Continuous Monitoring of Blood Pressure by Measuring Local Pulse Wave Velocity Using Wearable Micromachined Ultrasonic Probes

Continuous monitoring of dynamic blood pressure (BP) is crucial for cardiovascular status analysis and holds significant value in the clinical prevention and diagnosis of cardiovascular diseases. However, existing methods are often limited by their bulky design and complex procedures, which are incompatible with the demands of smart, portable devices. Here, we present a wearable, non-invasive, and continuous BP monitoring system based on piezoelectric micromachined ultrasound transducer (PMUT) with flexible encapsulation. This device is compact, lightweight (<2 grams) and comfortable for long-term use. It is motion-resistant and has a high signal-to-noise ratio (>29 dB), enabling it to capture distinct echoes from different arterial sites. The system adopts ultrasonic pulse-echo to record arterial diameter waveforms from dual sites and calculates the incremental local pulse wave velocity (PWV) beat-to-beat to determine arterial stiffness index and BP. When benchmarked against a cuff sphygmomanometer, our device demonstrates a mean absolute error and standard deviation for systolic BP and diastolic BP measurements of less than 4 mmHg and 3 mmHg, respectively, and a heart rate error of less than 3 bpm. Compared with a photoplethysmography finger clip as waveform references, the correlation coefficients for all measurements range from 0.951 to 0.998, and the root mean square error falls within an error band of ±5 mmHg, validating the reliability and stability of our device. Furthermore, the capability to track large-range dynamic changes in BP is also verified, highlighting its potential for daily BP management.