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Low-cost clip uses smartphone to measure blood pressure



Scientists at the University of California San Diego have developed a simple, low-cost clip that uses a smartphone’s camera and flash to monitor blood pressure at the user’s fingertip.

The clip works with a custom smartphone app and currently costs about 80 cents (64 pence) to make.

The researchers estimate that the cost could be as low as 10 cents (8 pence) apiece when manufactured at scale.

The engineers say it could help make regular blood pressure monitoring easy, affordable and accessible to people in resource-poor communities.

The device could benefit older adults and pregnant women, for example, in managing conditions such as hypertension.

Study senior author Edward Wang, a professor of electrical and computer engineering at UC San Diego and director of the Digital Health Lab, said:

“Because of their low cost, these clips could be handed out to anyone who needs them but cannot go to a clinic regularly.

“A blood pressure monitoring clip could be given to you at your check-up, much like how you get a pack of floss and toothbrush at your dental visit.”

Another major advantage of the clip is that it does not need to be calibrated to a cuff.

Other cuffless systems being developed for smartwatches and smartphones, Wang explained, require obtaining a separate set of measurements with a cuff so that their models can be tuned to fit these measurements.

He added:

“Our is a calibration-free system, meaning you can just use our device without touching another blood pressure monitor to get a trustworthy blood pressure reading.”

To measure their blood pressure, the user simply presses on the clip with a fingertip.

A custom smartphone app guides the user on how hard and long to press while the measurement is taken.

The clip is a 3D-printed plastic attachment that fits over a smartphone camera and flash.

Its optical design is similar to that of a pinhole camera.

When the user presses on the clip, the phone’s flash lights up the fingertip.

That light is then projected through a small channel to the camera as an image of a red circle.

A spring inside the clip enables the user to press with different levels of force.

The harder the individual presses, the bigger the red circle appears on the camera.

By looking at the size of the circle, the app can measure the amount of pressure applied by the user’s fingertip.

And then by looking at the brightness of the circle, the app can measure the volume of blood going in and out of the fingertip.

An algorithm converts the information into systolic and diastolic blood pressure readings.

The scientists tested the clip on 24 volunteers from the UC San Diego Medical Center, with results comparable to those taken by a blood pressure cuff.

Study co-author and medical collaborator Alison Moore, chief of the Division of Geriatrics in the Department of Medicine at UC San Diego School of Medicine, said:

“Using a standard blood pressure cuff can be awkward to put on correctly, and this solution has the potential to make it easier for older adults to self-monitor blood pressure.”

While the team has only proven the solution on a single smartphone model, the clip’s current design should in theory work on other phone models, first author Yinan (Tom) Xuan said.

Wang and one of his lab members, Colin Barry, a co-author on the paper who is an electrical and computer engineering student at UC San Diego, co-founded a company, Billion Labs Inc., to refine and commercialise the technology.

Next steps include making the tech more user friendly, especially for older adults; testing its accuracy across different skin tones; and creating a more universal design.

Image: Digital Health Lab / UC San Diego

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