Zero-Effort Ambient Heart Rate Monitoring Using Ballistocardiography Detected Through a Seat Cushion: Prototype Development and Preliminary Study (Preprint)

Abstract

BACKGROUND Cardiovascular diseases are leading cause of death and result in significant economic costs to the healthcare system. The prevalence of cardiovascular conditions that require monitoring are expected to increase as the average age of the global population continues to rise. While an accurate cardiac assessment can be done at medical centers, frequent visits for assessment is not feasible for most people, especially those with limited mobility. Vitals monitoring at home is becoming an increasingly desirable, accessible, and practical alternative. As wearables are not the ideal solution for everyone, parallel and complementary approaches need to be developed. OBJECTIVE The objective of this research is to develop a zero-effort, unobtrusive, low-cost, and portable option for home-based ambient heart rate monitoring. METHODS The prototype seat cushion uses load cells to acquire a user’s ballistocardiogram (BCG). The analog signal from the load cells is amplified and filtered by a signal conditioning circuit before being digitally recorded. A pilot study with 20 participants was conducted to analyze the prototype’s ability to capture BCG during five real-world tasks: sitting still, watching TV, reading, using a computer, and having a conversation. A novel algorithm based on the continuous wavelet transform (CWT) was developed to extract heart rate by detecting the largest amplitude values (J-peaks) in the BCG signal. RESULTS Data from the pilot study show that BCG signals from all five tasks had large enough portions to extract heart rate. The CWT-based algorithm for J-peak detection demonstrated an overall accuracy of 91.4% compared to electrocardiography (ECG). Excluding three outliers that had significantly noisy BCG data, the algorithm was able to achieve 94.6% accuracy, which is aligned with wearable devices. CONCLUSIONS This research suggests that that BCG acquired through a seat cushion is a viable alternative to wearable technologies. The prototype seat cushion presented in this research is an example of a relatively accessible, affordable, portable, and unobtrusive zero-effort approach to achieve frequent home-based ambient heart rate monitoring.