypothesized to be due to propagation path loss [28] within the body, body surface motions [29], [30], or changes in near-field coupling due to body tissue movement [24], [31], [32], or far field motions of the heart [33].…”

“…The distance between the radar and the heart with respect to the carrier wavelength affects signal linearity and hence, morphology [31], making feature based identification of systolic and diastolic intervals difficult. The arctangent was not calculated in either publication, making signal processing of non-linear signals impossible.…”

“…The arctangent was not calculated in either publication, making signal processing of non-linear signals impossible. Nonetheless, the authors' approach was interesting in the sense that they assume points of zero-velocity in cardiac motion, which will appear as zero crossings in the time derivative of the radar signal [31], [34].…”

Detecting changes in the human heartbeat with on-body radar

“…The knowledge of parts of the heartbeat matching characteristic points in the ECG and PCG was used to label the radar measurement with these heartbeat instances. In [11] and [12], 2.45 GHz radar heartbeat recordings were further explored. Radar recordings were matched with the heartbeat through Impedance Cardiography (ICG) and ECG.…”