Signal Separation Using a Mathematical Model of Physiological Signals for the Measurement of Heart Pulse Wave Propagation With Array Radar

Abstract

The arterial pulse wave, which propagates along the artery, is an important indicator of various cardiovascular diseases. By measuring the displacement at multiple parts of the human body, pulse wave velocity can be estimated from the pulse transit time. This paper proposes a technique for signal separation using an antenna array, so that pulse wave propagation can be measured in a non-contact manner. The body displacements due to the pulse wave at different body parts are highly correlated, and cannot be accurately separated using techniques that assume independent or uncorrelated signals. The proposed method formulates the signal separation as an optimization problem, based on a mathematical model of the arterial pulse wave. The objective function in the optimization comprises four terms that are derived based on a small-displacement approximation, unimodal impulse response approximation, and a causality condition. The optimization process was implemented using a genetic algorithm. The effectiveness of the proposed method is demonstrated through numerical simulations and experiments.

Experimental Demonstration of Accurate Noncontact Measurement of Arterial Pulse Wave Displacements Using 79-GHz Array Radar

“…(2) The user is required to hold their breath for a few seconds during the measurement process. To mitigate the first disadvantage, we will study application of advanced signal processing techniques [35] to improve the signal separation accuracy. To resolve the second disadvantage, it will be necessary to develop an algorithm that can suppress the respiratory components from the radar signals, and this will form part of our future studies.…”

“…The pulse wave propagation channel is evaluated quantitatively in terms of its impulse response, which is calculated based on the estimated displacement waveforms from the two body parts. Although our previous study [35] indicated the possibility of array-radar-based pulse wave propagation measurement, the accuracy of these measurements has not been evaluated experimentally to date. To the extent of the authors' knowledge, this study is the first to evaluate the accuracy of radar-based noncontact measurements of arterial pulse wave propagation quantitatively.…”

Generating a super-resolution radar angular spectrum using physiological component analysis

“…These techniques that use an array radar system require accurate signal separation so that tiny displacements at multiple body parts are estimated accurately. To improve the signal separation accuracy, [12] introduced an algorithm based on optimization with a mathematical model of physiological signals. This technique is called physiological component analysis (PHCA) and has achieved high accuracy in separating signals when the echoes are modulated by constant multiples of time-shifted displacement waveforms.…”

“…We proposed PHCA [12] to determine an N ×M matrix W = [w 1 w 2 • • • w N ] T and estimate echoes asŝ(t) = W x(t), which leads to the estimate of the displacementd(t) = (1/2k)∠ŝ(t), where ∠ denotes the argument of a complex number. Note that ambiguity is allowed in the permutation and constant multiplication when we estimated(t).…”

“…The objective function F (W ) comprises four functions that are derived from approximations based on a mathematical model of physiological signals [12]. The functions are defined as…”