A research team led by Prof. CHEN Yan at the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences developed a non-invasive radio frequency (RF) based system capable of monitoring heart rate variability (HRV) with clinical-grade accuracy over extended periods, representing a leap forward in cardiovascular health monitoring. The study was published in Nature Communications.

Cardiovascular diseases (CVDs) are the leading cause of death globally. Research shows that early diagnosis and intervention can effectively prevent many cases of cardiovascular illness. 

Existing detection techniques like electrocardiogram (ECG) and Holter are accurate but have drawbacks. The electrodes attached to the body in ECG and Holter can cause discomfort, making them unsuitable for long-term use. Other techniques like wearable devices, while more convenient, are less accurate and vulnerable to environmental interference.

The developed RF-HRV system overcomes the issue of interference from respiratory motion in far-field conditions by analyzing RF signals. It employs a signal selection algorithm to identify the signal rich in heartbeat information from multiple reflected signals, and the variational mode decomposition algorithm to extract high-frequency components, obtaining clear and accurate heartbeat patterns. By superimposing adjacent heartbeat harmonics, the system generates specific heartbeat patterns with a frequency equal to the heart rate to calculate HRV.

Researchers evaluated the system in a large-scale outpatient setting (with 6,222 participants) and a long-term daily life scenario. In the outpatient scenario, the median real-time inter-beat interval error of the system was 26.1 milliseconds, and in the daily scenario, it was 34.1 milliseconds, which was an improvement compared to existing systems that extract signals only from the heart rate frequency band. This system also performed well in the automatic classification of heartbeat abnormalities and was comparable to clinical-grade 12-lead ECG systems.

The innovation of this study lies in breaking the traditional signal processing framework by using previously unexplored high-frequency ranges (beyond 10-order heartbeat harmonics) to extract heartbeat signals. This study allows for long-term, non-invasive monitoring without the need for electrodes or clothing adjustments, which paves the way for comfortable cardiovascular care solutions, and lays a foundation for the application of millimeter-wave radar in cardiac monitoring.