A new wearable ultrasound patch that is a continuous, noninvasive blood pressure monitor could improve the quality of clinical and in-home cardiovascular health monitoring, according to the researchers at University of California San Diego who developed and tested it on more than 100 patients.
Details of the technology and its testing were published 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, who recently earned his doctorate in materials science and engineering from the UC San Diego Jacobs School of Engineering, said in a written statement.
The postage-stamp-sized device is soft and stretchy and adheres to the skin. The researchers said that wearing it on the forearm offers precise, real-time readings of blood pressure deep in the body. He said the silicone-based patch has an array of little transducers between stretchable copper electrodes. The transducers transmit and receive ultrasound waves that can track changes in the blood vessel diameters, which are then converted to blood pressure values.
The device when tested was comparable in its results to both a blood pressure cuff and an arterial line, which is a sensor inserted into the artery to continuously monitor blood pressure, per a news release on the work. The arterial line is the gold standard for blood pressure monitoring in intensive care units and operating rooms, but it’s invasive and can be painful. Nor can patients with an arterial line move around freely. Their movement is restricted.
The patch, comparable in its results, overcomes those issues.
The researchers reengineered an earlier patch made in the lab of Sheng Xu, a professor in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the university. They made a pair of improvements to bolster the performance. First, they packed the transducers closer together so they’d have broader coverage to do a better job of targeting smaller arteries such as the brachial and radial arteries. They also reduced vibrations to improve signal clarity and tracking accuracy of the arterial walls.
Testing the device
The device was tested in different ways with 117 different patients doing a variety of activities in different settings. In one test, seven participants wore the patch while cycling, raising an arm or leg, meditating, eating and doing other tasks. In 85 subjects, the patch was tested as they changed positions, including transitioning from sitting to standing.
In all cases, the results closely matched those of blood pressure cuffs. But they also matched findings from arterial lines used in patients in intensive care when the patches were used with 21 patients in a cardiac catheterization lab or who were admitted to intensive care after surgery.
The researchers hailed the findings, saying they showcase “its potential as a noninvasive alternative.”
“A big advance of this work is how thoroughly we validated this technology, thanks to the work of our medical collaborators,” said Xu. “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. 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 researchers are planning large-scale clinical trials. They also want to validate a wireless, battery-powered version for long-term use.