At the University of Missouri a team of researchers developed a custom finger clip device that can continuously measure a variety of vitals, including blood pressure. The novel device represents a new way to measure vitals, and contains two commercial photoplethysmography (PPG) sensors that operate at two different points on the finger. This approach allows the researchers to simultaneously calculate pulse wave velocity and also measure blood oxygen saturation, body temperature, heart rate, and respiratory rate.
Continuous blood pressure measurements can reveal trends that a single measurement can miss. Moreover, the very act of measuring someone’s blood pressure in a doctor’s office can cause their anxiety to spike, leading to a change in their blood pressure, in a phenomenon known as “white coat syndrome”. Clearly, continuous monitoring that non-invasively and unobtrusively takes measurements throughout the day is preferable.
“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,” said Richard Byfield, one of the leads on the development of the new device. “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.”
Once the clip obtains the pulse wave velocity data, it wirelessly transmits it to a computer, where machine-learning algorithms interpret it and calculate blood pressure. So far, in tests with volunteers, the clip has shown that it can measure systolic blood pressure with an accuracy of approximately 90%, and diastolic pressure with an accuracy of 63%.
The robust nature of the clip is key to making sure that the PPG data are reliable. “Typically, there are a few problems with PPG sensors,” said Byfield. “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.”
Study in IEEE Sensors Journal: Toward Robust Blood Pressure Estimation from Pulse Wave Velocity Measured by Photoplethysmography Sensors
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