Thin, Soft, Wearable Electronics for Continuous ECG Monitoring

Abstract

Cardiovascular disease stands as one of the most prevalent and deadliest health conditions globally, contributing significantly to mortality rates. According to statistics, cardiovascular disease, including heart disease and stroke, is a major contributing factor to mortality in many countries. In the context of preventive measures, continuous electrocardiogram (ECG) monitoring assumes a pivotal role. By providing real-time assessment of cardiac electrical activity, this monitoring technique enables the timely detection of potential hazards such as arrhythmias, thereby facilitating prompt intervention and treatment to mitigate the risk of cardiovascular incidents. Moreover, continuous ECG monitoring offers valuable insights into a patient's cardiac health status, thereby enabling the development of personalized treatment plans to effectively address the onset and progression of cardiovascular disease. This tailored approach takes into account individual factors, including lifestyle, genetic predispositions, and medical history, thereby ensuring a more targeted and efficacious preventive strategy. Notwithstanding its potential benefits, the implementation of continuous ECG monitoring is not without challenges. The comfort and portability of ECG monitoring devices emerge as primary concerns. Patients necessitate a monitoring system that seamlessly integrates into their daily lives, ensuring minimal discomfort and unhindered mobility. Furthermore, the acquisition of long-duration, high-quality data represents a significant obstacle. Given the prolonged monitoring periods, issues such as signal loss and artifacts may arise, potentially compromising the integrity of the data. Additionally, the complexity inherent in data processing and analysis poses considerable challenges in harnessing the full potential of continuous ECG monitoring.

To address the aforementioned challenges associated with continuous ECG monitoring, this thesis first introduces a novel wrist-worn heart rate monitoring device fabricated using flexible electronic technology. In contrast to traditional watch-style devices, our approach utilizes flexible printed circuit boards (FPCB) and encapsulation techniques, resulting in a lightweight and flexible device that enhances both stability during attachment and user comfort. This device employs Bluetooth Low Energy (BLE) technology to wirelessly transmit real-time heart rate data to a smartphone for further processing. Moreover, leveraging the low-power characteristics of flexible components, the device is powered by a thin and flexible sweat-activated battery (SAB). This design showcases the significant advantages of flexible electronic technology in achieving comfort and portability in ECG monitoring devices. By leveraging flexible electronic technology, we overcome the bulkiness and discomfort associated with conventional devices, providing users with a comfortable and convenient experience for continuous ECG monitoring.

To address the drawbacks of decreased electrode adhesion, increased motion artifacts (MAs), and potential allergies due to accumulated sweat during long-term device wear, we introduce a three-dimensional liquid diode (3D LD) design. The 3D LD design efficiently extracts sweat from the skin surface and directs it towards an outlet, achieving a maximum flow rate of 11.6 ml cm⁻² min⁻¹, which is 4,000 times greater than the physiological sweat rate during exercise. By optimizing the device's structural design and fabrication methods, this device maintains sufficient flexibility for comfortable adhesion while effectively eliminating the accumulation of sweat beneath the electrodes, which can degrade the quality of ECG signals. Additionally, the device incorporates the aforementioned wireless flexible circuit technology, eliminating the need for bulky connecting wires traditionally used with electrodes and greatly minimizing the generation of MAs. This novel approach using the 3D LD design and wireless flexible circuit technology offers a promising solution to overcome the challenges associated with sweat accumulation, electrode adhesion, and MAs in continuous ECG monitoring. Through these advancements, the device not only ensures reliable signal quality but also enhances user comfort and convenience during prolonged wear.

To address the challenges of handling large amounts of data and further reduce MAs, we have designed a contactless ECG monitoring system. By eliminating the need for electrode-skin contact, this system not only resolves issues related to skin breathability and sweat accumulation during long-term wear but also enhances overall comfort. To suppress MAs, we employ machine learning algorithms to remove MA noise from the signals and make preliminary assessments of abnormal ECG signals. This approach allows for more accurate and reliable ECG monitoring, even in the presence of motion or physical activity. The combination of a contactless ECG monitoring system and machine learning algorithms offers a comprehensive solution to the challenges associated with data processing and MAs.

In summary, continuous ECG monitoring plays a pivotal role in preventive measures against cardiovascular disease. Despite the challenges related to comfort, data quality, and data processing, advancements in flexible electronic technology, 3D LD design, and contactless monitoring systems offer promising solutions. These innovations enhance user comfort, ensure reliable signal quality, and enable efficient data processing, empowering healthcare professionals and researchers to make informed decisions and improve cardiovascular disease prevention and management strategies.

Date of Award	27 Aug 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Xinge YU (Supervisor)