Participant Study Data for Cardiovascular Metric Estimation with a Developed PPG Device

With the ongoing advancements of photoplethysmography (PPG) devices for clinical and domestic applications, there exists a distinct lack of publicly available literature addressing the best possible hardware design for these devices. In this project, this question was answered by investigating the hardware design configuration of a PPG device, especially focussing on the light source wavelength, light source brightness, number of light sources, photodetector lens shape, and sensor-to-skin contact pressure. This device was evaluated on the quality of the PPG signals it measures, as well as its ability to accurately estimate the user’s heart rate, blood oxygen saturation, and blood pressure over different skin tones. A participant study was also conducted to collect cardiovascular metric data from 110 participants with varying skin tones, which was used to develop a neural network for blood pressure estimation as well as determine the best hardware configuration of the PPG device. This resulted in the hardware configuration that consisted of a red-and-infrared light-emitting diode (LED) system, a flat lens photodiode, and high sensor-to-skin contact pressure. This configuration was setup with its two red LEDs at a medium level of brightness and four infrared LEDs at a high level of brightness and was primarily used to measure data on the user’s fingertip. The consequent estimations’ mean absolute errors were 3.511 BPM for heart rate, 0.615% for blood oxygen saturation, and 11.279 mmHg for the systolic blood pressure and 6.802 mmHg for the diastolic blood pressure estimations, respectively. Finally, the selected PPG device’s bias to skin tone was determined. It was concluded that the device had very little bias to skin tone, due to it having a 3.817 dB variance over all the skin tones tested. With the successful identification of the most optimal hardware design configuration, future devices are expected to perform with improved accuracy, usability, and versatility in clinical settings. Furthermore, it provides the necessary groundwork for future research to explore additional applications of PPG devices.