Photoplethysmography. Part 1. Comparison with laser Doppler flowmetry.

Area of Science:

• Biomedical Engineering
• Physiology

Background:

• Photoplethysmography (PPG) and laser Doppler flowmetry (LDF) are optical techniques used to measure blood perfusion.
• Understanding their comparative performance under varying physiological conditions is crucial for accurate physiological monitoring.

Purpose of the Study:

• To compare the sensitivity and response characteristics of PPG and LDF in measuring human skin perfusion changes.
• To evaluate the influence of physical principles, probe geometry, and optical conditions on PPG and LDF measurements.

Main Methods:

• Inducing changes in skin perfusion using cold and hot water provocation on the finger and forearm.
• Comparing measurements obtained from a commercial PPG device (red light, 630-660 nm) and LDF.
• Analyzing the impact of probe dimensions and light source characteristics on signal quality.

Main Results:

• Both LDF and PPG demonstrated comparable sensitivity in detecting increased skin perfusion following thermal elevation.
• PPG occasionally exhibited an inverse response to temperature elevation, particularly on finger skin.
• Laser light is unsuitable for PPG with small, unseparated optical fibers; probe dimensions critically affect measurement volume and signal quality.

Conclusions:

• PPG and LDF are generally comparable for detecting perfusion increases, but PPG's inverse response requires consideration.
• Probe design and optical conditions are critical factors influencing PPG measurement accuracy and reliability.
• Further research into optimized PPG probe design is warranted for improved physiological monitoring.