The future of health monitoring may be on your wrist. While smartwatches currently excel at tracking steps, heart rate, and sleep patterns, accurate blood pressure readings have remained elusive. However, researchers at the University of Texas at Austin have demonstrated a promising new method for non-invasive blood pressure monitoring using smartwatch technology, potentially bringing continuous, convenient blood pressure tracking closer to reality.
The team’s innovation centers around using radio waves to analyze subtle changes in blood vessels. Existing methods for blood pressure monitoring, such as traditional cuffs, ultrasound transducers, and sensors relying on light (photoplethysmography), all have limitations. Ultrasound requires consistent skin contact, while photoplethysmography has raised concerns about accuracy across different skin tones – a critical issue highlighted during the COVID-19 pandemic when disparities in healthcare were brought to light. The University of Texas approach aims to overcome these hurdles with a contactless and potentially more equitable solution.
Blood pressure is measured by two key numbers: systolic pressure, representing the peak pressure when the heart beats, and diastolic pressure, the pressure when the heart rests between beats. These pressures fluctuate as blood vessels expand and contract with each heartbeat. Researchers, including Deji Akinwande and Yaoyao Jia, reasoned that these changes in vessel properties would alter how radio waves reflect off the skin. “All these changes alter conductivity, dielectric properties, and other tissue properties, so they should show up in reflected near-field radio waves,” Akinwande explained, according to reporting from IEEE Spectrum.
To test this theory, the team utilized a vector network analyzer – a laboratory instrument capable of sensing radio frequency (RF) reflection – to correlate radio wave responses with traditional blood pressure measurements. They discovered that during systole, reflected radio waves were more out of phase with the transmitted signal, while during diastole, the reflections were weaker and more in phase. This correlation formed the basis for their wearable system.
Developing a Wearable Blood Pressure Monitor
Recognizing the impracticality of carrying a $50,000 vector network analyzer for daily monitoring, the researchers developed a compact wearable system. This system consists of a patch antenna placed on the wrist, connected to a circulator – which directs radio signals – and a custom-designed integrated circuit. The circuit emits a 2.4 gigahertz microwave signal, receives and amplifies the reflected signal, and digitizes it for analysis. Notably, the entire system consumes only 3.4 milliwatts of power.
“Our work is the only one to provide no skin contact and no skin-tone bias,” stated Yiming Han, a doctoral candidate involved in the research. This claim addresses a significant concern with existing optical sensors, which have been shown to be less accurate on individuals with darker skin tones. The team’s approach, by relying on radio waves, aims to provide a more universally accurate reading.
The researchers are already planning improvements to enhance accuracy. Jia indicated that future iterations will incorporate multiple radio frequencies – including 5 GHz (commonly used for Wi-Fi) and 915 megahertz (used in cellular communications) – to account for variations in individual tissue conditions. Different people’s bodies respond differently to radio frequencies, and utilizing a range could lead to more precise measurements.
From Lab to Smartwatch
The next step involves miniaturizing the technology and integrating it into a smartwatch form factor. The team intends to conduct broader testing to assess the device’s performance and explore potential commercialization opportunities. While a commercially available smartwatch with this capability is still a couple of years away, the progress represents a significant leap forward in non-invasive blood pressure monitoring.
This research builds on a growing trend of innovative approaches to blood pressure monitoring. Beyond the University of Texas’s work, researchers are exploring methods using electrocardiogram sensors, bioimpedance measurements, and combinations of these technologies. However, the contactless nature and potential for skin-tone independence of the UT Austin system set it apart.
The development of a reliable, non-invasive blood pressure monitor for smartwatches could have a profound impact on preventative healthcare. Continuous monitoring could provide valuable data for individuals managing hypertension, allowing for earlier detection of issues and more personalized treatment plans. As the technology matures and undergoes rigorous testing, it promises to empower individuals to take greater control of their cardiovascular health.
What comes next will depend on the results of broader testing and the ability to successfully miniaturize the technology for integration into a commercially viable smartwatch. The team’s continued research and development will be crucial in determining whether this innovative approach can truly revolutionize blood pressure monitoring. Share your thoughts on the potential of this technology in the comments below.
