Smartphone Selfie May Reveal BP Levels, Early Results Suggest

An effort to discover when children are lying has spawned a potential new approach for estimating blood pressure using nothing more than a smartphone camera.

It works like this: A person takes a 30-second scan using the front-facing camera, which uses reflected light to detect blood flow under the skin. Combining that information with real-time BP measurements, researchers were able to develop a method—called transdermal optical imaging—for estimating BP based solely on the facial scan.

In a proof-of-concept study, the technology performed well among normotensive adults, providing BP readings that fell within 5 mm Hg of reference measurements obtained using a continuous BP monitor. Models trained with advanced machine learning algorithms predicted systolic, diastolic, and pulse pressures with an accuracy of 94.81% to 95.75%.

Study author Kang Lee, PhD (University of Toronto, Canada), acknowledged that “there are many steps that need to be done” before this approach has any real-world application. But if those steps are successful, this could find a place as another health and wellness tool, he told TCTMD.

“The real-world application of our technology is really to make people aware of their blood pressure status, and then they can manage their blood pressure through lifestyle changes or through exercise and then prevent blood pressure [from going up and reaching] the prehypertensive or hypertensive level,” Lee said.

The findings were published online August 6, 2019, in Circulation: Cardiovascular Imaging, with lead authors Hong Luo, MD, PhD, and Deye Yang, MD (both Affiliated Hospital of Hangzhou Normal University, Zheijiang, China), and Andrew Barszczyk, PhD (University of Toronto, Canada).

From Detecting Lies to Monitoring BP

Lee, a developmental neuroscientist, said he has been studying how children learn to tell lies for about 20 years, with one of the goals being to find a way to detect, in a nonintrusive way, when someone is lying. That led to the discovery that video cameras can image the blood flow in children’s faces, a step toward the potential development of a contactless lie detector.

Over the course of that research effort, Lee’s group realized that the same blood flow information could be used to estimate BP changes, and they shifted their focus to that application.

Our smartphones are really smart. Kang Lee

This new paper is the culmination of about 3 years of work, which involved testing transdermal optical imaging for BP measurement in 1,328 normotensive adults recruited from Toronto and Hangzhou. All participants sat in a quiet room and had their faces recorded using a tripod-mounted iPhone (Apple) while their BP was measured using the US Food and Drug Administration-cleared CNAP Monitor 500 (CNSystems), a continuous monitor.

The results show that transdermal optical imaging has sufficient performance for estimating BP when compared with the continuous monitor, Lee said.

“However, transdermal optical imaging technology implemented on a smartphone would improve upon traditional cuff-based devices by being more convenient and more comfortable (eg, cuffless),” he and his colleagues write in their paper. “This is likely to encourage measurements in more places and with more regularity than before and provides a comprehensive picture of patients’ blood pressure throughout the day, much like an ambulatory blood pressure monitor.”

Not There Yet

But Lee stressed that this technology is not ready just yet. Among the major steps that remain to be completed are more tests in hypotensive or hypertensive patients; further research in groups of people with greater diversity in terms of race/ethnicity and skin tone; and evaluation of the approach in clinical settings and under less-controlled conditions.

In an accompanying editorial, Ramakrishna Mukkamala, PhD (Michigan State University, East Lansing), says “the potential of this concept is fascinating. Each time a person uses a smartphone, an application controlling the camera could continually search for opportunistic moments (eg, when the person is still) to make BP measurements. Such passive and frequent BP monitoring during daily life with devices that are already in the pockets of many could help improve on the currently low hypertension awareness and control rates around the world.”

The results reported here, however, “may not necessarily translate in practice,” he says, identifying areas in need of further research similar to those addressed by the investigators. “Nevertheless, the study . . . represents an auspicious start for video camera BP measurement.”

The big-picture message, Lee said, is that “our smartphones are really smart. We can use our smartphone beyond communication and social networking. We can actually use our smartphones as a health and wellness tool to help ourselves to improve our health and make us live better.”

Photo Credit: Adapted from Kang Lee and the American Heart Association.