The last time you had your blood pressure checked, it was probably at a doctor’s office with a bulky cuff wrapped around your arm. One day soon, perhaps, you will just need a simple stick-on patch on your neck, no bigger than a postage stamp.
That’s the goal of Sheng Xu and his team at the University of California, San Diego, who are working on a patch that can continuously measure someone’s central blood pressure—the pressure of blood coursing beyond your aorta, the artery in your heart that delivers blood to all the different parts of the body. It could make it a lot easier to monitor heart conditions and keep an eye on other vital organs like the liver, lungs, and brain.
The silicon elastomer patch works by sending out ultrasonic waves that penetrate the skin and reflect off the wearer’s tissues and blood. Those reflections are sent back to the sensor, and then to a laptop that processes the blood pressure data (for now, at least, the patch must be wired to a laptop and a power source, too). It is the first known wearable device that can sense deep below the surface of the skin.
In theory, the patch could be used at home to monitor patients over time. And because it’s not inserted into the body, there’s no risk of infection.
A study on Xu and his colleagues’ work, published last week in Nature Biomedical Engineering, found that the patch could continuously and accurately monitor central blood pressure when placed on different parts of the body, though putting it on the neck was most effective. In the study, they compared it to a noninvasive and useful (but hard to operate) device called a tonometer, which places a pressure sensor on the skin; the differences between the two devices’ results were a fraction of what’s considered to be the acceptable range for error with a standard blood pressure device.
It’s also much less invasive than the current gold standard for measuring central blood pressure, which uses a catheter with a sensor on it that’s inserted near the heart. One of the researchers’ next steps is to test their patch against such a catheter to see how it measures up.
The device can provide a lot more information than you can get with a standard blood pressure cuff. This information, Xu believes, can be useful for keeping an eye on patients with conditions like hypertension or a history of heart attack.
“You can’t wear a blood pressure cuff all the time,” he says.
Topol also points out that because the patch can be placed right near the jugular vein, it can measure how much blood is streaming into the heart. That might make it helpful for spotting whether someone is dehydrated, he says.
Not everyone is convinced. Mohan Thanikachalam, a cardiac surgeon at Tufts University, thinks a cuff that monitors peripheral blood pressure is probably still more useful.
“It could turn out that central blood pressure has more predictive value in terms of outcomes in the future, but as of now we don’t have that much data,” he says.
Still, the patch may also have uses beyond the body. Xu, who was one of MIT Technology Review’s 2018 35 Innovators Under 35, believes that such ultrasound patches could also be useful for finding small cracks in complicated mechanical parts, such as those in planes.