Wearable Radar Sensor Measures Blood Pressure Continuously

A new study describes how two clip-on sensors attached to the sternum and earlobe can provide real-time blood pressure results.

Under development at Monash University (Melbourne, Australia), the novel measurement technique is based on radar sensor methodology. Instead of the traditional arm cuff, it uses a small continuous wave radar (CWR) sensor adhered to the sternum, and a photoplethysmogram sensor (PPG) clipped to the left earlobe. Using both sensors, the system measures pulse arrival time (PAT), pre-ejection period (PEP), and pulse transit time (PTT), and calculate continuous systolic blood pressure (SBP) from the data.

The researchers then collected experimental data from 43 subjects (40-65 years of age) in various static postures, as well as in 26 subjects doing six different exercise tasks, such as cycling on a stationary bike. Two mathematical models were then used to calculate SBP from the PTT/PAT data, and compare then to simultaneous sphygmomanometer readings. The results showed that for participants in the posture tasks, the best cumulative error percentage (CEP) was 92.28%, and for those in the exercises group, the best CEP was 82.61%. Additionally, removing PEP from PAT lead to a 9% improvement in results. The study was published on November 27, 2019, in Nature Scientific Reports.

“Clinicians still cannot continuously measure blood pressure during sleep, nor during times of activity such as walking or running. This means people with high, low, or irregular blood pressure can’t get the critical information they need about the state of their health around the clock,” said senior author Mehmet Yuce, PhD, of the department of electrical and computer systems engineering. “A wearable device that can provide comfort and portability while people are going about their daily lives will be a significant development for the health sector in Australia and internationally.”

CWR uses known radiofrequency (RF) energy that is transmitted and then received from any reflecting objects. Any movement of the transmitter, target, or both causes a change in the frequency of the electromagnetic wave, known as the Doppler shift. It is also possible to use CWR to measure range instead of range rate by frequency modulation. By measuring the frequency of the return signal, the time delay between transmission and reception can be measured.

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