Contact-Free Blood Pressure Estimation Based on Pulse Wave Velocity Using mmWave Signals

Contact-free blood pressure (BP) estimation leverages the effect of arterial expansion on surrounding mmWave signals to capture pulse waves and subsequently estimate BP. Most current contact-free methods rely on pulse wave analysis, but pulse waves are inherently weak and often lack reliable morphological features. To address this issue, this paper proposes a physiologically interpretable contact-free pulse wave velocity (PWV)-based BP estimation strategy without relying on pulse wave morphological features. Specifically, we develop a PWV-based BP estimation framework, where PWV can be derived by measuring the pulse transit time and pulse transit distance between different body parts using the reflected mmWave signals. To acquire high quality PWV measurement, we exploit the non-uniformity of pulse wave quality in the spatial and frequency domains and the multi-domain characteristics of pulse waves. Based on that, we propose a two-stage candidate space construction strategy to obtain candidate pulse waves from multiple body parts, and a multi-domain filtering and fusion strategy to refine and combine these candidate signals. We design a PWV-based BP estimation system on a 77 GHz mmWave radar and extensively evaluate its performance, with ME ± STD of systolic and diastolic BP being 0.13 ± 4.87 mmHg and 0.33 ± 4.90 mmHg, respectively.