Smartphone Device May Allow Finger Touch Blood Pressure Reading

Marcia Frellick

March 07, 2018

A device that can be attached to the back of a smartphone and paired with an app has been found in a small study to take real-time blood pressure (BP) readings with accuracy similar to that of a finger cuff and a standard arm cuff, according to a paper published today in Science Translational Medicine.

One expert says the work is promising and is significantly different because it takes the smartphone BP reading technology a step further with an attachment. However, he cautions against drawing firm conclusions from the work and urges a formalized validation study.

The device, developed by Anand Chandrasekhar, a doctoral student in the Department of Electrical and Computer Engineering at Michigan State University in East Lansing, and colleagues, works through a three-dimensional printed phone case that contains an optical sensor over a force sensor. When a user presses down on the sensor with a finger, using the oscillometric method that the cuff usually provides, the device measures the pressure in an artery. The phone gives visual feedback to direct the amount of finger pressure to apply and calculates instant diastolic and systolic readings through the app.

According to the paper, the device yielded bias and precision errors of 3.3 and 8.8 mm Hg, respectively, for systolic BP over a 40 to 50 mm Hg range of blood pressure. The bias and precision errors were −5.6 and 7.7 mm Hg for diastolic BP.

Seth Martin, MD, MHS, a cardiologist and assistant professor of medicine at Johns Hopkins Medicine in Baltimore, Maryland, told Medscape Medical News, "It's a cool, exciting proof of concept study. It is exciting to see innovation towards easier measurement outside the clinic."

However, he cautions that the study is small, with just 30 participants, and that there were very few hypertensive people included. He notes that in future studies, a wider range of BPs and a wider age range should be tested, especially including older participants.

"This is a classic kind of situation that happens often with early testing of such devices," Martin said. "You test them on a bunch of normal, healthy people."

Martin was part of a team that conducted a formal validation study of the popular Instant Blood Pressure smartphone app (IBP; AuraLife), which they found to be "highly inaccurate." Four of five people who were hypertensive got a reading of normal from that app, he said, which used only the phone without an attachment. The app was removed from the market in 2015.

Other Technologies Are in Development

The authors of the current study acknowledge other cuffless technologies are being developed, but so far, many developing solutions have problems with either convenience or accuracy, they write.

The smartphone technology described in the current article has a couple of primary advantages, they say.

First, it can independently measure systolic and diastolic blood pressure without calibration. It also offers convenience.

People in settings with few resources may not have access to cuffs, and others may have to go to pharmacies and other locations to get them. Even if people own a cuff, they are unlikely to carry it with them wherever they go, but they would likely carry a phone.

The researchers note that about 3 billion people globally are expected to have smartphones by 2020, and widespread use in low-income nations is expected as marketplace competition increases.

"Screening for hypertension may be the main clinical application of the device, especially in the 20- to 50-year-old segment of the population who are often technology savvy and health conscious but may be at risk for early development of hypertension," the authors write.

Some limitations mentioned in the study are that the device can't take nighttime readings and may not be usable for people who lack fine motor skills.

In addition, the researchers did not test the device with the Association for the Advancement of Medical Instrumentation data collection protocol, "which involves a subject population that covers a prescribed range of BP values."

Trials Suggest It's Easy to Use

The device does appear to be relatively easy to use, according to data from the study. Each of the 30 users in the study was allowed practice trials to learn how to place the finger correctly and maintain applied pressure.

Participants had an average age of 39 years (range, 21-60 years) and 67% were women. They had not previously used the technology and had no cardiovascular disorders other than hypertension, and no problems with fine motor control.

"About 90% of the users learned the finger actuation after one or two trials," the authors report.

The user presses a finger against the sensor to steadily increase pressure on the artery just as a cuff presses the artery against the bone. After enough finger pressure is applied, the measurement ends and the device displays a reading. If there are problems with the reading, it asks the user to try again.

The researchers said when users got the "try again" message, it was a usually a computational error and not user error.

Benefits and Potential Dangers

Martin said if the Chandrasekhar et al device were properly validated it could be a big help in letting people know they have an abnormal reading and encourage them to get into a physician's office to get a medical-grade reading to prevent heart attacks and strokes.

"If you're really good at picking up high blood pressures in people who otherwise would not get that tested because you make it so easy for them, that could be really valuable," Martin said. "Unfortunately this study doesn't really tell us that."

The authors note that only about 55% of people with hypertension in developed nations and 45% of hypertensives in developing nations know they have the condition.

"The worry I have is that it could do harm if it falsely reassures someone who truly has hypertension and a blood pressure of 180 and this device tells them they're blood pressure is 130 and they don't need to worry and it discourages someone from paying attention," Martin said.

He added, "I hope to see more work on this device that will allow me to draw firmer conclusions about how well it works."

This work was supported by the National Institutes of Health and the Michigan State University Office of the Vice President for Research and Graduate Studies. Three coauthors are inventors on patent application PCT/US2017/020739 submitted by Michigan State University and the University of Maryland that covers the oscillometric finger-pressing method. The patent has been exclusively licensed to Digitouch Health LLC. They also provided initial, unpaid consulting to transition the method to the company. All other authors and Martin have disclosed no relevant financial relationships.

Sci Trans Med. Published online March 7, 2018. Article

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