Early research suggests a phone case might be able to measure blood pressure

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A new smartphone device allows people to easily measure their blood pressure without a cuff by squeezing their arm. It is still too early to tell if the technology is working properly, but if it does, it could allow more people, especially in developing countries, to check if they are at risk of heart disease.
The device, described in a study published today in Science Translational Medicine, consists of a 3D printed case that sits on the back of a smartphone. When a person presses a finger with a button-type sensor, an application can calculate blood pressure, according to the study. But the device was tested in so few people, the vast majority of them with normal blood pressure, that it is impossible to tell if their measurements are accurate, according to several experts.
"The big problem comes with precision."
High blood pressure or hypertension can cause strokes, heart attacks and kidney failure. But measuring blood pressure is notoriously difficult. Simple things like stress, drinking coffee or hanging legs on an examination table can lead to inaccurate measurements. In addition, the cuffs to tighten the arms are awkward, not portable, and can be painful for elderly patients or impractical for people with obesity. So scientists have been trying to create portable, sleeveless devices to easily monitor blood pressure several times a day.
"On the surface, it's a great idea and people would love to have it," says Edgar Raymond Miller, an expert in hypertension at the Johns Hopkins University School of Medicine, who was not involved in the study. "The big problem comes with precision."
Timothy Plante, an assistant professor at the Larner School of Medicine at the University of Vermont, agrees. While it would be a "game changer" to use a smartphone to measure blood pressure, it is still too early to say that this device works. You would like to investigate how well it works between people with high and low blood pressure. Otherwise, it is impossible to know if the device is accurate enough for use in the home.
Many have already tried to create devices without tips and have failed. A smartphone application called Instant Blood Pressure, for example, asked users to place their smartphone against their chest and a finger on the camera to take a measurement. But the research of Plante, Miller and Seth Martin at Johns Hopkins showed that the application could not identify high blood pressure in eight out of 10 patients. "That's really scary," says Martin, an assistant professor of medicine at Johns Hopkins. "People trust those readings." (The application is no longer available).

The device based on the smartphone. Photo of Anand Chandrasekhar

The device described in today's study also does not wear a bracelet; instead, it's like a smartphone case with sensors. It works like this: press a finger on a sensor in the housing to cut the flow of blood to an artery in your finger. An application tells you how much pressure to apply and then shows your blood pressure reading. "The fingertip is the most natural place to push," says study co-author Ramakrishna Mukkamala, a professor at the School of Engineering at Michigan State University. "That makes all this finger pressure approach viable."
The device was tested on 30 people, and 90 percent of them could use the device correctly after practicing once or twice. The smart phone's measurements were tested against a finger cuff device, and they were so accurate, says Mukkamala. But the cuffs for the fingers are "notoriously inaccurate," says Plante. "I would take any comparison with a couple of tablespoons of salt." (The device based on the smartphone also showed errors relative to a standard arm cuff that are large enough to suggest that it can not completely replace the cuff).
The study is still early, and most of the people analyzed had normal blood pressure. Before a device goes on the market, it must be tested on at least 85 people who have a range of blood pressure, says Bruce Alpert, a pediatric cardiologist who has done many validation studies for manufacturers of automatic blood pressure devices. Mukkamala accepts that the group has a long way to go before their device is approved. This study only shows that it is possible, he says. "Can you say we are ready to go to Best Buy and pick one up? I would say no," says Mukkamala. "There is more work to be done."
"That's the exciting thing, it's to keep people healthier."
Three of the study's authors, including Mukkamala, have also patented the technology and licensed it to a company called Digitouch Health. Therefore, it is important that the device be tested and validated by independent researchers who do not have a conflict of interest, Miller tells The Verge.
Mukkamala believes that, once validated, the device could help people easily control their blood pressure and determine if they need medication. According to the study, only about 45 percent of people with hypertension in developing countries know their condition. "If you are aware, then you can do things in your life to reduce your increased risk of stroke and heart attack," says Mukkamala. "For me, that's the most exciting thing: it's to keep people healthier."
However, before that happens, the device must be tested as safe and effective. Smartphones "are designed to take photos, surf the web, make phone calls, send text messages and launch Angry Birds to pigs," says Plante. "This does not mean that smartphones can not be modified to obtain blood pressure measurements, we just have to make sure that any blood pressure measuring device is accurate."

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