Ear and Finger PPG Wearables for Night and Day Beat-to-Beat Interval Detection

Area of Science:

• Biomedical Engineering
• Physiological Monitoring
• Wearable Technology

Background:

• Photoplethysmography (PPG) is a non-invasive optical technique used to measure blood volume changes.
• Inter-beat interval (IBI) estimation from PPG is crucial for cardiovascular health monitoring.
• Electrocardiography (ECG) provides R-to-R interval (RRI) as a gold standard for heart rate variability analysis.

Purpose of the Study:

• To compare the accuracy of ear and finger PPG for IBI detection and estimation against ECG-derived RRI.
• To evaluate the impact of sleep versus wake states on PPG-based IBI accuracy.
• To introduce and validate a novel fusion scheme combining ear and finger PPG data.

Main Methods:

• Simultaneous data acquisition using earbud PPG, ring PPG, and ECG devices on seven male subjects.
• Analysis of 43 recordings totaling over 72 hours, encompassing both sleep and wake states.
• Development and testing of a fusion algorithm integrating IBI data from both PPG devices.

Main Results:

• Earbud PPG demonstrated a higher beat detection rate and more accurate IBI estimation than ring PPG.
• PPG-based IBI detection and estimation performance were significantly better during sleep compared to wake states.
• The proposed fusion scheme achieved a 99.22% beat detection rate with Mean Absolute Error (MAE) of 7.42 ms and Root Mean Square Error (RMSE) of 13.45 ms.

Conclusions:

• Earbud PPG is a more accurate method for IBI estimation than finger PPG.
• Sleep state enhances the performance of PPG-based IBI monitoring.
• The novel fusion scheme offers a robust and accurate approach for PPG-based cardiovascular monitoring.