Non-Contact Wi-Fi Sensing of Respiration Rate for Older Adults in Care: A Validity and Repeatability Study

In recent years, considerable effort has been directed towards non-contact Wi-Fi sensing applications such as fall detection and vital sign monitoring. For emerging technologies in healthcare, it is essential to assess the validity and repeatability of new measurement instruments before real-world implementation. However, the existing literature has not addressed the clinical validity and repeatability of respiration rate measurements obtained from Wi-Fi CSI. This study draws on medical instrumentation statistics to address this research gap by investigating the validity and repeatability of Wi-Fi sensing in measuring respiratory rates. For this purpose, we first implement a non-contact Wi-Fi Channel State Information respiration rate sensing system using off-the-shelf ESP32 devices and signal processing methods. Then, we evaluated the validity of the Wi-Fi sensor's respiration rate measurement against respiration belt NUL-236 as a ground truth. The Bland-Altman method provided homoscedastic results across the standard range of respiration rates of older adults [12, 28] BPM achieving a validity of [1.29, 1.06] BPM, allowing us to analyze measurement repeatability at a single point. Hence, we assessed the measurement repeatability at 14 BPM using the spread of the data and the implications of random error in the measurements. The Wi-Fi CSI measurements dataset and corresponding belt data were made available for the validity and repeatability experiments. By providing appropriate measurement validity and repeatability metrics, care professionals can make informed decisions about the acceptability and generality of non-contact Wi-Fi sensing systems in measuring respiratory rate.