A wearable patch the size of a postage stamp that can monitor blood pressure continuously could soon help people manage their hypertension - a chronic medical condition where the pressure in your blood vessels is persistently elevated.

Researchers at the University of California, San Diego, have developed a wearable ultrasound patch report that has worked well in tests with more than 100 patients.

“Wearable devices have so far been limited to sensing signals either on the surface of the skin or right beneath it. But this is like seeing just the tip of the iceberg,” said Sheng Xu, a professor of nanoengineering at the UC San Diego Jacobs School of Engineering and the corresponding author of the study. “By integrating ultrasound technology into wearables, we can start to capture a lot of other signals, biological events, and activities going on way below the surface in a non-invasive manner.”

“We are adding a third dimension to the sensing range of wearable electronics,” said Xu.

Researchers, who described their work in a paper published in the journal Nature Biomedical Engineering, said the applications include real-time, continuous monitoring of blood pressure changes in patients with heart or lung disease, as well as those who are critically ill or undergoing surgery.

The patch uses ultrasound, so it could potentially be used to non-invasively track other vital signs and physiological signals from places deep inside the body. According to experts, it is important to maintain a normal blood pressure - 120/80 which is crucial in preventing many illnesses - from heart disease and stroke to kidney problems, dementia, and vision loss.

According to scientists, the soft and stretchy patch adheres to the skin and is worn on the forearm. The tiny transducers inside it send and receive ultrasound waves that track changes in the diameter of blood vessels, and they are then converted into blood pressure values.

Researchers said the patch produces results comparable not only to those of a standard blood pressure cuff but also to a highly accurate but invasive device inserted into an artery in intensive care units and operating rooms to continuously monitor pressure.

In tests involving four patients who were in intensive care after surgery and 21 who underwent cardiac catheterization, measurements from the patch were close to those from the arterial line. That, researchers said, shows its potential as a noninvasive alternative.

The patch measures central blood pressure - which differs from the blood pressure that is measured with an inflatable cuff strapped around the upper arm, known as peripheral blood pressure. Central blood pressure is the pressure in the central blood vessels, which send blood directly from the heart to other major organs throughout the body. Doctors consider central blood pressure to be more accurate than peripheral blood pressure and also say it is better at predicting heart disease.

Measuring central blood pressure is not typically done in routine exams

A non-invasive method exists, but it cannot consistently produce accurate readings and involves holding a pen-like probe known as a tonometer, which, for a good reading, must be held steady at just the right angle and with the right amount of pressure each time.

Researchers say the patch was tested on a male subject, who wore it on the forearm, wrist, neck, and foot. Tests were performed both while the subject was stationary and during exercise. Recordings collected with the patch were more consistent and precise than recordings from a commercial tonometer. The patch recordings were also comparable to those collected with a traditional ultrasound probe.

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