A Smart Wearable Oximeter Insole for Monitoring SpO2 Levels of Diabetics’ Foot Ulcer

This work presents the development of a fully functional prototype of a wearable smart shoe insole that can monitor arterial oxygen saturation (SpO2) levels at the foot of a diabetic patient using photoplethysmography (PPG) signals. Continuous monitoring of SpO2 levels in diabetic foot ulcer (DFU) patients can provide critical information on the severity of the ulcer, the wound healing process, and the possible need for oxygenation of the wound bed. The developed oximetry system seamlessly integrates the internet of things (IoT) via a custom developed Android mobile application, thus enabling "at-home" monitoring. Fifteen healthy subjects were tested, and the insole oximeter was able to successfully estimate SpO2 levels at the toe. An average error of ≈ 2.8% was calculated for the measured/estimated SpO2 levels at the subjects’ toe when compared to a reference oximeter attached to the finger. In people suffering from chronic DFU wounds, measuring and ensuring appropriate oxygen levels at the foot is critically important for healing the ulcer’s cells/tissues. The fabrication process of the system, details of the PPG tests and analysis of the obtained results are presented and reported in this paper.