Your Watch Will One Day Track Blood Pressure Using Reflected Radio Signals

USA - Ekhbary News Agency

Your Watch Will One Day Track Blood Pressure Using Reflected Radio Signals

Smartwatches have become ubiquitous tools for tracking various aspects of our health and fitness, from step counts to heart rate and sleep patterns. However, accurately measuring blood pressure has remained a significant challenge for wearable technology. This landscape is poised for a dramatic shift, thanks to pioneering research from the University of Texas at Austin. A team of scientists has unveiled a promising technique that utilizes reflected radio signals from wrist blood vessels to determine blood pressure. Their ambitious plan includes integrating this technology into smartwatches within the next couple of years, potentially revolutionizing personal health monitoring.

This development arrives at a time when the demand for accessible and non-invasive health monitoring solutions is soaring. Beyond the traditional, cumbersome blood pressure cuffs, researchers have been exploring a multitude of innovative methods. These include wearable ultrasound transducers, electrocardiogram (ECG) sensors, bioimpedance measurements, and photoplethysmography (PPG), often in various combinations. Despite the ingenuity behind these approaches, many have encountered significant limitations, hindering their widespread adoption in consumer devices.

"We found that existing methods all face limitations," stated Yiming Han, a doctoral candidate in the lab of Yaoyao Jia, during her presentation to engineers at the IEEE International Solid State Circuits Conference (ISSCC) last week in San Francisco. For instance, ultrasound sensing requires prolonged skin contact, which can be inconvenient. Even novel concepts like electronic tattoos, while intriguing, lack the comfort and ease of use associated with smartwatches. Photoplethysmography, which measures blood oxygenation using light, bypasses the need for direct contact. Indeed, researchers in Tehran and California recently employed PPG combined with sophisticated machine learning to monitor blood pressure. However, a critical concern with PPG sensors is their potential sensitivity to skin tone, a factor implicated in inadequate treatment for Black individuals in the United States during the COVID-19 pandemic, highlighting the urgent need for equitable technology.

Addressing these shortcomings, the University of Texas team focused on developing a non-contact solution that is inherently immune to skin-tone bias and can be miniaturized for integration into a small device. Understanding the physiological basis of blood pressure is crucial. Blood pressure measurements consist of two key readings: systolic pressure, the peak pressure during heart contractions that forces blood into arteries, and diastolic pressure, the lower pressure between beats when the heart relaxes. During systole, arteries expand and stiffen, and blood velocity increases. The opposite occurs during diastole. These cyclical changes in vessel volume and stiffness alter the electrical properties of the surrounding tissue, including its conductivity and dielectric characteristics.

The researchers, led by Professor Deji Akinwande and Dr. Yaoyao Jia, hypothesized that these subtle physiological changes would manifest in the way radio waves interact with the wrist. Specifically, they theorized that reflected near-field radio waves – electromagnetic waves close to the source – would carry information about these variations. Near-field waves are defined as radiation impacting a surface that is less than one wavelength from the radiation's source. By analyzing how these waves are reflected, they believed it might be possible to infer blood pressure changes.

To test their hypothesis, the team utilized a Vector Network Analyzer (VNA), a sophisticated laboratory instrument capable of measuring RF reflections. They successfully correlated the radio wave reflections from the wrist with blood pressure readings taken concurrently using standard medical equipment. Their key observation was that during systole, the reflected near-field waves exhibited a stronger phase shift relative to the transmitted signal, indicating significant changes in tissue properties. Conversely, during diastole, the reflections were weaker and closer in phase with the transmitted signal, reflecting the relaxation of the arteries.

Recognizing that a $50,000 VNA is impractical for everyday use, the researchers shifted their focus to developing a compact, wearable system. Their prototype comprises a patch antenna attached to the wrist, connected to a device called a circulator. This circulator acts as a radio signal traffic controller, directing outgoing signals to the antenna and channeling the weaker reflected signals to a separate processing circuit. A custom-designed integrated circuit then transmits a 2.4 GHz microwave signal, receives and amplifies the faint reflections, and digitizes the data. Remarkably, the entire system operates on an extremely low power budget of just 3.4 milliwatts, making it ideal for battery-powered wearables.

"Our work is the only one to provide no skin contact and no skin-tone bias," Han emphasized, highlighting the system's unique advantages. Professor Jia elaborated on future enhancements, stating that the next iteration will employ multiple radio frequencies (such as 5 GHz, common in Wi-Fi, and 915 MHz, used in cellular networks) in addition to the prototype's 2.4 GHz signal. This multi-frequency approach aims to improve accuracy, acknowledging that individual tissue conditions vary and may respond differently to specific frequencies.

Following further experimental validation, Jia's team plans to integrate the technology into a smartwatch form factor and conduct broader clinical trials to assess its commercial viability. This innovation represents a significant stride towards empowering individuals with continuous, convenient, and equitable access to vital cardiovascular health data, potentially paving the way for earlier detection and better management of hypertension and related conditions.

Ekhbary News Agency