Enhancing Beat-to-Beat Analysis of Heart Signals With Respiration Harmonics Reduction Through Demodulation and Template Matching

Heart rate variability (HRV) analysis using Doppler radar (DR) is a promising method for noninvasive health and stress assessment. However, the respiration signal harmonic content typically limits HRV parameter estimation accuracy. While several harmonic reduction techniques have been used to improve the average HR estimation accuracy, achieving high beat-to-beat interval (BBI) accuracy is still challenging. This article demonstrates that arctangent demodulation (AD) with wavelet-based signal processing enhanced with template matching is effective to estimate HRV parameters with accuracy on the order of 10 ms with 2.4 GHz DR. Moreover, it was theoretically and experimentally demonstrated that the cases where AD provides limited improvement due to phase delay between thorax and abdomen motion are easily identifiable, and can be alternatively processed using a single-channel data.