The ear as a location for wearable vital signs monitoring

Obtaining vital signs non-invasively and in a wearable manner is essential for personal health monitoring. We propose the site behind the ear as a location for an integrated wearable vital signs monitor. This location is ideal for both physiological and mechanical reasons. Physiologically, the reflectance photoplethysmograph (PPG) signal behind the ear shows similar signal quality when compared to traditional finger transmission PPG measurements. Ballistocardiogram (BCG) can be obtained behind the ear using 25mm×25mm differential capacitive electrodes constructed using fabric. The BCG signal is able to provide continuous heart rate and respiratory rate, and correlates to cardiac output and blood pressure. Mechanically, the ear remains in the same orientation relative to the heart when upright, thus simplifying pulse transit time calculations. Furthermore, the ear provides a discreet and natural anchoring point that reduces device visibility and the need for adhesives.