The device also measures four additional vital signs simultaneously, namely heart rate, blood oxygen saturation, body temperature and respiratory rate, said Richard Byfield, a mechanical and aerospace engineering graduate student in the MU College of Engineering, and the lead author on the study published in IEEE Sensors Journal.
“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,” Byfield said in a statement. “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.”
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This process is photoplethysmography (PPG) and the device uses two PPG sensors located at two different points on a finger to capture a person’s pulse to calculate pulse wave velocity. Once the data from the pulse wave velocity is gathered, it is transmitted wirelessly to a computer for signal processing and blood pressure calculation by a machine learning algorithm. According to the researchers, other studies have shown that pulse wave velocity has a strong correlation with blood pressure.
An early test of the device with 26 study participants has provided an accuracy rate of about 90 per cent for systolic blood pressure, and a 63 per cent accuracy rate for diastolic blood pressure. Byfield said the accuracy rate differs between systolic and diastolic because diastolic, which is a person’s minimum blood pressure, can change significantly depending on a person’s age, and can also be controlled by various factors, including age, artery stiffness, overall health and body weight.
Byfield and colleagues also acknowledge there are some issues with making PPG sensors work to obtain these measurements.
“Typically, there are a few problems with PPG sensors,” Byfield said. “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. 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 and the team is working on developing the device for at-home use. Their long-term goal includes potential clinical and commercial applications and Byfield said a clinical application could help relieve some burdens for nurses who deal with multiple devices to monitor a patient’s vital signs.
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