BallistoBud: Heart Rate Variability Monitoring using Earbud Accelerometry for Stress Assessment

This paper examines the potential of commercial earbuds for detecting physiological biomarkers like heart rate (HR) and heart rate variability (HRV) for stress assessment. Using accelerometer (IMU) and photoplethysmography (PPG) data from earbuds, we compared these estimates with reference electrocardiogram (ECG) data from 81 healthy participants. We explored using low-power accelerometer sensors for capturing ballistocardiography (BCG) signals. However, BCG signal quality can vary due to individual differences and body motion. Therefore, BCG data quality assessment is critical before extracting any meaningful biomarkers. To address this, we introduced the ECG-gated BCG heatmap, a new method for assessing BCG signal quality. We trained a Random Forest model to identify usable signals, achieving 82% test accuracy. Filtering out unusable signals improved HR/HRV estimation accuracy to levels comparable to PPG-based estimates. Our findings demonstrate the feasibility of accurate physiological monitoring with earbuds, advancing the development of user-friendly wearable health technologies for stress management.