Key result
In a simulation model, when dc increased from 10% to 90%, stabilized ac decreased from 1 to 0.89 ± 0.21, and when optical path length increased from 10% to 90%, stabilized ac increased to 1.53 ± 0.40.
A proposed model equation demonstrates that the ac component of photoplethysmographic signals is dependent on the dc component and optical path length.
Simulation links PPG ac to dc and path length; extends models but leaves clinical validation open.
Photoplethysmography is used in various areas such as vital sign measurement, vascular characteristics analysis, and autonomic nervous system assessment. Photoplethysmographic signals are composed of ac and dc, but it is difficult to find research about the interaction of photoplethysmographic components. This study suggested a model equation combining two Lambert-Beer equations at the onset and peak points of photoplethysmography to evaluate ac characteristics, and verified the model equation through simulation and experiment. In the suggested equation, ac was dependent on dc and optical path length. In the simulation, dc was inversely proportionate to ac sensitivity (slope), and ac and optical path length were proportionate. When dc increased from 10% to 90%, stabilized ac decreased from 1 to 0.89 ± 0.21, and when optical path length increased from 10% to 90%, stabilized ac increased from 1 to 1.53 ± 0.40.
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Lee et al. (2011) studied Photoplethysmography. Model equation combining two Lambert-Beer equations was evaluated on Relationship between ac, dc, and optical path length. In a simulation model, when dc increased from 10% to 90%, stabilized ac decreased from 1 to 0.89 ± 0.21, and when optical path length increased from 10% to 90%, stabilized ac increased to 1.53 ± 0.40.
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