1. Effect of external mechanical compression on optical properties of the human skin in vivo Inara A. Nakhaeva, Mohammod R. Mohammod, Olga A. Zyuryukina,Yury P. Sinichkin Saratov State University

2. Abstract This work presents the results of theoretical and experimental studies of the effect of the nonlocalized external mechanical pressure on human skin diffuse reflectance spectra in vivo. It was found that spectral changes are a result of absorption and scattering properties of the human skin decreasing during compression. The time of stabilization of the human skin optical parameters during external pressure (~ some minutes) significantly smaller the time of relaxation of the skin tissue in normal state after compression (~ one hour). Also blood content and the degree of hemoglobin oxygenation significantly increase in initial moment after compression.

3. Experiment Method: reflectance spectroscopy Object: the inner forearm human skin in vivo Experimental setup Fiber-optic probe Reflectance spectra: 400-1000 nm USB4000 (Ocean Optics, USA)

4. Results of experiment Dynamics of human skin reflectance under the external mechanical compression (m = 0.5 kg; p = 13.9 kPa)

5. Dynamics of human skin reflectance after the external mechanical compression (m = 0.5 kg; p = 13.9 kPa) Results of experiment

6. Dynamics of human skin reflectance under the external mechanical compression (m = 4.0 kg; p = 110 kPa)

7. Results of experiment Dynamics of human skin reflectance after the external mechanical compression (m = 4.0 kg; p = 110 kPa)

8. Results of experiment Temporal changes of the human skin reflectance coefficients at two wavelength s in the conditions of the external mechanical compression m = 8 kg; p = 111 kPa 0-225 sec ‑ under compression, 225 sec – 50 min ‑ after compression

9. Results of experiment Erythema index – apparent optical density., [nm] Dynamics of the human skin eryhema index under (0-290 s) and after (290 s -40 min) the external mechanical compression; m = 4 kg (p = 111 kPa )

10. Results of experiment Hemoglobin oxygenation degree,

11. Theory, A = 2.79 Absorption, ( Prahl S. http://omlc.ogi.edu)http://omlc.ogi.edu. ( Prahl S. http://omlc.ogi.edu)http://omlc.ogi.edu Scattering ( Bashkatov A.N., Genina E.A., Kochubey V.I., Tuchin V.V. Optical properties of human skin, subcutaneous and mucous tissues in the wavelength range from 400 to 2000 nm // J. Phys. D: Appl. Phys. 2005. Vol. 38. P. 2543-2555 ).

12. Results of modelling Effect of hemoglobin absorptionEffect of the scattering Effect of hemoglobin absorption and scattering 1- normal; 2- absorption was decreased 10 times, scattering was decreased in 1.5 times

13. Effect of the transport scattering coefficient on the skin reflectance Decreasing of reflection on 15% is result of decreasing of transport scattering coefficient in 2 times

14. 1.The external mechanical compression decreases the blood content and scattering properties of the human skin. 2. The time of blood content stabilization (about 3 minutes) is less than the time of the scattering properties stabilization (about 5 minutes). 3. Decreasing of blood content is accompanied with decreasing of hemoglobin oxygenation degree. 4. The blood content in the skin sharply increases (about 2.4 times as compared with normal skin) after removing of compression. 5. The hemoglobin oxygenation degree also increases (about 2.7 times as compared with normal skin) after removing of compression. 6. The time of relaxation of the human skin to normal state after compression ~ one hour. Conclusions