Trace: An Earlobe Mounted Sensor for Continuous Measurement of Heart Rate Dynamics

Wearable continuous heart rate monitors (CHRM) are widely used in fitness and health applications. The majority of existing devices are either wristwatches, which utilize photoplethysmography (PPG), or chest-straps, which rely on electrocardiography (ECG). Wristwatches are popular due to their comfortable form factor but are known to have lower accuracy than chest straps and also have significant lag, which precludes their ability to track rapid changes in heart rate. In this paper, we introduce Trace, a fully self-contained, earlobe-mounted, wireless PPG CHRM which is 10-fold smaller than previously reported devices. Placement on the earlobe, where there are no muscles or tendons, is less susceptible to noise artifacts. We demonstrate the tracking of heart rate during high intensity interval training (HIIT), where heart rate changes rapidly and sensor lag cannot be tolerated. Notable is Trace’s ability to measure heart rate recovery (HRR), an advanced metric commonly used by athletes to monitor fatigue, and by physicians to assess cardiovascular risk.