Sidorov Igor S, Romashko Roman V, Koval Vasily T, Giniatullin Rashid, Kamshilin Alexei A
R&D Center for Laser Physics, ITMO University, St. Petersburg, 197101, Russia.
Precision Optical Measurement Techniques Department, Institute for Automation and Control Processes of FEB RAS, 5 Radio St., Vladivostok, 690041, Russia.
PLoS One. 2016 Oct 21;11(10):e0165413. doi: 10.1371/journal.pone.0165413. eCollection 2016.
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.
我们最近指出，脉动动脉压引起的真皮变形在绿光下光电容积脉搏波信号形成中起着重要作用。本研究的目的是探讨这一新颖发现在近红外（NIR）光中的作用。使用基于发光二极管（LED）的成像光电容积脉搏波描记术（IPPG）系统，在34名健康个体手掌的逐帧切换绿光和近红外照明下，检测血液搏动的空间分布。我们观察到，手掌接触玻璃板后，两种照明波长下心跳频率处的光强度调制均显著增加。发现绿光和近红外光下测量的数据之间存在强正相关，表明从穿透深度独立读取相同信号。数据分析表明，由于动脉中血压变化导致真皮弹性变形，反射近红外光的一个重要部分在时间上受到调制。我们的观察结果表明，与经典模型不同，光电容积脉搏波波形源于大血管施加于皮肤的可变压力引起的毛细血管密度调制。特别是，动脉中逐搏跨壁压力压缩/解压真皮并使其结缔组织成分变形，从而影响毛细血管之间的距离，这导致绿光和近红外光的吸收和散射系数发生调制。这些发现对于正确解释这种广泛应用的医学技术很重要，该技术可能在衰老和皮肤疾病的诊断及治疗监测中有新的应用。
