Beat-to-beat Intervals of Speckle & Intensity-based Optical Plethysmograms compared to Electrocardiogram

This study evaluates video sequences obtained by a form of laser speckle imaging (LSI) - referred to as remote camera-derived Speckleplethysmography (rSPG) - in comparison to common clinical parameters (PPG & ECG). For 9 human subjects we illuminated the index finger with a laser (639 nm, 10 mW, spot diameter 5.6 mm), captured video streams with a camera (Basler acA2000-340km, 25 cm distance, 100 fps) and evaluated spatial variations in the captured speckle patterns. We simultaneously collected contact-mode transmissive photoplethysmography (PPG) and electrocardiography (ECG) signals. We derived beat-to-beat (b-2-b) intervals from both rSPG and contact-mode PPG signals and compared both with the ECG R-R intervals `goldstandard' (3234 heart-cycles in total). B-2-b interval error distributions of rSPG vs contact PPG showed: mean absolute deviation 10.4 vs 14.2 ms; standard deviation 25.2 vs 30.1 ms. Two-sample F-test revealed significantly different variances (p < 0.001, 99% confidence). Additional Levene's test: F (1, 6468) = 37.602, p = 0. This study demonstrates that contactless cameraderived rSPG can obtain b-2-b intervals at least as good as routine clinical contact-mode transmissive finger clip PPG. This might enable innovative applications.