In the resting fingertip, PPG signal variations are primarily due to volume changes, with blood density having no significant contribution.
Supports volume-based PPG interpretation at rest; leaves open validation across clinical conditions and populations.
Using simultaneous photoplethysmogram (PPG) and pulse transducer signals from the same finger, a high correlation (Mean: 98.6, STD: 1) is obtained between the AC part of the PPG and estimated volume changes (after normalization). These results point to the fact that in the resting fingertip, PPG signal variations are only due to volume changes and that blood density does not change thus has no contribution.
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Keikhosravi et al. (2013) studied this question.
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