Wearable ultrasound patch offers continuous blood pressure monitoring

The wearable ultrasound blood pressure sensor has been clinically validated on over 100 patients and could improve the quality of cardiovascular health monitoring in the clinic and at home. The sensor is detailed in Nature Biomedical Engineering.

“Traditional blood pressure measurements with a cuff, which are limited to providing one-time blood pressure values, can miss critical patterns. Our wearable patch offers a continuous stream of blood pressure waveform data, allowing it to reveal detailed trends in blood pressure fluctuations,” study co-first author Sai Zhou said in a statement.

When worn on the forearm, the sensor is said to offer precise, real-time readings of blood pressure deep within the body. The patch is made of a silicone elastomer that houses piezoelectric transducers sandwiched between stretchable copper electrodes. The transducers transmit and receive ultrasound waves that track changes in the diameter of blood vessels, which are then converted into blood pressure values.

The wearable ultrasound patch builds upon an earlier prototype that was pioneered by the lab of Sheng Xu, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at UC San Diego.

Researchers re-engineered the patch with two improvements to enhance its performance for continuous blood pressure monitoring. First, they packed the piezoelectric transducers closer together, enabling them to provide wider coverage so they could better target smaller arteries that are more clinically relevant. They then added a backing layer to dampen redundant vibrations from the transducers, resulting in improved signal clarity and tracking accuracy of arterial walls. 

In tests, the device produced comparable results to a blood pressure cuff and an arterial line, which is a sensor inserted into an artery to continuously monitor blood pressure.

While the arterial line is the gold standard for blood pressure measurement in intensive care units and operating rooms, it is highly invasive, limits patient mobility, and can cause pain or discomfort. The patch provides a simpler and more reliable alternative, as shown in validation tests conducted on patients undergoing arterial line procedures in cardiac catheterisation laboratories and intensive care units.

A total of 117 subjects participated in studies that evaluated blood pressure across a range of activities and settings. In one set of tests, seven participants wore the patch during daily activities such as cycling, raising an arm or leg, performing mental arithmetic, meditating, eating meals and consuming energy drinks.

In a larger cohort of 85 subjects, the patch was tested during changes in posture, such as transitioning from sitting to standing. Results from the patch closely matched those from blood pressure cuffs in all tests.

The patch’s ability to continuously monitor blood pressure was evaluated in 21 patients in a cardiac catheterization laboratory and four patients who were admitted to the intensive care unit after surgery. Measurements from the patch agreed closely with results from the arterial line, showcasing its potential as a noninvasive alternative.

“Blood pressure can be all over the place depending on factors like white coat syndrome, masked hypertension, daily activities or use of medication, which makes it tricky to get an accurate diagnosis or manage treatment,” said Xu. “That’s why it was so important for us to test this device in a wide variety of real-world and clinical settings. Many studies on wearable devices skip these steps during development, but we made sure to cover it all.”

The research team is preparing for large-scale clinical trials and plans to integrate machine learning to further improve the device’s capabilities. Efforts are also underway to validate a wireless, battery-powered version for long-term use and integration with existing hospital systems.