Origin of Infrared Light Modulation in Reflectance-Mode Photoplethysmography

• Published in: PloS one Vol. 11; no. 10; p. e0165413
• Main Authors: Sidorov, Igor S, Romashko, Roman V, Koval, Vasily T, Giniatullin, Rashid, Kamshilin, Alexei A
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 21.10.2016; Public Library of Science (PLoS)
• Subjects: Adolescent; Adult; Aged; Aging; Arteries; Biology and Life Sciences; Blood; Blood pressure; Blood Pressure Determination; Blood vessels; Capillaries; Clinical medicine; Correlation analysis; Data processing; Deformation mechanisms; Dermis; Digital cameras; Elastic deformation; Engineering and Technology; Experiments; Female; Glass plates; Heart Rate; Humans; I.R. radiation; Infrared radiation; Infrared Rays; LEDs; Light emitting diodes; Light modulation; Luminance distribution; Luminous intensity; Male; Measurement techniques; Medical research; Medical treatment; Medicine and Health Sciences; Middle Aged; Migraine; Network switches; Neurobiology; Neurosciences; Optical properties; Palm; Photonics; Photoplethysmography - methods; Physical Sciences; Physiology; Reflectance; Research and Analysis Methods; Scattering coefficient; Sensors; Skin; Skin - blood supply; Skin diseases; Spatial distribution; Wavelengths; Young Adult; Russia
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0165413

We recently pointed out the important role of dermis deformation by pulsating arterial pressure in the formation of a photoplethysmographic signal at green light. The aim of this study was to explore the role of this novel finding in near-infrared (NIR) light. A light-emitting diode (LED)-based imaging photoplethysmography (IPPG) system was used to detect spatial distribution of blood pulsations under frame-to-frame switching green and NIR illumination in the palms of 34 healthy individuals. We observed a significant increase of light-intensity modulation at the heartbeat frequency for both illuminating wavelengths after a palm was contacted with a glass plate. Strong positive correlation between data measured at green and NIR light was found, suggesting that the same signal was read independently from the depth of penetration. Analysis of the data shows that an essential part of remitted NIR light is modulated in time as a result of elastic deformations of dermis caused by variable blood pressure in the arteries. Our observations suggest that in contrast with the classical model, photoplethysmographic waveform originates from the modulation of the density of capillaries caused by the variable pressure applied to the skin from large blood vessels. Particularly, beat-to-beat transmural pressure in arteries compresses/decompresses the dermis and deforms its connective-tissue components, thus affecting the distance between the capillaries, which results in the modulation of absorption and scattering coefficients of both green and NIR light. These findings are important for the correct interpretation of this widely used medical technique, which may have novel applications in diagnosis and treatment monitoring of aging and skin diseases.