Health-related Indicators Measured by Earable Devices: Systematic Review (Preprint)

BACKGROUND Earable devices are novel, interactive wearable-IoT devices that are user-friendly and have potential applications in mobile healthcare. The position of the ear is advantageous for assessing vital status and detecting diseases through reliable and comfortable sensing devices. OBJECTIVE Our study aims to review the utility of health-related indicators derived from earable devices for disease prevention. We also propose future directions for research on the healthcare applications of earable devices. METHODS A systematic review was conducted of the PubMed, Google Scholar, and EMBASE databases. Keywords were used to identify studies on earable devices published between 2015 and 2020. Fifty-one articles met the inclusion criteria and were reviewed. RESULTS The earable devices were described in terms of target health outcomes, biomarkers, sensor types and positions, and their utility for disease prevention. Dietary status was determined based on muscle movements and PPG. Brain status was measured by electroencephalography (EEG), and head injuries were detected by motion sensors. Heart status was measured, and cardiovascular diseases (CVDs) detected, using electrocardiography (ECG) and photoplethysmography (PPG). Most indicators were related to secondary prevention, but dietary indicators were also relevant to primary prevention. Tongue motion, gait form, diet habit, facial expression has potential as an indicator in tertiary prevention/rehabilitation. The most used sensor type was the electric sensor, to collect EEG, ECG, and electromyography (EMG) data. In almost half of the studies, the sensor was positioned within the ear canal, although other positions were also used, including behind and around the ear. CONCLUSIONS Earable devices can provide biomarkers for various health outcomes. Brain status and CVD were the most frequently targeted outcomes among the studies. Earable devices were mostly used for secondary prevention via monitoring of health or disease status. Potential utility of earable devices for primary and tertiary prevention needs to be further explored. Earable devices connected to smartphones or tablets through cloud servers will guarantee user access to personal health information and facilitate comfortable wearing.