Self-Powered Cardiac Monitoring: Maintaining Vigilance With Multi-Modal Harvesting and E-Textiles

Remote patient monitoring has emerged from the intersection of engineering and medicine. Advances in sensors, circuits and systems have made possible the implementation of small, wearable devices capable of collecting and streaming data for long periods of time to help physicians track diseases and detect conditions in a non-intrusive manner. Cardiac monitoring comprises many of these applications, with the need to capture transient cardiac events motivating the adoption of wearable monitors in standard clinical practice. However, user burden and battery life limit the duration of monitoring or require heavy duty cycling, thus preventing the adoption of these technologies for use cases that require long-term vigilant monitoring, in which the sensor system cannot miss a critical cardiac event. To overcome these challenges, this paper introduces a self-powered system for uninterrupted vigilant cardiac and activity monitoring that senses and streams electrocardiogram (ECG) and motion data continuously to a smartphone while consuming only 683~μW on average. To achieve self-powered operation under environmental and wearability constraints, the system incorporates an energy combining technique to support multi-modal energy harvesting from indoor solar and thermoelectric energy. A custom ECG shirt made of a knitted compression fabric with embedded dry electrodes addresses issues of user comfort, skin irritation and motion artifacts. Vigilant Atrial Fibrillation (AF) monitoring is used as an example case study, analyzing sampling frequency and bit-depth quantization and their correlation to vigilant, self-powered operation. The integrated system demonstrates an important step forward for remote patient monitoring beyond the clinic.