UCSD researchers create a pocket

Researchers at UC San Diego have developed a new kind of blood pressure monitor that's small enough to fit in your pocket and attaches to a smartphone.

The team from the Jacobs School of Engineering outlined its invention, called the BPClip, in a paper published May 29 in the journal Scientific Reports.

Researchers say hypertension, or high blood pressure, is a leading cause of preventable premature death and disability worldwide. Monitoring blood pressure also is considered crucial for pregnant mothers who could be at risk of life-threatening conditions like preeclampsia, which can cause high blood pressure and damage to organs such as kidneys and the liver.

Edward Wang, a professor of electrical and computer engineering at UCSD and one of the authors of the study, highlighted the low cost to produce the BPClip — less than $1 — as a key to making the tool more accessible. Traditional at-home blood pressure monitors with a cuff can cost $30 to $75 to make.

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Ultimately, Wang said, the goal is not to replace the traditional blood pressure monitors but rather create an option that easily could be used in telemedicine or be provided to people in disadvantaged and rural areas at no cost.

Having a low-cost device like this could help change the dynamic of how people can assess their risk and measure blood pressure, he said.

After about three years of development, the UCSD researchers created a 3D-printed clip and a finger plate with a spring that attaches to the front-facing camera of an Android phone. While using the device, the phone screen displays prompts for the test and data for measuring blood pressure.

"What's nice ... about the system is that it just needs the camera and a flash or some light source," Wang said. "Every phone has that and there's nothing that's super special about the requirements of the phone."

The key to measuring blood pressure with the BPClip is the brightness of the camera light as the user applies different levels of pressure to a finger. As the user presses on the BPClip, the camera light shines through a pinhole on the finger plate.

The brightness of the light fluctuates with the amount of blood flowing in and out of the finger because the blood will absorb some amount of light, Wang said.

The phone camera captures the change in pressure applied visually based on the changing size of the circle created by the pinhole. For instance, when maximum pressure is applied, the circle will be the largest and the bright light will not fluctuate because the flow of blood has stopped.

The real goal, Wang said, is to measure when the cutoff of blood flow happens. The scientific method used by the BPClip to measure blood pressure is similar to traditional cuff monitors in the sense that it looks at how much blood is flowing at varying levels of pressure applied to the artery.

The BPClip application collects 20 data points of the user pressing on the device, then uses 18 of those data points to establish an estimate of blood pressure measurements.

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The study was based on the results of 24 participants with systolic blood pressure ranging from 80 to 156 mmHg and diastolic blood pressure ranging from 57 to 97 mmHg.

Another key feature of the BPClip is that it doesn't require calibration, Wang said. Other cuff-less blood pressure monitors on the market, such as watches, require users to first figure out their baseline measurements using a traditional cuff monitor, he said.

At the moment, the BPClip can do screenings — and, for instance, catch a spike in blood pressure — but there's still more refining to be done to try to cut the margin of error by half, Wang said.

The team now is focused on fine-tuning the mechanics of the device so it is user-friendly and improves the accuracy of data collection. Wang said the researchers recently submitted an application for a federal grant to help make those improvements.

Wang works with researchers in The Design Lab to develop tools and devices that are powered by everyday smartphones. Another idea to come out of that lab is using a smartphone camera to measure blood oxygen levels.

But taking those concepts from a research setting to a commercial product isn't easy, so Wang partnered with Colin Barry and Chelsea Maples to launch a stand-alone business called Billion Labs.

Wang said the small company's goal is to serve as a vehicle for commercializing UCSD-licensed technology — like the BPClip — that was developed in a lab and get it to work on any kind of smartphone.

The study outlining how the BPClip works was published by Wang, Barry, Yinan Xuan, Jessica De Souza, Jessica Wen, Nick Antipa and Alison Moore. ◆