Finger and forehead PPG signal comparison for respiratory rate estimation

Area of Science:

• Biomedical Engineering
• Physiological Monitoring
• Signal Processing

Background:

• Photoplethysmogram (PPG) sensors are increasingly used for physiological monitoring.
• Accurate respiratory rate estimation is crucial for patient assessment.
• The optimal placement of PPG sensors for respiratory rate estimation requires further investigation.

Purpose of the Study:

• To evaluate the impact of PPG sensor location (finger vs. forehead) on respiratory rate estimation accuracy.
• To compare different PPG-derived respiratory signals for their effectiveness in respiratory rate estimation.
• To identify optimal conditions for PPG-based respiratory rate monitoring.

Main Methods:

• Simultaneous recording of finger PPG, forehead PPG, and respiratory signals from 35 subjects.
• Extraction of four PPG-derived respiratory (PDR) signals: pulse rate variability (PRV), pulse width variability, pulse amplitude variability, and respiratory-induced intensity variability (RIIV).
• Estimation of respiratory rate from PDR signals at various controlled respiratory rates (0.1 Hz to 0.6 Hz).

Main Results:

• Finger PPG sensor placement demonstrated superior performance in successful estimation and reduced relative error compared to forehead placement.
• Optimal performance was observed for respiratory rates below 0.4 Hz.
• Excluding the respiratory-induced intensity variability (RIIV) signal improved estimation accuracy.

Conclusions:

• Finger-based PPG sensor placement is recommended for more accurate respiratory rate estimation.
• Respiratory rate estimation using PPG is more reliable at lower respiratory rates (≤ 0.4 Hz).
• Further research should focus on optimizing signal processing techniques for PPG-derived respiratory monitoring.