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Researchers Build Blood Pressure Monitoring Device Using Two Photoplethysmography Sensors

Regular monitoring of a person’s blood pressure can help health care specialists with early detection of a range of health problems such as high blood pressure, which has no symptoms or warning signs.

Researchers Build Blood Pressure Monitoring Device Using Two Photoplethysmography Sensors.
Researchers at the University of Missouri are customizing a commercial finger clip device to provide a rapid, noninvasive way for measuring and continually monitoring blood pressure. (Image Credit: University of Missouri).

However, a number of things can change an accurate blood pressure evaluation, including the nervousness of a patient having to check blood pressure at a doctor’s office, otherwise referred to as “white coat syndrome.”

Currently, scientists at the University of Missouri are tailoring a commercial finger clip device to deliver a fast, non-invasive way for measuring and continually tracking blood pressure.

The device can also concurrently measure four additional vital signs — heart rate, body temperature, blood oxygen saturation and respiratory rate, said Richard Byfield, a mechanical and aerospace engineering graduate student in the MU College of Engineering, and the study’s lead author.

Typically, calculating someone’s blood pressure at a hospital or clinic involves using an inflatable cuff wrapped around their arm, but there are three issues with that method — it can cause damage to someone’s arteries if done repeatedly within a short amount of time; people’s blood pressure can rise due to nervousness; and it can take up to 30 seconds to complete.

Richard Byfield, Graduate Student, Mechanical and Aerospace Engineering, College of Engineering, University of Missouri

“Our device can record someone’s blood pressure within five seconds by using optical sensors placed on the fingertip that measure the amount of light reflected off the blood vessels underneath the surface of the skin,” Byfield added.

This process is known as photoplethysmography (PPG), and the device uses two PPG sensors situated at two different points on a finger to record someone’s pulse so as to calculate pulse wave velocity, or how rapidly the blood is flowing through the bloodstream.

Once the data from the pulse wave velocity is collected, it is communicated wirelessly to a computer for signal processing and for calculation of blood pressure by a machine learning algorithm. The team said other studies have also revealed pulse wave velocity has a robust correlation with blood pressure.

An early test of the device with 26 study participants has delivered an accuracy rate of nearly 90% for systolic blood pressure and a 63% accuracy rate for diastolic blood pressure.

Byfield said the precision rate varies between systolic and diastolic because diastolic, which is the minimum blood pressure of a person, can vary considerably based on a person’s age, and can also be controlled by numerous factors including age, body weight, artery stiffness and overall health.

Byfield and his team also admit there are some concerns with making PPG sensors function to acquire these measurements.

Typically, there are a few problems with PPG sensors. One is called artifact motion — if you move a PPG sensor while it’s reading, it can affect the waves that are being recorded. On top of that, we found that differences in pressure can alter the waves, but with a finger clip design, a spring provides constant pressure.

Richard Byfield, Graduate Student, Mechanical and Aerospace Engineering, College of Engineering, University of Missouri

Byfield continued, “Another reason this method hasn’t been explored much before is typically these finger clips only have one sensor, but we have two sensors in our device.”

A provisional patent has been filed for the device. The scientists are at present working on creating the device for at-home use, and their long-term goal includes possible commercial and clinical applications. Byfield said a clinical application could help allay a few burdens for nurses who handle numerous devices to track the vital signs of a patient.

The scientists are also aiming to integrate the device in data collection for future studies by creating predictive computational models to help detect vital signs that could act as indicators for various human diseases, including COVID-19 and the flu, said Jian Lin, William R. Kimel Faculty Fellow and associate professor of mechanical and aerospace engineering.

Our goal is to develop a broader impact for our device beyond a new way to measure vital signs.

Jian Lin, Corresponding Author and William R. Kimel Faculty Fellow and Associate Professor, Mechanical and Aerospace Engineering, University of Missouri

“Toward Robust Blood Pressure Estimation from Pulse Wave Velocity Measured by Photoplethysmography Sensors,” was published in the IEEE Sensors Journal, a peer-reviewed, semi-monthly online journal dedicated to sensors and sensing phenomena. Other co-authors include Jonathan Miles, Morgan Miller and Giovanna Guidoboni at MU.

Journal Reference:

Byfield, R., et al. (2021) Toward Robust Blood Pressure Estimation from Pulse Wave Velocity Measured by Photoplethysmography Sensors IEEE Sensors Journal.


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