Medicine and engineering researchers at UC San Diego join forces on low-cost plastic clip for monitoring blood pressure

A team of researchers at the University of California, San Diego, have recently developed a low-cost cuffless clip for measuring blood pressure. Linked to a smartphone app that helps the setup infer blood pressure from the amount of blood passing through the finger, this new solution can improve blood pressure monitoring for persons who live far away from clinics or lack access to suitable diagnostic technology. Blood pressure measurements are essential metrics of good health, and the researchers look forward to the tech’s use in improving outcomes for patients without access to reliable blood pressure monitors.

A Cuffless Smartphone-Based Clip for Blood Pressure Monitoring

At the University of California, San Diego, researchers in the engineering and medicine departments have devised a low-cost, cuffless blood pressure monitor that can help patients measure their blood pressure rapidly and effectively, especially outside clinical settings. Consisting of a smartphone and a blood pressure monitoring clip that fits onto the index finger, the clips can be used by anyone who needs to measure their blood pressure regularly but cannot go to a clinic often. In addition to the apparent advantages of portability, one key feature that the clip adds is the lack of a need for calibration.

Currently, a few cuffless blood pressure monitoring systems have been developed. Still, their utility is hampered by one major limitation – the need for periodic per-user calibration. Per-user calibration means users must measure their BP with a cuff-based device at least once to calibrate the instrument properly. However, it is typical for users to calibrate these devices multiple times, especially for different BP levels.

Many of these devices use pulse transit time or pulse wave analysis, which is highly dependent on individual variations such as arterial stiffness, vascular structure, and arm length. This impacts the convenience and reliability of such devices when used over time. Although a team at Michigan State University was among the first to demonstrate the possibility of measuring blood pressure through methods that do not require calibration, it remained a concept.

The new device from the UC San Diego team is ready to go from the outset, working based on oscillometric methods, which calculate blood pressure based on the change of blood volume oscillations per heartbeat. “This is what distinguishes our devices from other blood pressure monitors,” said Edward Wang, a lead researcher and joint-corresponding author. “Ours 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,” he added.

A significant advantage of the device is the convenience it offers. Beyond being a low-cost solution, it is easy to use – patients only need a cuff and a smartphone to measure their blood pressure. As Edward Wang says, “A blood pressure monitoring clip could be given to you at your checkup, much like how you get a pack of floss and toothbrush at your dental visit.” Alison Moore, Professor of Medicine at the University of San Diego and a researcher in this study, added, “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.”

Accurate Blood Pressure Measurement in a Portable Package

The researchers published their findings in the May 2023 edition of Nature’s Scientific Reports, outlining how they devised a system to measure blood pressure using a plastic clip and a smartphone’s flash LED and camera. Titled ‘Ultra-low-cost mechanical smartphone attachment for no-calibration blood pressure measurement,’ the paper outlines how the principle of measuring oscillometry at the fingertip was applied in BPClip, the name they christened their new product.

To use the BPClip, users hold the phone horizontally and push down on a spring-loaded clip with the right index finger, adjusting the applied force based on prompts from the smartphone app. This applied pressure is transmitted to the transverse palmar arch, an artery of the hand. At the same time, the smartphone LED illuminates the fingertip by delivering light through a chrome-painted light guide, creating a circular image that encodes the pressure applied to the finger and the blood volume in the finger. The blood volume oscillation is detected using a measure of the pinhole projection’s brightness.

The researchers also endeavoured to measure the accuracy of the BPClip in measuring blood pressure. Recruiting 24 users with SBP ranging between 80 and 156 mmHg and DBO ranging from 57 to 97 mmHg, the researchers compared BPClip’s accuracy with that of a standard arm cuff device. The measurements resulted in a mean absolute error of 8.7 ± 10 mmHg for systolic pressure and 5.5 ± 7 mmHg for diastolic blood pressure. The mean blood pressure measurements resulted in an estimation error of 8.4 ± 10.3 mmHg, and a one-way ANOVA test among three ethnic groups revealed there was no significant difference in measurements among them.

BClip: Beating Hypertension with Tech

At only $0.80 per device, the UC San Diego team proposes a novel, effective solution to minimizing the progression of hypertension, an insidious problem in modern health. Hypertension affects more than 45% of US adults and is the leading cause of preventable premature deaths worldwide through cardiovascular complications such as stroke, heart disease, and chronic kidney disease. Screening has been demonstrated to be effective in curbing mortality. Still, unfortunately for low-income communities, access to screening services is a significant challenge. The new device can improve outcomes, providing an alternative that makes BP monitoring more accessible.

BPClip was developed by a seven-person team at the University of California, San Diego, with funding from MassAITC (under the National Institutes of Health), the Altman Clinical and Translational Research Institute Galvanizing Engineering in Medicine Awards, and a Google Research Scholar Award. Among the researchers are Yinan Xuan, Colin Barry, Jessica De Souza, and Nick Antipa, all from the Department of Electrical and Computer Engineering. Significant medical contributions were provided by Jessica Wen, Alison Moore, and Edward J. Wang, all affiliated with the Department of Medicine, UC San Diego. Edward Wang has recently cofounded a company – Billion Labs Inc – to refine and commercialize the technology, where he is working to make it more user-friendly and accurate.

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