Hypertension remains one of the world's leading causes of heart disease, stroke, and premature mortality, making accurate blood pressure monitoring essential for preventing cardiovascular events. Traditional cuff-based measurements disrupt daily activity and are unsuitable for continuous monitoring, while alternatives like photoplethysmography and wearable ultrasound patches often struggle with shallow penetration depth, dependence on gels, and significant sensitivity to misalignment or motion. Researchers from the University of California, Berkeley, and collaborating institutions have developed a solution: a minimally invasive, subcutaneously implanted ultrasonic device capable of capturing real-time arterial diameter changes to derive precise blood pressure values.
The study, published in Microsystems & Nanoengineering, presents a subcutaneous device built on a 5 × 5 mm² piezoelectric micromachined ultrasonic transducers array that continuously measures arterial diameter changes to reconstruct blood pressure waveforms. The newly developed system relies on a dense 37 × 45 PMUT array fabricated using CMOS-compatible processes, with each PMUT featuring a 29-µm diaphragm and operating at approximately 6.5 MHz in water to enable high axial resolution and strong echo penetration through tissue. The dual-electrode bimorph design significantly enhances acoustic output, while an optimized deep reactive ion etching process ensures high structural uniformity across the array.
To derive blood pressure, the device measures the time-of-flight between ultrasound echoes reflected from the anterior and posterior arterial walls, converting this time interval into a real-time diameter waveform that correlates directly with blood pressure through vessel stiffness models. Bench-top tube experiments confirmed the linear relationship between diameter and pressure, and simulations revealed that wearable systems can lose up to 60% signal strength with only 1 mm of misalignment—an issue the implanted design avoids. During in vivo testing, researchers implanted the PMUT system above the femoral artery of an adult sheep, where the device successfully captured detailed pressure waveforms, including features such as the dicrotic notch, and matched gold-standard arterial line measurements within −1.2 ± 2.1 mmHg for systolic and −2.9 ± 1.4 mmHg for diastolic pressure.
These results demonstrate that the minimally invasive design maintains stable coupling and accurate long-term performance, showing that ultrasound-based implants can achieve the stability and precision required for continuous blood pressure monitoring without the drawbacks of cuffs or fragile wearables. By capturing arterial diameter changes directly through subcutaneous sensing, the device avoids issues like gel dependence, environmental noise, and misalignment. The findings suggest this technology could support long-term hypertension management and provide clinicians with richer cardiovascular data than periodic measurements allow. The implantable PMUT-based system represents a promising alternative to conventional blood pressure monitoring tools for patients requiring continuous, unobtrusive measurement, with its stability against tissue growth, motion, and environmental interference making it particularly suitable for long-term hypertension management, early detection of cardiovascular abnormalities, and integration into digital health platforms.
