Study of a Ring-Type Surgical Pleth Index Monitoring System Based on Flexible PPG Sensor

Rings have attracted more and more attention in the study of wearable health monitoring. This study focused on a ring type Surgical Pleth Index (SPI) monitoring system based on photoplethysmography (PPG) signal acquired from finger root, where the unique sensor array structure was simulated and verified by Monte Carlo approach. The circuit board was fabricated in the form of rigid flexible PCB that can be bended according to different curve surface. The PPG signal acquired from the proposed system and SPI (GE Carestation 620 A2) data ware monitored from 24 patients simultaneously during surgical procedures. Subsequently, 55,547 heart beats with complete photoelectric tracing pulse waves from finger root were employed to extract different dynamic PPG features, where the index of analgesic depth or pain intensity is quantified. We utilized a machine learning strategy based on regularized linear regression to construct a specialized SPI model. The arithmetic mean and standard deviation of SPI_FR was 38.19± 21.54, compared with 36.54± 24.87 accordingly. A total 94.75% of the SPI value from finger root (SPI_FR) fell within the 95% confidence interval, and it also showed that the ring-type SPI monitoring system had good consistency and accuracy in comparison with the SPI data from GE. Generally, this study provides a ring-type healthcare system and makes an extensive use of sensors to gain understandings on patients’ status during surgical procedures, which has the potential application in future surgery.