Comparative Assessment of PPG Signal Quality Across Fingers for Wearable Health Monitoring and Implications for Sensor Design Optimization

Abstract

In clinical settings, every minute of delay in treating a cardiopulmonary emergency can reduce a patient's chance of survival by up to 10%. Photoplethysmography (PPG) is a low-cost, noninvasive method widely adopted in both clinical, and consumer settings to monitor cardiopulmonary signals. Therefore, clinical PPG pulse oximeter equipment is used on 88.8% of inpatient days in U.S. hospitals. However, poor PPG signal quality due to motion artifacts and improper sensor placement results in frequent cardio-respiratory monitor alarms, with 80% of these deemed insignificant, causing alarm fatigue that delays intervention in real cardiopulmonary emergencies. This study examines the effect of finger choice on PPG signal quality, utilizing the signal-to-noise ratio (SNR) as the primary signal quality index (SQI). PPG data were collected from all five fingers of 24 racially diverse participants using a MAX30102-based sensing platform. The statistical results based on repeated measures ANOVA, followed by post-hoc testing, showed that the thumb consistently exhibited the highest SNR, indicating superior signal quality compared to other fingers, and potentially enhancing the reliability of cardio-respiratory monitor alarms. The index finger also showed a statistically significant advantage in SNR over the middle finger. These findings potentially inform future wearable sensor design to incorporate thumb-specific fixtures, adaptive sensor positioning, and thumb-oriented mechanical and optical enhancements to optimize monitoring accuracy and reliability.