A patch-type wireless forehead pulse oximeter for SpO2 measurement

A patch-type wireless wearable pulse oximeter system has been developed to measure the heart beat rate and oxygen saturation of blood (SpO2) in reflective mode from a person's forehead. The system uses light sources of two wavelengths (red, 625 nm; infrared, 865 nm) in an optical sensor, separates photodetector signal and transimpedance amplifier output into infrared (IR) and red photoplethysmographic (PPG) signals, and then digitizes and transmits data wirelessly via a Bluetooth module to a remote PC in real time, where the SpO2 value is calculated. The optical sensor, mounted on a 7 cm × 2 cm flexible sheet, is interfaced with an 8.5 cm × 3.5 cm wireless SpO2 circuit board. The entire sensor and wireless SpO2 system, which weighs only 15 g, is readily wearable on the forehead, unlike conventional non-wearable wired forehead pulse oximeters. Using our system, the reduction of SpO2 value was observed from 100% to 89%, under an 80 s breathhold condition, which matched with the simultaneously measured SpO2 values obtained using commercial pulse oximeters.