Pipeline of smart technologies could expand detection of hypertension, save lives
It’s the drill at the start of virtually every doctor or hospital visit: having your blood pressure measured. A technician straps a cuff to your upper arm and tightly inflates it. The beeps begin as a machine generates numbers. The cuff slowly deflates. The tech announces the all-important readings.
For some, the experience can be unsettling—not simply because of increased pressure on the arm, but because of the nervous anticipation of what the numbers will tell.
Yet for more than a century, this bulky arm-cuff device—formally known as a sphygmomanometer—has been the gold standard for detecting hypertension, a treatable disease that affects half of the adult population in the United States and is the leading risk factor for stroke and heart disease.
But things are changing—and fast.
Researchers supported by the NIH are helping develop new and improved monitoring devices in a stepped-up effort to stem the epidemic rates of uncontrolled hypertension. They include a new wave of electronics—from skin patches to smartwatches—that can easily be used at home. And that’s good news, as recent studies show some of these devices can provide more reliable and informative readings than those taken in clinics and help significantly reduce a person’s chances of stroke and heart disease.
“In the U.S., less than half of people with high blood pressure have it under control,” said David Goff, M.D., Ph.D., director of the Division of Cardiovascular Sciences at NHLBI. “Given the poor level of control, it’s time to test creative approaches to preventing the development of hypertension and improving control. Technologies that empower patients to be more involved in monitoring their blood pressure are promising approaches that might benefit from more research and development.”
Better blood pressure devices that are less intrusive, faster, easier to use, and affordable could help improve blood pressure control, researchers say. At-home devices can also overcome challenges such as “white coat syndrome,” a condition that affects people who are so anxious about being in a medical setting that their blood pressure registers higher than it would in a normal setting. Finally, some devices may be able to facilitate continuous monitoring of blood pressure, which researchers say is important because blood pressure varies throughout the day and from one day to the next.
But while these new devices may be a potential improvement over the standard ones, they come with their own challenges. One is accuracy validation. A recent study showed that most home blood pressure monitors currently on the market have not been validated for accuracy by a testing agency that does not have ties to any manufacturer. Another hurdle is implementation—how to get the new devices into the community in a way that is effective, affordable, and sustainable in routine daily care and practice. But researchers are optimistic these challenges can be met over time as they continue testing the devices and consumers seek to take charge of their health.
“You have to know your blood pressure numbers,” said George Mensah, M.D., Director of the Center for Translation Research & Implementation Science at NHLBI. “And we have to take steps to improve those numbers.” This call to action, he said, is important for all men and women but particularly for African American men, who have the highest hypertension-related stroke and heart disease death rates of any racial or ethnic group in the country.
Here’s a glimpse at some of the technologies that are in the works:
Ramakrishna Mukkamala, Ph.D., a professor of electrical and computer engineering at Michigan State University, is leading a team of scientists that developed, with partial funding from NHLBI, smartphone-based devices that can monitor blood pressure using the pressure of a person’s index finger.
It works like this: A person steadily presses his or her index finger on the phone. Guided by an animated cursor on the phone screen, the user keeps pressing until prompted to lift the finger. Optical and force sensors in the phone then combine to translate the arterial pressure from the fingertip into a blood pressure reading in millimeters of mercury, just like the standard reading from a blood pressure cuff. The reading shows up on your phone, and the whole process takes place in less than half a minute. A normal blood pressure reading is less than 120/80 millimeters of mercury (mm Hg). The top number—known as systolic pressure— measures the pressure in your arteries when your heart beats, while the bottom number— known as diastolic pressure—measures the pressure in your arteries when your heart rests between beats.
In early tests on a few dozen people, the device performed just as accurately as an FDA-approved device called a volume-clamp, which uses a special cuff on a finger, but somewhat less accurately than a conventional arm-cuff device. “We want to develop truly cuff-less devices that are accurate and readily accessible,” Mukkamala said, noting that other cuff-less devices require cuff measurements periodically to give blood pressure in mm Hg. The devices could be on the market in a few years, he said.
The sensors can be inserted in an add-on phone case or integrated into the existing architecture of a cell phone, while some phones already have the necessary sensors. The researcher hopes to eventually turn the device into a complete hypertension management system, one that uses an alarm to warn users if they have high blood pressure or sends them a text to remind users when to take their blood pressure medication. The system also shows promise for addressing high rates of hypertension in developing areas of the world, where smartphone use is growing, Mukkamala said.
In 2017, a research team funded by the National Institute of Biomedical Imaging and Bioengineering (NIBIB) developed a noninvasive skin patch that can be worn on the neck for continuous measurement of blood pressure. Unlike conventional devices that measure peripheral blood pressure through arteries in the arm, the patch measures central blood pressure—the flow of blood from the heart through the carotid arteries in the neck. Doctors consider measurements taken from this area to be a more accurate predictor of developing heart problems, including heart attacks. This wearable patch can also measure blood pressure at other parts of the body including the arm, wrist, and foot.
The prototype device, which is made of a thin sheet of silicone polymer integrated with an array of tiny electronic parts, measures blood pressure through ultrasound, or high-frequency sound waves. The patch, which is the size of a postage stamp, is soft and can bend and twist in the presence of motion. It sends and picks up reflecting sound waves from the pulsing blood vessels in the neck and translates them into signals that are read by customized software in an external device that is wired to the patch. It is ideal for use in the ICU and operating room, the researchers said.
In early studies, the skin patch measurements were better than or comparable to those made by other instruments now used in the clinic to measure central blood pressure. Researchers hope to develop the patch into a completely wireless device in the future.
“Our patch represents a step toward precision medicine for monitoring blood pressure and managing and preventing acute and chronic cardiovascular diseases,” said Sheng Xu, Ph.D., study leader and an assistant professor of nanoengineering at the University of California San Diego in La Jolla. “The continuous data stream generated is unique for each subject, and that allows physicians and other healthcare providers to design specific regimens for that specific patient.”
One of the most sought-after pieces of real estate for blood pressure monitoring is the wrist, which means the ever-popular smartwatch continues to be transformed in even more functional ways.
In another project funded by NIBIB, researchers at the Georgia Institute of Technology developed a smartwatch that measures blood pressure by recording chest vibrations produced by the heartbeat. Called a SeismoWatch, it looks like any other smartwatch and contains miniature motion sensors.
To work it, you hold the watch up to your chest, and sensors in the watch detect micro-vibrations of the chest wall associated with the heartbeat. As pressure waves move along the artery walls from the heart to the wrist, an accelerometer and optical sensor on the watch measure the signals to estimate blood pressure. The whole process takes about 10 to 15 seconds.
So far, the researchers have tested the prototype on about 50 people, some in the lab and some at home, with results comparable to some conventional blood pressure devices. Although the prototype is externally wired to a monitor and contains no readable watch face, the researchers say the future version can be engineered to be wireless and have a readout like a regular smartwatch.
“Our hope is that the SeismoWatch will become an affordable, reliable tool for blood pressure measurement in medically underserved minority populations, where rates of hypertension are very high,” said study leader Omer Inan, Ph.D., an associate professor at the university.
NHLBI’s Mensah said he would welcome that. “Any of these innovative devices that are affordable, reliable, and easy to use will go a long way in helping us detect high blood pressure and inform our actions to control this silent killer,” he said.
While this new crop of measurement devices is being refined, doctors and researchers urge everybody to act now to reduce their risk of hypertension by limiting sodium intake, staying physically active, maintaining a healthy weight, taking medicines as prescribed, stopping smoking, limiting alcohol, and seeing their doctors on a regular basis. People are also encouraged to measure their blood pressure regularly.