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Photoplethysmography (PPG) is an optical non-invasive measuring technique and uses a light source and a photodetector to monitor regional blood volume changes in the vessel near the skin. It is a widespread clinical application, and traditionally, PPG signals are used to monitor oxygen saturation and heart rate. However, it can be utilized to extract further valuable information such as blood pressures, cardiac outputs, autonomic functions, and various cardiovascularrelated diseases. Overall, PPG has great potential for providing a simple and convenient but versatile diagnostic tool as an alternative of traditional cardiovascular health monitoring. However, very limited studies have been performed to understand the complex physiological variability in PPG signals measured simultaneously at different body sites. In addition, current PPG devices are relatively bulky and require adhesives or fasteners to collect reliable PPG signals, which make them applicable only for specific body locations and not suitable for long-term, continuous ambulatory monitoring. In this present work, an ultrathin, flexible conformal PPG device is developed. The overall thickness of the flexible circuit is maintained less than 25 μm in order that the circuit can demonstrate a high level of flexibility and conform to the curvilinear surfaces of the skin. Multiple conformal PPG devices are laminated on forehead, wrist, or ankle to monitor PPG signals in a synchronized manner. In addition, the similar setting of conformal PPG devices is used to evaluate cardiovascular changes induced by lower body negative pressures. Overall, our finding demonstrates the feasibility of our multiple conformal PPG device network as an accurate, low-profile, and low-resource monitoring devices for cardiovascular health.
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