New Smartphone Sensor Checks Your Blood Pressure

It’s more convenient than a cuff and could help patients monitor hypertension at home

Person holding a smartphone based device for real-time monitoring of BP
Photo: Anand Chandrasekhar
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For years, scores of engineers have been trying to develop a more unobtrusive, convenient device for blood pressure monitoring. Now, researchers at Michigan State University and University of Maryland appear to have succeeded.

In a paper published today in Science Translational Medicine, the researchers described a prototype blood pressure sensor that can be incorporated into a smartphone, and requires only the press of a fingertip.  

The convenient device could encourage people to check their blood pressure more often, allowing them to catch hypertension—persistently high blood pressure—sooner, says Ramakrishna Mukkamala, a biomedical engineer at Michigan State, in East Lansing, who led the study. 

Hypertension can lead to heart disease and stroke. But roughly half of people with the condition don’t know they have it, says Mukkamala. 

In his team’s design, phones would be embedded with a sensor consisting of two main components: photoplethysmography (PPG), an inexpensive optical tool that measures blood volume changes, and a thin-filmed force transducer that measures applied pressure. 

The user presses her finger on the sensor in a particular way, and an algorithm computes her blood pressure. The pressing of the fingertip generates external pressure on the underlying artery, much like that generated by a blood pressure cuff.  

Many other groups have been working on convenient, cuffless blood pressure monitors that don’t require bulky equipment. One of the most common approaches is the use of pulse transit time. Such systems require two separate sensors, one placed near the heart and the other placed further away, such as on the wrist. The device then measures the time it takes for a pressure wave to travel from the heart to the other location in the body.

Mukkamala has a grant to pursue the technology for cuffless blood pressure monitoring. And some groups have already dived in and commercialized it. But the challenge with pulse transit time devices is that the user must calibrate it every few months against a standard blood pressure monitor.

Mukkamala argues that people are more apt to use a blood pressure monitor if it’s embedded in a smartphone—a device the average adult is already using 2.5 hours a day.

And the technology he is proposing to use—PPG—is already commonly used to measure heart rate. It works by illuminating tissue and measuring the changes in light absorption due to changing blood volume. Some fitness trackers and even the Samsung Galaxy are equipped with PPG heart rate monitors.

Mukkamala’s prototype, which his team tested on 32 people, proved accurate. Groups such as the Association for the Advancement of Medical Instrumentation (AAMI) and the IEEE have accuracy standards by which cuffless blood pressure monitors are benchmarked, and the prototype delivered results in line with those standards. It also matched the results of a $25,000 finger cuff blood pressure monitor. 

About 90 percent of the users in the test trial were able to figure out the correct technique for pressing the sensor after a couple of practices, according to the study. 

One could argue that blood pressure monitoring is already convenient. Digital, battery-powered devices with arm cuffs are available at drug stores, Wal-Mart and Amazon for $20-$30. (I have one somewhere—probably buried in a cabinet.)  

Using one of those, we could easily make blood pressure checking part of our daily or weekly routine at home. Yet, we just don’t.

Perhaps dangling it in front of us every time we check our phones would help. What do you think? If you could check your blood pressure using just your phone, would you check it more often?

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