The effect of external mechanical compression on in vivo water content in human skin

We have studied the influence of external mechanical compression on diffuse reflection spectra of human skin tissue under in vivo conditions in the spectral range 800-2000 nm. It has been found that the external compression leads to a decrease in the reflection coefficient of the skin. Analysis of spectra based on the diffusion approximation of the radiation transfer theory has allowed us to find that the external compression weakens both absorbing and scattering properties of the skin. We have revealed that, of the two processes that control the in vivo reflection coefficient of skin in the near-infrared spectral range under conditions of its external mechanical compression, the weakening process of the scattering properties of tissue as a result of the displacement of water out of the volume of the skin subjected to the compression is predominating. It has been found that, under the application of an external compression of 110 kPa, the water content in the skin decreases by a value of about 10%. The stabilization process of diffuse reflection spectra under external compression conditions has an inertial character. In this case, under the application of an external compression of 110 kPa, the stabilization time of spectra is about 10 min, whereas, after the removal of the compression, the skin recovers its optical properties in the near-IR range within the period of time of about 50 min.