title: Origin of Infrared Light Modulation in Reflectance-Mode Photoplethysmography.
abstract: 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.
authors: R&D Center for Laser Physics, ITMO University, St. Petersburg, 197101, Russia.
authors: Igor S
authors: IS
authors: Sidorov
authors: Precision Optical Measurement Techniques Department, Institute for Automation and Control Processes of FEB RAS, 5 Radio St., Vladivostok, 690041, Russia.|Far Eastern Federal University, 8 Sukhanova St., Vladivostok, 690900, Russia.
authors: Roman V
authors: RV
authors: Romashko
authors: Federal State Institution "1477 Navy Clinical Hospital", Vladivostok, 690005, Russia.
authors: Vasily T
authors: VT
authors: Koval
authors: Department of Neurobiology, University of Eastern Finland, 70210 Kuopio, Finland.|Laboratory of Neurobiology, Kazan Federal University, 420000 Kazan, Russia.|Department of Computer Photonics and Videomatics, ITMO University, St. Petersburg, 197101, Russia.
authors: Rashid
authors: R
authors: Giniatullin
authors: Department of Computer Photonics and Videomatics, ITMO University, St. Petersburg, 197101, Russia.
authors: Alexei A
authors: http://orcid.org/0000-0003-2506-9736
authors: AA
authors: Kamshilin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001795:Blood Pressure Determination; D005260:Female; D006339:Heart Rate; D006801:Humans; D007259:Infrared Rays; D008297:Male; D008875:Middle Aged; D017156:Photoplethysmography / Q000379:methods*; D012867:Skin / Q000098:blood supply; D055815:Young Adult