Signal Quality of Reflective-Mode Photoplethysmograms Across Anatomical Sites

Area of Science:

• Biomedical Engineering
• Physiological Monitoring
• Optical Sensing

Background:

• Reflective-mode photoplethysmography (PPG) offers non-invasive physiological monitoring.
• PPG performance is influenced by perfusion, temperature, and tissue optical properties.
• Conventional sites like the finger and wrist have limitations.

Purpose of the Study:

• To systematically evaluate reflective-mode PPG signal quality at various anatomical sites.
• To identify optimal locations for accurate heart rate (HR) and pulse transit time (PTT) estimation.
• To explore non-conventional sites as alternatives for PPG acquisition.

Main Methods:

• Acquired PPG signals from finger, wrist, ear, nose, temple, upper lip, and lower lip using two commercial sensors.
• Quantified signal quality using Skewness, Kurtosis, Perfusion Index, and Shannon entropy.
• Computed HR and PTT, assessing accuracy across different sites and wavelengths.

Main Results:

• Skewness and Perfusion Index proved most informative for signal quality assessment.
• The finger exhibited the best signal quality, while the wrist was most challenging.
• Facial regions (lips, nose, temple) showed quality comparable to the finger.
• HR estimation was most accurate with GREEN wavelength, with lower lip yielding lowest error.
• PTT was longest at finger/wrist and shortest at lips.

Conclusions:

• Non-conventional anatomical sites, particularly facial regions, show significant potential for reflective-mode PPG.
• These sites offer comparable signal quality to the finger, providing alternatives to traditional locations.
• Optimizing PPG acquisition at diverse sites can enhance non-invasive physiological monitoring capabilities.