UCSD researchers created 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 out of the Jacobs School of Engineering outlined their invention and findings in a paper that was published in the peer-reviewed journal, Scientific Reports, last week.

Researchers note that hypertension, or high blood pressure, is a leading cause of preventable premature death and disability worldwide. Monitoring blood pressure is also crucial for pregnant mothers who could be at risk of life-threatening conditions like preeclampsia.

Edward Wang, a professor of electrical and computer engineering at UC San Diego and one of the authors of the study, highlighted the low cost to produce the BPClip as a key for making this tool more accessible.

It costs less than $1 to make a BPClip, while traditional at-home blood pressure monitors with a cuff can cost between $30 to $75.

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

He explained that having a low-cost device like this could help change the dynamic of how people can assess their risk and measure blood pressure.

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 I think about the system is that it just needs the camera and a flash or some light source. And so every phone has that and there's nothing that's super special about the requirements of the phone," Wang said.

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 their finger. As the user presses on the BPClip, the camera light shines through a pinhole on the finger plate.

That 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 explained, 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.

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. He explained that 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.

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

Now, the team is focused on fine-tuning the mechanics of the device so it is user-friendly and improves the accuracy of data collection. Wang said they recently submitted an application for a federal grant to help make these 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 this 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 standalone business called Billion Labs.

Wang said the goal of this small company 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 Yinan Xuan, Colin Barry, Jessica De Souza, Jessica H. Wen, Nick Antipa, Alison A. Moore and Edward J. Wang.