Video capillaroscopy clarifies mechanism of the photoplethysmographic waveform appearance

Photoplethysmography (PPG) devices are widely used in clinical practice but the origin of PPG signal is still under debating. The classical theory assumes that the PPG waveform stems from variations of blood volume in pulsating arteries. In this research we analysed high-speed video recordings of capillaries in a fingernail bed. It was found that speed of erythrocytes in capillaries has pronounced modulation in time, which follows variations of instantaneous blood pressure in arteries. However, the mean speed significantly differs even for neighbour capillaries whereas change of the speed occurs in phase for the most of capillaries. Moreover, the light intensity remitted from the papillary dermis is also modulated at the heartbeat frequency displaying significant correlation with waveforms of the RBC speed. Obtained results can hardly be explained by the classical theory of PPG signal formation. Shallow penetrating visible light acquires modulation of erythrocytes density in the capillary bed without interacting with deeper situated pulsating arteries. Therefore, the capillary bed could serve as a distributed sensor for monitor the status of deep vessels. Better understanding of the photoplethysmography basis will result in a wider range of applications of this fast growing technology in both medical and research practice.

[1]  L. O. Svaasand,et al.  Remote plethysmographic imaging using ambient light. , 2008, Optics express.

[2]  Ashley J. Welch,et al.  Effects of compression on soft tissue optical properties , 1996 .

[3]  M Intaglietta,et al.  Vasomotion patterns in skeletal muscle arterioles during changes in arterial pressure. , 1988, Microvascular research.

[4]  W. Zijlstra,et al.  Absorption spectra of human fetal and adult oxyhemoglobin, de-oxyhemoglobin, carboxyhemoglobin, and methemoglobin. , 1991, Clinical chemistry.

[5]  Alexei A. Kamshilin,et al.  Blood Peripheral Circulation Assessment Method Based on Combined Use of the Video-Capillaroscopy, Imaging Photoplethysmography, and Electrocardiography , 2016 .

[6]  J. Laidlaw,et al.  ANATOMY OF THE HUMAN BODY , 1967, The Ulster Medical Journal.

[7]  R. Romashko,et al.  A new look at the essence of the imaging photoplethysmography , 2015, Scientific Reports.

[8]  Mikhail V. Volkov,et al.  The phase correlation algorithm for stabilization of capillary blood flow video frames , 2015, Optical Metrology.

[9]  Oleg V Mamontov,et al.  Novel contactless approach for assessment of venous occlusion plethysmography by video recordings at the green illumination , 2017, Scientific Reports.

[10]  Tom Lister,et al.  Optical properties of human skin , 2012, Journal of biomedical optics.

[11]  H. Asada,et al.  Utility of the Photoplethysmogram in Circulatory Monitoring , 2008, Anesthesiology.

[12]  M. Jünger,et al.  Synchronous measurements of blood pressure and red blood cell velocity in capillaries of human skin. , 1996, The Journal of investigative dermatology.

[13]  Rashid Giniatullin,et al.  Accurate measurement of the pulse wave delay with imaging photoplethysmography. , 2016, Biomedical optics express.

[14]  Toshiyo Tamura,et al.  The Advantages of Wearable Green Reflected Photoplethysmography , 2011, Journal of Medical Systems.

[15]  A SIMPLE METHOD OF DEMONSTRATING CHANGES IN BLOOD SUPPLY OF THE EAR AND EFFECTS OF SOME MEASURES , 1936 .

[16]  Alexei A. Kamshilin,et al.  Photoplethysmographic imaging of high spatial resolution , 2011, Biomedical optics express.

[17]  John Allen.  Photoplethysmography and its application in clinical physiological measurement , 2007, Physiological measurement.

[18]  M Intaglietta,et al.  Elastic Environment of the Capillary Bed , 1966, Circulation research.

[19]  Oleg V Mamontov,et al.  Influence of a skin status on the light interaction with dermis. , 2015, Biomedical optics express.

[20]  A. N. Bashkatov,et al.  Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm , 2005 .

[21]  John A. Parrish,et al.  Optical Properties of Human Skin , 1982 .