Detecting Physiological Stress Using Earbuds

Continuous stress exposure negatively impacts mental and physical well-being. Stress arousal affects heart beat frequency, changes breathing pattern, and peripheral temperature, among several other bodily responses. Traditionally the stress detection is performed by collecting bio-signals such as electrocardiogram (ECG), breathing, and galvanic skin response using uncomfortable chestbands or chestpatches. In this study, we use earbuds that passively measure photoplethysmograph (PPG), core body temperature, and inertial measurements simultaneously. We conducted a lab study exposing 18 test subjects to Trier Social Stress Test (TSST) and going through several relaxing activities including listening to functional music and progressive muscle relaxation while measuring physiological signal using earbuds. Moreover, we have simultaneously collected PPG, ECG, impedance cardiogram (ICG), and blood pressure using gold-standard reference devices. We show that earbuds can reliably capture heart rate and heart rate variability. We further show that earbud signals can be used to classify the physiological stress arousal with 91.30\% recall and 80.52\% precision using a random forest classifier with leave-one-subject-out cross-validation.