Abstract
Imaging photoplethysmography (iPPG) is an emerging technology used to assess microcirculation and cardiovascular signs by collecting backscattered light from illuminated tissue using optical imaging sensors. The aim of this study was to study how effective smart garment fabrics could be capturing physiological signs in a non-contact mode. The present work demonstrates a feasible approach of, instead of using conventional high-power illumination sources, integrating a grid of surface-mounted light emitting diodes (LEDs) into cotton fabric to spotlight the region of interest (ROI). The green and the red LEDs (525 and 660 nm) placed on a small cotton substrate were used to locally illuminate palm skin in a dual-wavelength iPPG setup, where the backscattered light is transmitted to a remote image sensor through the garment fabric. The results show that the illuminations from both wavelength LEDs can be used to extract heart rate (HR) reaching an accuracy of 90% compared to a contact PPG probe. Stretching the fabric over the skin surface alters the morphology of iPPG signals, demonstrating a significantly higher pulsatile amplitude in both channels of green and red illuminations. The skin compression by the fabric could be potentially utilised to enhance the penetration of illumination into cutaneous microvascular beds. The outcome could lead a new avenue of non-contact opto-physiological monitoring and assessment with functional garment fabrics.
Highlights
Increasing demand for remote physiological measurement in areas such as healthcare, emergency response services, elite sports, and recreational fitness has stimulated research into numerous “smart” and wearable devices
The region associated with dark red was the area where light emitting diodes (LEDs) were mounted on the smart garment fabric
The experimental smart garment setup used in this study demonstrated a deviation from this assumption, where a shift in the forward current through each LED group resulted in a change in iPPGg−r signal quality and, the heart rate (HR) readings
Summary
Increasing demand for remote physiological measurement in areas such as healthcare, emergency response services, elite sports, and recreational fitness has stimulated research into numerous “smart” and wearable devices. A usual approach is to integrate physiological sensors, e.g., electrocardiograms (ECG) and photoplethysmographs (PPG), into all-in-one smart-watches or other body-worn hardware, which are attractive to the rehabilitation, sports, and fitness markets [1]. Another simple and cost-effective remote monitoring method is attaching a small sensor and power circuitry to smart garments, while all sensing, processing, and data distribution nodes are set remotely around the patient. This approach eliminates the need to secure hardware to the patient’s. A camera-based method, known as imaging (iPPG) or remote (rPPG)
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