A new implantable ultrasound-based blood pressure monitoring system has demonstrated clinically reliable measurements in an ambulatory sheep model, according to research published in Microsystems & Nanoengineering. The study addresses critical limitations in current blood pressure monitoring technologies, which are essential for preventing cardiovascular events but often suffer from discomfort, motion interference, and poor alignment.
Hypertension remains one of the world's leading causes of heart disease, stroke, and premature mortality. While regular blood pressure tracking can significantly reduce cardiovascular risks, traditional cuff-based measurements disrupt daily activity and are unsuitable for continuous monitoring. Alternatives such as photoplethysmography and wearable ultrasound patches attempt to address these limitations but often struggle with shallow penetration depth, dependence on gels, and significant sensitivity to misalignment or motion. The newly developed system, detailed in a paper published (DOI: 10.1038/s41378-025-01019-w) on November 6, 2025, offers a subcutaneous approach that avoids these issues.
The device features a 5 × 5 mm² piezoelectric micromachined ultrasonic transducers array that continuously measures arterial diameter changes to reconstruct blood pressure waveforms. Through comprehensive laboratory validation and an in vivo implantation in an ambulatory sheep, researchers demonstrated that the device achieves clinically reliable systolic and diastolic measurements with minimal calibration error. The 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.
To derive blood pressure, the device measures the time-of-flight between ultrasound echoes reflected from the anterior and posterior arterial walls. This time interval is converted into a real-time diameter waveform, which 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 by maintaining stable coupling.
During in vivo testing, researchers implanted the PMUT system above the femoral artery of an adult sheep. 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 pressures. These results demonstrate that the minimally invasive design maintains accurate long-term performance without the drawbacks of cuffs or fragile wearables.
The study suggests this technology could support long-term hypertension management and provide clinicians with richer cardiovascular data than periodic measurements allow. Its stability against tissue growth, motion, and environmental interference makes it particularly suitable for continuous monitoring, early detection of cardiovascular abnormalities, and integration into digital health platforms. Future advances—such as beamforming to mitigate positional shifts and data-driven analytics for individualized risk prediction—could further expand its clinical utility. The research was supported in part by BSAC (Berkeley Sensor and Actuator Center), and the full study is available at https://doi.org/10.1038/s41378-025-01019-w.
