New trends in non-invasive study of human skin microcirculation. A descriptive review

The aim of this descriptive review is to analyze the current state and further development of a new direction in functional diagnostics — non-invasive study of human skin microcirculation. The review considers the most frequently used non-invasive methods for research studying hu­man skin microcirculation. The diagnostic potential of various de­vices is assessed taking into account the physical characteristics of their functioning and the skin microcirculation angioarchitectonics. The article considers the main directions of improvement of computer videocapillaroscopy, laser Doppler flowmetry and photoplethysmography methods, which are based on modern computer technologies and microelectronics. The main trends in this direction are miniaturization of devices, remote data transmission and the use of modern methods of automatic data analysis. A completely new method of obtaining physiological information is the analysis of a video plethysmography records using a conventional webcam. The method is based on the analysis of changes in the contrast of pixels during video recording of the skin surface, where the transitional capillary zones are located, blood flow changes in which lead to a change in the contrast of the pixels recorded by a standard webcam.

1. Fedorovich AA. Microcirculation of the human skin as an object of re­search. Regional hemodynamics and microcirculation. 2017; 16(4):11-26. (In Russ.) doi:10.24884/1682-6655-2017-16-4-11-26.

2. Sangiorgi S, Manelli A, Congiu T, et al. Microvascularization of the human digit as studied by corrosion casting. J Anat. 2004; 204(2):123-31. doi:10.1111/j.1469-7580.2004.00251.x.

3. Fedorovich AA. Capillary hemodynamics in the nail bed а of fingers. Regional blood circulation and microcirculation. 2006; 19(1):20-9. (In Russ.) EDN: JWJRCP.

4. Gurfinkel YuI, Atkov OYu, Sasonko ML, Sarimov RM. A new approach to the integral assessment of the state of the cardio­vas­cu­lar system in patients with arterial hypertension. Rus­sian Journal of Cardiology. 2014;(1):101-6. (In Russ.) doi:10.15829/1560-4071-2014-1-101-106.

5. Gurov IP, Volkov MV, Margaryants NB, Potemkin AV. Method of bringing locally varying images into coincidence in video capillaroscopy. Journal of Optical Technology. 2019;86(12):35-42. (In Russ.) doi:10.17586/1023-5086-2019-86-12-35-42.

6. Abdou MAH, Truong TT, Dykyy A, et al. CapillaryNET: An automated system to quantify skin capillary density and red blood cell velocity from handheld vital microscopy. Artif Intell Med. 2022; 127:102287. doi:10.1016/j.artmed.2022.102287.

7. Krupatkin AI, Sidorov VV. Functional diagnostics of the state of mic­rocirculatory tissue systems. Oscillations. Information content. Nonlinearity. Guide for doctors. Ed. "Librocom". 2013. p. 496. (In Russ.) ISBN: 978-5-397-03943-7.

8. Krupatkin AI. Blood flow fluctuations are a new diagnostic language in the study of microcirculation. Regional blood circulation and microcirculation. 2014;13(1):83-99. (In Russ.) doi:10/24884/1682-6655-2014-13-1-83-99.

9. Kozlov VI, Azizov GA, Gurova OA, Litvin FB. Laser Doppler flowmetry in assessing the condition and disorders of microcirculation. Methodological manual for doctors. RUDN Publ., Moscow. 2012. р. 32. (In Russ.)

10. Fedorovich AA, Loktionova YI, Zharkikh EV, et al. Body position affects capillary blood flow regulation measured with wearable blood flow sensors. Diagnostics. 2021;11:436. doi:10.3390/diagnostics11030436.

11. Frolov AV, Loktionova YuI, Zharkikh EV, et al. Reaction of blood microcirculation in the skin of various parts of the body when performing yoga breathing exercises. Regional blood circulation and microcirculation. 2023;22(1):72-84. (In Russ.) doi:10.24884/1682-6655-2023-22-1-72-84.

12. Pashkova DV, Popova YuA, Fedorovich AA. Functional state of the micro­vasculature of the skin of healthy women under "dry" immersion conditions. Aerospace and environmental medicine. 2023;57(2):39-46. (In Russ.) doi:10.21687/0233-528X-2023-57-2-39-46.

13. Pashkova DV, Popova YuA, Fedorovich AA, Shpakov AV. Regional cutaneous blood flow in healthy subjects under conditions of 21-day headdown bed rest. Extreme Medicine. 2025;27(1):124-130. (In Russ.) doi:10.47183/mes.2025-267.

14. Fedorovich AA, Markov DS, Malishevsky MV, et al. Microcirculatory disorders in the forearm skin in the acute phase of COVID-19 according to laser Doppler flowmetry. Regional blood circulation and microcirculation. 2022;21(3):56-63. (In Russ.) doi:10.24884/1682-6655-2022-21-3-56-63.

15. Dunaev AV, Loktionova YuI, Zharkikh EV, et al. Study of blood microcirculation in conditions of weightlessness using portable laser Doppler flowmeters. Aerospace and environmental medicine. 2024;58(1):47-54. (In Russ.) doi:10.21687/0233-528X-2024-58-1-47-54.

16. Savo R, Pierrat R, Najar U, et al. Mean path length invariance in multiple light scattering. Science. 2017;358:765-8. doi:10.1126/science.aan4054.

17. Korolev AI, Fedorovich AA, Gorshkov AYu, et al. Photo­plethysmography factors associated with undiagnosed hypertension in men with low and moderate cardiovascular risk. Cardiovascular Therapy and Prevention. 2023;22(7):3649. (In Russ.) doi:10.15829/1728-8800-2023-3649.

18. Panwar M, Gautam A, Biswas D, Acharyya A. PP-Net: A deep learning framework for PPG-based blood pressure and heart rate esti­mation. IEEE Sens J. 2020;20(17):10000-11. doi:10.1109/JSEN.2020.2990864.

19. Fedorovich AA, Drapkina OM, Pronko KN, et al. Telemonitoring of capillary blood flow in human skin: new opportunities and prospects. Clin Pract. 2018;15(2):561-7. doi:10.4172/clinical-practice.1000390.

20. Fedorovich AA, Gorshkov AYu, Drapkina OM. Modern possibilities of non-invasive research and remote monitoring of capillary blood flow in human skin. Regional blood circulation and microcirculation. 2020;19(4):87-91. (In Russ.) doi:10.24884/1682-6655-2020-19-4-87-91.

21. Fedorovich AA, Drapkina OM. Web capillaroscopy — a new me­thod of non-invasive research of microcirculatory blood flow in human skin. The Russian Journal of Preventive Medicine. 2020; 23(4):115-8. (In Russ.) doi:10.17116/profmed202023041115.

22. Poh MZ, McDuff DJ, Picard RW. Non-contact, automated cardiac pulse measurements using video imaging and blind source se­pa­ration. Opt Express. 2010;18(10):10762-74. doi:10.1364/OE.18.010762.

23. Scully CG, Lee J, Meyer J, et al. Physiological parameter moni­toring from optical recordings with a mobile phone. IEEE Trans Bio­med Eng. 2012;59(2):303-6. doi:10.1109/TBME.2011.2163157.

24. Yan BP, Lai WHS, Chan CKY, et al. Contact-free screening of atrial fibrillation by a smartphone using facial pulsatile photo­plethysmographic signals. J Am Heart Assoc. 2020;7(8):e008585. doi:10.1161/JAHA.118.008585.

25. Yan BP, Lai WHS, Chan CKY, et al. High-throughput, contact-free detection of atrial fibrillation from video with deep learning. JAMA Cardiol. 2020;5(1):105-7. doi:10.1001/jamacardio.2019.4004.

26. Varma N, Cygankiewicz I, Turakhia M, et al. 2021 ISHNE/HRS/EHRA/APHRS collaborative statement on mHealth in ar­rhythmia management: digital medical tools for heart rhythm pro­fessionals. Ann Noninvasive Electrocardiol. 2021;26(2):e12795. doi:10.1111/anec.12795.

27. Luo H, Yang D, Barszczyk A, et al. Smartphone-dases blood pres­sure measurement using transdermal optical imaging technology. Circ Cardiovasc Imaging. 2019;12:e008857. doi:10.1161/CIRCIMAGING.119.008857.

28. Schoettker P, Degott J, Hofmann G, et al. Blood pressure measurements with the OptiBP smartphone app validated against reference auscultatory measurements. Sci Rep. 2020;10:17827. doi:10.1038/s41598-020-74955-4.